Channel estimation method with improved performance for the UMTS-TDD mode

Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Crámer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET, from low to high values of Eb/n0

Smart antennas in software radio base stations

The application of adaptive antenna techniques to fixed-architecture base stations has been shown to offer wide-ranging benefits, including interference rejection capabilities or increased coverage and spectral efficiency. Unfortunately, the actual implementation of these techniques to mobile communication scenarios has traditionally been set back by two fundamental reasons. On one hand, the lack of flexibility of current transceiver architectures does not allow for the introduction of advanced add-on functionalities. On the other hand, the often oversimplified models for the spatiotemporal characteristics of the radio communications channel generally give rise to performance predictions that are, in practice, too optimistic. The advent of software radio architectures represents a big step toward the introduction of advanced receive/transmit capabilities. Thanks to their inherent flexibility and robustness, software radio architectures are the appropriate enabling technology for the implementation of array processing techniques. Moreover, given the exponential progression of communication standards in coexistence and their constant evolution, software reconfigurability will probably soon become the only costefficient alternative for the transceiver upgrade. This article analyzes the requirements for the introduction of software radio techniques and array processing architectures in multistandard scenarios. It basically summarizes the conclusions and results obtained within the ACTS project SUNBEAM,1 proposing algorithms and analyzing the feasibility of implementation of innovative and softwarereconfigurable array processing architectures in multistandard settings.Peer Reviewe

High resolution DOA estimation technique for uplink TDD mode

This paper investigates a maximum likelihood (ML) approach for direction of arrival (DOA) estimation based on the algorithm suggested by the 3GPP for scalar channels in UTRA-TDD mode. The performance of the algorithm is assessed by resorting to simulations in typical UMTS scenarios. The results indicate that the proposed scheme overcomes the limitation of the angular resolution inherent to classical techniques like subspace or beam-forming methods. In particular, it is shown that waves exhibiting an arbitrarily small difference in azimuth and temporal spacing higher than one chip time interval can be easily separated. A threshold operation is included to select only the most significant paths, in terms of energy, of the estimated channel. The results show that a good performance can be achieved from low to high values of Eb/N0

ASILUM: A platform to evaluate advanced combinations of smart antennas and multi-user detection for UMTS FDD and TDD

The purpose of this paper is to present and explain some results of ASILUM, a project included into IST (Information Society Technologies), a research programme of European Community. This project aims to contribute to the technical innovation and policies of the European Community by validating new transceivers concepts to increase the capacity of UMTS (FDD and TDD modes) through new and efficient interference mitigation schemes. These schemes are jointly using smart antennas and multiuser detection. They have been validated through link and system level simulations

Spatial channel characterization for smart antenna solutions in FDD wireless networks

This paper introduces a novel metric for determining the spatial decorrelation between the up- and down-link wireless bearers in frequency division duplex (FDD) networks. This metric has direct relevance to smart or adaptive antenna array base-station deployments in cellular networks, which are known to offer capacity enhancement when compared to fixed coverage solutions. In particular, the results presented were obtained from field trial measurement campaigns for both urban and rural scenarios, with the observations having a direct impact on the choice of down-link beamforming architecture in FDD applications. Further, it is shown that significant spatial decorrelation can occur in urban deployments for bearer separations as small as 5 MHz. Results are presented in terms of both instantaneous characteristics as well as time averaged estimates, thus facilitating the appraisal of smart antenna solutions in both packet and circuit switched network

UNE PLATEFORME RADIO LOGICIELLE OUVERTE POUR LES SYSTÈMES 3G+

This paper describes a software-radio architecture developed for providing real-time wide-band radio communication capabilities in a form attractive for advanced 3G systems research. It is currently being used to implement signaling methods and protocols similar, but not limited to, evolving 3G radio standards (e.g. umts, cdma2000). An overview of the hardware system is provided along with example software implementations on both high-perfo-mance DSP systems and conventional microprocessor

On the modeling of WCDMA system performance with propagation data

The aim of this study was to develop calculation methods for estimating the most important system level performance characteristics of the WCDMA radio network (i.e. network capacity and coverage) in the presence of interference from various sources. The calculation methods described in this work enable the fast design of radio systems with a reasonable degree of accuracy, where different system parameters, propagation conditions and networks as well as frequency scenarios can be easily tested. The work also includes the development and verification of a propagation model for a microcellular environment. Traditionally, system level performance figures have been retrieved using system simulations where the radio network has been modeled as accurately as possible. This has included base stations and mobile stations, propagation models, traffic models and mobility models. Various radio resource management (RRM) algorithms, such as power controls and handovers have also been modeled. However, these system simulations are very complex and time consuming and typically the models are difficult to modify. The idea behind this work is to use the main statistical parameters retrieved from accurate, case specific propagation models and to use these statistics as input for the developed analytical radio network models. When used as output from these analytical models we are able to obtain the performance measures of the network. The specific application area for the developed methods is the evaluation of the effect of the interference from the adjacent frequency channels. Adjacent channel interference decreases the efficiency of the usage of the electromagnetic spectrum i.e. the spectral efficiency. The aim of a radio system design is to ensure that the reduction in the spectral efficiency is as low as possible. This interference may originate from the same or a different radio system and from the same or another operator's network. The strength of this interference is dependent on the system parameters and the network layout. The standard questions regarding adjacent system interference between different operators' network are what guard band is needed between the radio carriers in order to maintain the quality of the network or what are the main mobile and network parameters, such as adjacent channel emission levels or adjacent channel selectivity, required in order to achieve satisfactory network performance. With the developed method proposed here it is possible to answer these questions with reasonable accuracy. One important aspect of network performance is the radio wave propagation environment for which the radio systems are designed. This thesis presents methods evaluating radio wave propagation, especially for cases where the base station antenna is below the rooftops, i.e. in the case of microcellular network environments. The developed microcellular propagation model has been developed for network planning purposes and it has been verified using numerous field propagation measurements. The model can be used in cases where the mobile station is located either indoors or outdoors.reviewe