Results 11 - 20
of
357
Price-based spectrum management in cognitive radio networks
- Selected Topics in Signal Processing
, 2008
"... Abstract — Cognitive radios (CRs) have a great potential to improve spectrum utilization by enabling users to access the spectrum dynamically without disturbing licensed primary radios (PRs). A key challenge in operating these radios as a network is how to implement an efficient medium access contro ..."
Abstract
-
Cited by 76 (5 self)
- Add to MetaCart
(Show Context)
Abstract — Cognitive radios (CRs) have a great potential to improve spectrum utilization by enabling users to access the spectrum dynamically without disturbing licensed primary radios (PRs). A key challenge in operating these radios as a network is how to implement an efficient medium access control (MAC) mechanism that can adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most existing works address this issue via sub-optimal heuristic approaches or centralized solutions. In this paper, we propose a novel joint power/channel allocation scheme that improves the performance through a distributed pricing approach. In this scheme, the spectrum allocation problem is modeled as a non-cooperative game, with each CR pair acting as a player. A price-based iterative water-filling (PIWF) algorithm is proposed, which enables CR users to reach a good Nash equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved through pricing. Depending on the different orders according to which CRs take actions, we study sequential and parallel versions of the PIWF algorithm. We show that the parallel version converges faster than the sequential version. We then propose a corresponding MAC protocol to implement our resource management schemes. The proposed MAC allows multiple CR pairs to be first involved in an admission phase, then iteratively negotiate their transmission powers and spectrum via control-packet exchanges. Following the negotiation phase, CRs proceed concurrently with their data transmissions. Simulations are used to study the performance of our protocol and demonstrate its effectiveness in terms of improving the overall network throughput and reducing the average power consumption. I.
Cognitive Medium Access: Exploration, Exploitation and Competition
, 2007
"... This paper establishes the equivalence between cognitive medium access and the competitive multi-armed bandit problem. First, the scenario in which a single cognitive user wishes to opportunistically exploit the availability of empty frequency bands in the spectrum with multiple bands is considered ..."
Abstract
-
Cited by 61 (5 self)
- Add to MetaCart
(Show Context)
This paper establishes the equivalence between cognitive medium access and the competitive multi-armed bandit problem. First, the scenario in which a single cognitive user wishes to opportunistically exploit the availability of empty frequency bands in the spectrum with multiple bands is considered. In this scenario, the availability probability of each channel is unknown to the cognitive user a priori. Hence efficient medium access strategies must strike a balance between exploring the availability of other free channels and exploiting the opportunities identified thus far. By adopting a Bayesian approach for this classical bandit problem, the optimal medium access strategy is derived and its underlying recursive structure is illustrated via examples. To avoid the prohibitive computational complexity of the optimal strategy, a low complexity asymptotically optimal strategy is developed. The proposed strategy does not require any prior statistical knowledge about the traffic pattern on the different channels. Next, the multi-cognitive user scenario is considered and low complexity medium access protocols, which strike the optimal balance between exploration and exploitation in such competitive environments, are developed. Finally, this formalism is extended to the case in which each cognitive user is capable of sensing and using multiple channels simultaneously.
Indexability of Restless Bandit Problems and Optimality of Whittle's Index for Dynamic . . .
"... We consider a class of restless multi-armed bandit problems (RMBP) that arises in dynamic multichannel access, user/server scheduling, and optimal activation in multi-agent systems. For this class of RMBP, we establish the indexability and obtain Whittle’s index in closed-form for both discounted an ..."
Abstract
-
Cited by 59 (13 self)
- Add to MetaCart
We consider a class of restless multi-armed bandit problems (RMBP) that arises in dynamic multichannel access, user/server scheduling, and optimal activation in multi-agent systems. For this class of RMBP, we establish the indexability and obtain Whittle’s index in closed-form for both discounted and average reward criteria. These results lead to a direct implementation of Whittle’s index policy with remarkably low complexity. When arms are stochastically identical, we show that Whittle’s index policy is optimal under certain conditions. Furthermore, it has a semi-universal structure that obviates the need to know the Markov transition probabilities. The optimality and the semi-universal structure result from the equivalency between Whittle’s index policy and the myopic policy established in this work. For non-identical arms, we develop efficient algorithms for computing a performance upper bound given by Lagrangian relaxation. The tightness of the upper bound and the near-optimal performance of Whittle’s index policy are illustrated with simulation examples.
The primary exclusive regions in cognitive networks
- IEEE Trans. on Wireless Comm
, 2008
"... Abstract—In this paper, we consider a cognitive network in which a single primary transmitter communicates with primary receivers within an area of radius R0, called the primary exclusive region (PER). Inside this region, no cognitive users may transmit. Outside the PER, provided that the cognitive ..."
Abstract
-
Cited by 53 (4 self)
- Add to MetaCart
(Show Context)
Abstract—In this paper, we consider a cognitive network in which a single primary transmitter communicates with primary receivers within an area of radius R0, called the primary exclusive region (PER). Inside this region, no cognitive users may transmit. Outside the PER, provided that the cognitive transmitters are at a minimal distance ɛp from a primary receiver, they may transmit concurrently with the primary user. We determine bounds on the primary exclusive radius R0 and the guard band ɛp to guarantee an outage performance for the primary user. Specifically, for a desired rate C0 and an outage probability β, the probability that the primary user’s rate falls below C0 is less than β. This performance guarantee holds even with an arbitrarily large number of cognitive users uniformly distributed with constant density outside the primary exclusive region. I.
Optimal selection of channel sensing order in cognitive radio
- IEEE Transactions on Wireless Communication
"... Abstract—This paper investigates the optimal sensing order problem in multi-channel cognitive medium access control with opportunistic transmissions. The scenario in which the availabil-ity probability of each channel is known is considered first. In this case, when the potential channels are identi ..."
Abstract
-
Cited by 53 (10 self)
- Add to MetaCart
Abstract—This paper investigates the optimal sensing order problem in multi-channel cognitive medium access control with opportunistic transmissions. The scenario in which the availabil-ity probability of each channel is known is considered first. In this case, when the potential channels are identical (except for the availability probabilities) and independent, it is shown that, although the intuitive sensing order (i.e., descending order of the channel availability probabilities) is optimal when adaptive mod-ulation is not used, it does not lead to optimality in general with adaptive modulation. Thus, a dynamic programming approach to the search for an optimal sensing order with adaptive modulation is presented. For some special cases, it is proved that a simple optimal sensing order does exist. More complex scenarios are then considered, e.g., in which the availability probability of each channel is unknown. Optimal strategies are developed to address the challenges created by this additional uncertainty. Finally, a scheme is developed to address the issue of sensing errors. Index Terms—Cognitive radio, medium access control, dy-namic programming. I.
Opportunistic Spectrum Access with Multiple Users: Learning under Competition
"... The problem of cooperative allocation among multiple secondary users to maximize cognitive system throughput is considered. The channel availability statistics are initially unknown to the secondary users and are learnt via sensing samples. Two distributed learning and allocation schemes which maxi ..."
Abstract
-
Cited by 52 (1 self)
- Add to MetaCart
The problem of cooperative allocation among multiple secondary users to maximize cognitive system throughput is considered. The channel availability statistics are initially unknown to the secondary users and are learnt via sensing samples. Two distributed learning and allocation schemes which maximize the cognitive system throughput or equivalently minimize the total regret in distributed learning and allocation are proposed. The first scheme assumes minimal prior information in terms of pre-allocated ranks for secondary users while the second scheme is fully distributed and assumes no such prior information. The two schemes have sum regret which is provably logarithmic in the number of sensing time slots. A lower bound is derived for any learning scheme which is asymptotically logarithmic in the number of slots. Hence, our schemes achieve asymptotic order optimality in terms of regret in distributed learning and allocation.
A measurement-based model for dynamic spectrum access
- in Proc. IEEE Conference on Military Communications (MILCOM
, 2006
"... Abstract — In this paper we consider dynamically sharing the spectrum in the time-domain by exploiting whitespace between the bursty transmissions of a set of users, represented by an 802.11b based wireless LAN (WLAN). Realizing that exploiting the under-utilization of the channel requires a good mo ..."
Abstract
-
Cited by 47 (6 self)
- Add to MetaCart
(Show Context)
Abstract — In this paper we consider dynamically sharing the spectrum in the time-domain by exploiting whitespace between the bursty transmissions of a set of users, represented by an 802.11b based wireless LAN (WLAN). Realizing that exploiting the under-utilization of the channel requires a good model of the these users ’ medium access, we propose a continuous-time semi-Markov model that captures the WLAN’s behavior yet remains tractable enough to be used for deriving optimal control strategies within a decision-theoretic framework. Our model is based on actual measurements in the 2.4 GHz ISM band using a vector signal analyzer to collect complex baseband data. We explore two different sensing strategies to identify spectrum opportunities depending on whether the primary user’s transmission scheme is known. The collected data is used to statistically characterize the idle and busy periods of the channel. Furthermore, we show that a continuous-time semi-Markov model is able to capture the data with good accuracy. The Kolmogorov-Smirnov test is used to validate the model and to assess the model’s goodness-of-fit quantitatively. A conclusion summarizes the main results of the paper. I.
Cognitive Medium Access: Constraining Interference based on Experimental Models
- IEEE Journal, Selected Areas Comm. Vol.26 No.1
"... Abstract — In this paper we design a cognitive radio that can coexist with multiple parallel WLAN channels while abiding by an interference constraint. The interaction between both systems is characterized by measurement and coexistence is enhanced by predicting the WLAN’s behavior based on a contin ..."
Abstract
-
Cited by 45 (4 self)
- Add to MetaCart
(Show Context)
Abstract — In this paper we design a cognitive radio that can coexist with multiple parallel WLAN channels while abiding by an interference constraint. The interaction between both systems is characterized by measurement and coexistence is enhanced by predicting the WLAN’s behavior based on a continuous-time Markov chain model. Cognitive Medium Access (CMA) is derived from this model by recasting the problem as one of constrained Markov decision processes. Solutions are obtained by linear programming. Furthermore, we show that optimal CMA admits structured solutions, simplifying practical implementations. Preliminary results for the partially observable case are presented. The performance of the proposed schemes is evaluated for a typical WLAN coexistence setup and shows a significant performance improvement.
Optimal Sensing-Transmission Structure for Dynamic Spectrum Access. available at http : //www.cs.ucdavis.edu/ liu/preprint/huangsensing.pdf
"... Abstract—In cognitive wireless networks where secondary users (SUs) opportunistically access spectral white spaces of primary users (PUs), there exists an inherent tradeoff between sensing and transmission due to the competing goals of PU protection and SU access maximization. This paper studies mea ..."
Abstract
-
Cited by 45 (6 self)
- Add to MetaCart
(Show Context)
Abstract—In cognitive wireless networks where secondary users (SUs) opportunistically access spectral white spaces of primary users (PUs), there exists an inherent tradeoff between sensing and transmission due to the competing goals of PU protection and SU access maximization. This paper studies means of sensing-transmission for SUs to better manage the competing goals by defining utility function to reward the SU for successful packet transmissions and to penalize it for colliding with PU. To maximize the SU utility, we present a threshold-based sensing-transmission structure that is optimal under a technical constraint. Both perfect sensing and imperfect sensing are considered, with or without SU acknowledgement of reception. This SU access scheme optimizes SU access efficiency while protecting PU performance. It sets a benchmark and provides insight for the design of sensing-transmission control in cognitive networks such as IEEE 802.22. I.
Spectrum Sharing in Wireless Networks via QoS-Aware Secondary Multicast Beamforming
"... Abstract—Secondary spectrum usage has the potential to considerably increase spectrum utilization. In this paper, quality-of-service (QoS)-aware spectrum underlay of a secondary multicast network is considered. A multiantenna secondary access point (AP) is used for multicast (common information) tra ..."
Abstract
-
Cited by 40 (16 self)
- Add to MetaCart
(Show Context)
Abstract—Secondary spectrum usage has the potential to considerably increase spectrum utilization. In this paper, quality-of-service (QoS)-aware spectrum underlay of a secondary multicast network is considered. A multiantenna secondary access point (AP) is used for multicast (common information) transmission to a number of secondary single-antenna receivers. The idea is that beamforming can be used to steer power towards the secondary receivers while limiting sidelobes that cause interference to primary receivers. Various optimal formulations of beamforming are proposed, motivated by different “cohabitation ” scenarios, including robust designs that are applicable with inaccurate or limited channel state information at the secondary AP. These formulations are NP-hard computational problems; yet it is shown how convex approximation-based multicast beamforming tools (originally developed without regard to primary interference constraints) can be adapted to work in a spectrum underlay context. Extensive simulation results demonstrate the effectiveness of the proposed approaches and provide insights on the tradeoffs between different design criteria. Index Terms—Beamforming, multicasting, secondary spectrum usage, semidefinite programming (SDP). I.
