Performance of a UMTS uplink MIMO scheme

In this study, uplink (UL) performance was studied in the 3^rd generation UMTS (universal mobile telecommunications system) system assuming different SIMO/MIMO (single/multiple input multiple output) approaches. Link simulations and theoretical analysis were used to investigate the uplink capacity and coverage of the considered antenna configurations. Link simulations assumed that the user equipment (UE) has a maximum of two transmit antennas while the base station can employ up to four antennas. The considered MIMO scheme can be classified as diversity MIMO, which means that the UE transmits the same data symbols via two antennas. Results of the performance evaluation demonstrate that receive diversity is a dominant factor in improving uplink capacity and coverage. For example, in terms of isolated cell capacity, a MIMO technique with 2 transmit (Tx) and 2 receive (Rx) antennas performed approximately 50% worse than a traditional approach with 1 Tx and 4 Rx antennas. Results show also that MIMO transmission will provide some benefit (up to 2 dB) for UL coverage and UE battery consumption. However, doubling the number of receiving antennas is still much more efficient than introducing the 2^nd transmit antenna at the UE. Based on this study, the MIMO concept does not seem feasible for improving UMTS uplink performance.