Low complexity methods for bandwidth efficient communication.

摘要

Bandwidth efficiency has become a critical design criterion in communication systems, as spectrum has become an increasingly scarce resource. In this thesis we study two approaches to bandwidth efficient communications designed for applications requiring low decoding complexity and/or latency.; In the first part of the thesis we study a generalization of block coded modulation (BCM), referred to as block coded modulation with interblock memory (BCMIM). BCMIM schemes offer a rate gain over standard BCM for a given block length and minimum Euclidean distance. We present a table of maximal rates for QAM-based BCMIM systems with relatively short block lengths. Upper and lower bounds are derived for the general case. We derive permutation optimal trellis decoders for a number of these codes offering a basis for comparison with other systems. Computer simulations are used to compare these schemes to other coded modulation schemes in terms of decoding complexity and coding gain.; In the second part of the thesis we consider the bandwidth constraint imposed on an intersymbol interference (ISI) free system by Nyquist's first criterion, which states that for ISI free communications the symbol rate must not exceed twice the channel bandwidth. Transmitting at a higher rate increases the bandwidth efficiency, but results in a performance degradation due to the ISI. We quantify this degradation for simple matched filter receivers and generalize our analysis methods to more complex receivers.