Uplink RS (Reference Signal) in LTE?

Question

These signals are messing me up all down the road. If somebody knows about this then the answers would be welcome.

Answer 1

Uplink Reference Signals are of two types in LTE:

1. Demodulation Reference Signals (DM-RS): Which are used to enable coherent signal demodulation at ENodeB. These signals are time multiplexed with uplink data and are transmitted on the fourth or third SC-FDMA symbol of an uplink slot for normal or extended CP respectively, using the same bandwidth as the data.

2. Sounding Reference Signal (SRS): Which is used to allow channel dependent (i.e. frequency selective) uplink scheduling as the DM-RS cannot be used for this purposes since they are assigned over the assigned bandwidth to a UE. The SRS is introduced as a wider band reference signal typically transmitted in the last SC-FDMA symbol of a 1 ms subframe as shown in Figure below. User data transmission is not allowed in this block, which results in about 7% reduction in uplink capacity. The SRS is an optional feature and is highly configurable to control overhead--it can be turned off in a cell. Users with different transmission bandwidth share this sounding channel in the frequency domain.