Energy minimization of a QAM system with fading

• Published in: IEEE transactions on wireless communications 2008-12, Vol.7 (12), p.4837-4842
• Main Authors: Prabhu, R., Daneshrad, B.
• Format: Article
• Language: English
• Subjects: adaptive; Algorithms; Applied sciences; automatic repeat request; Channel state information; Channels; Communication channels; Computational modeling; Computer simulation; Constellations; Costs; Detection, estimation, filtering, equalization, prediction; Distributed computing; Energy efficiency; Energy minimization; Ergodic processes; Exact sciences and technology; Fading; fading channels; Frequency; Information, signal and communications theory; modulation; Modulation, demodulation; Noise levels; quadrature amplitude; Quadrature amplitude modulation; Radiocommunications; Rayleigh channels; Signal and communications theory; Signal, noise; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Transmitters; Transmitters. Receivers; Wireless communication
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/T-WC.2008.071120

In this paper, the problem of choosing constellation size and transmit power that minimizes the energy-per-goodbit in a frequency-flat, long-term static fading channel is considered. A goodbit is a bit that is received without error. A low-complexity, near-optimal algorithm to find constellation size and transmit power is presented. Although perfect channel state information (CSI) at the transmitter is assumed, fading can cause situations where the system cannot meet user constraints on acceptable performance. The implications of this type of system outage and the consequent trade-off between energy-efficiency and range are discussed. Assuming that the fading process is ergodic, the average energy-efficient spectral efficiency can be computed for various fading distributions of interest. As an application of the techniques developed, we evaluate, by simulation, the average minimum energy-per-goodbit for a Rayleigh fading channel and note that over a short range of distances (1 m to 10 m), it can cost at most 1 dB more than for the corresponding non-fading AWGN channel. We also show that the restriction of using only a square-QAM constellation does not incur a large penalty in cost.