18 E-DCH transmission in CELL_FACH state and Idle Mode (1.28Mcps TDD only)

25.3193GPPEnhanced uplinkOverall descriptionStage 2TS

For 1.28Mcps TDD, The E-DCH transmission in CELL_FACH state and Idle mode is a mechanism to improve the transmission performance. The Rel-7 enhanced random access procedure for E-DCH is used in the Enhanced Uplink in CELL_FACH and Idle mode.

For 1.28Mcps TDD, the E-DCH transmission is always linked with HS-DSCH reception in CELL_FACH state.

UE performs initial access on primary frequency, i.e. UE sends RRC Connection Request or CELL Update when entering a new cell after cell re-selection on primary frequency.

For initial access, UE uses a common E-RNTI and the enhanced random access procedure consists of common E-RNTI collision resolution: a group of common E-RNTIs are allocated in relation to each E-RUCCH. The common E-RNTIs are distributed on frame or sub-frame. UE selects an E-RUCCH and a common E-RNTI related to the E-RUCCH based on the SFN or SFN’ on which the E-RUCCH is sent. The common E-RNTI is provided as UE ID in E-RUCCH to the Node B. With the reception of random access request from common E-RNTI, Node B shall send E-AGCH with the common E-RNTI (through an E-RNTI-specific CRC attachment) within the common E-RNTI scheduling window. The common E-RNTI collision resolution phase ends when UE receives an E-AGCH with its common E-RNTI in the common E-RNTI scheduling window. If the UE does not receive its common E-RNTI on the E-AGCH upon the expiry of the common E-RNTI scheduling window, the random access fails.

When receiving UE’s initial access request, RNC configures a dedicated H-RNTI, E-RNTI and a working frequency for the UE. Uplink E-DCH transmission and downlink HS-DSCH reception for a specific UE is performed on the same frequency. The data transmission procedure over E-DCH is performed via scheduling request on E-RUCCH and scheduling grant on E-AGCH.

Note: An E-RNTI can be allocated to a UE in CELL_PCH state, which supports E-DCH transmission in CELL_FACH. For UL data transmission, the UE performs an autonomous state transition from CELL_PCH to CELL_FACH state, before starting E-DCH transmission.