A Measurement Study of MIMO Support with Radiating Cables in Passenger Rail Cars

Radiating cables (also known as leaky feeders) are often used to provide radio propagation in indoor and confined environments such as train passenger cars, aircraft cabins, subways or tunnels. Radiating cable deployments can typically provide more homogeneous and predictable coverage than deployments based on antennas. With the advent of 3GPP Long Term Evolution (LTE) and the IEEE 802.11n and 802.11ac amendments, multiple-input multiple-output (MIMO) support has become mandatory. MIMO generally requires to deploy more than one radiating cable. While there has been a tremendous amount of work on MIMO antenna deployment configurations and the relationship with higher layer performance e.g. throughput (see also [1]), there is little work addressing MIMO radiating cable deployments with two or more cables. This paper presents results of an extensive measurement campaign conducted to assess MIMO propagation characteristics and the throughput performance of an LTE system in a dual radiating cable deployment in a passenger car. In particular, measurements presented in this paper show that two radiating cables can ideally support spatial multiplexing. Under favorable signal-tonoise ratio (SNR) conditions, throughput in excess of 130 Mbit/s were recorded for a 2×2 MIMO 20 MHz LTE system. A median condition number of around 11 dB is measured for a 2×2 MIMO deployment. More surprisingly, they also show that deploying two radiating cables next to each other does not significantly degrade performance.