The Study Report of LTE Physical Layer Documents Sheng-Lung Cheng Department of Communication Engineering National Chiao Tung University 2011-10-17 Outline • Introduction • References • DL/UL transmission train • Discussible topics Introduction The goal of LTE is to provide a high-data-rate, low- latency and packet-optimized radioaccess technology supporting flexible bandwidth deployments. LTE system attributes Reference • • • • Farooq Khan ,“LTE for 4G Mobile Broadband: Air Interface Technologies and Performance References”, Cambridge , 2009-04-19. Erik Dahlman, Stefan Parkvall, Johan Skold ,“4G: LTE/LTE-Advanced for Mobile Broadband”, Academic Press , 2011-05-09. 3GPP TS 36.211: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation". van de Beek, J.J.; Sandell, M.; Borjesson, P.O.” ML estimation of time and frequency offset in OFDM systems ”, IEEE Transactions Signal Processing, 1800 – 1805, Jul 1997. DL/UL system model Frame structure(type1 for FDD and half-duplex FDD) DL/UL system model DL/UL system model Overview of By applying different scrambling sequences for neighboring cells, the interfering signal after downlink physical channel processing. descrambling is randomized, ensuring full utilization of the processing gain provided by the channel code. DL/UL system model Overview of uplink physical channel processing. DL/UL system model Downlink layer mapping (A) (B) DL/UL system model Downlink layer mapping (C) DL/UL system model Downlink layer mapping The rank assignment refers to RI DL/UL system model Downlink precoding (A) (B) (1) DL/UL system model Downlink precoding The precode matrix assignment refers to PMI DL/UL system model Downlink precoding (2) Here the W(i) is not selected by UE. DL/UL system model Downlink precoding (C) Precoding for transmit diversity Antenna Port Freq. Band x0 x1 x*1 * x0 DL/UL system model Downlink precoding Antenna Port Freq. Band x0 x1 0 0 0 x*1 0 x *0 x2 0 x3 0 0 0 x *3 x*2 Discussible topics Initial cell search Discussible topics Initial cell search Discussible topics Initial cell search ?? OFDM symbol timing synchronization FD PSS Radio frame timing synchronization Cell ID determination FD PSS and SSS a. Using TD PSS The length 62 FD Zadoff–Chu (ZC) sequence has bad TD performance when IFFT size is large. Discussible topics Initial cell search a. Using CP Discussible topics Initial cell search Downlink CRS in one antenna transmission Some OFDM symbols may not have any data, so the observation interval would be very large. Discussible topics DCI (Downlink Control Information) blind detection Downlink control information , DCI, provides the terminal with the necessary information for proper reception and decoding of the downlink data transmission. Puncturing or repetition Control-Channel Elements (CCEs), is a convenient name for a set of 36 useful resource elements. The number of CCEs, 1, 2, 4, or 8, required for a certain PDCCH depends on the DCI payload channel-coding rate. Discussible topics DCI blind detection As the number of CCEs for each of the PDCCHs may vary and is not signaled, the terminal has to blindly determine the number of CCEs used for the PDCCH it is addressed upon. In release 8/9, the number of blind decoding attempts is 44 per subframe, while for release 10 with uplink spatial multiplexing the number is 60.