A Performance of Cooperative Relay Network Based on OFDM/TDM Using MMSE-FDE in a Wireless Channel

Cooperative networking schemes provide spatial diversity gain (named cooperative diversity gain) using the antennas of spatially distributed users to form a multi an- tenna transmit situation. A variety of algorithms for orthogonal frequency division multiplexing (OFDM) networks have been developed to achieve cooperative diversity gain. OFDM signals, however, have a problem with a high peak-to-average power ratio (PAPR) leading to lower power efficiency, which may significantly increase the user power consumption. In this paper, instead of conventional OFDM, we present the performance of coop- erative network based on OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) in a frequency- selective fading channel. To fully exploit the channel frequency- selectivity and achieve a larger frequency diversity gain the equalization weights required for OFDM/TDM signaling based on MMSE criteria are derived. multiplexing (12) (in this paper called OFDM/TDM) can be used to solve the PAPR problem to some extent (13). In OFDM/TDM design, the inverse fast Fourier transform (IFFT) time window (i.e., OFDM/TDM frame) of conventional OFDM is divided into K slots. Within each slot an OFDM signal with reduced number of subcarriers is transmitted with- out the guard interval (GI) insertion. Unlike the conventional OFDM, only one GI is inserted in each frame and frequency domain equalization is used to exploit the channel frequency- selectivity. In this paper, we present the performance of cooperative relay network based on OFDM/TDM using minimum mean square error frequency domain equalization (MMSE-FDE) (13) in a frequency-selective fading channel. To fully ex- ploit the channel frequency-selectivity and achieve a larger frequency diversity gain the equalization weights required for OFDM/TDM signaling based on MMSE criteria are de- rived. Unlike cooperative relay network based on conventional OFDM, the use of OFDM/TDM achieves a better quality of service (i.e., a lower bit error rate (BER)) with a higher transmit power efficiency. The remainder of this paper is organized as follows. Sec- tion II presents the system model. We derive the required equalization weights for OFDM/TDM to achieve improved performance in Sect. III. In Sect. IV, computer simulation results and discussions are presented. Section V concludes the paper.