5 kHz) over 1 ms Uplink multitone (6x15 kHz) over 2 ms Uplink multitone (3x15 kHz) 1 PRB over 4 ms Uplink single-tone (1x15 kHz) over 8 ms Uplink single-tone (1x3.75 kHz) over 32 ms Figure 6.19 NPUSCH time-frequency mapping and uplink slot structure 11,19]. 774 Chapter 6 The signal in time domain is generated by applying an IFFT and inserting a cyclic prefix. For 15 kHz subcarrier spacing, the cyclic prefix is similar to that of LTE, while for 3.75 kHz, the cyclic prefix is 256 samples, corresponding to 8.3 us. For the latter case, a period of 2304 samples (75 us) at the end of each slot remains empty, which is used as a guard interval. For the in-band operation, this guard interval may be used to transmit sound- ing reference signals in the LTE system. Unlike downlink transmission, where HARQ ACK/NACK transmission is configurable, there is always HARQ acknowledgment in the associated downlink slot. The random-access signal s(t) for the ith symbol group is defined as follows [2]: where OSt<IsEQ+Tcp. BNPRACH is an amplitude scaling factor to conform to the transmit power PNPRACH, ko : - NUL /2, Afra = 3.75 kHz, and the location in the frequency domain controlled by the parameter NRA (i). For single-tone NPUSCH carrying uplink shared channel (UL-SCH), the uplink DMRSs are transmitted in the fourth block of the slot for 15 kHz sub- carrier spacing, and in the fifth block of the slot for 3.75 kHz subcarrier spacing. For multi- tone NPUSCH carrying UL-SCH, the uplink DMRSs are transmitted in the fourth block of the slot. The length of the uplink DMRS sequence is 16 for single-tone transmission and is equal to the size (number of subcarriers) of the assigned resource for multi-tone transmis- sion. In the uplink, the DMRS is defined and it is multiplexed with the data SO that it is only transmitted in the RUs containing data. There is no MIMO transmission mode defined for the uplink; consequently, all transmissions use a single antenna port. Depending on the NPUSCH format, DMRS is transmitted in either one or three SC-F