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Enhanced Radio Access Technologies for Next Generation Mobile Communication phần 9

Phối hợp, HSDPA và Enhanced Uplink thường được gọi là HSPA hay Truy cập gói tốc độ cao. Mục đích của Enhanced Uplink là nâng cao hơn nữa hỗ trợ WCDMA cho các dịch vụ dữ liệu gói tin, nhắm mục tiêu năng lực hệ thống cải thiện đáng kể đường lên - tiếp tục giảm chậm trễ / độ trễ tập trung vào đường lên - khả năng cao hơn đáng kể đường lên tốc độ dữ liệu | EVOLVED UTRA TECHNOLOGIES 229 domain compared to the reference symbols of the first OFDM symbol. It was reported that by multiplexing reference signals into two OFDM symbols within a sub-frame low-to-high mobility environments up to e.g. 350 km h can be supported without additional reference signals in the time domain. 4.1.2 Orthogonal reference signals In E-UTRA it should be possible to provide orthogonal reference signals between cells of the same Node B as well as between different transmit antennas of the same cell. Orthogonal reference signals between transmit antennas within the same cell is e.g. needed to support downlink transmit diversity and MIMO transmission. 1 Orthogonal reference signals for different transmission antennas Orthogonal reference signals for different transmit antennas of the same cell beam is established by means of FDM possibly in combination with TDM. Thus referencesignal multiplexing with different antenna-specific frequency or time shifts is used for each antenna. The main reason for relying on FDM TDM-based orthogonality between transmit antennas of the same cell beam is that it provides more accurate orthogonality compared to CDM-based orthogonality since no inter-code interference occurs in a frequency-selective fading channel. A high level of orthogonal accuracy is necessary to separate composite streams from different antennas in MIMO multiplexing and MIMO diversity schemes. 2 Orthogonal reference signals for different cells in the same Node B CDM-based reference-signal orthogonality is used between different cells beams belonging to the same Node B in order to suppress the mutual interference particularly near the cell boundary. The merit of CDM-based orthogonality compared to FDM-based orthogonality between cells of the same Node B is a better tracking ability for the channel estimation particularly UEs far from sector borders since the density of the CDM-based orthogonal reference symbols in the frequency domain is higher .