Performance analysis of distributed time division multiple access protocols in mobile ad hoc environments

Tactical wireless mobile ad hoc networks rely upon distributed medium access control (MAC) protocols for coordination and assignment of channel resources among dispersed and mobile users. One such protocol is the distributed time division multiple access (TDMA) scheme where different users contend for time slots via a signaling mechanism. Several key performance criteria for such protocols are the convergence time, average packet delay, and throughput. The convergence time is defined as the duration of time within which all nodes across the network collaboratively and in a distributed manner obtain conflict-free slots. The convergence time can be further exacerbated by mobility of the users. The average packet delay and throughput are important to the application layer quality of service (QoS) requirements. In this paper, the authors will quantify the aforementioned performance metrics for a distributed TDMA protocol.

Introduction

¹In tactical Mobile Ad Hoc Networks (MANET), communicating nodes have to collaborate, cooperate, and contend for resources in order to construct routing and forwarding tables and obtain communication links. In Figure 1, a group of mobile communications nodes equipped with packet-switched devices and MANET signaling protocols coordinate and reserve resources at the link layer in order to construct routing and communications path throughout the network for delivery of application layer traffic. One of the challenges in the MANET communications systems is the design of efficient and robust medium access control (MAC) protocols. Generally speaking, the MAC schemes fall into two broad categories, the random access based and the reservation based. Many existing MAC protocols are suitable to operate in environments with a central control (e.g., cellular systems with the base stations) [1] and [8]. When operating in infrastructureless, distributed, and dynamic environments such as the tactical operations, the MAC protocol plays two key roles: 1) provide a signaling mechanism for the communications nodes for exchanging information for neighbor discovery and resource allocation (e.g., TDMA slots) in a timely and conflict-free manner; and 2) satisfy latency and throughput performance requirements. Figure 1:

Topology of a distributed ad hoc network.