Rahim Tafazolli

A survey of QoS routing solutions for mobile ad hoc networks

In mobile ad hoc networks (MANETs), the provision of quality of service (QoS) guarantees is much more challenging than in wireline networks, mainly due to node mobility, multihop communications, contention for channel access, and a lack of central coordination. QoS guarantees are required by most multimedia and other time- or error-sensitive applications. The difficulties in the provision of such guarantees have limited the usefulness of MANETs. However, in the last decade, much research attention has focused on providing QoS assurances in MANET protocols. The QoS routing protocol is an integral part of any QoS solution since its function is to ascertain which nodes, if any, are able to serve applications¿ requirements. Consequently, it also plays a crucial role in data session admission control. This document offers an up-to-date survey of most major contributions to the pool of QoS routing solutions for MANETs published in the period 1997¿2006. We include a thorough overview of QoS routing metrics, resources, and factors affecting performance and classify the protocols found in the literature. We also summarize their operation and describe their interactions with the medium access control (MAC) protocol, where applicable. This provides the reader with insight into their differences and allows us to highlight trends in protocol design and identify areas for future research.

On the relaying capability of next-generation GSM cellular networks

The latest developments and experimentation in mobile ad hoc networks show that MANETs will be an alternative candidate in many private and public multimedia networks. Current interest in MANET systems has grown considerably because they can rapidly and economically extend the boundaries of any terrestrial network; integrating MANET and GSM offers a great number of benefits (e.g., increasing capacity, improving coverage) at the cost of increasing the complexity of the mobile terminal and its battery consumption. The objective of this article is to address new concepts in the GSM system, dealing with both standardized features as well as theoretically and technologically feasible improvements, which contribute to evolutionary changes in general. Dynamic evolution of GSM presents a platform for Universal Mobile Telecommunication System introduction and major trends in GSM development are addressed, in particular progress towards a generic platform to accommodate relaying capability in GSM cellular networks. A GSM simulation tool has been constructed for quantifying the integrated system characteristics.

An Energy-Efficient Clustering Solution for Wireless Sensor Networks

Hot spots in a wireless sensor network emerge as locations under heavy traffic load. Nodes in such areas quickly deplete energy resources, leading to disruption in network services. This problem is common for data collection scenarios in which Cluster Heads (CH) have a heavy burden of gathering and relaying information. The relay load on CHs especially intensifies as the distance to the sink decreases. To balance the traffic load and the energy consumption in the network, the CH role should be rotated among all nodes and the cluster sizes should be carefully determined at different parts of the network. This paper proposes a distributed clustering algorithm, Energy-efficient Clustering (EC), that determines suitable cluster sizes depending on the hop distance to the data sink, while achieving approximate equalization of node lifetimes and reduced energy consumption levels. We additionally propose a simple energy-efficient multihop data collection protocol to evaluate the effectiveness of EC and calculate the end-to-end energy consumption of this protocol; yet EC is suitable for any data collection protocol that focuses on energy conservation. Performance results demonstrate that EC extends network lifetime and achieves energy equalization more effectively than two well-known clustering algorithms, HEED and UCR.

RDMAR: a bandwidth-efficient routing protocol for mobile ad hoc networks

We present a loop-free routing protocol for ad hoc mobile networks. The protocol is highly adaptive, efficient and scaleable; and is well-suited in large mobile networks whose rate of topological changes is moderate. A key concept in its design is that protocol reaction to link failures is typically localised to a very small region of the network near the change. This desirable behaviour is achieved through the use of a novel mechanism for route discovery, called Relative Distance Micro-discovery (RDM). The concept behind RDM is that a query flood can be localised by knowing the relative distance (RD) between two terminals. To accomplish this, every time a route search between the two terminals is triggered, an iterative algorithm calculates an estimate of their RD, given an average nodal mobility and information about the elapsed time since they last communicated and their previous RD. Based on the newly calculated RD, the query flood is then localised to a limited region of the network centred at the source node of the route discovery and with maximum propagation radius that equals to the estimated relative distance. This ability to localise query flooding into a limited area of the network serves to minimise routing overhead and overall network congestion. Simulation results illustrate its performance and demonstrate its good behaviour comparing to other protocols proposed by IETF Working Group. We refer to the protocol as the Relative Distance Micro-discovery Ad Hoc Routing (RDMAR) protocol.

Dynamic spectrum allocation in composite reconfigurable wireless networks

Future wireless systems are expected to be characterized by increasing convergence between networks and further development of reconfigurable radio systems. In parallel with this, demand for radio spectrum from these systems will increase, as users take advantage of high quality multimedia services. This article aims to investigate and review the possibilities for the dynamic allocation of spectrum to different radio networks operating in a composite reconfigurable wireless system. The article first looks into the current interest of regulators in this area, before describing some possible schemes to implement dynamic spectrum allocation and showing some example performance results. Following this, the technical requirements that a DSA system would have, in terms of reconfigurable system implementation, are discussed.

Analytical Study of the IEEE 802.11p MAC Sublayer in Vehicular Networks

This paper proposes an analytical model for the throughput of the enhanced distributed channel access (EDCA) mechanism in the IEEE 802.11p medium-access control (MAC) sublayer. Features in EDCA such as different contention windows (CW) and arbitration interframe space (AIFS) for each access category (AC) and internal collisions are taken into account. The analytical model is suitable for both basic access and the request-to-send/clear-to-send (RTS/CTS) access mode. Different from most of existing 3-D or 4-D Markov-chain-based analytical models for IEEE 802.11e EDCA, without computation complexity, the proposed analytical model is explicitly solvable and applies to four access categories of traffic in the IEEE 802.11p. The proposed model can be used for large-scale network analysis and validation of network simulators under saturated traffic conditions. Simulation results are given to demonstrate the accuracy of the analytical model. In addition, we investigate service differentiation capabilities of the IEEE 802.11p MAC sublayer.

Integrated Radio Resource Allocation for Multihop Cellular Networks With Fixed Relay Stations

Recently, the notion that a logical next step towards future mobile radio networks is to introduce multihop relaying into cellular networks, has gained wide acceptance. Nevertheless, due to the inherent drawbacks of multihop relaying, e.g., the requirement for extra radio resources for relaying hops, and the sensitivity to the quality of relaying routes, multihop cellular networks (MCNs) require a well-designed radio resource allocation strategy in order to secure performance gains. In this paper, the optimal radio resource allocation problem in MCNs, with the objective of throughput maximization, is formulated mathematically and proven to be NP-hard. Considering the prohibitive complexity of finding the optimal solution for such an NP-hard problem, we propose an efficient heuristic algorithm, named integrated radio resource allocation (IRRA), to find suboptimal solutions. The IRRA is featured as a low-complexity algorithm that involves not only base station (BS) resource scheduling, but also routing and relay station (RS) load balancing. Specifically, a load-based scheme is developed for routing. A mode-aware BS resource-scheduling scheme is proposed for handling links in different transmission modes, i.e., direct or multihop. Moreover, a priority-based RS load balancing approach is presented for the prevention of the overloading of RSs. Within the framework of the IRRA, the above three functions operate periodically with coordinated interactions. To prove the effectiveness of the proposed IRRA algorithm, a case study was carried out based on enhanced uplink UMTS terrestrial radio access/frequency-division duplex with fixed RSs. The IRRA is evaluated through system level simulations, and compared with two other cases: 1) nonrelaying and 2) relaying with a benchmark approach. The results show that the proposed algorithm can ensure significant gains in terms of cell throughput

Admission control schemes for 802.11-based multi-hop mobile ad hoc networks: a survey

Mobile ad hoc networks (MANETs) promise unique communication opportunities. The IEEE 802.11 standard has allowed affordable MANETs to be realised. However, providing quality of service (QoS) assurances to MANET applications is difficult due to the unreliable wireless channel, the lack of centralised control, contention for channel access and node mobility. One of the most crucial components of a system for providing QoS assurances is admission control (AC). It is the job of the AC mechanism to estimate the state of the networks resources and thereby to decide which application data sessions can be admitted without promising more resources than are available and thus violating previously made guarantees. Unfortunately, due to the aforementioned difficulties, estimating the network resources and maintaining QoS guarantees are non-trivial tasks. Accordingly, a large body of work has been published on AC protocols for addressing these issues. However, as far as it is possible to tell, no wide-ranging survey of these approaches exists at the time of writing. This paper thus aims to provide a comprehensive survey of the salient unicast AC schemes designed for IEEE 802.11- based multi-hop MANETs, which were published in the peer-reviewed open literature during the period 2000-2007. The relevant considerations for the design of such protocols are discussed and several methods of classifying the schemes found in the literature are proposed. A brief outline of the operation, reaction to route failures, as well as the strengths and weaknesses of each protocol is given. This enables patterns in the design and trends in the development of AC protocols to be identified. Finally, directions for possible future work are provided.

On the Energy Efficiency-Spectral Efficiency Trade-off over the MIMO Rayleigh Fading Channel

Along with spectral efficiency (SE), energy efficiency (EE) is becoming one of the key performance evaluation criteria for communication system. These two criteria, which are conflicting, can be linked through their trade-off. The EE-SE trade-off for the multi-input multi-output (MIMO) Rayleigh fading channel has been accurately approximated in the past but only in the low-SE regime. In this paper, we propose a novel and more generic closed-form approximation of this trade-off which exhibits a greater accuracy for a wider range of SE values and antenna configurations. Our expression has been here utilized for assessing analytically the EE gain of MIMO over single-input single-output (SISO) system for two different types of power consumption models (PCMs): the theoretical PCM, where only the transmit power is considered as consumed power; and a more realistic PCM accounting for the fixed consumed power and amplifier inefficiency. Our analysis unfolds the large mismatch between theoretical and practical MIMO vs. SISO EE gains; the EE gain increases both with the SE and the number of antennas in theory, which indicates that MIMO is a promising EE enabler; whereas it remains small and decreases with the number of transmit antennas when a realistic PCM is considered.

On Interference Avoidance Through Inter-Cell Interference Coordination (ICIC) Based on OFDMA Mobile Systems

The widely accepted OFDMA air interface technology has recently been adopted in most mobile standards by the wireless industry. However, similar to other frequency-time multiplexed systems, their performance is limited by inter-cell interference. To address this performance degradation, interference mitigation can be employed to maximize the potential capacity of such interference-limited systems. This paper surveys key issues in mitigating interference and gives an overview of the recent developments of a promising mitigation technique, namely, interference avoidance through inter-cell interference coordination (ICIC). By using optimization theory, an ICIC problem is formulated in a multi-cell OFDMA-based system and some research directions in simplifying the problem and associated challenges are given. Furthermore, we present the main trends of interference avoidance techniques that can be incorporated in the main ICIC formulation. Although this paper focuses on 3GPP LTE/LTE-A mobile networks in the downlink, a similar framework can be applied for any typical multi-cellular environment based on OFDMA technology. Some promising future directions are identified and, finally, the state-of-the-art interference avoidance techniques are compared under LTE-system parameters.