es the Zadoff- Chu root sequence index [3]. The sequence di(n) is multiplied with an amplitude scaling factor of 72/62BPSBCH and mapped to resource elements on a single antenna port in the first slot of the subframe according to ak.1=di(n)Vn= 0,...,61; k=n- NSLNRB/2 with l=1,2 (normal cyclic prefix) and l=0,1 (extended cyclic prefix). The SSSS is transmitted in two adjacent SC-FDMA symbols in the same subframe. Each of the two sequences d;(0),...,d,(61)Vi=1,2 is used for the SSSS. The sequence d(0),.. d(61) used for the second synchronization signal is an interleaved concatenation of two length-31 binary sequences. The concatenated sequence is scrambled with a scrambling sequence given by the primary synchronization signal assuming subframe 0 with and NIZ = NSL/168 for transmission modes 1 and 2, and subframe 5 for transmission modes 3 and 4 [3]. The sequence di(n) is multiplied with the amplitude scaling factor BSSSS in order to adjust the transmit power and mapped to resource elements on a single antenna port in the second slot in the subframe according to =di(n)Vn=0, 61; with l=4,5 (normal cyclic prefix) and l=3,4 (extended cyclic prefix) [3]. 7.5 Layer 2/3 Aspects The LTE layer-2 functions are divided into three sublayers: MAC, RLC, and PDCP. Fig. 7.28 depicts the layer-2 structure for the LTE-based sidelink. In this figure, the service access points (SAP) for peer-to-peer communication are marked with circles at the interface 832 Chapter 7 Radio bearers Security Security Security Security Segmentation Segmentation Reassembly Reassembly SBCCH SBCCH Logical channels Scheduling and priority handling Demultiplexing Multiplexing Packet filtering Transport channels SL-SCH(TX) SL-SCH(RX) SL-BCH(TX) SL-BCH(RX) SL-DCH(TX) SL-DCH(RX) Figure 7.28 Layer-2 structure for sidelink [6]. between sublayers. The SAP between the physical layer and the MAC sublayer provides the transport channels. The SAPs between the MAC sublayer and the RLC sublayer provide the logical channels. The multiplexing of several logical channels (i.