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36
Spectrum sharing between wireless networks
 in Proc. IEEE INFOCOM’08
"... We consider the problem of two wireless networks operating on the same (presumably unlicensed) frequency band. Pairs within a given network cooperate to schedule transmissions, but between networks there is competition for spectrum. To make the problem tractable, we assume transmissions are schedule ..."
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Cited by 14 (0 self)
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We consider the problem of two wireless networks operating on the same (presumably unlicensed) frequency band. Pairs within a given network cooperate to schedule transmissions, but between networks there is competition for spectrum. To make the problem tractable, we assume transmissions are scheduled according to a random access protocol where each network chooses an access probability for its users. A game between the two networks is defined. We characterize the Nash Equilibrium behavior of the system. Three regimes are identified; one in which both networks simultaneously schedule all transmissions; one in which the denser network schedules all transmissions and the sparser only schedules a fraction; and one in which both networks schedule only a fraction of their transmissions. The regime of operation depends on the pathloss exponent α, the latter regime being desirable, but attainable only for α> 4. This suggests that in certain environments, rival wireless networks may end up naturally cooperating. To substantiate our analytical results, we simulate a system where networks iteratively optimize their access probabilities in a greedy manner. We also discuss a distributed scheduling protocol that employs carrier sensing, and demonstrate via simulations, that again a near cooperative equilibrium exists for sufficiently large α. 1
Bandwidth Partitioning in Decentralized Wireless Networks
"... This paper addresses the following question, which is of interest in the design of a multiuser decentralized network. Given a total system bandwidth of W Hz and a fixed data rate constraint of R bps for each transmission, how many frequency slots N of size W/N should the band be partitioned into in ..."
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Cited by 13 (7 self)
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This paper addresses the following question, which is of interest in the design of a multiuser decentralized network. Given a total system bandwidth of W Hz and a fixed data rate constraint of R bps for each transmission, how many frequency slots N of size W/N should the band be partitioned into in order to maximize the number of simultaneous links in the network? Dividing the available spectrum results in two competing effects. On the positive side, a larger N allows for more parallel, noninterfering communications to take place in the same area. On the negative side, a larger N increases the SINR requirement for each link because the same information rate must be achieved over less bandwidth, which in turn increases the area consumed by each transmission. Exploring this tradeoff and determining the optimum value of N in terms of the system parameters is the focus of the paper. Using stochastic geometry, the optimal SINR threshold – which directly corresponds to the optimal spectral efficiency – is derived for both the low SNR (powerlimited) and high SNR (interferencelimited) regimes. This leads to the optimum choice of the number of frequency bands N in terms of the path loss exponent, power and noise spectral density, desired rate, and total bandwidth. I.
Fractional power control for decentralized wireless networks
 in Allerton Conference on Communication, Control, and Computing
, 2007
"... We propose and analyze a new paradigm for power control in decentralized wireless networks, termed fractional power control. Transmission power is chosen as the current channel quality raised to an exponent −s, where s is a constant between 0 and 1. Choosing s = 1 and s = 0 correspond to the familia ..."
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Cited by 12 (5 self)
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We propose and analyze a new paradigm for power control in decentralized wireless networks, termed fractional power control. Transmission power is chosen as the current channel quality raised to an exponent −s, where s is a constant between 0 and 1. Choosing s = 1 and s = 0 correspond to the familiar cases of channel inversion and constant power transmission, respectively. Choosing s ∈ (0, 1) allows all intermediate policies between these two extremes to be evaluated, and we see that neither extreme is ideal. We prove that using an exponent of s ∗ = 1 2 optimizes the transmission capacity of an ad hoc network, meaning that the inverse square root of the channel strength is the optimal transmit power scaling. Intuitively, this choice achieves the optimal balance between helping disadvantaged users while making sure they do not flood the network with interference. I.
Rethinking information theory for mobile ad hoc networks
 IEEE Communications Magazine, Submitted
, 2007
"... The subject of this paper is the longstanding open problem of developing a general capacity theory for wireless networks, particularly a theory capable of describing the fundamental performance limits of mobile ad hoc networks (MANETs). A MANET is a peertopeer network with no preexisting infrast ..."
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Cited by 10 (2 self)
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The subject of this paper is the longstanding open problem of developing a general capacity theory for wireless networks, particularly a theory capable of describing the fundamental performance limits of mobile ad hoc networks (MANETs). A MANET is a peertopeer network with no preexisting infrastructure. MANETs are the most general wireless networks, with singlehop, relay, interference, mesh, and star networks comprising special cases. The lack of a MANET capacity theory has stunted the development and commercialization of many types of wireless networks, including emergency, military, sensor, and community mesh networks. Information theory, which has been vital for links and centralized networks, has not been successfully applied to decentralized wireless networks. Even if this was accomplished, for such a theory to truly characterize the limits of deployed MANETs it must overcome three key roadblocks. First, most current capacity results rely on the allowance of unbounded delay and reliability. Second, spatial and timescale decompositions have not yet been developed for optimally modeling the spatial and temporal dynamics of wireless networks. Third, a useful network capacity theory must integrate rather than ignore the important role of overhead messaging and feedback. This paper describes some of the shifts in thinking that may be needed to overcome these roadblocks and
1 Random Access Transport Capacity
, 909
"... We develop a new metric for quantifying endtoend throughput in multihop wireless networks, which we term random access transport capacity, since the interference model presumes uncoordinated transmissions. The metric quantifies the average maximum rate of successful endtoend transmissions, multi ..."
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Cited by 4 (1 self)
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We develop a new metric for quantifying endtoend throughput in multihop wireless networks, which we term random access transport capacity, since the interference model presumes uncoordinated transmissions. The metric quantifies the average maximum rate of successful endtoend transmissions, multiplied by the communication distance, and normalized by the network area. We show that a simple upper bound on this quantity is computable in closedform in terms of key network parameters when the number of retransmissions is not restricted and the hops are assumed to be equally spaced on a line between the source and destination. We also derive the optimum number of hops and optimal per hop success probability and show that our result follows the wellknown square root scaling law while providing exact expressions for the preconstants as well. Numerical results demonstrate that the upper bound is accurate for the purpose of determining the optimal hop count and success (or outage) probability. I.
Transmission capacity: applying stochastic geometry to uncoordinated ad hoc networks
, 2008
"... ..."
Understanding the Design Space for Cognitive Networks
"... Abstract—This paper studies a cognitive network where licensed primary users and unlicensed but ‘cognitive ’ secondary users share spectrum. Many system design parameters affect the joint performance, e.g., outage and capacity, seen by the two user types in such a scenario. We explore the sometimes ..."
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Cited by 3 (3 self)
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Abstract—This paper studies a cognitive network where licensed primary users and unlicensed but ‘cognitive ’ secondary users share spectrum. Many system design parameters affect the joint performance, e.g., outage and capacity, seen by the two user types in such a scenario. We explore the sometimes subtle system tradeoffs that arise in such networks. To that end, we propose a new simple stochastic geometric model that captures the salient interdependencies amongst spatially distributed primary and secondary nodes. The model allows us to evaluate the performance dependencies between primary and secondary transmissions in terms of the outage probability, node density and transmission capacity. From the design perspective the key design parameters determining the joint transmission capacity and tradeoffs, are the detection radius (detection SINR threshold), decoding SINR threshold, burstiness of coverage and/or transmit powers. We show how the joint transmission capacity region can be optimized or affected by these parameters. Index Terms—cognitive network, stochastic geometry, network information theory, transmission capacity I.
Impact of secondary users field size on spectrum sharing opportunities
 in Proc. IEEE Wireless Communications and Networking Conference (WCNC
, 2010
"... Abstract — Previous works studied the effect of many system parameters on spectrum sharing opportunities where secondary users access the spectrum of primary users. However, a parameter that has received little attention is the spatial size of the field of secondary users. Usually, the field size is ..."
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Cited by 3 (1 self)
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Abstract — Previous works studied the effect of many system parameters on spectrum sharing opportunities where secondary users access the spectrum of primary users. However, a parameter that has received little attention is the spatial size of the field of secondary users. Usually, the field size is assumed to be infinite. Using results developed for infinite fields might be too pessimistic leading to missing spectrum sharing opportunities. This paper studies the effect of the field size on spectrum sharing opportunities. We verify that asymptotic results obtained for infinite fields are applicable for finite but relatively large fields as well, i.e., when the radial depth of the field is much greater than the minimum distance to the primary user. We demonstrate that in some cases, however, asymptotic results are too pessimistic hiding some spectrum sharing opportunities. Moreover, the paper shows that in certain situations a small reduction in the field size may create spectrum sharing opportunities while in certain other situations a huge increase in the field size may not eliminate spectrum sharing opportunities. Our results also suggest the possibility of a secondary network to concurrently share the spectrum with a primary user without the need for spectrum sensing techniques or other cognitive radio functionalities.
IMPACT OF FADING ON THE PERFORMANCE OF ALOHA AND CSMA
"... This paper considers the performance of the ALOHA and CSMA MAC protocols in wireless ad hoc networks in the presence of fading. Increasing the rate of successful reception of packets is our objective, and thus, outage probability is used as the performance evaluation metric. In our network model, pa ..."
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Cited by 2 (1 self)
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This paper considers the performance of the ALOHA and CSMA MAC protocols in wireless ad hoc networks in the presence of fading. Increasing the rate of successful reception of packets is our objective, and thus, outage probability is used as the performance evaluation metric. In our network model, packets belonging to specific transmitters arrive randomly in space and time according to a 3D Poisson point process, and are then transmitted to their intended destinations using a fullydistributed MAC protocol. A packet transmission is considered successful if the received SINR is above a predefined threshold for the duration of the packet. Approximate expressions are derived for the outage probability of ALOHA and the different flavors of CSMA, namely CSMA with transmitter sensing, receiver sensing, and joint transmitterreceiver sensing. The introduction of fading adds to the hidden and exposed node problems of CSMA, resulting in an up to 75 % increase in the outage probability. Interestingly, however, the relative difference between the protocols remains unchanged. 1.