Spectrum handoff reduction for cognitive radio ad hoc networks

Transcription

1 Published Research in Conference: International Symposium on Wireless Communication Systems - ISWCS, pp , 2010 Spectrum handoff reduction for cognitive radio ad hoc networks Mohamed A. Kalil, Hassan Al-Mahdi, Andreas Mitschele-Thiel Spectrum handoff is one of the main challenges in cognitive radio ad hoc networks. Spectrum handoff occurs when the owner of the spectrum or the primary user (PU) appears in the same channel that is already occupied by a secondary user (SU). In this case, the SU should vacate this channel and determine another free one. This process may continue till SU finishes its transmission. Spectrum handoff has a negative impact on the performance of SU in terms of delay and link maintenance; therefore the number of handoffs should be reduced. Opportunistic Spectrum Access with Backup channels (OSAB) is a new spectrum access concept for managing and increasing the spectrum capacity for ad hoc networks. Reducing the number of spectrum handoffs is one of the main features of OSAB. This is achieved by utilizing the unlicensed channels as backup channels in case of the appearance of the PUs. In this paper, an extensive mathematical model is presented to evaluate the performance of the OSAB in terms of the link maintenance probability and the expected number of spectrum handoffs. Numerical results show that OSAB outperforms the classical opportunistic spectrum access concept in terms of the aforementioned performance metrics.

2 Published Research in Conference: Analytical and Stochastic Modeling Techniques and Applications - ASMTA, pp , 2009 Analysis of Opportunistic Spectrum Access in Cognitive Ad Hoc Networks Mohamed Abd Rabou Kalil, Hassan Al-mahdi, Andreas Mitschele-thiel Cognitive radio (CR) is a promising technology for increasing the spectrum capacity for ad hoc networks. Based on CR, the unlicensed users will utilize the unused spectrum of the licensed users in an opportunistic manner. Therefore, the average spectrum usage will be increased. However, the sudden appearance of the licensed users forces the unlicensed user to vacate its operating channel and handoff to another free one. Spectrum handoff is one of the main challenges in cognitive ad hoc networks. In this paper, we aim to reduce the effect of consecutive spectrum handoff for cognitive ad hoc users. To achieve that, the licensed channels will be used as operating channels and the unlicensed channels will be used as backup channels when the primary user appears. Therefore, the number of spectrum handoff will be reduced, since unlicensed bands are primary user free bands. A Markov chain model is presented to evaluate the proposed scheme. Performance metrics such as blocking probability and dropping probabilities are obtained. The results show that the proposed scheme reduces all the aforementioned performance metrics.

3 Published Research in Journal of IEEE Communications Letters - IEEE Commun. Lett., vol. 13, no. 9, pp , 2009 Increasing spectrum capacity for ad hoc networks using cognitive radios: an analytical model Hassan Al-Mahdi, Mohamed A. Kalil, Florian Liers, Andreas Mitschele-Thiel In this letter, an analytical model to evaluate the performance of ad hoc devices equipped with cognitive radio capabilities, is investigated. By applying cognitive radio technology, the ad hoc devices will utilize the unused spectrum of the existing legacy systems in an opportunistic manner in addition to using the unlicensed spectrum. Therefore, the network throughput will be increased. The results show that the performance is improved in terms of blocking and dropping probabilities.

4 Published Research in Journal of Computer Communications - COMCOM, vol. 32, no. 7-10, pp , 2009 Design and analysis of a TDMA call assignment scheme for cellular networks Hamed Nassar, Hassan Al-Mahdi In this paper, we introduce a TDMA channel assignment scheme suitable for personal communication services (PCS) networks. This scheme, called Handoff TDMA (H-TDMA), assumes three type of traffic: new voice calls, handoff voice calls and data packets, all competing for a finite number of channels. In the present scheme, priority is given to handoff voice calls over data calls, while a number of channels is exclusively dedicated to data calls.the performance of the scheme is analyzed using a Markov chain model. We evaluate major performance metrics such as forced termination probability, blocking probability, and data packets loss probability. The analytical results obtained are validated by simulation and good agreement is obtained.

5 Published Research in Journal of Aeu-international Journal of Electronics and Communications - AEU-INT J ELECTRON COMMUN, vol. 63, no. 9, pp , 2009 Collision reduction mechanism for masked node problem in ad hoc networks Hassan Al-Mahdi, Mohamed A. Kalil, Florian Liers, Andreas Mitschele-Thiel IEEE MAC uses RTS/CTS mechanism to avoid DATA packet collisions. RTS/CTS mechanism has been introduced to solve the problems of carrier sense multiple access (CSMA) in ad hoc networks such as hidden/exposed node problem. However, it creates a new problem called masked node problem. In this paper, a collision reduction mechanism named RTS/CTS/TTM with resume is introduced. This mechanism aims to minimize the probability of DATA packet collisions due to the masked nodes in an ad hoc network. We develop a new control packet called time-to-mask (TTM), which contains the time that the node will be masked. The proposed mechanism has been evaluated with a mathematical analysis and a simulation on a small IEEE ad hoc network. The numerical results indicate that the RTS/CTS/TTM with resume reduces the probability of DATA packet collision.