 The field results indicate a three times higher uplink capacity. CoMP gains in downlink have been difficult to obtain in LTE because UE support was missing and because CoMP in FDD requires fast feedback signaling. 5G has better potential to take advantage of CoMP in downlink also compared to LTE. 3.4.9 Waveforms A number of different waveforms have been used in mobile technologies from Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) 3 Technology Components Centralized unit Remote radio unit A Remote radio unit B Remote radio unit C Figure 3.16 Distributed MIMO transmission. in 2G Global System for Mobile Communications (GSM) to Code-Division Multiple Access (CDMA) in 3G Wideband Code-Division Multiple Access (WCDMA), and to Orthogonal Frequency Division Multiple Access (OFDMA) in 4G LTE downlink. The uplink solution in LTE is Single Carrier Frequency Division Multiple Access (SC-FDMA), which was selected to minimize UE RF requirements. The SC-FDMA option is included also in 5G for maximum coverage. The main waveform in 5G uplink is OFDMA, which is different from the LTE uplink. The motivation is that OFDMA can be shown to have clearly better performance than SC-FDMA, especially with multiantenna transmission and higher-order modulation. Multiantenna uplink transmission was not implemented in LTE, while it is expected to be part of 5G deployments. The drive for a higher data rate in 5G explains why OFDMA is preferred in the 5G uplink. Table 3.4 illustrates the multiple access solutions in different mobile generations. Table 3.5 shows the link performance with OFDMA and SC-FDMA with 4X4 MIMO and with Quadrature Phase Shift Keying (QPSK), 16-QAM, and 64-QAM. There is a 1.6-3.9 dB performance benefit for OFDMA compared to SC-FDMA. Table 3.4 Waveforms and multiple access solutions from 2G to 5G. 2G GSM 3G WCDMA 4G LTE Downlink OFDMA OFDMA Uplink SC-FDMA OFDMA/SC-FDMA Table 3.5 Uplink SNR requirement with 4x4 MIMO. QPSK (dB) 16-QAM (dB) 64-QAM (dB) OFDMA SC-FDMA 3.4 Flexible Physical