 (Part 2) 597 Table 4.23: DM-RS positions for PUCCH format 3 and 4 [6]. PUCCH Length DM-RS Position / within PUCCH Allocation No Additional DM-RS Additional DM-RS No Hopping Hopping No Hopping Hopping 1,3,6,8 1,3,6,9 1,4,7,10 1,4,7,11 1,5,8,12 and time index l is given in Table 4.23 with and without intraslot frequency hopping as well as with and without additional DM-RS, where l = 0 corresponds to the first OFDM symbol of the PUCCH transmission [6]. 4.2.2.2 Phase-Tracking Reference Signals There is typically a mismatch between the oscillator frequencies of the transmitter and receiver in a communication system, resulting in a shift of the received signal spectrum at the baseband. In OFDM, this effect creates a misalignment between the FFT bins and the peaks of the sinc(.) pulses of the received signal, which would compromise the orthogonality between the subcarriers and would result in a spectral leakage. Each subcarrier interferes with other subcarriers, although the effect is dominant between adjacent subcarriers. Since there are many subcarriers, this is a random process is equivalent to a noise with Gaussian distribu- tion. This random frequency offset degrades the SINR of the receiver. Therefore, an OFDM receiver will need to track and compensate the phase noise. The PT-RS is mainly introduced to compensate the CPE; however, PT-RS can also be used for ICI mitigation in higher fre- quency bands and potentially for CFO and Doppler estimation [54]. There is a trade-off between phase tracking accuracy and signaling overhead. If the density of PT-RS is high, phase tracking accuracy is high, and the CPE can be better compensated to achieve better performance. However, higher PT-RS density also means larger signaling over- head, which might lead to lower spectral efficiency or effective transmission rate. The studies show that the reduction of PT-RS density in time domain will degrade the BLER performance regardless of modulation order. However, the performance degradation is particularly signifi- cant when time d