Abstract
Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.
Highlights
A new form of spatial diversity called “cooperative diversity” has attracted much research interest because it provides effective diversity benefits for those devices that cannot be equipped with multiple antennas due to their size, complexity, and cost
Using the asymptotical upper bound (AUB) of the SER, we present the criterion for the parameter choice in the pilot symbol assisted modulation (PSAM) scheme and show that two parameters used in this scheme, i.e., pilot spacing and Wiener filter length, can be chosen in a tradeoff between system performance, pilot overhead, and receiver complexity
While a smaller pilot spacing L leads to a better channel estimation, the overhead imposed by the pilot symbols reduces the effective SNR and transmission efficiency
Summary
A new form of spatial diversity called “cooperative diversity” has attracted much research interest because it provides effective diversity benefits for those devices that cannot be equipped with multiple antennas due to their size, complexity, and cost. Problem of parameter optimization and optimum power allocation for variable gain AF cooperative communication systems with a PSAM scheme. The difficulty in optimizing the system design lies in the fact that the accurate SER expression is given in form of a double integral [14]. This prevents us from minimizing the SER directly. We derive a tight expression for the AUB of the SER for the AF cooperative communication system with a PSAM scheme. With the derived tight AUB, an optimum power allocation problem is formulated for the AF cooperative communication system. The symbol E[⋅] denotes the expectation operator, | z | represents the absolute value of a complex number z , and the complex Gaussian distribution with mean m and covariance P is denoted by C N (m, P)
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