Tham khảo tài liệu 'recent advances in signal processing 2011 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | On the role of receiving beamforming in transmitter cooperative communications 407 scenario in the previous section. Although only the case with one interfering cluster is modelled the extension to several clusters is straightforward and will reinforce the Gaussian hypothesis for the interference that we will claim. The received signal i1 at sensor 1 our reference in the original cluster coming from the interfering one is - lap. . m H F X . 36 11 yj aPMMO m 1 F intx int Where m1 is the flat fading channel from interfering cluster to the reference sensor Fint also assumed power normalized is the precoding performed at that cluster and xint is the transmitted sequence. yfa e 0 1 means the extra loss compared to the desired link to represent the fact that the interfering cluster may be further away according to Figure 1 a 1 . The mean interference power clearly becomes Pint - PMIMOaaa1 FintFint m 1 - PMIMOa 37 Central Limit Theorem confirms the Gaussian hypothesis as a linear combination of . random variables. So the equivalent effect of interference makes effective noise to be increased from ơ eff - ơ PMMOa 38 Clearly the SNR becomes negative if we consider the circular distributions of sensors in figure 4 and in any case the throughput degrades very significantly. Fig. 6 shows this performance degradation compared to the no interference case in a 4x4 system 4 transmit sensors 4 receive sensors . Recalling that the interference is modelled as an additional AWGN contribution the sum rate of the system is depicted for different Gains G already described and for different values of the noise variance Ơeff2. Fig. 6. Performance degradation due to interference This previous result states that independently of the cooperation strategy wireless ad hoc networks need some kind of coordination between neighbouring clusters in terms of multiple access strategy to avoid this large performance degradation. 408 Recent Advances in Signal Processing In order to provide a .
