【文章內(nèi)容簡介】 LTE 3GPP LTE Evolved UTRA Radio Interface Concepts Reference signals Reference signals are transmitted ? during the first and fifth OFDM symbols of each slot when the shortCP is used ? And during the first and fourth OFDM symbols when the long CP is used. Physical Resource Block (PRB) = 14 OFDM Symbols x 12 Subcarrier f Subframe (1 ms) Reference Symbol Reference signal is staggered in the timefrequency plane。 mobile interpolates to obtain a 2D picture of the channel Slot ( ms) 12 Subcarriers 27 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts Reference Signals ? In DL, one reference signal is transmitted per antenna port to estimate the channel response for each antenna. ? In UL, two types of reference signals are supported: DL Reference Signals Cell Search /Acquisition Channel Estimation UL Reference Signals Demodulation Channel Sounding The estimated channel response is used for channel equalization to estimate channel quality 28 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts LTE Antenna port configurations(1/2) LTE specifications define several transmission mode with specifics DL reference signals ? Single antenna, 2 or 4 antennas – Antenna port 0 up to antenna port 3: SISO, Diversity, CL and OL MIMO 29 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts LTE Antenna port configurations(2/2) ? Single virtual antenna port 5 (can be used for BF in TDD) ? MBMS using virtual antenna port 4 ? Physical Mulicast channels (PMCH) iso PDSCH ? PMCH shall not be transmitted in SF 0 and 5 on carrier supporting mix of data ? Specific RS pattern 0?l 5?l 0?l 5?le v e n n u m b e r e d slo ts odd n u m b e r e d slo tsA n t en n a p o rt 44R4R4R4R4R4R4R4R4R4R4R4R4R4R4R4R4R4R 0?le v e n n u m b e r e d s lo ts odd n u m b e r e d s lo tsA n t en n a p o rt 55R5R5R5R5R5R5R5R5R5R5R5R0?l 6?l6?lMUUSDUUUSD16MMMMDMMUSD65MMMMDMUUSD54MMMMDUUUSD43MMUSDMMUSD42MUUSDMUUSD21UUUSDUUUSD009876543210Su b fr am e n u mb erM B SF N cap a b i l i t y i n SF n u mb ersU p l i n k d o w n l i n k co n f i g u r ati o n30 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts Transmission Mode ? TS36 Rel 8 defined 7 DL transmit mode ? TM1: Singleantenna port。 port 0 ? TM2: Transmit diversity, based on space frequency block coding (SFBC) ? TM3: Openloop spatial multiplexing ? TM4: Closedloop spatial multiplexing ? TM5: Multiuser MIMO ? TM6: Closedloop Rank=1 precoding ? TM7: Singleantenna port。 port 5 ? UE is semistatically configured by eNB via RRC signaling to operate in any of the above 7 modes. Supported in DL MIMO Transmission Mode TxDiv SFBC MIMO 2x2 (SFBC) TM2 OL SM 2 ant MIMO 2x2 OL (SM) TM3 with 2 antennas CL SM 2 ant MIMO 2x2 CL (SM) TM4 with 2 antennas 31 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts MIMO and MRC ? The LTE PHY can optionally exploit multiple transceivers at both the eNB and UE in order to enhance link robustness and increase data rates for the LTE downlink. ? In particular, maximal ratio bining (MRC) is used to enhance link reliability in challenging propagating conditions when signal strength is low and multipath conditions are challenging. ? MIMO is a related technique that is used to increase system data rates. Baseband XCVR Baseband XCVR XCVR Conventional Single Channel Receiver w/Antenna Diversity MRC/MIMO Receiver Configuration (2ch) 32 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts MIMO and MRC ? With MRC, a signal is received via two (or more) separate antenna/transceiver pairs. ? Note that the antennas are physically separated, and therefore have distinct channel impulse responses. Channel pensation is applied to each received signal within the baseband processor before being linearly bined to create a single posite received signal. ? Received signals add coherently within the baseband processor ? Increasing in SNR of 3 dB on average for a twochannel MRC receiver in a noise limited environment. 33 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts Reference signals from each transmitting antenna for MIMO ? In order to successfully receive a MIMO transmission, ? the receiver must determine the channel impulse response from each transmitting antenna. ? In LTE, channel impulse responses are determined by sequentially transmitting known reference signals from each transmitting antenna 34 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts MIMO Operation (1/2) ChAC ChAD Note that while one transmitter antenna is sending the reference signal, the other antenna is idle. Referring to the MIMO2x2 system, there are a total of four channel impulse responses (C1, C2, C3 and C4) Baseband XCVRA XCVRB Baseband XCVRC XCVRD Reference Signal Transmitted from Antenna B ChBD ChBC Reference Signal Transmitted from Antenna A Baseband XCVRA XCVRB Baseband XCVRC XCVRD 35 | LTE 3GPP LTE Evolved UTRA Radio Interface Concepts MIMO Operation (2/2) Baseband XCVRA XCVRB Baseband XCVRC XCVRD Once the channel impulse responses are known, data can be transmitted from both antennas simultaneously.