DS-CDMA microcellular networks with adaptive antennas

This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the basestation site of a microcell. Results for a typical microcellular environment produced with the help of a ray tracing tool highlight the behaviour of the adaptive antenna and with the help of a Monte-Carlo type DS-CDMA capacity analysis, the potential performance enhancement of the system is evaluated. Finally, scenarios with inter-cell interference and moving users are discussed, and the fixed beam steering and the reduced sidelobe techniques are considered against the adaptive antenna technique

A new stochastic spatio-temporal propagation model (SSTPM) for mobile communications with antenna arrays

In order to evaluate the performance of third-generation mobile communication systems, radio channel models are required. The models should be capable of handling nonstationary scenarios with dynamic evolution of multipath. In this context and due to the introduction of advanced antenna systems to exploit the spatial domain, a further expansion is needed in order to include the nonstationary characteristics of the channel. In an attempt to solve these problems, this paper presents a new stochastic spatio-temporal propagation model. The model is a combination of the geometrically-based single reflection and the Gaussian wide-sense stationary uncorrelated scattering models, and is further enhanced in order to be able to handle nonstationary scenarios. The probability density functions of the number of multipath components, the scatterers' lifetime, and the angle of arrival are calculated to support these features. The input parameters of the model are based on results from measurement campaigns published in the open literature

Orthogonal re-spread for uplink WCDMA beamforming

This paper presents a new extraction method for the spatial correlation matrix of interference and noise only based on orthogonal re-spreading. The method uses one of the remaining orthogonal variable spreading factor (OVSF) code that is orthogonal to all traffic and control channels to spread energy form the desired user while attempting to maintain the same level of co-channel interference. De-spreading with the assigned OVSF codes that is performed in parallel provides the usual noisy correlation matrix. With those two matrices at hand optimal beamforming using maximal signal-to-interference ratio (MSIR) criterion is readily performed. Although the matrix extracted by the orthogonal re-spread is not a statistically consistent estimate, remarkable potentials in practical situations are demonstrated

Application of adaptive antenna technology to third generation radio architectures

Work at Bristol has considered the application of adaptive antenna technology to a mixed cell architecture employing DS-CDMA as the air interface. In the scenario considered, both the umbrella cells and the underlying micro cells operate within the same RF bandwidth in an attempt to support a seamless handover between different cell types. The paper presents an overview of the proposed mixed cell architecture employing adaptive antenna technology at the umbrella cell site, as well as the benefits that can be obtained from such a deployment. This is expressed in terms of the critical near-far problem and the system's capacity. Simulation and propagation results provide evidence for the claimed capabilities of the proposed system and estimates of the likely increased spectrum efficiency

On the sensitivity of the capacity enhancement of a TDMA system with adaptive multibeam antennas

The paper presents results for the likely capacity improvement when an adaptive multibeam antenna is used in conjunction with air interface parameters akin to the DCS1800 system. The analysis investigates the possible capacity enhancement whilst taking into account parameters such as power control, number of available handover channels, radiation pattern, radio channel characteristics and different frequency reuse patterns. The results show that a substantial capacity improvement can be achieved with adaptive antennas and also underline the sensitivity of the capacity upon several operational parameters. Finally, based on observations made from the simulation results, a more efficient architecture which fully supports onward beamforming on the handover process, is proposed

Calibration and linearity issues for an adaptive antenna system

Adaptive antennas are among the favourite techniques to help the current systems evolve towards third generation mobile communication systems. However, among the major concerns for adaptive antenna systems are the calibration process and the non-linearity effects of the RF-IF chains upon the performance of the beamforming network. This article investigates these issues based on experimental results produced with the adaptive antenna testbed that was developed under the RACE TSUNAMI project. Results highlight the sensitivity of the system on both the linearisation and the calibration processes employed

Intelligent antennas for DS-CDMA systems

This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the basestation site. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presented. Results for a typical microcellular environment highlight the behaviour of the adaptive antenna. Finally, with the help of a DS-CDMA capacity analysis, the potential spectrum efficiency enhancement is evaluated and the improvement of some of the statistics of the system is discussed

Performance enhancement of DS-CDMA microcellular networks with adaptive antennas

This paper considers the performance of a DS-CDMA system which employs adaptive antenna technology at the base station site of a microcell. By utilising the capability of ray-tracing to provide the complex channel impulse response, a new ray-based simulation methodology for an adaptive antenna in a DS-CDMA system is presented. Results for a typical microcellular environment highlight the behaviour of the adaptive antenna. Finally, with the help of a Monte-Carlo type DS-CDMA capacity analysis, the potential performance enhancement and the sensitivity of the system upon the misspointing of the main beam, are evaluated