Mark D. Austin

Performance of switched-beam smart antennas for cellular radio systems

The performance and feasibility of switched-beam smart antennas for cellular radio systems is investigated. Switched-beam smart antenna systems are shown to either increase the capacity or extend the radio coverage by increasing the carrier-to-interference ratio (CIR). The trunking efficiency degradation caused by narrow-beam sectoring can be recovered or even improved by using a variety of trunkpool techniques. One drawback of switched-beam smart antennas is that the improvement in reverse-channel performance is not uniform over the entire cell area, and this presents a limiting factor on the achievable gains, practical considerations such as power control and the limited deployment of smart antenna cells are also addressed.

In-service signal quality estimation for TDMA cellular systems

In-service interference plus noise power (I+N) and signal-to-interference plus noise power S/(I+N) estimation methods are examined for TDMA cellular systems. A simple (I+N) estimator is developed whose accuracy depends on the channel and symbol estimate error statistics. Improved (I+N) and S/(I+N) estimators are developed whose accuracy depends only on the symbol error statistics. The proposed estimators are evaluated through software simulation with an IS-54 frame structure. For high speed mobiles, it is demonstrated that S/(I+N) can be estimated to within 2 dB in less than a second.

Single antenna interference cancellation (SAIC) for GSM networks

This paper presents field trial results for downlink interference cancellation in a live GSM network. Uplink interference cancellation techniques have been developed in the past, which exploit the use of multiple receive antennas. However, downlink techniques are typically limited to just the use of a single receive antenna due to space limitations, cost considerations and aesthetics associated with current mobile station designs. A prototype mobile station, using a low complexity single antenna interference cancellation (SAIC) algorithm, was constructed, and used to assess the network gain in both asynchronous and synchronous GSM networks. The performance results measured show that SAIC techniques can provide significant gains in C/I. In addition, network simulations indicate that this same algorithm can support voice capacity gains of 39-57%. Thus, SAIC is seen to be a very viable technology for GSM capacity improvement, which can be realized in the next generation of mobile stations.

Physical layer design for packet data over IS-136

Several forward error correction (FEC), interleaving and automatic repeat request (ARQ) schemes are evaluated for transmitting packet data over IS-136 TDMA. The objective is to identify the combination of FEC, interleaving and ARQ that provides maximum data throughput at reasonable computational complexity. The FEC schemes considered are rate-n/n+1 punctured convolutional codes, long constraint length convolutional codes and punctured turbo codes. The ARQ schemes considered are ARQ with majority voting, ARQ with metric combining and ARQ with code combining (or Type III ARQ). The performance of these techniques when used with one-slot and two-slot interleaving is studied. Results show that highest throughput is achieved when a rate-5/6 convolutional code is used with one-slot interleaving and Type III ARQ scheme.

Eigen-based Doppler estimation for differentially coherent CPM

Eigen-based methods are developed for obtaining fast and accurate Doppler estimates in both land-mobile satellite and urban microcellular applications. By showing that the correlations of a set of differentially processed CPM signals have the same form as the autocorrelations of a complex exponential in noise, eigen-based spectral estimation techniques are used to provide improved Doppler estimates in noise. The eigen-based Doppler estimators are shown to have significantly less variance and mean square error than previously proposed Doppler estimators that use only simple averaging. >

Velocity adaptive handoff algorithms for microcellular systems

Fast handoff algorithms for urban microcells using velocity adaptation and corner detection are presented. Three velocity estimators are compared with respect to their accuracy, sensitivity to non-isotropic scattering, capability of detecting when a mobile turns a corner, and response time in typical microcell environments. Simulation results show that velocity adaptive corner detecting handoff algorithms yield faster and more consistent handoff performance than traditional methods.

Service and system enhancements for TDMA digital cellular systems

Throughout 1998, the TDMA community investigated and defined an enhanced suite of voice and data services for TIA/EIA-136 while also improving its basic system capabilities. These enhancements, collectively named 136+, provide improved voice quality, increased capacity, higher data rates, and improved tools for RF system engineering. The enhancements are obtained by introducing a new modulation scheme (8-PSK), new slot formats, and the addition of several new interleaving and coding options. As a result, TIA/EIA-136 now supports a new vocoder mode, the GSM enhanced full-rate (US1) for improved fidelity applications, a robust IS-641 vocoder mode with a 4 dB BER enhancement on the IS-136 downlink, and a new packet data service capable of providing usable data rates of 14.4, 28.8, or 43.2 kb/s on a full-rate, double full-rate, or triple full-rate channel, respectively. The packet data service is truly evolutionary in nature, having a new medium access control layer with a network layer very similar to that used for the existing digital control channel. In addition, it maximizes commonalities among TDMA technologies, using identical higher layers and network architecture to the general packet radio service specified in GSM. Furthermore, by using a concept known as tunneling to pass TIA/EIA-136 messages through the GPRS network elements, the existing features defined on the DCCH are maintained. This article provides an overview of these 136+ applications, as well as insight into near-term improvements, such as the ability to support six voice users per 30 kHz (IDMA6), downlink time diversity, and fast power control.

Performance of switched beam smart antennas for cellular radio systems

Switched beam smart antennas are shown to either increase the capacity or extend the radio coverage of cellular systems, by increasing the carrier-to-interference ratio. The trunking efficiency degradation caused by narrow beam sectoring can be recovered or even improved by using a variety of trunkpool techniques. One drawback of switched beam smart antennas is that uplink performance is not uniform over the entire cell area, and this presents a limiting factor on the achievable gains.

Measurement sampling criteria for optimization of the Lee's macroscopic propagation model

Lees (1974) macroscopic propagation model is one of the most widely used propagation models due to its ability to achieve good prediction accuracy while still remaining relatively simple and intuitive. Another very important feature of the Lee model is that its prediction ability can be significantly improved by the incorporation of measurement data. Commonly, the measured data is used to optimize two parameters of the model, namely one-mile intercept and slope. This paper addresses the incorporation of the measured data from the standpoint of received signal level sampling. In particular, we discuss statistical criteria imposed on the received signal level sampling that have to be satisfied in order to achieve a valid propagation model optimization.