David I. Laurenson

Survey of channel and radio propagation models for wireless MIMO systems

This paper provides an overview of the state-of-the-art radio propagation and channel models for wireless multiple-input multiple-output (MIMO) systems. We distinguish between physical models and analytical models and discuss popular examples from both model types. Physical models focus on the double-directional propagation mechanisms between the location of transmitter and receiver without taking the antenna configuration into account. Analytical models capture physical wave propagation and antenna configuration simultaneously by describing the impulse response (equivalently, the transfer function) between the antenna arrays at both link ends. We also review some MIMO models that are included in current standardization activities for the purpose of reproducible and comparable MIMO system evaluations. Finally, we describe a couple of key features of channels and radio propagation which are not sufficiently included in current MIMO models.

Vehicle-to-vehicle channel modeling and measurements: recent advances and future challenges

Vehicle-to-vehicle communications have recently received much attention due to some new applications, such as wireless mobile ad hoc networks, relay-based cellular networks, and intelligent transportation systems for dedicated short range communications. The underlying V2V channels, as a foundation for the understanding and design of V2V communication systems, have not yet been sufficiently investigated. This article aims to review the state-of-the-art in V2V channel measurements and modeling. Some important V2V channel measurement campaigns and models are briefly described and classified. Finally, some challenges of V2V channel measurements and modeling are addressed for future studies.

An adaptive geometry-based stochastic model for non-isotropic MIMO mobile-to-mobile channels

In this paper, a generic and adaptive geometrybased stochastic model (GBSM) is proposed for non-isotropic multiple-input multiple-output (MIMO) mobile-to-mobile (M2M) Ricean fading channels. The proposed model employs a combined two-ring model and ellipse model, where the received signal is constructed as a sum of the line-of-sight, single-, and doublebounced rays with different energies. This makes the model sufficiently generic and adaptable to a variety of M2M scenarios (macro-, micro-, and pico-cells). More importantly, our model is the first GBSM that has the ability to study the impact of the vehicular traffic density on channel characteristics. From the proposed model, the space-time-frequency correlation function and the corresponding space-Doppler-frequency power spectral density (PSD) of any two sub-channels are derived for a non-isotropic scattering environment. Based on the detailed investigation of correlations and PSDs, some interesting observations and useful conclusions are obtained. These observations and conclusions can be considered as a guidance for setting important parameters of our model appropriately and building up more purposeful measurement campaigns in the future. Finally, close agreement is achieved between the theoretical results and measured data, demonstrating the utility of the proposed model.

A new statistical wideband spatio-temporal channel model for 5-GHz band WLAN systems

In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature.

Revisiting the Hidden Terminal Problem in a CSMA/CA Wireless Network

Recently research interest in the performance analysis of wireless networks was revived. An issue of an utmost importance in this class of networks, classified as one of the severest reasons for the degradation of their performance, is the hidden terminal problem. In this paper we argue that an accurate analysis of the effect of hidden nodes in the performance of a random access protocol is still an open issue. Firstly, we thoroughly explain the reasons behind the limitations of previous modelling methods, and show that their performance is reliable only for certain configurations. Secondly, and most importantly, we propose a novel method of modelling time that uses a fixed-length channel slot as the unit of time and does not rely on renewal theory. With these features the model is able to successfully take into account the desynchronisation of nodes in a hidden terminal environment. Our analytical model is shown to have a very close match to simulation results for an IEEE 802.11 MAC protocol and for all the system parameters considered, unlike conventional methods.

Techniques for improving cellular radio base station energy efficiency

The last ten years have witnessed explosive growth in the number of subscribers for mobile telephony. The technology has evolved from early voice only services to todays mobile wireless broadband (Internet) data delivery. The increasing use of wireless connectivity via smartphones and laptops has led to an exponential surge in network traffic. Meeting traffic demands will cause a significant increase in operator energy cost as an enlarged network of radio base stations will be needed to support mobile broadband effectively and maintain operational competitiveness. This article explores approaches that will assist in delivering significant energy efficiency gains in future wireless networks, easing the burden on network operators. It investigates three approaches to saving energy in future wireless networks. These include sleep mode techniques to switch off radio transmissions whenever possible; femtocell and relay deployments; and multiple antenna wireless systems. The impact of these approaches on achieving energy-efficient wireless communication systems is discussed.

Computationally Tractable Model of Energy Detection Performance over Slow Fading Channels

Energy detection (ED) has been widely used for detecting unknown deterministic signals in many wireless communication applications, e.g., cognitive radio, and ultra-wideband (UWB). However, the performance analysis of ED over slow fading channels is cumbersome, because it is difficult to derive closed-form expressions for the average probability of detection involving the generalised Marcum Q-function and the log-normal distribution. In this letter, we derive an approximation of the average probability of detection over a slow fading channel by replacing the log-normal distribution with a Wald distribution. In addition, we analyze the detection performance of the ED using a square-law combining scheme over multiple independent and identically distributed slow fading channels.

Energy Efficiency of High QoS Heterogeneous Wireless Communication Network

Energy efficiency is becoming a very important issue in modern wireless communication systems. At the same time, maintaining QoS is also critical when trying to reduce power consumption. This paper describes a heterogeneous wireless communication network architecture, and analyses its power consumption and QoS support levels. The result shows that combining cellular communications with femtocells can significantly reduce overall power consumption, depending on the uptake of femtocell usage. Also, QoS remains high when the power consumption drops. The simulation results also suggest that the femtocell implementation rate should be limited under a certain degree, around 60%, in consideration of power efficiency. Finally, indifference curves of power consumption and QoS indicate the optimal femtocell adoption schemes under different requirements.

A robust location estimator architecture with biased Kalman filtering of TOA data for wireless systems

This paper presents a robust location estimator architecture for a time difference of arrival (TDOA) system, which mitigates non-line of sight (NLOS) and multipath errors, using biased Kalman filtering of time of arrival (TOA) estimates. With additional Kalman filtering of location estimates a high degree of location accuracy is demonstrated. Simulations of an idle period downlink (IPDL) UMTS system give an accuracy to within 50 m at the 67th percentile for most scenarios.

A Geometry-Based Stochastic Model for Wideband MIMO Mobile-to-Mobile Channels

In this paper, based on the tapped delay line (TDL) structure, we propose a geometry-based stochastic model (GBSM) for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M2M) Ricean fading channels. The proposed wideband model is the first GBSM that has the ability to study the impact of the vehicular traffic density (VTD) on channel statistics for different time delays, i.e., for every tap in our model. From the proposed model, the space-time (ST) correlation function (CF) and the corresponding space-Doppler (SD) power spectral density (PSD) are derived. Excellent agreement is achieved between the theoretical Doppler PSDs and measured data, demonstrating the utility of the proposed model.