DMRS
Demodulation Reference Signal: a reference signal transmitted alongside data on PDSCH/PUSCH/PDCCH that enables coherent demodulation by providing channel estimation.
DMRS is the reference signal that rides alongside data so the receiver can estimate the channel and demodulate coherently — and unlike LTE's always-on cell reference signals, NR's DMRS is sent only when and where there's something to demodulate. That "on-demand" design is deliberate: it cuts the constant overhead and the inter-cell interference that always-on pilots create, which is part of NR's lean-carrier philosophy.
Because it's beamformed together with the data it serves, DMRS is UE-specific and travels through exactly the same channel as the payload, giving an accurate estimate. The placement is configurable. The front-loaded DMRS sits early in the allocation so the UE can start decoding without waiting for the whole slot — good for latency. For high-mobility UEs, additional DMRS symbols are added later in the slot so channel estimation tracks the fast-changing channel rather than going stale. There are separate DMRS designs for PDSCH/PUSCH and for PDCCH and PBCH, each tuned to its channel's needs.
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