Antenna Diversity Performance in Mitigating the Effects of Portable Radiotelephone Orientation and Multipath Propagation

Antenna diversity can mitigate signal impairments caused by random angular orientation and multipath radio propagation when using portable radiotelephones. Cumulative distributions of signal-to-noise ratio (S/N) were determined for antenna diversity using realistic orientation and multipath propagation models. In a random orientation and multipath propagation environment with -6 dB average crosspolarization coupling, two-branch selection diversity with two perpendicular antennas yields anS/Ndistribution with the same slope as two-branch selection diversity in the fixed-oriented mobile radio environment. The distribution for random orientation is about 4.5 dB worse, however, than the mobile radio distribution.     

Cross-polarization coupling measured for 800 MHz radio transmission in and around houses and large buildings

The scatterers and reflectors that produce multipath propagation in the portable radiotelephone environment also scatter energy from the transmitted polarization into the orthogonal polarization. This cross-polarization coupling improves the signal quality on portable radio links by mitigating the effects of random antenna orientation and by providing an additional signal path for diversity combining. Measurements were made of cross-polarization coupling at 800 MHz within and around eight suburban houses and within two commercial buildings. Nearly complete coupling between polarization was seen for all propagation paths except for a few residential paths having high co-polarized signal levels. Because of the high cross-polarization coupling, random orientation of portable radio sets will not cause significant degradation of signal quality.     

Random FM noise with selection combining

Random FM noise using two-branch selection combining with correlated Rayleigh fading signals is analyzed for land mobile radio systems. General expressions are derived for the cumulative distribution function and mean square value of the random FM noise; they can be applied to any type of diversity such as space, polarization, etc. Calculated results show that, if two horizontally spaced antennas parallel with the direction of vehicle motion are used at a mobile station, random FM noise can be significantly reduced for small antenna spacings     

Performance Analysis of a Built-In Planar InvertedFAntenna for 800 MHz Band Portable Radio Units

The pattern averaging gain (PAG) method to estimate the average gain of mobile antennas in a multipath propagation environment is proposed. By using this method and a wire-grid model, the radiation characteristics of the planar invertedFantenna (PIFA) mounted on a portable radio case is analyzed. In particular, the variation of the antenna gain with the radio case dimensions and inclination angle of the radio case during operation is clarified. Also, the effect on antenna patterns of the operator holding the portable radio is experimentally investigated. Based on this analysis, the antenna configuration with the PIFA element mounted on the lateral side of the radio case is found to be most suitable for portable radio units. In addition, an appropriate selection of the radio case dimensions is found to result in further improvements in the antenna bandwidth.     

A random matrix model of communication via antenna arrays

A random matrix model is introduced that probabilistically describes the spatial and temporal multipath propagation between a transmitting and receiving antenna array with a limited number of scatterers for mobile radio and indoor environments. The model characterizes the channel by its richness delay profile which gives the number of scattering objects as a function of the path delay. Each delay is assigned the eigenvalue distribution of a random matrix that depends on the number of scatterers, receiving antennas, and transmitting antennas. The model allows one to calculate signal-to-interference-and-noise ratios (SINRs) and channel capacities for large antenna arrays analytically and quantifies to what extent rich scattering improves performance.     

A mobile radio single-frequency "Two-way" diversity system using adaptive retransmission from the base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "two-way diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

A Mobile Radio Single-Frequency "Two-Way" Diversity System Using Adaptive Retransmission from the Base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

Performance of Feedback and Switch Space Diversity 900 MHz FM Mobile Radio Systems with Rayleigh Fading

A theoretical and experimental comparison of performance has been made between two types of predetection switching space diversity mobile radio systems. This comparison was made at a frequency of 840 MHz using simulated Rayleigh fading for a vehicle speed of about 80 mi/h. The switch diversity system was a conventional receiver antenna switching technique with two simulated physically separated receiving antennas and a single transmitting antenna. The feedback diversity system used a single receiving antenna with two simulated physically separated transmitting antennas. The transmitting antennas were switched remotely from the receiver. The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique.     

The implementation of channel diversity in mobile software radio receivers

A novel channel diversity concept is proposed and demonstrated, which avoids receiving signal deterioration due to multipath fading in mobile receivers. The system is based on coherent superposition of the signals received from several transmitters supplying the same information at different frequencies. Based on a software radio architecture this concept may increase the quality of mobile reception in modern car receivers considerably. Compared with multiantenna-receivers which overcome the multipath fading problem by simultaneously receiving the same program with several antennas, the proposed solution is advantageous, since it requires only a single antenna.     

Performance of feedback and switch space diversity 900 MHz FM mobile radio systems with Rayleigh fading

A theoretical and experimental comparison of performance has been made between two types of predetection switching space diversity mobile radio systems. This comparison was made at a frequency of 840 MHz using simulated Rayleigh fading for a vehicle speed of about 80 mi/h. The switch diversity system was a conventional receiver antenna switching technique with two simulated physically separated receiving antennas and a single transmitting antenna. The feedback diversity system used a single receiving antenna with two simulated physically separated transmitting antennas. The transmitting antennas were switched remotely from the receiver. The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique.     

Universal portable radio communications

In our highly mobile society, the provision of voice and data communications to people away from their wireline telephones has become a major communications frontier. Some emerging radio systems, e.g., cellular mobile radio, cordless telephone, and radio paging, have begun to penetrate this frontier. However, each of these approaches only partially satisfies portable communication needs. That is, the approaches do not provide overall portable communication service. Some of the problems involved and the technologies and system configurations needed for an advanced radio communications system are discussed. The goal for the system is to provide high quality ubiquitous service to low power portable radiotelephones and data terminals. Frequency reuse radio system configurations applicable to residential and large building environments will be described along with multipath and other 800 MHz radio propagation limitations. The system would use fixed radio ports attached to the telephone network and spaced about 2000 ft in residential areas. The residential ports would have antenna heights of less than 30 ft. The horizontal spacing of ports within large buildings would be 200 ft or more. In service areas, more than 99 percent radio link availability would be provided for 5 mW portable transmitters.     

Transmitter diversity effect in TDMA/TDD mobile radio transmission

Transmitter diversity, which employs a single transmit/receive antenna at the portable stations and two transmit/receive antennas at the base station, is experimentally investigated for a TDMA/TDD (time division duplex) mobile radio system. Experimental results show that transmitter diversity can significantly improve the BER (bit error rate) performance of the portable station, due to AWGN (additive white gaussian noise), delay spread, and CCI (cochannel interference) in Rayleigh fading environments.<>     

Binomial array as a multistate phase diversity antenna

If two in-phase plane waves arrive at an antenna from different directions, the resulting signal is not necessarily the coherent sum of the two incoming signals. This is due to the fact that the antenna radiation pattern is actually a complex quantity containing amplitude and phase properties. Thus, it can be stated that antenna phase characteristics may vary as a function of direction. In free space, the antenna phase pattern does not have any role in radio communications in contrast to mobile communications in an urban microcell where the radio channel is very complicated due to multipath propagation. Array antennas offer possibilities to control its phase properties in transmission and reception, which offer a simple technique to improve the combination of received multipath signal components. Binomial arrays are one possibility to implement similar directive beams which, however, have different phase patterns compared to each other. A set of these beams could be used in a discretely optimizing receiver system much in the same way as other diversity techniques are used. A four-element array and results from a microcell radio channel environment simulation are presented as a demonstration of this technique     

Mobile radio performance for a two-branch equal-gain combining receiver with correlated signals at the land site

It has generally been accepted that in a two-branch diversity receiver a near maximum diversity advantage is realized when the cross correlation between the two branches is less than 0.7. Based on this figure, space diversity reception at the mobile presents little problem since the antenna separation distances that achieve this mount of decorrelation in the mobile environment are very small (≤20 cm at 850 MHz). However, the space diversity antenna separation requirement at the land site necessary to achieve the same amount of signal decorrelation is in the range of 10 wavelengths or more at antenna elevations of 150 ft or greater. Therefore, a comprehensive characterization of the effect of changing the cross correlation between the two received signals at the land site is important to effective system design. The performance of the two-branch equal-gain diversity system as a function of the cross-correlation between the two received signals from the diversity antennas is described. The cumulative probability distribution, level crossing rates, and duration of fades from a two-branch equal-gain combined diversity signal with variable correlation between the two branches are described also.     

Vehicle location system experiment

A vehicle location system concept which utilizes narrow-band-radio trilateration has been developed for use in command and control systems designed to dispatch mobile vehicles. A comprehensive system experiment was carried out in Schenectady, N.Y., designed to evaluate the system's performance in a severe radio multipath environment, and to evaluate the improvement in performanee realized by system design options developed to improve performance degradation of multipath, that is, redundant receiving stations and space diversity antennas. Experimental results from the system experiment show that although high instrumental precision can be realized by narrow-band-radio trilateration techniques, a severe multipath environment, such as the Schenectady area produces by surrounding hills and valleys, degrades the instrumental precision. The results also indicate that four receiving stations each having four space diversity antennas will improve performance yielding a total vehicle location error radius of 900 ft, which is standard deviation for the Schenectady area.     

Effect of imperfect channel estimation on transmit diversity in CDMA systems

In this paper, the effect of imperfect channel estimation on the transmit diversity based on space-time block coding for the downlink of a direct-sequence code-division multiple-access system is studied. Two transmit antenna and one receiving antennas are employed. However, the results of this paper can be extended to the system with more receiving antennas. Each channel is modeled as frequency-selective Rayleigh fading and the pair of channels corresponding to two transmit antennas are mutually independent. Both spatial diversity gain and multipath diversity gain are obtained in the system. The system performance is evaluated in terms of bit-error rate under the perfect and imperfect channel estimation. A pilot-assisted channel-estimation scheme with one common spreading code sequence is exploited. It is shown that the inaccurate channel estimates suffering from multiple access and multipath interference significantly degrade the system performance and can be effectively improved by use of a simple low-pass filter. The investigation of the power ratio of pilot to data channels illustrates that the base station should dynamically adjust the transmit power of the pilot channel according to the varying system configurations in order to achieve the best performance.     

A study of the relationship between multipath distortion and wavenumber spectrum of refractive index in radio links

The study reported here is concerned with relating the multipath and frequency selective fading characteristics of radio links caused by scatter phenomena to the statistical spatial characteristics of the refractive index. Two specific antenna configurations are studied in detail: the LOS (line-of-sight) case where the two antennas are pointed concentrically and the OTH (over-the-horizon) case where the antennas point along a great circle path. For each of these antenna configurations two scatter situations are considered: isotropic scatter with the propagation medium controlling the focusing of energy and locally isotropic scatter with narrow-beam antennas. In all cases single scattering theory is used and narrow-band signal transmission is assumed. It is found that when multipath is of any importance in causing signal distortion for a LOS link, the scatter portion of the channel may be modeled as a continuum of uncorrelated scatterers. Also OTH links are found to be characterizable in the same way. Single integrals and specific analytic and numerical examples are given relating frequency correlation functions and delay power spectra to the wavenumber spectra of assumed refractive index fluctuations. It is shown that a measurement of the frequency correlation function or delay power spectrum can yield an estimate of the wavenumber spectrum of the refractive index fluctuations.     

Experiment on coherent adaptive antenna array for wideband DS-CDMAmobile radio

A four-element pilot symbol-assisted coherent adaptive antenna array diversity receiver for 4.096 Mchip/s wideband direct sequence code division multiple access mobile radio is implemented and its performance in a multipath fading environment is evaluated by a laboratory experiment using hardware fading simulators. The receiver comprises an adaptive antenna array using the normalised least mean square algorithm and Rake combiner. It is demonstrated that, for the three-user case, the required average signal-to-interference ratio obtaining average BER of 10^-3 can be reduced by ~8 dB compared to four-branch antenna diversity     

Transmitter diversity for OFDM systems and its impact on high-ratedata wireless networks

Transmitter diversity and down-link beamforming can be used in high-rate data wireless networks with orthogonal frequency division multiplexing (OFDM) for capacity improvement. We compare the performance of delay, permutation and space-time coding transmitter diversity for high-rate packet data wireless networks using OFDM modulation. For these systems, relatively high block error rates, such as 10%, are acceptable assuming the use of effective automatic retransmission request (ARQ). As an alternative, we also consider using the same number of transmitter antennas for down-link beamforming as we consider for transmitter diversity. The investigation indicates that delay transmitter diversity with quaternary phase-shift keying (QPSK) modulation and adaptive antenna arrays provides a good quality of service (QoS) with low retransmission probability, while space-time coding transmitter diversity provides high peak data rates. Down-link beamforming together with adaptive antenna arrays, however, provides a higher capacity than transmitter diversity for typical mobile environments