receiver window of the eNB. The timing advance command is on a per need basis with a granularity in the step size of 0.52 us (16 X Ts). 3.5.5 Transport Channels The physical layer offers information transfer services to MAC and higher layers. The physical layer transport services are described by how and with what characteristics data are transferred over the radio interface via Transport Channels. This should be clearly separated from the classification of what is transported, which relates to the concept of logical channels at MAC sublayer [14]. Downlink Transport Channels are: Broadcast Channel (BCH) which is characterized by fixed, pre-defined transport format and it is broadcasted in the entire coverage area of the cell. Downlink Shard Channel (DL-SCH) supports HARQ and dynamic link adaptation by varying the modulation, coding and transmit power. It also supports both dynamic and semi-static resource allocation and UE discontinuous reception (DRX) to enable UE power saving. It can also be broadcasted in the entire cell and can use beamforming. Paging Channel (PCH) is broadcast in the entire coverage area of the cell. It helps in supporting for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated by the network to the UE). Multicast Channel (MCH) is characterized by support for MBSFN combining of MBMS transmission on multiple cells. It can support semi-static resource allocation for example, with a time frame of a long cyclic prefix. It can be broadcast in the entire coverage area of the cell. Uplink Transport Channels are: Uplink Shared Channel (UL-SCH) supports dynamic link adaptation by varying the transmit power and potentially modulation and coding. It also supports HARQ, both dynamic and semi-static resource allocation and beamforming. Random Access Channel(s) (RACH) is characterized by limited control information and collision risk. 3.5.5.1 Mapping Between Transport and Physical Channels Figures 3.11 and 3.12 illustrate the mapping between transport and physical channels. 