Diffuse channel model and experimental results for array antennasin mobile environments

A wide-band spatial model of the mobile channel has been developed. The model allows the inclusion of array antennas at the base station. The diffuse scattering is modeled using dense discrete scatterers. An algebraic power decay is used for the path loss to the scatterers of the environment and to the mobile. Results from the model are compared with experimental results obtained at 1800 MHz. The parameters that are used are delay spread, power window, and angular spread of incident power. The model elucidates the general diffuse background scattering in a rural and an urban environment. It can be extended with inclusion of spatial specular scatterers where appropriate     

UHF propagation prediction for wireless personal communications

Propagation characteristics of radio signals in the UHF band place fundamental limits on the design and performance of wireless personal communications systems, such as cellular mobile radio (CMR), wireless LANs, and personal communication services (PCS). Because the radio link is direct to each subscriber, the prediction of signal characteristics is most important in urban areas where subscriber density is high, and the buildings have a profound influence on the propagation. The paper starts by reviewing the characteristic signal variations observed in CMR systems employing high base station antennas to cover macrocells having radius out to 20 km. Theoretical models incorporating diffraction are shown to explain the observed range dependence and shadow loss statistics. For the low base station antennas envisioned to cover microcells of radius out to 1 km for PCS applications, signal propagation is more strongly dependent on the building environment and on the location of the antennas in relation to the buildings. Various levels of theoretical modeling of this dependence are discussed in conjunction with measurements made in various building environments. Finally, the paper discusses advances in site specific prediction for outdoor and indoor propagation     

Precise Incident Power Density Pattern Measurement through Antenna Pattern Deconvolution

Future cellular and fixed wireless loops (FWL) systems employing highlydirective base stations antennas (5 to 8 degrees beamwidth) and moderatelydirective subscribers' antennas (15 to 25 degrees beamwidth) offer very largecapacity due to reduced interference. An important property of the environmentof such systems is the interference caused by scattering of the signal froma subscriber transmitter into directions other than the direct line of sightbetween the subscriber and the base station. In particular, for multibeam basestation applications scattering could arrive at the base station in thedirection being used by a different beam, resulting in interference that isdifficult to reduce by normal nulling techniques. Thus interference can behighly dependent on the incident power density pattern (IPDP) caused byscattering of the signal radiated from the subscriber. We discuss herein theuse of a uniformly illuminated array accompanied by electric fielddeconvolution to measure the crucial IPDP with the same performance as a lowsidelobe array of the same size. The mathematical correction technique usesdeconvolution of the measured complex electric field pattern with that of theantenna in free space by means of the Fourier Series and limiting the rangeof Fourier coefficients to those that are not negligible in the free spacepattern. Application of the technique to an experimental uniform array witha 2.5 degree azimuthal beamwidth shows the practicality of the deconvolutionwith real antennas in real environments. The improved resolution and accuracyprovided by Taylor weighting versus unweighted deconvolution when trying tomeasure weak scattered components in the presence of a nearby strong specularcomponent is demonstrated. The IPDP was measured from many sites surroundinga suburban base station. A plot of the cumulative distribution of the ratioof the widely scattered power to that within a prescribed beamwidth summarizesthe result of using the deconvolution technique on this experimental data.     

Improving MIMO capacity with directive antennas for outdoor-indoor scenarios

MIMO systems are usually associated with high scattering isotropic propagation while the use of directive antennas is associated with free space conditions. We found outdoor-indoor channels to be in between these two extremes, in the sense that we observed directivity - and - MIMO gain, for the same ensemble of channels. Our observation is based on measurements with directive (8 dB) and dipole antennas. Median MIMO capacities were found to be about 80% of the ideal (Rayleigh i.i.d.), at 5 dB Signal to Noise Ratio (SNR), for both types of antennas. Using properly aimed directive antennas, the SNR was found on average to be 5.4 dB above that obtainable with dipoles, somewhat less than the 7 dB antenna gain difference. Thus, isotropic propagation, which would have negated directivity gains, cannot be justified in general. We empirically established that aiming for largest received power is the best array pointing strategy with directive antennas. Combining MIMO processing and angular search resulted on average in gains of 70% over the median capacities obtained with dipoles. Therefore it may in some cases be convenient to arrange subgroups of antennas for beamforming, and then process the thus reduced number of radio channels for MIMO gain.     

Spherical outdoor to indoor power spectrum model at the mobile terminal

Mobile terminals are often used indoor with the base station outdoors. At the mobile terminal the major part of the signal energy comes through openings in the building such as windows. Typically, only one of the sides in a room has windows, and seldom does a room have windows on all sides. Hence, the dominating signal can be expected to arrive at the mobile terminal from a narrow range of angles. Mobile terminal antennas used next to the head in the speaking position will be directional due to the fact that part of the radiation pattern facing the head will be attenuated and reflected. Having a directive antenna in a directive environment, the performance will depend on the orientation of the antenna in the radio environment. A new statistical spherical outdoor to indoor power spectrum model has been proposed to be able to calculate the directional performance of mobile terminals with a single or multiple antennas. The model consists of a major scattering area in one direction and more uniformly distributed minor scatterers in the other directions. A verification of the proposed model was performed and 60 data sets of spherical power spectrum measurements were collected in a typical urban environment. Using the new model, the directional performance of mobile terminal antennas including a human operator has been investigated through directional mean effective gain, branch power ratio, and correlation calculations using spherical radiation pattern measurements of a mobile terminal including the effect of 42 different persons. The accuracy of the calculated values was verified by directly measured values using 200 persons walking with the mobile terminal in the same office-like environments as where the spherical power spectrum measurements were performed.     

Biconical horn antennas for near uniform coverage in indoor areasat mm-wave frequencies

A method is presented for designing and dimensioning biconical horn antennas in such way that the level of received power does not depend strongly on the separation distance between a centralized base station and a remote radio terminal within an indoor pico-cell. Results of cell-coverage measurements at 58 GHz are presented using these antennas within eight different indoor environments. The measurement results show that, using biconical horn antennas, an overall uniform coverage can be achieved for both line-of-sight and obstructed line-of-sight topologies     

Range-dependent path-loss model in residential areas for the VHFand UHF bands

Implementation digital fixed wireless systems, such as digital FM, high definition TV (HDTV) and wireless local loop (WILL), require a high level of accuracy of propagation prediction in the VHF and UHF bands. This paper presents a theoretical model that predicts the average path loss from an elevated base station to subscriber antennas at rooftop level in residential areas for frequencies in the approximate band from 30 MHz up to 3 GHz. In addition, the model gives the standard deviation of the path loss at the average rooftop level and the height gain for subscriber antennas above or below the average rooftop level. The approach used here generalizes that of Walfisch and Bertoni (1988), who developed a theoretical model of UHF propagation in urban environments. The rows of buildings in residential areas are modeled as a series of dielectric screens having random heights and uniform spacing. Propagation takes place over and through the dielectric screens, and ground reflections are included. The fields at the plane of each screen are obtained in terms of repeated numerical evaluation of the physical optics (PO) integral. Results obtained for the variation of the range dependence on frequency and row spacing are consistent with those previously found for high frequencies by assuming the screens to be totally absorbing. Using the results at different heights of receiving antenna allows computation of the height gain. The predictions are in agreement with the International Telecommunication Union Radio Communication (ITRU-R) recommendations in the VHF and UHF bands     

Occupational exposure to RF fields from base station antennas on rooftops

At specific situations, workers need to approach very close to the transmitting base station antennas. In this study, occupational exposure to RF fields from base station antennas was assessed at several rooftops. The measurements were carried out by mapping the power densities around the antennas. The results were compared with the ICNIRP guidelines. The results indicate that the reference levels for workers and the general public may be exceeded in front of the transmitting antenna at distances up to 1 and 2 m, respectively.     

Design and implementation of optical wireless communications with optically powered smart dust motes

Complete electronic and micro-mechanical systems can now be fabricated on the scale of hundreds of microns. Implementing radio frequency wireless communications with such 'smart dust' is challenging, due to the power required and the small size of any antennas that can be implemented. Optical wireless communications, using a modulated retro-reflector at the smart dust has the advantages of low-power consumption and highly directive channels that allow long communications ranges. In this paper we report the design and implementation of a communications system that uses a base station to communicate with, and power, smart dust motes, over ranges of 10s of metres. A base station that uses holographic beamsteering is described, and dust motes that use silicon ICs to provide communications, power and modulation control. Results indicate the dust mote will operate at a range of over 30m from the base station.     

移动通信系统中光纤直放站的设计

移动通信系统引入光纤直放站后使基站接收端的噪声发生变化,通过对光纤直放站之间的传输距离分析以及引入光纤直放站后基站接收端的噪声变化分析发现,噪声增量主要由直放站增益和基站发射机至直放站的路径损耗决定,并进一步推导出光纤直放站的上行增益应比路径损耗小8 dB,而其下行增益的设计应充分考虑到系统上下行的平衡。最后,设计了系统噪声系数为3 dB,上行增益为30 dB,下行输出功率设为36 dBm的光纤直放站。实际投放后发现,网络盲区的比例减小到3.18%,说明该直放站的效果相当显著,并且性能稳定,与原基站兼容性好。     

Some propagation experiments relating foliage loss and diffraction loss at X-band and UHF frequencies

Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced at X-band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas at X-band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found.     

Some Propagation Experiments Relating Foliage Loss and Diffraction Loss at X-Band and UHF Frequencies

Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced atX-band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas atX-band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found.     

智能天线技术对TD-SCDMA系统容量的改善

近年来,智能天线技术已成为移动通信中最具吸引力的技术之一,使用智能天线可以大大降低移动系统内的干扰,提高系统的性能和容量.基于TD-SCDMA系统,对系统的干扰及载干噪比进行了分析,重点对不同路径损耗以及误码率下,基站采用智能天线技术对系统容量的改善进行了计算和仿真.仿真结果表明,在相同的路径损耗和误码率下,采用智能天线技术可以显著地提高TD-SCDMA系统的容量.     

Effects of antenna height, antenna gain, and pattern downtiltingfor cellular mobile radio

Results of wideband path loss and delay spread measurements using high gain, high and low antenna heights with pattern tilting are presented. The measurements were done in the frequency range 905-915 MHz, at two existing cellular mobile radio (CMR) sites. Also presented are potential approaches for analyzing data from high gain antennas. It is shown that, to a large extent, existing models can be used to predict path loss for high gain antennas with downtilting. The results further support the notion that high sites together with high gain antennas and suitably selected pattern tilting can result in a significant reduction in path loss and delay spread, as well as reduction in power transmitted from the cell site and reduction in system interference     

Imperfect sector antenna diversity in slotted ALOHA mobile network

In a wireless network with path loss and fading channels, receiver capture is known to substantially enhance the performance of the slotted ALOHA random access protocol. The efficiency of narrowband slotted ALOHA radio networks can be enhanced further by using sector antennas, each receiving signals from a particular segment of the network area. This paper investigates the effect of realistic, i.e., partially overlapping antenna patterns and the resulting correlation of received power levels at different receiver branches. A method is derived for computing the joint throughput from two base station receivers with overlapping antennas patterns. The a posteriori information provided by the event of one message capturing one antenna is used to find conditional probabilities of capturing the other antennas as well. The paper shows that any overlap in the antenna patterns decreases the throughput, but transmissions from the overlapping area may face a larger probability of capture than signals from directions in which one antenna has maximum gain     

On the available diversity gain from different dual-polarizedantennas

Dual-polarized antennas are traditionally characterized in terms of port-to-port isolation and co- and cross-polar radiation patterns. For base station antennas in a mobile communications system, the critical parameter is instead the far-field coupling between the two channels. In a mobile communication system, base station antennas with a nominal ±45° to vertical linear polarization are commonly used. Such antennas are difficult to design with constant polarization characteristics in azimuth. We calculate the antenna output power correlation and diversity gain under Rayleigh fading conditions and different values of the environment cross-polar discrimination. Two different antennas are compared: a dual-polarized aperture coupled patch and a slanted dipole configuration, both over an infinite groundplane. We show that the aperture coupled patch provides lower output correlation and higher diversity gain than the slanted dipoles in all investigated cases     

Path loss, scattering and multipath delay statistics in fourEuropean cities for digital cellular and microcellular radiotelephone

The authors present typical and worst-case root mean square (RMS) delay spreads and excess delay spreads (10 dB) and mean channel path loss at 900 MHz in four European cities using typical cellular and microcellular antenna locations. Several thousand power delay profile measurements were made at six typical cellular and microcellular base station locations in the four cities. The data were obtained at local worst-case time-dispersion locations over hundreds of kilometers of typical operating routes, such as highways, bridges, and city streets, and form the basis for statistical models which can be used to predict the percentage of locations or the percentage of time in which channels will possess particular values of RMS delay spread and excess delay spread. The effect of reference distance on wideband path loss and the propagation path loss laws for cellular and microcellular radio channels are given. Radar cross sections computed from the data for typical scatterers in cellular and microcellular radio channels are given     

Effects of antenna directivity and polarization on indoor multipathpropagation characteristics at 60 GHz

In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas     

Path loss model for in-body communication in homogeneous human muscle tissue

Proposed is the first in-body path loss model in homogeneous human muscle tissue at 2.4 GHz for implants in the human body. This model is valid for insulated dipole antennas up to a distance of 8 cm. Excellent agreement is obtained between measurements, simulations and the models. The path loss model can be used to design an in-body communication system.     

Dynamics of path losses between a mobile terminal and multiple basestations in a cellular environment

We investigate the dynamics of the path losses between a mobile terminal and a small group of base stations, when the mobile traverses an area containing zones where different base stations have the least path loss to the mobile. While moving through the area, the mobile measures signals transmitted by each base station. The measurements involve calculating a running average of the measured signal power over a fixed time period. It is presumed that based on these measurements and typically other inputs, the wireless network supporting the mobile makes handoff decisions. In this paper, we do not attempt to analyze the performance of a practical handoff algorithm. Instead, we focus on the average number of times per meter traveled that a moving mobile must switch base stations in order to be always served by the base station with the least path loss. The switching rate is a function of the mobiles location with respect to the base stations and the velocity of the mobile. For low velocities, the multipath fading is not averaged out completely and, therefore, affects the measured results, while at high velocities the multipath fading is averaged out, but the resolution of the measurement is compromised, and any possible handoff will be delayed (in terms of location)