WO2012037638A1

WO2012037638A1 - A tri-phase code generator in a cdma wireless communication system

Info

Publication number: WO2012037638A1
Application number: PCT/CA2010/001474
Authority: WO
Inventors: Saleh Omar Al-Jazzar
Original assignee: Jazzar, Samer Omar
Priority date: 2010-09-21
Filing date: 2010-09-21
Publication date: 2012-03-29
Also published as: GB2497219A; GB201301598D0

Abstract

A tri-phase code generator for use with a bi-phase code generator in a CDMA based wireless communication system, where the tri-phase code generator is configured for receiving from the bi-phase code generator a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,1 }, for automatically processing the bi-phase code sequence, and for generating, as a function of the processing, a tri-phase code sequence having a same size as the bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,0,1 } such that the generated tri-phase code sequence is absent of any direct transition between {-1 } and {1 } and between { 1 } and {-1 } and the plurality of tri-phase coding chips have a better orthogonality between each other than the plurality of bi-phase coding chips. There is further provided a method of generating a tri-phase code sequence using a bi-phase code sequence, a method of retrieving a bi-phase code sequence from a signal using a tri-phase code sequence, as well as a signal transmission method and a signal reception method in a CDMA based communication system.

Description

TITLE: A TRI-PHASE CODE GENERATOR IN A CDMA WIRELESS COMMUNICATION SYSTEM

FIELD OF THE INVENTION

[001] The present disclosure relates generally to the field of communication systems and more particularly to methods and systems for generating substantially orthogonal code sequences in asynchronous Code Division Multiple Access (CDMA) systems in order to reduce inter-symbol interference (ISI), multi-access interference (MAI) and power consumption.

BACKGROUND OF THE INVENTION

[002] The 3G mobile phones mainly use the code division multiple access (CDMA) technique to separate the different users' signals. In CDMA, each user has a distinguished code by which the user's message is modulated at the transmitter side. To retrieve back the signal at the receiver the received signal is demodulated using the same code signature used at the transmitter. Thus, the CDMA system performance is affected by the cross-correlation between the codes of different users. As the cross-correlation between the codes increases, the multiple access interference (MAI) will increase, causing degradation in the system performance. Also, a problem that faces the Original CDMA codes is that successive chips may transfer directly between the two parities {+1 } and {- 1 } and vice versa. Such transition increases the power consumption of the communication system and results in another type of interference called inter symbol interference which degrades the overall system performance by increasing the Bit Error Rate (BER).

[003] Noticeable examples of prior art documents are US Patent 6, 317, 422 Bl and US Patent 6, 618, 430 Bl . These prior art documents suggest methods and apparatus for receiving chip resistant codes by replacing some chips with zero values or inducing zeros between the original chips. However, when replacing some chips with zero values or inducing zeros between chips, there is no guarantee that ISI is minimized because zeros might not be placed between chips of opposite parities. Moreover, where zeros are induced between chips, the number of chips in the code is increased and the bit rate is reduced, which negatively affects the performance of the communication system.

SUMMARY OF THE INVENTION

[004] It is therefore an object of the present disclosure to provide methods and devices that overcome the above mentioned drawbacks.

[005] The main objectives of the present disclosure are to provide methods and devices (i.e. code generators) for generating tri-phase code sequences having values belonging to the group of numbers {-1,0,1 } using bi -phase code sequences having values belonging to the group of numbers {-1,1 } such as Walsh codes and Gold codes without increasing the size of the code sequence and thus the bit rate, in such a way that the new generated tri-phase code sequences are absent of any direct transition between {-1 } and { 1 } (and vice versa) and the generated tri-phase coding chips are more orthogonal between each other than the bi-phase coding chips. This allows for Multiple Access Interference (MAI), Inter-Symbol Interference (ISI) and power consumption reduction in CDMA based communication systems (wire and wireless communication systems), the all without increasing the size of the code sequence and thus the bit rate. The simulation results generated in accordance with the present disclosure illustrates reduction of MAI and ISI and a higher performance in terms of bit error rate than the 3G-CDMA and the 4G-OFDMA systems. The present disclosure can be implemented over the 3G systems, the all without increasing the size of the code sequence, thus preserving the bit rate. Another illustrated result is that the present disclosure allows for power consumption reduction in CDMA systems which would help to preserve battery lifetime in mobile devices for longer time periods.

[006] As illustrated in the preferred embodiment of the disclosure, each tri-phase coding chip can be generated by taking the average between two consecutive chips in the tradition bi-phase code sequence. Thus the generated tri-phase coding chips are more orthogonal between each other since some chips will comprise {0} value which causes the cross-correlation between the various chips to be reduced, thus allowing for MAI reduction. Also, the generated tri-phase code sequence is absent of any direct chip transition between the two parities {+1 } and {-1 } and vice versa (instead, the chips will go to {0} when transferring between the two parities). This absence of direct transition between extreme parities allow for ISI reduction when the tri-phase code sequence is used for user data spreading before transmission in a multi-path channel. This also allows for power consumption reduction in CDMA wireless mobile devices.

[007] The various aspects of the disclosure are described more in detail hereinafter.

[008] As a first aspect of the disclosure, there is provided a method of generating a tri- phase code sequence in a CDMA based communication system, the method comprising: receiving a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,1 } ; and processing the bi-phase code sequence for generating a tri-phase code sequence having a same size as the bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to the group of numbers {- 1,0,1 }, such that said generated tri-phase code sequence is absent of any direct transition 5 between {-1 } and { 1 } and between { 1 } and {-1 } and said plurality of tri-phase coding chips have a better orthogonality between each other than said plurality of bi-phase coding chips.

[009] The CDMA based communication system can be a wire or a wireless communication system.

10 [010] Preferably, the tri-phase code sequence' values are determined, through the processing, as a function of the bi-phase code sequence' values exclusively.

[011] The processing of the bi-phase code sequence for generating a tri-phase code sequence is preferably carried out automatically.

[012] Preferably, the tri-phase coding chips are generated by taking i c ^ak,n ^{+ a}k,(n+l) _{c 1 \} _ ^ak,N ^{+ a}k, l . _{x r} ,

15 i_{k n} - — - for « = 1 -> (N -I) and a_{k N} =— ^: — for n = N , where

N represents a number of coding chips, where c¾ _n e {— 1,1 } and represents a w * bi- th

phase coding chip of a Λ user in the bi-phase code sequence, and where a_{k n} E {—1 ,0,1 } and represents a « ^th tri-phase coding chip of the k ^th user in the tri- phase code sequence.

20 [013] The bi-phase code sequence can be any bi-phase code sequence having substantially orthogonal coding chips such as a Walsh code and a Gold code.

[014] As another aspect of the disclosure, there is provided a method of retrieving a biphase code sequence in a CDMA communication system, the method comprising: receiving a signal comprising a tri-phase code sequence generated using a bi-phase code

25 sequence in accordance with the method mentioned hereinabove; and processing the signal using the tri-phase code sequence for retrieving said bi-phase code sequence.

[015] As a further aspect of the disclosure, there is provided a signal transmission method for a CDMA based communication system, the method comprising: providing a tri-phase code sequence generated in accordance with the present disclosure; and using

30 the tri-phase code sequence for spreading user data before transmission.

[016] The transmission is more resistant to multi-access interference than an equivalent transmission using a bi-phase code sequence.

[017] Moreover, the transmission is more resistant to inter-symbol interference than an equivalent transmission using a bi-phase code sequence.

[018] Also, the transmission provides a better error rate ratio than an equivalent transmission using a bi-phase code sequence. Even when the transmission is not an OFDMA transmission, it provides for a better error rate ratio than an OFDMA transmission using a bi-phase code sequence.

[019] Besides, the transmission requires lower power consumption than an equivalent transmission using a bi-phase code sequence.

[020] As a further further aspect of the present disclosure, there is provided a signal reception method for a CDMA based communication system, the method comprising: receiving a signal comprising user data spread using a tri-phase code sequence and transmitted in accordance with the method mentioned hereinabove; and dispreading the signal using the tri-phase code sequence for retrieving the user data.

[021] As a another aspect of the disclosure, there is provided a tri-phase code generator for use with a bi-phase code generator in a CDMA based communication system, where the tri-phase code generator is configured for receiving from the bi-phase code generator a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,1 }, for automatically processing the bi-phase code sequence, and for generating, as a function of the processing, a tri-phase code sequence having a same size as the bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,0,1 }, such that said generated tri-phase code sequence is absent of any direct transition between {-1 } and { 1 } and between { 1 } and {- 1 } and said plurality of tri-phase coding chips have a better orthogonality between each other than said plurality of bi-phase coding chips.

[022] Preferably, the tri-phase code sequence' values are determined, through the processing, as a function of the bi-phase code sequence' values exclusively.

[023] Preferably, the tri-phase coding chips are generated by the generator by taking

~ _ ^Qk,n ^{+ a}k,{n+\) . . _{1 λ} , _Λ _ ^ak,N ^{+ a}k,l - _{x r} ,

<¾,« — ^for H = l -» (N -l) and a_{k N} =— — for n— N , where

2 2

N represents a number of coding chips, where a_{k n} e {-1,1 } and represents a w * bi- phase coding chip of a k ^th user in the bi-phase code sequence, and where a_{k n} e {-1,0,1 } and represents a n ^th tri-phase coding chip of the k ^th user in the tri- phase code sequence.

[024] The processing of the bi-phase code sequence and the generation of the tri-phase code sequence can be carried out using a pre-configured microprocessor running a mathemtical algorithme.

[025] The processing of the bi-phase code sequence and the generation of the tri-phase code sequence can also be carried out using an electronic-circuit including an arithmetic summer, an arithmetic divider and a time delay circuit.

[026] The bi-phase code generator can be any bi-phase code generator generating biphase code sequences having substantially orthogonal coding chips such as a Walsh code generator and a Gold code generator.

BRIEF DESCRIPTION OF THE DRAWINGS

[027] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[028] FIG. 1 depicts a tri-phase code generator for use with a bi-phase code generator in accordance with an example of an embodiment of the present disclosure;

[029] FIG. 2 depicts an Augmented CDMA communication system employing a tri- phase code sequence to modulate-demodulate the transmitted user signal in accordance with an example of an embodiment of the present disclosure;

[030] FIG. 3 depicts simulation results comparing the crosscorrelation magnitude of two users (1^st and 2^nd users) under different delay shifts by using, from one side, a CDMA transmission with a bi-phase code sequence (Original CDMA) and, from another side, a CDMA transmisstion using a tri-phase code sequence generated in accordance with an example of an embodiment of the present disclosure (Augmented CDMA);

[031] FIG. 4 depicts simulation results comparing the crosscorrelation magnitude of two users (1^st and 5^th users) under different delay shifts by using, from one side, a CDMA transmission with a bi-phase code sequence (Original CDMA) and, fron another side, a CDMA transmisstion using a tri-phase code sequence generated in accordance with an example of an embodiment of the present disclosure (Augmented CDMA);

[032] FIG. 5 depicts simulation results comparing the crosscorrelation magnitude of

th

two users (3rd and 4 users) under different delay shifts by using, from one side, a CDMA transmission with a bi-phase code sequence (Original CDMA) and, from another side, a CDMA transmisstion using a tri-phase code sequence generated in accordance with an example of an embodiment of the present disclosure (Augmented CDMA);

[033] FIG. 6 depicts simulation results comparing the Bit Error Rate (BER) as a function of Signal-to-Noise Ration (SNR) between an Original CDMA, an Augmented CDMA and an OFDMA wireless transmissions in accordance with an example of an embodiment of the present disclosure ;

[034] FIG. 7 is a chart flow illustrating a method of generating a tri-phase code sequence in a CDMA communication system in accordance with an example of an embodiment of the present disclosure;

[035] FIG. 8 is a chart flow illustrating a method of retrieving a bi-phase code sequence in a CDMA communication system in accordance with an example of an embodiment of the present disclosure;

[036] FIG. 9 is a chart flow illustrating a signal transmission method for a CDMA communication system in accordance with an example of an embodiment of the present disclosure; and

[037] FIG. 10 is a chart flow illustrating a signal reception method for a CDMA communication system in accordance with an example of an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[038] Introduction: Multiple access systems were developed to utilize the channel resources to provide services to different wireless communications' users. Code division multiple access (CDMA) is one type of multiple access techniques. In CDMA systems, different users are assigned different codes that can be orthogonal or at least have low crosscorrelation between each other. The crosscorrelation between the codes causes the multiple access interference (MAI). Thus, to minimize the MAI, the crosscorrelation between the codes must be minimized.

[039] Definitions: In the present disclosure, a new method of generating a code sequence for CDMA wireless communication systems is introduced. A code sequence generated in accordance with the present disclosure is called herein a "tri-phase code sequence" because chips thereof have three different values among {-1,0,1 }, whereas the traditional code sequence is called herein a "bi-phase code sequence" or a "traditional biphase code sequence" because chips thereof have only two different values among {- 1,1 }. Walsh codes and Gold codes are examples of such bi-phase code sequences. Original CDMA code(s) have the same meaning herein as bi-phase codes or bi-phase code sequence(s).

[040] A CDMA communication system that uses a tri-phase code sequence as generated in accordance with the present disclosure for spreading user data before transmission is called herein an "Augmented CDMA". A CDMA communication system that uses a biphase code sequence for spreading user data before transmission is called herein an "Original CDMA".

[041] Overall: The Augmented CDMA gives better overall performance than the Original CDMA codes (used in third generation wireless phones (3G)) and OFDMA (used in fourth generation wireless phones (4G)). As for the 3G comparison, the proposed method has better immunity to multiple access interference (MAI) than the Original CDMA system. This enhancement occurs because the Augmented CDMA system has less code crosscorrelation between the different users than the Original CDMA system. Also, the Augmented CDMA consumes less power than the Original CDMA system which makes batteries in wireless devices be charged for longer time. Another benefit for the Augmented CDMA is that the chips do not jump instantaneously between '+Γ and '-Γ and vice versa, i.e., it combats inter symbol interference (ISI). The fact that the Augmented CDMA has better immunity to MAI results in bit error rate (BER) advantage over the 4G OFDMA system for wireless phones. Computer simulations are presented to assess the suggested method performance compared to the Original CDMA and OFDMA systems.

[042] The Augmented CDMA codes are formulated by choosing the chip to be the average between two consecutive chips of the Original CDMA codes. This will cause the Augmented CDMA chip, a_{k n}, to have three values '+Γ, Ό' and '-Ι', instead of two values 0+Γ and '-1 ') in the Original CDMA chip, a_{k n} . The occurrence of zeros in the codes will reduce the crosscorrelation, the MAI and will reduce the power consumption. Also, taking the average between two consecutive chips will ensure that the new chips will not jump instantaneously between '+Γ and '-Γ, which will reduce the ISI. These new formulated codes are then used to modulate each user's signal in the wireless link. Thus, each user's signal is separated from each other by modulating each one of them by a separate Augmented CDMA code. In fig. 2, an example is shown for the wireless communication link for the & th user where the message at the transmitter side is modulated by the Augmented CDMA code before the transmission. Then, at the receiver, to retrieve back the message, the received signal is demodulated using the Augmented CDMA code _k .

[043] As will be shown in the simulation section, the Augmented CDMA has better performance when compared to the OFDMA system used in 4G wireless phones. This is true beacuse in the Augmented CDMA the crosscorrelation between the different users' signals is very low. Thus, different users are more orthogonal to each others which will give better performance than the 4G OFDMA system.

[044] Problem Formulation: An asynchronous multiuser CDMA system is assumed that employs BPSK modulation. The number of users assumed is K and each user's signal suffers L multipath reflections in the channel. The chip duration is T_c = TIN where T is the data bit duration and N is the number of chips per bit. The PN spreading waveforms are assumed to be of period NT_C and each chip has the waveform denoted by

P_T (t) . The transmitted baseband signal of the kth user over the m th bit interval (m c

takes on integer values), s_k (t) , is formed by modulating the m th data bit, d_{k m} , with the spreading code waveform, c_k ( ) , as

s_k{t) = A_kd_{k m}c_h{t - {m - \)T), (m - \)T≤t < mT (1)

where A_k is the amplitude for the k th user signal and c_k (t) is the transmitted spreading code sequence. The representation of c_k(t) is ¾« ⁼∑¾ _Γ (^ί -«τ ) (2)

Λ=0 °

where a_{k n} is the « th chip of the & th user spreading code and has the values k_n G {-1,1 } in the Original CDMA system and a_{k n} ε {-1,0,1} in the Augmented CDMA system, where the notation { ? } on any variable in this document is used for the Augmented CDMA variables and distinguish them from the Original CDMA variables.

The chip waveform signal is P_T (t) .

c

[045] Assuming each user transmitted signal suffers from L distinct multipath reflections while ropagating through the channel, the filtered received signal is

where d_k / is the delay for the / th path of the k th user.

[046] At the receiver, to retain the m th data bit of the k th user the signal of the signal is first passed through a matched filter, i.e., ^rk,rn = C_ ₎f{t)c_k{t)dt . (4)

[047] Thus, for the asynchronous case, and without any loss of generality, assuming that

.≤S ≤-≤S_K,_L . then, ,(rr -l)Pjk ⁺ⁿk,m (⁵)

where is the crosscorrelation factor between the codes c^t) and Cj(t) .

[048] Original CDMA: In the Original CDMA system, the chip a_{k n} of the spreading code c_k (t) has the values fl^ e {-l,l } . Many techniques where introduced in the literature to generate such codes such as: Gold-code generator, Walsh code generator, etc.

[049] The codes orthogonality plays an important role in the MAI effect. The performance of the system is enhanced (i.e., the MAI is decreased) by decreasing the crosscorrelation factors (i.e., increasing the orthogonality between the codes).

[050] Augmented CDMA: The need for increasing the orthogonality between the codes arises from the fact that high MAI will cause high bit error rate (BER). Thus, a new method for choosing the code sequence in CDMA is proposed which is called Augmented CDMA. According to the present disclosure, the code c_k (t) is first generated using any bi -phase generator that produce chips of a_{k n} e÷ {—l,l } like Goldsequence, Walsh, etc. Then, the Augmented CDMA codes, c_k(t) , are generated by ^ak,n ^{+ a}k,(n+\ ) taking the average between two consecutive chips. For instance a_k n

2 for n = l→(N - 1) . Since a_{k n} e {-l ,l } then a_{k n} e {-l ,0, l } -

[051] As for calculating the chip at the end of the code c_k t) , i.e, a_{k N} , the average ak,N ^{+ a}k, \

between a_{k N} and a_{k j} is taken, i.e., -¾,N—

2

[052] FIG. 1 shows a tri-phase generator 40 for use with a bi-phase generator 20 for generating a tri-phase code sequence in accordance with a preferred embodiment of the present disclosure. The tri-phase generator 40 can be implemented using software or hardware. In other terms, the tri-phase generator 40 can be implemented using a microprocessor running an appropriate algorithme for generating a tri-phase code sequence (not shown), or it can be implemented using an electronic circuit configured to carry out the functionnalities of an arithmetic adder 44, an arithmetic divider 46 and a time delay circuit 42. As mentionned hereinabove, the tri-phase code generator 40 is configured for receiving from the bi-phase code generator a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {- 1 , 1 } , for automatically processing the bi-phase code sequence, and for generating, as a function of the processing, a tri-phase code sequence having a same size as the bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to the group of numbers {- 1,0,1 }, such that the generated tri-phase code sequence is absent of any direct transition between {-1 } and { 1 } and between { 1 } and {-1 } and the plurality of tri-phase coding chips have a better orthogonality between each other than the plurality of bi-phase coding chips.

[053] Now, after showing how to generate the Augmented CDMA codes, the next subsection will proof mathematically the fact the Augmented CDMA codes are more orthogonal to each other than the Original CDMA codes.

[054] Proof of the higher orthogonality of Augmented CDMA than Original CDMA codes: Without any loss of generality, let us consider two users (two codes) with the number of chips in each code to be four, i.e., N = 4. Then, the codes for the first and second user (using the Original CDMA coding technique) are shown as follows:

Ci = [a_hla_l a_{l 3}a_{l 4}\ (6), and

c2 ⁼ [¾l^fl2,2¾3^a2,4 j · (7) [055] Now, the codes for the first and second user (using the Augmented CDMA coding technique) are calculated as follows:

«1,1 + «1,2 «1,2 + «1,3 «1,3 + «1,4 «1,4 + «1,1

, (8)

2 2 2 2

«2,1 + «2,2 «2,2 + «2,3 «2,3 + «2,4 «2,4 + «2,1

c • (9)

2 2 2 2

[056] Now, to show that the Augmented CDMA has less crosscorrelation between the codes than the Original CDMA, let us show the crosscorrelation between two Augmented

CDMA codes, i.e.,

Pi 2 ^{_ C}l ^C2 ^_

(«1,1 + <¾,2)0¾, l + ¾2 ) ₊ («1,2 + «1,3 ½ ⁺ <¾,3_)

4 4

+ («1,3 + <¾,4 )(¾3 + «2,4) («1,4 + «l,l )(«2,4 + «2,l )

• (10)

[057] Rearranging (10) as follows:

_A _ «1,1«2,1 + «1,1«2,2 + «1,2«2,1 + «1,2«2,2 + «1 ,2«2,2 + «1 ,2«2,3 + «1,3«2,2 + «1,3«2,3 Pi 2

4

«1 ,3«2,3 ⁺ «1 ,3«2,4 ⁺ «1 ,4«2,3 + «1 ,4«2,4 + «1 ,4«2,4 ⁺ «1 ,4«2, 1 ⁺ «1 , 1«2,4 ⁺ «1 , 1«2, 1

. (11)

«1,1«2,1 ⁺ «1,2«2,2 + «1,3«2,3 ⁺ «1,4«2,4

[058] Thus, ₁₂ =

«1,1«2,2 + «1,2«2,1 + «1,2«2,3 + «1,3«2,2 + «1,3«2,4 + «1,4«2,3 + «1,4«2,1 + «1,1«2,4

. (12)

[059] Rearranging (12) as follows:

- _ «1 , 1«2, 1 ⁺ «1 ,2«2,2 ⁺ «1 ,3«2,3 ⁺ «1 ,4«2,4

Pl2 -

[060] Let by = ^{Z 2,4} , b₂ = ^{, 1 ,} . Then, (14) becomes

«1, 1«2,1 + «1,2«2,2 + «1,3«2,3 + «1,4«2,4 + «1, A + «1,2¾ + «1,3¾ + «1,4¾

Pl2 .(14)

[061] Since a_{k n} e {—1,1 } , and from the definition of by and b₂ then it is probable that b_j and b₂ "vvill have zero value. Thus, there will be some terms in the crosscorrelation factor ₁₂ that have zero value which will make ₁₂ has less value than the crosscorrelation between the Original CDMA codes (i.e., ?₁₂ )·

[062] Augmented CDMA Implementation: The Augmented CDMA can be easily implemented using existenting CDMA technology. FIG. 2 shows an Augmented CDMA communication system 60 implemented in accordance with the present disclosure. First a user data bit stream 62 is received at the transmitter side of the Augmented CDMA system 60. The user data bit stream 62 is then phase modulated by a carrier using a phase modulator 64 located at the transmitter side. Once the user data stream 62 is phase modulated, it passes to a tri-phase code modulator 66 located at the transmitter side to be modulated by a tri-phase code sequence as generated in accordance with the present disclosure. The modulated user information is then amplified and broadcasted using a conventional antenna 68 (i.e. in case of a wireless communication). From the receiver side, the signal is received by a conventional antenna 70 before it passes to a tri-phase code demodulator 72 which demodulates the received signal using the tri-phase code generated in accordance with the present disclosure. The signal then passes to a conventional phase demodulator 74 located at the receiver side in order to be phase demodulate the signal and regenerate the user data bit stream 76.

[063] Simulation Results: The simulation results are presented to illustrate the performance of the Augmented CDMA system as compared to the Original CDMA used in 3G wireless systems and OFDMA used in 4G wireless systems. The code signature used is Gold-codes to model the CDMA code sequence with 31 chips length and generated using the polynomials x 5 + x 2 + 1 and x 5 + x 4 + x 3 + x 2 + 1 .

[064] Crosscorrelation comparison: In this subsection, a crosscorrelation performance comparison for the Augmented CDMA codes and the Original CDMA codes used in 3G wireless systems is represented. The crosscorrelation is represented under different delay shifts, i.e., the crosscorrelation between two codes for two different users is taken at a time and one of the codes is slided in the time domain and the crosscorrelation for each delay shift is calculated. The delay shift is taken by 1 T _c at a time.

[065] A five user case is assumed, i.e., five different codes. FIGS. 3, 4 AND 5 illustrate the crosscorrlations (P]2>Pn > (Ρ₁₅Ά₅) ^M& (PW P ) respectively. Clearly the crosscorrelation between the Augmented CDMA codes is lower than that of the Original CDMA codes used in 3G under different delay shifts.

[066] Another comparison parameter is to show the mean and the standard deviation of the magnitude of the crosscorrelation Ρ and β under different delay shifts. The magnitude mean is calculated by P_jk is the shifted

N

_ n=\ ^Cj ^Ck

version of with shift of n chips. Similarly, P_jk

N

[067] Three cases were studied and the results where as follows:

p_l2 = 3.4667 , ¾₂ = 2.4000

p_ls = 4.8667 , ¾₅ = 3.8667

p_M = 3.2000 , ¾₄ = 2.0667

[068] The results indicate that the crosscorrelation magnitude mean is lower for the Augmented CDMA than that of the Original CDMA. Which indicate that the Augmented CDMA has less crosscorrelation than the Original CDMA whether the different users' signals are synchronized with each other or not. This shows that the Augmented CDMA combats MAI more efficiently than the Original CDMA used in 3G.

[069] As for the standard deviation, the notation (7 and ά are given for the

Original CDMA and Augmented CDMA cases. The variable σ is given by and &_jk is given by

[070] Three cases were studied and the results where as follows:

σ₁₂ = 3.0932 , ₁₂ = 1.5888

σ₁₅ = 3.7484 , σ₁₅ = 2.5015

σ₃₄ = 3.2099 , σ₃₄ = 1.3629

[071] The results indicate that the crosscorrelation magnitude standard deviation is less for the Augmented CDMA than that of the Original CDMA. Which indicate that the Augmented CDMA has less crosscorrelation standard deviation than the Original CDMA whether the different users' signals are synchronized with each other or not. This shows that the Augmented CDMA is more robust to MAI than the Original CDMA used in 3G.

[072] Power and energy consumption: From the power point of view, since the Augmented CDMA codes have some zero elements then they have less energy than the Original CDMA codes. Which means that the Augmented CDMA codes will consume less power than the Original CDMA used in 3G wireless systems and will provide more battery life time. To illustrate this, Table I shows the codes' energy of five users for the

Original CDMA (which will be given the notation E_k = c_kc_k ) and that for the Augmented CDMA (which will be given the notation E_k— C^ C^ ).

[073] Table I shows the energy related to different codes for different users which clearly illustrates that the codes for the Augmented CDMA have less energy than those of the Original CDMA. Thus, the Augmented CDMA consumes less power than the Original CDMA used in 3G.

Table 1

[074] Inter symbol interference (ISI): The Augmented CDMA has another advantage over the Original CDMA used in 3G wireless systems because it is more robust against ISI which occurs when there is a jump between adjacent bits. Taking the first user for example and looking at the Original CDMA and Augmented CDMA codes as follows: cf = [- 1 - 1 - 1 - 1 1 1 - 1 1 1 - 1-] (15) £[ = [- 1 - 1 - 1010010 - 1· · ·] (16)

[075] It is clear that in the Original CDMA codes, adjacent chips jump directly from — 1 to +1 and vice versa. As for the Augmented CDMA the chips go to 0 before transferring from - 1 to + 1 and vice versa. Which indicates that the Augmented CDMA is more robust to ISI than the Original CDMA used in 3G.

[076] Bit error rate (BER): Since the codes of the Augmented CDMA have less energy than Original CDMA codes, i.e., E_k < E_k , then, to compare the bit error rate (BER) performance of both systems, the Augmented CDMA codes will be normalized to have the same energy as the Original CDMA system. In other words, the Augmented CDMA codes that will be used in this simulation subsection will be where formal *^{s me} normalized version of . A five user

case is assumed with each user having four multipaths.

[077] Table II shows the delays corresponding to the different multipaths of the different users. The performance of the Orignal CDMA, OFDM A and Augmented CDMA systems are assessed under different signal to noise ratios (SN )s and the results are shown in FIG. 6. The results indicate clearly that the Augmented CDMA gave better performance than both the Original CDMA used in 3G wireless systems and the OFDM A employing bi-phase codes used in 4G wireless systems.

Table II

[078] From the process side, FIG. 7 illustrates a chart flow illustrating a method of generating a tri-phase code sequence in a CDMA communication system in accordance with an example of an embodiment of the present disclosure. The method comprises the actions of: receiving a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {- 1,1 } 100; and processing the bi-phase code sequence for generating a tri-phase code sequence having a same size as the bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,0,1 }, such that said generated tri-phase code sequence is absent of any direct transition between {-1 } and {1 } and between {1 } and {-1 } and said plurality of tri-phase coding chips have a better orthogonality between each other than said plurality of biphase coding chips 102.

[079] FIG. 8 illustrates is a chart flow illustrating a method of retrieving a bi-phase code sequence in a CDMA communication system in accordance with an example of an embodiment of the present disclosure. The method comprises the actions of: providing a tri-phase code sequence generated in accordance with the present disclosure 104; and using the tri-phase code sequence for spreading user data before transmission 106.

[080] FIG. 9 illustrates a chart flow illustrating a signal transmission method for a CDMA communication system in accordance with an example of an embodiment of the present disclosure. The method comprises the actions of: providing a tri-phase code sequence generated in accordance with the present disclosure 108; and using the tri-phase code sequence for spreading user data before transmission 110.

[081] FIG. 10 illustrates a chart flow illustrating a signal reception method for a CDMA communication system in accordance with an example of an embodiment of the present disclosure. The method method comprises the actions of: receiving a signal comprising user data spread using a tri-phase code sequence and transmitted in accordance with the signal transmission method of the present disclosure 112; and dispreading the signal using the tri-phase code sequence for retrieving the user data 114.

[082] Conclusion: A novel code formulation for CDMA systems used in wireless communication links is introduced. The proposed code formulation (Augmented CDMA) is more efficient in combating MAI and ISI than the Original CDMA. Also, the Augmented CDMA consumes less power than the Original CDMA system. So, it has the advantage of conserving energy which is very useful in keeping batteries charged for longer periods of time in wireless communication devices. Also, the Augmented CDMA system provides for a better BER performance than the Original CDMA used in 3G wireless systems and the OFDMA used in 4G wireless communication systems. Thus, the Augmented CDMA system has better overall performance than the Orginal CDMA system and the OFDMA system.

[083] While illustrated in the block diagrams as groups of discrete components communicating with each other via distinct data signal connections, it will be understood by those skilled in the art that the preferred embodiments are provided by a combination of hardware and software components, with some components being implemented by a given function or operation of a hardware or software system, and many of the data paths illustrated being implemented by data communication within a computer application or operating system. The structure illustrated is thus provided for efficiency of teaching the present preferred embodiment.

[084] Although the above description contains many specificities, these should not be construed as limitations on the scope of the disclosure but is merely representative of the presently preferred embodiments of this disclosure. The embodiment(s) of the disclosure described above is(are) intended to be exemplary only. The scope of the disclosure is therefore intended to be limited solely by the scope of the appended claims.

Claims

1. A method of generating a tri-phase code sequence in a CDMA communication system, said method comprising: receiving a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,1 }; and processing said bi-phase code sequence for generating a tri-phase code sequence having a same size as said bi-phase code sequence and including a plurality of tri- phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,0,1 }, such that said generated tri-phase code sequence is absent of any direct transition between {-1 } and {1 } and between {1} and {-1 } and said plurality of tri-phase coding chips have a better orthogonality between each other than said plurality of bi-phase coding chips.

The method as claimed in claim 1, wherein said tri-phase code sequence' values are determined, through said processing, as a function of said bi-phase code sequence' values exclusively.

The method as claimed in anyone of claims 1 to 2, wherein said processing is carried out automatically.

The method as claimed in anyone of claims 1 to 3, wherein said tri-phase coding

ak,n + ^ak.

chips are generated by taking ⁼ — -— - for w = l -» (N-l) and a_{k N} =— ¹— — for n = N , where N represents a number of coding chips, where a_{k n}€ {-1 , 1 } and represents a n ^th bi-phase coding chip of a k ^th user in said bi-phase code sequence, and where a_{k n} e {-1,0,1 } and represents a n ^ih tri-phase coding chip of said k ^th user in said tri-phase code sequence.

5. The method as claimed in anyone of claims 1 to 4, wherein said bi-phase code sequence is selected from the group consisting of a Walsh code and a Gold code.

6. The method as claimed in anyone of claims 1 to 5 wherein said CDMA communication system is a wireless communication system.

7. A method of retrieving a bi-phase code sequence in a CDMA communication system, the method comprising: receiving a signal comprising a tri -phase code sequence generated using a biphase code sequence in accordance with the method of anyone of claims 1 to 6; and processing said signal using said tri-phase code sequence for retrieving said bi- phase code sequence.

8. A signal transmission method for a CDMA based communication system, the method comprising: providing a tri-phase code sequence generated in accordance with the method of anyone of claims 1 to 5; and using said tri-phase code sequence for spreading user data before transmission.

9. The method as claimed in claim 8, wherein said transmission is more resistant to multi-access interference than an equivalent transmission using a bi-phase code sequence.

10. The method as claimed in anyone of claims 8 to 9, wherein said transmission is more resistant to inter-symbol interference than an equivalent transmission using a bi-phase code sequence.

11. The method as claimed in anyone of claims 8 to 10, wherein said transmission provides for a better error rate ratio than an equivalent transmission using a bi- phase code sequence.

The method as claimed in anyone of claims 8 to 11, wherein said transmission is not an OFDMA transmission and wherein said transmission provides for a better error rate ratio than an OFDMA transmission using a bi-phase code sequence.

The method as claimed in anyone of claims 8 to 12, wherein said transmission requires lower power consumption than an equivalent transmission using a biphase code sequence.

The method as claimed in anyone of claims 8 to 13, wherein said CDMA communication system is a wireless communication system.

A signal reception method for a CDMA based communication system, the method comprising: receiving a signal comprising user data spread using a tri-phase code sequence and transmitted in accordance with any one of claims 8 to 14; and dispreading said signal using said tri-phase code sequence for retrieving said user data.

A tri-phase code generator for use with a bi-phase code generator in a CDMA based communication system, where said tri-phase code generator is configured for receiving from said bi-phase code generator a bi-phase code sequence including a plurality of bi-phase substantially orthogonal coding chips having values belonging to the group of numbers {-1,1 }, for automatically processing said bi-phase code sequence, and for generating, as a function of said processing, a tri-phase code sequence having a same size as said bi-phase code sequence and including a plurality of tri-phase substantially orthogonal coding chips having values belonging to said the of numbers {-1,0,1 } such that said generated tri- phase code sequence is absent of any direct transition between {-1 } and {1 } and between {1 } and {-1 } and said plurality of tri-phase coding chips have a better orthogonality between each other than said plurality of bi-phase coding chips.

The tri-phase code generator as claimed in claim 16, wherein said tri-phase code sequence' values are determined, through said processing, as a function of said bi-phase code sequence' values exclusively.

18. The tri-phase code generator as claimed in anyone of claims 16 to 17, wherein

• , . · , ,· , · - ^ak,n ^{+ a}k.

said tri-phase coding chips are generated by taking a^ _n = for n - \→(N -]) and a_{k N} =— - — for n = N , where N represents a number of coding chips, where a_{k n} ε {— 1,1 } and represents a w * bi-phase coding chip of a k^th user in said bi-phase code sequence, and where <¾ _n e {— 1,0,1 } and represents a n ^th tri-phase coding chip of said user in said tri-phase code sequence.

The tri-phase code generator as claimed in anyone of claims 16 to 18 wherein said processing of said bi-phase code sequence and said generation of said tri- phase code sequence are carried out using a pre-configured microprocessor running a mathematical algorithme.

The tri-phase code generator as claimed in anyone of claims 16 to 19, wherein said processing of said bi-phase code sequence and said generation of said tri- phase code sequence are carried out using an electronic-circuit including an arithmetic summer, an arithmetic divider and a time delay circuit.

The tri-phase code generator as claimed in anyone of claims 16 to 20, wherein said bi-phase code generator is selected from the group consisting of a Walsh code generator and a Gold code generator.

The tri-phase code generator as claimed in anyone of claims 16 to 21 wherein said CDMA communication system is a wireless communication system.