R1-094856: SRS Enhancements for LTE-A Agenda: 7.4.2 Document for: Discussion/Decision 3GPP RAN WG1 #59, Jeju, South Korea November 9-13, 2009 Motorola

Introduction LTE Rel-10 uplink enhancements compared to Rel-8/9 Multi-antenna transmission up to four Tx antenna Uplink spatial multiplexing of up to four layers Frequency Non-contiguous resource allocation Possible support for CoMP Rel-8 SRS design features SRS transmitted on last symbol in configured subframes IFDMA comb SRS structure reusing DM RS base sequences SRS BW restricted to be multiple of 4 RBs (contiguous) Four SRS BWs can be simultaneously supported in a cell Cyclic shift orthogonality: 8 equally spaced cyclic time shifts per comb supported (spacing = 4.17us) SRS Frequency hopping supported; Optional SRS transmit antenna switching Configurable UE-specific SRS BW, Starting subcarrier, comb index, CS, SRS periodicities – 2, 5, 10, 20, 40, 80, 160 or 320 ms via RRC signaling SRS base sequence group = PUCCH base sequence group No cyclic shift hopping for SRS Rel-8 SRS design provides sufficient flexibility and can be straightforwardly extended to support Rel-10 multi-antenna transmissions Propose to re-use Rel-8 SRS structure as much as possible New features/enhancements/signaling should be considered only if they provide “significant” benefit over Rel-8 mechanisms

SRS Extension to support UL MIMO in LTE-A (slide 1 of 2) Current Baseline Agreement [TR 36.814] Non-precoded and Antenna-specific SRS Rel-8 principles re-used for SRS multiplexing UL MIMO Likely a new transmission mode is defined for SU-MIMO (2 Tx and 4 Tx UE transmit antenna configuration based on UE capability) As in DL Rel-8/9, UE is configured in new MIMO mode via RRC signaling SRS transmission can be configured via RRC signaling Simultaneous SRS transmission from multiple transmit antennas when configured via RRC Most likely when UE is suitable for UL-MIMO (i.e., precoding) Take into account SNR condition and antenna effect (e.g., antenna gain imbalance, coupling, etc.) Antenna-specific SRS have same SRS BW, Frequency RB position Orthogonality via cyclic shift multiplexing and/or different comb assignments CS, comb assignment can be explicit or implicit relative to first antenna configuration

SRS Extension to support UL MIMO in LTE-A (slide 2 of 2) Similar to “Single Antenna Port Mode” defined for UE with multiple transmit antennas, such mode can be configured for SRS too In order to save power and SRS resource if UE is not likely to support UL-MIMO/precoding (e.g., low SINR, large AGI, etc.) Different transmit PA architectures supported [R1=093750, RAN4 LS Response] E.g 2 Tx antenna UE: A: 20dBm + 20dBm B: 23dBm + 23dBm C: 23dBm + x, where x ≤ 23dBm the total transmit power, Pmax , defined as 23dBm regardless of the number of antennas, PAs and precoding used Implementation issue on how PAs are used in “single-port” SRS transmission Achieve same coverage (23dBm max Tx power) as Rel-8 single antenna UE “Long-term” precoding: based on UE implementation Antenna virtualization: correspond to a fixed synthesized pattern Turn-off all but one PA But the same implementation should be used for SRS and PUSCH, since eNB still use SRS to track power control and frequency-selectiveness of the UL channel

Non-contiguous RA and Carrier Aggregation No non-contiguous SRS transmissions with a component carrier Independent SRS transmission and configuration for each component carrier with UL Carrier Aggregation Component carrier-specific SRS sequence

Conclusions Rel-8 SRS design provides sufficient flexibility and can be straightforwardly extended to support Rel-10 multi-antenna transmissions Propose to re-use Rel-8 SRS structure as much as possible New features/enhancements/signaling should be considered only if they provide “significant” benefit over Rel-8 mechanisms Simultaneous SRS transmission from multiple transmit antennas when configured via RRC Take into account SNR condition and antenna effect (e.g., antenna gain imbalance, coupling, etc.) Antenna-specific SRS have same SRS BW, Frequency RB position Orthogonality via cyclic shift multiplexing and/or different comb assignments SRS configured in Single Antenna Port Mode for Multi-transmit antenna UE Implementation issue on how PAs are used in “single-port” SRS transmission Long-term” precoding, Antenna virtualization, Turn-off all but one PA Same implementation should be used for SRS and PUSCH, since eNB still use SRS to track power control and frequency-selectiveness of the UL channel No non-contiguous SRS transmissions with a component carrier Independent SRS transmission and configuration for each component carrier with UL Carrier Aggregation Component carrier-specific SRS base sequence