  The use of multiple antennas in a transmit and receive antenna array for MIMO
wireless communication allows the spatial degrees of freedom in rich scattering
environments to be exploited. However, for line-of-sight (LOS) MIMO channels
with uniform linear arrays (ULAs) at the transmitter and receiver, the antenna
separations at the transmit and receive array need to be optimized to maximize
the spatial degrees of freedom and the channel capacity. In this paper, we
first revisit the derivation of the optimum antenna separation at the transmit
and receive ULAs in a LOS MIMO system, and provide the general expression for
the optimum antenna separation product, which consists of multiple solutions.
Although only the solution corresponding to the smallest antenna separation
product is usually considered in the literature, we exploit the multiple
solutions for a LOS MIMO design over a range of distances between the
transmitter and receiver. In particular, we consider the LOS MIMO design in a
vehicle-to-vehicle (V2V) communication scenario, over a range of distances
between the transmit and receive vehicle.
