Hassan Al-Mahdi

Increasing spectrum capacity for ad hoc networks using cognitive radios: an analytical model

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.

Analysis of Opportunistic Spectrum Access in Cognitive Ad Hoc Networks

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.

Spectrum handoff reduction for cognitive radio ad hoc networks

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.

Lha: logical hierarchical addressing protocol for mobile ad-hoc networks

A mobile Ad-hoc network (MANET) is an autonomous system of mobile routers that are self-organizing and decentralized without any need for infrastructure support. While much effort has been made to handle seamless handoff by developing routing algorithms, other fundamental issues such as dynamic and fast addressing mechanisms were neglected. In the paper, we present a new address auto-configuration protocol named Logical Hierarchical Addressing (LHA) which is designed to work in MANET. The proposed protocol allows nodes to get a unique address fast and dynamically. LHA efficiently supports merging and partitioning of networks. We present an analytical model to investigate the performance of LHA and compare it with the token-based protocol. Our results show that the LHA protocol reduces the latency to obtain an IP address by 50%.

Performance Evaluation of Hop-Aware Buffer Management Scheme in Multihop Ad Hoc Networks

End-to-end delay and loss probability are two important parameters for evaluating the performance of multihop ad hoc networks. One of the main reasons for increasing the value of those parameters; is the buffer management scheme in the intermediate nodes. The number of hops that the packet traversed is not taken into account in most existing buffer management schemes. Dropping a packet which traversed a large number of hops; results in more retransmission overhead and therefore more congestion in networks than dropping a packet with a small number of hops. In this paper, we propose a buffer management scheme named hop-aware buffering (HAB). HAB is based on virtual partitioning of the buffer at each node according to the number of hops that the packets traversed from source to relaying node. The partitions are correlated and dynamically changed according to the traffic load. An analytical model based on a 4-dimensional Markov chain and simulation is carried out. The results show that HAB outperforms droptail in terms of end-to-end delay and loss probability.

Performance Evaluation of Secondary Users Operating on a Heterogeneous Spectrum Environment

Radio spectrum is a limited natural resource and with the increasing number of wireless devices, an efficient spectrum management concept to make a better utilization of this resource is essential. Opportunistic spectrum access (OSA) concept is a solution to increase the spectrum capacity and thus reducing the data collision for wireless ad hoc networks. Cognitive radio (CR) technology is developed to realize OSA. Based on CR, the secondary users access opportunistically the spectrum owned by primary users. However, the consequence appearance of primary users affects greatly the performance of secondary users within OSA. Thus, a new spectrum management scheme is a must to reduce such effect. In this paper, a new spectrum management scheme over a heterogeneous spectrum environment is proposed. The proposed scheme is based on using channels from both licensed and unlicensed bands as spectrum environment for ad hoc networks. An analytical model based on Markov chains is developed to evaluate the proposed scheme.

Design and Analysis of a Channel Assignment Scheme for CDMA/TDMA Mobile Networks

In this paper, a channel assignment scheme is proposed for use in CDMA/TDMA mobile networks carrying voice and data traffic. In each cell, three types of calls are assumed to compete for access to the limited number of available channels by the cell: new voice calls, handoff voice calls, and data calls. The scheme uses the movable boundary concept in both the code and time domains in order to guarantee the quality of service (QoS) requirements of each type. A traditional Markov analysis method is employed to evaluate the performance of the proposed scheme. Measures, namely, the new call blocking probability, the handoff call forced termination probability, the data call loss probability, the expected number of handoff and the handoff link maintenance probability are obtained from the analysis. The numerical results, which are validated by simulation, indicate that the scheme helps meet the QoS requirements of the different call types.

Design and analysis of a TDMA call assignment scheme for cellular networks

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.

Modeling of an efficient queue management scheme for multihop ad hoc networks

End-to-end delay is an important parameter in evaluating the performance of multihop ad hoc networks. To improve that, an efficient queue management scheme should be developed. Most existing queue management schemes do not take into account the number of hops that a packet traversed to reach its destination. In this paper, an efficient queue management scheme is proposed. The principal feature of the proposed scheme is to reduce the loss probability of the packets with large number of hops, by assigning more buffer space for those packets. This will lead to decrease the end-to-end delay and energy consumption. A Markovian model, is proposed to investigate the performance of the proposed scheme and to demonstrate that effective queueing scheme can improve the performance of ad hoc networks. The numerical results show that the proposed scheme outperforms the drop tail scheme in terms of end-to-end delay and loss probability.

A Dynamic Hop-Aware Buffer Management Scheme for Multi-Hop Ad Hoc Networks

In this letter, we propose a dynamic hop-aware buffering scheme to reduce the packets loss and delay in MANETs. In that scheme, the buffer is partitioned virtually based on the number of traversed hops and the significance of the packet. Furthermore, each virtual partition size changes dynamically according to the traffic load and the partition’s safeguard thresholds. We evaluate the performance of the proposed scheme through a multi-dimensional continuous-time Markov chain and simulation, where important performance metrics, i.e., end to end delay and blocking probability are derived.