Title of Invention	A METHOD AND APPARATUS FOR DEMODULATING AN INFORMATION SIGNAL
Abstract	The present invention relates to a method and apparatus for demodulating an signal for a transmitter and a receiver (202) which enhance the performance of a system coherent demodulation by utilizing non-pilot sub-channels to enhance the accuracy of estimates of amplitude and phase noise inherent in the transmission channel. This enhancement is accomplished by utilizing the corrected received data on a fundamental channel to enhance a pilot channel estimate, which is subsequently utilized by a dot product module in demodulating a supplementary data channel.

Title of Invention

A METHOD AND APPARATUS FOR DEMODULATING AN INFORMATION SIGNAL

Abstract

The present invention relates to a method and apparatus for demodulating an signal for a transmitter and a receiver (202) which enhance the performance of a system coherent demodulation by utilizing non-pilot sub-channels to enhance the accuracy of estimates of amplitude and phase noise inherent in the transmission channel. This enhancement is accomplished by utilizing the corrected received data on a fundamental channel to enhance a pilot channel estimate, which is subsequently utilized by a dot product module in demodulating a supplementary data channel.

Full Text	L Field of the Invention The current invention relates a method and apparatus for demodulating an information signal. More particularly, the present invention relates to a novel and improved method of compensating for phase and amplitude distortion of multiple signals transmitted through a single channel. II. Description of the Related Art The use of code division multiple access (CDMA) modulation 15 techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division maniple access (FDMA) and AM modulation schemes such as amplitude commanded single sideband (ACSSB) are known in the art. Techniques for distinguishing different concurrently-transmitted signals in multiple access communication systems are also known as channelization. The spread spectrum modulation technique of CDMA has significant advantages over other multiple access techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", and in U.S. Patent No. 5,751,761, entitled "SYSTEM AND METHOD FOR ORTHOGONAL SPREAD SPECTRUM SEQUENCE GENERATION IN VARIABLE DATA RATE SYSTEMS", both assigned to the assignee of the present invention and incorporated by reference herein. Code division multiple access communications systems have been standardized in the United States in Telecommunications Industry Association TIA/EIA/IS-95-A, entitled "MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM", hereafter referred to as IS-95 and incorporated by reference herein. The International Telecommunications Union recently requested the submission of proposed methods for providing high rate data and high- quality speech services over wireless communication channels, A first of these proposals was issued by the Telecommunications Industry Association, entitled "The cdma2000 ITU-R RTT Candidate Submission" hereafter referred to as cdma2000 and incorporated by reference herein. A second of these proposals was issued by the European Telecommunications Standards Institute (ETSI), entitled "The ETSI UMTS Terrestrial Radio Access (UTRA) ITU-R RTT Candidate Submission". And a third proposal was submitted by U.S. TG 8/1 entitled "The UWC-136 Candidate Submission" (referred to herein as EDGE). The contents of these submissions is public record and is well known in the art. In the CDMA demodulator structure used in some IS-95 systems, the pseudonoise (PN) chip interval defines the minimum separation two paths must have in order to be combined. Before the distinct paths can be demodulated, the relative arrival times (or offsets) of the paths in the received signal must first be determined. The demodulator performs this function by "searching" through a sequence of offsets and measuring the energy received at each offset. If the energy associated with a potential offset exceeds a certain threshold, a demodulation element, or "finger" may be assigned to that offset. The signal present at that path offset can then be summed with the contributions of other fingers at their respective offsets. The use of CDMA searchers is disclosed in U.S. Patent No. 5,764,687, entitled "MOBILE DEMODULATOR ARCITECTURE FOR A SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM", assigned to the assignee of the present invention and incorporated by reference herein. In the CDMA receiver structure used in some IS-95 systems, data passing from transmitter to receiver is divided into frames which are transmitted at fixed time intervals. Depending on the varying amount of data to be transmitted during each interval, the transmitter places the data into one of several sizes of frame. Since each of these frame sizes corresponds to a different data rate, the frames are often referred to variable- rate frames. The receiver in such a system must determine the rate of each received frame to properly interpret the data carried within the received frame. Such rate determination methods often include the generation of frame quality metrics, which may be used to assess the level of uncertainty, associated with the determined frame rate. Methods of performing rate determination and generating frame quart metrics are disclosed in U.S. Patent No. 5,751,725, entitled "METHOD AND APP ARA TUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM", assigned to the assignee of the present invention and incorporated by reference herein. Signals in a CDMA system may be complex PN spread as described in U.S. Patent Application Serial No, 08/856,428, entitled "REDUCED PEAK TO AVERAGE TRANSMIT POWER HIGH DATA RATE IN A CDMA WIRELESS COMMUNICATION SYSTEM," filed April 9, 1996, assigned to the assignee of the present invention and incorporated by reference herein, and in accordance with the following equations: I where PNi and PNQ are distinct PN spreading codes and I' and Q' are two channels being spread at the transmitter. As described in cdma2000, transmission signals are constructed utilizing orthogonal Walsh coding, with one Walsh code used to transmit pilot sub-channel signal. The orthogonal Walsh sub-channels used to construct such transmission signals are added together before being transmitted, and travel through the same transmission charnels or pathways before being received at the receiver. Each transmission channel, by its inherent nature, alters the phase and amplitude of the signals passing through it, and also adds a component of thermal noise. These channel characteristics change with any movement by transmitter or receiver, but may vary over time even when both receiver and transmitter are stationary. Channel characteristics generally change very slowly compared with the data symbols transmitted through the channel. Some CDMA receivers employ circuits which estimate the phase and amputee distortion of the channel. These estimates are then used to compensate for channel distortion, enabling more accurate decoding and demodulation of the received signals. One such circuit for estimating phase and amplitude of a channel, and performing a dot product of that output with the demodulated data signal, is described in detail in U.S. Patent No.5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", assigned to the assignee of the present invention and incorporated by reference herein. In that described implementation, an all-zero pilot channel is received and used to estimate the channel characteristics. The resultant channel estimates are then used to convert demodulated signals to scalar digital values. All CDMA signals transmitted on orthogonal sub-channels cause mutual interference to each other, as well as acting as jammers for adjacent cell areas. To enable coherent demodulation of orthogonal sub-channel signals, one sub-channel is often dedicated as a pilot carrier. As detailed in aforementioned U.S. Patent No, 5,506,865, the pilot carrier is used in the receiver to produce estimates of the channel characteristics. The accuracy of these channel estimates is dependent on the strength of the pilot channel signal. Unfortunately, the pilot channel carries no data, so it is desirable to minimize the pilot transmit power. Conventionally the pilot power relative to the data signal power is selected by balancing between these two factors such that the best overall system performance can be achieved. For this reason, a method of producing accurate channel estimates which does not require increased pilot signal strength is highly desirable. SUMMARY OF THE INVENTION The present invention describes a method and apparatus for improving the performance of a receiver that receives multiple sub-channel signals transmitted together through a common propagation path, also called a transmission channel. In order to compensate for phase and amplitude distortion introduced into the signals by the transmission channel, the receiver uses a pilot sub-channel signal to estimate the phase and amplitude distortion of the transmission channel. The process of estimating of distortion inherent in the transmission chattel is called channel estimation, which is used to produce channel estimates. The invention includes a novel method of utilizing data-carrying sub-channels (not the pilot sub-channel) to improve the accuracy of channel estimates. The present invention is applicable to any communication system employing simultaneous transmission of multiple sub channels and coherent demodulation. The sub-channel signals within an information signal may be either time division multiplexed (TDMed) or code division multiplexed (CDMed). The exemplary embodiment describes the present invention in the context of the reverse link proposed in cdma2000. Because of overriding commonalties in channel structure, the present invention is equally applicable to reception of the reverse link transmissions according to the candidate submission proposed by the European Telecommunications Standards Institute (ETSI), entitled 'The ETSI UMTS Terrestrial Radio Access (VTRA) ITU-R RTT Candidate Submission" (hereafter WCDMA). Moreover, the present invention is equally applicable to reception of the formal lilt of these systems. In cdma2000, the data-bearing sub-channels include a high data rate (C.L! '(> X kbps) supplemental channel and a low data rate (e.g. 9.6 kbps) fundamental chum. I The nominal power of the pilot channel is optimized for demodulation fundamental channel (e.g., -of the fundamental channel power). In order lo CIVIC proper demodulation of the high data rate supplemental channel, the cdnKi'ooo standard proposes to increase the pilot power beyond nominal levels when ilu supplemental channel is in use. In addition, the cdma2000 standard proposed 1M i.e. different levels of pilot power depending on which of several available data lays ice supplemental channel is using. Varying the pilot power according to data rate causes other daiquiris m system design. For example, it requires the receiver to know the data rate.m. e in order for the power control loop to behave correctly. This also makes the of searching/fogger locking more difficult. Moreover, it is desirable to overhead to improve overall system performance if it can be done without saei it Kmv demodulation performance. By enabling the formation of channel estimates based on the channel signal, the present invention enables a system to supplementary channel demodulation performance. If enough channel sinker information can be extracted from the fundamental channel, acceptable channel demodulation performance may be achieved without varying the at all. Because the fundamental signal can be transmitted with as much as 4 tin us ilk power of the pilot signal, a channel estimate formed using both signals is nuclei than an estimate based on the pilot signal alone. Subsequent dcniocluliiion using the more accurate channel estimate will have improved performance as well In cdma2000, the transmit power of the fundamental channel is four of the nominal pilot. The combined power of the pilot and fundamental LITHE I. would be five times the power of just the nominal pilot channel. A comical chime estimate derived from both the nominal pilot and fundamental channels woo Inaccurate enough for demodulating a cdma2000 supplemental channel. TIUMIJ'II increasing the pilot power whenever the supplemental channel is in use would si Ml be an option, it may not be necessary given the enhanced accuracy of the channel estimate. The added accuracy of a channel estimate extracted from the fundamental channel depends on the use of a correct reference signal. optimally identical to the transmitted fundamental channel signal. Any InaCom m the decoded symbols used in forming fundamental channel estimates will quality of the combined channel estimate. Though the supplemental channel is likelyto be a packet data channel, which has a high tolerance for frame errors, it he desirable to minimize the frame error rate when demodulating the supplant nil channel. In the preferred embodiment of the invention, the received fichu ninja channel signal is first deinterleaved and forward error correction (FEC) decoct IM take advantage of the transmitter's complementary FEC encoding and functions. Then, the corrected symbol stream is re-encoded and re- in produce an ideal replica of the transmitted signal for use as a reference signal In ih. channel estimator. In an alternative embodiment of the invention, fundamental channel increased as necessary to reduce the fundamental channel error decreasing the fundamental channel error rate produces a more accurate clinic I estimate, increasing fundamental channel power also results in a reduced when demodulating the supplemental channel. When the data rate ratio supplemental and the fundamental channels is large, a slight increase in channel power has little effect on the total transmitted power and hence causes laic degradation. In a more general sense, the present invention can be used where a smile channel of information is transmitted. In an alternate embodiment using a simple channel, the channel is artificially split into two physical channels, which ate transmitted synchronously at different data rates. Upon receipt, the low rate channel first demodulated and decoded using pilot based channel estimates. The defied lies are then re-encoded and used to improve the channel estimates used to coherent demodulate the high data rate supplemental channel. This scheme may entailment throughput which draws nearer to the theoretical capacity limit in a Laurie environment. (t. Accordingly the present invention provides a method of demodulaim;.' n information signal, wherein the information signal is received through a claim having channel characteristics, and wherein the information signal comprises a signal, a first data-carrying signal, and a second data-carrying signal, the milieu comprising: first estimating the channel characteristics based on the pilot signal to provide a IMAM channel estimate; second estimating the channel characteristics based on the first data- carrying Sinai provide a data channel estimate; and combining said pilot channel estimate with said data channel estimate to; combined channel estimate. Accordingly the present invention also provides an apparatus for demodnlaim' an information signal, wherein the Information signal is received through a CACHE I having channel characteristics, and wherein the information signal comprises a piling signal, a first data-carrying signal, and a second data-carrying signal the apparatus-comprising: first means for estimating the channel characteristics based on the received piloi SEMI to provide a pilot channel estimate; second means for estimating the channel characteristics based on the first dale-carrying signal to provide a data channel estimate; and means for combining said pilot channel estimate with said data channel skim provide a combined channel estimate. BRIEF DESCRIPTION OF THE DRAWINGS The features, objects, and advantages of the present invention will more apparent from the detailed description set forth below when taken in with the drawings in which like reference characters identify throughout and wherein: FIG. 1 is a diagram illustrating basic components of a wireless incorporating an embodiment of the invention, FIG. 2 is a block diagram of a preferred embodiment of the invention in a transmitter. FIG. 3 is a block diagram of a preferred embodiment of the invention in a wails. receiver. FIG. 4 is a block diagram of an exemplary channel estimator circuit. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows the present invention in the context of a wireless communication system. In the exemplary embodiment, subscriber station 2 transmits. division multiplexed signals through a transmission chime 8 to a base a;i(u)it transceiver subsystem (BT5) 4 through receive antenna 6. In the embodiment of a cdma2000 or WCOMA reverse link, the code division ad channels are distinguished from one another using orthogonal coding. This M1 providing orthogonal coding is described in detail in aforementioned s Patent Application Serial No, 08/856,428. In the exemplary embodiment, the three types of CDMA signals truism d from subscriber station 2 to base station transceiver subsystem 4 arc piloi lo fundamental 12, and supplemental 14. In the exemplary embodiment, the signal, transmitted from subscriber station 2 are code division multiple access including a pilot channel, a fundamental channel, and a supplemental COUGH i as defined in cdma2000. The generation and transmission of code division. Communication signals is well known in the art and is described in detail in in aforementioned U.S. Patent No. 5,103,459 and in the IS-95 specification. The subscriber station 2 is shown as a mobile station, but could also \\: a wireless modem, wireless local loop subscriber station, a BTS, or any other. communication equipment which transmits multiple synchronous sub-channels I lie receiver station 4 is shown as a BTS, but could also be a wireless subscriber suasion oi any other receiver which coherently demodulates multiple sub-channels. The nieilnul and apparatus for simultaneously receiving multiple transmissions is wail known 111 the art. In the exemplary embodiment, the signals transmitted from subscribe)- SKUIMM 2 are received at BTS 4 using a RAKE receiver, the implementation of which is wail known in the art and is described in the aforementioned U.S. Patent No. 5,109, V)() FIG pilot channel is sent directly ink) a Wall J spreader 110 which spreads the data according to a pilot channel Walsh rankle)n W p thus producing a Walsh covered pilot channel signal. The Walsh covered piloi ethane signal is then sent to a relative gain module 116, which adjusts the appliance of igloo covered pilot channel signal relative to the signals carried by other orthogonal irons sub- channels. In the preferred embodiment, the pilot charnel Walsh Incision is all-zero Walsh code, the pilot channel Walsh spreader 110 is omitted, and a I)( sigma is sent directly into relative gain module 116. The fundamental channel data is first sent to a forward error correction (1 1 ( i encoder 102, which produces an encoded fundamental channel signal. The redshank encoded fundamental channel signal is sent to an interleave 106, which produces an interleaved fundamental channel signal. The interleaved fundamental channel then sent to the Walsh spreader 112, which spreads the data u a fundamental channel Walsh function W ^ thus producing a covered channel signal. The covered fundamental charnels signal is then sent to a relative jam module 118, which adjusts the amplitude of the covered fundamental channel lative to the signals carried by other orthogonal transmit sub-channels. The supplemental channel data is first sent to a forward error correction (lit) encoder 104, which produces an encoded supplemental channel signal. The ivsnluif encoded supplemental channel signal is sent to an interleave 108, which produces an interleaved supplemental channel signal. The interleaved supplemental channel SILMI-II is then sent to the Walsh spreader 114, which spreads the data aecorchnL' lo ,i supplemental channel Walsh function W s' thus producing a covered supiilenieni.il channel signal. The covered supplemental channel signal is then sent to a module 120, which adjusts the amplitude of the covered supplemental channel sera relative to the signals carried by other orthogonal transmit sub-channels. Though the preferred embodiment shown uses orthogonal Walsh (unions lo accomplish sub-channel coding, one skilled in the art will appreciate doing could also be accomplished using TDMA or PN coding departing from the current invention. In an embodiment utilizing VN melanin ilk-reference signals Ws, Wp, and Wp are replaced by PN codes supplemental, pilot, and fundamental channels respectively. One skilled m appreciate that the FEC modules 102 and 104 could employ any of a iunnlxr oi forward error correction techniques without departing from the current Such techniques include turbo-code encoding, convolutional coding, coding such as block coding. In addition, the interleavers any of a number of interleaving techniques, including convolutional turbo-interleaving, block interleaving and bit reversal interleaving, encoders and turbo interleaves are described in aforementioned .(MKi specification. The output of each relative gain module 116,118, and 120 is then skin lo PN spreader module 122. The output of the PN spreader module 122 is transmitter 124. Transmitter 124 provides additional control of transmit varying the gain of the entire composite signal received from PN spreads module 111 before transmitting the signal through antenna 126. In an alternative embodiment, the optional relative gain module 1 16 is and the pilot signal is sent directly to the PN spreader module 122. The yoyos channels are adjusted with respect to the gain of the pilot channel. One skilled in ilk-art will appreciate that the two methods of controlling relative gains ol' the chasmal , using the system including relative gain module 116 or without relative gain module 116, are functionally equivalent. appreciate that one may use either method of setting a sub-channel's gain to zero without departing from the present invention. PN spreader 122 spreads the orthogonal channel signals using a pseudoraiulom generated spreading sequence and sends the resultant composite signal transmitter 124 for transmission through relative gain modules IK). IIS. and 120 are controlled dynamically by gain control processor 128. The gain ol cav li module may be altered according to data rates of the channels. For example, hick piloi channel gain may be increased when data is being transmitted on both and the supplemental channel. Or, the fundamental channel gain n)a\ ix-increased when data is being transmitted on the supplemental channel. FIG. 4 shows an exemplary embodiment of a channel estimator 2 IX. Ilk-complex input signal is provided to channel estimator 218 as I and Q sample sylvan. The I samples are mixed with a reference signal in mixer 302a, to component of the complex input signal. The output of mixer 302a is provided lo nois. rejection filter 304a to remove noise from the extracted real component. In nnxcr 302b, The Q samples are mixed with the same reference signal as used in niixei M)'.\A in order to extract an imaginary component of the complex input signal. Tlie i>ui\|)iii oi mixer 302b is provided to noise rejection filter 304b to remove noise troni ihe extracted imaginary component. One skilled in the art will appreciate thai the ntn .e rejection filters 304 may be implemented as low-pass filters, matched Idlers, oi accumulators without departing from the current invention. The reference signal used in a channel estimator 218 could be reah inuiLiin;ii\ or complex. In an alternative embodiment of a channel estimator 218 appioiMiiiie loi use with a complex reference signal, mixers 302 are complex multipliers (wineli MI.IN also be called complex mixers), each having both real and imaginary outputs. The ie;il outputs of mixers 302 are then summed before being filtered in rcal-coniponeni iihei 304a. The imaginary outputs of mixers 302 are summed before being fiheied in imaginary-component filter 304b. In the same fashion, complex mulliplieis eould IK used in a Walsh spreader or despreader to allow the use of complex Walsh eiides ;i. reference functions during spreading and despreading. Walsh spreachni] n: in:' complex Walsh codes is known as complex Walsh spreading, and Walsh des\|iieadmL' using complex Walsh codes is known as complex Walsh despreading. In the proposed cdma2000 standard, the pilot channel is transmitted 90 dei'iee. out of phase with the fundamental and supplemental channels. In the iMelerred embodiment, therefore, the pilot channel estimator 218a rotates iis output In '^ degrees. This rotation may be accomplished in many ways, including nuiiiipl\ inv ih reference by an imaginary value, or by rotating the real and imaginary outputs ol nui. rejection filters 304. The same end result may also be accomplished b\' lotatmij ih signals of the fundamental and supplementary channels without dcparlini! Irom ih current invention. Also, the relative rotation of the pilot channel in rclatit^n \o \\\ fundamental and supplementary channels may be positive or negaii\c wiihoi departing from the current invention. Together, the extracted real and imaginary components constitute a channel estimate vector containing amplitude and phase information for any signal comp^uum which correlates with the reference signal. The quality of the channel esinnaie depends on the degree of correlation between the received complex input sienal ami the reference signal. To achieve the highest degree of correlation between ilu received complex input signal and the reference signal, the reference signal used In the receiver must exactly match that transmitted by the transmitter, for example W aMi code W p in the case of the pilot channel. Any difference between the reterenee sienal and the transmitted signal can cause inaccuracy in the channel estimate. In an IS-95 system, the pilot Walsh code W p is an all-zero Walsh eoUr. n which case a channel estimate can be made using just a pair of filters, as is JescnlKt in aforementioned U.S. Patent 5,506,865. In this case, pilot channel Walsh spu\uki 110 is omitted from the transmitter. The channel estimator in the recei\er e(uiM ihci be implemented such that the mixers 302 could be omitted from pilot CIKHIDLI estimator 218a. A channel estimator for an all-zero Walsh code pilot, consisiiiij' oi filters without mixers, is also known as a pilot filter. The embodiment of Ihc chaiuRi estimator depicted in FIG. 4, however, allows the use of a pilot Walsh code oilu-r ihan the all-zero Walsh code. Together, the Pilot I and Pilot Q signals are used as an cstimalc ti! IIK amplitude and phase characteristics of the CDMA transmission channel S, MK resultant Pilot 1 and Pilot Q along with the decovered fundamental channel I aiul (.> components are provided to dot product module 208. Dot product module 2()X wliieh computes the scalar projection of the fundamental channel signal onto ihe pi lot channel estimate vector, in accordance with the circuit described in albrenK-niioned U.S. Patent No. 5,506,865. Because the pilot channel signal 10, the rundanieiiial channel signal 12, and the supplemental channel signal 14 have traversed the same propagation path 8, the channel induced phase error is the same for all three siyjials This phase error is removed by performing the dot product operation desei IIK\I in aforementioned U.S. Patent 5,506,865. In the exemplary embodinieni. ilie fundamental channel is coherently demodulated in a dot product module 2()S usmi' i pilot channel estimate. The dot product module produces a scalar signal lor eaeh symbol period, which is indicative of the magnitude of the fundamental channel sienal that is in phase with the pilot signal received through the transmission channel K. The fundamental channel symbols output by the dot product inodiilc 20N i then sent into deinterleaver 210, which performs the inverse of the tunLiiDii n\ transmit interleaver 106. The resultant deinterleaved signal is then sent lo ri)r\\;iiJ error correction (FEC) decoder 212. Decoder 212 performs the inverse riinction ol \\K FEC encoder 102 and outputs a forward error corrected signal. The corrected signal output by decoder 212 is also sent lo an encoder 21\. which re-encodes the signal using the same FEC function as the traiisnuilci I i ( encoder 102. In this way, encoder 224 produces an ideal representation ol ihc transmitted fundamental signal This ideal representation is then sent to an inlcilc;i\ cr 226, which performs the same function as the transmitter interleaver 106. prodiicinL' an ideal representation of the interleaved fundamental channel data transmiucd h\ subscriber station 2. The I and Q component samples produced by Walsh despreader arc also inpni into delays 220, which produce I and Q components which are synchroni/cd \\ iih IIK output of the interleaver 226. Delays 220 are designed to compensate lor ilic tlcla\. introduced by the dot product module 208, the deinterleaver 210, the decoder 212. ilic encoder 224, and the interleaver 226. The synchronized I and Q components output by delays 220 arc ihcn scni along with the output of interleaver 226, into channel estimator 2l8h. (iianiic estimator 218b uses the output of interleaver 226 as a reference signal, and uses ilu outputs of delays 220 as the I and Q sample stream from which it forms a channel estimate output. The corrected bits output by FEC decoder 212 are re-encoded and re-interleaved to produce a reference signal which has a higher probability of matching what was actually transmitted on the fundamental channel. By using this more reliable reference signal as input for channel estimator 218b, the accuracy of fundamental channel estimates produced by channel estimator 218b is improved. In a suboptimal embodiment, instead of using deinterleaver 210, decoder 212, encoder 224, and interleaver 226 to create an ideal representation of the fundamental channel signal, the output of dot product module 208 could be provided directly to channel estimator 218b, In this case, delay elements 220 would only compensate for the time required to perform the dot product operation in dot product module 208. However, the fundamental channel estimator would not gain the error correction benefits of the bypassed components. The complex output components of the pilot channel estimator 218a are subjected to delay elements 222 to compensate for the delay inherent in performing channel estimation using the fundamental channel signal. The channel estimation parameters produced by processing of the fundamental charmel is sent, along with the delayed channel estimation parameters from the delay elements 220 and 222 into channel estimate combiner 230. Channel estimate combiner 230 combines the channel estimation data for both pilot and fundamental channel processing and produces output containing a third, combined channel estimate. As the characteristics of the transmission channel change over time, pilot channel estimator 218a and channel estimator 218b provide updated channel estimates to channel estimate combiner 230, which updates the combined channel estimation output accordingly. In the preferred embodiment, the output of decoder 212 sent to encoder 224 is additionally sent to control processor 216. Control processor 216 produces frame rate information for each received frame of data. Control processor 216 also performs validity checking of the received frames. Control processor 216 produces a fundamental channel quality metric based on the results of its rate determination and validity checking of received data. The fundamental channel quality metric is used to assign an appropriate v^eighting factor to the fundamental channel estimate in relation to the weighting factor assigned to the pilot channel estimate. The fundamental channel quality metric varies based on the validity of received frames based on the correctness of the CRC. Since different rate frames may also use different numbers of CRC bits, or have varying degrees of frame error checking protection, control processor 216 may additionally vary the fundamental channel quality metric according to received frame rate. Control processor 216 is also connected to encoder 224, Control processor 216 sends frame rate information to encoder 224 for use in re- encoding the data received from decoder 212. In the exemplary embodiment, channel estimate combiner 230 is a weighted-average combiner, which produces the combined channel estimation signal by performing a weighted average of the pilot and fundamental channel estimates in accordance with the following equations: RcOMB ~ X RpiLOT + (1-X) RpUND (3) ICOMB ~ X IpiLOT + (1 "X) IpUND (4) where RCOMB and ICOMB are the real an imaginary components of the combined channel estimate, RPILOT and IPILOT are the real an imaginary components of the pilot channel estimate, RFUND and IFUND are the real an imaginary components of the fundamental channel estimate, and X is a scaling factor. The scaling factor X has a value from 0 to 1. A scaling factor value of 1 results in a combined channel estimate which is equal to the pilot channel estimate. A scaling factor value of 0 results in a combined channel estimate which is equal to the fundamental channel estimate. The value of X represents a first muUiplier, which is muUiplied by the pilot channel estimate to produce a scaled channel estimate for the pilot charmel. The value of (1-X) represents a second multiplier, which is multiplied by the fundamental channel estimate to produce a scaled channel estimate for the fundamental channel. The two scaled channel estimates are added together to produce the combined channel estimate. Channel estimate combiner 230 additionally uses the fundamental channel quality metric provided by control processor 216 as a dynamic weighting factor to the channel estimates produced from the fundamental channel. When the fundamental channel quality metric indicates a high rate of frame errors, channel estimate combiner 230 increases the value of the scaling factor X. When frame errors occur, therefore, the combined channel estimate used for demodulating the supplemental channel is derived more from the pilot channel estimate and less from the fundamental channel estimate. In an alternative embodiment, a frame error causes the value of scaling factor X to be equal to 1 until a valid frame is received. In an alternative embodiment of the invention, control processor 216 includes a smoothing module, which performs smoothing, or low-pass filtering, of the fundamental channel quality metric before it is sent to channel estimate combiner 230. This smoothing helps to make the weighted average performed by channel estimate combiner 230 less susceptible to high-frequency noise inherent in the channel. In yet another embodiment of the current invention, the receiver knows the relative gains used by relative gain modules 116 and 118 when transmitting the pilot and fundamental channel signals. In this embodiment, the value of X is adjusted such that the ratio of the first multiplier over the second multiplier is equal to the ratio of the transmit gain of the pilot channel over the transmit gain of the fundamental channel. In the preferred embodiment, the fundamental channel quality 1 metric provided by control processor 216 to channel estimate combiner 230 is synchronized with the reference signal provided to channel estimator 218b, This can be accomplished by incorporating a delay or buffer into control processor 216. Control processor 216 may also perform a smoothing function to the fundamental channel quality metric before providing it to channel estimator 218b. In the preferred embodiment, however, the fundamental channel quality metric produced by control processor 216 is not smoothed, and may change suddenly on frame boundaries. The I and Q component samples used as input to Walsh despreader 236 are sent through delay elements 232, which serve to synchronize the output of Walsh despreader 236 with the output of channel estimate combiner 238. Delay elements 232 could instead be placed between Walsh despreader 236 and dot product module 238 without departing from the present invention. Walsh despreader 236 uses the Walsh function W s used by the transmitter's Walsh spreader 114, and produces decovered supplemental channel I and Q components. These decovered supplemental channel components, along with the combined channel estimation signal from channel estimate combiner 230, are used as input for dot product module 238. Dot product module 238 computes the magnitude of the projection of the supplemental channel signal onto the combined channel estimate vector, resulting in a scalar projection output. The output of dot product module 238 is then deinterleaved in deinterleaver 240, which performs the inverse function of interleaver 108, The output of deinterleaver 240 is provided to decoder 242, which performs the inverse function of interleaver 104. Throughout the wireless receiver portrayed in FIG. 3, one slcilled in the art will appreciate that any of the delay elements 220,222, or 232 could be implemented as accumulators or buffers without departing from the current invention. In addition, one skilled in the art will appreciate that pairs of delay elements, for example delay elements 232a and 232b, may be implemented separately, or combined into a single delay module which performs the same function, without departing from the current invention. Though the preferred embodiment shown uses orthogonal Walsh functions to accomplish sub-channel decoding, one skilled in the art will appreciate that the subchannel decoding could also be accomplished using TDMA or PN coding without departing from the current invention. In an embodiment utilizing PN coding, reference signals W s' W p, and W F are replaced by PN codes corresponding to the supplemental, pilot, and fundamental channels respectively. We Claim: 1, A method of demodulating an information signal, wherein the information signal is received through a channel having channel characteristics, and wherein the information signal comprises a pilot signal, a first data-carrying signal, and a second data-carrying signal, the method comprising: first estimating the channel characteristics based on the pilot signal to provide a pilot channel estimate; second estimating the channel characteristics based on the first data- carrying signal to provide a data channel estimate; and Combining said pilot channel estimate with said data channel estimate to provide a combined channel estimate. 2. The method as claimed in claim 1 comprising generating a scalar projection of the information signal in accordance with the combined channel estimate. 3- The method as claimed in claim 1 comprising pseudonoise despreading the information signal 4. The method as claimed in claim 3 wherein the pseudonoise despreading is complex pseudonoise despreading. 5. The method as claimed in claim 1 wherein said second estimating comprises generating a scalar projection of the information signal in accordance with the pilot channel estimate. 6. The method as claimed in claim 5 wherein said second estimating comprises generating an ideal representation of the first data-carrying signal. 7. The method as claimed in claim 6 wherein said generating an ideal representation comprises: deinterleaving the first data-carrying signal to provide a deinterleaved signal; and interleaving the deinterleaved signal. 8. The method as claimed in claim 6 wherein said generating an ideal representation comprises: decoding the first data-carrying signal to provide a decoded signal; and encoding the decoded signal. 9, The method as claimed in claim 1 comprising introducing a delay into the pilot channel estimate to provide synchronization between the pilot channel estimate and the data channel estimate. 10. The method of claim 1 wherein said combining comprises: multiplying said pilot channel estimate by a pilot multiplier to produce a scaled pilot channel estimate; multiplying said data channel estimate by a data multiplier to produce a scaled data channel estimate; and adding said scaled pilot channel estimate to said scaled data channel estimate to provide said combined channel estimate. 11. The method as claimed in claim 10 wherein a ratio of said pilot multiplier over said data multiplier is based on a ratio of a gain used to transmit the pilot signal over a gain used to transmit said first data-carrying signal. 12. The method as claimed in claim 10 comprising generating the pilot multiplier and the data multiplier. 13. The method as claimed in claim 10 comprising changing a ratio of the pilot multiplier to the data multiplier based on a data rate of the first data-carrying signal. 14, The method as claimed in claim 10 comprising changing a ratio of the pilot multiplier to the data multiplier based on a frame quality metric of the first data-carrying signal. 15. The method as claimed in claim 1 wherein said first estimating comprises filtering the information signal to provide the pilot channel estimate. 16. The method as claimed in claim 15 wherein said first estimating comprises moiling the information signal by a reference pilot code. 17. The method as claimed in claim 1 wherein said second estimating comprises: generating a scalar projection of the information signal in accordance with the pilot channel estimate to provide a scalar information signal; decoding the scalar information signal to provide a decoded signal; encoding the decoded signal to provide an ideal representation of the first data-carrying signal; and multiplying the information signal by the ideal representation to provide the data charmed estimate. 18. The method of claim 17 wherein said first estimating further comprises: deinterleaving the scalar information signal prior to said decoding; and interleaving the ideal representation prior to said muhiplying. . 19. An apparatus for demodulating an information signal, wherein the information signal is received through a channel having channel characteristics, and wherein the information signal comprises a pilot signal, a first data-carrying signal, and a second data-carrying signal, the apparatus comprising: first means for estimating the channel characteristics based on the received pilot signal to provide a pilot channel estimate; second means for estimating the channel characteristics based on the first data-carrying signal to provide a data channel estimate; and means for combining said pilot charmel estimate with said data channel estimate to provide a combined channel estimate. 20. The apparatus as claimed in claim 19 comprising means for generating a scalar projection of the information signal in accordance with the combined channel estimate. 21. The apparatus of claim 19 comprising means for pseudonoise despreading the information signal. 22, The apparatus of claim 19 further comprising means for complex pseudonoise despreading the information signal. 23. The apparatus of claim 19 wherein said second means for estimating comprises means for generating a scalar projection of the information signal in accordance with the pilot channel estimate, 24. The apparatus as claimed in claim 23 wherein said second means for estimating comprises means for generating an ideal representation of the first data-carrying signal. 25. The apparatus as claimed in claim 24 wherein said means for generating an ideal representation comprises: means for deinterleaving the first data-carrying signal to provide a deinterleaved signal; and means for interleaving the deinterleaved signal. 26. The apparatus as claimed in claim 24 wherein said means for generating an ideal representation comprises: means for decoding the first data-carrying signal to provide a decoded signal; and means for encoding the decoded signal. 27. The apparatus as claimed in claim 19 comprising means for introducing a delay into the pilot channel estimate to provide synchronization between the pilot channel estimate and the data channel estimate. 28, The apparatus as claimed in claim 19 wherein said means for combining comprises: means for multiplying said pilot channel estimate by a pilot multiplier to produce a scaled pilot channel estimate; means for multiplying said data channel estimate by a data multiplier to produce a scaled data channel estimate; and means for adding said scaled pilot channel estimate to said scaled data channel estimate to provide said combined channel estimate. 29- The apparatus of claim 28 comprising means for generating the pilot multiplier and the data multiplier. 30. The apparatus of claim 28 comprising means for changing a ratio of the pilot mushily to the data multiplier based on a data rate of the first data- carrying signal, 31. The apparatus as claimed in claim 28 comprising means for changing a ratio of the pilot multiplier to the data multiplier based on a frame quality metric of the first data-carrying signal. 32. The apparatus as claimed in claim 19 wherein said first means for estimating comprises means for filtering the information signal to provide the pilot channel estimate. 33. The apparatus as claimed in claim 32 wherein said first means for estimating comprises means for multiplying the information signal by a reference pilot code. 34, The apparatus as claimed in claim 19 wherein said second means for estimating comprises: Means for generating a scalar projection of the information signal in accordance with the pilot channel estimate to provide a scalar information signal; means for decoding the scalar information signal to provide a decoded signal; means for encoding the decoded signal to provide an ideal representation of the first data-carrying signal; and means for multiplying the information signal by the ideal representation to provide the data channel estimate. 35. The apparatus of claim 34 wherein said first means for estimating further comprises: means for deinterleaving the scalar information signal prior to said decoding; and means for interleaving the ideal representation prior to said multiplying. 36. An apparatus for demodulating an information signal, wherein the information signal is received through a channel having channel characteristics, and wherein the information signal comprises a pilot signal, a first data-carrying signal, and a second data-carrying signal, the apparatus comprising: pilot channel estimator configured to estimate the channel characteristics based on the pilot channel signal to provide a pilot channel estimate; data channel estimator configured to estimate the channel characteristics based on the first data channel signal to provide a data channel, estimate; channel estimate combiner configured to combine said pilot channel estimate with said data channel estimate to generate a combined channel estimate. 37. The apparatus as claimed in claim 36 comprising a first dot product module configured to modify a phase of the information signal based on the combined channel estimate to producing a sub-channel symbol stream. 38. The apparatus as claimed in claim 36 comprising a first dot product module configured to modify a phase of the information signal based on the combined channel estimate to producing a sub-channel symbol stream. 39. The apparatus as claimed in claim 36 comprising dot product module for generating a scalar projection of the information signal in accordance with the combined channel estimate. 40. The apparatus as claimed in claim 36 comprising pseudonoise despreader for multiplying the information signal by a pseudonoise code. 41. The apparatus as claimed in claim 40 wherein the pseudonoise despreader is a complex pseudonoise despreader for multiplying the information signal by a complex pseudonoise code. 42. The apparatus as claimed in claim 36 wherein said data channel estimator comprises dot product module for generating a scalar projection of the information signal in accordance with the pilot channel estimate to provide a scalar information signal. combiner. 48, The apparatus as claimed in claim 36 wherein said channel estimate combiner is a weighted-average combiner configured to provide the combined channel estimate in accordance with the following equations: the real an imaginary components of the combined channel estimate, RPLLOT and IRLLOT are the real an imaginary components of the pilot channel estimate, RDATA and IDATA are the real an imaginary components of the fundamental channel estimate, and X is a scaling factor. 49. The apparatus as claimed in claim 48 wherein said weighted-average combiner is configured to use a value of X that is based on a ratio of a gain used to transmit the pilot signal over a gain used to transmit said first data-carrying signal. 50. The apparatus of claim 48 comprising control processor configured to provide the value X to said weighted-average combiner. 51. The apparatus as claimed in claim 50, wherein said control processor is configured to adjust said value X based on a data rate of the first data-carrying signal. 52. The apparatus as claimed in claim 48, wherein said control processor is configured to adjust said value X based on a frame quality metric of the first data-carrying I signal. 53. The apparatus as claimed in claim 36 wherein said pilot channel estimator comprises filter for filtering the information signal to provide the pilot channel estimate. 54. The apparatus as claimed in claim 53 wherein said pilot channel estimator comprises mixer for multiplying the information signal by a reference pilot code. 55. The apparatus of claim 36 wherein said data channel estimator comprises: dot product module configured to multiply the information signal with the pilot channel estimate to provide a scalar information signal; decoder configured to decode the scalar information signal to provide a decoded signal; encoder configured to encode the decoded signal to provide an ideal representation of the first data-carrying signal; and mixer for multiplying the information signal by the ideal representation to provide the data channel estimate. 56. The apparatus as claimed in claim 55 wherein said data channel estimator comprises: deinterleaver configured to deinterleave the scalar information signal; and interleave configured to interleave the ideal representation. 57. A method of demodulating an information signal, substantially as herein described, with reference to the accompanying drawings. 58. An apparatus for demodulating an information signal, substantially as herein described, with reference to the accompanying drawings.

Full Text

L Field of the Invention
The current invention relates a method and apparatus for demodulating an information signal. More particularly, the present invention relates to a novel and improved method of compensating for phase and amplitude distortion of multiple signals transmitted through a single channel. II. Description of the Related Art
The use of code division multiple access (CDMA) modulation 15 techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division maniple access (FDMA) and AM modulation schemes such as amplitude commanded single sideband (ACSSB) are known in the art. Techniques for distinguishing different concurrently-transmitted signals in multiple access communication systems are also known as channelization. The spread spectrum modulation technique of CDMA has significant advantages over other multiple access techniques.
The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", and in U.S. Patent No. 5,751,761, entitled "SYSTEM AND

METHOD FOR ORTHOGONAL SPREAD SPECTRUM SEQUENCE GENERATION IN VARIABLE DATA RATE SYSTEMS", both assigned to the assignee of the present invention and incorporated by reference herein. Code division multiple access communications systems have been standardized in the United States in Telecommunications Industry Association TIA/EIA/IS-95-A, entitled "MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM", hereafter referred to as IS-95 and incorporated by reference herein.
The International Telecommunications Union recently requested the submission of proposed methods for providing high rate data and high- quality speech services over wireless communication channels, A first of these proposals was issued by the Telecommunications Industry Association, entitled "The cdma2000 ITU-R RTT Candidate Submission" hereafter referred to as cdma2000 and incorporated by reference herein. A second of these proposals was issued by the European Telecommunications Standards Institute (ETSI), entitled "The ETSI UMTS Terrestrial Radio Access (UTRA) ITU-R RTT Candidate Submission". And a third proposal was submitted by U.S. TG 8/1 entitled "The UWC-136 Candidate Submission" (referred to herein as EDGE). The contents of these submissions is public record and is well known in the art.
In the CDMA demodulator structure used in some IS-95 systems, the pseudonoise (PN) chip interval defines the minimum separation two paths must have in order to be combined. Before the distinct paths can be demodulated, the relative arrival times (or offsets) of the paths in the received signal must first be determined.

The demodulator performs this function by "searching" through a sequence of offsets and measuring the energy received at each offset. If the energy associated with a potential offset exceeds a certain threshold, a demodulation element, or "finger" may be assigned to that offset. The signal present at that path offset can then be summed with the contributions of other fingers at their respective offsets. The use of CDMA searchers is disclosed in U.S. Patent No. 5,764,687, entitled "MOBILE DEMODULATOR ARCITECTURE FOR A SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM", assigned to the assignee of the present invention and incorporated by reference herein.
In the CDMA receiver structure used in some IS-95 systems, data passing from transmitter to receiver is divided into frames which are transmitted at fixed time intervals. Depending on the varying amount of data to be transmitted during each interval, the transmitter places the data into one of several sizes of frame. Since each of these frame sizes corresponds to a different data rate, the frames are often referred to variable- rate frames. The receiver in such a system must determine the rate of each received frame to properly interpret the data carried within the received frame. Such rate determination methods often include the generation of frame quality metrics, which may be used to assess the level of uncertainty, associated with the determined frame rate. Methods of performing rate determination and generating frame quart metrics are disclosed in U.S. Patent No. 5,751,725, entitled "METHOD AND APP ARA TUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM", assigned to the assignee of the present invention and incorporated by reference herein.

Signals in a CDMA system may be complex PN spread as described in U.S. Patent Application Serial No, 08/856,428, entitled "REDUCED PEAK TO AVERAGE TRANSMIT POWER HIGH DATA RATE IN A CDMA WIRELESS COMMUNICATION SYSTEM," filed April 9, 1996, assigned to the assignee of the present invention and incorporated by reference herein, and in accordance with the following equations:
I
where PNi and PNQ are distinct PN spreading codes and I' and Q' are two channels being spread at the transmitter.
As described in cdma2000, transmission signals are constructed utilizing orthogonal Walsh coding, with one Walsh code used to transmit pilot sub-channel signal. The orthogonal Walsh sub-channels used to construct such transmission signals are added together before being transmitted, and travel through the same transmission charnels or pathways before being received at the receiver. Each transmission channel, by its inherent nature, alters the phase and amplitude of the signals passing through it, and also adds a component of thermal noise. These channel characteristics change with any movement by transmitter or receiver, but may vary over time even when both receiver and transmitter are stationary. Channel characteristics generally change very slowly compared with the data symbols transmitted through the channel.

Some CDMA receivers employ circuits which estimate the phase and amputee distortion of the channel. These estimates are then used to compensate for channel distortion, enabling more accurate decoding and demodulation of the received signals. One such circuit for estimating phase and amplitude of a channel, and performing a dot product of that output with the demodulated data signal, is described in detail in U.S. Patent No.5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", assigned to the assignee of the present invention and incorporated by reference herein. In that described implementation, an all-zero pilot channel is received and used to estimate the channel characteristics. The resultant channel estimates are then used to convert demodulated signals to scalar digital values.
All CDMA signals transmitted on orthogonal sub-channels cause mutual interference to each other, as well as acting as jammers for adjacent cell areas. To enable coherent demodulation of orthogonal sub-channel signals, one sub-channel is often dedicated as a pilot carrier. As detailed in aforementioned U.S. Patent No, 5,506,865, the pilot carrier is used in the receiver to produce estimates of the channel characteristics. The accuracy of these channel estimates is dependent on the strength of the pilot channel signal. Unfortunately, the pilot channel carries no data, so it is desirable to minimize the pilot transmit power. Conventionally the pilot power relative to the data signal power is selected by balancing between these two factors such that the best overall system performance can be achieved. For this reason, a method of producing accurate channel estimates which does not require increased pilot signal strength is highly desirable.

SUMMARY OF THE INVENTION
The present invention describes a method and apparatus for improving the performance of a receiver that receives multiple sub-channel signals transmitted together through a common propagation path, also called a transmission channel. In order to compensate for phase and amplitude distortion introduced into the signals by the transmission channel, the receiver uses a pilot sub-channel signal to estimate the phase and amplitude distortion of the transmission channel. The process of estimating of distortion inherent in the transmission chattel is called channel estimation, which is used to produce channel estimates. The invention includes a novel method of utilizing data-carrying sub-channels (not the pilot sub-channel) to improve the accuracy of channel estimates. The present invention is applicable to any communication system employing simultaneous transmission of multiple sub channels and coherent demodulation.
The sub-channel signals within an information signal may be either time division multiplexed (TDMed) or code division multiplexed (CDMed). The exemplary embodiment describes the present invention in the context of the reverse link proposed in cdma2000. Because of overriding commonalties in channel structure, the present invention is equally applicable to reception of the reverse link transmissions according to the candidate submission proposed by the European Telecommunications Standards Institute (ETSI), entitled 'The ETSI UMTS Terrestrial Radio Access (VTRA) ITU-R RTT Candidate Submission" (hereafter WCDMA).

Moreover, the present invention is equally applicable to reception of the formal lilt of these systems.
In cdma2000, the data-bearing sub-channels include a high data rate (C.L! '(> X kbps) supplemental channel and a low data rate (e.g. 9.6 kbps) fundamental chum. I The nominal power of the pilot channel is optimized for demodulation fundamental channel (e.g., -of the fundamental channel power). In order lo CIVIC proper demodulation of the high data rate supplemental channel, the cdnKi'ooo standard proposes to increase the pilot power beyond nominal levels when ilu supplemental channel is in use. In addition, the cdma2000 standard proposed 1M i.e. different levels of pilot power depending on which of several available data lays ice supplemental channel is using.
Varying the pilot power according to data rate causes other daiquiris m system design. For example, it requires the receiver to know the data rate.m. e in order for the power control loop to behave correctly. This also makes the of searching/fogger locking more difficult. Moreover, it is desirable to overhead to improve overall system performance if it can be done without saei it Kmv demodulation performance.
By enabling the formation of channel estimates based on the channel signal, the present invention enables a system to supplementary channel demodulation performance. If enough channel sinker information can be extracted from the fundamental channel, acceptable channel demodulation performance may be achieved without varying the
at all. Because the fundamental signal can be transmitted with as much as 4 tin us ilk power of the pilot signal, a channel estimate formed using both signals is nuclei than an estimate based on the pilot signal alone. Subsequent dcniocluliiion using the more accurate channel estimate will have improved performance as well
In cdma2000, the transmit power of the fundamental channel is four of the nominal pilot. The combined power of the pilot and fundamental LITHE I. would be five times the power of just the nominal pilot channel. A comical chime estimate derived from both the nominal pilot and fundamental channels woo Inaccurate enough for demodulating a cdma2000 supplemental channel. TIUMIJ'II increasing the pilot power whenever the supplemental channel is in use would si Ml be an option, it may not be necessary given the enhanced accuracy of the channel estimate.
The added accuracy of a channel estimate extracted from the fundamental channel depends on the use of a correct reference signal. optimally identical to the transmitted fundamental channel signal. Any InaCom m the decoded symbols used in forming fundamental channel estimates will quality of the combined channel estimate. Though the supplemental channel is likelyto be a packet data channel, which has a high tolerance for frame errors, it he desirable to minimize the frame error rate when demodulating the supplant nil channel.

In the preferred embodiment of the invention, the received fichu ninja channel signal is first deinterleaved and forward error correction (FEC) decoct IM take advantage of the transmitter's complementary FEC encoding and functions. Then, the corrected symbol stream is re-encoded and re- in produce an ideal replica of the transmitted signal for use as a reference signal In ih. channel estimator.
In an alternative embodiment of the invention, fundamental channel increased as necessary to reduce the fundamental channel error decreasing the fundamental channel error rate produces a more accurate clinic I estimate, increasing fundamental channel power also results in a reduced when demodulating the supplemental channel. When the data rate ratio supplemental and the fundamental channels is large, a slight increase in channel power has little effect on the total transmitted power and hence causes laic degradation.
In a more general sense, the present invention can be used where a smile channel of information is transmitted. In an alternate embodiment using a simple channel, the channel is artificially split into two physical channels, which ate transmitted synchronously at different data rates. Upon receipt, the low rate channel first demodulated and decoded using pilot based channel estimates. The defied lies are then re-encoded and used to improve the channel estimates used to coherent demodulate the high data rate supplemental channel. This scheme may entailment throughput which draws nearer to the theoretical capacity limit in a Laurie environment.

(t.
Accordingly the present invention provides a method of demodulaim;.' n information signal, wherein the information signal is received through a claim having channel characteristics, and wherein the information signal comprises a signal, a first data-carrying signal, and a second data-carrying signal, the milieu comprising:
first estimating the channel characteristics based on the pilot signal to provide a IMAM channel estimate;
second estimating the channel characteristics based on the first data- carrying Sinai provide a data channel estimate; and
combining said pilot channel estimate with said data channel estimate to; combined channel estimate.
Accordingly the present invention also provides an apparatus for demodnlaim' an information signal, wherein the Information signal is received through a CACHE I having channel characteristics, and wherein the information signal comprises a piling signal, a first data-carrying signal, and a second data-carrying signal the apparatus-comprising:
first means for estimating the channel characteristics based on the received piloi SEMI to provide a pilot channel estimate;
second means for estimating the channel characteristics based on the first dale-carrying signal to provide a data channel estimate; and
means for combining said pilot channel estimate with said data channel skim provide a combined channel estimate.

BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of the present invention will more apparent from the detailed description set forth below when taken in with the drawings in which like reference characters identify throughout and wherein:
FIG. 1 is a diagram illustrating basic components of a wireless incorporating an embodiment of the invention,
FIG. 2 is a block diagram of a preferred embodiment of the invention in a transmitter.
FIG. 3 is a block diagram of a preferred embodiment of the invention in a wails. receiver. FIG. 4 is a block diagram of an exemplary channel estimator circuit.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows the present invention in the context of a wireless communication
system. In the exemplary embodiment, subscriber station 2 transmits.
division multiplexed signals through a transmission chime 8 to a base a;i(u)it
transceiver subsystem (BT5) 4 through receive antenna 6. In the
embodiment of a cdma2000 or WCOMA reverse link, the code division ad channels are distinguished from one another using orthogonal coding. This M1 providing orthogonal coding is described in detail in aforementioned s Patent Application Serial No, 08/856,428.

In the exemplary embodiment, the three types of CDMA signals truism d from subscriber station 2 to base station transceiver subsystem 4 arc piloi lo fundamental 12, and supplemental 14. In the exemplary embodiment, the signal, transmitted from subscriber station 2 are code division multiple access including a pilot channel, a fundamental channel, and a supplemental COUGH i as defined in cdma2000.
The generation and transmission of code division. Communication signals is well known in the art and is described in detail in in aforementioned U.S. Patent No. 5,103,459 and in the IS-95 specification.
The subscriber station 2 is shown as a mobile station, but could also \\: a wireless modem, wireless local loop subscriber station, a BTS, or any other. communication equipment which transmits multiple synchronous sub-channels I lie receiver station 4 is shown as a BTS, but could also be a wireless subscriber suasion oi any other receiver which coherently demodulates multiple sub-channels. The nieilnul and apparatus for simultaneously receiving multiple transmissions is wail known 111 the art. In the exemplary embodiment, the signals transmitted from subscribe)- SKUIMM 2 are received at BTS 4 using a RAKE receiver, the implementation of which is wail known in the art and is described in the aforementioned U.S. Patent No. 5,109, V)()

FIG pilot channel is sent directly ink) a Wall J spreader 110 which spreads the data according to a pilot channel Walsh rankle)n W p thus producing a Walsh covered pilot channel signal. The Walsh covered piloi ethane signal is then sent to a relative gain module 116, which adjusts the appliance of igloo covered pilot channel signal relative to the signals carried by other orthogonal irons sub- channels. In the preferred embodiment, the pilot charnel Walsh Incision is all-zero Walsh code, the pilot channel Walsh spreader 110 is omitted, and a I)( sigma is sent directly into relative gain module 116.
The fundamental channel data is first sent to a forward error correction (1 1 ( i encoder 102, which produces an encoded fundamental channel signal. The redshank encoded fundamental channel signal is sent to an interleave 106, which produces an interleaved fundamental channel signal. The interleaved fundamental channel then sent to the Walsh spreader 112, which spreads the data u a fundamental channel Walsh function W ^ thus producing a covered channel signal. The covered fundamental charnels signal is then sent to a relative jam

module 118, which adjusts the amplitude of the covered fundamental channel lative to the signals carried by other orthogonal transmit sub-channels.
The supplemental channel data is first sent to a forward error correction (lit) encoder 104, which produces an encoded supplemental channel signal. The ivsnluif encoded supplemental channel signal is sent to an interleave 108, which produces an interleaved supplemental channel signal. The interleaved supplemental channel SILMI-II is then sent to the Walsh spreader 114, which spreads the data aecorchnL' lo ,i supplemental channel Walsh function W s' thus producing a covered supiilenieni.il channel signal. The covered supplemental channel signal is then sent to a module 120, which adjusts the amplitude of the covered supplemental channel sera relative to the signals carried by other orthogonal transmit sub-channels.
Though the preferred embodiment shown uses orthogonal Walsh (unions lo accomplish sub-channel coding, one skilled in the art will appreciate doing could also be accomplished using TDMA or PN coding departing from the current invention. In an embodiment utilizing VN melanin ilk-reference signals Ws, Wp, and Wp are replaced by PN codes supplemental, pilot, and fundamental channels respectively. One skilled m appreciate that the FEC modules 102 and 104 could employ any of a iunnlxr oi forward error correction techniques without departing from the current Such techniques include turbo-code encoding, convolutional coding, coding such as block coding. In addition, the interleavers
any of a number of interleaving techniques, including convolutional turbo-interleaving, block interleaving and bit reversal interleaving, encoders and turbo interleaves are described in aforementioned .(MKi specification.
The output of each relative gain module 116,118, and 120 is then skin lo PN spreader module 122. The output of the PN spreader module 122 is transmitter 124. Transmitter 124 provides additional control of transmit varying the gain of the entire composite signal received from PN spreads module 111 before transmitting the signal through antenna 126.
In an alternative embodiment, the optional relative gain module 1 16 is and the pilot signal is sent directly to the PN spreader module 122. The yoyos channels are adjusted with respect to the gain of the pilot channel. One skilled in ilk-art will appreciate that the two methods of controlling relative gains ol' the chasmal , using the system including relative gain module 116 or without relative gain module 116, are functionally equivalent.

appreciate that one may use either method of setting a sub-channel's gain to zero without departing from the present invention.
PN spreader 122 spreads the orthogonal channel signals using a pseudoraiulom generated spreading sequence and sends the resultant composite signal transmitter 124 for transmission through relative gain modules IK). IIS. and 120 are controlled dynamically by gain control processor 128. The gain ol cav li module may be altered according to data rates of the channels. For example, hick piloi channel gain may be increased when data is being transmitted on both and the supplemental channel. Or, the fundamental channel gain n)a\ ix-increased when data is being transmitted on the supplemental channel.

FIG. 4 shows an exemplary embodiment of a channel estimator 2 IX. Ilk-complex input signal is provided to channel estimator 218 as I and Q sample sylvan. The I samples are mixed with a reference signal in mixer 302a, to
component of the complex input signal. The output of mixer 302a is provided lo nois. rejection filter 304a to remove noise from the extracted real component. In nnxcr 302b, The Q samples are mixed with the same reference signal as used in niixei M)'.\A in order to extract an imaginary component of the complex input signal. Tlie i>ui|)iii oi mixer 302b is provided to noise rejection filter 304b to remove noise troni ihe extracted imaginary component. One skilled in the art will appreciate thai the ntn .e rejection filters 304 may be implemented as low-pass filters, matched Idlers, oi accumulators without departing from the current invention.
The reference signal used in a channel estimator 218 could be reah inuiLiin;ii\ or complex. In an alternative embodiment of a channel estimator 218 appioiMiiiie loi use with a complex reference signal, mixers 302 are complex multipliers (wineli MI.IN also be called complex mixers), each having both real and imaginary outputs. The ie;il outputs of mixers 302 are then summed before being filtered in rcal-coniponeni iihei 304a. The imaginary outputs of mixers 302 are summed before being fiheied in imaginary-component filter 304b. In the same fashion, complex mulliplieis eould IK used in a Walsh spreader or despreader to allow the use of complex Walsh eiides ;i. reference functions during spreading and despreading. Walsh spreachni] n: in:' complex Walsh codes is known as complex Walsh spreading, and Walsh des|iieadmL' using complex Walsh codes is known as complex Walsh despreading.
In the proposed cdma2000 standard, the pilot channel is transmitted 90 dei'iee. out of phase with the fundamental and supplemental channels. In the iMelerred

embodiment, therefore, the pilot channel estimator 218a rotates iis output In '^ degrees. This rotation may be accomplished in many ways, including nuiiiipl\ inv ih reference by an imaginary value, or by rotating the real and imaginary outputs ol nui. rejection filters 304. The same end result may also be accomplished b\' lotatmij ih signals of the fundamental and supplementary channels without dcparlini! Irom ih current invention. Also, the relative rotation of the pilot channel in rclatit^n \o \\\ fundamental and supplementary channels may be positive or negaii\c wiihoi departing from the current invention.
Together, the extracted real and imaginary components constitute a channel estimate vector containing amplitude and phase information for any signal comp^uum which correlates with the reference signal. The quality of the channel esinnaie depends on the degree of correlation between the received complex input sienal ami the reference signal. To achieve the highest degree of correlation between ilu received complex input signal and the reference signal, the reference signal used In the receiver must exactly match that transmitted by the transmitter, for example W aMi code W p in the case of the pilot channel. Any difference between the reterenee sienal and the transmitted signal can cause inaccuracy in the channel estimate.
In an IS-95 system, the pilot Walsh code W p is an all-zero Walsh eoUr. n which case a channel estimate can be made using just a pair of filters, as is JescnlKt in aforementioned U.S. Patent 5,506,865. In this case, pilot channel Walsh spu\uki 110 is omitted from the transmitter. The channel estimator in the recei\er e(uiM ihci

be implemented such that the mixers 302 could be omitted from pilot CIKHIDLI estimator 218a. A channel estimator for an all-zero Walsh code pilot, consisiiiij' oi filters without mixers, is also known as a pilot filter. The embodiment of Ihc chaiuRi estimator depicted in FIG. 4, however, allows the use of a pilot Walsh code oilu-r ihan the all-zero Walsh code.
Together, the Pilot I and Pilot Q signals are used as an cstimalc ti! IIK amplitude and phase characteristics of the CDMA transmission channel S, MK resultant Pilot 1 and Pilot Q along with the decovered fundamental channel I aiul (.> components are provided to dot product module 208. Dot product module 2()X wliieh computes the scalar projection of the fundamental channel signal onto ihe pi lot channel estimate vector, in accordance with the circuit described in albrenK-niioned U.S. Patent No. 5,506,865. Because the pilot channel signal 10, the rundanieiiial channel signal 12, and the supplemental channel signal 14 have traversed the same propagation path 8, the channel induced phase error is the same for all three siyjials
This phase error is removed by performing the dot product operation desei IIK\I in aforementioned U.S. Patent 5,506,865. In the exemplary embodinieni. ilie fundamental channel is coherently demodulated in a dot product module 2()S usmi' i pilot channel estimate. The dot product module produces a scalar signal lor eaeh symbol period, which is indicative of the magnitude of the fundamental channel sienal that is in phase with the pilot signal received through the transmission channel K.

The fundamental channel symbols output by the dot product inodiilc 20N i then sent into deinterleaver 210, which performs the inverse of the tunLiiDii n\ transmit interleaver 106. The resultant deinterleaved signal is then sent lo ri)r\\;iiJ error correction (FEC) decoder 212. Decoder 212 performs the inverse riinction ol \\K FEC encoder 102 and outputs a forward error corrected signal.
The corrected signal output by decoder 212 is also sent lo an encoder 21\. which re-encodes the signal using the same FEC function as the traiisnuilci I i ( encoder 102. In this way, encoder 224 produces an ideal representation ol ihc transmitted fundamental signal This ideal representation is then sent to an inlcilc;i\ cr 226, which performs the same function as the transmitter interleaver 106. prodiicinL' an ideal representation of the interleaved fundamental channel data transmiucd h\ subscriber station 2.
The I and Q component samples produced by Walsh despreader arc also inpni into delays 220, which produce I and Q components which are synchroni/cd \\ iih IIK output of the interleaver 226. Delays 220 are designed to compensate lor ilic tlcla\. introduced by the dot product module 208, the deinterleaver 210, the decoder 212. ilic encoder 224, and the interleaver 226.
The synchronized I and Q components output by delays 220 arc ihcn scni along with the output of interleaver 226, into channel estimator 2l8h. (iianiic estimator 218b uses the output of interleaver 226 as a reference signal, and uses ilu

outputs of delays 220 as the I and Q sample stream from which it forms a channel estimate output.
The corrected bits output by FEC decoder 212 are re-encoded and re-interleaved to produce a reference signal which has a higher probability of matching what was actually transmitted on the fundamental channel. By using this more reliable reference signal as input for channel estimator 218b, the accuracy of fundamental channel estimates produced by channel estimator 218b is improved.
In a suboptimal embodiment, instead of using deinterleaver 210, decoder 212, encoder 224, and interleaver 226 to create an ideal representation of the fundamental channel signal, the output of dot product module 208 could be provided directly to channel estimator 218b, In this case, delay elements 220 would only compensate for the time required to perform the dot product operation in dot product module 208. However, the fundamental channel estimator would not gain the error correction benefits of the bypassed components.
The complex output components of the pilot channel estimator 218a are subjected to delay elements 222 to compensate for the delay inherent in performing channel estimation using the fundamental channel signal. The channel estimation parameters produced by processing of the fundamental charmel is sent, along with the delayed channel estimation parameters from the delay elements 220 and 222 into channel estimate combiner 230. Channel estimate combiner 230 combines the channel

estimation data for both pilot and fundamental channel processing and produces output containing a third, combined channel estimate. As the characteristics of the transmission channel change over time, pilot channel estimator 218a and channel estimator 218b provide updated channel estimates to channel estimate combiner 230, which updates the combined channel estimation output accordingly.
In the preferred embodiment, the output of decoder 212 sent to encoder 224 is additionally sent to control processor 216. Control processor 216 produces frame rate information for each received frame of data. Control processor 216 also performs validity checking of the received frames. Control processor 216 produces a fundamental channel quality metric based on the results of its rate determination and validity checking of received data. The fundamental channel quality metric is used to assign an appropriate v^eighting factor to the fundamental channel estimate in relation to the weighting factor assigned to the pilot channel estimate. The fundamental channel quality metric varies based on the validity of received frames based on the correctness of the CRC. Since different rate frames may also use different numbers of CRC bits, or have varying degrees of frame error checking protection, control processor 216 may additionally vary the fundamental channel quality metric according to received frame rate.
Control processor 216 is also connected to encoder 224, Control processor 216 sends frame rate information to encoder 224 for use in re- encoding the data received from decoder 212.

In the exemplary embodiment, channel estimate combiner 230 is a weighted-average combiner, which produces the combined channel estimation signal by performing a weighted average of the pilot and fundamental channel estimates in accordance with the following equations:
RcOMB ~ X RpiLOT + (1-X) RpUND (3)
ICOMB ~ X IpiLOT + (1 "X) IpUND (4)
where RCOMB and ICOMB are the real an imaginary components of the combined channel estimate, RPILOT and IPILOT are the real an imaginary components of the pilot channel estimate, RFUND and IFUND are the real an imaginary components of the fundamental channel estimate, and X is a scaling factor. The scaling factor X has a value from 0 to 1. A scaling factor value of 1 results in a combined channel estimate which is equal to the pilot channel estimate. A scaling factor value of 0 results in a combined channel estimate which is equal to the fundamental channel estimate. The value of X represents a first muUiplier, which is muUiplied by the pilot channel estimate to produce a scaled channel estimate for the pilot charmel. The value of (1-X) represents a second multiplier, which is multiplied by the fundamental channel estimate to produce a scaled channel estimate for the fundamental channel. The two scaled channel estimates are added together to produce the combined channel estimate.

Channel estimate combiner 230 additionally uses the fundamental channel quality metric provided by control processor 216 as a dynamic weighting factor to the channel estimates produced from the fundamental channel. When the fundamental channel quality metric indicates a high rate of frame errors, channel estimate combiner 230 increases the value of the scaling factor X. When frame errors occur, therefore, the combined channel estimate used for demodulating the supplemental channel is derived more from the pilot channel estimate and less from the fundamental channel estimate. In an alternative embodiment, a frame error causes the value of scaling factor X to be equal to 1 until a valid frame is received.
In an alternative embodiment of the invention, control processor 216 includes a smoothing module, which performs smoothing, or low-pass filtering, of the fundamental channel quality metric before it is sent to channel estimate combiner 230. This smoothing helps to make the weighted average performed by channel estimate combiner 230 less susceptible to high-frequency noise inherent in the channel.
In yet another embodiment of the current invention, the receiver knows the relative gains used by relative gain modules 116 and 118 when transmitting the pilot and fundamental channel signals. In this embodiment, the value of X is adjusted such that the ratio of the first multiplier over the second multiplier is equal to the ratio of the transmit gain of the pilot channel over the transmit gain of the fundamental channel. In the preferred embodiment, the fundamental channel quality 1 metric provided by control processor 216 to channel estimate combiner 230 is synchronized

with the reference signal provided to channel estimator 218b, This can be accomplished by incorporating a delay or buffer into control processor 216. Control processor 216 may also perform a smoothing function to the fundamental channel quality metric before providing it to channel estimator 218b. In the preferred embodiment, however, the fundamental channel quality metric produced by control processor 216 is not smoothed, and may change suddenly on frame boundaries.
The I and Q component samples used as input to Walsh despreader 236 are sent through delay elements 232, which serve to synchronize the output of Walsh despreader 236 with the output of channel estimate combiner 238. Delay elements 232 could instead be placed between Walsh despreader 236 and dot product module 238 without departing from the present invention. Walsh despreader 236 uses the Walsh function W s used by the transmitter's Walsh spreader 114, and produces decovered supplemental channel I and Q components. These decovered supplemental channel components, along with the combined channel estimation signal from channel estimate combiner 230, are used as input for dot product module 238.
Dot product module 238 computes the magnitude of the projection of the supplemental channel signal onto the combined channel estimate vector, resulting in a scalar projection output. The output of dot product module 238 is then deinterleaved in deinterleaver 240, which performs the inverse function of interleaver 108, The output of deinterleaver 240 is provided to decoder 242, which performs the inverse function of interleaver 104.

Throughout the wireless receiver portrayed in FIG. 3, one slcilled in the art will appreciate that any of the delay elements 220,222, or 232 could be implemented as accumulators or buffers without departing from the current invention. In addition, one skilled in the art will appreciate that pairs of delay elements, for example delay elements 232a and 232b, may be implemented separately, or combined into a single delay module which performs the same function, without departing from the current invention.
Though the preferred embodiment shown uses orthogonal Walsh functions to accomplish sub-channel decoding, one skilled in the art will appreciate that the subchannel decoding could also be accomplished using TDMA or PN coding without departing from the current invention. In an embodiment utilizing PN coding, reference signals W s' W p, and W F are replaced by PN codes corresponding to the supplemental, pilot, and fundamental channels respectively.

We Claim:
1, A method of demodulating an information signal, wherein the information
signal is received through a channel having channel characteristics, and wherein the
information signal comprises a pilot signal, a first data-carrying signal, and a second
data-carrying signal, the method comprising:
first estimating the channel characteristics based on the pilot signal to provide a pilot channel estimate;
second estimating the channel characteristics based on the first data- carrying signal to provide a data channel estimate; and
Combining said pilot channel estimate with said data channel estimate to provide a combined channel estimate.
2. The method as claimed in claim 1 comprising generating a scalar projection of
the information signal in accordance with the combined channel estimate.
3- The method as claimed in claim 1 comprising pseudonoise despreading the information signal
4. The method as claimed in claim 3 wherein the pseudonoise despreading is complex pseudonoise despreading.

5. The method as claimed in claim 1 wherein said second estimating comprises generating a scalar projection of the information signal in accordance with the pilot channel estimate.
6. The method as claimed in claim 5 wherein said second estimating comprises generating an ideal representation of the first data-carrying signal.
7. The method as claimed in claim 6 wherein said generating an ideal representation comprises:
deinterleaving the first data-carrying signal to provide a deinterleaved signal; and interleaving the deinterleaved signal.
8. The method as claimed in claim 6 wherein said generating an ideal representation comprises:
decoding the first data-carrying signal to provide a decoded signal; and encoding the decoded signal.
9, The method as claimed in claim 1 comprising introducing a delay into the pilot channel estimate to provide synchronization between the pilot channel estimate and the data channel estimate.
10. The method of claim 1 wherein said combining comprises:

multiplying said pilot channel estimate by a pilot multiplier to produce a scaled pilot channel estimate; multiplying said data channel estimate by a data multiplier to produce a scaled data channel estimate; and adding said scaled pilot channel estimate to said scaled data channel estimate to provide said combined channel estimate.
11. The method as claimed in claim 10 wherein a ratio of said pilot multiplier over said data multiplier is based on a ratio of a gain used to transmit the pilot signal over a gain used to transmit said first data-carrying signal.
12. The method as claimed in claim 10 comprising generating the pilot multiplier and the data multiplier.
13. The method as claimed in claim 10 comprising changing a ratio of the pilot multiplier to the data multiplier based on a data rate of the first data-carrying signal.
14, The method as claimed in claim 10 comprising changing a ratio of the pilot multiplier to the data multiplier based on a frame quality metric of the first data-carrying signal.
15. The method as claimed in claim 1 wherein said first estimating comprises filtering the information signal to provide the pilot channel estimate.

16. The method as claimed in claim 15 wherein said first estimating comprises moiling the information signal by a reference pilot code.
17. The method as claimed in claim 1 wherein said second estimating comprises: generating a scalar projection of the information signal in accordance with the
pilot channel estimate to provide a scalar information signal;
decoding the scalar information signal to provide a decoded signal; encoding
the decoded signal to provide an ideal representation of the first data-carrying signal;
and
multiplying the information signal by the ideal representation to provide the
data charmed estimate.
18. The method of claim 17 wherein said first estimating further comprises: deinterleaving the scalar information signal prior to said decoding; and interleaving the ideal representation prior to said muhiplying.

.

19. An apparatus for demodulating an information signal, wherein the information
signal is received through a channel having channel characteristics, and wherein the
information signal comprises a pilot signal, a first data-carrying signal, and a second
data-carrying signal, the apparatus comprising:

first means for estimating the channel characteristics based on the received pilot signal to provide a pilot channel estimate;

second means for estimating the channel characteristics based on the first data-carrying signal to provide a data channel estimate; and
means for combining said pilot charmel estimate with said data channel estimate to provide a combined channel estimate.
20. The apparatus as claimed in claim 19 comprising means for generating a scalar projection of the information signal in accordance with the combined channel estimate.
21. The apparatus of claim 19 comprising means for pseudonoise despreading the information signal.
22, The apparatus of claim 19 further comprising means for complex pseudonoise despreading the information signal.
23. The apparatus of claim 19 wherein said second means for estimating comprises means for generating a scalar projection of the information signal in accordance with the pilot channel estimate,
24. The apparatus as claimed in claim 23 wherein said second means for estimating comprises means for generating an ideal representation of the first data-carrying signal.

25. The apparatus as claimed in claim 24 wherein said means for generating an
ideal representation comprises:
means for deinterleaving the first data-carrying signal to provide a deinterleaved
signal; and
means for interleaving the deinterleaved signal.
26. The apparatus as claimed in claim 24 wherein said means for generating an ideal representation comprises:
means for decoding the first data-carrying signal to provide a decoded signal; and means for encoding the decoded signal.
27. The apparatus as claimed in claim 19 comprising means for introducing a delay into the pilot channel estimate to provide synchronization between the pilot channel estimate and the data channel estimate.
28, The apparatus as claimed in claim 19 wherein said means for combining comprises:
means for multiplying said pilot channel estimate by a pilot multiplier to produce a scaled pilot channel estimate;
means for multiplying said data channel estimate by a data multiplier to produce a scaled data channel estimate; and
means for adding said scaled pilot channel estimate to said scaled data channel estimate to provide said combined channel estimate.

29- The apparatus of claim 28 comprising means for generating the pilot multiplier and the data multiplier.
30. The apparatus of claim 28 comprising means for changing a ratio of the pilot mushily to the data multiplier based on a data rate of the first data- carrying signal,
31. The apparatus as claimed in claim 28 comprising means for changing a ratio of the pilot multiplier to the data multiplier based on a frame quality metric of the first data-carrying signal.
32. The apparatus as claimed in claim 19 wherein said first means for estimating comprises means for filtering the information signal to provide the pilot channel estimate.
33. The apparatus as claimed in claim 32 wherein said first means for estimating comprises means for multiplying the information signal by a reference pilot code.

34, The apparatus as claimed in claim 19 wherein said second means for estimating comprises:
Means for generating a scalar projection of the information signal in accordance with the pilot channel estimate to provide a scalar information signal;
means for decoding the scalar information signal to provide a decoded signal;

means for encoding the decoded signal to provide an ideal representation of the first data-carrying signal; and
means for multiplying the information signal by the ideal representation to provide the data channel estimate.
35. The apparatus of claim 34 wherein said first means for estimating further comprises:
means for deinterleaving the scalar information signal prior to said decoding; and
means for interleaving the ideal representation prior to said multiplying.
36. An apparatus for demodulating an information signal, wherein the information signal is received through a channel having channel characteristics, and wherein the information signal comprises a pilot signal, a first data-carrying signal, and a second data-carrying signal, the apparatus comprising:
pilot channel estimator configured to estimate the channel characteristics based on the pilot channel signal to provide a pilot channel estimate;
data channel estimator configured to estimate the channel characteristics based on the first data channel signal to provide a data channel, estimate;
channel estimate combiner configured to combine said pilot channel estimate with said data channel estimate to generate a combined channel estimate.

37. The apparatus as claimed in claim 36 comprising a first dot product module configured to modify a phase of the information signal based on the combined channel estimate to producing a sub-channel symbol stream.
38. The apparatus as claimed in claim 36 comprising a first dot product module configured to modify a phase of the information signal based on the combined channel estimate to producing a sub-channel symbol stream.
39. The apparatus as claimed in claim 36 comprising dot product module for generating a scalar projection of the information signal in accordance with the combined channel estimate.
40. The apparatus as claimed in claim 36 comprising pseudonoise despreader for multiplying the information signal by a pseudonoise code.
41. The apparatus as claimed in claim 40 wherein the pseudonoise despreader is a complex pseudonoise despreader for multiplying the information signal by a complex pseudonoise code.

42. The apparatus as claimed in claim 36 wherein said data channel estimator comprises dot product module for generating a scalar projection of the information signal in accordance with the pilot channel estimate to provide a scalar information signal.

combiner.

48, The apparatus as claimed in claim 36 wherein said channel estimate combiner is a weighted-average combiner configured to provide the combined channel estimate in accordance with the following equations:
the real an imaginary components of the combined channel estimate, RPLLOT and IRLLOT are the real an imaginary components of the pilot channel estimate, RDATA and IDATA are the real an imaginary components of the fundamental channel estimate, and X is a scaling factor.
49. The apparatus as claimed in claim 48 wherein said weighted-average combiner is configured to use a value of X that is based on a ratio of a gain used to transmit the pilot signal over a gain used to transmit said first data-carrying signal.
50. The apparatus of claim 48 comprising control processor configured to provide the value X to said weighted-average combiner.
51. The apparatus as claimed in claim 50, wherein said control processor is configured to adjust said value X based on a data rate of the first data-carrying signal.
52. The apparatus as claimed in claim 48, wherein said control processor is configured to adjust said value X based on a frame quality metric of the first data-carrying I signal.

53. The apparatus as claimed in claim 36 wherein said pilot channel estimator comprises filter for filtering the information signal to provide the pilot channel estimate.
54. The apparatus as claimed in claim 53 wherein said pilot channel estimator comprises mixer for multiplying the information signal by a reference pilot code.
55. The apparatus of claim 36 wherein said data channel estimator comprises:
dot product module configured to multiply the information signal with the pilot channel estimate to provide a scalar information signal;
decoder configured to decode the scalar information signal to provide a decoded signal;
encoder configured to encode the decoded signal to provide an ideal representation of the first data-carrying signal; and
mixer for multiplying the information signal by the ideal representation to provide the data channel estimate.
56. The apparatus as claimed in claim 55 wherein said data channel estimator
comprises:
deinterleaver configured to deinterleave the scalar information signal; and interleave configured to interleave the ideal representation.
57. A method of demodulating an information signal, substantially as herein
described, with reference to the accompanying drawings.

58. An apparatus for demodulating an information signal, substantially as herein described, with reference to the accompanying drawings.

Documents:

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in-pct-2001-1562-che-abstract.pdf

in-pct-2001-1562-che-assignement.pdf

in-pct-2001-1562-che-claims filed.pdf

in-pct-2001-1562-che-claims granted.pdf

in-pct-2001-1562-che-correspondnece-others.pdf

in-pct-2001-1562-che-correspondnece-po.pdf

in-pct-2001-1562-che-description(complete)filed.pdf

in-pct-2001-1562-che-description(complete)granted.pdf

in-pct-2001-1562-che-drawings.pdf

in-pct-2001-1562-che-form 1.pdf

in-pct-2001-1562-che-form 19.pdf

in-pct-2001-1562-che-form 26.pdf

in-pct-2001-1562-che-form 3.pdf

in-pct-2001-1562-che-form 5.pdf

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Patent Number

211964

Indian Patent Application Number

IN/PCT/2001/1562/CHE

PG Journal Number

02/2008

Publication Date

11-Jan-2008

Grant Date

13-Nov-2007

Date of Filing

09-Nov-2001

Name of Patentee

M/S. QUALCOMM INCORPORATED

Applicant Address

5775 Morehouse Drive, San Diego, California 92121,

Inventors:

#	Inventor's Name	Inventor's Address
1	LING, Fuyun	11382 Wills Creek Road, San Diego, CA 92131,

PCT International Classification Number

H04L 25/02

PCT International Application Number

PCT/US00/12792

PCT International Filing date

2000-05-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	09/310,232	1999-05-12	U.S.A.