Ramesh Chembil Palat

An overview of configurable computing machines for software radio handsets

The advent of software radios has brought a paradigm shift to radio design. A multimode handset with dynamic reconfigurability has the promise of integrated services and global roaming capabilities. However, most of the work to date has been focused on software radio base stations, which do not have as tight constraints on area and power as handsets. Base station software radio technology progressed dramatically with advances in system design, adaptive modulation and coding techniques, reconfigurable hardware, A/D converters, RF design, and rapid prototyping systems, and has helped bring software radio handsets a step closer to reality. However, supporting multimode radios on a small handset still remains a design challenge. A configurable computing machine, which is an optimized FPGA with application-specific capabilities, show promise for software radio handsets in optimizing hardware implementations for heterogeneous systems. In this article contemporary CCM architectures that allow dynamic hardware reconfiguration with maximum flexibility are reviewed and assessed. This is followed by design recommendations for CCM architectures for use in software radio handsets.

An Efficient Method for Evaluating Information Outage Probability and Ergodic Capacity of OSTBC System

Several numerical methods have been suggested in the past to compute the outage probability and the ergodic capacity of an orthogonal space-time block coding system. In this paper we add to this body of work by describing a simpler yet general method that relies on a more efficient Fixed-Talbot algorithm for numerical Laplace inversion. The framework developed can be applied to a wide range of fading distributions (including Rice, Nakagami-m, Nakagami-Hoyt and Weibull stochastic channel models) with unequal channel gains and also to independent and non-identically distributed (i.n.d) multiple input multiple output channels.

Estimating ergodic capacity of cooperative analog relaying under different adaptive source transmission techniques

Upper bounds on link spectral efficiency of amplify-and-forward cooperative diversity networks with independent but non-identically distributed wireless fading statistics are studied by deriving the Shannon capacity of three distinct adaptive source transmission techniques: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). Asymptotic capacity bound is also derived which show that optimal rate adaptation with constant power policy provides roughly the same ergodic capacity as the optimal joint power and rate adaptation policy at high mean signal-to-noise ratios (SNRs). Different previous related studies, we advocate a simple numerical procedure for unified analysis of ergodic channel capacity in a myriad of fading environments. This framework allows us to gain insights as to how fade distributions and dissimilar fading statistics across the diversity paths affect the Shannon capacity, without imposing any restrictions on the fading parameters.

Tight bounds on the ergodic capacity of cooperative analog relaying with adaptive source transmission techniques

Tight bounds for the Shannon capacity of amplify-and-forward cooperative diversity networks are derived for three different adaptive source transmission policies in a myriad of fading environments: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). Our unified framework based on the moment-generating function (MGF) approach allows us to gain insights as to how fade distributions and dissimilar fading statistics across the distinct communication links will affect the Shannon capacity, without imposing any restrictions on the fading parameters.

Accurate Bit-Error-Rate Analysis of Bandlimited Cooperative OSTBC Networks Under Timing Synchronization Errors

The distributed multiple-input-multiple-output (MIMO) system (e.g., intercluster communication via cooperating nodes in a wireless sensor network) is a topic of emerging interest. Many previous studies have assumed perfect synchronization among cooperating nodes and identically distributed communication links. Such assumptions are rarely valid in practical operating scenarios. This paper develops an analytical framework for computing the average bit error rate (ABER) of a distributed multiple-input-single-output (MISO) space-time-coded system with binary phase shift keying (BPSK) modulation affected by timing synchronization errors. The cooperating nodes use data pulse-shaping filters for transmission over generalized frequency-nonselective fading channels. As an illustrative example, the performance evaluation of a 2 times 1 MISO system that uses distributed orthogonal space-time block coding (OSTBC) is presented, although this approach can be readily extended to analyze distributed transmit diversity with a larger number of cooperating nodes. We show that under certain conditions, a distributed MISO system with time synchronization errors can still outperform a perfectly synchronized single-input-single-output (SISO) system.

Log-Likelihood-Ratio based Selective Decode and Forward Cooperative Communication

This paper presents exact ABER performance analysis for selective decode and forward (SDF) cooperative diversity system with BPSK modulation under Rayleigh fading where the relay has a MAP based receiver and the retransmission is based on log- likelihood-ratio (LLR) threshold. We also derive the optimum LLR threshold that minimizes ABER performance. It is shown that the LLR relay based SDF cooperative diversity system performs better than a SNR threshold based SDF system with lower implementation complexity than lambda-MRC and C-MRC schemes.

Virginia Tech Space-Time Advanced Radio (VT-STAR)

With the integration of the Internet and multimedia applications in next generation wireless communications, the demand for reliable high data rate services is rapidly growing. Traditional wireless communications systems use a single input single output (SISO) channel, meaning one antenna at each side of the link. Information theory research has shown an enormous potential growth in the capacity of wireless systems by using multiple element array (MEA) technology at both ends of the link. Space-time coding exploits the spatialtemporal diversity provided by the multiple input multiple output (MIMO) channel, significantly increasing both the system capacity and the reliability of the wireless link. The Virginia Tech Space-Time Advanced Radio (VT-STAR) system presents a visual demonstration of the capabilities of space-time coding techniques. The VT-STAR system has integrated an MPEG-2 video stream to show a representation of the effect of the wireless channel on a video transmission in real-time. Core algorithms are implemented on Texas Instruments TMS320C67 Evaluation Modules (EVM). Data conversion between the digital and analog domains is performed by TI THS5661 EVM and TI THS1206 EVM for the transmitter and receiver, respectively. The radio frequency subsystem is composed of multi-channel transmitter and receiver chains implemented in hardware. The capabilities of the MIMO channel are demonstrated in a non-line of sight (NLOS) indoor environment. Real-time monitoring of physical layer parameters, such as the bit error rate and diversity advantage, as well as a video display are presented on an attached personal computer.

Upper bound on bit error rate for time synchronization errors in bandlimited distributed MIMO networks

Distributed multiple-input-multiple-output system (e.g., inter-cluster communication with cooperating nodes in a wireless sensor network) is a topic of emerging interest. Much of the previous studies in this area, however, assumed perfect synchronization among cooperating nodes and identically distributed communication links. Such assumptions are rarely valid in practical operating scenarios. This paper develops an analytical framework for computing an upper bound on the average bit error rate of a distributed space-time coded system with inter-symbol interference (due to imperfect location predictions and clock jitters between cooperating nodes and choice of data pulse shaping filters) over generalized fast fading channels. As an illustrative example, the performance of 2x1 multiple-input-single-output system that uses distributed orthogonal space-time block coding is presented, although this approach can be readily extended to analyze distributed transmit maximal ratio diversity and other variants of space-time schemes

Smart antenna base station open architecture for SDR networks

Software-defined radio system architecture must be openly structured to various system standards. It should also provide capability for distributed processing, object-oriented design, and software controllability. This implies that the software to be used in the SDR system should be independent of a given hardware platform. In order to achieve these goals, the proposed SDR system utilizes modularization to maximize hardware reuse and design flexibility, which provides the system reconfigurability. The objective of this article is to provide an open architecture of a smart antenna base station (SABS) operating in the SDR with architecture that is object-oriented and software-controlled. For this purpose, the software and hardware of a SABS is first modularized and partitioned into modules, respectively. Then the interface among the modules is specified to determine the smart antenna application programming interface proper for the SDR network. The suitability of the proposed open architecture of SABS is verified through a design example of SABS implemented in accordance with the proposed architecture. The performance of the proposed system is shown in practical signal environments of CDMA2000 1X with commercial handsets operating at various data rates ranging from 9.6 to 153.6 kb/s in terms of frame error rate and signal-to-Interference-plus-noise ratio, which is dramatically improved through the nicely shaped beam pattern.

MIMO channel capacity measurements using the VT-STAR architecture

The Virginia Tech Space-Time Advanced Radio (VT-STAR) has been used to collect and process narrowband multiple-input multiple-output (MIMO) channel measurements in a non line-of-sight (NLOS) indoor environment. Following the description of the radio architecture we report here initial representative results of the capacity measured in our indoor laboratory settings. As part of the validation process, the effect of pattern distortion associated with the orientation of the antenna arrays is discussed. We compare the theoretical capacity results of [2] with the measured capacities obtained by a MIMO configuration, receive diversity (with single transmit antenna), transmit diversity (with single receive antenna) and a single-input single output (SISO) channel only.