Title of Invention	METHOD AND DEVICE FOR SPREADING AND MODULATION TO REDUCE PEAK -TO-AVERAGE POWER RATIO OF TRANSMITTED POWER OF MOBILE
Abstract	A device and method are provided for reducing the peak-to average power ratio of a mobile station's transmit power in a mobile communication system by spreading and modulating the transmission data by a complex spreading sequence. The complex spreading sequence is generated to have a plurality of chips and a phase difference of 90° between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence. The device and method flexibly control the mobile transmit power by limiting its peak-to-average power ratio to a specific range and thus confining the mobile transmit power to a linear characteristic curve of a power amplifier. The phase of the complex spreading sequence is prevented from shifting by 180° (i.e.. IT) to maintain the mobile transmit power in the linear portion of the power amplifier characteristic curve.

Title of Invention

METHOD AND DEVICE FOR SPREADING AND MODULATION TO REDUCE PEAK -TO-AVERAGE POWER RATIO OF TRANSMITTED POWER OF MOBILE

Abstract

A device and method are provided for reducing the peak-to average power ratio of a mobile station's transmit power in a mobile communication system by spreading and modulating the transmission data by a complex spreading sequence. The complex spreading sequence is generated to have a plurality of chips and a phase difference of 90° between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence. The device and method flexibly control the mobile transmit power by limiting its peak-to-average power ratio to a specific range and thus confining the mobile transmit power to a linear characteristic curve of a power amplifier. The phase of the complex spreading sequence is prevented from shifting by 180° (i.e.. IT) to maintain the mobile transmit power in the linear portion of the power amplifier characteristic curve.

Full Text	DEVICE AND METHOD FOR REDUCING THE PEAKTO-AVERACE POWER RATIO OF A MOBILE STATION'S TRANSMIT POWER BACKGROUND OF THE INVENTION 1. Field 01" the Invcnlion The present invention relates generally :o mobile communication systems, ami in particular, 10 a device and method for reducing the pcak-lo-average power ratio of a mobile station's transmit power in a mobile communication system. 2. Description of tfre Related Art A typical CDMA mobile communication system focuses on voice service, whereas a 3G mobile communication system provides the additional services of high quality voice, high speed data, moving pictures, and Internet browsing. In such a mobile communication system, a radio link consists of a forward link directed from a base station (BS) to a mobile station (MS) and a reverse link directed from the MS to the BS. When zero-crossing occurs during spreading and modulation in a reverse link transmission (a phase variation is r.)t the peak-to-average power ratio of the mobile station's irnnvuit power (mobile transmit power) increases, thereby producing regrowlh. Rcgrowth Adversely affects the communication quality of calls being made by other subscribers Hence. the peak-to-average power ratio is a significant factor in the design and performance of a power amplifier in an MS Rcgrowth occurs due the existence of a linear portion and a non-linear portion :n a ch"rsctcristic curve of the mobile station's power amplifier As the mobile transmit power increases, a transmit signal of the MS due to the non-linear characteristics generates /./] interference in the frequency area of a different user causing the regrowth phenomenon. Regrowth can be prevented by shrinking down a cell and sending a signal from an MS in the cell to a corresponding BS at a low power level. Thus, mobile transmit power can be flexibly controlled if the mobile station's peak-to-average power ratio can be limited to a specific range. However, it is not economical to physically shrink a cell, since more cells arc then needed for a given area and each cell requires its own communications equipment. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide device and method for reducing the peak-to-average power ratio of a mobile station's transmit power in a mobile Another object of the present invention is to provide a method of flexibly controlling mobile transmit power by limiting its peak-to-average power ratio to a specific range. A farther object of the present invention is to provide a method of flexibly varying a cell site in a mobile communication system to counteract regrowth. A still further object of the present invention is to provide a method of enhancing auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users. To achieve these and other objects, a device and method for reducing the peak-to-nvcrage power ratio of mobile transmit power in a mobile communication system are provided. The.device and method spread mobile transmission data by a complex spreading sequence. The complex spreading sequence includes a plurality of chips and is generated to have a phase difference of 90* between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence. -2- BBIEF DESCRIPTION OF THE/DRAWINGS FIG I is a block diagram of a mobile station for performing the spreading and modulating method according lo an embodiment of the present invention, FIG. 2 is a block diagram of a first embodiment of a JI/2 DPSK (Differential Phase Shift Keying) shown in FIG. 1; FIGS. 3Aand 3B illustrate signal constellation and phase transition of complex spreading sequences according to the structure of the it/2 DPSK generator shown in FIG 2. FIG. 4 is a block diagram of a second embodiment of a r/2 DPSK generator shown in FIG. 1; FIGS. 5A and 5B illustrate signal constellation and phase transition of complex spreading sequences according to the structure of the T:/2 DPSK generator shown in FIG. 4, FIG. 6 is a block diagram of a mobile station in a 3G 1S-95 system to which the spreading and modulating method according to the present invention is applied; and FIG 7 is a block diagram of a mobile station in a W-CDMA (Wideband Code Division Multiple Access) system to which the spreading and modulating method according to the present invention is applied. -3 DETAILED DESCRIPTION OF PREFERRED EMBO^M^N^ Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known constructions or functions are not described in detail so as not to obscure the present invention. u , nas advantages The present invention¦wtluda the following novel and inventive feptmea: (1) mobile transmit power can be flexibly controlled by limiting its peak-to-average power ratio to a specific range and thus confining the mobile transmit power to a linear characteristic portion in a characteristic curve of a power amplifier; (2) the phase of a complex spreading sequence is prevented from shifting by 180° (i.e., ft) to maintain the mobile transmit power in the linear portion of the power amplifier characteristic curve; (3) the phase difference between every two successive complex chips of a complex spreading sequence (PN, and PN^) is 90° (i.e., tt'2) to limit the output power range of baseband filters and thereby, reduce the peak-to-average power ratio of mobile transmit power; and (4) auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users are improved by respreading a signal which has passed through a complex spreader by a spreading sequence PN: generated from a PN code generator. It is to be appreciated in the embodimenl of the present invention that "TI/2 DPSK. (Di fferemial Phase Shift Keying)" does not refer to a typical DPSK and is so named because the complex spreading sequence PN.-^/PN^ generated in the it/2 DPSK generator has a phase variation of TT/2 for one chip duration. -4- With reference to FIG. 1, there is shown a schematic block diagram of a mobile station (MS) which will be referred to far describing methods of spreading and modulating mobile transmission data for reducing the peak-to-average power ratio of mobile transmit power according to embodiments of the present invention. A complex signal including m-phase data (-data and quadrature-phase data Q-dala is applied as a first input signal to a complex spreader 2, A PN, generator 4 generates a sequence PNM nnd a TT/2 DPSK generator 6 generates complex spreading sequences PN, and PNQ with the sequence PN, received from the PN, generator 4. The complex spreading sequences PN, and PN0 are fed as a second input signal to the complex spreader 2. The embodiment of the present invention is characterised in that there is no zero-crossing since the phase difference between every two successive complex chips of the complex spreading sequence (PN, and PNQ) is it/2. The structure and operation of the JI/2 DPSK generator 6 is described in detail below with reference to FIGS. 2 to 5B. In FIG. I > the complex spreader 2 includes multipliers 8, 10, L2, and Hand adders 16 and 18 for complex-spreading the complex signal by the complex spreading sequences PN, and PN0. A detailed description of the operation of the complex spreader 2 can be found in Korean Patent Application No. 98-7667 having a common assignee. Multipliers 20-1 and 20-2 multiply the resulting in-phase spread signal XI and quadrature-phase spread signal XQ received from the complex spreader 2 by a sequence PN. generated from a PN: generator 21 for additional spreading. In the embodiment of the present invention, the sequences PN, andPN2 are independent. It is contemplated that sequences PN, and PNj may entail a PN sequence generated by user identification code. And in this invention, multiplying the output of complex spreader 2 by PN 2 could be optional feature. The outputs of the multipliers 20-1 and 20-2 are subjected to baseband filtering by -5- baseband filters 22-1 and 22-2, and to gain (Gp) control by gain controllers 24-1 and 24-2, respectively Then, mixers 26-1 and 26-2 multiply the outputs of the gain controllers 24-1 and 24 2 by their respective corresponding carriers, cos(2nf t) and sin(2nf In accordance with the present invention, auto-correlation characteristic of a multipath signal and cross correlation characteristics relative to other users are improved by spreading an input complex signal two times: once time by the sequence PN. and another time by the sequence PN,. Here, the sequences PN,, PN., PN,, and PNQ have the same chip rate If the phase of a complex spreading sequence PN,+/PNQ output from a spreading sequence generator drastically changes, (for example, from 0° to 180°) it causes increase of the peak-to-average power ratio of mobile transmit power leads to regrowth and degrades the communication quality of a different user. However, the spreading sequence generator is configured that no zero-crossing (no phase variation of n) is produced in generating the complex spreading sequence PN,-yPNy in the embodiment of the present invention. FIG. 2 is a block diagram of the n/2 DPSK. generator 6 provided as the spreading sequence generator according to the present invention. The feature of the n/2 DPSK generator 6 is that a maximum phase difference between every two successive complex chips of the complex spreading sequence PN,+yWc is n/2. The Tt/2 DPSK generator 6 includes a complex function calculator 32, a complex multiplier 34. and delay registers 36 and 38. A multiplier 30 multiplies the PN chips of the sequence PN, by (+-)/2 or (+-)3T:/2. It is contemplated that the multiplier 30 multiplies everyone PN chip of the sequence PN, by any phase in the range of (-)n/2 or (+-)3n/2. The complex function calculator 32 produces complex data Rc-ylm by operating -6- every one phase shifted PN chip outpul of the multiplier 30 in a complex function exp{j(-))-Thecomplcx multiplier 34 complex-multiplies the complex data Re+ylm by values (complex data) received from the delay registers 36 and 38 and outputs the complex spreading sequence PN,+/PNQ chip unit The delay register 36 stores the value PN, for one chip duration and the delay register 38 stores the value PNy for one chip duration. The initial values (complex data) of the delay registers 36 and 38 are determined by (Equation 1) delay register 36 = Re[exp(jQ)] delay register 38 " /m[exp(/6)], where 8 may be any value, preferably it.'4 Assuming that the consecutive chips of the sequences PN. and PN; arc {1, -1, I, -1, ...} and {-1,1,-1,1, ..(.respectively, and the initial values of the delay registers 36 and 38 are 1, the consecutive chips of the complex spreading sequence PN,~/PN0 generated from the n/2 DPSK generator 6 are {(- \+j\ (\+j). (- 1+y), (I/). ¦ ¦}. and the consecutive chips of a complex spreading sequence input to the baseband filters 22-1 and 22-2 are f (1 -j), (1 -y), (\|-", (I-V). -.)¦ The sequences PN, andPN. can be long codes for user identification in the 3G CDMA system. FIGS 3 A and 3B illustrate signal constellations and phase transitions of the complex spreading sequence PN,-yPNQ output from the n/2 DPSK generator 6 and the complex spreading sequence input to the baseband filters 22-1 and 22-2, respectively. Refemng to FIGS. 1 to 3B, for the first PN chip 1 of the sequence PN,, the output of the multiplier 30 in the n/2 DPSK generator 6 is Tt/2 since the other input to the multiplier 30 is it/2, and the m complex data output from the complex function calculator is e'2 expressed as (0* \J) in the complex numeral form (Re-ylm) Therefore, the complex multiplier 34 produces complex -7- data (-1 +/) "¦ (0+/)x{ 1+/). Here, (0+/) is the complex data output from the complex function calculator 32 and (1+/) is the initial values of the delay registers 36 and 38. In FIG. 3A, the complex data {-1+J) exists in the second quadrant of an orthogonal coordinates graph defined by teal components (Re) and imaginary components (lm) of a complex signal The real part -1 of the complex data (- t+/) is stored in the delay register 36 for one chip duration, and the imaginary part J is stored in the delay register 38 for one chip duration. For the second PN chip -1 of the sequence PN{, the output of the multiplier 30 in the it/2 DPSK generator 6 is - n/2, and the complex data output from the complex function calculator 32 is e'J 2 expressed as (0-/) in the complex numeral form (Re+/lm). Therefore, the complex multiplier 34 produces complex data (1+/) - (0-y)x(- l+y). Here, (0-J) is the complex data output from the complex function calculator 32 and (- }¦+/) is the previous values of the delay registers 36 and 38. In FIG. 3A, the complex data {14/} exists in the first quadrant of the orthogonal coordinates graph. The real part I of the complex data (1-+J) is stored in the delay register 36 for one chip duration, and the imaginary part 1 is stored in the delay register 38 for one chip duration. In this manner, the complex data output from the complex multiplier 34 is (- 1 +/) for the third PN chip 1 of the sequence PN," and (1+0 for the fourth PN chip - I of the sequence PN,. With continued reference to FIG. 3A, the complex spreading sequence PN^+yPN^ exists in the second and first quadrants of the orthogonal coordinates graph defined by the neal components (Re) and the imaginary components (lm) of a complex sigtwt), with a phase difference of tt/2 between every two successive complex chips. The nil phase difference between every two successive complex chips is maintained -a- in a complex spreading sequence obtained by respreading ihc sequence PN, Referring to FIG I. a complex spreading sequence {(!-/). (!+", (l-", (!+/), ...) is produced by multiplying the chips {(-1+", (1+/). (-1+/). (1+/)....} of tlie complex spending sequence PN,-7?Ng by the chips {-1. 1. -1, 1. --} of the sequence PN,. As shown in FIG 3B, the complex spreading sequence input to the baseband fillers 22-1 and 22-2 has ihc phase difference ot'rJ2 between every two successive complex chips like the complex spreading sequence PN.+yPN^ Since the phase difference between every two successive complex chips of the complex spreading sequences is small, that is, w'2 as noted by FIGS 3A and 3B, the peak-to-average power ratio of mobile transmit power after processing in the baseband fillers 22-1 and 22-2 is reduced, decreasing the influence of regrowth. As a result, communication quality and performance are improved. If a predetermined radian value input to the multiplier 30 of the rJ2 DPSK generator f" is - 3it/2, the complex spreading sequence PN,+/PNQ also shows the signal constellation of FIG 3A If the radian value is-n/2 or 3rr'2, the chips of the complex spreading sequence PN,+/PN are successively shown at the same positions in the alternating first and second quadrants, starting from the first quadrant in FIG. 3 A. FIG. 4 is a block diagram of a second embodiment of the n/2 DPSK generator 6 shown in FIG. 1. As with the firat embodiment, the maximum phase difference between every two successive complex chips of the complex spreading sequence PN,+/PNy is (+o) TT/2. The n/2 DPSK generator 6 of the second embodiment includes an addr 40, a delay register 42. and a complex function calculator 44. The adder 40 adds a PN chip of the sequence PN,with the previous output of the adder 40 stored in the delay register 42. It is preferable to set the initial value of the delay register 42 to 1/2. The complex function -9- calculator 44 produces the complex spreading sequence PN,+>PNQ by operating the output of the adder 40 in a complex flinction exp[(j(^'2())]. The phase variation of the complex spreading sequence PN,+yPNc is given by (Equation 2) Q(k) = Q(k~i)+~PNr It is noted from equation (2) that the phase in the current chip of the complex spreading sequence PN;;PNQ is the sum of the phase in the previous chip thereof and the product of the current chip of the sequence PN, by r.!2. Assumtng that the consecutive chips of the sequences PN, andPN, are {1, -1,1, -1, ...} and {-1, 1. - 1, 1....}, respectively and the initial value of the delay register 42 is l'2, then the consecutive chips of the complex spreading sequence PN,+/PNQ generated from the ml DPSK generator 6 are {(- !?". (l-y), (" ' tf% O"V)i ¦ }, and the consecutive chips of the complex spreading sequence input to tiic baseband filters 22-1 ond 22-2 are {(] -f). (1-/). (I ./).{! ¦¦;.), ..}¦ The sequences PN, undPNj can be long codes for user identification mthe ^GCDMAs>-stem. FIGS 5A and 5B are views illustrating the signal constellations and phase transitions of the complex spreading sequence PN,+>PN0 output from the rc/2 DPSK generator 6 and the complex spreading sequence input to the baseband filters 22-1 and 22-2, respectively Referring to FIGS. 1 to 5B, for the first PN chip \ of the sequence PN:, the output of ihe udder 40 is 3/2 (=1+1/2). which is stored in the delay register 42 for one chip duration, and the complex data output from the complex function calculator 44 is ¦' ' expressed as (- I +/) in the complex numeral form (Re-y1m), and a chip of the complex spreading sequence PN,+/PN,j Here, (-!+" exists in the second quadrant of an orthogonal coordinates graph - 10- shown in FIG. 5A. For the second PN chip -1 of the sequence PN,, the output of the adder 40 is 1/2 (=-1+3/2), which is stored in the delay register 42 for one chip duration, and the complex data output from the complex function calculator 44 is eJ 4 expressed as (1+1/) in the complex numeral form (Rc+/Im). Here, (1 + 1/) is present in the first quadrant of the orthogonal coordinates graph shown in FIG. 5A. In this manner, the complex data output from the complex function calculator 44 is (- \+j) for the third PN chip 1 of the sequence PN,, and (1 +y) for the fourth PN chip - 1 of the sequence PN,. With continued reference to FIG. 5A, the complex spreading sequence PN,+/PNC exists in the second and first quadrants of the orthogonal coordinates plane defined by the real components (Re) and the imaginary components (Im) of a complex signal, with a phase difference n/2 between every two successive complex chips. The phase difference of n/2 between every two successive complex chips is maintained in a complex spreading sequence obtained by respreading the complex spreading sequence PN,+/PNy by the sequence PNj (It is noted that the complex spreading sequence can also be respread by the original sequence PN or different PN sequence.). Referring to FIG. 1, a complex spreading sequence f(l-y). 0+/). (W), (l+". -o-} is produced by multiplying the chips {(- 1+/), (1+/), (- l+j), (1+/). ...} of the complex spreading sequence PN,+/PN0 by the chips {-1, 1, -I, I, ...} of the sequence PN3. As shown in FIG. 5B, the complex spreading sequence input to the baseband filters 22-1 and 22-2 has the phase difference n/2 between every two successive complex chips like the complex spreading sequence PN,+/PN0. Since the phase difference between every two successive complex chips of the complex spreading sequence is small, that is, 7t/2 as noted from FJGS. 5 A and 5B, the pcak- ¦ 11 - to average power ratio of mobile transmit power after processing in the baseband filters 22-1 and 22-2 is reduced, thereby, counteracting the regrowth phenomenon As a result, communication quality and performance are improved. FIG. 6 is a block diagram of an MS in a 3G IS-95 system to which the spreading and modulation method according to the embodiment of the present invention is applied. Reverse communication channels are comprised of a pilot channel which is always activated, a control channel, a fundamental channel deactivated in a specific frame, and a supplemental channel. The pilot channel is unmodulated and used for performing initial acquisition, time tracking, and synchronization of a rake receiver This allows reverse-link closed-loop power control A dedicated control channel transmits an uncoded fast power control bit and coded control information. The two types of information are multiplexed and sent on one control channel. The fundamental channel is used to send RLP (Radio Link Protocol) frames and packet data The channels arc spread by Walsh codes for orthogonal channelization. Control, supplemental, and fundamental channel signals are multiplied by corresponding Walsh codes in multipliers 50, 52, and 54, respectively. Relative gain controllers 56, 58, and 60 control the relative gains G( of the outputs of the multipliers 50, 52, and 54, respectively. An adder 62 adds a pilot channel signal with a control channel signal received from the relative gam controller 56. The added information of the adder 62 is applied as an I-channel signal. An adder 64 adds a supplemental channel signal output from the relative gain controller 58 with a fundamental channel signal output from the relative gain controller 60. The added information of the adder 64 is assigned as a Q-channel signal. A signal sent on the pilot, dedicated control, fundamental, and supplemental channel signals is o complex signal as shown in FIG. 1. The sum of the pilot channel and the control -12- channel is assigned as the I-charmcl. and the sum of the fundamental channel and the supplemental channel is assigned as the Q-channei. The complex signal of the I and Q channels is complex-spread by the complex spreading sequence PN,+/PN^, in the complex spreader 2 of FIG. 6. The complex-spread signal is multiplied by the sequence P"2, that is" a long code for user identification. The resulting complex spreading sequence is subjected to baseband filtering in the baseband filters 22-1 and 22-2, and sent through the gain controllers 24-1 and 24-2, the mixers 26-1 and 26-2, and the adder 28 with a low peak-to-average power ratio, FIG. 7 is a block diagram of an MS in a W-CDMA system to which the spreading and modulating method of the presem invention is applied. In FIG. 7, a traffic signs! is sent on a dedicated physical data channel (DPDCH), and a control signal is sent on a dedicated physical control channel (DPCCH). The DPDCH is multiplied by a channelization code CD at a chip rate in a multiplier 70 and assigned as an I channel. The DPCCH is multiplied by a channelization code Cc at a chip rate in a multiplier 72, converted to an imaginary numeral form by an imaginary operand (j) 74, and assigned as a Q channel. Here, Ct, and Cc are mutually orthogonal codes. The I and Q channels form a complex signal The complex signal is complex-spread by the complex spreading sequence PN,+yPNQ in the complex spreader 2 of FIG. 7, and multiplied by the sequence PN3; that is, a long code for user identification generated in rhe PN, generator 21. The resulting complex spreading sequence is subject to baseband Filtering in the baseband filters 22-1 and 22-2, and sen! through the gain controllers 24-1 and 24-2, the mixers 26-1 and 26-2, and the adder 28 with a low peak-to-average power ratio. According to the present invention as described above, the peak-to-average power ratio of mobile transmit power is limited to a specific range by ensuring a phase difference -13- of 90° between every two successive complex chips of a complex spreading sequence. Therefore, the mobile transmit power appears only in a linear portion of a characteristic curve of a power amplifier, thereby allowing the mobile traniimit power and the cell size to be flexibly controlled. In addition, auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users can be improved by respreading a signal which has passed through a complex spreader by another W sequence generated from a PN code generator. While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. -14 WftAJUS-Ci-AlMfeaiS: 1. A method for reducing the peak-to-average power ratio of a mobile station's transmit power in a mobile communication system, comprising the steps of generating a complex spreading sequence having a plurality of chips and a phase 5 difference of 00° between every two successive complex chips in response to each chip of spreading ancTmodulating mobile transmission data by the complex spreading sequence 2. The method of claim 1, wherein che step of generating the complex spreading 10 sequence comprises the steps of: multiplying the chips of the PN sequence by a predetermined phase value to produce phase shifted chips; converting the phase shifted chips to complex data using each of the phase shifted chips as a phase; and 15 multiplying the converted complex data by previously converted complex data to generate the plurality of chips of the complex spreading sequence. 3 The method of claim 2, wherein the step of con verting uses a complex function cxp(j( ]) to convert the phase shifted chips to complex data. A. The method of claim 2, wherein the predetermined phase value is within the 20 range of n/2 to 3:t/2. -IS- 5. The method of claim 1, wherein the step of generating the complex spreading sequence comprises the steps of: adding every chip of the PN sequence with a respective pre-stored chip to obtftin added chips; and 5 converting the added chips to complex data to generate the plurality of chips of the complex spreading sequence. 6. The method of claim 5, wherein the step of converting uses a complex function exp[j(it/2())] to convert the added chips to complex data. 7. The method of claim 1. further comprising the step of respreading the spread 10 and modulated mobile transmission data by an independent PN sequence 8. A device for reducing the peak-to-average power ratio of a mobile station's transmit power in a mobile communication system, comprising: a complex spreading sequence generator for generating a complex spreading sequence having a plurality of chips and a phase difference of 90* between every* two successive 15 complex chips in response to each chip of a P\ sequence; and a spreader for spreading and modulating mobile transmission data by the complex spreading sequence. 9. The device of claim 8, wherein the complex spreading sequence generator comprises: 0 a multiplier for multiplying the chips of the PN sequence by a predetermined phase - 16- value to produce phase shifted chips; a complex data generator for converting the phase shifted chips to complex data using each of the phase shifted chips as a phase; and a complex multiplier for generating the plurality of chips of the complex spreading 5 sequence by multiplying the converted complex data by previously converted complex data 10. The device of claim 9, wherein a complex function cxp(j[]) is used in converting the phase shifted chips to complex data. 11. The device of claim 9, wherein the predetermined phase value is within the range of xn/2 and 3n/2. 10 J2. The device of claim 8, wherein the complex spreading soquence generator comprises: an adder for adding every chip of the PN sequence with a respective prc-stored chip to obtain added chips; and a complex data generator for generating the plurality of chips of the complex 15 spreading sequence by converting the added chips to complex data. 13. The device of claim 12, wherein a complex function txp[j(rJ2(-))] is used in converting the added chips to complex data. 14. The device of claim 8, further comprising a re-spreader for rcspreading the spread and modulated mobile transmission data by an independent PN sequence. -17- 15. The device of claim 14, wherein the independent PN sequence ts identical to the PN sequence. 16. A device for reducing the peak-to-average power ratio of a mobile station's transmit power in a mobile communication system, comprising: (6) complex spreading sequence generating means/for generating a complex spreading sequence having a plurality of chips and a phase difference of 90° between every two successive complex chips, jn. response to each chip of a PN sequence; and spreading means Abr spreading and modulating mobile transmission data by the complex spreading sequence. 17. The device of claim 16, wherein the complex spreading sequence generating means comprises: (30) multiplying means(for multiplying the chips of the PN sequence by a predetermined phase value to produce phase shifted chips: it32- complex data generating meansubr converting the phase shifted chips to complex data using each of the phase shifted chips as a phase; and pu) complex multiplying meansffor generating the plurality of chips of the complex spreading sequence by multiplying the converted complex data by previously converted complex data. 18. The device of claim 17, wherein the predetermined phase value is within the range of f n/2 and *3TT/2. - 18- 19, The device of claim 16, wherein the complex spreading sequence generating means comprises: adding means for adding every chip of the PN sequence with a respective pre-stored chip to obtain added chips; and complex data generating means for generating the plurality of chips of the complex spreading sequence by converting the added chips to complex data. 2G. The device of claim 16, further comprising re-spreading means for respreading &e spread and modulated mobile transmission data by an independent PN sequence. A device and method are provided for reducing the peak-to average power ratio of a mobile station's transmit power in a mobile communication system by spreading and modulating the transmission data by a complex spreading sequence. The complex spreading sequence is generated to have a plurality of chips and a phase difference of 90° between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence. The device and method flexibly control the mobile transmit power by limiting its peak-to-average power ratio to a specific range and thus confining the mobile transmit power to a linear characteristic curve of a power amplifier. The phase of the complex spreading sequence is prevented from shifting by 180° (i.e.. IT) to maintain the mobile transmit power in the linear portion of the power amplifier characteristic curve.

Full Text

DEVICE AND METHOD FOR REDUCING THE PEAKTO-AVERACE POWER RATIO OF A MOBILE STATION'S TRANSMIT POWER
BACKGROUND OF THE INVENTION
1. Field 01" the Invcnlion
The present invention relates generally :o mobile communication systems, ami in particular, 10 a device and method for reducing the pcak-lo-average power ratio of a mobile station's transmit power in a mobile communication system.
2. Description of tfre Related Art
A typical CDMA mobile communication system focuses on voice service, whereas a 3G mobile communication system provides the additional services of high quality voice, high speed data, moving pictures, and Internet browsing. In such a mobile communication system, a radio link consists of a forward link directed from a base station (BS) to a mobile station (MS) and a reverse link directed from the MS to the BS.
When zero-crossing occurs during spreading and modulation in a reverse link transmission (a phase variation is r.)t the peak-to-average power ratio of the mobile station's irnnvuit power (mobile transmit power) increases, thereby producing regrowlh. Rcgrowth Adversely affects the communication quality of calls being made by other subscribers Hence. the peak-to-average power ratio is a significant factor in the design and performance of a
power amplifier in an MS
Rcgrowth occurs due the existence of a linear portion and a non-linear portion :n a ch"rsctcristic curve of the mobile station's power amplifier As the mobile transmit power increases, a transmit signal of the MS due to the non-linear characteristics generates
/./]

interference in the frequency area of a different user causing the regrowth phenomenon.
Regrowth can be prevented by shrinking down a cell and sending a signal from an MS in the cell to a corresponding BS at a low power level. Thus, mobile transmit power can be flexibly controlled if the mobile station's peak-to-average power ratio can be limited to a specific range. However, it is not economical to physically shrink a cell, since more cells arc then needed for a given area and each cell requires its own communications equipment.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide device and method for reducing the peak-to-average power ratio of a mobile station's transmit power in a mobile
Another object of the present invention is to provide a method of flexibly controlling mobile transmit power by limiting its peak-to-average power ratio to a specific range.
A farther object of the present invention is to provide a method of flexibly varying a cell site in a mobile communication system to counteract regrowth.
A still further object of the present invention is to provide a method of enhancing auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users.
To achieve these and other objects, a device and method for reducing the peak-to-nvcrage power ratio of mobile transmit power in a mobile communication system are provided. The.device and method spread mobile transmission data by a complex spreading sequence. The complex spreading sequence includes a plurality of chips and is generated to have a phase difference of 90* between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence.
-2-

BBIEF DESCRIPTION OF THE/DRAWINGS
FIG I is a block diagram of a mobile station for performing the spreading and modulating method according lo an embodiment of the present invention,
FIG. 2 is a block diagram of a first embodiment of a JI/2 DPSK (Differential Phase Shift Keying) shown in FIG. 1;
FIGS. 3Aand 3B illustrate signal constellation and phase transition of complex spreading sequences according to the structure of the it/2 DPSK generator shown in FIG 2.
FIG. 4 is a block diagram of a second embodiment of a r/2 DPSK generator shown in FIG. 1;
FIGS. 5A and 5B illustrate signal constellation and phase transition of complex spreading sequences according to the structure of the T:/2 DPSK generator shown in FIG. 4,
FIG. 6 is a block diagram of a mobile station in a 3G 1S-95 system to which the spreading and modulating method according to the present invention is applied; and
FIG 7 is a block diagram of a mobile station in a W-CDMA (Wideband Code Division Multiple Access) system to which the spreading and modulating method according to the present invention is applied.
-3

DETAILED DESCRIPTION OF PREFERRED EMBO^M^N^
Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known constructions or functions are not described in detail so as not to obscure the present
invention. u ,
nas advantages
The present invention¦wtluda the following novel and inventive feptmea:
(1) mobile transmit power can be flexibly controlled by limiting its peak-to-average
power ratio to a specific range and thus confining the mobile transmit power to a linear
characteristic portion in a characteristic curve of a power amplifier;
(2) the phase of a complex spreading sequence is prevented from shifting by 180°
(i.e., ft) to maintain the mobile transmit power in the linear portion of the power amplifier
characteristic curve;
(3) the phase difference between every two successive complex chips of a complex
spreading sequence (PN, and PN^) is 90° (i.e., tt'2) to limit the output power range of
baseband filters and thereby, reduce the peak-to-average power ratio of mobile transmit
power; and
(4) auto-correlation characteristics of a multipath signal and cross-correlation
characteristics relative to other users are improved by respreading a signal which has passed
through a complex spreader by a spreading sequence PN: generated from a PN code
generator.
It is to be appreciated in the embodimenl of the present invention that "TI/2 DPSK. (Di fferemial Phase Shift Keying)" does not refer to a typical DPSK and is so named because the complex spreading sequence PN.-^/PN^ generated in the it/2 DPSK generator has a phase variation of TT/2 for one chip duration.
-4-

With reference to FIG. 1, there is shown a schematic block diagram of a mobile station (MS) which will be referred to far describing methods of spreading and modulating mobile transmission data for reducing the peak-to-average power ratio of mobile transmit power according to embodiments of the present invention. A complex signal including m-phase data (-data and quadrature-phase data Q-dala is applied as a first input signal to a complex spreader 2, A PN, generator 4 generates a sequence PNM nnd a TT/2 DPSK generator 6 generates complex spreading sequences PN, and PNQ with the sequence PN, received from the PN, generator 4. The complex spreading sequences PN, and PN0 are fed as a second input signal to the complex spreader 2. The embodiment of the present invention is characterised in that there is no zero-crossing since the phase difference between every two successive complex chips of the complex spreading sequence (PN, and PNQ) is it/2. The structure and operation of the JI/2 DPSK generator 6 is described in detail below with reference to FIGS. 2 to 5B.
In FIG. I > the complex spreader 2 includes multipliers 8, 10, L2, and Hand adders 16 and 18 for complex-spreading the complex signal by the complex spreading sequences PN, and PN0. A detailed description of the operation of the complex spreader 2 can be found in Korean Patent Application No. 98-7667 having a common assignee.
Multipliers 20-1 and 20-2 multiply the resulting in-phase spread signal XI and quadrature-phase spread signal XQ received from the complex spreader 2 by a sequence PN. generated from a PN: generator 21 for additional spreading. In the embodiment of the present invention, the sequences PN, andPN2 are independent. It is contemplated that sequences PN, and PNj may entail a PN sequence generated by user identification code. And in this invention, multiplying the output of complex spreader 2 by PN 2 could be optional feature.
The outputs of the multipliers 20-1 and 20-2 are subjected to baseband filtering by
-5-

baseband filters 22-1 and 22-2, and to gain (Gp) control by gain controllers 24-1 and 24-2, respectively Then, mixers 26-1 and 26-2 multiply the outputs of the gain controllers 24-1 and 24 2 by their respective corresponding carriers, cos(2nf t) and sin(2nf In accordance with the present invention, auto-correlation characteristic of a multipath signal and cross correlation characteristics relative to other users are improved by spreading an input complex signal two times: once time by the sequence PN. and another time by the sequence PN,. Here, the sequences PN,, PN., PN,, and PNQ have the same chip rate
If the phase of a complex spreading sequence PN,+/PNQ output from a spreading sequence generator drastically changes, (for example, from 0° to 180°) it causes increase of the peak-to-average power ratio of mobile transmit power leads to regrowth and degrades the communication quality of a different user.
However, the spreading sequence generator is configured that no zero-crossing (no phase variation of n) is produced in generating the complex spreading sequence PN,-*yPNy in the embodiment of the present invention.
FIG. 2 is a block diagram of the n/2 DPSK. generator 6 provided as the spreading sequence generator according to the present invention. The feature of the n/2 DPSK generator 6 is that a maximum phase difference between every two successive complex chips of the complex spreading sequence PN,+yWc is n/2.
The Tt/2 DPSK generator 6 includes a complex function calculator 32, a complex multiplier 34. and delay registers 36 and 38. A multiplier 30 multiplies the PN chips of the sequence PN, by (+-)*/2 or (+-)3T:/2. It is contemplated that the multiplier 30 multiplies everyone PN chip of the sequence PN, by any phase in the range of (*-)n/2 or (+-)3n/2.
The complex function calculator 32 produces complex data Rc-ylm by operating
-6-

every one phase shifted PN chip outpul of the multiplier 30 in a complex function exp{j(-))-Thecomplcx multiplier 34 complex-multiplies the complex data Re+ylm by values (complex data) received from the delay registers 36 and 38 and outputs the complex spreading sequence PN,+/PNQ chip unit The delay register 36 stores the value PN, for one chip duration and the delay register 38 stores the value PNy for one chip duration. The initial values (complex data) of the delay registers 36 and 38 are determined by
(Equation 1)
delay register 36 = Re[exp(jQ)]
delay register 38 " /m[exp(/6)], where 8 may be any value, preferably it.'4
Assuming that the consecutive chips of the sequences PN. and PN; arc {1, -1, I, -1, ...} and {-1,1,-1,1, ..(.respectively, and the initial values of the delay registers 36 and 38 are 1, the consecutive chips of the complex spreading sequence PN,~/PN0 generated from the n/2 DPSK generator 6 are {(- \+j\ (\+j). (- 1+y), (I*/). ¦ ¦}. and the consecutive chips of a complex spreading sequence input to the baseband filters 22-1 and 22-2 are f (1 -j), (1 -y), (|-", (I-V). -.)¦ The sequences PN, andPN. can be long codes for user identification in the 3G CDMA system.
FIGS 3 A and 3B illustrate signal constellations and phase transitions of the complex spreading sequence PN,-yPNQ output from the n/2 DPSK generator 6 and the complex spreading sequence input to the baseband filters 22-1 and 22-2, respectively. Refemng to FIGS. 1 to 3B, for the first PN chip 1 of the sequence PN,, the output of the multiplier 30 in the n/2 DPSK generator 6 is Tt/2 since the other input to the multiplier 30 is it/2, and the
m
complex data output from the complex function calculator is e'2 expressed as (0* \J) in the complex numeral form (Re-ylm) Therefore, the complex multiplier 34 produces complex
-7-

data (-1 +/) "¦ (0+/)x{ 1+/). Here, (0+/) is the complex data output from the complex function calculator 32 and (1+/) is the initial values of the delay registers 36 and 38.
In FIG. 3A, the complex data {-1+J) exists in the second quadrant of an orthogonal coordinates graph defined by teal components (Re) and imaginary components (lm) of a complex signal The real part -1 of the complex data (- t+/) is stored in the delay register 36 for one chip duration, and the imaginary part J is stored in the delay register 38 for one chip duration.
For the second PN chip -1 of the sequence PN{, the output of the multiplier 30 in the it/2 DPSK generator 6 is - n/2, and the complex data output from the complex function calculator 32 is e'J 2 expressed as (0-/) in the complex numeral form (Re+/lm). Therefore, the complex multiplier 34 produces complex data (1+/) - (0-y)x(- l+y). Here, (0-J) is the complex data output from the complex function calculator 32 and (- }¦+/) is the previous values of the delay registers 36 and 38.
In FIG. 3A, the complex data {14/} exists in the first quadrant of the orthogonal coordinates graph. The real part I of the complex data (1-+J) is stored in the delay register 36 for one chip duration, and the imaginary part 1 is stored in the delay register 38 for one chip duration. In this manner, the complex data output from the complex multiplier 34 is (- 1 +/) for the third PN chip 1 of the sequence PN," and (1+0 for the fourth PN chip - I of the sequence PN,.
With continued reference to FIG. 3A, the complex spreading sequence PN^+yPN^ exists in the second and first quadrants of the orthogonal coordinates graph defined by the neal components (Re) and the imaginary components (lm) of a complex sigtwt), with a phase difference of tt/2 between every two successive complex chips.
The nil phase difference between every two successive complex chips is maintained
-a-

in a complex spreading sequence obtained by respreading ihc sequence PN, Referring to FIG I. a complex spreading sequence {(!-/). (!+", (l-", (!+/), ...) is produced by multiplying the chips {(-1+", (1+/). (-1+/). (1+/)....} of tlie complex spending sequence PN,-7?Ng by the chips {-1. 1. -1, 1. --} of the sequence PN,. As shown in FIG 3B, the complex spreading sequence input to the baseband fillers 22-1 and 22-2 has ihc phase difference ot'rJ2 between every two successive complex chips like the complex spreading sequence PN.+yPN^
Since the phase difference between every two successive complex chips of the complex spreading sequences is small, that is, w'2 as noted by FIGS 3A and 3B, the peak-to-average power ratio of mobile transmit power after processing in the baseband fillers 22-1 and 22-2 is reduced, decreasing the influence of regrowth. As a result, communication quality and performance are improved.
If a predetermined radian value input to the multiplier 30 of the rJ2 DPSK generator f" is - 3it/2, the complex spreading sequence PN,+/PNQ also shows the signal constellation of FIG 3A If the radian value is-n/2 or 3rr'2, the chips of the complex spreading sequence PN,+/PN are successively shown at the same positions in the alternating first and second quadrants, starting from the first quadrant in FIG. 3 A.
FIG. 4 is a block diagram of a second embodiment of the n/2 DPSK generator 6 shown in FIG. 1. As with the firat embodiment, the maximum phase difference between every two successive complex chips of the complex spreading sequence PN,+/PNy is (+o) TT/2. The n/2 DPSK generator 6 of the second embodiment includes an add*r 40, a delay register 42. and a complex function calculator 44. The adder 40 adds a PN chip of the sequence PN,with the previous output of the adder 40 stored in the delay register 42. It is preferable to set the initial value of the delay register 42 to 1/2. The complex function
-9-

calculator 44 produces the complex spreading sequence PN,+>PNQ by operating the output of the adder 40 in a complex flinction exp[(j(^'2())].
The phase variation of the complex spreading sequence PN,+yPNc is given by
(Equation 2)
Q(k) = Q(k~i)+~PNr
It is noted from equation (2) that the phase in the current chip of the complex spreading sequence PN;*;PNQ is the sum of the phase in the previous chip thereof and the product of the current chip of the sequence PN, by r.!2.
Assumtng that the consecutive chips of the sequences PN, andPN, are {1, -1,1, -1, ...} and {-1, 1. - 1, 1....}, respectively and the initial value of the delay register 42 is l'2, then the consecutive chips of the complex spreading sequence PN,+/PNQ generated from the ml DPSK generator 6 are {(- !?". (l-*y), (" ' tf% O"V)i ¦ }, and the consecutive chips of the complex spreading sequence input to tiic baseband filters 22-1 ond 22-2 are {(] -f). (1-/). (I ./).{! ¦*¦;.), ..}¦ The sequences PN, undPNj can be long codes for user identification mthe ^GCDMAs>-stem.
FIGS 5A and 5B are views illustrating the signal constellations and phase transitions of the complex spreading sequence PN,+>PN0 output from the rc/2 DPSK generator 6 and the complex spreading sequence input to the baseband filters 22-1 and 22-2, respectively
Referring to FIGS. 1 to 5B, for the first PN chip \ of the sequence PN:, the output of ihe udder 40 is 3/2 (=1+1/2). which is stored in the delay register 42 for one chip duration, and the complex data output from the complex function calculator 44 is *¦' ' expressed as (- I +/) in the complex numeral form (Re-*y1m), and a chip of the complex spreading sequence PN,+/PN,j Here, (-!+" exists in the second quadrant of an orthogonal coordinates graph
- 10-

shown in FIG. 5A.
For the second PN chip -1 of the sequence PN,, the output of the adder 40 is 1/2 (=-1+3/2), which is stored in the delay register 42 for one chip duration, and the complex data output from the complex function calculator 44 is eJ 4 expressed as (1+1/) in the complex numeral form (Rc+/Im). Here, (1 + 1/) is present in the first quadrant of the orthogonal coordinates graph shown in FIG. 5A. In this manner, the complex data output from the complex function calculator 44 is (- \+j) for the third PN chip 1 of the sequence PN,, and (1 +y) for the fourth PN chip - 1 of the sequence PN,.
With continued reference to FIG. 5A, the complex spreading sequence PN,+/PNC exists in the second and first quadrants of the orthogonal coordinates plane defined by the real components (Re) and the imaginary components (Im) of a complex signal, with a phase difference n/2 between every two successive complex chips.
The phase difference of n/2 between every two successive complex chips is maintained in a complex spreading sequence obtained by respreading the complex spreading sequence PN,+/PNy by the sequence PNj (It is noted that the complex spreading sequence can also be respread by the original sequence PN or different PN sequence.). Referring to FIG. 1, a complex spreading sequence f(l-y). 0+/). (W), (l+". -o-} is produced by multiplying the chips {(- 1+/), (1+/), (- l+j), (1+/). ...} of the complex spreading sequence PN,+/PN0 by the chips {-1, 1, -I, I, ...} of the sequence PN3. As shown in FIG. 5B, the complex spreading sequence input to the baseband filters 22-1 and 22-2 has the phase difference n/2 between every two successive complex chips like the complex spreading sequence PN,+/PN0.
Since the phase difference between every two successive complex chips of the complex spreading sequence is small, that is, 7t/2 as noted from FJGS. 5 A and 5B, the pcak-
¦ 11 -

to average power ratio of mobile transmit power after processing in the baseband filters 22-1 and 22-2 is reduced, thereby, counteracting the regrowth phenomenon As a result, communication quality and performance are improved.
FIG. 6 is a block diagram of an MS in a 3G IS-95 system to which the spreading and modulation method according to the embodiment of the present invention is applied. Reverse communication channels are comprised of a pilot channel which is always activated, a control channel, a fundamental channel deactivated in a specific frame, and a supplemental channel. The pilot channel is unmodulated and used for performing initial acquisition, time tracking, and synchronization of a rake receiver This allows reverse-link closed-loop power control A dedicated control channel transmits an uncoded fast power control bit and coded control information. The two types of information are multiplexed and sent on one control channel. The fundamental channel is used to send RLP (Radio Link Protocol) frames and packet data
The channels arc spread by Walsh codes for orthogonal channelization. Control, supplemental, and fundamental channel signals are multiplied by corresponding Walsh codes in multipliers 50, 52, and 54, respectively. Relative gain controllers 56, 58, and 60 control the relative gains G( of the outputs of the multipliers 50, 52, and 54, respectively. An adder 62 adds a pilot channel signal with a control channel signal received from the relative gam controller 56. The added information of the adder 62 is applied as an I-channel signal. An adder 64 adds a supplemental channel signal output from the relative gain controller 58 with a fundamental channel signal output from the relative gain controller 60. The added information of the adder 64 is assigned as a Q-channel signal.
A signal sent on the pilot, dedicated control, fundamental, and supplemental channel signals is o complex signal as shown in FIG. 1. The sum of the pilot channel and the control
-12-

channel is assigned as the I-charmcl. and the sum of the fundamental channel and the supplemental channel is assigned as the Q-channei. The complex signal of the I and Q channels is complex-spread by the complex spreading sequence PN,+/PN^, in the complex spreader 2 of FIG. 6. The complex-spread signal is multiplied by the sequence P"2, that is" a long code for user identification. The resulting complex spreading sequence is subjected to baseband filtering in the baseband filters 22-1 and 22-2, and sent through the gain controllers 24-1 and 24-2, the mixers 26-1 and 26-2, and the adder 28 with a low peak-to-average power ratio,
FIG. 7 is a block diagram of an MS in a W-CDMA system to which the spreading and modulating method of the presem invention is applied. In FIG. 7, a traffic signs! is sent on a dedicated physical data channel (DPDCH), and a control signal is sent on a dedicated physical control channel (DPCCH). The DPDCH is multiplied by a channelization code CD at a chip rate in a multiplier 70 and assigned as an I channel. The DPCCH is multiplied by a channelization code Cc at a chip rate in a multiplier 72, converted to an imaginary numeral form by an imaginary operand (j) 74, and assigned as a Q channel. Here, Ct, and Cc are mutually orthogonal codes. The I and Q channels form a complex signal The complex signal is complex-spread by the complex spreading sequence PN,+yPNQ in the complex spreader 2 of FIG. 7, and multiplied by the sequence PN3; that is, a long code for user identification generated in rhe PN, generator 21. The resulting complex spreading sequence is subject to baseband Filtering in the baseband filters 22-1 and 22-2, and sen! through the gain controllers 24-1 and 24-2, the mixers 26-1 and 26-2, and the adder 28 with a low peak-to-average power ratio.
According to the present invention as described above, the peak-to-average power ratio of mobile transmit power is limited to a specific range by ensuring a phase difference
-13-

of 90° between every two successive complex chips of a complex spreading sequence. Therefore, the mobile transmit power appears only in a linear portion of a characteristic curve of a power amplifier, thereby allowing the mobile traniimit power and the cell size to be flexibly controlled. In addition, auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users can be improved by respreading a signal which has passed through a complex spreader by another W sequence generated from a PN code generator.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
-14

WftAJUS-Ci-AlMfeaiS:
1. A method for reducing the peak-to-average power ratio of a mobile station's
transmit power in a mobile communication system, comprising the steps of
generating a complex spreading sequence having a plurality of chips and a phase 5 difference of 00° between every two successive complex chips in response to each chip of spreading ancTmodulating mobile transmission data by the complex spreading sequence
2. The method of claim 1, wherein che step of generating the complex spreading
10 sequence comprises the steps of:
multiplying the chips of the PN sequence by a predetermined phase value to produce phase shifted chips;
converting the phase shifted chips to complex data using each of the phase shifted chips as a phase; and
15 multiplying the converted complex data by previously converted complex data to
generate the plurality of chips of the complex spreading sequence.
3 The method of claim 2, wherein the step of con verting uses a complex function cxp(j( ]) to convert the phase shifted chips to complex data.
A. The method of claim 2, wherein the predetermined phase value is within the
20 range of *n/2 to *3:t/2.
-IS-

5. The method of claim 1, wherein the step of generating the complex spreading
sequence comprises the steps of:
adding every chip of the PN sequence with a respective pre-stored chip to obtftin added chips; and
5 converting the added chips to complex data to generate the plurality of chips of the
complex spreading sequence.
6. The method of claim 5, wherein the step of converting uses a complex function
exp[j(it/2())] to convert the added chips to complex data.
7. The method of claim 1. further comprising the step of respreading the spread
10 and modulated mobile transmission data by an independent PN sequence
8. A device for reducing the peak-to-average power ratio of a mobile station's
transmit power in a mobile communication system, comprising:
a complex spreading sequence generator for generating a complex spreading sequence having a plurality of chips and a phase difference of 90* between every* two successive 15 complex chips in response to each chip of a P\ sequence; and
a spreader for spreading and modulating mobile transmission data by the complex spreading sequence.
9. The device of claim 8, wherein the complex spreading sequence generator
comprises:
0 a multiplier for multiplying the chips of the PN sequence by a predetermined phase
- 16-

value to produce phase shifted chips;
a complex data generator for converting the phase shifted chips to complex data using each of the phase shifted chips as a phase; and
a complex multiplier for generating the plurality of chips of the complex spreading 5 sequence by multiplying the converted complex data by previously converted complex data
10. The device of claim 9, wherein a complex function cxp(j[]) is used in
converting the phase shifted chips to complex data.
11. The device of claim 9, wherein the predetermined phase value is within the
range of xn/2 and *3n/2.
10 J2. The device of claim 8, wherein the complex spreading soquence generator
comprises:
an adder for adding every chip of the PN sequence with a respective prc-stored chip to obtain added chips; and
a complex data generator for generating the plurality of chips of the complex 15 spreading sequence by converting the added chips to complex data.
13. The device of claim 12, wherein a complex function txp[j(rJ2(-))] is used in
converting the added chips to complex data.
14. The device of claim 8, further comprising a re-spreader for rcspreading the
spread and modulated mobile transmission data by an independent PN sequence.
-17-

15. The device of claim 14, wherein the independent PN sequence ts identical to
the PN sequence.
16. A device for reducing the peak-to-average power ratio of a mobile station's
transmit power in a mobile communication system, comprising:
(6) complex spreading sequence generating means/for generating a complex spreading
sequence having a plurality of chips and a phase difference of 90° between every two successive complex chips, jn. response to each chip of a PN sequence; and
spreading means Abr spreading and modulating mobile transmission data by the complex spreading sequence.
17. The device of claim 16, wherein the complex spreading sequence generating
means comprises:
(30) multiplying means(for multiplying the chips of the PN sequence by a predetermined
phase value to produce phase shifted chips:
it32-* complex data generating meansubr converting the phase shifted chips to complex data
using each of the phase shifted chips as a phase; and
pu) complex multiplying meansffor generating the plurality of chips of the complex
spreading sequence by multiplying the converted complex data by previously converted complex data.
18. The device of claim 17, wherein the predetermined phase value is within the
range of f n/2 and *3TT/2.
- 18-

19, The device of claim 16, wherein the complex spreading sequence generating means comprises:
adding means for adding every chip of the PN sequence with a respective pre-stored chip to obtain added chips; and complex data generating means for generating the plurality of chips of the complex spreading sequence by converting the added chips to complex data.
2G. The device of claim 16, further comprising re-spreading means for respreading &e spread and modulated mobile transmission data by an independent PN sequence.
A device and method are provided for reducing the peak-to average power ratio of a mobile station's transmit power in a mobile communication system by spreading and modulating the transmission data by a complex spreading sequence. The complex
spreading sequence is generated to have a plurality of chips and a phase difference of 90° between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence. The device and method flexibly control the mobile transmit power by limiting its peak-to-average power ratio to a specific range and thus confining the mobile transmit power to a linear characteristic curve of a power amplifier. The phase of the complex spreading sequence is prevented from shifting by 180° (i.e.. IT) to maintain the mobile transmit power in the linear portion of the power amplifier characteristic curve.

Documents:

00442-cal-1999-abstract.pdf

00442-cal-1999-claims.pdf

00442-cal-1999-correspondence.pdf

00442-cal-1999-description(complete).pdf

00442-cal-1999-drawings.pdf

00442-cal-1999-form-1.pdf

00442-cal-1999-form-18.pdf

00442-cal-1999-form-2.pdf

00442-cal-1999-form-3.pdf

00442-cal-1999-form-5.pdf

00442-cal-1999-g.p.a.pdf

00442-cal-1999-letters patent.pdf

00442-cal-1999-priority document others.pdf

00442-cal-1999-priority document.pdf

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Patent Number

203317

Indian Patent Application Number

442/CAL/1999

PG Journal Number

10/2007

Publication Date

09-Mar-2007

Grant Date

09-Mar-2007

Date of Filing

12-May-1999

Name of Patentee

SAMSUNG ELECTRONICS CO LTD

Applicant Address

416,MAETAN-DONG ,PALDAL-GU SUWON-CITY, KYUNGKI-DO,

Inventors:

#	Inventor's Name	Inventor's Address
1	JE WOO KIM	405-304 GRANDBIL,KUMI-DONG, PUNTANG-GU SONGNAM-SHI ,KYONGGI-DO
2	YOUNG JUN HWANG	476-166,TAPSHIMNI-DONG,TONGDAENMUN -GU, SEOUL
3	SOON YOUNG YOON	185 KAEPO-DONG ,KANGNAM -GU SEOUL
4	JAE HEUNG YEOM	680-7 IRWON-1-DONG ,KANGNAM-GU

PCT International Classification Number

H04B 7/005

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	17046/1999	1998-05-12	Republic of Korea