ABSTRACT
We propose a CDMA-based power controlled medium accessprotocol for mobile ad hoc networks (MANETs). Unlikepreviously proposed protocols, ours accounts for the multipleaccess interference (MAI), thereby addressing the notoriousnear-far problem that undermines the throughputperformance in MANETs. Channel-gain information obtainedfrom overheard RTS and CTS packets over an outof-band control channel is used to dynamically bound thetransmission power of mobile terminals in the vicinity ofa receiver. By properly estimating the required transmissionpower for data packets, the proposed protocol allowsfor interference-limited simultaneous transmissions to takeplace in the neighborhood of a receiving terminal. Simulationresults indicate that compared to the IEEE 802.11 approach,the proposed protocol achieves a significant increasein network throughput at no additional cost in energy consumption.
Categories and Subject Descriptors
2.1 [Network Architecture and Design]: Wireless Communication;C.
2.2 [Network Protocols]General TermsAlgorithm, Design, Performance
KeywordsAd hoc networks, CDMA, multi-access interference, near-farproblem, power control, code assignment.
1. INTRODUCTION
1.1 Motivation
Mobile ad hoc networks (MANETs) have recently beenthe topic of extensive research. The interest in such networksstems from their ability to provide a temporary wirelessnetworking capability in scenarios where fixed infrastructuresare lacking and are expensive or infeasible to deploy(e.g., disaster relief efforts, battlefields, etc.). Whilewide deployment of MANETs is yet to come, many effortsare currently underway to standardize protocols for the operationand management of such networks [26, 2].One of the fundamental challenges in MANETs research ishow to increase the overall network throughput while maintaininglow energy consumption for packet processing andcommunications. The low throughput is attributed to theharsh characteristics of the radio channel combined with thecontention-based nature of medium access control (MAC)protocols commonly used in MANETs. The focus of thispaper is on improving the network throughput of a MANETby means of a CDMA-based design of the MAC protocol.Compared to the DCF (Distributed Coordination Function)mode of the IEEE 802.11 standard [3], which is currently thede facto MAC protocol for MANETs, our MAC protocol isshown to achieve a significant increase in network throughputfor the same or less energy consumption per deliveredpacket.CDMA is based on spread spectrum (SS) techniques, inwhich each user occupies the entire available bandwidth.At the transmitter, a digital signal of bandwidth, say B1bits/sec, is spread using (i.e., multiplied by) a pseudo-randomnoise (PN) code of bandwidth, say B2 bits/sec (B2/B1 _ 1is called the processing gain). The PN code is a binarysequence that statistically satisfies the requirement of a randomsequence, but that can be exactly reproduced at theintended receiver through precise mathematical rules. Usinga locally generated PN code, the receiver de-spreads thereceived signal, recovering from it the original information.The enhancement in performance obtained from spreadingthe signal makes it possible for several, independently codedsignals to occupy the same channel bandwidth, provided thateach signal has a distinct PN code. This type of communicationin which each transmitter-receiver pair has a distinctPN code for transmitting over a common channel is calledCDMA [24].


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