Hrishikesh Venkataraman

Cognitive Radio and its Application for Next Generation Cellular and Wireless Networks

This book provides a broad introduction to Cognitive Radio, which attempts to mimic human cognition and reasoning applied to Software Defined Radio and reconfigurable radio over wireless networks. It provides readers with significant technical and practical insights into different aspects of Cognitive Radio, starting from a basic background, the principle behind the technology, the inter-related technologies and application to cellular and vehicular networks, the technical challenges, implementation and future trends. The discussion balances theoretical concepts and practical implementation. Wherever feasible, the different concepts explained are linked to application of the corresponding scheme in a particular wireless standard. This book has two sections: the first section begins with an introduction to cognitive radio and discusses in detail various, inter-dependent technologies such as network coding, software-based radio, dirty RF, etc. and their relation to cognitive radio. The second section deals with two key applications of cognitive radio next generation cellular networks and vehicular networks. The focus is on the impact and the benefit of having cognitive radio-based mechanisms for radio resource allocation, multihop data transmission, co-operative communication, cross-layer solutions and FPGA-level framework design, as well as the effect of relays as cognitive gateways and real-time, seamless multimedia transmission using cognitive radio.

Performance analysis of real-time multimedia transmission in 802.11p based multihop hybrid vehicular networks

Real-time multimedia communications over vehicular ad-hoc networks (VANET) will play an extremely significant role in the next generation intelligent transport systems. In recent years, there has been an upsurge of interest in the quality-oriented adaptive multimedia delivery, including over VANET. In this paper, a hybrid IEEE 802.11p-based multihop network communication solution is presented, which makes use of both in frastructure and ad-hoc modes in order to deliver quality-oriented real-time multimedia content to high-speed vehicles. Simulation-based testing shows how multimedia delivery to vehicles when using the multihop hybrid mechanism achieves significantly higher throughput in comparison to the case when the in frastructure mode is employed and the vehicles communicate directly with the base station. This result is obtained while the average delay and packet loss in the two cases are similar.

MBE: Model-Based Available Bandwidth Estimation for IEEE 802.11 Data Communications

Wireless bandwidth estimation is a critical issue for quality-of-service (QoS) provisioning in IEEE 802.11 wireless local area networks (WLANs). Current bandwidth estimation solutions focus on either probing techniques or cross-layer techniques and require either significant bandwidth resources or protocol modifications. To alleviate these problems, this paper proposes an analytical model-based bandwidth estimation algorithm (MBE) for multimedia services over IEEE 802.11 networks. The MBE module for available bandwidth estimation is developed based on novel transmission control protocol/user datagram protocol throughput models for wireless data communications. The novel aspects in comparison with other works include the fact that no probing traffic is required and that no modification of medium access control (MAC) protocol is needed. Extensive simulations and real tests were performed, demonstrating that MBE has very good bandwidth estimation results for content delivery in conditions with different packet sizes, dynamic wireless link rate, and different channel noises. Additionally, MBE has lower overhead and lower error rate than other state-of-the-art bandwidth estimation techniques.

Cluster-Based Design for Two-hop Cellular Networks

Optimal resource allocation with an objective of maximizing the system capacity is an NP-hard problem in multihop cellular networks. Hence, different heuristic algorithms have been developed over the years that would improve the network system capacity. In this paper, a novel cluster-based architecture is proposed for a two-hop cellular network whereby the transmission distance between any communicating pair is restricted to half the cell radius. In this design, a given radio resource is used by two simultaneously communicating pairs in every hexagonal cell, but for only half the time slot period. The characteristic feature of this cluster-based design is that it enables a frequency reuse ratio of one. The proposed hierarchical system is analyzed and tested under realistic propagation conditions including lognormal shadowing. It has been observed that the system capacity of a cluster-based design is 2.5 times that obtained from the single-hop cellular system with no relaying. In addition, the cluster-based design achieves higher capacity compared to state-of-the-art two-hop algorithms. This is an important finding since the hierarchical cluster-based approach has fewer degrees of freedom in the selection of the routing path for the end-to-end connection. Practical routing algorithms should be able to benefit from this.

iPAS: An user perceived quality-based intelligent Prioritized Adaptive Scheme for IPTV in Wireless Home Networks

There are several real-time dynamic adaptation mechanisms that exist today for improving end user perceived quality for IPTV services in wireless local networks. However, an adaptation scheme based on stream priorities, combined with terminals characteristics and the expected service quality levels, has not been explicitly considered by the existing approaches. This paper proposes a novel solution - the intelligent Prioritized Adaptive Scheme (iPAS) for adapting the encoding and transmission bitrates of video traffic based on stream priority and current network bandwidth resources as estimated by the bandwidth estimation technique, iBE. Results show how iPAS outperforms an equal priority solution in terms of distribution of both bandwidth between streams with different requirements and associated user perceived quality.

iBE: A Novel Bandwidth Estimation Algorithm for Multimedia Services over IEEE 802.11 Wireless Networks

Recently, multimedia streaming services over IEEE 802.11 based wireless networks have increased dramatically. This results in manifold increase in the bandwidth requirement, especially for high-quality multimedia services. Given the bandwidth constraint in the wireless networks, one of the most critical factors in improving the end-to-end performance of multimedia application is the fast and accurate estimation of bandwidth. This paper proposes a novel bandwidth estimation algorithm, iBE. The significant feature of iBE is that it relies on multimedia packets only from the application layer. In addition, iBE recognizes the dynamic fluctuations of the wireless channel quickly, which in-turn enables iBE to be used for real-time services. The experimental results demonstrate that the accuracy of the bandwidth estimated by iBE is significantly superior to other methods like Spruce. Secondly, even in high traffic conditions, the bandwidth estimated by iBE is very close to the actual measured bandwidth, unlike the other state-of-the-art methods.

Dynamic stream control for energy efficient video streaming

Gartner predicts that by 2013 mobile devices will overtake PCs as the most popular type of device used for accessing Internet-based services. Meanwhile, mobile phones are becoming increasingly complex and powerful. However, battery technology has not been increasing at the same pace and hence, there is an urgent need for solutions to balance the battery performance of mobile devices and their functionality. An efficient solution would be to analyze the application(s) running on the device and manipulate all available device parameters, in order to maximize the power saving while minimizing the effect on the Quality of Service. As an initial step towards this unified solution, this paper takes an extremely important functionality as a starting point - video streaming. Different mechanisms for adaptive multimedia streams in mobile devices are investigated. Furthermore, an enhanced version of the Battery and Stream-Aware Adaptive Multimedia Delivery algorithm (BaSe-AMy) is tested on a real-world mobile device. The experiments result in an increase to the maximum playtime of a video stream of up to 10%, as compared to non-energy-aware streaming solutions, while also maintaining a high stream PSNR value.

Energy Consumption Analysis and Adaptive Energy Saving Solutions for Mobile Device Applications

Recent trends, motivated by user preferences towards carrying smaller and more complex devices, have focused on integrating different user-centric applications in a single general-purpose mobile hand-held device. Hence, Laptops, smart phones and PDAs are rapidly replacing computers as the most commonly-used Internet-access devices. This has resulted in much higher energy consumption and consequently, a reduced battery life of a wireless device. In fact, the biggest problem today in the mobile world is that they are battery driven and the battery technologies are not matching the required energy demand. This chapter focuses on different energy consuming components in the high-end wireless devices, with specific emphasis on adaptive energy efficient display and decoding mechanisms.

Dynamic Time Slot Partitioning for Multimedia Transmission in Two-Hop Cellular Networks

In recent years, there has been an exponential increase in the number of mobile phone users. In addition, a significant growth in the demand for high-rate multimedia services over wireless networks, such as video conferencing, multimedia streaming, etc., was noted. Different solutions were proposed to support high-quality high data rate delivery to mobile users, including resource allocation techniques for packet-radio-based next generation cellular networks. In this paper, an efficient time slot allocation method-Dynamic Time Slot Partitioning (DTSP) algorithm based on statistical multiplexing is proposed for a two-hop cellular architecture. In DTSP, the available bandwidth resources are increased by partitioning each time slot into several minislots wherein different numbers of minislots are allocated to different users. The DTSP algorithm is based on asynchronous time-division multiplexing, wherein users with variable number of packets in their buffers can transmit data sequentially without any loss in the overall available resources. The key advantage of DTSP is that it can flexibly adapt to different quality of service requirements, especially when combined with adaptive modulation. It has been observed that the system capacity achieved by the DTSP algorithm in the downlink mode using adaptive modulation is up to 41 percent higher than when existing solutions are employed. In addition, DTSP results in significantly lower time for data transmission than the state-of-the-art region and time partitioning techniques.

A novel bandwidth estimation algorithm for IEEE 802.11 TCP data transmissions

Efficient bandwidth estimation is significant for Quality of Service (QoS) of multimedia services in IEEE 802.11 WLANs. Many bandwidth estimation solutions have been developed such as probing-based technique and cross-layer scheme. However, these solutions either introduce additional traffic or require modification to the standard protocols. This paper develops a model based bandwidth estimation algorithm at application layer when TCP traffic is delivered in the IEEE 802.11 networks. The proposed model firstly considers both TCP congestion control mechanism and IEEE 802.11 contention-based channel access mechanism. The bandwidth estimation process at the server estimates the achievable bandwidth using two types of parameters: data size to be sent and the feedback information from receivers, i.e. packet loss rate and the number of clients. The two tailed T-test analysis demonstrates that there is a 95% confidence level that there is no statistical difference between the results from the proposed bandwidth estimation algorithm and the results from the real test. Additionally, the proposed algorithm achieves higher accuracy and lower standard deviation of bandwidth, in comparison with other state-of-the art bandwidth estimation schemes.