Incremental relaying effect on the outage probability of correlated sources Transmission Zina Chkirbene 1 and Noureddine Hamdi 2 Universit´ e de Tunis El Manar, Ecole Nationale d’Ingnieurs de Tunis LR-99-ES21 Laboratoire de Syst` emes de Communications, 1002, Tunis, Tunisie E-mails: 1 zina.chk@gmail.com, 2 noureddine.hamdi@ept.rnu.tn Abstract—In this paper we investigate different relaying strategies for correlated source transmission in block Rayleigh fading channels. Outage probability close form expressions are derived for both the cases where incremental decode and forward and only simple decode and forward techniques are used in the relays. We show that when using incremental technique in the principal relay, not only we gain in terms of channel resource saving but we get also a significant outage performance improvement compared to simple decode and forward system. Another finding of this paper is that if incremental relaying technique is used in the principal relay, the system reaches a diversity order of 2 with a significant power gain compared to a two links maximum ratio combining system. Index— Decode and forward, incremental system, Outage probaility, Slepian-Wolf. I. I NTRODUCTION Cooperative communication has been recently used as a powerful technique which can fundamentally change the ab- straction of a wireless link and offer significant potential advantages for wireless communication networks [1] [2]. In general, sources can be correlated and in order to exploit this correlation to reduce the communication requirements, a commonly used technique is Distributed Source Coding (DSC). This technique consists on compressing separately highly correlated sources and decoding them jointly. From a theoretical point of view, DSC is based on Slepian-Wolf and Wyner-Ziv compression schemes [3], [4]. The correlation between the two information sources is assumed to be expressed by the bit flipping model, where the information bits transmitted from the second transmitter are the flipped version of the information bits transmitted from the first one, with a probability . In [5], the authors studied the outage performance for a direct link system when two correlated sources are used based on slepian-wolf theorem. However, these studies have not been done for relaying systems. Thus, we propose in this paper a model including DSC in deocde and forward (DF) system by combining the data using both maximum ratio combining (MRC) and slepian-wolf technique. To reduce the effect of error propagation, we introduce also incremental relaying technique which shows its ability to enhance the diversity order of the system. In this paper, the main purpose is to derive the theoretical outage probability of correlated sources transmitting with the intermediate of relays using decode and forward or incremen- tal relaying technique. The effect of the correlation factor and of the choice of the threshold are also investigated. The paper is organized as follows. In section II, the system model is described. In section III, we proceed to the outage probability analysis of the system. Section IV validates the analysis by simulation results. Finally, section VI summarizes and concludes the paper. II. SYSTEM MODEL The adopted system model in this paper is described in Figure1 and consists of two correlated sources (1 and 2) transmitting their data (1 and 2) to one destination () by the intermediate of two relays 1 and 2. The communication is supposed to be done over chan- nels with a slow and frequency-flat Rayleigh fading coefficients . Where and denotes the dif- ferent system nodes. We assume that all the additive white Gaussian noise (AWGN) terms in the 6 links ( 1 1 1 1 2 2 2 2 ) have equal vari- ance 0 and all the channels coefficients are independent. All terminals are equipped with a single antenna. To understand the effect of path-loss on the performance of the proposed techniques, we use the model (which is com- monly used in the literature e.g., [2]), where ¡ | ()| 2 ¢ = ( 1 ) . Where stands for the distance between the nodes and , is the path-loss exponent and () denotes the statistical average operator. We denote by and the instantaneous received SNR from the link X-Y and its inverse respectively. For each source, the transmission is done in two time slots. Concerning 1, in the first time slot, it sends its signal to 1 and . Then, in the second time slot, two different models are used. For the first one, denoted by ”simple decode and forward” technique, the relay 1 directly forwards its data to . In the second model, denoted by ”incremental” technique, the relay waits for a feedback from the destination to decide if it is needed to forward the data based on the comparison of the received SNR for the link 1 to a threshold 0 . Then, if two signals are received, they are combined using MRC technique. The same operation is done for 2 using time multiplexing (4 total time slots) or frequency multiplexing (1 and 2 send on different frequencies). U.S. Government work not protected by U.S. copyright