The authors describe cross-correlation properties for compact urban base station antenna configurations, nearly all of which result in very low envelope cross-correlation coefficients of about 0.1 to 0.3. Specifically, polarization diversity systems are examined for their potential in improving link quality when hand-held terminals are involved. An expression is given for the correlation function of compound space and polarization diversity systems. Dispersion and envelope dynamic statistics are presented for the measured environments. For microcell applications, it is found that systems such as GSM having a bandwidth of 200 kHz or less can use narrowband cross-correlation analysis directly. >

Antenna systems for base station diversity in urban small and micro cells

This paper presents basic short-term angular domain propagation descriptions relevant for beam-oriented SDMA operations, i.e. for spatially based algorithms, contrary to temporally based. A distinction is made between angular variant and invariant situations, i.e. whether the antenna system radiation pattern remains unchanged or not when sweeping over the angular domain. For the angular invariant case, multibeam diversity relations are explained, as well as simple data enhancement techniques for measurement refinements. For the angular variant case using linear arrays, this paper suggests a representation in the invariant virtual Doppler domain. A key benefit of generating beams in the Doppler domain instead of directly in the angular domain is a substantial saving in numerical complexity.

Angular Propagation Descriptions Relevant for Base Station Adaptive Antenna Operations

The channel estimation techniques for pilot-based OFDM systems are investigated. The channel estimation is studied for different pilot densities (2, 4, 6, and 10) in frequency-domain and fixed pilot allocation in temporal-domain for low delay spread and high delay spread channels. The estimation of channel in frequency-domain is based on interpolation, polynomial-based generalized linear model (or least-squares method) and Wiener filtering (or Linear Minimum Mean Square Error) methods. The estimation of channel in temporal-domain is done using linear interpolation. We have compared the performance of all these schemes by measuring raw bit-error-rate with QPSK modulation on Rayleigh fading channel based on Clarks scattering model. I would like to take this opportunity to express my gratitude to the supervisors for their guidance and help throughout the project. In addition, I would also like to extend special thanks to Pedro Højen-Sørensen and Thierry Bellier for taking their time to discuss various aspects of the report. Finally, I would like to thank Engineering Manager Niels Mørch for providing me the opportunity to pursue a thesis in his group.

Pilot-based Channel Estimation in OFDM Systems

An analogy between the temporal and angular domain propagation channel descriptions is presented, as well as dispersion metrics and channel classifications. This analysis is relevant when considering angular fixed and dynamic (adaptive beam) base station antennas.

Angular-temporal domain analogies of the short-term mobile radio propagation channel at the base station

By applying a propagation model which combines Rayleigh fast fading with typical, prescribed delay power profiles, the authors analyze intersymbol interference error performance of a single-bit differential detector. A quadrature modulation with +or- pi /2 phase rotation within one symbol period, which is the case for MSK, is assumed. An analytic expression is derived for the error probability as a function of the ratio of the average energies of the relevant symbol and the preceding interfering symbols. This interference is caused by the channel time dispersion. The error probability lies between an upper and a lower bound with a margin that never exceeds 3 dB. The upper bound error probability turns out to be almost identical to the cochannel interference as calculated by the model of K. Hirade et al. (1979). Using typical delay power profiles of European propagation environments, the authors calculate error probability versus symbol duration. For bad-urban and hilly-terrain cases, in which error bursts may last for a few milliseconds, several tens to several hundreds of successive symbols will be corrupted, unless proper signal recovery measures are taken. >

Modeling of intersymbol-interference in a Rayleigh fast fading channel with typical delay power profiles

The various error mechanisms in the time-varying, frequency-selective mobile channel are discussed from a propagation point of view. Starting with a two-ray model, both the frequency and time domain are discussed for the narrowband case, where the delay spread is less than the symbol period, and for the more general broadband case. the major importance of the product of bandwidth and delay spread is stressed. >

Propagation aspects of datacommunication over the radio channel-a tutorial

Measurements of complex impulse responses and transmission of pan-European mobile telephone system GSM timeslots have been carried out in different environments. The short-term variations of the mobile channel have been simulated on computer for comparison. Power, time and phase gradients put demands on the receiver. The variations of these parameters are discussed in theoretical, numerical, and experimental terms. The experimentally obtained values of power gradients are on the order 10 dB between two frames at the 1% level, while the variation from one timeslot to the next is on the order 3 dB at normal speeds of about 50 km/h. Theoretically obtained values show considerably higher variations. The distributions of time-jitter as a function of different environments are also given. >

B.L. Andersen

Papers

Propagation aspects of datacommunication over the radio channel-a tutorial

Short-term variations of the mobile channel and the GSM signal