Multi-Objective Scheduling for MUD based Ad-Hoc Networks M. Bouharras Z.Dziong F. Gagnon M. Haidar Department of Electrical Engineering, Ecole de Technologie Supérieure Montreal, Quebec, Canada, H3C 1K3 (Mohamed.bouharras.1, Mohamad.Haidar.1}@ens.etsmtl.ca, {Zbigniew.Dziong, Francois.Gagnon}@etsmtl.ca ABSTRACT Common channel multi-hop Ad Hoc networks have some inherent constraints related to throughput and Quality of Service (QoS). Multiuser detection (MUD) based Medium Access Control (MAC) can relax some of these constraints and provide significant gains in throughput and Quality of Service (QoS). These gains can be realized by implementing a distributed neighborhood scheduling algorithm that needs to choose one from several possible transmission configurations in each frame. This feature allows formulating different scheduling performance objectives such as delay minimization or throughput maximization. In this paper we focus on analysis and comparison of the system performance under different objectives including multi- objective formulations. First we implement a scheduling scheme that minimize delay using Start Time Fair Queuing (STFQ) algorithm and compare its performance with scheduling that maximises the throughput. Then we formulate multi-objective functions that are used to achieve a trade-off between delay and throughput performance. One of these formulations is based on the Nash arbitration scheme from cooperative game theory. The numerical results demonstrate the flexibility and efficiency of the proposed approach. Keywords Multiuser detection; Multiuser reception; MAC protocol; scheduling; fairness and wireless ad hoc networks. 1. INTRODUCTION Wireless ad hoc networks are expected to support multimedia applications in emergency disaster management and military operations. This class of mission-critical applications demands a certain level of quality of services (QoS) for proper operation. Many MAC protocols have been developed for wireless networks which are based on a common channel shared by mobile hosts in the network. These protocols, such as IEEE 802.11 are referred to as single-channel protocols. Due to relatively high probability of contentions and collisions, the performance of single-channel MAC protocols deteriorates quickly while the number of mobile hosts increases, especially for muli-hop connections [1]. To mitigate this problem, one can consider utilizing multiuser detection (MUD) or multiuser reception (MUR) CDMA technology that allows the reception of multiple CDMA channels at the same time. In [2] and [3] the authors proposed a novel MAC and scheduling algorithms to take advantage of MUD and MUR. One of the key elements of their approach is a distributed neighborhood scheduling mechanism that is based on a protocol that exchanges information between neighbors. They presented numerical results indicating significant gains in the QoS (delay) and network throughput. The objective of their scheduling mechanism was based on a principle that priority was given to the voice packets that waited the longest time in the neighborhood’s queues. This principle is not necessary optimal as shown in the studies of fair queuing mechanisms. Also, the network operation can have multi-objective formulation where the scheduling should balance network throughput maximization objective with traffic class fair access optimization. In this paper, we first propose an approach for analyzing and comparing close to optimal distributed neighborhood scheduling schemes with different objectives. The approach is based on the notion of a flow contention graph that takes into account the topology of the network. Using this notion, we construct a dependence matrix of flows in each node that constitutes a base for selecting optimal configuration of transmissions in a given slot according to the chosen objective. Then, using the above platform we implement several scheduling mechanisms. We start with single objective schemes such as scheduling that minimize delay using Start Time Fair Queuing (STFQ) algorithm and scheduling that maximizes the throughput. Then we formulate multi-objective functions that are used to achieve a trade-off between delay and throughput performance. Two concepts are considered. The first one is based on the Nash arbitration scheme from cooperative game theory where the objective is to maximize the product of two utility functions. The second one is based on maximization of the weighted sum of these utility functions. The numerical results demonstrate the viability of the proposed scheduling platform. First we compare the delay and throughput performance of the scheduling scheme that utilizes Start Time Fair Queuing (STFQ) algorithm WICON'08, November 17-19, 2008, Maui, Hawaii, USA. Copyright 2008 ICST 978-963-9799-36-3 1