In this study, a relay assisted mth order energy harvesting-based non-orthogonal multiple access (NOMA) network is considered where the relay harvests energy from radio frequency signal of the source. A transmit antenna selection scheme is considered at the source under imperfect channel state information (CSI). The outage probability of mth order NOMA network is analysed and a closed-form expression of it is obtained. A comparative performance study is carried out with perfect and imperfect successive interference cancellation at the receiver. The impact of a number of antennas available at the source on outage performance and the effect of imperfect CSI on the outage performance are also presented in this work. The upper limit of the order of the NOMA network to be supported for a given threshold signal to interference plus noise ratio (SINR) is also estimated.