A. Hamid Aghvami

Performance evaluation of receiver based MAC using configurable framework in WSNs

Receiver-based MAC (RB-MAC) is a preamble-sampling MAC protocol for WSNs in which a receiver node is dynamically elected, among potential neighbors of the sender node, based on current channel conditions. In this paper, we evaluate the performance of RB-MAC and compare it with a senderbased preamble-sampling MAC protocol by using analytical methods, and implementation in real sensor nodes. We have used Configurable MAC (C-MAC), which is a framework to develop different MAC protocols in WSNs. This framework is realized as a component architecture that can produce application-specific communication protocols. The experimental results presented in the paper corroborate with the analytical and numerical results showing how RB-MAC outperforms sender-based MAC protocols in terms of transmission delay, and energy consumption.

Adaptive antennas: the calibration problem

Adaptive antennas are recognized as a means of increasing the performance of communications systems. However, practical realization of such systems relies on suitable calibration of distortion effects caused by the circuitry and antenna structures. This work presents a detailed analysis of the classes of distortion that degrade the performance of adaptive antennas. This uses the results of an adaptive antenna testbed employing an eight-element circular array to illustrate the impact of temperature on performance. Design techniques that aid calibration are then described. In particular, digital downconversion, array design, harmonic sampling, sample clock dither, and clock management are discussed as a means of designing an adaptive array with the calibration problem in mind.

SACRP: A Spectrum Aggregation-Based Cooperative Routing Protocol for Cognitive Radio Ad-Hoc Networks

Cooperative routing and spectrum aggregation are two promising techniques for Cognitive Radio Ad-Hoc Networks (CRAHNs). In this paper, we propose a spectrum aggregation-based cooperative routing protocol, termed as SACRP, for CRAHNs. To the best of our knowledge, this is the first contribution on spectrum aggregation-based cooperative routing for CRAHNs. The primary objective of SACRP is to provide higher energy efficiency, improve throughput, and reduce network delay for CRAHNs. In this regard, we design the MAC and Physical (PHY) layer, and proposed different spectrum aggregation algorithms for cognitive radio (CR) users. We propose two different classes of routing protocols; Class A for achieving higher energy efficiency and throughput, and Class B for reducing end-to-end latency. Based on stochastic geometry approach, we build a comprehensive analytical model for the proposed protocol. Besides, the proposed protocol is compared with the state of the art cooperative and non-cooperative routing algorithms with spectrum aggregation. Performance evaluation demonstrates the effectiveness of SACRP in terms of energy efficiency, throughput, and end-to-end delay.

Green spectrum management for mobile operators

This paper proposes intra-operator dynamic spectrum access, i.e., dynamic spectrum access by an operators networks of its available spectrum bands, as a means to improve power efficiency. It is based around four areas of interest: (i) dynamically moving users into particularly active bands from other bands to allow radio network equipment in those other bands to be switched off when possible, (ii) the dynamic sharing of spectrum in order to take advantage of better propagation bands and reduce necessary transmission power, (iii) the sharing of spectrum to allow channel bandwidths to be increased thus allowing transmission power to be significantly decreased, and (iv) the better hierarchical management of spectrum in cases where different types of cells coexist. Numerical results show a significant potential for such spectrum management solutions to reduce power consumption for the operator by some 50% or more, with further potential saving if there is a lower correlation in traffic loads among the operators networks/frequencies. It is noted that although the main objective of this paper is power saving, the concepts presented can also be used for other purposes, such as to increase achievable capacity.

Distributed Antennas: The Concept of Virtual Antenna Arrays

We introduce a communication paradigm where spatially adjacent mobile termi- nals or nodes cooperate and thereby form a virtual transceiver entity, which we refer to as virtual antenna array (VAA). It is the prime aim of this chapter to shed some historical background on the developments around the concept of VAAs, as well as to analyse and synthesise some specific topologies. As such, by means of prior derived closed form capacity expressions, we will derive cross-layer opti- mised communication protocols for distributed and cooperative relaying VAAs. These protocols are shown to be robust, of low complexity, and to perform near- optimum; they are hence easily applicable to cellular, ad hoc and wireless sensor networks. As of today, VAA-type communication topologies have gained signif- icantly in research momentum, mainly due to their ability to boost capacity and their inherent attribute of scalability. Indeed, it is in hot-spots where an increasing amount of users competes for the same capacity; however, hot-spots bring along an increasing number of terminals which, if cooperating, counteract the decrease in available system capacity by further increasing it.

Cross-Layer Design to Improve Wireless TCP Performance with Link-Layer Adaptation

Transmission control protocol (TCP), the almost universally used reliable transport protocol in the Internet, has been engineered to perform well in wired networks where packet loss is mainly due to congestion. TCP throughput, however, degrades over wireless links, which are characterized by a high and greatly varying bit error rate and by intermittent connectivity. Over such wireless links, the performance achieved by TCP can be improved through the use of cross-layer algorithms at the link-level, which interact with the TCP state machine. In this paper, a TCP-aware dynamic ARQ algorithm is therefore proposed, which utilizes TCP timing information to prioritize ARQ packet retransmissions. Numerical investigation of the proposed algorithm demonstrates the performance improvements that can be attained through this approach, in comparison with TCP-agnostic link-layer approaches.

Closed-Form Symbol Error Probabilities of STBC and CDD MC-CDMA With Frequency-Correlated Subcarriers Over Nakagami-

The performances of cyclic delay diversity and space-time block-coded multicarrier code-division multiple-access (MC-CDMA) systems operating in a Nakagami-m fading channel with correlated subcarriers are investigated. By using the moment-generating function of the correlated Nakagami-m random variable, explicit closed-form formulas for the exact average symbol error rate (SER) of M-ary signals for an MC-CDMA system employing the aforementioned diversity techniques are derived with a maximum ratio combining detection technique. The average SERs are expressed in terms of higher transcendental functions, such as the Gauss and Appell hypergeometric functions. Both numerical and simulation results are presented, showing excellent agreement.

m

M2M communications enables devices with an ability to communicate autonomously and thus acts as the enabling technology for Internet-of-Things. It is expected that a multitude of connected devices will exist in near future. In order to avoid any spectrum scarcity issues, there is a need to explore alternate spectrum opportunities. Thus the need of cognitive radio technology for M2M communications will be indispensable. On the other hand, the unique features of M2M communications create a number of challenges for existing communication networks, especially at the MAC layer. We aim to design a MAC protocol for generic M2M communications that uses cognitive radio technology at the physical layer. For this purpose, we propose PRMA, carry out its feasibility study, adapt and significantly enhance it with modifications especially tailored for M2M communications. Analytical and simulation results show a promising combination for application in practical M2M scenarios.

Fading Channels

We investigate Quality-of-Service (QoS) driven energy efficient design of SC-FDMA uplink. The resource allocation problem is formulated as a maximization of effective capacity based bits-per-joule capacity under statistical QoS provisioning, which is complicated due to specific constraints of SC-FDMA. We solve the problem using Canonical duality theory. Numerical results show that the proposed energy efficient design significantly enhances the energy efficiency while satisfying the QoS requirements of different users.

A PRMA based MAC protocol for cognitive machine-to-machine communications

Wireless Sensor Networks (WSNs) allow for untethered sensing of the environment. It is anticipated that, within the next few years, sensors will be deployed in a variety of scenarios, ranging from environmental monitoring to health care, from public to private sector and other areas. This paper investigate the utilization of receiver-based Medium Access Control (MAC) protocol in enhancing the performance of routing protocols such as IETF ROLLs RPL. Receiver-Based MAC (RB-MAC) is a preamble-sampling MAC protocol which dynamically elects the next-hop among a number of potential relay neighbors, based on current channel conditions and status of the sensor nodes. The proposed scheme is resilient to lossy links by nature, and hence reduces the number of retransmissions. We show by analysis how it outperforms the state-of-the-art sender-based preamble sampling MAC protocols in terms of energy and delay.