Reference Signal Pattern for Early Channel Estimation
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Solution Overview
Problem
In 5G wireless communications, existing approaches delay channel estimation and decoding due to the inability to efficiently transmit reference signals in the first OFDM symbol of a subframe, as user equipment is unaware of other users' PDCCH transmissions, leading to non-equally spaced reference signals and potential 'holes' in the frequency domain.
Innovation Solution
Reserving resource elements in the first OFDM symbol for reference signals and modulating them to overlap with data transmission in the second symbol, allowing user equipment to perform channel estimation and decoding more efficiently by determining the location of data transmission based on scheduling information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If reference signals are transmitted in the first OFDM symbol, then channel estimation can be performed earlier, but resource elements needed for control information may be conflicted
Solution Approach 1:
The first OFDM symbol is segmented into multiple resource elements with different functions: some reserved for reference signals (RS), others for control information (PDCCH). This segmentation allows simultaneous transmission of both RS and control information without mutual interference, resolving the resource conflict while enabling early channel estimation.
Solution Approach 2:
Reference signals are placed in the first OFDM symbol before data transmission begins, allowing the receiver to perform channel estimation in advance. This preliminary action of transmitting RS early enables faster channel characterization and reduces overall decoding delay.
2Adaptability or versatility
If reference signals are mapped around other users' PDCCH, then control information can be transmitted to multiple users, but reference signals become non-equally spaced creating holes in frequency domain
Solution Approach 1:
Different resource elements in the first OFDM symbol are assigned different qualities/functions: specific resource elements are reserved for reference signals with fixed, equally-spaced positions, while other resource elements are dynamically allocated for control information. This local differentiation maintains reference signal uniformity while enabling flexible multi-user control transmission.
3Quantity of substance
If the first OFDM symbol is used exclusively for control information, then control region capacity is maximized, but channel estimation is delayed until the second symbol
Solution Approach 1:
The first OFDM symbol is designed to serve multiple functions simultaneously: it carries control information (PDCCH) in certain resource elements while also transmitting reference signals in reserved resource elements. This multi-functionality allows the system to maintain high control information capacity while enabling early channel estimation through the presence of reference signals.
Data Source
AI summary
A method in a node (110, 115) comprises generating (704) a frame structure comprising at least a first subframe (305, 405, 505), the first subframe comprising a first symbol (310A, 510A) and a second symbol (310B, 510B), each of the first and second symbols comprising a plurality of resource elements. The method comprises reserving (708) one or more of the plurality of resource elements in the first symbol for reference signals (335A-G, 435A-G, 535A-G), modulating (712) one or more of the reserved resource elements in the first symbol with reference symbols (335B-D, 435B-D, 535B-D), the modulated one or more of the reserved resource elements in the first symbol comprising a subset of the one or more reserved resource elements that overlap in frequency domain the data transmission carried in the second symbol, and transmitting (716) the at least one subframe to another node.