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Abstract-The use of constant-power, rate-adaptive M -QAM transmission with an amplify-and-forward cooperative system is proposed. The upper bound expressions are derived for the outage probability, achievable spectral efficiency, and error rate performance for the amplify-and-forward cooperative system over both independent and identically distributed (i.i.d.) and non-i.i.d. Rayleigh fading environments. The analysis is based on an accurate upper bound on the total effective signal-tonoise ratio SNR at the destination. Adaptive continuous rate M -QAM achieves a capacity that comes within a constant gap of the Shannon capacity of the channel, but adaptive discrete rate M -QAM suffers additional performance penalties.

This paper considers the signal design problems for quaternary digital communications with nonuniform sources. The designs are considered for both the average and equal energy constraints and for a two-dimensional signal space. A tight upper bound on the bit error probability (BEP) is employed as the design criterion. The optimal quarternary signal sets are presented and their BEP performance is compared with that of the standard QPSK and the signal set previously designed for nonuniform sources. Results shows that a considerable saving in the transmitted power can be achieved by the proposed signal sets for a highly nonuniform source.

Clipping and filtering (CF) is a simple but effective technique for peak-to-average ratio (PAR) reduction of orthogonal frequency division multiplexing (OFDM) signals. This paper determines the optimal clipping value for the CF method in order to maximize the power efficiency of the high power amplifier (HPA). A transmission spectral mask is placed on the output of the HPA as a design constraint in determining the optimal clipping value. The optimal clipping value is obtained for each specified bit error rate (BER) level. Results show that the optimal clipping value maximizes the efficiency of the HPA modelled as a travelling wave tube amplifier (TWTA), without causing a deterioration in BER performance.

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