Patrick Claus F. Eggers

A Time Reversal Transmission Approach for Multiuser UWB Communications

We propose and evaluate the performance of the time reversal technique in impulse radio ultrawideband (UWB) communications. The evaluation was based on measured channel impulse responses of a 4times1 multiple input single output (MISO) system in the UWB frequency bandwidth of 3 to 5 GHz with both vertical and horizontal polarization at the receiver. The results show that there is a great potential in combining time reversal and UWB technique with respect to both reducing the receiver complexity and improving the system performance. Simultaneous communication is illustrated with 5 users, each with a bit error rate (BER) of less than 10-3 at an average signal to noise ratio (SNR) of 15 dB

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

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. >

Investigations of outdoor-to-indoor mobile-to-mobile radio communication channels

The mobile-to-mobile radio channel was investigated in different suburban outdoor-to-indoor environments. System performance parameters in terms of un-encoded BER and outage probability have been extracted from hardware and software TETRA simulations. In several scenarios, the measured signal envelope statistics were found to be a combination of single and double Rayleigh distributions. The system performances obtained in these scenarios were in general lower than the reference ETSI limits.

Time reversal in wireless communications: a measurement-based investigation

Interference caused by other users in a multi-user environment degrades the system performance significantly. Conventionally, user separation in a multi-user environment is achieved by signal separation in time, frequency or code. The use of multiple elements antenna (MEA) systems can apply separation of the users in space by targeting the transmitted power to the user of interest. Inevitably in that case, the separation is not ideal and there is interference on the other users in the systems. Moreover in a wideband transmission, frequency selective fading causing inter symbol interference (ISI) is a big challenge for point to point wireless communications. In this paper, we study the feasibility of applying the time reversal technique (TR) in multiple input single output (MISO) systems to alleviate the effect of ISI. The ability of TR to focus the signal on the receiver of interest in a multi-user environment is also considered. The studies are supported by measured complex channel impulse responses with 10 MHz bandwidth centered at 2.14 GHz. For an 8times1 MISO system, using TR the root mean square delay spread is reduced by a factor of 2. To evaluate the capability of the TR in reducing the ISI, simulation of the bit error rate (BER) was made. The irreducible BER of the TR-MISO system was shown to be lower than that of the SISO system by at least an order of magnitude. By using TR and assuming that two users are communicating simultaneously with the same BS the two signals have 17 dB of isolation

Angular dispersive mobile radio environments sensed by highly directive base station antennas

Typical DECT and UMTS radio environments have been investigated with high gain directional base station (BS) antennas. Experiments have been performed as preparation for field tests with an adaptive BS antenna testbed. The dispersion of the radio environment leads to a distortion of the perceived BS antenna sidelobe levels, though still providing increase in effective gain. The spatial selectivity of directive antennas leads to a reduction in time dispersion by about a factor of two, while the cross polarization discrimination is increased a few dB. Quantitative measures of the spatial environment spreading are given, so a numerical comparison between different environments is possible.

Urban area radio propagation measurements at 955 and 1845 MHz for small and micro cells

Path-loss in urban area small and microcell environments is discussed. Results from dual-frequency measurements performed in urban areas at 955 MHz and 1845 MHz are presented. The mean difference in path loss between the two frequencies was found to be 10 dB, whereas the free-space loss is only 6 dB. The shadow-fading at the two frequencies was highly correlated. Therefore much of the experience from the 900-MHz band can be used for planning of new cellular systems in the 1800-2000-MHz band. M. Hatas (1980) prediction model was fitted to the data at both frequencies, but predicted too-low path loss at 1845 MHz. A modified Hata prediction model is proposed for use in the frequency range 1500 to 2000 MHz. The effect of low base station antenna heights is also discussed.<<ETX>>

Time reversal techniques for wireless communications

The application of the time reversal (TR) technique in a multiple input-single output (MISO) configuration can reduce the delay spread of the channel impulse response by a factor of 2-3, depending on the power allocation scheme. Moreover, this technique provides a gain of about 20 dB in peak signal power. These effects are demonstrated with measurements of fixed wireless access channels in the 5 GHz band. The measurements were performed at 3 different locations in downtown Toronto, and the channel has been measured with 8 element uniform linear antenna arrays at both ends, thus providing an 8/spl times/8 configuration.

Ultra wideband radio propagation in body area network scenarios

This work presents novel, very-short range UWB radio channel investigations performed in typical body area network (BAN) scenarios using small size, low profile terminal antennas. A novel RF fiber optic connection has been employed for the small antenna set-up in order to maximize the accuracy of the measurements. Several test users have been investigated and significant changes of the UWB antenna radiation characteristics when close to the human body were disclosed using numerical simulations. The measurements with different UWB device positions on the human body showed drastic changes in the calculated radio channel parameters (frequency and time-delay domain) not only due to the body area but also due to the total propagation environment.

Time Reversal and Zero-Forcing Equalization for Fixed Wireless Access Channels

We consider a wideband system with an M -element transmit array. In this paper we combine conventional zeroforcing pre-equalization and time reversal: we present a beamformer that perfectly equalizes the channel and preserves the spatial focusing properties of time reversal. We compare it to a pure zero-forcing beamformer and a pure time reversal system and demonstrate its superior bit error rate performance and low probability of intercept properties using actual measurements of a fixed wireless access system in an urban environment.

Jitter diversity in multipath environments

The lack of capacity in mobile communication systems is an increasing problem. A channel model for the use of antenna arrays at the base station is presented. A new diversity scheme, jitter diversity, is suggested with a simple algorithm. The technique is to use an antenna array and move the main beam slightly to avoid deep fades, giving substantial improvement in the fading distribution and the mean power. Linear antenna arrays with 1-19 elements are applied to propagation environments with different scatterer spread. The influence of the environments on the received antenna pattern, such as the effective gain, is investigated. Experiments support the main findings, namely that the environments reduce the directivity of the perceived antenna diagram by several dB. Jitter diversity is a very simple approach, compared to other combining methods, as it only includes the variation of a single parameter, the phase between elements. It should therefore be simple to implement in practice.