In this paper, we propose a space-time-frequency cross-correlation function (CCF) for multiple-input multiple-output (MIMO) multicarrier channels in a two-dimensional (2D) random scattering outdoor medium. The MIMO channel is considered to be wideband. In our mathematical model CCF is calculated taking into account the clustering phenomenon, frequency selectivity and antenna characteristics. Because in outdoor environments the scatterers are distributed non-uniformly we consider the radio channel as being non-isotropic.

In this study, we propose a least mean square-partial parallel interference cancellation (LMS-PPIC) method named parallel LMS-PPIC (PLMS-PPIC) in which the normalised least mean square (NLMS) adaptive algorithm with optimised chip time-varying step-size is engaged to obtain the cancellation weights. The former LMS-PPIC method is based on fixed not optimised step-size, which causes propagation of error from one stage to the next one and increases the bit error rate (BER). The unit magnitude of the cancellation weights is the principal property in our step-size optimisation. To avoid computational complexity a small set of NLMS algorithms with different step-sizes are executed. In each iteration the parameter estimate of that NLMS algorithm which the elements magnitudes of its cancellation weight estimate have the best match with unit is chosen. Magnificent decrease in BER is achieved by executing the proposed method. Moreover PLMS-PPIC like former LMS-PPIC method comes to practice only when the channel phases are known. When they are unknown, having only their quarters in (0, 2π), we propose modified versions of LMS-PPIC and PLMS-PPIC to find the channel phases and the cancellation weights simultaneously. Simulation scenarios are given to compare the performance of our methods with that of LMS-PPIC in two cases: balanced channel and unbalanced channel. The results show that in both cases the proposed method outperforms LMS-PPIC, especially for high processing gains.

Parallel least mean square-partial parallel interference cancellation (PLMS-PPIC) is a partial interference cancellation which employs adaptive multistage structure (Shahtalebi et al., 2007). In this algorithm the channel phases for all users are assumed to be known. Having only their quarters in (0, 2pi), a modified version of PLMS-PPIC is proposed in this paper to simultaneously estimate the channel phases and the cancellation weights. Simulation examples are given in the cases of balanced, unbalanced and time varying channels to show the performance of the modified PLMS-PPIC method.

The impact of non-straight movements of a mobile station (MS), for example rotation of the MS, on the statistics of a wireless propagation channel needs to be studied in the modern literature of wireless channel modelling. The authors formulate the effects of MS rotation on a cross-correlation model for a multiple-input multiple-output Rayleigh fading channel in a two-dimensional (2D) multipath propagation medium. The authors consider communication over a non-isotropic wave propagation environment employing directional antenna propagation patterns (APPs) at both transmitter and receiver arrays. The cross-correlation function (CCF) is computed when the MS rotates with a constant angular velocity and moves with a constant linear speed on the 2D plane. It is shown that the angular movement of the MS results in a cyclostationary channel process. In such a situation, the authors analyse the derived CCF using the continuous-time Fourier series in terms of the MS angular velocity, the parameters of the propagation environment and the employed antennas. The numerical evaluation shows that the energy dispersion in different frequencies is significantly influenced by the type of the directional APP, the distribution of scatterers and the angular Doppler shift. Furthermore, the authors establish an approximate relationship between the coherence-time and the MS angular velocity using a numerical curve fitting.

In outdoor environments, waves propagate non- isotropically because of non-uniform distribution of scatterers. In addition directional antennas, which are efficient for communication applications, have considerable impact on the response of the communication channel. The impact of non-isotropic propagation and directional antennas is more significant when the system employs multiple antennas. In this paper, we propose a space-time-frequency cross-correlation function (CCF) for multiple-input multiple-output multicarrier channels in a two-dimensional (2D) random scattering medium. The expression of the CCF turns out to be a multiplication of three CCFs. Two of these terms characterize the impact of mobile station and base station, respectively and are linear Bessel expansions, where the coefficients are given by the linear convolution of the Fourier series coefficients (FSC)s of the employed antenna patterns and the FSCs of the probability density function describing 2D non-isotropic environment. The third expression characterizes the impact of the wireless channel. In the stationary case, we derive the expression of the fading channel power spectrum (CPS) in terms of the non-isotropic pdf and antenna patterns. Using the expression of the CCF, we also calculate coherence-bandwidth (CB)/coherence-time (CT) as a function of carrier-frequency/time separations. Our numerical results show a good fit to the available experimental results obtained for the CB/CT of realistic outdoor channels.

There are two types of scatterers in a multipath propagation environment: fixed and non-fixed scatterers. Fixed scatterers like buildings, mountains and tree stems do not move, while non-fixed (moving) scatterers like cars, people and tree leaves move from their initial positions. In addition to different movements of the mobile station (MS) that cause different kinds of Doppler fading, movements of non-fixed scatterers are also anticipated to generate other kinds of fading/correlation. This fading changes depend on the type of the propagation environment and the type of movements of local surrounding scatterers. In this paper we characterize these effects in terms of temporal correlations. In this study we assume constant speed for the MS and random displacements for scatterers based on stationary-increment Wiener vector process. As it will be verified, these random movements have direct effect on the channel process power spectral density (PSD).

In this paper we propose a new model for multiple-input multiple-output (MIMO) multicarrier channels in a 3D scattering medium. The proposed model describes the cross-correlation function (CCF) between two sub-channels of an outdoor MIMO channel employing directional antennas in the presence of non-isotropic wave propagation in the 3D space. The derived CCF consists of some correlation terms. Each correlation term is in the form of a linear expansion of averaged Bessel functions of the first kind with different orders. In practice, each correlation term has a limited number of components. Our evaluations of the CCF show the impact of different parameters of the propagation environment and the employed antennas. Our numerical results appear as a good match to the available reported experimental data of some 3D outdoor propagation media.

In this paper, we characterize the cross-correlation function (CCF) between the time-frequency transfer functions (TF)s of two sub-channels of a multiple-input multiple-output (MIMO) wireless fading channel. The TF of each sub-channel consists of a number of multi-path components caused by propagation of a transmitted signal in random scattering media. The proposed CCF is expressed in terms of several environmental parameters (such as the moment generating function (MGF) of the delay profile (DP) and the pathloss exponent). It is a summation of two terms: the first term is due to the autocorrelation of multi-path components while the second term is due to the cross-correlation of multi-path components. Each term is a product of several correlation functions. Each of these correlation functions represents different dependencies of the wireless channel in terms of time, carrier frequency and the position of the antenna elements around both the transmitter and the receiver site. Interestingly, the last two terms of these functions are (n/2)-order (or n-order) integrations of the MGF of the DP, evaluated at two carrier frequencies (or the difference between carrier frequencies), where n is the pathloss exponent of the environment

We introduce a multiple-input multiple-output (MIMO) space-time-frequency wireless channel model for the wave propagation in three-dimensional (3D) space. The cross-correlation function (CCF) between two subchannels of the MIMO communication system is decomposed into some non-negative functions. These functions are expressed in terms of a selection of channel parameters, such as the carrier frequencies, the delay profile, the path-loss exponent, the softness factor, /spl theta/, the non-uniform distribution of directions of arrival and departure, array geometries, and the mobile speed. We introduce a class of distributions for the elevation angle (EA) spreads as a basis such that any arbitrary (isotropic or non-isotropic) EA distribution can be represented by a convex linear combination of this class. The corresponding term of the CCF of the 3D-MIMO model for any EA distribution equals to the same linear combination of the basic CCF terms associated to the class. This 3D-MIMO model formulates the CCF as a function the spacial separation of antennas, time, and carrier frequencies in terms of physical channel parameters such as mobile speed, delay profile and distribution of scavengers around mobile and base stations.

This paper studies the effect of rotation of a mobile station (MS) on the cross-correlation function (CCF) derived for a microcellular isotropic wave propagation environment with enough number of scatterers. The statistical model characterizes the propagation media when the MS rotates with a constant angular velocity around an axis perpendicular to the azimuthal plane, and moves with a constant velocity on the azimuthal plane in an arbitrary direction. The moving MS, with a constant speed, produces the conventional linear Doppler while the rotating MS introduces angular Doppler. The research shows that the rotation of the MS results in a non-stationary random process as the CCF. The only exception in which the result follows a stationary function is a narrow-band communication system, when either the MS angular velocity or the MS speed is zero.

The paper first formulates the error propagation effect that is caused by certain ambiguities in joint data detection/channel tracking algorithms for space-time (ST) schemes. The occurrence of any combination of two types of ambiguities, phase ambiguity (PhA) and permutation ambiguity (PeA), initiated in deep fades, produces error propagation in joint channel estimation/data detection for the dual transmit diversity method. A new time-varying space-time coding (TVST) scheme is suggested as a bandwidth efficient method to combat the PeA impairment. This coding scheme, in conjunction with a differential detector, can resolve the ambiguity problem. Finally, some remedies used to prevent error propagation are listed. These remedies are called space-time ambiguity remedies (STARs).

A receiver for a dual transmit diversity system is designed that takes into account the channel estimation error, assuming the unknown channel to have a given complex bivariate Gaussian probability density function (PDF) (i.e., a Rician PDF). This criterion of the receiver, which is based on the maximum a posteriori (MAP) algorithm, is expressed in a quadratic form, and in extreme cases, represents either a linear detector or a non-coherent-non-linear detector. Simulations of the symbol error probability (SEP) of the receiver and analysis of an upper bound (UB) and a lower bound (LB) confirm that the proposed detector achieves robust performance against channel imperfections.