Title of Invention

METHOD AND APPARATUS FOR IMPROVING CHANNEL ESTIMATION IN PRESENCE OF SHORT SPREADING CODES

Abstract A method and apparatus for estimating a communication channel impulse response h(t) is disclosed. The method comprises the steps of generating com(t) = co(t + mNTcc) for m = 0,1,Lambda , M by correlating a received signal r(t) with a spreading sequence Si of length N (208), wherein the received signal r(t) comprises a chip sequence cj applied to a communication channel characterizable by an impulse response h(t)(204), and wherein the chip sequence ci is generated from a data sequence di spread by the spreading sequence Si (202); generating an estimated communication channel impulse response hM (t) as a combination of com(t) and dm for m = 0,1, Lambda ,M (210); and filtering the first estimated communication channel impulse response hM (t) to generate the estimated communication channel impulse response h(t) with a filter f selected at least in part according to the spreading sequence Si (212).
Full Text

METHOD AND APPARATUS FOR IMPROVING CHANNEL ESTIMATE IN PRESENCE OF SHORT SPREADING CODES
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to systems and methods for communicating
information, and in particular to a system and method for estimating the impulse response of a communication channel using short synchronization codes.
2. Description of the Related Art
[0002] In packet-based communication systems, spreading codes are used for
packet detection and synchronization purposes. Correlation techniques are used to identify and synchronize to its timing. In many instances, the spreading code sequence can be in the order of 1000 chips or more. Since the receiver must correlate through all possible delays, this process can result in unacceptable delays.
[0003] To ameliorate this problem, a short spreading code with good aperiodic
autocorrelation can be used for packet detection and synchronization purposes. One example is the IEEE 802.11 Wireless Local Area Network (WLAN) system, which uses a length 11 Barker code as a spreading sequence for the preamble and the header of a packet. The short length of the spreading sequence makes it easy for receivers to quickly detect the presence of a packet in the communication channel and to synchronize to its timing.
[0004] In the case of a linear channel, for the purpose of receiver design, it is
often desirable to estimate the impulse response of the communication channel. In the context of the WLAN, a multi-path linear channel is often utilized, and such communication channels require equalization for effective reception. Given an estimate of the impulse response of the communication channel, we can directly calculate equalizer coefficients through matrix computations, as opposed to the conventional adaptive algorithms. This is described in "Digital Communications," by John G. Proakis, 4th edition, August 15, 2000, which reference is hereby incorporated by reference herein. This allows equalizer coefficients to be computed in a digital signal

processor (DSP) instead of in more expensive and less adaptable dedicated hardware implementing the adaptation algorithms.
[0005] Unfortunately, because the spreading code used is short (e.g. on the order
of 11 symbols) a straightforward correlation using the spreading code will produce a distorted estimate. What is needed is a simple, computationally efficient technique that can be used to compute substantially undistorted communication channel impulse response estimates, even when the received signal was chipped with a short spreading code. The present invention satisfies that need.
SUMMARY OF THE INVENTION
[0006] To address the requirements described above, the present invention
discloses a method and apparatus for estimating a communication channel impulse response h(t). The method comprises the steps of generating com(t) = co(t + mNTc) for
m = 0,l,A 9M by correlating a received signal r(t) with a spreading sequence St of length N9 wherein the received signal r(t) comprises a chip sequence c. applied to a communication channel characterizable by an impulse response h(t), and wherein the chip sequence cy is generated from a data sequence di spread by the spreading sequence
5,-; generating an estimated communication channel impulse response hM(t)%s a combination of com(i) and dm for ?n = 0,l,A ,M; and filtering the first estimated
communication channel impulse response hM (t) to generate the estimated communication channel impulse response /z(f)with a filter / selected at least in part according to the spreading sequence Sg. The apparatus comprises a correlator for generating com(t) = co(t + mNTc) for w = 0,l,A ,M by correlating a received signal r(t) with a spreading sequence S§ of length N9 wherein the received signal r(f) comprises a chip sequence c. applied to a communication channel characterizable by an impulse response h(i), and wherein the chip sequence c. is generated from a data sequence di spread by the spreading sequence 5f; an estimator for generating an
estimated communication channel impulse response hM (t) as a combination of com (t) and dm for m = 0,l,A 9M; and a filter / selected at least in part according to the

spreading sequence Sg , the filter for filtering the first estimated communication channel
impulse response hM(t) to generate the estimated communication channel impulse
response h(t).
[0007] The foregoing permits the impulse response h(t) of the communication
channel to be accurately estimated, even with short chip codes. Non-intuitively, in the case of a time-limited channel impulse response, the present invention yields an estimate that can be made perfect in the limit of high signal-to-noise ratio (SNR).
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Referring now to the drawings in which like reference numbers represent
corresponding parts throughout:
[0009] FIG. 1 is a diagram of a transceiver system;
[0010] FIG. 2 is a block diagram illustrating process steps that can be used to
implement the present invention;
[0011] FIG. 3 is a diagram of a transceiver system utilizing a filter/to improve
the estimated communication channel impulse response;
[0012] FIG. 4 is a diagram showing the response of the filter;
[0013] FIG. 5 is a flowchart describing exemplary processing steps that can be
used to improve the reconstruction of the value of the communication channel impulse
response using super codes imposed on the portion of the data sequence;
[0014] FIG. 6 is a diagram of a transceiver system utilizing super code to
transmit sequences;
[0015] FIG. 7 is a diagram presenting a correlator output using 11 symbol long
Barker code;
[0016] FIG. 8 is a diagram presenting a correlator output using Walsh codes as
an input super code;
[0017] FIG. 9 is a diagram presenting a correlator output after postprocessing
with a filter/as described in FIG. 2 and FIG. 3;
[0018] FIG. 10 is a diagram presenting a more detailed view of the main lobe
peak, showing the estimate of the communication channel impulse response in the actual communications channel impulse response; and

[0019] FIG. 11 is a diagram presenting one embodiment of a processor that can
be used to practice the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] In the following description, reference is made to the accompanying
drawings which form a part hereof, and which is shown, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
System Model
[0021] FIG. 1 is a diagram of a transceiver system 100. Using signal spreader
103, a random data symbol sequence d. 102, comprising a series of data packets 128
(each of which may include a preamble 124 used by the receiver for identification purposes, as well as a data payload 126) is spread by a sequence 5-104 of length
N:{Sn,0 Eq. (1)
[0022] This spread chip sequence c; 106 is transmitted through a linear
transmission channel 108 having a combined channel impulse response h(t). The transmitted signal is received by a receiver 112. The received waveform r(i) 114 is:
Eq. (2)
where ?i(t) 121 is an additive noise component.
[0023] This formulation does not explicitly impose a causality requirement on
h(t) 108. If explicit causality is desired, this can be accomplished by setting
h{t) - 0, t
Complex sequences could be easily accommodated if needed, but they are not common for synchronization purposes.
[0024] The receiver 112 receives the transmitted signal, and correlates the
received signal r(t) 114 with the known spreading sequence St 104 to identify the data
as intended to be received by the receiver 112. Once the received signal r(t) 114 is
received, the preamble can be examined to determine the address of the data and whether further processing is necessary.
[0025] Such systems also use the received signal to estimate fee input response
of the communication channel 108. This information is used to improve later detection and reception of signals from the transmitter 110. In circumstances where the spreading sequence St. 104 is relatively short, the data packet 128 must be detected quickly, and
there is less data available to estimate the response of the communication channel 108.
Conventional Detection and Synchronization
[0026] For detection and synchronization purposes, the search for the spreading
code is conventionally performed by correlating the received signal r(t) 114 with the
spreading sequence. This is accomplished by the correlator 116. Although this correlation is typically done after sampling in the time domain, for notational simplicity, we do not perform the time domain discretization. The correlator 116 output co(t) 118 is
given by:

where !)(/) is the correlation between the chip sequence and the spreading sequence and we will refer to it as the chip correlation.









lobes disappear. However, when the spreading sequence S. 104 is short, the sidelobes
of the autocorrelation are not negligible and will cause significant distortion to the estimate of the communication channel impulse response h(t).
Improved Channel Estimates for Short Spreading Sequences
[0042] As is demonstrated below, the present invention improves the
communication channel impulse response estimate by filtering the first estimated
communication channel impulse response hM (t) to generate the estimated communication channel impulse response h(t)vnHi a filter/ selected at least in part according to the spreading sequence Ss. In particular, when the time span of the
communication channel 108 is limited, a zero-forcing deconvolution can be used to
improve the estimate.
[0043] FIG. 2 is a block diagram illustrating process steps that can be used to
implement the present invention.
[0044] FIG. 3 is a diagram of a transceiver system 300 utilizing the filter /
described above to filter the first estimated communication channel impulse response
hM (t) to generate an improved estimate suitable for short spreading sequences Sf 104.
[0045] Referring to FIG. 2 and FIG. 3, blocks 202 througji 208 recite steps that
are used to generate com(t) IIS. A spread chip sequence c. 106 is generated from a
data symbol sequence dt 102 and a spreading sequence 5,- 104 of length N, as shown in block 202. The chip sequence c. 106 is transmitted via a communication channel 108
as shown in block 204, and received as shown in block 206. The communication channel includes the transmitter 110 and the receiver 112. The received signal r(t) 114
is then correlated with the spreading sequence S. 104, by the correlator 116 to generate com (t) as shown in block 208.
[0046] In block 210, an estimated communications channel impulse response hM (/) is generated by the estimator 120 as a combination of com(f)mA. dm for m = 0,l,K ,M
This can be accomplished, for example using the relationship described in Eq. (24) above.



[0052] Then, the filtered estimate ft,(or, in the earlier notation, hf(f)) is
composed of an exact copy of h(h(t))9 plus some aliased versions of it in non-overlapping locations. So in this case h is resolvable from hf.
[0053] Such a filter with length 21 + 1 can be designed with the simple zero-
forcing criteria:

Sf 104. L can be chosen such that the product LTC (the chip period Tc is known) is
approximately equal to the time span (e.g. the approximate duration of the impulse
response) of the channel 108.
[0054] Note that the value A(n - i) is well defined ... it is a property of the
spreading sequence S( 104, which is known apriori.
[0055] As usual, the matrix structure of the linear equations is Toeplitz. By the
design requirement of the spreading sequence Sg9 the matrix should be well
conditioned. The filter coefficients can be computed offline given the spreading sequence and desired window width L.
[0056] While the foregoing has been described in respect to non recursive filters,
other filters, such as recursive filters may also be used. A recursive filter, for example, may provide perfect filtering of the sidelobes, but the result may not be the quell conditioned matrix, hence the solution may be more difficult to determine. In fact, any filter of length 2L +1 can be defined.
Super Coded Transmit Sequences
[0057] It has been shown that given h and with filtering, it is possible to recover
the true channel impulse response for a time limited channel. However, in the foregoing



[0062] If the condition that - /,N > (27V + L) I 12N>(2N + L) can be satisfied,
h can be reconstructed free of aliasing interference, and by deconvolution
(aforementioned filtering technique), h can be reconstructed as well.
[0063] From the foregoing, it can be determined that a small supercode imposed
on a portion of the data sequence can provide an alias free estimate of the
communication channel impulse response when the channel response is time-limited.
The only source of distortion from this estimate comes from the additive noise, which
can be suppressed by the spreading gain times a factor of 2 (to account for the
supercode). When the noise is low, such an approach is preferable over long
integrations.
[0064] For moderate values of Z, such code sequences can be easily embedded
within a longer preamble to packet data, probably with multiple copies, without
adversely affecting the spectrum properties of the transmission. In addition, when the
signal to noise ratio (SNR) is low, traditional integration as outlined in the first half of
this section can still be carried out on such a preamble to obtain a higher processing gain
against the additive noise.
[0065] FIG. 5 is a flowchart describing exemplary processing steps that can be
used to improve the reconstruction of the value of the communication channel impulse
response by using supercode imposed on a portion of the data sequence.
[0066] FIG. 6 is a diagram of a transceiver system 600 utilizing super coded
transmit sequences to generate an improved communication channel impulse response
estimate suitable for short spreading sequences £,104.
[0067] In block 502, a data sequence d{ 102 is generated. The data sequence^
102 includes one or more data packets 128, each data packet having a preamble 124 including a constrained portion Cdi 602. The preamble 124, can be, for example, in the
form of a pseudorandom code.
[0068] The constrained portion Cdi 602 is associated with at least two codes,
w0 and Wj. The codes w0 and w} are selected such that the correlation Acode{k) of the constrained portion Cd. 602 and at least one of the codes w0 and wx, is characterized by a maximum value at k = 0, and they value less than the maximum value at k * 0.

[0069] Ideally, the correlation Acode(k) of the constrained portion Cdi 602 is an
impulse, with Acode{k) equal to one at £ = 0, and equal at all other values for h However, because such correlation characteristics are typically not realizable, codes w0 and wx can be chosen to approximate this ideal. For example, codes w0 and wx can be chosen such that the correlation ^e(fc) of the constrained portion Cdi 602 and at least one of the codes wQ and wl9 is such that Acode(k) = l at & = 0and ^code(fc)«0for substantially all k * 0. Or, codes w0 and w^ can be chosen such that the correlation Acode(k) of the constrained portion Cdi 602 and at least one of the codes w0 and wl9is such that Acode(k) = 0 for 0 fc*0.
[0070] In one embodiment, the constrained portion Cdi 602 comprises the pair
of length two Walsh codes in the first sequence described above. Other embodiments
are envisioned in which the codes are of another length (other than length two), or are
codes other than a Walsh code.
[0071] In block 504, a chip sequence Cj 106 is generated. The chip sequence c.
106 is generated by applying a spreading sequence Si 104 of length N and having a chip
period Tc to the data sequence dx 102.
[0072] This spread chip sequence c. 106 is transmitted through a linear
transmission channel 108 having a combined channel impulse response h(t). The
transmitted signal is received by a receiver 112.
[0073] In block 506, the receiver 112 receives the transmitted signal, and
correlates the received signal r(t) 114 with the known spreading sequence 5,104 to
identify the data as intended to be received by the receiver 112. This is accomplished by generating com (t) = co(t + mNTc) for m = 0,1,A 9M, using techniques analogous to
those which were described above.
[0074] In block 508, an estimated communication channel impulse
responsehM(t) is generated as a combination of the correlationcom(t) and the data sequence dm for m = 0,1,A 9M.









adjustments were made for group delays introduced by correlation, filtering and windowing, therefore time coordinates should be treated in the relative sense. FlGs. 7-10 also do not include the effects of additive noise.
[0092] FIG. 7 is a diagram presenting a correlator 116 output using a length 11
Barker code and conventional communication channel impulse response estimation techniques. The correlator 116 output shows a main lobe peak 702, and multiple spurious peaks 704. These spurious peaks 704 (which are 11 chips, or NTC seconds,
apart due to the length 11 Barker code) are due to the repeated transmission of the short code S; 104, which are "aliased" back upon each other. If the length of the periodic
spreading sequence 5-104 were longer, there would be fewer spurious peaks 704, and
the peaks 704 would not overlap the main lobe peak 702 as much as is shown in FIG. 7.
[0093] FIG. 8 is a diagram presenting a correlator 116 output using the Walsh
codes in conjunction with the supercode technique described in FIG. 5. To generate this plot, the input data was constrained with two symbol-long Walsh codes wQ and w}9 and
the output was processed by summing two successive outputs of the correlator 116 as shown in Eq. (36). For the 11 chips on either side of the main lobe peak 702, there is zero correlation, and many of the spurious correlator peaks 704 that were apparent in FIG. 7 are no longer evident. Note, however that since only six bits of the data sequence are constrained ...+,+,+,-,-,-..., some aliased versions of the main lobe peak 704 (labeled 802) are present (33 chips from the main lobe peak 702). However, since these aliased versions 802 are widely separated from the main lobe peak 702, an accurate estimate of the communications channel impulse response can be obtained. Note that a similar result can also be achieved without constraining the input sequence with the super code, but this would require integration over large number of symbols (e.g. M in Eq. (26) would be large). Note also that the main lobe peak 704 still includes minor
peaks because the estimator 120 produces h, which is a smeared version of h. These
undesirable components 804, caused by the autocorrelation of the spreading sequence
104, cannot be removed by constraining the data sequence. Instead, these undesirable
components 804 can be removed by filtering as described with respect to FIG. 9 below.
[0094] FIG. 9 is a diagram presenting a correlator 116 output shown in FIG. 8
after postprocessing with a filter/as described in FIGs. 2 and 3. Note that the sidelobes 802 shown in FIG. 8, have been pushed away from the main lobe peak 702, and some of

the undesirable components 804 of the main lobe peak 702 have been filtered. Also note that the data indexing (the chips shown as the time axis) of FIG. 9 has changed relative to the data indexing of FIG. 8. As described above, this difference is an artifact of the software used to plot FIG. 7- FIG. 11 and is not associated with the applicant's invention.
[0095] FIG. 10 is a diagram presenting a more detailed view of the main lobe
peak 702, showing the estimate of the communication channel impulse response (indicated by the asterisks) and the actual communication channel impulse response. Note that the estimated communication channel impulse response follows that of the actual response very closely.
Hardware Environment
[0096] FIG. 11 and is a diagram illustrating an exemplary processor system 1102
that could be used in the implementation of selected elements of the present invention (including, for example, portions of the transmitter 110, the receiver 112, the correlator 116, the estimator 120, or the filter 302).
[0097] The processor system 1102 comprises a processor 1104 and a memory
1106, such as random access memory (RAM). Generally, the processor system 1102 operates under control of an operating system 1108 stored in the memory 1106. Under control of the operating system 1108, the processor system 1102 accepts input data and commands and provides output data. Typically, the instructions for performing such operations are also embodied in an application program 1110, which is also stored in the memory 1106. The processor system 1102 may be embodied in a microprocessor, a desktop computer, or any similar processing device.
[0098] Instructions implementing the operating system 1108, the application
program 1110, and the compiler 1112 may be tangibly embodied in a computer-readable medium, e.g., data storage device 1124, which could include one or more fixed or removable data storage devices, such as a zip drive, floppy disc drive, hard drive, CD-ROM drive, tape drive, etc. Further, the operating system 1108 and the application program 1110 are comprised of instructions which, when read and executed by the computer 1102, causes the computer 1102 to perform the steps necessary to implement and/or use the present invention. Application program 1110 and/or operating instructions may also be tangibly embodied in memory 1106 and/or data

communications devices 1130, thereby making an application program product or article of manufacture according to the invention. As such, the terms "article of manufacture," "program storage device" and "computer program product'" as used herein are intended to encompass a computer program accessible from any computer readable device or media.
[0099] Those skilled in the art will recognize many modifications may be made
to this configuration without departing from the scope of the present invention. For example, those skilled in the art will recognize that any combination of the above components, or any number of different components, peripherals, and other devices, may be used with the present invention. For example, an application-specific integrated circuit (ASIC) or a Field-Programmable Gate Array (FPGA) can be used to implement selected functions, including the correlator 116, and filtering functions can be performed by a general-purpose processor, as described above.

Conclusion
[0100] This concludes the description of the preferred embodiments of the
present invention. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

CLAIMS What is Claimed is:
1. A method of estimating a communication channel impulse response
h(t), comprising the steps of:
generating com(t) = co(t + mNTc) for m = 0,l,A,M by correlating a received signal r(i) with a spreading sequence Ss of length N, wherein the received signal r(0 comprises a chip sequence c. applied to a communication channel characterizable by an impulse response h(t), and wherein the chip sequence Cj is generated from a data sequence dt spread by the spreading sequence £,.and wherein Tc is the chip period of the chip sequence c.;
generating an estimated communication channel impulse response hM(t)as a combination of com(t) and dm for m = O,1?A 9M; and
filtering the first estimated communication channel impulse response hM (t) to generate the estimated communication channel impulse response h(t)vriih a filter/ selected at least in part according to the spreading sequence St.
2. The method of claim 1, wherein the filter/ is further selected at least in
part according to an autocorrelation A(n) of the spreading sequence St.
3. The method of claim 2, wherein the filter/ is further selected at least in
part according to the duration of the impulse response of the communication channel
*(0-

4. The method of claim 2, wherein the filter/ is further selected at least in
part according to a zero-forcing criteria
wherein:
/(/)is the impulse response of the filter/such that Af(n)is a convolution of
A(n) and /(/);
Sr
5. The method of claim 4, wherein:
the parameter L is chosen such that a time duration of the impulse response of the communication channel h(t) is less than LTC.
6. The method of claim 4, wherein:
the parameter L is chosen such that a time duration of the impulse response of the communication channel h{t)is approximately equal to LTC.
7. The method of claim 1, wherein N is less than 20.
8. The method of claim 1, wherein M= 0.
9. The method of claim 1, wherein the data sequence di includes a
constrained portion Cds associated with at least two codes w09w}, wherein a correlation
Acode(k) of the constrained portion Cdt with one of the codes M>0,WJ is characterized by
a maximum value at k = 0 less than maximum values at k * 0.

10. The method of claim 9, wherein the step of generating an estimated
communication channel impulse response hM (t) as a combination of com(t) and dm for
m = 0,l?A yM comprises the step of computing
11. The method of claim 10, wherein M^2.
12. The method of claim 9, wherein the data sequence di includes a preamble
having a pseudorandom code including the constrained portion of the data sequence dt.
13. The method of claim 9, wherein Acode(k) = 1 at k = 0 and AaHk(k) = 0 for
substantially all k * 0.
14. The method of claim 9, wherein Acode(k) = 0 for 0 selected to minimize the correlation of the constrained portion Cd- with the one of the
codes w0, M\ for substantially all k^O.
15. The method of claim 14? wherein 2/is a length of the constrained portion
Cdt.
16. The method of claim 1, wherein Acode(k) = 1 at k = 0 and Acode(k) = Ofor
substantially all k * 0.
17. The method of claim 1, wherein each of the two codes wo,w^ comprises
two symbols.

18. The method of claim 1, wherein the each of the two codes
w0, wx comprises no more than two symbols.
19. The method of claim 1, wherein the codes w09wx comprise Walsh codes.

20. An apparatus for estimating a communication channel impulse response
h(f), comprising:
means for generating com (t) = co(t + mNTc) for m - 0,1,A 9M by correlating a received signal r(t) with a spreading sequence Si of length AT, wherein the received signal r(0 comprises a chip sequence c. applied to a communication channel characterizable by an impulse response h(t), and wherein the chip sequence c. is generated from a data sequence d( spread by the spreading sequence Sf and wherein Tc is the chip period of the chip sequence c.;
means for generating an estimated communication channel impulse response hM (r) as a combination of com (t) and dm for m = 0,1,A ,M; and
a filter means /, selected at least in part according to the spreading sequence S{, the filter means for filtering the first estimated communication channel impulse response hM(t)io generate the estimated communication channel impulse response h(t) with
21. The apparatus of claim 20> wherein the filter means/ is further selected
at least in part according to an autocorrelation A(n) of the spreading sequence 5-.
22. The apparatus of claim 21, wherein the filter means/ is further selected
at least in part according to the duration of the impulse response of the communication
channel h(i).

23. The apparatus of claim 21, wherein the filter means/ is further selected
at least in part according to a zero-forcing criteria

/(/)is the impulse response of the filter means / such that ^4/(n)is a convolution of A(n) and f(i);
s,.
24. The apparatus of claim 23, wherein:
the parameter L is chosen such that a time duration of the impulse response of the communication channel h(f) is less than LTC.
25. The apparatus of claim 23, wherein:
the parameter L is chosen such that a time duration of the impulse response of the communication channel h(t) is approximately equal to LTC.
26. The apparatus of claim 20, wherein AT is less than 20.
27. The apparatus of claim 20, wherein M- 0.
28. The apparatus of claim 20, wherein the data sequence df includes a
constrained portion Cd. associated with at least two codes w09wl9 wherein a correlation
Acode(k) of the constrained portion Cdi with one of the codes wQ9wx is characterized by
a maximum value at k = 0 less than maximum values at k * 0.
29. The apparatus of claim 28, wherein the means for generating an
estimated communication channel impulse response hM(f)as a combination of com(t)

and dm for m = 0,1,A ,Mcomprises means for computing hM{t)as
30. The apparatus of claim 29, wherein M=2.
31. The apparatus of claim 28, wherein the data sequence dt includes a
preamble having a pseudorandom code including the constrained portion of the data sequence dr
32. The apparatus of claim 28, wherein Acode(k) = 1 at k = 0 and
i4corfc (fc) = 0 for substantially all k * 0.
33. The apparatus of claim 28, wherein Acode(k) = 0 for 0 i/is selected to minimize the correlation of the constrained portion Q/,.with the one of
the codes w09wx for substantially all k * 0.
34. The apparatus of claim 33, wherein 2J is a length of the constrained
portion Cdi.
35. The apparatus of claim 20, wherein A^^k) = 1 at k = 0 and
i4cwfc (&) = 0 for substantially all k * 0.
36. The apparatus of claim 20, wherein each of the two codes
w0, M\ comprises two symbols.
37. The apparatus of claim 20, wherein the each of the two codes
w0, Wj comprises no more than two symbols.

38. The apparatus of claim 20, wherein the codes W09M\ comprise Walsh
codes.
39. An apparatus for estimating a communication channel impulse response
h(t), comprising:
a correlator generating com (t) = co(i -f mNTc) for m = 0,1,A ,M by correlating a received signal r{i) with a spreading sequence Si of length N9 wherein the received signal r(t) comprises a chip sequence Cj applied to a communication channel characterizable by an impulse response h(t), and wherein the chip sequence c. is generated from a data sequence di spread by the spreading sequence Sf and wherein Tc is the chip period of the chip sequence c};
an estimator for generating an estimated communication channel impulse response hM (t) as a combination of com if) and dm for m = 0,1,A ,M; and
a filter/selected at least in part according to the spreading sequence S. , the
filter for filtering the first estimated communication channel impulse response hM (t) to generate the estimated communication channel impulse response hit).
40. The apparatus of claim 39, wherein the filter/ is further selected at least
in part according to an autocorrelation A(n) of the spreading sequence Si.
41. The apparatus of claim 40, wherein the filter/ is further selected at least
in part according to the duration of the impulse response of the communication channel
hit).

Documents:

692-CHENP-2006 CLAIMS GRANTED.pdf

692-CHENP-2006 CORRESPONDENCE OTHERS.pdf

692-CHENP-2006 CORRESPONDENCE PO.pdf

692-CHENP-2006 FORM 18.pdf

692-chenp-2006-abstract.pdf

692-chenp-2006-claims.pdf

692-chenp-2006-correspondence-others.pdf

692-chenp-2006-description(complete).pdf

692-chenp-2006-drawings.pdf

692-chenp-2006-form 1.pdf

692-chenp-2006-form 26.pdf

692-chenp-2006-form 3.pdf

692-chenp-2006-form 5.pdf

692-chenp-2006-pct.pdf

EXAMINATION REPORT REPLY.PDF


Patent Number 237831
Indian Patent Application Number 692/CHENP/2006
PG Journal Number 3/2010
Publication Date 15-Jan-2010
Grant Date 08-Jan-2010
Date of Filing 24-Feb-2006
Name of Patentee QUALCOMM INCORPORATED
Applicant Address 5775 MOREHOUSE DRIVE, SAN DIEGO, CALIFORNIA 92121 USA
Inventors:
# Inventor's Name Inventor's Address
1 ZHANG, HAITAO, 11018 CORTE MAR DE DELFINAS, LA JOLLA, CALIFORNIA 92130 , USA
PCT International Classification Number H04B 1/707
PCT International Application Number PCT/US04/27722
PCT International Filing date 2004-08-25
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/650,272 2003-08-28 U.S.A.