This paper reports multi-user D-MIMO system capacity calculations for 4x4 D-MIMO channels, simulated using transmission loss and indirect path loss variation models derived from channel sounding measurements made with a vector-network-analyser (VNA) based channel sounding system. The channel sounding measurements were made with a bandwidth of 500 MHz at centre frequencies of 2.4 GHz, 18 GHz, and 28 GHz, in a small cluttered study room. Transmission was from an emulated sector antenna mounted with a downtilt of 62.5 degrees above the suspended ceiling in the room at a height of 4 m above floor level. Reception was at 45 desk-top-height locations scattered throughout the room using an omni directional antenna at 2.4 GHz, and step-wise azimuth and elevation scanning horn antennas with 10 deg. beamwidths in both planes, which scanned for maximum received power at 18 GHz and 28 GHz. Reported results show that, given the same average SNR, D-MIMO system capacities are approximately the same with no beam steering at UEs at 2 GHz and with beam steering at UEs at 18 and 28 GHz. In the scenario considered, between 20 dB and 25 dB and between 30 dB and 35 dB more system gain is required at 18 GHz and at 28 GHz, respectively, to achieve the same SNR as at 2 GHz. However, it is considered that when beams are steered at a UE to receive maximum power from specular reflections, it might be possible to avoid the deleterious effects of correlations in spatial transmission loss variations and interference. In this case, significant increases in outage capacity (e.g. 3 bits/s/Hz, compared with 1 bit/s/Hz, at SNR=6 dB) can be achieved at the same SNR, with respect to that in conventional 2 GHz systems, when the steering of narrow beams to the direction of maximum received power is employed.

The future use of cellular radio systems incorporating relay links is viewed [1-3] as key to the satisfaction of ever-increasing demands for greater capacity, while maintaining installation and operating costs at manageable levels. However, because of the scarcity of published propagation measurements on relay channels, channel models that have heretofore been used to support the claimed advantages of systems incorporating relays must be considered as only provisional until more measured results are available. This paper therefore reports radio propagation measurements that were made to observe quasi-simultaneous characteristics on direct and indirect (relay) radio links in base-relay-mobile terminal configurations that result in an emulation of radio links in urban microcells. Statistics for both wide and narrowband channel parameters, models for narrowband fading, and comparisons of results for direct and indirect links pertinent to both amplify and forward (AF) and decode and forward (DF) relay systems are reported.

A procedure for the analysis of narrowband fast fading data with statistically non-stationary characteristics is proposed and applied to data obtained from wideband radio propagation experiments involving two-hop relay channels at 2.25 GHz. The reported experiments were conducted from two channel sounder base station sites in Ottawa to enable a study of the characteristics of relay links in urban microcell environments and of vehicle-to-vehicle communications in relay-based cellular networks. It is shown that empirically-derived cumulative probability distributions for narrowband fast fading on relay links during time intervals when such fading exhibits quasi-stationary characteristics conform closely to a Double-Rician model, the derivation of which is detailed. Analysis of the Double-Rician distribution shows that Double-Rician fading is deeper than Rician fading, unless the K-ratios of the Rician links comprising the relay link are highly dissimilar (having 10 dB difference or more). In such cases, fading on the relay link has a distribution that is very similar to that of the constituent link with the smallest K-ratio. While, in general, relaying is meant to increase average received SNR, it is shown that when the fast fading on the links constituting a relay channel is i.i.d., N-hop relaying reduces the specular-to-random power ratio on the relay link by N times, or significantly increases the depth of fading. This result indicates a need for significant gains at relay stations in some cases.

In this paper, a new algorithm that is able to identify and track multipath clusters in the delay-angular domain is introduced. The introduced algorithm avoids calculations of a single distance measure from quantities with different nature; instead it performs the clustering via extracting multiple 1D waveforms from the 2D delay-angular domain. The results from applying this algorithm to measured radio propagation data (recorded using a sounding system with 32 receive antenna) is used to classify the identified multipath clusters into different groups. The lengths of the active intervals (which are defined as the lengths of the intervals in which clusters exists) of the multipath clusters as well as their powers in the different groups are modelled. It was shown that the power of multipath clusters in these different groups can be modelled using the Generalized Extreme Value distribution and that this model passes the Kolmogorov-Smirnov (KS) goodness of fit test at the 5% significance level.

In this paper, we introduce a new technique that allows the coexistence of secondary users (SUs) with a primary user (PU), in the same frequency and time. The proposed technique (i.e., the cluster-based spatial opportunistic spectrum sharing (CB-SOSS) technique) exploits the spatial degrees of freedom resulting from the use of multiple antennas at both the secondary base station (SBS) and SUs; also it does not have any requirement regarding the number of antennas at the primary base station nor the PU. The CB-SOSS benefits from the fact that in wireless channels, the multipath components travel in clusters that are non-uniformly distributed in the spatio-temporal space. The key idea is to have the SBS become aware of the locations of the strong clusters in the surrounding environment and utilize them opportunistically for data transmission to the SUs, without causing a harmful interference at the PU receiver.

This paper introduces a novel transmission technique for MIMO broadcasting directional channels, herein called the Angle-of-Departure-Aided Opportunistic Space-Division Multiple Access (AOD-OSDMA) technique. In AOD-OSDMA, the knowledge of angles-of-departure (AODs) at the BS of the strongest signal received by each user is used to design multiple opportunistic beams so that advantage is made of the clustering nature of wireless channels. Compared to the OSDMA-S using 4 x 2 (8 x 2) MIMO system, the proposed technique provides gains in system capacity of up to 50% (160%), and reduces the number of channel directional feedback bits by 33% (55%), when evaluated using MIMO directional channel model such as WINNER.

This paper is concerned with modeling and identification of wireless channels using noisy measurements. The models employed are governed by stochastic differential equations (SDEs) in state space form, while the identification method is based on the expectation-maximization (EM) algorithm and Kalman filtering. The algorithm is tested against real channel measurements. The results presented include state space models for the channels, estimates of inphase and quadrature components, and estimates of the corresponding Doppler power spectral densities (DPSDs), from sample noisy measurements. Based on the available measurements, it is concluded that state space models of order two are sufficient for wireless flat fading channel characterization.

Work reported in this paper contributes to the characterisation of 4.9 GHz radio channels in a scenario in which emergency vehicles are parked outside a building and operate as a communications centre for communications with rescue crews and equipment inside the building. Transmission loss, rms delay spreads, equivalent CW envelope fading characteristics, and frequency correlation characteristics are reported for the measured channels. Achievable IEEE 802.16 performance on the measured channels is also predicted, using simulations based on time series of 50 Mchps PN channel soundings.

For planning purposes, there is a need for the evaluation of expected performance on mobile radio links in anticipated new frequency bands and comparison of results with 2 GHz band performance estimates evaluated by the same methods. To that end, this paper reports the application of a semi-analytical technique to estimate average binary phase shift keyed direct sequence spread spectrum mobile link error rates at 1.9 and 5.8 GHz from time series of channel response estimates derived from data recorded during propagation experiments with a 5 mchps pseudo-noise channel sounder. This work is unique, as the methods used incorporate the consideration of self interference as well as random channel variations based on direct analysis of the experimentally-determined channel response estimates, rather than simplified models for either the self interference or the channel variations.

A key problem in high-resolution multidimensional parameter estimation via unitary ESPRIT is to jointly solve a set of invariance equations by means of least-squares minimization. It has been shown previously that existing least-squares techniques fail when applied to the category of cross arrays, which consist of perpendicular uniform linear arrays crossing at the center of the array. Cross array geometries are of special interest because they provide a larger aperture and, hence, better resolution for a given number of array elements than other multidimensional uniform array geometries. This letter proposes an improved structured least-squares method that enables successful application of unitary ESPRIT to cross arrays. Results of simulated direction-of-arrival estimation experiments using a three-dimensional cross array indicate that considerable performance improvements can be achieved if the new method is used.

A significant number of propagation and channel modeling papers have reported channel parameters like RMS delay spread, correlation bandwidth, and the Rician K factor, derived by various new methods from instantaneous, or snapshot measurements. This conflicts with the original definitions of these parameters, which formally should be derived from time averages, under an assumption of ergodicity and applied for the assessment of time-averaged link performance. It appears that the origins of fading channel characterization parameters, and the conditions under which they can be estimated and applied are now often ignored, leaving interpretation of new results subject to skepticism. This paper, therefore, provides a critical review of the estimation of frequency correlation and one of these parameters, correlation bandwidth, using channel impulse response estimates derived from propagation measurements. The practical application for knowledge of frequency correlation is summarized. Then, the derivation of the equation relating a channel's average power delay profile to its frequency correlation function via a Fourier transform is reviewed, with emphasis on conditions needed for validity. An alternate method, free from most of these conditions is also reported. Examples are given and comparisons are made of results from analyses using the two methods to estimate frequency correlation on Rayleigh and Rician mobile radio channels, which are shown to have significantly different frequency correlation characteristics. Finally, a measure of frequency correlation that is free from ambiguity concerning the value (e.g., 0.5, 0.75, or 1/e) at the correlation band edges is recommended.

An examination of potential advantages of cell-site diversity with selection combining in the context of MM-wave fixed cellular systems is reported. The study involves simulation of converging radio links over weather radar images of the radar reflectivity factor, from which the specific attenuation of rain at 30 GHz is derived. The average correlation of attenuation on two converging links as a function of their angular separation is shown to indicate the potential benefits in the use of cell-site diversity, especially in heavy rain. Results show that diversity gain exhibits a dependence on angular separation /spl theta/ in the general form of sin/sup k/ (/spl theta//2). For links of identical lengths the model reduces to a root-sinusoidal shape (k=0.5), whereas links of unequal lengths lead to the ITU-R recommended model (k=1). Based on the sin/sup k/ (/spl theta//2) model and observation of the length ratio of the links, a set of criteria for determining the benefit of cell-site diversity for a given subscriber location is proposed.

This paper reports the analysis of data that were measured on 1.8 GHz microcellular-type channels in four Canadian cities, with one of the objectives being propagation loss modelling. Various transmit configurations are considered, including different antenna heights, different antenna patterns and both horizontal and vertical polarisation. CW as well as wideband (impulse response) data were recorded on both line-of-sight (LOS) and non-line-of-sight (NLOS) channels. The CW results indicate that on about 40% of the streets in an urban area, LOS power loss has a continuous slope that is proportional to R/sup n/, where n is close to 2, as for free space. For the other 60% of the streets, loss is proportional to R/sup -2/ for short ranges. For ranges greater than a breakpoint range, R/sub b/, n takes on greater values that are believed to depend upon position of the mobile station antenna on the vehicle, street geometries, shadowing, and the orientation of structures, such as sign posts and power lines. It was found that the power loss exponent in this region rarely takes on values near 4 nor is R/sub b/ often close to the edge of the first Fresnel zone, as would be expected from the flat-earth model, proposed by others for application in microcellular systems. Like the results from the flat-earth model, however, it was found that R/sub b/ is greater for higher base station transmit antennas. Results for base station antennas with different radiation patterns and polarisations also indicate that it may be possible to vary these parameters in order to control R/sub b/, and thus cell size, and intra-cell interference.

The authors report experimental and modeling studies that investigate the dependence of indoor radio channel multipath characteristics on a transmit/receive range. Specifically, a simple model for estimation of the complex baseband equivalent impulse response for indoor channels is explained. Using this model, the relationship between RMS delay spread and range on static indoor channels is estimated. Results show that this relationship is nonmonotonic and has a maximum at a range that depends on the building dimensions and the electrical properties of reflecting surfaces. The model is used in infinite, as well as finite, resolution modes to supplement the measurements of impulse response characteristics in different buildings using a limited resolution channel sounder. Experimental and modeling results are combined to derive conclusions that confirm the anticipated nonmonotonic relationship exists in empty buildings. Measurement results demonstrate that furniture has the effect of destroying this relationship, making RMS delay spread almost independent of range.>

This paper reports work in which a method for error performance predictions on flat fading, statistically non-stationary radio channels is proposed and evaluated. The method involves consideration of three types of channel behaviour (quiescent, fading, and faded) and the use of statistics characterizing each in a three-term probability of error equation. Results give error probabilities that would not be exceeded for "x" percent of the time on indoor and mu cellular land mobile links having signal-to-noise ratios computed using routine link budget calculations, without fade margins.>

The results of measurements made to determine propagation characteristics on urban mobile radio channels with low base-station antennas and line of sight between the base and mobile units are reported. Results show that multipath propagation conditions would be significantly less severe if small-celled systems were implemented. Root-mean-square delay spread averages computed by considering all multipath signal components with powers greater than 25 dB below the peak were reduced by a factor of approximately four in comparison to those typical in conventional systems. In addition, microcellular-type channels have Rician, rather than Rayleigh, envelope fading characteristics and correspondingly different frequency correlation statistics. The area bounded by the correlation envelope is introduced as a measure of channel quality, and these areas are shown to be larger for Rician channels than for Rayleigh channels.>

The results of temporally and spatially distributed wideband (impulse response) propagation experiments in the 900 MHz and 1.7 GHz radio frequency bands in two different buildings on fixed indoor radio links are reported. Results from the temporal experiments show that, for a specific location in either of the two buildings, the dynamics of indoor channels are slightly less random at 910 MHz than at 1.7 GHz. It is believed that this would result in marginally better performance on a given transmit/receive link in the 900 MHz band. The spatially distributed measurements showed that the structures of average impulse-response envelopes differed for channels in the two buildings. In one building, RMS delay spreads were slightly greater in the 1.7 GHz band for over 90% of transmit/receive link configurations. In the other building, RMS delay spreads were marginally greater in the 900 MHz band for 70% of the configurations.>

The probability of error for the transmission of digital information on fading radio channels is influenced by the statistical behavior of fading. This is characterized by the cumulative distribution function (CDF) for the received signal envelope, and the correlation of random variations across the channel bandwidth. It is therefore important for system design purposes to determine the distribution function for envelope fading, and the frequency correlation characteristics of radio channels in propagation environments where the use of digital radio systems is planned. This paper details experiments that were conducted under conditions similar to those which would be typical on 800/900 MHz band satellite-mobile channels in rural environments. The impulse response functions of measured channels were estimated by operating a pseudonoise channel probe from a 65 m tower through deciduous trees to a receiver at close range. Measurement results include: channel impulse response estimates, envelope fading statistics, and double-sided frequency correlation plots. Comparisons are made between channel characteristics during the summer and during the autumn after the leaves have fallen from the trees. Estimates of digital channel capacity limitations are also given. Aside from the fading statistics, these channel characteristics have not previously been reported.