S. M. Shajedul Hasan

Wireless distributed computing: a survey of research challenges

Recent advancements in radio technology provide great flexibility and enhanced capabilities in executing wireless services. One of these capabilities that can provide significant advantages over traditional approaches is the concept of collaborative computing in wireless networks. With collaborative radio nodes, multiple independent radio nodes operate together to form a wireless distributed computing (WDC) network with significantly increased performance, operating efficiency, and abilities over a single node. WDC exploits wireless connectivity to share processing- intensive tasks among multiple devices. The goals are to reduce per-node and network resource requirements, and enable complex applications not otherwise possible, e.g., image processing in a network of small form factor radio nodes. As discussed in this article, WDC research aims to quantify the benefits of distributed processing over local processing, extend traditional distributed computing (DC) approaches to allow operation in dynamic radio environments, and meet design and implementation challenges unique to WDC with the help of recently available enabling technologies, such as software radios and cognitive radios.

Designing and deploying a building-wide cognitive radio network testbed

Wireless communication technology is constantly advancing with the primary objective being to improve the quality of service for the end user. Cognitive radio is a technology capable of advancing wireless communications to the next generation of intelligent devices. Integrating cognition into wireless applications such as dynamic spectrum access, radio resource management, wireless distributed computing, and even traditional protocol stacks has already been shown to provide benefits related to the communications quality of service. The majority of cognitive radio related research has been limited to theoretical frameworks and simulations or in a few cases, demonstrating prototype DSA devices on a small scale. In order to continue advancing in this area, larger-scale experiments that are reproducible and able to be moved beyond theoretical simulations are required. Virginia Tech has built a testbed for software-defined and cognitive radio related research for the purpose of rapid next-generation communication system prototyping using a medium scale size network of flexible wireless nodes. In this article we present the details of the development, design decision rationale, and deployment of this testbed in hopes that it will be both used by the research community, and duplicated and improved in order to further the development of the many different facets of cognitive radio research.

Wireless distributed computing in cognitive radio networks

Individual cognitive radio nodes in an ad-hoc cognitive radio network (CRN) have to perform complex data processing operations for several purposes, such as situational awareness and cognitive engine (CE) decision making. In an implementation point of view, each cognitive radio (CR) may not have the computational and power resources to perform these tasks by itself. In this paper, wireless distributed computing (WDC) is presented as a technology that enables multiple resource-constrained nodes to collaborate in computing complex tasks in a distributed manner. This approach has several benefits over the traditional approach of local computing, such as reduced energy and power consumption, reduced burden on the resources of individual nodes, and improved robustness. However, the benefits are negated by the communication overhead involved in WDC. This paper demonstrates the application of WDC to CRNs with the help of an example CE processing task. In addition, the paper analyzes the impact of the wireless environment on WDC scalability in homogeneous and heterogeneous environments. The paper also proposes a workload allocation scheme that utilizes a combination of stochastic optimization and decision-tree search approaches. The results show limitations in the scalability of WDC networks, mainly due to the communication overhead involved in sharing raw data pertaining to delegated computational tasks.

Green Communications: A Call for Power Efficient Wireless Systems

Telecommunication usage has skyrocketed in recent years and will continue to grow as developing world reaches to wireless as the communication medium of choice. The telecommunications world is only now addressing the significant environmental impact it is creating as well as the incredible cost on power usage. This realization has led to a push towards Green Communications that strives for improving energy efficiency as well as energy independence of telecommunications. A survey of existing metrics for energy efficiency is discussed with specific adaptations for a communication centric viewpoint. This paper reviews recent energy efficient advances made at specific point within the communications cycle such as components, network operation and topology, and incorporating renewable and alternative energy into base stations. We further survey several holistic approaches that illustrate the dependencies between layers of the communications stack and operation/deployment. These approaches include cross layer design, cognitive radio, and wireless distributed computing.

Cross-layer resource allocation for wireless distributed computing networks

The allocation of communication power consumption and computing rate is inherently one of the cross-layer problems in wireless distributed computing networks (WDCNs). This paper exploits a subgradient approach to choose the optimal power-rate pair for maximizing the network computing capability and minimizing the power consumption. The impact of heterogeneous channel conditions for different nodes are modeled as a penalty term in the objective function to balance the performance and power consumption, and increase the amount of the power for the computing task. Simulation results show that both energy efficiency and the distributed computing power ratio (DCPR) can be increased by considering the wireless channel conditions. These results provide some guidelines for designing the protocol dedicated to WDCNs.

Multiband antenna-receiver integration using an RF multiplexer with sensitivity-constrained design

In this paper we consider an alternative approach which exploits the fact that the single-chip transceivers from which practical multiband radios are likely to be built consist of multiple receivers operating in parallel, each of which can be directly connected to a dedicated off-chip filter. In this case an RF multiplexer can be used to segment the tuning range into multiple bands. Once partitioned in this manner, the interface for lower frequency bands - the most troublesome as noted above - can be separately optimized not for match efficiency, but rather for effective sensitivity, exploiting the high levels of environmental noise known to exist at these frequencies [4]. We demonstrate the technique by designing an antenna interface which yields acceptable performance for operation in four bands - 138-174 MHz, 220-222 MHz, 406-512 MHz, and 764-862 MHz - when used with a monopole just 20 cm long with 5 mm radius, assuming front end noise figure in the range 1-2 dB. Such noise figures are well within the capabilities of existing low-cost electronics.

Wideband RF front end design considerations for a flexible white space software defined radio

This paper introduces a flexible RF front end for whitespace communication. The designed front end can operate over any frequency from 100 MHz to 2.5 GHz and the channel bandwidth can be programmable from 4.5 kHz to 10 MHz. This large frequency range and wide bandwidth makes this hardware suitable for implementing most wireless standards. A direct conversion RFIC developed by Motorola, drives the core of the RF front end. The various RF parameters can be changed by programming this RFIC through a serial peripheral interface (SPI). As part of this work we further develop an intelligent software driver to control different parameters of the RFIC. Thus the combination of highly flexible front end and flexible software driver makes this hardware an excellent choice for whitespace devices. The performance of this front end has been tested and measured and has been integrated into a daughterboard format for the Universal Software Radio Peripheral (USRP), a hardware device which enables the rapid design and implementation of software defined radio (SDR).

Efficient detection of primary users in cognitive radio networks

This paper proposes an approach to detect the primary user during the communication of the secondary users, using the concept of interference detection in the presence of a desired signal. The detection problem is first formulated as a multi-class classification problem. The pattern with medium bit error rate (BER) and low interference to signal power ratio (ISR) is identified as the most difficult case. A classifier based on a support vector machine (SVM) is proposed to solve this problem. Simulation results yield 76% classification accuracy with ISR larger than -10 dB and a heterogenous channel condition between the primary link and secondary link. Both the channel vacation time and the usage of idle time can be reduced by the proposed approach.

Integration of Simple Antennas to Multiband Receivers Using a Novel Multiplexer Design Methodology

This paper presents a new concept in RF multiplexer design to integrate a single monopole-type antenna to a receiver with large, multiband tuning ranges. Traditional techniques to integrate a single antenna with such receivers are limited in their ability to handle simultaneous channels distributed over very large tuning ranges, which is important for frequency-agile cognitive radio, surveillance, and other applications requiring wideband or multiband monitoring. In our approach, the goal is first to achieve sensitivity which is nominally dominated by external (environmental) noise, and then secondly to improve bandwidth to the maximum possible consistent with this goal. A procedure is described for designing antenna-multiplexer-preamplifier assemblies using this philosophy. It is shown that the approach can significantly increase the usable bandwidth and number of bands that can be supported by a single, traditional antenna. A three channel (10-28 MHz, 32-50 MHz, and 54-80 MHz) multiplexer for a VHF monopole antenna was designed and performance was validated through field experiment.

Innovation and Standardization: Oxymoron or Pleonasm?

Although the importance of innovation and standardization (I&S) of technology is well understood in the information and communications technology (ICT) community, there is a lack of awareness of the definitions of I&S, the relationship between I&S, and popular theories of I&S. The IEEE Communications Societys Emerging Technical Subcommittee on Innovations and Standards in Information and Communication Technology (ISICT) recently conducted a survey that captures the current state of awareness of I&S theories in the ICT community. The survey is intended to help understand the problems that hinder popular adoption of I&S theories in mainstream industry and academic research processes. This paper analyzes the results of the survey to achieve two goals, namely, to quantify the problems and challenges encountered in understanding and studying I&S in ICT and to identify potential solutions to address the problems.