Chapter 15
Uplink Reference Signals
15.1 Introduction
As in the downlink, the LTE Single-Carrier Frequency Division Multiple Access (SC-FDMA) uplink incorporates Reference Signals (RSs) for data demodulation and channel sounding. In this chapter, the design principles behind these RSs are explained, including in particular features related to interference randomization and coordination, and the flexible configuration of channel sounding.
The roles of the uplink RSs include enabling channel estimation to aid coherent demodulation, channel quality estimation for uplink scheduling, power control, timing estimation and direction-of-arrival estimation to support downlink beamforming. Two types of RS are supported on the uplink:
- DeModulation RS (DM-RS), associated with transmissions of uplink data on the Physical Uplink Shared CHannel (PUSCH) and/or control signalling on the Physical Uplink Control CHannel (PUCCH).1 These RSs are primarily used for channel estimation for coherent demodulation.
- Sounding RS (SRS), not associated with uplink data and/or control transmissions, and primarily used for channel quality determination to enable frequency-selective scheduling on the uplink.
The uplink RSs are time-multiplexed with the data symbols. The DM-RSs of a given UE2 occupy the same bandwidth (i.e. the same Resource Blocks (RBs)) as its PUSCH/PUCCH data transmission. Thus, the allocation of orthogonal (in frequency) sets of RBs to different UEs for data transmission ...
