MIMO-OFDM NB-PLC Designs in Underground Medium-Voltage Networks

In this paper, we investigate the application of multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) to narrowband powerline communications (NB-PLC) over medium-voltage (MV) underground (UG) networks. We study different MIMO transmission scenarios with different injection configurations utilizing both the cable conductor and sheath phases. Multiconductor transmission line theory is used to accurately characterize the UG MV NB-PLC channel transfer function and evaluate the spatial correlation between the different conductor phases. The achievable data rates are evaluated for all configurations at different line lengths after optimizing the transmit energy allocation across the different spatial information streams subject to a transmit power spectral density constraint. The achievable data rates for MIMO configurations are shown to be significantly higher (by up to three times higher) compared to single-input single-output OFDM transmission. Moreover, we investigate the effects of practical design constraints, such as cyclic prefix length and bit caps, on the achievable data rates. Finally, we show how to reduce the complexity of both the transmitter and receiver implementations while minimizing the data rate loss.