Optimal management in packet radio networks

Abstract

In a packet radio network (PRN), since all users share a single channel, unconstrained transmission may lead to the packet collision, resulting in damaged useless packets at the destination. Collided packets must be retransmitted, thus increasing the system delay and the bandwidth usage, which in turn lowers the system throughput. Therefore, there needs multiple access protocol to minimize or eliminate collisions. Multiple access protocols can be divided into two classes: dynamic protocols and static protocols. Dynamic protocols only reduce the number of collisions, but do not eliminate all of them. On the other hand, static protocols can avoid collisions perfectly through the prior broadcast scheduling, which is the most important factor of static protocols. In this thesis, we study on optimal broadcast scheduling in the following multiple access protocols: TDMA (time division multiple access), synchronous CDMA (code division multiple access), and asynchronous CDMA. We propose a centralized algorithm to find a collision-free broadcast schedule in a TDMA frame. In order to minimize the system delay, the optimal schedule must be defined as the one that has the minimum frame length and provides the maximum slot utilization. The proposed algorithm is based on the sequential vertex coloring algorithm. Numerical examples and comparisons with previous algorithm have shown that the proposed algorithm can find near-optimal solutions in respect of the system delay. CDMA protocol has the advantage that it can be operated in both synchronous and asynchronous manner. Synchronous CDMA is the combination of CDMA and TDMA. In synchronous CDMA, we are able to schedule transmissions in the time domain like TDMA. In synchronous CDMA PRN, we propose a collision-free broadcast scheduling algorithm, which works for general traffic distribution, independently of the particular network topology. Asynchronous CDMA PRN is the one that CSMA (carrier sense multiple access) and CDMA p...