Comparison of CDMA and OFDMA Reverse Link for Cellular Voice Communications

This paper presents a comparison between CDMA and OFDMA for reverse link (RL) cellular voice communications. The spectral efficiencies of the two systems are compared for the large numbers of users per cell case - applicable to voice communications - via an analytical model. We see that the spectral efficiency of a CDMA system with SIC (successive interference cancellation) exceeds that of an OFDMA system when the number of receive antennas is greater than or equal to two. We also compare the performance of CDMA and OFDMA with practical systems using circuit-switched voice over CDMA2000 1x-RevE and packet-switched VoIP over LTE-Release 8. The comparison is focused on the operating capacity of the uplink as that is expected to be the limiting link of VoIP over LTE. Our simulations indicate that CDMA2000 1x-RevE capacity (defined as number of simultaneous voice calls per cell) is more than 2X that of LTE-Rel8 and air-link latency of the CDMA2000 1x-RevE system is approximately 50% lower. In addition, the CDMA system has a 10dB link budget advantage. These differences are due to higher rate speech codec - AMR 12.2k instead of EVRC-B, degree of freedom limitation, overhead channel constraint for a scheduled reverse link (LTE-Release8), and lack of soft and softer handoff. Using simulations, we provide insight into each of these aspects of system performance for both technologies.