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Optimized Space-Time Coding for Channel Estimation Errors Impaired Links

The main goal of emerging 4th generation WLANs is to provide broadband access to mobile users for real-time multimedia and Internet services with data rates up to 150 Mb/s at guaranteed Quality of Service (QoS) [5,12,15]. For meeting this goal, new wireless architectures are being developed for achieving both high spectral and power efficiencies. Tradeoff between these efficiencies may be substantially improved in faded applications by resorting to Multiple-Antenna systems that exploit both transmit and receiving diversity for increasing system capacity [1,14 and references therein]. Up to now, a large part of research on coded Multiple-Antenna systems has been carried out under assumption of perfect channel-estimate available at the receiver and in the last years several good codes and optimized receivers tailored for fully-coherent applications have been developed [2,4,5,9]. However, for high-performance WLANs it may be appealing to relax the assumption of this perfect channel estimate so to reduce length of training sequences and then increase spectral efficiency [25]. Towards this end, in [3] and in [8,10,11,27,28] unitary Space-Time Block-Codes (STBC) and Differential Space-Time Modulations (DSTMs) have been developed that do not require channel-estimates and rely on fully incoherent detection procedures. However, performance loss of about 3 dB is paid by these incoherent systems.