3GPP LongTerm Evolution

We describe the 3GPP Long Term Evolution (LTE) standard, a member of the IMT-Advanced family for fourth-generation cellular communications. The system consists of radio access network (RAN) and core network (System Architecture Evolution SAE or Enhanced Packet Core EPC). Layers of the transmission protocol range from Packet Data Convergence Protocol (PDCP) to Radio Link Control (RLC), MAC, and PHY. After an overview of the physical layer, the division of the time axis into frames, subframes, and slots is discussed. The modulation format is OFDM for the downlink, and single-carrier transmission with frequency domain equalization (SC-FDE) for the uplink. We define resource element and resource blocks (RB). Data are mapped onto physical resources by first mapping symbols onto virtual resource blocks (VRBs), and from there to physical resource blocks (PRBs). There exist two types of reference signals RS (pilot tones): demodulation RS, and sounding RS; both based on Chadoff-Zhu sequences. Error control coding includes cyclic redundancy check (CRC), convolutional codes or turbo codes, and Hybrid ARQ (HARQ). Multiple-antenna techniques include Alamouti codes, possibly combined with antenna selection, for transmit diversity and (open-loop or closed-loop) spatial multiplexing. LTE distinguishes between logical channels and physical channels (time/frequency resources). Logical subchannels include Traffic channels (DTCH, MTCH) and Control channels (BCCH, PCCH, CCCH, DCCH, MCH). These are then mapped, via certain transport channels, to the physical channels. Primary and secondary synchronization signals carry timing information and cell ID. We discuss control information associated with downlink shared channel and uplink signaling (uplink control information, random access, and control signaling for the uplink shared channel). We also describe physical layer procedures, including establishing of a connection, retransmission methods, scheduling, power control, and handover.