Geometric Channel Model Research Articles

New super-orthogonal space-time trellis codes using differential M-PSK for noncoherent mobile communication systems with two transmit antennas

In this paper, we develop super-orthogonal space-time trellis codes (SOSTTCs) using differential binary phase-shift keying, quadriphase-shift keying and eight-phase shift keying for noncoherent communication systems with two transmit antennas without channel state information at the receiver. Based on a differential encoding scheme proposed by Tarokh and Jafarkhani, we propose a new decoding algorithm with reduced decoding complexity. To evaluate the performance of the SOSTTCs by way of computer simulations, a geometric two-ring channel model is employed throughout. The simulation results show that the new decoding algorithm has the same decoding performance compared with the traditional decoding strategy, while it reduces significantly the overall computing complexity. As expected the system performance depends greatly on the antenna spacing and on the angular spread of the incoming waves. For fair comparison, we also design SOSTTCs for coherent detection of the same complexity as those demonstrated for the noncoherent case. As in the case of classical single antenna transmission systems, the coherent scheme outperforms the differential one by approximately 3 dB for SOSTTCs as well.

On the bounds of frequency-selective channel capacity with doubly correlated geometrical MIMO channel model

The multi-input multi-output (MIMO) technology plays an important role in link transmissions. This article considers the general case for the ergodic capacity in doubly correlated frequency-selective MIMO channel. In the study, the geometrical MIMO channel model is presented. Based on the formula of MIMO ergodic capacity, the capacity limits are studied with arbitrary finite number of antennas in the frequency-selective MIMO channel. It first derives the exact expressions for the upper bound and lower bound in doubly correlated MIMO channel. The results for the single-ended correlation and independent identically distributed (i.i.d.) MIMO channel are also obtained as special cases. Then the simple expressions of the capacity bounds are attained at high SNR. Finally, results are provided by Monte Carlo simulations to verify the tightness of the derived bounds.

GEOMETRICALLY BASED CHANNEL MODEL FOR INDOOR RADIO PROPAGATION WITH DIRECTIONAL ANTENNAS

A geometrically based channel model is proposed to describe radio propagation in an indoor environment with directional antennas. In conventional geometric channel models (GCMs), distribution of scatterers does not take into account the antenna properties. A difierent approach is taken here for directional channel modeling. The locations of scattering objects are deflned using non- Cartesian coordinates comprising an auxiliary geometric parameter ‰ and angle-of-arrival (AOA) `. Subsequently, we present a systematic method to study the in∞uence of antenna pattern on scatterer distribution by applying two heuristic rules, which underpin the connection between the physical wave-propagation process and its canonical GCM. Provided with model preliminaries, important channel parameters including power azimuthal spectrum (PAS), power delay spectrum (PDS), mean efiective gain (MEG), and antenna-decoupled PAS are derived and compared against the published data in the existing literature to demonstrate the usefulness of the proposed model.

Angle-of-Arrival Statistics of a Three-Dimensional Geometrical Scattering Channel Model for Indoor and Outdoor Propagation Environments

In this letter, a three-dimensional geometrical scattering channel model is introduced to simultaneously describe the angular distribution of multipath waves in the azimuth and the elevation angles. The angle-of-arrival probability density functions of the received multipath waves are provided. These functions facilitate independent control of the angular spread in both the azimuth and the elevation angles via the model's parameters. To establish the model verification, it has been compared against the results from a site-specific propagation prediction technique at indoor and outdoor wireless communication environments.

GEOMETRY-BASED STATISTICAL MODEL FOR RADIO PROPAGATION IN RECTANGULAR OFFICE BUILDINGS

We present a new approach to the modeling of angle and time of arrival statistics for radio propagation in typical office buildings, in which the majority of interior scattering objects are either parallel or perpendicular to the exterior walls. We first describe the reradiating elements in office buildings as randomly distributed arrays of thin strips. The amount of clutter and the amount of transmission/reflection loss are then accounted for through several key parameters of the site-specific features of indoor environment, such as the layout and materials of the building under consideration. Subsequently, the important channel parameters including power azimuthal spectrum (PAS) and power delay spectrum (PDS) are derived. An appealing observation is that when the path angles from multiple channel trials are measured and collectively analyzed, deterministic angle clustering becomes evident. This phenomenon agrees well with the existing ray-tracing (RT) results reported by Jo et al. in buildings of this type and cannot be explained by other geometric channel models (GCMs). Furthermore, the proposed model predicts an asymmetric cluster PAS for a single-channel-trial scenario, which yields an excellent fit to the experimental data presented by Poon and Ho. Finally, we have also investigated the behaviors of the superimposed PAS and PDS under various channel conditions.

A Simple 3-D Geometric Channel Model for Macrocell Mobile Communications

One of the fundamental research areas in wireless communications is the development of realistic models that can efficiently and accurately describe the wireless propagation channel. Most of the proposed models disregard the three dimensional character of the signal spread or use techniques with excessive computational complexity. In this paper, we develop a simple 3-D geometric scattering model for the uplink of a macrocell mobile environment that provides the statistics of Angle-of-Arrival (AoA) of the multipath components. The model extends the 2-D geometrical-based single bounce macrocell (GBSBM) model. Explicit closed-form expressions are derived for the statistics of the AoA of the multipaths in the azimuth and elevation planes. Analysis of the results exhibits the advantages of our proposal compared to 2-D and 3-D ones published in the literature. Comparisons with experimental data confirm its validity. Interesting conclusions for the effective evaluation of mobile communication systems have been derived. Moreover, an application of the model to mobile location estimation has been developed and evaluated.

Range improvement of UWB systems using adaptive multicarrier spread‐spectrum and MIMO techniques

AbstractIn this paper, we investigate the use of multiple‐input multiple‐output (MIMO) techniques with a linear precoded orthogonal frequency division multiplexing (LP‐OFDM) waveform, known as spread‐spectrum multicarrier multiple access (SS‐MC‐MA), for high data rate ultra‐wideband (UWB) systems. This scheme is an evolution of the well‐known multiband OFDM (MB‐OFDM) solution supported by the WiMedia Alliance. The aim of this paper is to improve the UWB system range while not significantly increasing the system complexity compared to the WiMedia solution. Firstly, an analytical study of the single‐input single‐output (SISO) LP‐OFDM waveform allows to find how to efficiently precode an OFDM signal in order to improve the system range. To go further and exploit the available spatial diversity, a MIMO component is added and a new geometric statistic MIMO channel model is considered. Secondly, a global MIMO LP‐OFDM system study is led to highlight the benefits of combining MIMO and LP techniques for UWB applications. The analytical and simulation results show that the joint use of MIMO and LP‐OFDM leads to a significant range improvement compared to the WiMedia solution. Copyright © 2008 John Wiley & Sons, Ltd.

Measurement of Large-Scale Cluster Power Characteristics for Geometric Channel Models

Directional urban radio channel measurements are analyzed in this paper. The mean powers, the shadow fading, and the lifetimes of individual propagation clusters extracted from the measured data are studied. The cluster shadow fading is an input parameter of several directional channel models, but measured values for the fading have not been published previously. Also, measured numbers of strong, significant propagation clusters are essential for the channel models.

On the Solution of Scatter Density in Geometry-Based Channel Models

Assuming a single bounce scattering geometric channel model with circularly symmetric scatter density we deduce a general integral relation between angle of arrival (AOA) and scatter density function. Then we show that this relation can be expressed in terms of an integral equation that admits an accurate numerical solution provided that AOA is known. Furthermore, we show that similar integral equation relation between time of arrival (TOA) and scatter density function can be efficiently solved numerically for a given TOA. Results indicate that the scatter density can be numerically computed for a given AOA or TOA. Since these marginal distributions can be directly fit in channel measurements, the method provides means to adjust the applied geometrical channel model through field measurements. Hence, we follow the idea of inverse scattering theory where the far field pattern of scattered waves is known and the aim is to define the structure of the scattering medium. We consider two example AOA distributions, Gaussian and Student's t-distribution, found in literature. Our results show that scatter densities as well as the corresponding TOAs greatly vary depending on the assumed AOA

Effect of Antenna Directivity on Angular Power Distribution at Mobile Terminal in Urban Macrocells: A Geometric Channel Modeling Approach

We present a geometric channel model to study the effect of antenna directivity on angular power distribution at the mobile terminal in urban macrocells. The methodology reviewed in this paper integrates the antenna effect into the model geometry, thereby facilitating a system-dependent channel characterization. As each device is limited in terms of measurement sensitivity, the effective scatterer distribution is essentially dependent on the antenna beam pattern. Subsequently, two heuristic rules are proposed to establish the underlying relationship between the model geometry and the corresponding wave-propagation processes. It is shown that the influence of directional antenna is twofold. First, it alters the spatial distribution of scatterers by providing a different sample space for the random field, and secondly, it distributes signal components into the angles-of-departure or collects them from the angles-of-arrival by weighted combination. Important channel parameters measured at the mobile terminal such as the angular power distribution, Doppler spectrum, and multipath shape factors are also investigated to further exemplify the usefulness of the proposed model.

Outage Capacity of Spatially Correlated Multipath Fading Channels

In this paper, we study the effect of the scattering environment on the capacity of a single carrier linear modulation used in a multipath, multiple antenna channel. The work incorporates detailed 3D geometric channel models to assess the effect of spatial correlation. The analysis techniques, based on the pioneering work of Hirt and Massey (1988), provide a method to evaluate outage capacity. Channels that are derivatives of the ETSI standard hilly terrain and typical urban are considered in detail. The results quantify the loss of capacity produced by higher spatial correlation. When comparing signals of different bandwidth, wideband systems produce more diversity due to better temporal resolution. Surprisingly, narrowband systems gain some diversity back by being less susceptible to loss of diversity from spatial correlation

An Azimuth-Frequency Domain Geometric Model for Ultrawide Bandwidth Signal Propagation

An azimuth-frequency domain (AFD) geometric channel model aimed at establishing the fundamental propagation characteristics for an ultrawideband (UWB) time-invariant channel is proposed. This modeling approach envisages the spatial pattern of scatterer distribution in a hypothetical azimuth-frequency space. One of the main advantages of this approach is the availability of analytical expressions relating signal properties in the AFD to channel properties. A further virtue of this method is to exploit the geometric distribution of scatterers for different spectral components from a physical wave-propagation viewpoint. The workhorse is the wideband semi-geometrically based statistical model and three heuristic rules proposed, which are an extension of the rules presented in the previous work. These rules are so proposed as to provide the underlying connection between the canonical model and the physical channel it represents. The important channel properties such as power azimuthal spectrum (PAS) and power delay spectrum (PDS) are calculated using this model and compared with the published data in the existing literature.

Spatially and Temporally Correlated MIMO Channels: Modeling and Capacity Analysis

Wireless communication systems employing multiple antennas at both the transmitter and receiver have been shown to offer significant gains over single-antenna systems. Recent studies on the capacity of multiple-input-multiple-output (MIMO) channels have focused on the effect of spatial correlation. The joint effect of spatial and temporal correlation has not been well studied. In this paper, a geometric MIMO channel model is presented, which considers motion of the receiver and nonisotropic scattering at both ends of the radio link. A joint space-time cross-correlation function is derived from this model and variates with this joint correlation are generated by using the vector autoregressive stochastic model. The outage capacity of this channel is considered where the effects of antenna spacing, antenna array angle, degree of nonisotropic scattering, and receiver motion are investigated. When n transmit and n receive antennas are employed, it is shown that the outage capacity still increases linearly with respect to n, despite the presence of spatial and temporal correlation. Furthermore, analytical expressions are derived for the ergodic capacity of a MIMO channel for the cases of spatial correlation at one end and at both ends of the radio link. The latter case does not lend itself to numerical evaluation, but the former case is shown to be accurate by comparison with simulation results. The proposed analysis is very general, as it is based on the transmit and receive antenna correlations matrices.

A space-time model for mobile radio channel with hyperbolically distributed scatterers

We present a geometrical and time-variant wireless vector channel model with hyperbolically distributed scatterers for a macrocell mobile environment. This model is based on the assumption that the scatterers are arranged circularly around the mobile station, whereby the distance between the mobile and the local scatterers and the distance between the local scatterers and the dominant scatterers are distributed hyperbolically. The proposed model allows investigation of beamforming aspects as well as space-time processing techniques. Simulation results for this model are presented and compared with the exponential model results.

Conductivity noise in transmembrane ion channels due to ion concentration fluctuations via diffusion

A Green's function approach is developed from first principles to evaluate the power spectral density of conductance fluctuations caused by ion concentration fluctuations via diffusion in an electrolyte system. This is applied to simple geometric models of transmembrane ion channels to obtain an estimate of the magnitude of ion concentration fluctuation noise in the channel current. Pure polypeptide alamethicin forms stable ion channels with multiple conductance states in artificial phospholipid bilayers isolated onto tips of micropipettes with gigaohm seals. In the single-channel current recorded by voltage-clamp techniques, excess noise was found after the background instrumental noise and the intrinsic Johnson and shot noises were removed. The noise que to ion concentration fluctuations via diffusion was isolated by the dependence of the excess current noise on buffer ion concentration. The magnitude of the concentration fluctuation noise derived from experimental data lies within limits estimated using our simple geometric channel models. Variation of the noise magnitude for alamethicin channels in various conductance states agrees with theoretical prediction.

Geometrical channel models for space-time systems

Based on the unified concept of space-time system field theory, a general space-time channel model can be constructed from the statistics of the space-time system field function (S-TSFF) for an arbitrary medium. This statistical characterization of the medium (channel) can be expressed in terms of the space-time correlation function, or, equivalently, the space-time power spectral density of the S-TSFF. The space-time correlation function of the S-TSFF generalizes the concept of the mutual coherence function (MCF) for a random electric field to an arbitrary space-time field. There are three different geometrical channel models depending on the choice of the coordinate systems, e.g. rectangular, cylindrical, and spherical. Using the notions of channel correlation time and correlation distance— i.e. doppler spread and delay spread—various geometrical tap-delay channel models are derived. From a system point of view, the space-time correlation parameters can be interpreted as a measure of the spatial and tem...