Some radio implementation challenges in 3G-LTE context

This paper addresses some radio implementation related RF impairment issues in long-term evolution (LTE) of 3G mobile radio system context, with special emphasis on the so-called I/Q imbalance and the resulting mirror-frequency interference problems. The relative roles of transmitter and receiver mirror-frequency attenuation characteristics on the overall link and system performance are discussed and analyzed, with most focus on the LTE uplink. Furthermore, we demonstrate that the limited mirror-frequency attenuation of the transmitter and receiver analog front-ends can be greatly improved using proper DSP techniques. Realistic example case studies in LTE uplink are given, demonstrating the feasibility and efficiency of such I/Q compensation or calibration techniques. Based on the obtained results, analog front-end attenuations typically around 25-40 dB can easily be improved up to 50-80 dB range or so, under very reasonable assumptions on the implementation resources allocated to the calibration and compensation circuitries.