ration where the moment for checking the channel being available is fixed or with the load-based operation where the channel is being monitored for longer period of time (if the channel was not free at start of the monitoring), with example shown in Figure 10.3. The example in Figure 10.3 assumes in any case some elements being fixed in time domain for the load-based operation though the detailed design is still to be determined by 3GPP. For facilitating the cell search (or discovery), the regulation allows the so-called 'short control signalling' (SCS) to be used. Within ETSI specifications [1] this is limited to be 5% channel occupancy over 50 ms measurement interval. This allows periodic signals such as the current primary synchronization signal (PSS) and secondary synchronization signal (SSS) to be transmitted periodically. As with the operation on 5 GHz band, one is first going to be synchronized to the network via the licensed band carrier and the expected mobility with 5 GHz band is foreseen to be less than 350 km/h, the requirements are not as stringent for the structure of the synchronization/discovery signals as with licensed band LTE. Thus, it is not likely to be needed to send them with the same internal (every 5 ms) as with the current LTE frame structure (as covered in Chapter 2 and in Reference 2), but rather sending them every 10 or 20 ms or even less seldom should be sufficient. SCS can be transmitted regardless of the LBT considerations, as shown in Figure 10.4. Note that the timing in Figure 10.4 is only for illustration purposes and assumes the same periodicity as the current Release 8-based frame structure. The Release 8 TDD-based frame structure is expected to be modified accordingly to fit the 5 GHz band operation. The regulation does not determine detailed use for the SCS operation, but allows consid- ering different uses, such as discovery and HARQ feedback. In LTE design, one may always count on the existence of the licensed band carrier, thus only such control signalling, foreseen neces