Performance of Adaptive DFE and Antenna Modems for Wireless Personal Communications

| Decision feedback equalization (DFE) and antenna diversity combining are two practical techniques for combating multipath fading. In this paper, we investigate the performance of diversity combining together with DFE under various numbers of antenna branches and equalization taps in a wireless communication environment with AWGN and co-channel interference (CCI). Speciically, we present extensive results demonstrating the performance and computational complexity of diversity combining together with decision feedback equalization with nite taps in quasi-stationary frequency-selective fading channels with AWGN and CCI. Our results show that using antenna diversity and DFE with joint optimization combining provides performance improvement with lower computational complexity compared to that of using a DFE alone for combating the detrimental eeects of time delay spread. I. INTRODUCTION The next-generation wireless communications systems are expected to support a wide range of high-quality services which may include data, high-quality voice, still pictures and even motion images. These services are likely to include applications which require high transmission rates of several Mbps. Communicating at these high transmission rates over the harsh wireless environment encounters the problem of multipath inter-symbol interference (ISI) due to frequency-selective fading. To combat ISI, the classical technique of adaptive equalization is often suggested as a possible method 1]-4]. There are three broad classes of equalization-linear transversal equalizer (LTE), decision feedback equalizer (DFE) and maximum likelihood sequence estima-tor (MLSE). Among these classes, DFE is usually considered as a good compromise between complexity and performance. The European wireless local-area-network (LAN) system, HIPERLAN, is a typical example of a high speed wireless communication application with a bit rate over 20 Mbps, that adopts DFE to overcome the adverse eeect of multipath ISI 5], 6]. Diversity combining (or antenna arrays) can be also used as another countermeasure against multipath ISI 7]-9]. The combination of diversity reception and equalization can provide even greater reductions in ISI, and the ultimate performance of this has been investigated by Balaban and Salz 10]. Their results show signiicant performance improvement from diversity reception with optimum combining and innnite-tap DFE assuming no error propagation in the feedback loop. However, in practice, determining the least number of antenna branches and equalization taps to provide this