Naufal Saad

... Antennas JA Guama, NM Saad ... MMAC is a MAC protocol that uses multi-hop RTSs to establish links between distant nodes and then transmits CTS, DATA, and ACK over a single hop. MMAC does not solve the problems of deafness and hidden terminals. ...

In this paper, we conducted a comparison study of the existing directional MAC protocols that use Smart Antennas by contrasting their features. We found that, most of these protocols are not applicable in mobile environment This investigation discusses the challenges in improving some of these smart antenna-based MAC protocols. We proposed to upgrade two protocols, Tone-DMAC protocol and Angular-MAC protocol. We proposed to model the behavior of these two protocols analytically and carry the improvement performance by using two omni-directional control packets. We suggested that using these two packets and Adaptive Array Antennas in the above protocols will make them applicable in mobile environment and as well as improve routing performance.

In this paper, we consider the potential use of adaptive arrays to improve the performance of multihop-RTS MAC protocol. In addition to this, we proposed to improve the performance of this MAC protocol by using two omni-directional control packets. These control packets are busy node list (BNL) and overall link state table (OLST). The performance of the protocol is evaluated and compared with existing MMAC that uses switched-beam antenna and IEEE 802.11. The results show that MMAC can produce improvement in throughput when using adaptive arrays and the two omnidirectional control packets.

Cognitive radio (CR) is expected to be the key enabling technology for increased spectrum utilization. As primary user activity is not spatially localized, a collaborative measure amongst multiple cognitive radio nodes has been suggested as a more accurate model of activity. This scheme was proposed to combat noise fading and shadowing as well as improves the probability of detection by collaborating to detect primary user signal. This paper studies cooperative spectrum sensing and signal detection in cognitive radio system by implementing hard decision combining in data fusion centre. Through computer simulation, we evaluate the performances of cooperative signal detection by employing OR and AND rules as decision combining. Energy detector is used to observe the presence of primary user signal. The results are compared to non-cooperative signal detection for evaluation. They show that greater than 10 dB of SNR and 15 collaborated users in cognitive radio system is optimal value for probability of detection.

Energy efficiency is the major point of consideration in Wireless Sensor Networks (WSN). The protocols of Media Access Control (MAC) layer provide the most effective energy utilization. Idle listening is a major source of energy wastage in wireless sensor networks; the nodes do not remain in the idle listening state when no data is available to them. Lowering the duty cycle reduces the active period of the sensor nodes; a fixed duty cycle does not adapt to the varying traffic rate in sensor networks and a high duty cycle results in significant energy wastage when traffic rate is low. For a low traffic load, low message data delivery and long queuing delay occur, in fixed synchronous duty cycle increasing the possibility of collision. A basic mechanism is followed in this paper to achieve energy efficiency due to low duty cycle for periodic traffic. Moreover, we have aimed to reduce the energy cost of sensor nodes using Simple Energy Aware Medium Access Control (SEA-MAC) protocol. The performance enhancement work has been analyzed and validated in Network Simulator (NS-2).

Opportunistic Spectrum Access (OSA) brings new research challenges in MAC protocol design. It allows unlicensed users to share licensed spectrum in space and time with no or little interference to Primary Users (PUs). When designing an OSA MAC protocol, one of the most difficult but important problem is how the unlicensed users decide when and which channel they should sense and access without conflicting the communications among PUs. To solve this problem, the unlicensed users should have the ability of adaptively and dynamically seeking and exploiting opportunities in both licensed and unlicensed spectrum and along both the time and the frequency dimensions. Secondary Users (SUs) as unlicensed users are required to sense radio frequency band, and when PU are detected, they must vacate the channel immediately within certain amount of time. Due to hardware and energy constraints, full spectrum availability cannot be sensed as well as they do not monitor when there is no data to be transmitted. In this paper, we study MAC protocol design for OSA in Cognitive Radio (CR) ad hoc network under Partially Observable Markov Decision Process (POMDP) algorithm that maximizes achievable throughput for SUs with sufficient protection to PUs. Furthermore, we study tractable greedy algorithm to reduce the complexity of POMDP calculation. The derivation of greedy approach proves that sensing problem can be solved either optimally or approximate the optimal solution. Computer simulation is used to evaluate the performances both of optimal and sub optimal strategy.