Performance Analysis of Energy-Efficient Adaptive Modulation

Raghavendra S. Prabhu
Advisor: Babak Daneshrad

Friday, May 21, 2010 at 12:00pm
Engr. IV Faraday Room 67-124

Abstract:
The focus of this dissertation is on the development and performance analysis of techniques that use perfect channel state information (CSI) at the transmitter to configure the system to operate in the most energy-efficient manner. In order to perform a mathematical optimization, we define and motivate a metric called energy-per-goodbit (EPG), which represents the total energy cost (in Joules) to convey one bit of information without error at the receiver. Although the methods developed are quite general and can be extended to several communication scenarios of interest, it is convenient to classify the work into two main categories: a) scalar channels b) parallel channels.

First we consider a single-carrier QAM system, where we find the QAM constellation size and transmit power that minimizes the EPG. Then we extend this to a scalar beamforming scheme called MIMO-MRC, where multiantenna beamforming is performed at both transmit and receive sides. We characterize the statistical distribution of the minimum EPG under a fading channel in order to evaluate the tradeoff between the number of antennas (circuit cost) and a worst-case EPG (outage EPG). Next we consider minimizing the EPG of an OFDM (parallel channels in frequency) system in a frequency-selective channel, by developing an energy-efficient water-filling (power allocation) algorithm. We show that the energy-efficiency formulation subsumes both the classical maximum rate (MR) and maximum margin (MM) problems as specific cases. Finally, we extend the parallel channel formulation to a MIMO-OFDM-SVD system where parallel channels are created in both frequency and space. Using a numerical example, we characterize the optimum (for a minimum outage EPG) number of antennas and also the average number of spatial streams that are utilized as a function of transmit cost and fading conditions. We also study the impact that frequency diversity has on MIMO-OFDM EPG performance. We conclude by suggesting some areas for further research.

Biography:
Raghavendra holds a BS and MS, both in Electrical Engineering (EE) and is working on a Ph.D in EE.