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82
Sensor Networks with Mobile Agents
 in Proc. 2003 Military Communications Intl Symp
, 2003
"... An architecture for large scale low power sensor network is proposed. Referred to as sensor networh with mobile agents (SENMA). SENMA exploit node redundancies by introducing mobile agents that communicate opportunistically with a largefreld of sensors. The addition of mobile agents shifIs computat ..."
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Cited by 108 (37 self)
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An architecture for large scale low power sensor network is proposed. Referred to as sensor networh with mobile agents (SENMA). SENMA exploit node redundancies by introducing mobile agents that communicate opportunistically with a largefreld of sensors. The addition of mobile agents shifIs computationally intensive task awayfrom primitive sensors to more powerful mobile agents, which enables energy effcient operations under severely limited power constraints. An opportunistic ALOHA random access coupled with a direct sequence spread spectrum physical layer is proposed. A comparison ofSENMA with apor ad hocsensor network shows a substantial gain in energy efficiency.
On the Maximum Stable Throughput Problem in Random Networks with Directional Antennas
 IN PROC. ACM MOBIHOC
, 2003
"... We consider the problem of determining rates of growth for the maximum stable throughput achievable in dense wireless networks. We formulate this problem as one of finding maximum flows on random unitdisk graphs. Equipped with the maxflow/mincut theorem as our basic analysis tool, we obtain rates ..."
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Cited by 66 (6 self)
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We consider the problem of determining rates of growth for the maximum stable throughput achievable in dense wireless networks. We formulate this problem as one of finding maximum flows on random unitdisk graphs. Equipped with the maxflow/mincut theorem as our basic analysis tool, we obtain rates of growth under three models of communication: (a) omnidirectional transmissions; (b) "simple" directional transmissions, in which sending nodes generate a single beam aimed at a particular receiver; and (c) "complex " directional transmissions, in which sending nodes generate multiple beams aimed at multiple receivers. Our main finding is that an increase of 54 54 in maximum stable throughput is all that can be achieved by allowing arbitrarily complex signal processing (in the form of generation of directed beams) at the transmitters and receivers. We conclude therefore that neither directional antennas, nor the ability to communicate simultaneously with multiple nodes, can be expected in practice to effectively circumvent the constriction on capacity in dense networks that results from the geometric layout of nodes in space.
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 52 (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.
Distributed opportunistic scheduling for ad hoc communications with imperfect channel information,” Submitted to
 V. CONCLUSION In
"... Abstract — Distributed opportunistic scheduling is studied for wireless adhoc networks, where many links contend for one channel using random access. In such networks, distributed opportunistic scheduling (DOS) involves a process of joint channel probing and distributed scheduling. It has been show ..."
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Cited by 47 (9 self)
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Abstract — Distributed opportunistic scheduling is studied for wireless adhoc networks, where many links contend for one channel using random access. In such networks, distributed opportunistic scheduling (DOS) involves a process of joint channel probing and distributed scheduling. It has been shown that under perfect channel estimation, the optimal DOS for maximizing the network throughput is a pure threshold policy. In this paper, this formalism is generalized to explore DOS under noisy channel estimation, where the transmission rate needs to be backed off from the estimated rate to reduce the outage. It is shown that the optimal scheduling policy remains to be thresholdbased, and that the rate threshold turns out to be a function of the variance of the estimation error and be a functional of the backoff rate function. Since the optimal backoff rate is intractable, a suboptimal linear backoff scheme that backs off the estimated signaltonoise ratio (SNR) and hence the rate is proposed. The corresponding optimal backoff ratio and rate threshold can be obtained via an iterative algorithm. Finally, simulation results are provided to illustrate the tradeoff caused by increasing training time to improve channel estimation at the cost of probing efficiency. I.
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 35 (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.
Distributed approaches for exploiting multiuser diversity in wireless networks
 IEEE Transactions on Information Theory
, 2006
"... In wireless fading channels, multiuser diversity can be exploited by scheduling users so that they transmit when their channel conditions are favorable. This leads to a sum throughput that increases with the number of users and, in certain cases, achieves capacity. However, such scheduling requires ..."
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Cited by 33 (2 self)
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In wireless fading channels, multiuser diversity can be exploited by scheduling users so that they transmit when their channel conditions are favorable. This leads to a sum throughput that increases with the number of users and, in certain cases, achieves capacity. However, such scheduling requires global knowledge of every user’s channel gain, which may be difficult to obtain in some situations. This paper addresses contentionbased protocols for exploiting multiuser diversity with only local channel knowledge. A variation of the classic ALOHA protocol is given in which users attempt to exploit multiuser diversity gains, but suffer contention losses due to the distributed channel knowledge. We characterize the growth rate of the sum throughput for this protocol in a backlogged system under both shortterm and longterm average power constraints. A simple “fixedrate ” system is shown to be asymptotically optimal and to achieve the same growth rate as in a system with a centralized scheduler. Moreover, asymptotically, the fraction of throughput lost due to contention is shown to be 1/e. Also, in a system with random arrivals and an infinite user population, a variation of this ALOHA protocol is shown to be stable for any total arrival rate, given that users can estimate the backlog. I.
Stability and capacity of regular wireless networks
 IEEE TRANS. INF. THEORY
, 2005
"... We study the stability and capacity problems in regular wireless networks. In the first part of the paper, we provide a general approach to characterizing the capacity region of arbitrary networks, find an outer bound to the capacity region in terms of the transport capacity, and discuss connection ..."
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Cited by 28 (3 self)
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We study the stability and capacity problems in regular wireless networks. In the first part of the paper, we provide a general approach to characterizing the capacity region of arbitrary networks, find an outer bound to the capacity region in terms of the transport capacity, and discuss connections between the capacity formulation and the stability of node buffers. In the second part of the paper, we obtain closedform expressions for the capacity of Manhattan (twodimensional grid) and ring networks (circular array of nodes). We also find the optimal (i.e., capacityachieving) medium access and routing policies. Our objective in analyzing regular networks is to provide insights and design guidelines for general networks. The knowledge of the exact capacity enables us to quantify the loss incurred by suboptimal protocols such as slotted ALOHA medium access and randomwalkbased routing. Optimal connectivity and the effects of link fading on network capacity are also investigated.
Sensor Networks with Mobile Access: Optimal Random Access and Coding
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS: SPECIAL ISSUE ON SENSOR NETWORKS
, 2004
"... We consider random access and coding schemes for sensor networks with mobile access (SENMA). Using an orthogonal codedivision multiple access (CDMA) as the physical layer, an opportunistic ALOHA (OALOHA) protocol that utilizes channel state information is proposed. Under the packet capture model ..."
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Cited by 26 (5 self)
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We consider random access and coding schemes for sensor networks with mobile access (SENMA). Using an orthogonal codedivision multiple access (CDMA) as the physical layer, an opportunistic ALOHA (OALOHA) protocol that utilizes channel state information is proposed. Under the packet capture model and using the asymptotic throughput as the performance metric, we show that OALOHA approaches the throughput equal to the spreading gain with an arbitrarily small power at each sensor. This result implies that OALOHA is close to the optimal centralized scheduling scheme for the orthogonal CDMA networks. When side information such as location is available, the transmission control is modified to incorporate either the distribution or the actual realization of the side information. Convergence of the throughput with respect to the size of the network is analyzed. For networks allowing sensor collaborations, we combine coding with random access by proposing two coded random access schemes: spreading code dependent and independent transmissions. In the low rate regime, the spreading code independent transmission has a larger random coding exponent (therefore, faster decay of error probability) than that of the spreading code dependent transmission. On the other hand, the spreading code dependent transmission gives higher achievable rate.
An Integrated Approach to EnergyAware Medium Access for Wireless Sensor Networks
 IEEE TRANSACTIONS ON SIGNAL PROCESSING
, 2005
"... This report addresses the design of distributed medium access control (MAC) protocols for wireless sensor networks under the performance measure of network lifetime. Integrated in the design of MAC schemes are two key physical layer parameters: the channel state and the residual energy of each senso ..."
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Cited by 16 (2 self)
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This report addresses the design of distributed medium access control (MAC) protocols for wireless sensor networks under the performance measure of network lifetime. Integrated in the design of MAC schemes are two key physical layer parameters: the channel state and the residual energy of each sensor. The impact of incorporating these parameters in MAC design on network lifetime is studied. Furthermore, we show that a lifetimemaximizing protocol should dynamically trade off the channel state information (CSI) and the residual energy information (REI) according to the age of the network. Specifically, lifetimemaximizing protocols should be more opportunistic by prioritizing sensors with better channels for transmission when the network is young and more conservative by favoring sensors with more residual energies when the network is old. Following this general design principle, we propose a dynamic protocol for lifetime maximization (DPLM) that exploits both CSI and REI. Analytical results are provided to demonstrate the dynamic property and the asymptotic optimality of DPLM.
On Throughput Optimality with Delayed NetworkState Information
, 2008
"... We study the problem of routing/scheduling in a wireless network with partial/delayed Network (channel and queue) State Information (NSI). We consider two cases: (i) centralized routing/scheduling, where a central controller obtains heterogeneous delayed information from each of the nodes (thus, the ..."
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Cited by 16 (1 self)
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We study the problem of routing/scheduling in a wireless network with partial/delayed Network (channel and queue) State Information (NSI). We consider two cases: (i) centralized routing/scheduling, where a central controller obtains heterogeneous delayed information from each of the nodes (thus, the controller has NSI with different delays from different nodes), and makes the routing/scheduling decisions; (ii) decentralized routing/scheduling, where each node makes a decision based on its current channel and queue states along with homogeneous delayed NSI from other nodes. For each of the cases (with additional flow restrictions for the decentralized routing/scheduling case), we first characterize the optimal network throughput regions under the above described NSI models and show that the throughput regions shrinks with the increase of delay. Further, we propose channel and queue length based routing/scheduling algorithms that achieve the above throughput regions.