CDMA-OFDM combination method for enhancing capacity of voice over LTE Uplink in PMR context

In this paper, we introduce a new Code Division Multiple Access (CDMA)-Orthogonal Frequency-Division Multiplexing (OFDM) combination method for Enhancing Capacity of Voice over LTE (VoLTE) Uplink in PMR context. In this method, voice payloads of different User Equipments (UEs) having the same Modulation and Coding Scheme (MCS) can be spread by different orthogonal codes and mapped to the same set of resource elements. The selection of spreading factor allows a maximum reduction of the difference between the LTE Uplink packet size and PMR voice payload. The proposed method allows reducing both data overhead and control overhead issues for VoLTE uplink in PMR context. The CDMA-OFDM combination method gives a significant increasing in capacity of VoLTE uplink over PMR context. In the best case, the proposed method can improve the voice capacity by the factor of 7 in comparison with the standard LTE.