Turbo-coded CDMA-based two-way relaying

In this contribution, we have studied the performance of a Turbo-Coded (TC) Code Division Multiple Access (CDMA) based two-way relaying scheme. More explicitly, we employ a seven-user CDMA model, where two of the CDMA users are communicating with each other with the aid of an additional relay node, while the other flve CDMA users are interferers. More explicitly, two CDMA users exchange their information frames within two timeslots. Note that the conventional one-way relaying system can only transmit one information frame within two timeslots because the relay node is half-duplex, where it cannot listen and transmit simultane- ously. We found that our proposed TC-CDMA two-way relaying scheme is capable of attaining over 4dB of SNR gain at a Bit Error Rate (BER) of 10 i6 when compared to a conventional non-cooperative TC-CDMA system. We also found that there is about two dB of SNR loss at a BER of 10 i6 , due to the error propagation from the relay node. The proposed scheme exploits the beneflts of TC and CDMA schemes in order to assist the two-way relaying system to operate with a reduced transmit power. The reduction of the transmit power can also be exploited for increasing the coverage area of a cellular cell. Hence, the TC-CDMA two-way relaying scheme is a good candidate for future generation mobile systems. We proposed a Turbo-coded Code-Division Multiple Access (CDMA) based two-way relaying scheme for cooperative communications with the aid of a relay node. More speciflcally, Turbo Codes (TCs) (1) are power-e-cient channel coding schemes that can perform near channel capac- ity, while CDMA (2) is an attractive multiple access scheme that allows multiple users to access the same frequency band at the same time. Both TC and CDMA schemes have been adopted in the current 3G mobile standard. By contrast, cooperative communications (3{5) is a new paradigm where each mobile unit collaborates with one partner or a few partners for the sake of reliably transmitting its own information and of its partners jointly. More speciflcally, source nodes can transmit their signals to their destination nodes via relay nodes. Cooperative communications can increase the capacity, transmission reliability, energy e-ciency and coverage area of the overall system. Due to these advantages, cooperative communication schemes based on relaying have been considered in the recent LTE-Advance standard (6). In this contribution, we studied the performance of the TC-CDMA scheme under the two- way relaying system (7) based on the Decode-And-Forward (DAF) protocol. More explicitly, we employ a seven-user CDMA model, where two of the CDMA users are communicating with each other with the aid of an additional relay node, while the other flve CDMA users are interferers. In a conventional one-way relaying schemes (5,8), two timeslots are required for the transmission of one information frame from the source node to the destination node, via a half-duplex relay node. Four timeslots would be required for the transmission of two information frames according to the conventional one-way relaying technique. In our system, only two timeslots are required for two CDMA users to exchange two information frames. This is because in a CDMA system, each user is equipped with a unique spreading code for enabling an efiective multiuser detection at the destination node or relay node. Hence, time-orthogonality is not required to separate the two user signals. Our proposed TC-CDMA two-way relaying scheme is capable of attaining over 4dB of SNR gain at a Bit Error Rate (BER) of 10 i6 when compared to a conventional non-cooperative TC-CDMA system. We also found that there is about two dB of SNR loss at a BER of 10 i6 , due to the error propagation from the relay node. The proposed scheme exploits the beneflts of TC and CDMA schemes in order to assist the two-way relaying system to operate with a reduced transmit power. The reduction of the transmit power can also be exploited for increasing the coverage area of a cellular cell. The paper is organised as follows. The system model is described in Section 2 while the perfor- mance of the proposed scheme is evaluated in Section 3. Our conclusion is ofiered in Section 4.