Multi-phase optimal sequences for fast initialization of channel estimation and equalization

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