LAMAN: Load Adaptable MAC for Ad Hoc Networks
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LAMAN: Load Adaptable MAC for Ad Hoc Networks Marc Realp Telecommunications Technological Centre of Catalonia, Catalonia, 08034 Barcelona, Spain Email: [email protected]
´ Ana I. Perez-Neira Telecommunications Technological Centre of Catalonia, Catalonia, 08034 Barcelona, Spain Email: [email protected] Received 31 July 2003; Revised 26 May 2004 In mobile ad hoc radio networks, mechanisms on how to access the radio channel are extremely important in order to improve network efficiency. In this paper, the load adaptable medium access control for ad hoc networks (LAMAN) protocol is described. LAMAN is a novel decentralized multipacket MAC protocol designed following a cross-layer approach. Basically, this protocol is a hybrid CDMA-TDMA-based protocol that aims at throughput maximization in multipacket communication environments by efficiently combining contention and conflict-free protocol components. Such a combination of components is used to adapt the nodes’ access priority to changes on the traffic load while, at the same time, accounting for the multipacket reception (MPR) capability of the receivers. A theoretical analysis of the system is developed presenting closed expressions of network throughput and packet delay. By simulations, the validity of our analysis is shown and the performances of a LAMAN-based system and an Aloha-CDMA-based one are compared. Keywords and phrases: cross-layer, MAC, ad hoc, CDMA, TDMA, multiuser detection.
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INTRODUCTION
Traditionally, medium access control (MAC) mechanisms are used to face off the classical collision resolution problem in multiple-access channels with single-packet communications. That is, if two or more nodes send packets through the radio channel simultaneously, these packets collide and consequently, information is lost. To recover the information, the collided packets have to be retransmitted. Although the common aim in such channels is a MAC able to come close to efficiency equal to one, by avoiding collisions as much as possible, the approach considered in MAC design is different whether the system is centralized or decentralized. While centralized systems mainly present a node scheduling problem of variable complexity, decentralized systems present many different new challenges, like the availability of each node to communicate directly with any other node or the half-duplex transceiver characteristics, that must be overcome. In this paper, we will focus on decentralized systems. Regarding decentralized MAC algorithms, multiple access with collision avoidance (MACA) [1] presented a request-to-send (RTS) and clear-to-send (CTS) handshake for channel reservation during transmission. Afterwards, many works have been done in order to minimize the effect of this RTS/CTS information exchange (see [2] and
references therein). In other mechanisms such as carriersense multiple access (CSMA) [3, 4], the channel is sensed to know whether it is idle or busy; if the channel is sensed idle for a period longer than a guard time, transmission is done. In the case of collisi
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