when no real transmission takes place on an SCell and a reference format is used (e.g. when the SCell is de-activated). The second PHR type, originally introduced in LTE for simultaneous PUSCH and PUCCH transmission, is not applicable to the 5G radio link. A PHR is triggered when the path loss seen by the UE changes abruptly (up to a threshold configured by the gNB), when a configured timer expires (to allow for peri- odic reporting), or when an SCell is activated (in the case of CA). A PHR is only useful when data exchange between the UE and the gNB is taking place, and thus - unlike a BSR - a PHR never triggers a scheduling request procedure. Consequently, a triggered PHR remains pending until an uplink grant allows it to be sent. 7.6.9 Discontinuous reception (DRX) provides sleeping opportunities to the UE by mandating the time periods during which it must be awake to receive (and decode) the PDCCH for possible downlink transmissions and uplink grants. Even without transmissions, keep- ing the RF ON for PDCCH reception and performing blind decoding attempts to figure out if any of the PDCCH transmissions within the PDCCH search space are intended for the UE consumes power. By allowing the UE to switch its RF OFF and not perform any PDCCH decoding, DRX greatly enhances battery life. The DRX framework of 5G is built upon the same principles as in LTE: the DRX cycle defines how often the UE needs to wake up, and once awake, for how long the PDCCH monitoring activity needs to last. The main difference compared to LTE is related to the HARQ operation in the uplink (see Section 7.6.4). With asynchronous HARQ, the retransmission opportunities do not occur at a fixed point in time, and the monitoring activity is more dynamic. 7.6.10 Bandwidth Parts While DRX reduces UE activity in the time domain, BWP aims at reducing it in the fre- quency domain. With BWP, it becomes possible to constrain the UE to operate within a limited portion (i.e. a part) of the frequency bandwidth of the cell. Consider a voice ser- vice in the