• SNR Estimation for Non-Coherent FSK Receivers

Estimates of signal-to-noise ratio (SNR) are used in many wireless receiver functions, including signal detection, power control algorithms and turbo decoding etc. Although SNR is an important parameter in studying performance analysis of different communication systems, it can also be used in determining which nodes to participate in the Cooperative Transmission (CT), which is an emerging area of research.  A major problem for network sustainability, especially in battery-assisted networks, is that the batteries are drained pretty quickly during the operation of the network. However, in dense sensor networks, this problem can be alleviated by using a subset of nodes which take part in CT, thereby saving the network energy. SNR is an important parameter in determining which nodes to participate in CT. The more distant nodes from the source having least SNR are most suitable to transmit the message to next level. However, practical real-time SNR estimators are required to do this job. Therefore,  this research deals with  the design of optimal SNR estimators for synchronized as well as non-synchronized FSK receivers, which can work with both the symbol-by-symbol Rayleigh fading channels as well as slow flat fading channels in a wireless medium. The Cramer-Rao lower bounds for the SNR estimators are derived to judge the overall performance of the estimators

  • Stochastic Modeling of Cooperative Wireless Networks

Multi-hop wireless transmission, where radios forward the message of other radios, is becoming popular both in cellular as well as sensor networks. This research is concerned with the statistical modeling of multi-hop wireless networks that do cooperative transmission (CT). CT in a physical layer wireless communication scheme in which spatially separated wireless nodes collaborate to form a virtual array antenna for the purpose of increased reliability. The key contribution of this research is to model the transmissions that hop from one layer of nodes to another under the effects of channel variations, carrier frequency offsets, and path loss. It has been shown that the successive transmission process can be modeled as a quasi-stationary Markov chain in discrete time. By studying various properties of the Markov chain, the system parameters, for instance, the transmit power of relays and distance between them can be optimized. This optimization is used to improve the performance of the system in terms of maximum throughput, range extensions, and minimum delays while delivering the data to the destination node using the multi-hop wireless communication system.

  • Comparison of WiMAX with WiDOCSIS in Rural Environments

The objective of this study is a comparison of WiMAX and Wireless DOCSIS, two access technologies for fixed wireless access (FWA), for rural environments. The band of interest is 2.5 GHz. In this band, WiMAX is called Mobile WiMAX, even though it is used also for FWA. The technologies will be compared in terms of data density, expressed as Mbps per km. The study is to be limited to the PHY layer and for a single cell in the downlink direction. The basic purpose is to show the performance of two technologies in terms of average data rate delivered over a specified distance and number of users getting the service (capacity), in a cell.

  • Wireless Multi-hop networks in homes

    The IEEE 802.11 WiFi standard has been widely used in wireless local area networks (WLAN), which specifies an over-the-air interface between wireless clients and access point or between two wireless clients. With the recent development of multiple-input multiple-output (MIMO) systems at the physical (PHY) layer and frame aggregation at the medium access control (MAC) layer, the IEEE 802.11n standard provides the fastest data rates and larger coverage areas in different environments. However, as wireless network proliferates in indoor environments specially homes, the network topology has evolved from simple single access point-based network into more complex multi-hop topologies. This research deals with the study of throughput delivered to end terminals in a WiFi indoor environment, when additional relays or extenders are placed between the router and the clients to develop


  • Blind Source Separation in Wireless Systems

Blind source separation (BSS) has become an area of prime interest. Conventional adaptive source separation systems use a training sequence to estimate and separate sources with the help of predefined optimization criteria. In BSS, the key idea is to use the data statistics to get apriori knowledge and thus separate the sources blindly. Two important approaches to this regime are the maximum likelihood (ML) estimation and higher-order statistical (HOS) estimation. This research presents the BSS problem in separating sources for a dual antenna MIMO communication system using the aforementioned algorithms. It has been shown that ML estimation outperforms HOS estimation for a wireless medium with noisy data transmission.

  • Full Rate Transmission, Dual Hop Wireless Relay Networks

Cooperative relaying methods have attracted a lot of interest in the past few years. A conventional cooperative relaying scheme has a source, a destination, and a single relay. This cooperative scheme can support one symbol transmission per time slot, and is called full rate transmission. However, existing full rate cooperative relay approaches provide asymmetrical gain for different transmitted symbols. In this research, we propose a cooperative relaying scheme that is assisted with dual relays and provides full transmission rate with the same macro-diversity to each symbol.We also address equalization for the dual relay transmission system in addition to addressing the issues concerning the improvement of system performance in terms of optimal power allocations.