K. Peppas

Statistical Analysis for On-Body Spatial Diversity Communications at 2.45 GHz

An investigation of the fading experienced by on-body diversity channels at 2.45 GHz is presented by focusing on the effects of the receive antennas position and the human body movement. This investigation is based on the conduction and analysis of signal measurements in an indoor office environment using bodyworn antennas. Three principal combining techniques, namely selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. A statistical characterization of the fading experienced by dual diversity on-body channels is performed in terms of first and second order statistics. Our investigations have shown that among several distributions tested, the α - μ distribution provides sufficient fit to measured combined signal envelopes and also offers a good approximation to second order statistics for the majority of test cases.

On-body channel modelling: Measurements and statistical analysis

This paper investigates the propagation phenomena and the fading experienced by on-body channels at 2.45 GHz, focusing on the effect of the human body. This investigation is based on signal measurements conducted for both stationary and mobile user cases using bodyworn antennas placed in various positions on the human body. The effect of the antenna location and the human body movement on the fading characteristics of the on-body channels is extensively studied through statistical analysis of the measurement data.

Performance evaluation at the system level of reconfigurable space-time coding techniques for HSDPA

A reconfigurable space-time coding technique is investigated, for a high-speed downlink packet access multiple-antenna network, which combats the effects of antenna correlation. Reconfigurability is achieved at the link level by introducing a linear precoder in a space-time block coded system. The technique assumes knowledge of the long-term characteristics of the channel, namely the channel correlation matrix at the transmitter. The benefits of the proposed reconfigurable technique as compared to the conventional non-reconfigurable versions are evaluated via system-level simulations. In order to characterize the system-level performance accurately and, at the same time, use a feasible approach in terms of computational complexity, a suitable link-to-system interface has been developed. The average system throughput and the number of satisfied users are the performance metrics of interest. Simulation results demonstrate the performance enhancements achieved by the application of reconfigurable techniques as compared to their conventional counterparts.

The Impact of the Position of MIMO Terminal User's Hand on Channel Capacity

In this paper the impact of the position of users hand holding a multiple-input-multiple-output (MIMO) terminal on system performance and more specifically on channel capacity is investigated. We consider a 4times4 MIMO system with a personal digital assistant (PDA) equipped with a compact array of 4 patch elements. Radiation field patterns of the antenna elements in the presence of the other elements as well as in the presence of a users hand are simulated. Different positions of the users hand are taken into account. The covariance matrix of the receiving antennas is evaluated by means of the obtained patterns. A correlation-based channel model is considered, where the antenna patterns are incorporated. Extensive simulations showed that the performance of the MIMO systems varies significantly with the position of the users hand.

Design and control of the interconnecting network of the access segment of mobile communications systems

In mobile communication systems, the network segment interconnecting the Base Station (BS) layout with the Base Station Controllers (BSCs) and the BSCs with the Fixed Network Switches (FNSs) should be carefully designed and controlled. This paper presents techniques for the efficient design and control (reconfiguration) of this network segment. The corresponding problems are formally defined and mathematically formulated. Two solutions are presented to the design problem, based on the genetic algorithm and the simulated annealing paradigms. Additionally, a third solution, based on neural networks, is proposed for the control (reconfiguration) problem. Results are provided indicating the efficiency of the proposed algorithms.

Moments-based analysis of dual-hop amplify-and-forward relaying communications systems over generalised fading channels

The authors present an alternative moments-based approach for the performance analysis of dual-hop relaying communications systems over generalised fading channels. A unified analytical approach for the computation of the nth moment of the harmonic mean of N≥2 arbitrarily distributed random variables (RVs) is proposed. On the basis of this statistical result, we analyse the outage and the average error rate performance of dual-hop cooperative wireless systems employing amplify-and-forward (AF) relays. Moreover, our newly derived results can be applied to evaluate the average sum rate of AF relaying systems. Extensive numerical and simulation results are presented to substantiate the proposed analysis.

Handheld terminal vs. bodyworn antenna systems: A comparative study of MIMO systems performance

In this paper a comparative study of MIMO systems performance is presented by investigating a bodyworn antenna system and a handheld terminal system, taking into account the presence of the users body. The effects of the correlation coefficient, the radiation efficiency and the number of receiving antennas on MIMO channel capacity are addressed. Extensive study is carried out to examine how these three parameters influence the performance of the two MIMO systems under study, in order to be able to select between a handheld multiple antennas terminal and a bodyworn multiple antennas system for a MIMO system implementation.

Evaluation of Interoperability Criteria and Mechanisms for Seamless Inter-Working Between UMTS-HSDPA and WLAN Networks Enhanced with MIMO Techniques

This article proposes criteria and mechanisms that achieve seamless inter-working between the multi-radio access technologies that will compose the fourth-generation (4G) wireless mobile environment. We address the problem of incorporating system interoperability in order to provide the user with seamless mobility across different radio access technologies; namely we focus on inter-working UMTS-High Speed Downlink Packet Access (HSDPA) and WLAN networks, as these two networks are believed to be major components of the 4G wireless network. Interoperability results in providing the user with a rich range of services across a wide range of propagation environment and mobility conditions, using a single terminal. Specifically, the article aims at defining the criteria and mechanisms for interoperability between the two networks. Our approach considers the use of Cost functions to monitor the essential parameters at the system level in order to trigger an interoperability procedure. Initial user assignment and inter-system handover are considered the incidents that initiate the interoperability algorithm execution. The overall objective of this work is to assess the performance of our developed interoperability platform and to optimize system performance by guarantying a minimum QoS requirement and maximizing network capacity.

Reconfigurability to antenna correlation: System level performance enhancements in HSDPA

The system level performance of an HSDPA MIMO network, which combats the effects of antenna correlation by applying novel reconfigurable techniques, is investigated. The impact of antenna correlation on adaptive array techniques has been thoroughly investigated and it has been shown that fading correlations reduce MIMO channel capacity and system performance. Nevertheless, considerable capacity and performance gains can be obtained by transmission on the eigen-modes of the transmit antenna correlation matrix. Reconfigurability to antenna correlation is achieved at the link level by applying a linear precoding scheme at the transmitter space-time block encoder, which is based on the well known Alamouti scheme. The linear precoder is determined so as to minimise a given criterion, such as an upper bound on the pairwise error probability (PEP) of a codeword. An appropriate link to system interface has been developed, taking into account the linear precoding technique. The system level performance metrics of interest are the average system and user throughput as well as the satisfied users. Simulation results are presented in order to demonstrate the performance enhancements achieved by the application of reconfigurable techniques compared to the conventional ones.

Interoperability Criteria and Mechanisms for Seamless Inter-working between UMTS-HSDPA and HIPERLAN/2 Networks Enhanced with MIMO Techniques

The concept 4G wireless communication systems is to provide a user with a rich range of services across different radio access technologies, while maintaining the service’s minimum QoS requirement, independently on the coverage area, mobility conditions, and using a single mobile terminal. To achieve this goal the need for interoperable heterogeneous wireless networks emerges. In this article we identify the challenges that arise when enhancing interoperability functionality to two different radio access networks. Specifically we will focus on inter-working UTRA FDD HSDPA and WLANs networks, as two strong candidates for composing the 4G environment. We also propose an interoperable architecture to achieve seamless inter-working between the aforementioned networks. The article also introduces two interoperable criteria that triggers interoperability based on the use of Cost functions. Namely, these triggers are the initial user assignment to the optimal network and inter-system handover. Each of the two triggers initiates a respective interoperability algorithm. Finally, In order to characterize the interoperability mechanisms behaviour and address an accurate QoS performance analysis, a software simulation platform has been developed. The platform is enhanced with MIMO transceivers and takes into consideration: network configuration, propagation conditions, fast fading, and service requirements.