at-M deployment was slowed down in some markets because a number of legacy LTE devices turned out to be incompatible with Cat-M signaling in the master information blocks (MIBs), and all those legacy devices had to be software upgraded before Cat-M could be launched. LTE-M 3GPP Releases 8-12 for LTE assumed that every device must support 20 MHz RF bandwidth even if the system can be deployed on smaller bandwidths down to 1.4MHz Cat-M is the first UE category with narrowband RF. The actual transmission bandwidth is a maximum of six physical resource blocks (PRBs) or 1.08 MHz. The bandwidth of 1.4 MHz includes also guard bands. Cat-M users can be multiplexed within a normal wideband LTE carrier. A Cat-M UE can receive synchronization signals and broadcast channels from the wideband LTE carrier because those common channels are transmitted using the middle 1.4 MHz. The legacy Physical Downlink Control Channel (PDCCH) uses full-band transmission and cannot be received by Cat-M UEs. Therefore, Cat-M uses a new control channel, the MPDCCH (LTE-M PDCCH), which has 1.4 MHz bandwidth and can be located outside the middle 1.4 MHz. Cat-M UE retunes to that new frequency within the LTE carrier. The functionality is illustrated in Figure 14.3. The new control channel MPDCCH uses the resources that are normally used for the Physical Downlink Shared Channel (PDSCH). Note also that a Cat-M UE cannot receive legacy Physical Control Format Indicator Channel (PCFICH) and Physical Hybrid ARQ Indicator Channel (PHICH) that use full-band transmission. There is no need for PCFICH for Cat-M because the MPDCCH size is fixed, and there is no need for PHICH because HARQ feedback after uplink transmission is not provided at all. Instead, eNodeB informs the UE about the need for retransmission via a new data indicator. The new downlink physical channels for LTE-M are listed in Table 14.3. The MPDCCH and PDSCH can be transmitted in different subframes. The reason is that a Cat-M UE uses only six PRBs, and there would not be much space in one 