Karl J. Molnar

Adaptive antennas for GSM and TDMA systems

Adaptive antennas have generated great interest in previous years, and at present several manufacturers and operators are separately or jointly performing field tests to gain more detailed knowledge of the potential of the technology. This article summarizes many of the experiences that have been collected since 1996 during field trials carried out for both GSM and TDMA (IS-136) by Ericsson in cooperation with two major network operators, Mannesmann Mobilfunk and AT&T Wireless Services.

Per-antenna-rate-control (PARC) in frequency selective fading with SIC-GRAKE receiver

In this paper we consider a generalization of the per-antenna-rate-control (PARC) MIMO scheme for the HSDPA option of WCDMA. The scheme, called PARC-N, allows the number of transmitted data substreams N to be less than the number of transmit antennas M and selects the best N antennas for transmission. We investigate PARC-N specifically in frequency selective fading environments. First, we develop a novel receiver structure that combines successive interference cancellation (SIC) with generalized-RAKE technology that achieves a good balance between performance and complexity. We then draw several interesting conclusions: (1) data throughput can be maximized by using N /spl les/ M, where N may be adaptively selected based on operating conditions; (2) data throughput is maximized by allocating all non-data signal power (pilots, voice, overhead, etc.) to as few transmit antennas as possible; and (3) the use of pilot subtraction at the receiver is much more beneficial in MIMO systems than in single-antenna or receive diversity systems.

Field test performance results for D-AMPS in PCS bands with array processing

For the digital-AMPS (D-AMPS or IS-136) standard, performance gains for diversity and interference cancellation are quantified for a prototype system that implements a combination of array processing and adaptive equalization using MLSE techniques. For the site location, field tests show a 3.5 dB C/N improvement at 1% bit error-rate for a four-branch space and polarization diversity receiver relative to a receiver with two space diversity antennas. A 5 dB C/I improvement is observed for an interference cancellation receiver with two antennas and one interferer present, and 9 dB gain in C/I is measured for a combined space-polarization diversity antenna configuration. Furthermore, measurement results confirm that interference cancellation performance is not dependent upon the angular separation between the desired and interfering mobiles.

A novel fractionally-spaced MLSE receiver and channel tracking with side information

The performance of adaptive MLSE receivers depends upon channel estimation accuracy and the metric being optimized. In this paper, channel estimation is improved by estimating the transmission medium response, using pulse shaping side information. An optimal fractionally-spaced MLSE metric is formulated in terms of the pulse shape autocorrelation and the transmission medium response. Performance gains are quantified for the IS-136 (D-AMPS) digital cellular system.

Co-channel interference cancellation for D-AMPS hand set

Co-channel interference is a major impairment for IS-136 handsets. Joint estimation of cochannel signals can be used to minimize this effect, but traditional approaches require transmissions from different base-stations to be synchronized. In this paper, we consider a semi-blind approach for cancelling asynchronous interference using generalized per-survivor processing for channel acquisition and tracking. Signal delays and medium responses are jointly estimated for symbol-asynchronous co-channel signals assuming knowledge of the signal structure. Simulation results are presented that show C/I gains of 15 dB in the presence of one interferer.

Optimal and reduced complexity receivers for MISO antenna systems

MISO antenna systems employing feedback of the downlink channel state are attractive for achieving diversity in the downlink of cellular systems. In this paper we consider a particular MISO transmit diversity scheme with rich feedback (TDRF), and derive the optimal receiver structure taking into account intersymbol interference, colored noise, and the self-interference from pilot signals used for downlink channel estimation. We then compare the bound on performance established by the optimal receiver with the performance of a low complexity alternative consisting of a fixed receive filter followed by a sampler. Our results show that the application of TDRF to the WCDMA downlink gives substantial gains compared to a single antenna system, even when the extremely simple sampler receiver is used at the mobile terminal.