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180
An Aloha protocol for multihop mobile wireless networks
 IEEE Trans. Inf. Theory
, 2006
"... Abstract—An Alohatype access control mechanism for large mobile, multihop, wireless networks is defined and analyzed. This access scheme is designed for the multihop context, where it is important to find a compromise between the spatial density of communications and the range of each transmission. ..."
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Cited by 225 (24 self)
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Abstract—An Alohatype access control mechanism for large mobile, multihop, wireless networks is defined and analyzed. This access scheme is designed for the multihop context, where it is important to find a compromise between the spatial density of communications and the range of each transmission. More precisely, the analysis aims at optimizing the product of the number of simultaneously successful transmissions per unit of space (spatial reuse) by the average range of each transmission. The optimization is obtained via an averaging over all Poisson configurations for the location of interfering mobiles, where an exact evaluation of signal over noise ratio is possible. The main mathematical tools stem from stochastic geometry and are spatial versions of the socalled additive and max shot noise processes. The resulting medium access control (MAC) protocol exhibits some interesting properties. First, it can be implemented in a decentralized way provided some local geographic information is available to the mobiles. In addition, its transport capacity is proportional to the square root of the density of mobiles which is the upper bound of Gupta and Kumar. Finally, this protocol is selfadapting to the node density and it does not require prior knowledge of this density. Index Terms—Medium access control (MAC) layer, multipleaccess protocol, network design, optimization, point process, queuing theory, signaltointerference ratio, stochastic geometry, stochastic process, transport capacity. I.
On coding for reliable communication over packet networks
, 2008
"... We consider the use of random linear network coding in lossy packet networks. In particular, we consider the following simple strategy: nodes store the packets that they receive and, whenever they have a transmission opportunity, they send out coded packets formed from random linear combinations of ..."
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Cited by 217 (37 self)
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We consider the use of random linear network coding in lossy packet networks. In particular, we consider the following simple strategy: nodes store the packets that they receive and, whenever they have a transmission opportunity, they send out coded packets formed from random linear combinations of stored packets. In such a strategy, intermediate nodes perform additional coding yet do not decode nor wait for a block of packets before sending out coded packets. Moreover, all coding and decoding operations have polynomial complexity. We show that, provided packet headers can be used to carry an amount of sideinformation that grows arbitrarily large (but independently of payload size), random linear network coding achieves packetlevel capacity for both single unicast and single multicast connections and for both wireline and wireless networks. This result holds as long as packets received on links arrive according to processes that have average rates. Thus packet losses on links may exhibit correlations in time or with losses on other links. In the special case of Poisson traffic with i.i.d. losses, we give error exponents that quantify the rate of decay of the probability of error with coding delay. Our analysis of random linear network coding shows not only that it achieves packetlevel capacity, but also that the propagation of packets carrying “innovative ” information follows the propagation of jobs through a queueing network, thus implying that fluid flow models yield good approximations.
Stability of Multipacket Slotted Aloha with Selfish Users and Perfect Information
, 2003
"... Aloha is perhaps the simplest and moststudied medium access control protocol in existence. Only in the recent past, however, have researchers begun to study the performance of Aloha in the presence of selfish users. In this paper, we present a gametheoretic model of multipacket slotted Aloha with ..."
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Cited by 113 (5 self)
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Aloha is perhaps the simplest and moststudied medium access control protocol in existence. Only in the recent past, however, have researchers begun to study the performance of Aloha in the presence of selfish users. In this paper, we present a gametheoretic model of multipacket slotted Aloha with perfect information. We show that this model must have an equilibrium and we characterize this equilibrium. Using the tools of stochastic processes, we then establish the equilibrium stability region for some wellknown channel models.
Exploiting Decentralized Channel State Information for Random Access
, 2002
"... We study the use of channel state information for random access in fading channels. Traditionally, random access protocols have been designed by assuming simple models for the physical layer where all users are symmetric and there is no notion of channel state. We introduce a reception model that ta ..."
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Cited by 82 (18 self)
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We study the use of channel state information for random access in fading channels. Traditionally, random access protocols have been designed by assuming simple models for the physical layer where all users are symmetric and there is no notion of channel state. We introduce a reception model that takes into account the channel states of various users. Under the assumption that each user has access to his channel state information (CSI), we propose a variant of Slotted ALOHA protocol for medium access control, where the transmission probability is allowed to be a function of the CSL The function is called the transmission control scheme. Assuming the finite user infinite buffer model we derive expressions for the maximum stable throughput of the system. We introduce the notion of asymptotic stable throughput (AST) that is the maximum stable throughput as the number of users goes to infinity. We consider two types of transmission control namely population independent transmission control (PITC) where the transmission control is not a function of the size of the network and population dependent transmission control where the transmission control is a function of the size of the network. We obtain expressions for the AST achievable with PITC. For population dependent transmission control, we introduce a particular transmission control that can potentially lead to significant gains in AST. For both PITC and PDTC, we show that the effect of transmission control is equivalent to changing the probability distribution of the channel state. The theory is then applied to CDMA networks with Linear Minimum Mean Square Error (LMMSE) receivers and Matched Filters (MF) to illustrate the effectiveness of utilizing channel state. It is shown that through the use of channel state, with an...
Cognitive multiple access via cooperation: Protocol design and performance analysis
 IEEE Trans. on Information Theory
, 2007
"... Abstract—In this paper, a novel cognitive multipleaccess strategy in the presence of a cooperating relay is proposed. Exploiting an important phenomenon in wireless networks, source burstiness, the cognitive relay utilizes the periods of silence of the terminals to enable cooperation. Therefore, no ..."
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Cited by 77 (24 self)
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Abstract—In this paper, a novel cognitive multipleaccess strategy in the presence of a cooperating relay is proposed. Exploiting an important phenomenon in wireless networks, source burstiness, the cognitive relay utilizes the periods of silence of the terminals to enable cooperation. Therefore, no extra channel resources are allocated for cooperation and the system encounters no bandwidth losses. Two protocols are developed to implement the proposed multipleaccess strategy. The maximum stable throughput region and the delay performance of the proposed protocols are characterized. The results reveal that the proposed protocols provide significant performance gains over conventional relaying strategies such as selection and incremental relaying, specially at high spectral efficiency regimes. The rationale is that the lossless bandwidth property of the proposed protocols results in a graceful degradation in the maximum stable throughput with increasing the required rate of communication. On the other hand, conventional relaying strategies suffer from catastrophic performance degradation because of their inherent bandwidth inefficiency that results from allocating specific channel resources for cooperation at the relay. The analysis reveals that the throughput region of the proposed strategy is a subset of its maximum stable throughput region, which is different from random access, where both regions are conjectured to be identical. Index Terms—Cooperative communications, delay analysis, diversity techniques, multiple access, queueing theory, relay channel, stability analysis, stability region. I.
Stability and Delay of FiniteUser Slotted ALOHA With Multipacket Reception
 IEEE TRANS. INFORM. THEORY
, 2005
"... The effect of multipacket reception (MPR) on stability and delay of slotted ALOHA based randomaccess systems is considered. A general asymmetric MPR model is introduced and the mediumaccess control (MAC) capacity region is specified. An explicit characterization of the ALOHA stability region for t ..."
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Cited by 56 (1 self)
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The effect of multipacket reception (MPR) on stability and delay of slotted ALOHA based randomaccess systems is considered. A general asymmetric MPR model is introduced and the mediumaccess control (MAC) capacity region is specified. An explicit characterization of the ALOHA stability region for the twouser system is given. It is shown that the stability region undergoes a phase transition from a concave region to a convex polyhedral region as the MPR capability improves. It is also shown that after this phase transition, slotted ALOHA is optimal i.e., the ALOHA stability region coincides with the MAC capacity region. Further, it is observed that there is no need for transmission control when ALOHA is optimal i.e., ALOHA with transmission probability one is optimal. Next, these results are extended to a symmetric P user ALOHA system. Finally, a complete characterization of average delay in capture channels for the twouser system is given. It is shown that in certain capture scenarios, ALOHA with transmission probability one is delay optimal for all stable arrival rates. Further, it is also shown that ALOHA with transmission probability one is optimal for stability and delay simultaneously in the twouser capture channel.
The Stability Region of the FiniteUser Slotted ALOHA Protocol
 IEEE Trans. Inform. Theory
, 1991
"... A version of the discrete time slotted ALOHA protocol operating with finitely many buffered terminals is considered. The stability region is defined to be the set of vectors of arrival rates A = (A,..., A4) for which there exists a vector of transmission probabilities such that the system is stable. ..."
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Cited by 44 (0 self)
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A version of the discrete time slotted ALOHA protocol operating with finitely many buffered terminals is considered. The stability region is defined to be the set of vectors of arrival rates A = (A,..., A4) for which there exists a vector of transmission probabilities such that the system is stable. It is assumed that arrivals are independent from slot to slot, and assume the following model for the arrival distribution in a slot: The total number of arrivals in any slot is geometrically distributed, with the probability that such an arrival is at node i being Ai(EkAk) , independent of the others. With this arrival model, it is proven that the closure of the stability region of the protocol is the same as the closure of the Shannon capacity region of the collision channel without feedback, as determined by Massey and Mathys. At present, it is not clear if this result depends on the choice of arrival distribution. The basic probabilistic observation is that the stationary distribution and certain conditional distributions derived from it have positive correlations for bounded increasing functions. Similar techniques may be of use in studying other interacting systems of queues.
A Multiqueue Service Room MAC Protocol for Wireless Networks with Multipacket Reception
 IEEE/ACM Trans. Networking
, 2003
"... An adaptive mediumaccess control (MAC) protocol for heterogeneous networks with finite population is proposed. Referred to as the multiqueue service room (MQSR) protocol, this scheme is capable of handling users with different qualityofservice (QoS) constraints. By exploiting the multipacket rece ..."
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Cited by 43 (12 self)
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An adaptive mediumaccess control (MAC) protocol for heterogeneous networks with finite population is proposed. Referred to as the multiqueue service room (MQSR) protocol, this scheme is capable of handling users with different qualityofservice (QoS) constraints. By exploiting the multipacket reception (MPR) capability, the MQSR protocol adaptively grants access to the MPR channel to a number of users such that the expected number of successfully received packets is maximized in each slot. The optimal access protocol avoids unnecessary empty slots for light traffic and excessive collisions for heavy traffic. It has superior throughput and delay performance as compared to, for example, the slotted ALOHA with the optimal retransmission probability. This protocol can be applied to randomaccess networks with multimedia traffic.
Challenges: Towards Truly Scalable Ad Hoc Networks
 MobiCom'07
, 2007
"... The protocols used in ad hoc networks today are based on the assumption that the best way to approach multiple access interference (MAI) is to avoid it. Unfortunately, as the seminal work by Gupta and Kumar has shown, this approach does not scale. Recently, Ahlswede, Ning, Li, and Yeung showed that ..."
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Cited by 43 (19 self)
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The protocols used in ad hoc networks today are based on the assumption that the best way to approach multiple access interference (MAI) is to avoid it. Unfortunately, as the seminal work by Gupta and Kumar has shown, this approach does not scale. Recently, Ahlswede, Ning, Li, and Yeung showed that network coding (NC) can attain the maxflow mincut throughput for multicast applications in directed graphs with pointtopoint links. Motivated by this result, many researchers have attempted to make ad hoc networks scale using NC. However, the work by Liu, Goeckel, and Towsley has shown that NC does not increase the order capacity of wireless ad hoc networks for multipair unicast applications. We demonstrate that protocol architectures that exploit multipacket reception (MPR) do increase the order capacity of random wireless ad hoc networks by a factor Θ(log n) under the protocol model. We also show that MPR provides a better capacity improvement for ad hoc networks than NC when the network experiences a singlesource multicast and multipair unicasts. Based on these results, we introduce design problems for channel access and routing based on MPR, such that nodes communicate with one another on a manytomany basis, rather than onetoone as it is done today, in order to make ad hoc networks truly scalable.
Stability and Delay of Finite User Slotted ALOHA with Multipacket Reception
 IEEE Trans. Inform. Theory
, 2003
"... The effect of Multipacket Reception (MPR) on stability and delay of slotted ALOHA based random access systems is considered. A general asymmetric MPR model is introduced and the MAC capacity region is specified. An explicit characterization of the ALOHA stability region for the two user system is ..."
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Cited by 36 (9 self)
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The effect of Multipacket Reception (MPR) on stability and delay of slotted ALOHA based random access systems is considered. A general asymmetric MPR model is introduced and the MAC capacity region is specified. An explicit characterization of the ALOHA stability region for the two user system is given. It is shown that the stability region undergoes a phase transition from a concave region to a convex region bounded by lines as the MPR capability improves. It is also shown that after this phase transition, slotted ALOHA is optimal i.e., the ALOHA stability region coincides with the MAC capacity region. Further, it is observed that there is no need for transmission control when ALOHA is optimal i.e., ALOHA with transmission probability one is optimal. These results are extended to a symmetric N > 2 user ALOHA system, where it is shown that for a large class of symmetric MPR channels no transmission control is optimal from a stability viewpoint. This finding suggests that if the physical layer is even reasonably good, there is no need for sophisticated Medium Access Control protocols.