lte概述-免費閱讀
【正文】 aGW ? Interworking, smooth migration, service continuity and investment protection LTE System Architecture e N BM M E / S G W M M E / S G We N Be N BS1S1S1S1X2X2X2E U T R A NControl Plane User Plane Protocol Stacks MAC L2 eNB S1 RLC PHY PHY eUE eUu L1 aGW L2 L1 IP IP UDP UDP GTPU GTPU PDCP MAC RLC PDCP L2 X2 L1 eNB L2 L1 IP IP UDP UDP GTPU GTPU eNB MAC L2 eNB S1 RLC PHY PHY eUE eUu L1 MME L2 L1 IP IP SCTP SCTP S1AP S1AP PDCP MAC RLC PDCP RRC RRC NAS NAS L2 X2 L1 L2 L1 IP IP SCTP SCTP X2AP X2AP eNB eNB LTE Physical Layer Functionality of Physical Layer ? Data Transfer via Transport Channels. ? Error Detection. Hybrid ARQ Combining. ? Channel Coding and Rate Matching. ? Modulation and Demodulation. ? Measurements. ? MIMO, Transmit Diversity, Beamforming. ? RF Processing. Orthogonal Frequency Division Multiplexing Figure 1: FrequencyTime Representation of an OFDM Signal OFDM is a digital multicarrier modulation scheme, which uses a large number of closelyspaced orthogonal subcarriers. Each subcarrier is modulated with a conventional modulation scheme (such as QPSK, 16QAM, 64QAM) at a low symbol rate similar to conventional singlecarrier modulation schemes in the same bandwidth. LTE Radio principles ? Power efficient uplink increasing battery lifetime ? Improved cell edge performance by low peak to average ratio ? Reduced Terminal plexity Uplink: SCFDMA ? Enabling peak cell data rates of 173 Mbps DL and 58 Mbps in UL * ? Scalable bandwidth: / 3 / 5 / 10 /15 / 20 MHz also allows deployment in lower frequency bands (rural coverage, refarming) ? Short latency: 10 – 20 ms ** ? Improved spectral efficiency ? Reduced interference ? Very well suited for MIMO Downlink: OFDMA * At 20 MHz bandwidth, FDD, 2 Tx, 2 Rx, DL MIMO, PHY layer gross bit rate ** roundtrip ping delay (server near RAN) OFMD Downlink amp。 SCFDMA Uplink TDD Timing SCFDMA: PRB‘s are grouped to bring down Peak to Average Power Ratio (PAPR) better power efficiency at the terminal MHz = 72 Tones 20 MHz = 1200 Tones Subchannels / Tones (each 15 kHz) 1 TTI = 1ms 1 PRB (Physical Resource Block) = 12 Subcarriers = 180 kHz 1 PRB = 2 Slots = 2 * ms User 1 User 2 User 3 User .. Special subframe containing guard
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鄂ICP備17016276號-1