Indrakshi Dey

Joint Fading and Shadowing Model for Large Office Indoor WLAN Environments

This paper presents measurements and a propagation model for an indoor wireless LAN (WLAN) scenario that represents an open concept office or laboratory layout with few large obstacles to reflect and refract the transmitted signal. Most mobile WLAN users generally restrict their movements to a small area due to the inability of most WLANs to accommodate hand-offs. As a result, users travel through at most one or two scattering clusters and experience only one or two discrete shadowing values. Hence, this paper will use propagation measurements collected over bandwidths of 10 MHz, to develop a statistical model for shadowing suitable for such an indoor WLAN scenario. Moreover, in indoor environments shadowing varies quickly enough to require some channel estimation algorithms to account for both small scale and large scale statistics. Therefore, this paper will present a distribution that jointly models variations due to both Rician fading and the new shadowing model. An analytical expression for the probability density function (PDF) of the joint distribution will be derived and fit to the experimental propagation data.

Fading Statistics for the Joint Fading and Two Path Shadowing Channel

New expressions for the joint moments, mean, variance and amount of fading (AF) of the Joint Fading and Two-path Shadowing (JFTS) distribution are derived in this letter. The derived expressions for theoretical mean and variance are shown to agree with the experimental results. The AF expression is used for comparing the severity of fading imparted by the JFTS distribution to the fading severity of other common small scale fading and composite fading / shadowing distributions.

Performance Analysis of BPSK over Joint Fading and Two-Path Shadowing Channels

The performance of Binary Phase Shift Keying (BPSK) in a Joint fading and Two-path Shadowing (JFTS)environment is analyzed. Closed form expression for the exact Average Bit Error Rate (ABER) of coherent BPSK scheme is presented using the Moment Generating Function (MGF) of the JFTS distribution. Finally the coherent BPSK ABER of a wireless communication system is simulated over JFTS fading / shadowing channels with and without non- iterative Forward Error Correction (FEC) coding and compared with the analytical ABER expression.

Semi-Blind Adaptive Space-Time Shift Keying Systems Based on Iterative Channel Estimation and Data Detection

We develop a semi-blind adaptive space-time shift keying (STSK) based multiple-input multiple-output system using a low-complexity iterative channel estimation and data detection scheme. We first employ the minimum number of STSK training blocks, which is related to the number of transmitter antennas, to obtain a rough least square channel estimate (LSCE). Low-complexity single-stream maximum likelihood (ML) data detection is then carried out based on the initial LSCE and the detected data are utilised to refine the decision-directed LSCE. We show that a few iterations are sufficient to approach the optimal ML detection performance obtained with the aid of perfect channel state information.

Achievable Channel Cutoff Rate and Bandwidth Efficiency in Indoor Wireless Environments

In this paper, analytical expressions for the channel capacity, channel cutoff rate, and achievable bandwidth efficiency associated with M-ary signaling and Joint Fading Two-path Shadowing (JFTS) fading/shadowing channel model that characterize mobility-constrained indoor propagation scenarios are derived. Expressions for the bandwidth efficiency of a JFTS fading channel involve infinite-series summation since the probability density function of the JFTS signal-to-noise ratio (SNR) contains infinite series. We derive lower and upper bounds on the errors resulting from truncating the infinite series in the bandwidth efficiency expression. The cutoff rate and bandwidth efficiency analysis can be used to demonstrate how much throughput can be practically achieved when M-ary signaling techniques are implemented over indoor composite fading/shadowing channel conditions. Simulation results show that in order to achieve 3 bits/symbol, the average SNR for a 16-quadrature-amplitude-modulation (16-QAM) system requires almost 10 dB more for a JFTS channel model compared with a traditional Rayleigh channel model, thus reinforcing the necessity of using proper channel models for indoor communication systems.

The Cumulative Distribution Function for the Joint Fading and Two Path Shadowing Channel: Expression and Application

A new expression for the Cumulative Distribution Function (CDF) of the Joint Fading and Two-path Shadowing (JFTS) distribution is derived in this paper. The derived theoretical CDF expression is shown to agree with the experimental results. The CDF expression is used to derive an outage expression for non-diversity transmission which is then used to illustrate the performance of adaptive transmission over the JFTS link.

Performance analysis of relay-assisted mobile-to-mobile communication in double or cascaded Rayleigh fading

We consider a mobile-to-mobile (M2M) communication scenario in a crowded city or suburban area, where each mobile terminal is surrounded by a group of scatterers. The non-line of sight (NLOS) communication channel is modelled as non-frequency selective double or cascaded Rayleigh distributed. Cooperative relaying with amplify and forward (AF) protocol is used to improve the overall system performance. System performance is investigated in two sets. In the first case, the source (S) to destination (D) direct link is double Rayleigh distributed. The relay (R) or access point is assumed to be located above rooftop level and the cooperative links are flat Rayleigh faded. In the second case, both the direct and cooperative links are considered double Rayleigh faded. Modelling and simulations are used to evaluate overall performance in conditions, when the cooperative link is uncorrelated, partially correlated and completely correlated with the direct link.

On the Capacity of Joint Fading and Two-Path Shadowing Channels

The ergodic and outage channel capacity of different optimal and suboptimal combinations of transmit power and modulation rate adaptation strategies over a joint fading and two-path shadowing (JFTS) fading/shadowing channel is studied in this paper. Analytically tractable expressions for channel capacity are obtained, assuming perfect channel side information (CSI) at the receiver and/or the transmitter with negligible feedback delay. Furthermore, the impacts of the JFTS parameters on the channel capacity achieved by these adaptive transmission techniques are determined.

Probability of Outage Due to Self-Interference in Indoor Wireless Environments

In this letter, we derive a mathematically tractable expression for the outage probability in the presence of self-interference over indoor wireless environments modeled through the recently proposed joint fading and two-path shadowing channel model. The effect of self-interference is studied under two different conditions encountered in single-frequency network architectures: 1) long propagation delay and correlated shadow fading in a densely deployed single access point to single mobile user communication scenario and 2) interference between radiated and received signal power in full-duplex radios equipped with multiple antennas both for transmission and reception of data. The analysis is validated numerically both for single-channel and multiple-channel receivers.

Adaptive coded modulation for mobility constrained indoor wireless environments

The performance of rate adaptive trellis-coded and uncoded M-ary quadrature amplitude modulation (M-QAM) over large open office indoor wireless environments is studied in this paper. An appropriate composite fading/shadowing channel model termed the joint fading and two-path shadowing (JFTS) model is adopted for such an indoor wireless environment, where mobility of users remains constrained within a small space. Mathematically tractable expressions for the spectral efficiency and average bit error rate (ABER) of adaptive coded and uncoded M-QAM over the JFTS channel are derived. Numerical results demonstrate that in contrast to conventional fading models like Rayleigh and Nakagami-m distributions, the error probability performance of rate adaptive M-QAM over a JFTS faded/shadowed link never approaches zero for lower channel signal-to-noise ratios (CSNRs).