The next-generation wireless communication systems are expected to support high-speed data transmission. Associated with high transmission rates, however, is the problem of multipath intersymbol interference (ISI) due to frequency-selective fading. Decision feedback equalization (DFE) and antenna diversity combining are two practical techniques for combating multipath ISI. Through simulations we investigate the performance of diversity combining, together with DFE, under various numbers of antenna branches and equalization taps, in a quasistationary frequency-selective fading environment with additive white Gaussian noise (AWGN) and cochannel interference (CCI). We consider joint optimization combining and power selection diversity combining. We simulate the combiner, using quaternary phase shift keying (QPSK) modulation with up to four antenna branches. Our results show that using antenna diversity and DFE with joint optimization combining provides performance improvement with lower computational complexity, as compared to that of using either DFE or diversity combining alone for combating ISI.

Optimal sounding sequences which satisfy a certain autocorrelation property are useful for fast channel estimation techniques which are based on noniterative channel sounding methods. We study optimal sequences consisting of complex symbols with constant magnitude. An indirect sequence construction method is derived by considering the phase difference between sequence symbols. Our construction method includes periodic and nonperiodic optimal sequences, and provides insight into the nature and properties of optimal sequences that are based on consecutive roots-of-unity phase difference sequences.

Adaptive equalization is a technique commonly used for correcting the multipath intersymbol interference (ISI) caused by frequency selective fading. For most equalization schemes, channel estimation is required. However, fast start-up channel estimation is needed to ensure quick equalizer convergence. As result, there has been much interest in finding fast channel estimation techniques which are based on non-iterative channel sounding methods. To obtain the best estimation performance, certain optimal sequences are required. Generally, it is difficult to construct optimal sequences with binary symbols because the optimal sequence length grows very rapidly as the channel impulse response length increases. In this paper, we propose a sequence construction method for sounding sequences consisting of complex symbols with constant amplitude and multiple phases. The advantage of using complex symbols is that an optimal sequence can always be constructed with a minimum sequence length. Our construction method generates new complex optimal sequences which are aperiodic in addition to the periodic sequences previously known.