In this paper, we propose a novel forwarding technique based on geographical location of the nodes involved and random selection of the relaying node via contention among receivers. We focus on the multihop performance of such a solution, in terms of the average number of hops to reach a destination as a function of the distance and of the average number of available neighbors. An idealized scheme (in which the best relay node is always chosen) is discussed and its performance is evaluated by means of both simulation and analytical techniques. A practical scheme to select one of the best relays is shown to achieve performance very close to that of the ideal case. Some discussion about design issues for practical implementation is also given.

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In this paper, we study a novel forwarding technique based on geographical location of the nodes involved and random selection of the relaying node via contention among receivers. We provide a detailed description of a MAC scheme based on these concepts and on collision avoidance and report on its energy and latency performance. A simplified analysis is given first, some relevant trade offs are highlighted, and parameter optimization is pursued. Further, a semi-Markov model is developed which provides a more accurate performance evaluation. Simulation results supporting the validity of our analytical approach are also provided.

Abstra& "smiaPon of data Mocks on a fading mobile radio channel is considered. The binary p~~cesp of the success and failure of the data blocks is investigated, and the accuracy of a Markov approximation is studied. It is shown through analysis and simulation that a first-order Markov process is a good approximation. Data-link pep formance of ARQ protocols is considered as an example of application. I. INTRODUCIlONInterest in wireless communication has increased in recent years, primarily to foster Personal Communication Services (PCS). In this context, there is a greater demand for capacity and a need to integrate voice. data and other types of traffic over radio channels. One of the key technical problem areas that has emerged out of this, is the need to determine the effect of fading on network performance. One specific problem that arises in this Context is the performance evaluation of data block transmission, e.g., in data-link protocols.In the past litemure, most models that have been used for this purpose assumed that the block transmissions were independent and identically distributed (iid). Also, many protocols were designed for an iid channel, and techniques were developed to eliminate channel memory (e.g., interleaving). A newer approach is to take advantage of the channel memory (e.g., exploiting some prediction techniques) to obtain better performance, instead of destroying it.In the latter context, the study of channels with memory bemmesofprimaryimportance. Ontheotherhand,somerealworld channels do not lend theanselves to an analytical study, and the development of some simplied models is desirable. A natural approach is to approximate a h n e l with memory by means of a Markov model. Recently, in [l], Wang investigated the accuracy of a firstorder Markov process in modeling data transmission on a Rayleigh fading channel, finding that such an approximation is in fact satisfactory. The process he refers to is the sequence of values of the envelope of the complex Gaussian process used to model the multiplicative effect of the channel.On the other hand, more often it is not the value of the channel envelope (or of the SNR, which is proportional to the square of it) which is of direct interest, but rather some nonlinear function of it, which depends on the transmission techniques, modulation, coding, and so on. In particular, the binary process which describes the SUCC~SS~S and the failures of the block transmissions is of primary importance, and very often is the only information which is available. Therefore, the study of its behavior is an important issue.In this paper, we investigate the accuracy of a lirst-order binary Markov model for the success/failure process of data ?his work has been supported by the Center f a Wireless CommunicptionS, UCSD. blocks; this will be done by using mutual information, following an approach similar to that used in [ 11. Also, an example of application to data-link performance analysis will be provided. It is seen that a Markov model gives significantly differen...

In this paper, we consider the slotted ALOHA protocol with capture, in a mobile communication environment, in the presence of Rayleigh fading and log-normal shadowing. The capture probabilities and their asymptotic value, as the number of colliding packets tends to infinity, are computed. A sufficient condition, under which this limit is positive, is identilled and expressed in terms of the spatial distribution of the users. Also, various models for this latter distribution are discussed. These results help identify the region in which the system may achieve a positive stable throughput. Finally, a retransmission control scheme, that enhances the throughput, is considered, and the stability of the system is rigorously proven. We also show that the use of retransmission control is unavoidable if the network performance predicted in some recent literature is to be achieved.