Zakhia G. Abichar

WiMax: The Emergence of Wireless Broadband

This paper presents WiMAX technology (worldwide interoperability for microwave access) that aims to provide business and consumer wireless broadband services on the scale of the metropolitan area network (MAN). WiMAX can be used in disaster recovery scenes where the wired networks have broken down. In recent hurricane disasters, WiMAX networks were installed to help in recovery missions. Similarly, WiMAX can be used as backup links for broken wired links. The certification working group has developed a WiMAX product certification program, which aims to ensure interoperability between WiMAX equipment from vendors worldwide. The certification process also considers interoperability with the high performance radio metropolitan area network (HiperMAN), the European Telecommunications Standards Institutes MAN standard

Roadside-Aided Routing (RAR) in Vehicular Networks

Inter-Vehicle Communications (IVC) and Roadside-to-Vehicle Communications (RVC) in vehicular networks based on IEEE 802.11 are emerging technologies for future Intelligent Transportation Systems (ITS). This paper presents a new efficient routing approach, called RAR (Roadside-Aided Routing), that is the first one to exploit the unique characteristics of vehicular networks. A novel affiliation method is proposed to affiliate a vehicle to several Roadside Units based on road constraints. This scheme allows (a) agent advertisement to be broadcast in one hop (instead of multi-hop), (b) routing to be done in single phase, comparing to two phases, (c) to eliminate the use of hierarchical addressing which is commonly used in single-phase schemes. Simulation results of ns-2 show that RAR approach can provide a high packet delivery rate in vehicular networks with a low and constant overhead.

WiMAX or LTE: Who will Lead the Broadband Mobile Internet?

Two main technologies are competing for the International Mobile Telecommunications (IMT)-Advanced initiative: WiMAX and LTE. This comparison reviews their development and deployment and provides an outlook on their adoption as 4G technologies.

CONTI: constant-time contention resolution for WLAN access

Designing an efficient and fair access control protocol is a challenging task in the field of wireless networks. Often in the known schemes, one of the important performance metrics is enhanced at the expense of another. In this paper, we present a distributed access scheme that is based on the binary countdown mechanism. The proposed scheme has two main features: 1) the ability to resolve the contention in a constant number of time slots, hence the name constant-time (CONTI) and 2) a very low collision rate even at large network sizes. The simulation results show that CONTI outperforms the IEEE 802.11 DCF scheme in all the essential performance metrics: CONTI achieves a higher throughput by up to 55%, reduces the collision rate by up to 84%, renders the delay less variant and exhibits high fairness.

Group-Based Medium Access Control for IEEE 802.11n Wireless LANs

The latest generation of Wireless Local Area Networks (WLANs) is based on IEEE 802.11n-2009 Standard. The standard provides very high data rates at the physical layer and aims to achieve a throughput at the Medium Access Control (MAC) layer that is higher than 100 Mbps. To do that, the standard introduces several mechanisms to improve the MAC efficiency. The most notable ones are the use of frame aggregation and Block-ACK frames. The standard, however, does not introduce a mechanism to reduce the probability of collision. This issue is significant because, with a high data rate, an AP would be able to serve a large number of stations, which would result in a high collision rate. In this paper, we propose a Group-based MAC (GMAC) scheme that reduces the probability of collision and also uses frame aggregation to improve the efficiency. The contending stations are divided into groups. Each group has one station that is the group leader. Only the leader stations contend, hence, reducing the probability of a collision. We evaluate the performance of our scheme with analytic and simulation results. The results show that GMAC achieves a high throughput, high fairness, low delay and maintains a high performance with high data rates.

A Medium Access Control Scheme for Wireless LANs with Constant-Time Contention

In todays wireless networks, stations using the IEEE 802.11 Standard contend for the channel using the Distributed Coordination Function (DCF). Research has shown that DCFs performance degrades especially with the large number of stations. This becomes more concerning due to the increasing proliferation of wireless devices. In this paper, we present a Medium Access Control (MAC) scheme for wireless LANs and compare its performance to DCF and to other efficient schemes. Our scheme, which attempts to resolve the contention in a constant number of slots (or constant time), is called CONTI. The contention resolution happens over a predefined number of slots. In a slot, the stations probabilistically send a jam signal on the channel. The stations listening retire if they hear a jam signal. The others continue to the next slot. Over several slots, we aim to have one station remaining in the contention, which will then transmit its data. We find the optimal parameters of CONTI and present an analysis on its performance. More comprehensive evaluation is presented in the simulation results where we compare CONTI, DCF, and other efficient schemes from the literature. We consider the number of slots used, the collision rate, the throughput, the delay, and the fairness. The highest throughput was achieved by CONTI. Moreover, our results provide measurements from each of the schemes that we consider and provide the insight on each schemes operation.

Planning of Relay Station Locations in IEEE 802.16 (WiMAX) Networks

Broadband wireless access networks have received a tremendous amount of research and development in the recent years. There have also been pilot networks deployed in many cities around the globe. In the IEEE 802.16j standard, Relay Stations (RS) play a promising role of extending the range of a Base Station (BS). This architecture is suitable to areas with limited infrastructure, such as rural areas, since it is difficult to install many BSs, with each having a wired connection. In this paper, we present an optimization model that finds the number of RSs and their locations to serve a customer base. We also show how our model can be adapted to make the planning in real-life scenarios where there are obstacles, such as mountains and lakes, in the planning area.

Group-based medium access for next-generation wireless LANs

Recently, there has been extensive research interest in increasing the data rates supported by IEEE 802.11 wireless LANs. For this purpose, IEEE 802.11 formed Task Group N to develop specifications for high-data-rate wireless LANs. The medium access in the legacy 802.11 is not scalable as it exhibits a large control overhead when the data rates increase and a large collision rate when the number of stations is large. In this paper, we introduce a group-based medium access control (GMAC) protocol for wireless LANs with high data rates and a large number of stations. With GMAC, stations are divided into groups that are free of hidden nodes. Each group has a leader and only group leaders contend using CSMA/CA. Once a group leader wins the contention, it reserves transmission time for all the stations in its group and issues a polling packet specifying the groups schedule. Stations in the same group transmit after their leader according to the polling packet. GMAC achieves significant throughput gain over DCF by reducing the collision rate and the control overhead. Simulation studies show that GMAC maintains a high throughput as the data rates and the number of stations increase

Optimizing Spectrum-Energy Efficiency in Downlink Cellular Networks

The popularity of smart mobile devices has brought significant growth of data services for mobile service providers. Mobile users of data services are charged based on the amount of data used. Raising served data amount seemingly increases the profit; energy consumption rises correspondingly. Besides, spectral resources are licensed and limited for mobile operators to allocate. Increasing data services over the spectrum for the profit does not count the cost of energy. To assess the profitability, considered is the revenue-to-cost ratio. Optimizing the ratio is an economic incentive for mobile operators. Revenue is regarded as efficiency in spectrum use, the cost as energy consumption; therefore we interpret the revenue-to-cost ratio as spectrum-energy efficiency. In this paper, we study the spectrum-energy efficiency optimization problem where BSs are with the ability to perform cell zooming, sleep mode, and user migration. We formulate the problem into an integer linear program which is solvable by CPLEX to maximize spectrum-energy efficiency; meanwhile traffic demands by associated users in multicell/multiuser networks are met. To avoid high computation time, a heuristic algorithm is proposed to efficiently solve the formulated problem. Numerical analysis through case studies demonstrates energy consumption and efficiency improvements, and comparisons between near-optimal solutions against optimality.

Energy-conservation in 802.11 WLANs via transmission-strategy-aware airtime allocation

In a typical 802.11 wireless local area network (WLAN), different wireless stations may communicate with the access point (AP) with different transmission rates, transmit-power levels, and data payload sizes. Such phenomenon is often referred to as transmission-strategy diversity. In this paper, we study the energy-conservation problem in 802.11 WLANs in the presence of transmission-strategy diversity. This problem is addressed from a unique angle - the system-level fairness which is quite different from most of current research that focuses on improving the performance of each individual wireless station. To emphasize fair energy consumption among contending stations, we introduce a new fairness notion, called energy-conservation fairness, which is in sharp contrast to the conventional throughput fairness and airtime fairness. Another contribution of this paper is an energy-efficient scheme that allocates airtime shares to contending stations so as to achieve combined airtime and energy-conservation fairness. Our simulation results show that, when the energy-conservation fairness is considered, both aggregate system throughput and overall system energy-efficiency can be improved significantly with all contending stations consuming a similar amount of energy.