Turbo codes: principles and applications
Turbo codes: principles and applications
Frequency domain equalization for single-carrier broadband wireless systems
IEEE Communications Magazine
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This paper deals with Cyclic Prefix (CP)-assisted block transmission solutions for future mobile broadband systems, in the context of a Single Carrier (SC)-Frequency Division Multiple Access (FDMA) uplink. Two alternative choices are considered regarding the subcarrier mapping rule: a "localized" subcarrier mapping where user's data occupy a set of consecutive subcarriers (Rule R1); a "distributed" subcarrier mapping where user's data occupy a set of uniformly spaced subcarriers (Rule R2). Detailed performance evaluations, in this paper, involve the consideration of two iterative FDE receiver techniques, with different complexity levels, which can be regarded as extensions of iterative receiver techniques proposed previously within a single user context. A selected class of multipath radio channels, providing a range of channel time dispersion levels, is assumed for performance evaluation purposes, and a set of matched filter bounds on receiver performance plays a relevant role in "achievable performance" comparisons. Both the impact of the mapping rules and that of the iterative receiver techniques considered here are evaluated in detail. This paper also studies the performance degradation due to a channel impulse response longer than the CP: such degradation is related to an "ICI (Inter-Channel Interference) effect" (possibly involving a multi-user interference component) which is inherent to the insufficient-CP conditions. The performance advantages under rule R2 are emphasized for a low or moderate channel time dispersion, and both specific iterative receiver techniques; for a higher time dispersion, receiver performances become very similar with both rules, at the BER values of practical interest (say, BER=10-5). Having in mind that rule R2 has a power efficiency advantage regarding transmitter implementation (due to the reduced envelope fluctuations), we can conclude that this rule provides a clear overall power efficiency advantage, regarding both transmitter and receiver issues, for the entire range of channel time dispersion levels.