| 1. |
- Haghighi, Kasra, 1978, et al.
(författare)
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An LLR-based Cognitive Transmission Strategy for Higher Spectrum Reutilization
- 2011
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Ingår i: IEEE GLOBECOM 2011 - Cognitive Radio and Networks Symposium. - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- Reutilization of the spectrum licensed to services with low occupancy is of great interest for cognitive radios (CRs). To achieve this goal, we introduce a simple hidden Markov model which captures the primary users activity, signal uncertainties, and noise. For evaluating the performance of any CR, two new criteria are presented entitled spectrum utilization ratio (UR) and interference ratio (IR). Based on this model and new measures, a new a-posterior log-likelihood-ratio based CR is designed and implemented. Its performance is compared with standard energy-detection based spectrum-sensing CR. We demonstrate more than 300% increase in UR for up to 1% allowed interference at the SNR of -5dB.
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| 2. |
- Haghighi, Kasra, 1978, et al.
(författare)
-
On Optimum Causal Cognitive Spectrum Reutilization Strategy
- 2012
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 30:10, s. 1911-1921
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we study opportunistic transmission strategies for cognitive radios (CR) in which causal noisy observation from a primary user(s) (PU) state is available. PU is assumed to be operating in a slotted manner, according to a two-state Markov model. The objective is to maximize utilization ratio (UR), i.e., relative number of the PU-idle slots that are used by CR, subject to interference ratio (IR), i.e., relative number of the PU-active slots that are used by CR, below a certain level. We introduce an a-posteriori LLR-based cognitive transmission strategy and show that this strategy is optimum in the sense of maximizing UR given a certain maximum allowed IR. Two methods for calculating threshold for this strategy in practical situations are presented. One of them performs well in higher SNRs but might have too large IR at low SNRs and low PU activity levels, and the other is proven to never violate the allowed IR at the price of a reduced UR. In addition, an upper-bound for the UR of any CR strategy operating in the presence of Markovian PU is presented. Simulation results have shown a more than 116% improvement in UR at SNR of -3dB and IR level of 10% with PU state estimation. Thus, this opportunistic CR mechanism possesses a high potential in practical scenarios in which there exists no information about true states of PU.
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| 3. |
- Haghighi, Kasra, 1978, et al.
(författare)
-
Sensing or Transmission: Causal Cognitive Radio Strategies with Censorship
- 2014
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 13:6, s. 3031-3041
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel opportunistic transmission strategy for cognitive radios (CRs). The primary user (PU) is assumed to transmit in a time-slotted manner according to a two-state Markov model, and the CR is either sensing, that is, obtaining a causal, noisy observation of a primary user (PU) state, or transmitting, but not both at the same time. In other words, the CR observations of the PU are censored whenever the CR is transmitting. The objective of the CR transmission strategy is to maximize the utilization ratio (UR), i.e., the relative number of the PU-idle slots that are used by the CR, subject to that the interference ratio (IR), i.e., the relative number of the PU-active slots that are used by the CR, is below a certain level. We introduce an a-posteriori LLR-based CR transmission strategy, called CLAPP, and evaluate this strategy in terms of the achievable UR for different PU model parameters and received signal-to-noise ratios (SNRs). The performance of CLAPP is compared with a simple censored energy detection scheme. Simulation results show that CLAPP has 52% gain in UR over the best censored energy detection scheme for a maximum IR level of 10% and an SNR of -2dB. © 2002-2012 IEEE.
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| 4. |
- Haghighi, Kasra, 1978, et al.
(författare)
-
Wideband Sequential Spectrum Sensing with Varying Thresholds
- 2010
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Ingår i: Proceedings IEEE Global Communications Conference, Wireless Communications Symposium, Miami, Florida, USA. - 9781424456383
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Konferensbidrag (refereegranskat)abstract
- In this contribution, time varying threshold sequentialdetectors are employed for energy detection-based spectrumsensing in low-SNR regimes. Sequential detection is proven to befaster (on average) than any other multi-sample detector for a setof given probabilities of detection and false-alarm. In this report,exact performance of a sequential detector for spectrum sensingis analyzed using the direct method. The theoretical resultspresented herein are verified with Monte-Carlo simulations. Itis shown that for a SNR of −10 dB, among tests with Wald andtriangular thresholds with similar probabilities of mis-detectionand false-alarm, triangular performs 54% faster in terms ofmaximum detection time (90 percentile).
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