Frode Bøhagen

Construction and capacity analysis of high-rank line-of-sight MIMO channels

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.

Optimal Design of Uniform Planar Antenna Arrays for Strong Line-of-Sight MIMO Channels

We investigate the optimal design of uniform planar antenna arrays employed in multiple-input multiple-output communications where a strong line-of-sight (LOS) component is present. A new general geometrical model is introduced to model the LOS channel, which allows for any orientation of the two arrays. Based on this model, we derive the optimal design equations with respect to maximizing Shannon capacity, which turn out to be solvable for several interesting cases. The solutions reveal that the proposed principle is best suited for fixed applications, as e.g. fixed wireless access. The LOS channel matrix is used in a Ricean channel model to evaluate performance under different channel conditions. Results show that even with some deviation from the optimal design, we get good performance compared to the case of uncorrelated Rayleigh subchannels

Optimal design of uniform rectangular antenna arrays for strong line-of-sight MIMO channels

We investigate the optimal design of uniform rectangular arrays (URAs) employed in multiple-input multiple-output communications, where a strong line-of-sight (LOS) component is present. A general geometrical model is introduced to model the LOS component, which allows for any orientation of the transmit and receive arrays, and incorporates the uniform linear array as a special case of the URA. A spherical wave propagation model is used. Based on this model, we derive the optimal array design equations with respect to mutual information, resulting in orthogonal LOS subchannels. The equations reveal that it is the distance between the antennas projected onto the plane perpendicular to the transmission direction that is of importance with respect to design. Further, we investigate the influence of nonoptimal design, and derive analytical expressions for the singular values of the LOS matrix as a function of the quality of the array design. To evaluate a more realistic channel, the LOS channel matrix is employed in a Ricean channel model. Performance results show that even with some deviation from the optimal design, we get better performance than in the case of uncorrelated Rayleigh subchannels.

Modeling and analysis of a 40 GHz MIMO system for fixed wireless access

The throughput of a future fixed wireless access multiple-input-multiple-output (MIMO) system operating at high frequencies is investigated. We extend our previous theoretical work on MIMO for line-of-sight (LOS) channels to show that a considerable gain in throughput is achieved compared to single-input-single-output transmission for a practical system, which among other things is subject to antenna array size constraints. In our investigation we apply a propagation model applicable for high frequencies, where often LOS is required for sufficient coverage, and where weather phenomena like rain have considerable impact on the quality of the radio link. A state of the art transmission scheme is utilized with low density parity check coded modulation, as well as power control and bit loading.

Exact capacity expressions for dual-branch ricean MIMO channels

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.

On the Shannon capacity of dual MIMO systems in Ricean fading

We derive exact analytical expressions for the probability density function and cumulative distribution function for the capacity of a dual multiple-input multiple-output system (either two transmit or two receive antennas) transmitting in Ricean fading. In contrast to earlier work we do not require the line-of-sight (LOS) channel matrix to be of rank one. As an example, we investigate the special case of uniform linear arrays, and derive expressions for the eigenvalues of a possibly full rank LOS channel matrix for this case. The results are verified by comparing the analytical expressions with Monte Carlo simulations.

Maximizing the Average Spectral Efficiency of Dual-Branch MIMO Systems With Discrete-Rate Adaptation

The capacity of multiple-input-multiple-output (MIMO) systems with perfect transmitter and receiver channel state information (CSI) can be attained by decoupling the MIMO channel into a set of independent subchannels and distributing the power among these subchannels in accordance with the water-filling solution. Implementation of this scheme on a time-varying channel, however, requires continuous-rate adaptation and is not feasible in any such practical system. In this paper, we show how to maximize the average spectral efficiency (ASE) of dual-branch MIMO systems (either two transmit or two receive antennas) with perfect transmitter and receiver CSI when using a fixed number of codes (discrete-rate adaptation). This maximum ASE is compared with the systems ergodic capacity and with the maximum ASE that can be attained if the available power is distributed among the different subchannels in accordance with the water-filling solution although only discrete-rate adaptation is possible. We assume that capacity-achieving codes for additive white Gaussian noise (AWGN) channels are available and that the power available to the transmitter to transmit the ith symbol frame is fixed and independent of the frame index i.The capacity of MIMO systems with perfect transmitter and receiver channel state information (CSI) can be attained by decoupling the MIMO channel into a set of independent subchannels, and distributing the power among these subchannels in accordance with the water-fitting solution. Implementation of this scheme on a time-varying channel requires however continuous rate adaptation and is not feasible in any practical such system. In this paper, we show how to maximise the average spectral efficiency (ASE) of dual-branch MIMO systems (either two transmit or two receive antennas) with perfect transmitter and receiver CSI when using a fixed number of codes (discrete rate adaptation), and subsequently compare the resulting maximum ASE to the systems ergodic capacity. We assume that capacity-achieving codes for AWGN channels are available, and that the power available to the transmitter for transmitting the ith symbol frame is fixed and independent of the frame index i.