The Block Error Rate in Block Interference Channels and its Applications to Medium Access Control

Doktorsavhandling, 2010

This thesis may be distinguished into two interdependent parts. The first part outlines the outcome of our efforts to construct accurate and yet simple models that account for the probability of successful reception of a packet for a wide range of physical layer parameters. The probability of successful reception of a packet in many applications can be accurately approximated by the probability of successfully receiving the payload, which in turn is a simple function of the block error rate (BLER). The presented studies are limited to block interference fading channels for which there exists few analytical solutions to the BLER. Therefore when needed, various numerical solutions are employed to obtain an approximation of the BLER. A large part of this thesis is devoted to a detailed study of one of these numerical methods, known as the threshold method. We study the applicability of this method to Nakagami-$m$ block fading channels and to Rayleigh block interference channels. We also investigate the effect of physical layer and channel parameters on the accuracy of this approximation method and the value of the threshold. As a result, a low complexity method of approximating the BLER in Nakagami-$m$ block fading channels is developed which is shown to be accurate for a wide range of different physical layer parameters and the practical values of $m$. The second part of the thesis is devoted to applications of above models towards the study of various issues at the medium access control (MAC) layer. For instance, we formulate the scheduling problem in TDMA based clustered ad hoc networks as an optimization problem for which the cost function is obtained from the BLER models. The optimum schedule for maximizing the network throughput was obtained using the Lagrangian relaxation method. In addition, a simpler sub-optimum version of this algorithm with adaptable complexity is proposed. The developed BLER model is also utilized to obtain both an accurate solution and a less-complex estimate of the link throughput in slotted Aloha networks. The main advantage of these methods is that the detailed state of all nodes in the network is taken into account. Therefore, the obtained results are applicable to arbitrary topologies and traffic models.