A performance criterion for any coded modulation schemes is the cutoff rate. This is examined for schemes employing generalized selection combining (GSC). The cutoff rate expression is derived and presented for the GSC. A simplified performance analysis of coherent M-ary phase shift keying (nPSK) for GSC is also given for independently and identically distributed Rayleigh fading. These expressions are valid for any arbitrary number of diversity branches, M and combining order, m.

The demand for high speed wireless systems dictates the use of bandwidth efficient modulation schemes. Trellis coded I-Q 16-QAM is shown here to be suitable for such applications. The performance of this scheme with decision feedback equalization is evaluated over a two-ray Rayleigh channel. Comparisons between the I-Q scheme with a conventional TCM scheme based on 8-PSK show coding gains of about 4 dB at a BER of 10/sup -3/.

This paper presents the design of space-time codes suitable for rapid fading channels. The codes are designed using the QPSK signal constellation. The design of the proposed codes utilizes two different encoding methods. The first method uses a large time diversity trellis encoder, and the second one uses the I-Q encoding technique. Both methods are expected to produce space-time codes that perform better than the codes presented in the literature. The proposed codes were simulated over different Rayleigh fading channels. Coding gains up to 3 dB have been observed over similar codes in the literature.

This paper presents the performance of space-time (ST) codes over rapid fading channels. A tight upper bound on the pairwise error probability (PWEP) of ST codes over rapid fading channels is derived. Also, an upper bound on the bit error probability (BEP) is evaluated using the derived PWEP. The existing and new bounds are evaluated for different QPSK ST codes and compared to the simulation results. The new bound is shown to be tighter than the existing bound by almost 2 dBs and is very tight to the simulation results.

The transfer function technique has been used to give an upper bound on the bit error probability of turbo codes in the high signal-to-noise ratio (SNR) regions. Existing bounds use numerical integration to get the exact value of the pairwise error probability over the ideal flat Rayleigh channel. A new expression for the pairwise error probability over the ideal flat Rayleigh channel is derived in this paper. Using this expression, numerical integration can be avoided and this substantially reduces the computation time. This was obtained without compromising on the accuracy of the results. Examples for the (1,5/7,5/7) and (1,7/5,7/5) codes are given.

A general expression for the channel throughput of slotted ALOHA under Nakagami fading is obtained assuming different fading statistics and unequal average power levels for the desired and the interfering packets. The expression provides a better alternative to the previously reported expressions derived under similar conditions. With this general expression the effect of the use of modulation on the system performance is then studied. It is observed that the inclusion of the deleterious effects like white noise, bit error rate and the packet length reduces the throughput over the one observed under idealized conditions.

An unequal error protection approach for the reliable communication of visual information over additive white Gaussian noise channels is proposed and studied. This method relies on a bandwidth-efficient coded modulation scheme that employs selective channel coding and transmission energy allocation in conjunction with sequence maximum a posteriori soft-decision detection. Experimental results indicate that this scheme exhibits graceful performance degradation as the channel conditions deteriorate and provides substantial objective and subjective improvements over uncoded and equal-error protection systems. Coding gains of up to 4 dB in E/sub b//N/sub o/ are achieved.

This paper presents some trellis codes that provide high coding gain to channels with slow, non frequency-selective Rayleigh fading. It is shown that the use of two encoders in parallel-used to specify the in-phase and quadrature components of the transmitted signal-results in greater minimum time diversity than the conventional design in which a single encoder is used. Using this approach-which we label "I-Q TCM"-codes with bandwidth efficiencies of 1, 2, and 3 bits/s/Hz are described for various constraint lengths. The performance of these codes is bounded analytically and approximated via simulation; the results show a large improvement in the bit error rate (BER) when compared with conventional trellis-coded modulation (TCM) schemes when perfect channel state information (CSI) is available to the receiver. Indeed, when this approach is applied to channels with independent Rayleigh fading, the resulting coding gain is close to that implied by the cutoff rate limit, even for only moderately complex systems. The proposed codes are also simulated under less ideal assumptions. For instance, results for a 1-bit/s/Hz IQ-TCM code without CSI show a significant gain over conventional coding. Finally, simulations over channels with correlated fading were undertaken; it is concluded that an interleaver span of 4/spl nu/ yields performance close to what is achieved with ideal interleaving.