A Multi-Ray Analysis of LOS V2V Links for Multiple Antennas with Ground Reflection

This paper presents a vehicle-to-vehicle (V2V) geometric multi-ray tracing model for an improved line-of-sight (LOS) estimation. The model is especially suited for distributed antenna transceivers in the presence of ground reflections. The multiple antennas are assumed to be spaced regularly in horizontal and vertical directions over contiguous vehicles. The main focus of our study is the ability of the multiple antenna system to counteract or exploit, respectively, the destructive or constructive interference of multiple rays in the LOS channel component. This work is a complement to existing V2V channel models by providing more details on how ground reflections affect the LOS channel. The analysis is initially framed in the context of MIMO (multiple-input multiple-output) systems to investigate general aspects such as capacity limits and singular value distribution. The work then focuses on a scheme with single symbol repetition across the transmit antennas and two different strategies for signal combining at the receiver: maximum-ratio and equal-gain combining (MRC and EGC, respectively). These solutions are compared with a full diversity solution as well as with the information theoretical limits. An adaptive antenna selection mechanism is finally proposed that outperforms all other solutions. The paper shows both vertical and horizontal polarization results with corrected complex Fresnel reflection coefficients for lossy materials. Moreover, it is shown that multiple antenna design in V2V systems can be useful to counteract the destructive interference created by multiple rays on the LOS channel component.