Complexity reduction of soft-decision mapper and soft-decision demapper for turbo equalization

The next generation of wireless broadband communication systems targets higher data rates, greater spectral efficiency and improved data integrity. Over the past several decades, significant developments have been made at improving the two fundamental issues of wireless broadband communication systems: bandwidth efficiency and quality of service. Limitations in channel bandwidth have spurred the development of digital modulation techniques such as Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) which aim to utilise the scarce radio spectrum as efficiently as possible. Another important development is turbo equalization, which concatenates a soft-input soft-output (SISO) detector with a soft channel decoder to perform joint, iterative data detection and channel decoding through the exchange of soft information. Turbo equalization has been shown to signi cantly improve the quality of wireless transmission in the presence of intersymbol interference. Higher order modulation techniques increase the number of bits, Q, mapped to a symbol, which is central to exploiting channel bandwidth more efficiently. Turbo equalization coupled with higher order modulation techniques are crucial to achieve the targets set for the next generation of wireless broadband communication systems. For higher order modulation techniques (Q > 1), the output of the SISO detector and the output of the SISO decoder are not directly applicable to each other. The exchange of soft information between these processes requires an appropriate conversion via a SISO mapper and SISO demapper. Increasing the order of modulation increases the computational complexity of both the soft decision mapper and soft decision demapper.