Soumaya Hamouda

RMC-MAC: A Reactive Multi-Channel MAC Protocol for Opportunistic Spectrum Access

The development of mobile communication services has lead to the increase the use of wireless spectrum. However, the persuasion of the overly crowded spectrum is not due to the scarcity of usable radio frequencies but to the current static spectrum management policy. This reveals many idle frequency bands in both time and space. The cognitive radio network (CRN) is a key solution to exploit the existing spectrum dynamically. In this paper, we propose a new Reactive Multi-Channel cognitive MAC protocol (RMC-MAC) that integrates a novel cooperative sensing scheme which reliably detects the presence of incumbents even if the secondary users are transmitting. Then, a recovery scheme is proposed to ensure the continuity of SU transmission and to reduce the forced termination probability. This recovery solution also shows that bandwidth utilization is higher than the one achieved by a common protocol without handoff and another buffering based protocol.

Cooperative Bandwidth Sharing for Relaying in LTE-Advanced Using Game Theory

Heterogeneous networks (HetNets) are likely to provide ubiquitous access to mobile broadband services as they involve various small cells, each targeting a different environment in the network. In this paper, we are interested in improving the system performance at the cell edge. Hence, we consider a HetNet composed of an eNodeB (eNB) coexisting with different relay nodes (RNs) situated at the cell border. We propose a cooperative physical resource blocks (PRBs) sharing scheme in a dual-hop LTE-Advanced in which every node can transmit on some of the PRBs assigned to a coexisting node without causing it harmful interference. To do so, we use a powerful mathematical tool, i.e., game theory. First, we consider two nodes in the macrocell and define a new repeated game in which a selfish node is encouraged to cooperate under the threat of punishment. Then, we enlarge the number of RNs in the network and find the optimal pairs of nodes that will cooperate, due to a new coalition formation game. Simulation results show that the proposed cooperative PRB sharing scheme significantly improves the utilization of the spectrum and the achieved total throughput in the system. We also demonstrate that both games rapidly attain Pareto efficiency.

A novel relay selection scheme for LTE-advanced system under delay and load constraints

Deploying decode-and-forward relay nodes is a promising solution for LTE-advanced networks in order to meet the growing data rate demand and the challenging requirements for coverage extension. However, relay selection scheme plays a crucial role in enhancing the benefit of this technology. In this paper, we have proposed a new relay selection scheme which achieves a more balanced load in the network, respects the users quality of service requirements, but more importantly, avoids recurrent handovers and reduces the transmission delay. Simulation results proved a significant enhancement of the system performance in terms of outage probability, total system throughput and delay as compared to common relay selection strategies.

Dynamic spectrum access in heterogeneous networks: HSDPA and WiMAX

The next generation of radio wireless networks is expected to support spectrum decision operations that will allow a cognitive radio terminal to share the frequency bandwidth with primary users without impairing their QoS requirements. This can indeed enhance the utilization of the limited spectrum resources, and help meet the growing bandwidth demand. In this paper, we propose a new, cross-layer algorithm that allows a cognitive terminal to share and access to either HSDPA or WiMAX licensed spectrum while giving priority to the primary users. This algorithm not only considers the interference caused by the cognitive terminal, but also enhances the achievable throughput of this cognitive terminal. Simulation results show the effectiveness of our spectrum access scheme. Under our proposed scheme, the achievable data rate of the cognitive radio terminal is increased by 30% when compared with that obtained under common access schemes.

A new PRB sharing scheme in dual-hop LTE-advanced system using game theory

Relaying is a promising technique for the next generation cellular networks. It is highly recommended in the 3GPP LTE-Advanced because it is expected to satisfy the ever growing capacity and coverage demands in a cost-efficient way. Yet, in order to fully exploit the benefits of relaying, we should examine the radio resource allocation between the eNB and the relay nodes. In this paper, we propose a dynamic Physical Resource Blocks (PRBs) allocation scheme in a dual-hop LTE-advanced by using game theory. We define a new repeated game in which a selfish node can achieve cooperative spectrum opportunities sharing under the threat of punishment. Simulation results show that the proposed scheme significantly improves the spectrum utilization and total achieved throughput in the system. We also demonstrate that the game rapidly attain Pareto-efficiency.

WiMAX subchannelization modes: Performance analysis and spectrum efficiency enhancement

In this paper, both distributed and adjacent subchannelization modes for WiMAX system based on IEEE 802.16d standard are investigated. Sensitivity to the co-channel interference is evaluated for each mode in downlink communications. We provide a comparative analysis in terms of spectrum efficiency and present a new scheme to enhance the system performance. Our solution proposes a joint deployment of the distributed subchannelization modes using the benefits of each mode. In case of adjacent subchannelization mode, a water-filling algorithm is suggested to increase the spectral efficiency of the system. Snapshots-based simulations show that our scheme can significantly improve the spectral efficiency as compared to common usage of these subchannelization modes.

Minimization of delays in multi-service Cloud-RAN BBU pools

Cloud Radio Access Network (C-RAN) is a cost-effective solution for cellular operators which not only offers resource allocation and interference management flexibility, but also helps them enhance the energy efficiency of the network. The key character of the C-RAN architecture is a centralized Baseband Unit (BBU) pool which consists of high-capacity processing units and real-time virtualization. However, this centralized architecture can affect the system latency. As a consequence, the minimization of the execution delay of each user services in the BBU pool can be perceived as a major performance objective. In this paper, we consider different delay sensitive services and optimize their execution time inside the BBU pool. We present a new approach of BBU selection based on queuing theory in order to minimize the response time in the BBU pool under resource cost constraint. Simulation results showed that our proposed approach is more efficient than benchmark algorithms in terms of response time and throughput.

A new inter-cell selection strategy for reducing ping-pong effect

Carrier Aggregation (CA) is a promising solution to enhance peak throughput in LTE-Advanced or Small Cells Networks (SCN). Thanks to this technique, a terminal becomes able to transmit on one or multiple component carriers. However, many issues in terms of radio resource allocation and mobility should be addressed. In this paper, we aim at improving carrier component allocation during inter-cell handovers. We propose a new algorithm that minimizes the number of inter-cell handovers while meeting QoS user requirement. A novel cost function is introduced to optimize the carrier component selection and reduce the ping-pong effect. Simulation results conducted with two user mobility patterns show that not only the successful handover rate is improved but also radio capacity is increased by more than 15% as compared to a common inter-cell selection scheme.

A Cooperative Incumbent User Detection for Cognitive MAC Protocol

The Cognitive Radio (CR) is a recent technology that aims at increasing the spectrum utilization under the current static spectrum management. With appropriate CR MAC protocols, the unlicensed users, also called secondary users (SUs), are able to access the unused portion of spectrum in an opportunistic way. These protocols should also provide a coordinated access between the SUs and protect the licensed users (or primary users, PUs) from the induced interference. In this paper, we propose a novel multi-channel cognitive MAC protocol based on a cooperative spectrum access among the SUs, which enhances the throughput of the cognitive radio network (CRN) subject to a SU transmit power constraint. Our proposed protocol introduces a new reactive sensing period and a novel recovery scheme to instantly detect the presence of a PU, and proposes an adaptive handoff to preserve the continuity of the SU transmission. The results of simulation show the effectiveness of our protocol. The aggregate throughput of the SUs is improved and the handoff delay is considerably reduced.

Joint mode selection and power allocation for better traffic offloading in D2D communications

Device-to-Device (D2D) technology underlying the cellular network is an attractive solution for future generation network to increase cellular traffic offloading. When two devices are close enough, D2D communication allows a direct communication between them without the mediation of the cellular base station. However, since D2D communication shares the same uplink cellular network radio resource, D2D communication mode selection remains challenging to limit the mutual interference between D2D and cellular links. In this paper, a new D2D mode selection scheme based on a new criterion is proposed aiming at maximizing the cellular traffic offload while respecting the quality of service of cellular users. More precisely, we introduce a noise rise parameter which takes into account the cellular link distance, the D2D link distance, and user’s required throughput. The D2D links are admitted under the constraint of a certain noise rise threshold. To further enhance the achieved throughput of D2D users while respecting the overall interference level in the network, a new power control algorithm is also proposed. Simulation results show that our proposed mode selection scheme provides a tradeoff between traffic offloading and the overall radio capacity in the network. They also prove that the D2D communication mode is more attractive at the cell edge and when D2D users are close enough to each other. In addition, we show the effectiveness of our proposed power control scheme as compared to both static and Rate-Adaptive Water Filling power allocation schemes.