The dependence of multi-antenna capacity on bandwidth is characterized empirically for narrowband, wideband and ultrawideband indoor channels using spatial and polar arrays. It is shown that both the mean and the outage MIMO capacity increase with bandwidth, whilst the capacity coefficient of variation asymptotically vanishes.

In this letter, we propose a novel receive antenna selection algorithm based on cross entropy optimization to maximize the capacity over spatially correlated channels in multiple-input multiple-output (MIMO) wireless systems. The performance of the proposed algorithm is investigated and compared with the existing schemes. Simulation results show that our low complexity algorithm can achieve near-optimal results that converge to within 99% of the optimal results obtained by exhaustive search. In addition, the proposed algorithm achieves near-optimal results irrespective of the mutual relationship between the number of transmit and receive antennas, the statistical properties of the channel and the operating signal-to-noise ratio.

Cyclic delay diversity (CDD) is an attractive diversity scheme due to its low complexity and compatibility to the existing standard orthogonal frequency division multiplexing systems. This paper presents an novel receiver antenna selection criterion for transmit CDD systems to obtain the maximal diversity gain. The performance of the proposed system is very close to the corresponding orthogonal space-time block coding diversity schemes with optimum receiver antenna selection, but CDD has the advantages of much lower complexity and no data rate reduction. Moreover, in order to make the proposed system simpler for implementation, a low complexity antenna selection algorithm has been presented.

Correlated fading adversely affects the spatial multiplexing and diversity performance of multiple-antenna systems. This paper presents an empirical investigation of spatial correlation in ultrawideband (UWB) indoor channels in the FCC- allocated 3.1-10.6 GHz band. The impact of a number of system parameters on spatial correlation at the receiver is evaluated. It is found that the coherence distance falls with channel bandwidth in endfire arrays but not in broadside arrays. The complex correlation decays less rapidly with distance in broadside arrays than in endfire arrays, especially under line-of-sight, but the envelope correlation is circularly symmetric in space. Strong dependence of spatial correlation and coherence distance on the channel center frequency is observed. Furthermore, horizontally polarized links are found to exhibit less correlation than vertically polarized links. A discussion of the implications of these results for multiple-antenna UWB systems is provided.

Propagation measurements using a large array are used to study the angle of arrival (AOA) across the ultrawideband (UWB) frequency range of 3.1 to 10.6 GHz. A two-dimensional Unitary ESPRIT algorithm is employed to give a high resolution estimation of AOA including both the azimuth and elevation angles of multipath components. The frequency dependence of AOA is investigated over the UWB frequency band. The multipath rays form clusters in both angular and temporal domains. Within a cluster the azimuth and elevation AOAs are determined to follow Laplacian and Gaussian distributions respectively. In the indoor environment considered, a typical cluster extends over an angular sector of approximately 14 degrees in azimuth and 9 degrees in elevation, with up to 5 clusters observed. We note that these propagation characteristics will allow UWB systems to utilise smart antennas or MIMO structures to improve overall throughput.

Abstract—A low complexity user scheduling algorithm based on a novel adaptive Markov chain Monte Carlo (AMCMC) method is proposed to achieve the maximal sum capacity in an uplink multiple-input multiple-output (MIMO) multiuser system. Compared with the existing scheduling algorithms, our algorithm is not only more efficient but also converges to within 99 % of the optimal capacity obtained by exhaustive search. We demonstrate the convergence of the proposed scheduling algorithm and study the tradeoff between its complexity and performance. Index Terms—Adaptive Markov chain Monte Carlo (AM-CMC), multiple-input multiple-output (MIMO), multiuser selec-tion, scheduling, sum capacity. I.

This paper investigates the impact of channel bandwidth on fading in wireless channels using indoor measurements. The variation of channel energy over a local region is examined for narrowband, wideband and ultrawideband (UWB) channels, and the corresponding fade depth is evaluated. The relation between bandwidth and fade depth is then captured with a simple dual-slope model. The effect of antenna polarization and line-of- sight blockage is also investigated. We observe that the fade depth initially falls rapidly with bandwidth, reaching 4 dB at 1 GHz, but further reduction in fading with bandwidth is much slower.

Polarized single-input multiple-output (SIMO) arrays can improve system robustness and rate while offering a compact design. We investigate the error performance of Impulse Radio ultrawideband (UWB) systems with multiple- antenna arrays employing polarization orthogonality. Based on indoor channel measurements, we evaluate the improvement in the link reliability due to dual- or triple-polar antenna arrays. Using a two-dimensional combining receiver, it is demonstrated that polarization diversity can be very effective in reducing the overall system complexity, making Impulse Radio implementation practically feasible.

In most wireless communications research, the channel models considered experience less severe fading than the classic Rayleigh fading case. In this work, however, we investigate MIMO channels where the fading is more severe. In these environments, we show that the coefficient of variation of the channel amplitudes is a good predictor of the link mutual information, for a variety of models. We propose a novel channel model for severely fading channels based on the complex multivariate t distribution. For this model, we are able to compute exact results for the ergodic mutual information and approximations to the outage probabilities for the mutual information. Applications of this work include wireless sensors, RF tagging, land-mobile, indoor-mobile, ground-penetrating radar, and ionospheric radio links. Finally, we point out that the methodology can also be extended to evaluate the mutual information of a cellular MIMO link and the performance of various MIMO receivers in a cellular scenario. In these cellular applications, the channel itself is not severely fading but the multivariate t distribution can be applied to model the effects of inter-cell interference.

Providing diversity is one of the two possible objectives (the other one is providing multiplexing) of a multi-input multi-output (MIMO) system. For ultra wideband (UWB) impulse radio systems using rake receivers, there are already richly inherent multipath diversities. However, there may be UWB applications making use of more than one UWB transmit antenna and/or receive antenna, which leads to UWB MIMO systems. The difference between the diversity analyse of a UWB MIMO system from that of a narrow band system lies in the different choice of propagation channel model for the branches linking each transmit antenna and receive antenna. Similar to the narrow band system, the existence of the correlation between the branches can severely degrade the diversity performance, and complicate the performance analyse. In this paper, the wideband propagation channel for the UWB MIMO system, with pre-defined correlation model for the branches, is broken down into several uncorrelated elementary narrow-band propagation channels with equivalent diversity performance. Based on this, a novel method for evaluating the diversity performance of a MIMO UWB impulse radio system is presented.

A simple and efficient virtual-source ray-tracing technique for the simulation of indoor wideband radio and optical propagation channels is proposed. The parametric deterministic model considers the room geometry, transceiver locations, material properties and probe signal types. It is applied to the indoor ultrawideband channel in the FCC-allocated 3.1–10.6 GHz band, and a range of novel results are presented to illustrate several possible applications. The channel small-scale fading statistics and spatial variability are examined by synthesising a densely sampled aperture. Multiple-antenna array systems are simulated to evaluate multiple-input multiple-output performance. The multipath angular characteristics are analysed from the simulated azimuth-delay profile. The simulation results closely match previous channel measurement studies and statistical models, validating the proposed technique. It is shown that specular reflection is dominant, and power convergence is achieved with three reflections in a typical indoor environment. Thus, it is demonstrated that despite its simplicity, the model yields reliable and accurate results, and can therefore be a useful tool for indoor wireless network planning and performance prediction.

This paper experimentally investigates the performance of multiple-input multiple-output (MIMO) systems in indoor ultra wideband channels. The improvement in robustness and information rate due to spatial and polar antenna arrays is evaluated. The subchannel correlation, power gains of supported eigenmodes, and branch power ratios are analyzed. The polar arrays are found to experience lower correlation than spatial arrays. SNR gains of up to 3–5 dB are reported with 1$\,\times\,$2 and 1$\,\times\,$3 spatial arrays, respectively; the latter is shown to double the coverage range. The mutual information capacity is found to scale almost linearly with the MIMO array size, with very low variance. It is confirmed that the device compactness achieved by the polar array comes with only a small penalty in the achievable capacity and SNR gain compared to the spatial array. The multiple-antenna UWB techniques explored in this paper offer the potential for high data rate and robust communications.

This paper experimentally investigates the performance of multiple-input multiple-output (MIMO) systems in indoor ultrawideband (UWB) channels. The improvement in robustness and information rate due to spatial and polar antenna arrays is evaluated. The subchannel correlation, power gains of supported eigenmodes, and branch power ratios are analyzed. The polar arrays are found to experience lower correlation than that of spatial arrays. SNR gains of up to 3 and 5 dB are reported with 1times2 and 1times3 spatial arrays, respectively; the latter is shown to double the coverage range. The mutual information capacity is found to scale almost linearly with the MIMO array size, with very low variance. It is confirmed that the device compactness achieved by the polar array comes with only a small penalty in the achievable capacity and SNR gain compared to the spatial array. The multiple-antenna UWB techniques explored in this paper offer the potential for high-data-rate, robust communications.

The variation of channel fading and dispersion statistics between the ultrawideband (UWB) channel subbands is characterized experimentally. Within the FCC-allocated UWB frequency range (3.1-10.6 GHz), the multipath characteristics in various subbands are found to be highly dissimilar. It is demonstrated that the higher subbands suffer greater attenuation, and the rms delay spread varies significantly with the center frequency. The impact of this variation on multiband-OFDM UWB system performance is evaluated, and a large performance variation across the band is reported

The frequency-dependent pathloss characteristics of an indoor radio channel are investigated over the FCC-allocated ultrawideband (UWB) frequency range (3.1-10.6 GHz). Complex channel transfer functions are measured under a variety of propagation conditions. The dispersion index is introduced as a measure of the frequency-dependence pathloss and is estimated for each measured channel response. Its first order statistics exhibit significant deviation from the nominal value. The small-scale spatial analysis of the dispersion index reveals a periodic structure for vertically polarized channels. Fractional calculus is used to demonstrate the impact of this dispersion on system performance, and the consequent signal waveform distortion is evaluated.

The accurate detection of the direct path in a dense multipath environment is vital for reliable performance of time-based and angle-of-arrival (AOA) based location estimation techniques. This paper investigates the effect of measurement bandwidth and antenna directivity on the detection of the direct path in a typical indoor scattering environment. It is experimentally shown that the ranging error diminishes with increase in measurement bandwidth and the standard deviation of the root mean square ranging error (RMSRE) is reduced by using directional transmit antennas. The results are obtained in a line-of-sight (LOS) propagation environment and are based on the time-of-arrival (TOA) based ranging technique.