In this paper we consider pure line-of-sight multiple-input multiple-output (MIMO) channels employing uniform linear antenna arrays. We investigate the influence of exact spherical wave propagation modeling versus approximate plane wave propagation modeling on the properties of the MIMO channel matrix. When the transmission distance increases, the properties of the singular values of the MIMO channel matrix given by the spherical wave model approach the properties given by the simpler plane wave model. We investigate this transition between the two channel models, which results in a new tool giving us analytical expressions describing when spherical wave modeling is necessary and when plane wave modeling gives sufficient modeling accuracy. The parameters of interest are the transmission distance, the frequency, the array orientation, and the array size. The tool introduced is general, in the sense that it supports different performance measures when deciding on the transition between the two models. As an example, we investigate underestimation of the mutual information in this paper. The results show that the spherical wave model should be applied e.g. in some practical WLAN scenarios where plane wave modeling is commonly applied today.

In this paper we derive exact expressions for the mutual information (MI) probability density function and the MI cumulative distribution function of dual-branch multipleinput multiple-output (MIMO) systems (either two transmit (Tx) or two receive (Rx) antennas) communicating over a Ricean channel with no constraint on the rank of the line-of-sight (LOS) channel matrix. This is done both for the case where the channel is only known at the Rx, and for the case where the channel is known both at the Tx and the Rx. As an example, to evaluate the expressions, we employ uniform linear arrays and give expressions for the eigenvalues of the LOS channel matrix for the dual-branch case.

This paper describes a technique for realizing a high-rank channel matrix in a line-of-sight (LOS) multiple-input multiple-output (MIMO) transmission scenario. This is beneficial for systems which are unable to make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading subchannels. The technique is based on optimization of antenna placement in uniform linear arrays with respect to mutual information (MI). By introducing a new and more general 3-D geometrical model than that applied in earlier work, additional insight into the optimal design parameters is gained. We also perform a novel analysis of the sensitivity of the optimal design parameters, and derive analytical expressions for the eigenvalues of the pure LOS channel matrix which are valid also when allowing for non-optimal design. Furthermore, we investigate the approximations introduced in the derivations, in order to reveal when the results are applicable. The LOS matrix is employed in a Ricean fading channel model, and performance is evaluated with respect to the average MI and the MI cumulative distribution function. Our results show that even with some deviation from the optimal design, the LOS MEMO case outperforms the i.i.d. Rayleigh case in terms of MI.

In this paper we consider pure line-of-sight multiple-input multiple-output channels employing uniform linear antenna arrays. We investigate the influence of exact spherical wave propagation modeling versus approximate plane wave propagation modeling on the properties of the channel matrix. Our earlier work on 2 times 2 systems is extended to include arbitrary MIMO dimensions. As before, when transmission distance increases, the properties of the spherical wave model converge to the properties given by the simpler plane wave model. The investigation results in a new tool which gives us analytical expressions describing when spherical wave modeling is necessary and when plane wave modeling is sufficient. The parameters of interest are the transmission distance, the frequency, and the array size, and the results show that the spherical wave model should be applied e.g. in some practical WLAN scenarios where plane wave modeling is commonly applied today.

We investigate the influence of exact spherical wave propagation modeling and approximate plane wave propagation modeling on the properties of a pure line-of-sight 2 times 2 multiple-input multiple-output channel. As transmission distance increases, the properties of the true spherical wave model converge to the properties given by the more simple plane wave model. We present a new model evaluation tool based on an analysis of the rank and singular values of the channel matrix, which can be employed to find the region where spherical wave modeling is necessary. The derivation results in new exact analytical expressions for which of the two models that should be applied, and the results based on mutual information show that the spherical wave model should be applied in many practical scenarios, e.g. indoor WLAN scenarios, where plane wave modeling is most frequently used today

This paper describes a technique for realizing a high rank channel matrix in a line-of-sight (LOS) multiple-input-multiple-output (MIMO) transmission scenario. This is beneficial for systems which can not make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading channels. Typical applications are fixed wireless access and radio relay systems. The technique is based on optimization of antenna placement in a uniform linear array. By introducing a new and more general geometrical model than that applied in earlier works, additional insight into the optimal design parameters is gained. A novel analysis of the sensitivity of the optimal design parameters is performed. The LOS transmission matrix is used in a Rician fading channel model, and performance is evaluated with respect to ergodic capacity, outage capacity, and effective degrees of freedom. The results show that even with some deviation from optimal design, the LOS MIMO case outperforms the i.i.d. Rayleigh case in terms of Shannon capacity.