Josef Fuhl

High-resolution 3-D direction-of-arrival determination for urban mobile radio

The in-depth knowledge of the mobile radio channel is particularly important for radio communication modeling and advanced technology system design. We propose an accurate method to determine jointly the azimuth and elevation angle and the delay of waves incoming at the receiver. The method is applied to measurements of the complex impulse response of the mobile radio channel, performed on a planar array placed on a mobile in an urban cellular environment. The directions-of-arrival (DOA) were obtained by the means of a direction finding algorithm-two-dimensional (2-D) unitary ESPRIT. Two-dimensional spatial smoothing as an extension of ordinary spatial smoothing is utilized to decorrelate coherent waves. The application of 2-D unitary ESPRIT increases the angular resolution over conventional Fourier analysis or the scattering function by an order of magnitude and overcomes difficulties due to secondary lobes. The time delay is determined from wideband channel sounder measurements. The results confirm some assumptions on propagation mechanisms: (1) the wave-guiding property of streets (canyon effect), which is especially pronounced for long-delayed paths; (2) the variation of the number of incoming waves with their excess delay-the larger the excess delay, the lower the number of paths comprising an echo in the power delay profile; (3) if a single path remains, the privileged DOA is the direction of the street; (4) the exponential part of the power delay profile due to scatterers all around the receiver; and (5) the elevation dependence or the impinging power. In the tested receiver locations, paths with elevations between 0/spl deg/ and 40/spl deg/ dominate, containing about 90% of the received power.

Capacity enhancement and BER in a combined SDMA/TDMA system

This paper considers the performance of a TDMA system employing smart antennas at the base station. Two adaptation schemes are analyzed-the switched beam approach and an adaptive array based on an adaptation algorithm to maximize the Signal-to-Interference and Noise ratio. For an SDMA system the switched beam approach performs worse than the adaptive array. Adaptive arrays based on gradient-vector estimation (e.g. LMS) are not suitable for mobile radio. The class of Least Squares (LS, RLS, SQRLS) algorithms shows satisfactory performance. For a linear array with 8 elements a minimum angular separation of 10/spl deg/ between two users is sufficient for the adaptive array to achieve as good performance as a system serving one user per traffic channel.

Model Scenarios for Direction-Selective Adaptive Antennas in Cellular Mobile Communication Systems – Scanning the Literature

Intelligent antennas offer the possibility of greatly increasing the capacity of cellular mobile radio systems. We give a comprehensive overview of the literature concerning model scenarios for applications of direction-selective intelligent antennas. Measurement campaigns and simplified models are described that have been derived from these measurements or from physical considerations. Furthermore, directional fading simulators are reviewed which are essential for testing of smart antenna systems.

Error floor of MSK modulation in a mobile-radio channel with two independently fading paths

We investigate the error probability bit error rate (BER) of minimum shift keying (MSK) modulation with differential detection in a two-path fading channel without noise (error floor). We develop a new method for the computation of the BER: we show that errors occur if the phasors of the instantaneous impulse response fall into certain regions of the complex plane; then we average over the statistics of the phasors to arrive at the mean BER. With this method, we derive analytical expressions for the BER for arbitrary amplitude statistics of the paths. For the special case of two Rayleigh-fading paths with small delay, we find that the BER is proportional to the square of the mean delay spread (normalized to the bit length) if we sample between the two pulses. This proves the qualitative behavior of previous estimates, but our results allow also a more exact quantitative formulation. The quadratic dependence of the BER on the delay spread breaks down if we have one Rayleigh-fading and one Rician-fading path. We find that the bit combinations 1-11 and -11-1 do not lead to errors in the two-path model. However, additional Monte Carlo simulations show that these bit combinations do lead to errors in a three-path model.

Capacity increase in cellular PCS by smart antennas

This paper considers the increase in spectral efficiency of a TDMA PCS system employing smart antennas at the base station. Two different strategies are analyzed: spatial filtering for interference reduction (SFIR) and space division multiple access (SDMA). Our results indicate that a cluster size of N/sub cl/=1 is possible by utilizing smart antennas. The use of SDMA increases the spectral efficiency over SFIR by 80%. Additionally, SDMA adds flexibility to the whole network.

Bit error probability of MSK modulation with switched diversity in a mobile-radio channel with two independently-fading paths

We investigate the bit error probability of an indoor mobile communications system WSK modulation with differential detection) with RSSIcontrolled and error-controlled switched antenna diversity. We model the mobile radio channel as a two-path Rayleigh fading channel; we sample in the middle between the two pulses. We derive analytical expressions for the error probabilities (BERs) for both diversity methods. We confirm our results with Monte Carlo simulations. For small delays, we show that the BER is proportional to the fourth power of the mean delay spread for both diversity methods, and that the lowcost RSSIcontrolled diversity gives a BER that is only a factor 3 worse than error-controlled diversity but shows the same basic dependence on the delay spread. For typical indoor situations (delay spread equal to one-tenth of the bit length), we find that the BER is on the order of when using no diversity, for RSSI-controlled diversity, and loe6 for BER-controlled diversity.

Reduction of the error floor of MSK by selection diversity

We examine the error floor of minimum shift keying (MSK) when the receiver uses selection diversity. Both received signal strength indication (RSSI)-driven diversity and bit error rate (BER)-driven diversity are analyzed. The considered channel is a two-delay Rayleigh-fading channel; detection is done by differential detectors with either fixed or adaptive determination of the sampling time. Analysis is based on the method of error regions, where the instantaneous impulse response is represented by phasors in the complex plane. We first compute the joint probability density function (pdf) of the phasors of the two diversity branches. Depending on the selection criterion, the error probability is then computed as an integral over certain functions of this pdf. In the limit of small delay spreads S, the integrals are evaluated analytically. For fixed sampling, the admissible delay spread for BER=10/sup -3/ is increased by about a factor of three (as compared to the no-diversity case) for RSSI-driven diversity and a factor of four for BER-driven diversity. For adaptive sampling, RSSI-driven diversity gives little improvement in the admissible S for BER=10/sup -3/ while BER-driven diversity increases it by some 50%. Results are confirmed by comparison with Monte Carlo simulations and measurements.

Internal broadband antenna for hand-held terminals with reduced gain in the direction of the user's head

We analyze the performance of a radiation-coupled dual-L antenna (RCDLA). It is mounted on the back side of the hand-held terminal, making use of the metallic housing as a shielding structure. In terms of shielding effectiveness and radiation characteristics, our simulations and measurements show a similar performance of this structure compared to the short circuit planar inverted-F antenna (FS-PIFA). Placement of the antenna on the back side of the housing, instead of the terminal top, results in a radiation pattern that points away from the user. The gain in the direction of the users head is about 10 dB less than in the main beam region.

Pattern distortion of mobile radio base station antennas by antenna masts and roofs

We analyze the influence of antennamasts, mounting structures, and roofs on the radiation pattern of base station antennas tor mobile communications. The distortions in the horzontal radiation pattern of omni-antennas caused by the mast can be up to 10dB, but the mast conductivity has only minor effects. The antenna mast also leads to a reduction in the sidelobe attenuation of the vertical radiation pattern of an array antenna. Mounting structures (horizontal metallic bars) have only a very small influence on the pattern. Finally, the rooftops on which the antennas are mounted can also lead to very strong (>10dB) distortions of the radiation pattern. These effects must be considered in the cell planning for mobile radio communications networks.

Temporal Reference Algorithms versus Spatial Reference Algorithms forSmart Antennas

This paper compares algorithms from three different classes of adaptation schemes for smart antennas – the switched beam approach, a Temporal-Reference (TR) technique based on Direct Matrix Inversion or Least Squares adaptation, and a Spatial-Reference (SR) technique with direction finding by Unitary ESPRIT.The simulations are based on a channel model including directions of arrival (DOA) and flat Rayleigh fading. The fading signal is spread out in angle over several degrees dependent on the distance of the mobile from the base station.The results indicate that, in the uplink, TR algorithms and SR algorithms perform equally well, given perfect synchronization and successful user identification (for SR algorithms). TR algorithms are the most robust against close-by interference. For a Uniform Linear Array (ULA) with M=8 elements and an element spacing ofd equal to half a wavelength, they are able to separate two co-channel users that are as close as 5 degrees in angle. For an angular threshold as low as 10° an 8-element ULA is also sufficient to obtain nearly the same BER performance as for a single user.As concerns SR algorithms, we demonstrate their applicability to situations where no discrete DOAs exist, as it is the case in mobile communications.Mutual coupling of individual antenna elements increases the BER by an order of magnitude for the switched beam approach and for SR algorithms, in contrast to TR algorithms, where the influence of mutual coupling on the BER is negligible.