Distributed scheduling and multi-channel opportunistic media access for ad hoc networks

Abstract

Current wireless ad hoc networks suffer from two main performance limitations. First, current ad hoc networks do not efficiently utilize the scarce and dynamic wireless spectrum. As a result, the goodput of current ad hoc networks is often lower than the maximum radio transmission rate. Second, current ad hoc networks provide only best effort service, and there is little related work to provide general mechanisms to enable more powerful services (such as guaranteed services, differentiated services and flow protection). Consequently, current ad hoc networks are unable to provide quality-of-service (throughput or delay targets, QoS differentiation and fairness) and can incur severe unfairness even in simple topologies. In this thesis I design and evaluate mechanisms that together address the above mentioned two main performance limitations of current ad hoc networks. In particular this thesis has two main contributions. First, I propose and evaluate Distributed Wireless Ordering Protocol (DWOP), which provides a framework for design of join scheduling and MAC in ad hoc networks. The goal of DWOP is to ensure that to the closest extent possible, packets are serviced in the order as defined by a centralized reference scheduler. By ensuring that packets access the medium in an exact reference order, DWOP serves as a framework to apply the wealth of packet scheduling service disciplines developed for wireline networks to wireless ad hoc networks thereby making it possible to achieve the desired goals of fairness, throughput and delay targets and service differentiation in such networks. Second, I propose MAC mechanisms to opportunistically exploit the scarce and variable wireless channel to maximize net system throughput of ad hoc networks. In particular I devise Multi-channel Opportunistic Auto Rate (MOAR), a distributed MAC protocol which exploits the presence of frequency diversity in ad hoc networks to maximize the net throughput of such networks. MOAR is opportunistic across both users and channels and exploits temporal variations across multiple frequency channels present at the physical (PHY) layer to opportunistically transmit data at a higher rate on high quality channels. The two contributions, namely joint design of distributed MAC and scheduling and design of multi-channel opportunistic MAC protocol, together form a frame-work for high performance ad hoc networks which not only support QoS but also achieve high throughput by efficiently exploiting the scarce and dynamic wireless channel