Iterative decoding and demodulation of bit-interleaved coded modulation (BICM) is investigated. The union bound on the error probability of BICM with maximum-likelihood (ML) decoding is derived with the assumption of a uniform interleaver. Based on the union bound, it is shown that an interleaving gain is achievable for BICM at high signal-to-noise ratio (SNR). The design rules on the symbol mapper for optimal asymptotic performance at high SNR are derived and a new symbol mapper, called the maximum squared Euclidean weight (MSEW) symbol mapper, is proposed with examples given for 8-PSK and 16-QAM. The MSEW mapper is shown by means of an extrinsic information transfer (EXIT) chart to provide the best error-floor performance for BICM at high SNR. At low SNR, a mapper doping technique is proposed that combines the MSEW mapper with Gray mapper to provide a good match to a given outer code. Simulation results are also presented to confirm our analysis.

A special complex sequence called a complex quadratic sequence is proposed as the frequency-spreading sequence for the multicarrier spread-spectrum (MC-SS) modulation scheme. The resulting MC-SS signal has constant envelope in both time and frequency domains. This feature provides flexibility for the MC-SS system to mitigate the effects of both partial-band and pulse jamming. For partial-band jamming, the MC-SS system with frequency domain detection and combining can outperform direct sequence spread spectrum. For pulse jamming, the MC-SS system with time-domain detection and combining can outperform other MC-SS systems. The proposed MC-SS signal has a constant envelope, thus, reducing linearity requirements on the power amplifier. A simple jammer state estimation scheme for both partial-band and pulse-jamming channels is also proposed. Furthermore, multiaccess with the MC-SS system is possible by assigning users different cyclic-shifts of the complex quadratic sequence.

Frequency-domain equalization for continuous phase modulation (CPM) is investigated. A discrete representation of the CPM signal is obtained by using the Gram-Schmidt orthonormalization procedure. The CPM discrete signal representation admits frequency-domain equalization for the purpose of mitigating intersymbol interference. General full- and partial-response CPM waveforms, and specific examples of MSK and GMSK with BT=0.3 are considered. Frequency-domain equalization is shown to be effective for CPM on severe frequency-selective fading channels.

Multicarrier delay diversity modulation (MDDM) is a scheme that uses orthogonal frequency division multiplexing (OFDM) on a "multipath" channel that is generated by using delay diversity. The full diversity criterion for MDDM is proven and illustrative examples of full-diversity codes are obtained based on the established criterion. Coding gains and interleaver designs are also considered and analyzed. Simulation results for MDDM on quasi-static flat and frequency-selective fading channels are discussed. MDDM is established as a strong competitive technique to existing space-time block codes and space-time tellis codes techniques for multiple input multiple output systems.

Multicarrier delay diversity modulation (MDDM) is a scheme that uses orthogonal frequency division multiplexing (OFDM) on a "multipath" channel that is generated by using delay diversity. The full diversity criterion for MDDM is proven and illustrative examples of full-diversity codes are obtained based on the established criterion. Coding gains and interleaver designs are also considered and analyzed. Simulation results for MDDM on quasistatic flat and frequency-selective fading channels are discussed. MDDM is established as a strong competitive technique to existing STBC and STTC techniques for MIMO systems.

A special complex sequence, called a complex quadratic sequence, is proposed as the frequency-spreading sequence for multicarrier spread spectrum (MC-SS) modulation scheme. The resulting MC-SS signal has constant envelope in both time and frequency domains. This feature provides flexibility for the MC-SS system to mitigate the effects of both partial-bond jamming and pulse jamming. For partial-band jamming, the MC-SS system with frequency domain detection and combining can outperform DS/SS. for pulse jamming, the MC-SS system with time-domain detection and combining can outperform MC-SS systems. The proposed MC-SS signal has a constant envelope thus reducing linearity requirements on the power amplifier. A simple jammer state estimation scheme for both partial-band and pulse jamming channel is also proposed and analyzed. Furthermore multi-access with the MC-SS system is possible by assigning users with different cyclic-shifts of the complex quadratic sequence. Simulation results are provided to verify our analysis.

A new maximum a posteriori (MAP)-equivalent soft-input soft-output (SISO) algorithm is derived together with its simplified versions. The proposed SISO algorithms provide a good compromise between complexity and performance. Our simplest SISO algorithm has lower complexity than the log-MAP, the max-log-MAP, and the soft-output Viterbi (1998) algorithm SISO algorithms, and it is an equivalent max-log-MAP algorithm. When this algorithm is used, turbo codes with block length as short as 150 bits will outperform convolutional codes when compared on the basis of equal decoder complexity.

Iterative decoding of bit-interleaved coded modulation (BICM) is analyzed. The interleaver of a BICM system is shown to provide not only time diversity gain as a channel interleaver, but also interleaving gain as a code interleaver. Our performance analysis of BICM assumes a uniform interleaver, and it is shown that the interleaving gain can be achieved at high SNR. The design rules on the symbol mapper are derived and a new symbol mapper design, called the maximum squared Euclidean weight (MSEW) symbol mapper, is presented for both 8-PSK and 16-QAM. Extensions to other signal constellations is straight forward. Simulation results confirm our analysis and show that BICM with MSEW symbol mapping achieves near Shannon limit performance.

An analytical model for the extrinsic information of iterative max-log-MAP decoding of turbo codes is established based on a maximum probability approximation. The extrinsic information can be expressed as a Gaussian random variable with a mean and variance that are linear combinations of the received symbols. An important measure, called the effective weight, which is related to the pairwise error probability, is defined to explain the iterative decoding effect on a given code sequence. The evaluation of the pairwise error probability performance through decoder iterations can be calculated based on this model. The proposed approach can serve as a tool for the analysis of iterative max-log-MAP decoding.

An optimal MAP equivalent SOVA decoding algorithm and its simplified suboptimal algorithm for non-binary codes are proposed. The implementation of its suboptimal algorithm is simpler, while its performance is very close to the optimal log-MAP algorithm. The proposed SOVA can be used as a decoder for turbo trellis coded modulation (TTCM). Simulation results for both the proposed SOVA and the log-MAP algorithms for TTCM and binary turbo codes are presented. It is concluded that the proposed SOVA performs very close to the log-MAP algorithm for both the TTCM and binary turbo codes, and its performance is better than the conventional SOVA.