Voice capacity over Long Term Evolution (LTE), despite the fact that LTE supports high-speed data transmission, is still low due to the large data and control overhead. This is one of the primary obstacles to apply LTE to Professional Mobile Radio (PMR) system because the voice capacity is one of the main requirements of the public safety network. To overcome this issue, there are several studies aiming at reducing one of the two overheads in LTE, data or control. However, in most cases the voice capacity gain can only be improved by both reducing data and control overhead. This is because these two factors are strongly related in carrying out the resource allocation. In [1], we proposed a Multi-users Multiplexing Radio Voice Transmission method. This method clusters voice packets from different users into one same LTE packet in the downlink transmission for reducing the data overhead caused by the difference between LTE packet size and the PMR voice payload. This paper presents a new Radio Network Temporary Identifier (RNTI) aggregation method to solve the control overhead issue for the multiplexing scheme of Voice over LTE (VoLTE) in PMR context. Our method uses Physical Downlink Control Channel (PDCCH) channel with high format, created by the aggregation of PDCCH channels with low format, to transmit several RNTIs of different User Equipments (UEs) in a same multiplexing group. The number of RNTIs in one PDCCH is calculated to ensure that there is no increase of Bit Error Rate (BER) for receiving PDCCH channel. The results show that the RNTI aggregation method can increase the control capacity of the multiplexing scheme up to 170%. The combination of Multi-users Multiplexing Radio Voice Transmission method and RNTI aggregation method allows reducing both data and control overhead of VoLTE in the PMR context. Index Terms-Aggregation, RNTI, scheduling, LTE, PMR