Title :
Performance of Optimum Switching Adaptive
-QAM for Amplify-and-Forward Relays
Author :
Nechiporenko, Tyler ; Kalansuriya, Prasanna ; Tellambura, Chintha
Author_Institution :
Dept. of Electr. & Comput. Eng., Univ. of Alberta, Edmonton, AB
fDate :
6/1/2009 12:00:00 AM
Abstract :
Optimization of the switching thresholds for constant-power adaptive five-mode M-ary quadrature amplitude modulation (M -QAM) transmission with an amplify-and-forward (AF) relay network is developed. The optimization criterion is the maximization of spectral efficiency subject to an average bit-error-rate (BER) constraint. This approach results in a constant-BER variable-rate M-QAM AF relay system, which requires feedback of log2(N) bits for N modes. The performance analysis is based on an upper bound on the total effective SNR. Expressions are derived for the outage probability, the achievable spectral efficiency, and the error-rate performance for the AF cooperative system over both independent identically distributed (i.i.d.) and non-i.i.d. Rayleigh fading environments. The tightness of the upper bound is validated by Monte Carlo simulation. Adaptive five-mode M-QAM with optimum switching levels is shown to offer performance gains of 2-2.5 dB compared with fixed switching in terms of the transmit SNR to achieve specific spectral efficiency. Furthermore, the spectral efficiency of adaptive five-mode M-QAM with optimized switching comes within ~6 dB of the theoretical Shannon channel capacity. However, this performance gain, which is obtained by employing adaptive M -QAM under cooperative diversity, comes at the cost of increased system complexity that is incurred due to the additional complexity of transmitter and receiver design.
Keywords :
Monte Carlo methods; Rayleigh channels; channel capacity; error statistics; optimisation; quadrature amplitude modulation; spectral analysis; AF cooperative system; BER; Monte Carlo simulation; Rayleigh fading environments; Shannon channel capacity; amplify-and-forward relay; bit-error-rate; optimization criterion; optimum switching adaptive M -QAM transmission; quadrature amplitude modulation; spectral efficiency maximization; Adaptive transmission; Rayleigh fading; amplify and forward (AF);
Journal_Title :
Vehicular Technology, IEEE Transactions on
DOI :
10.1109/TVT.2008.2010217