MIMO Pilot Symbol Mapping for Multi-Stream Transmission
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Solution Overview
Problem
The existing 3GPP LTE MIMO communication system is limited in its ability to transmit multiple data streams using UE-specific downlink reference signals, as the current structure can only transmit a single data stream and cannot be easily extended to support multiple data streams.
Innovation Solution
The method involves mapping pilot symbols to a subframe where user-specific pilot symbols, recognizable only by the second UE, are transmitted, with cell-specific pilot symbols for transmission antenna ports 0 to N-1 recognizable by both UEs and user-specific pilot symbols for ports N to M-1 recognizable only by the second UE, which are cyclically shifted in the time or frequency domain, allowing for the transmission of multiple data streams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the existing 3GPP LTE MIMO system uses UE-specific downlink reference signals, then a single data stream can be transmitted, but the system cannot transmit multiple data streams
Solution Approach 1:
The patent segments the reference signal structure by introducing two types of reference signals: cell-specific reference signals (CRS) for channel estimation and UE-specific reference signals (URS) for demodulation. This segmentation allows the system to maintain backward compatibility with single-stream transmission while enabling multi-stream transmission through the additional URS structure
Solution Approach 2:
The patent extends the reference signal structure by adding a new dimension - UE-specific reference signals that are orthogonal to cell-specific reference signals. This is achieved through orthogonal resource allocation in time-frequency domains and code division multiplexing, allowing the system to transmit multiple data streams without interfering with the existing single-stream structure
2Measurement precision
If pilot symbols are transmitted for all transmission antenna ports, then channel measurement accuracy improves, but pilot symbol overhead increases
Solution Approach 1:
The patent applies local quality by making reference signal transmission adaptive to the specific UE's needs. UE-specific reference signals are transmitted only to UEs that require them for demodulation, while cell-specific reference signals are transmitted for general channel estimation. This localized approach ensures that pilot overhead is incurred only where necessary, rather than uniformly across all transmissions
Solution Approach 2:
The cell-specific reference signals serve multiple functions: they provide channel estimation for all UEs and enable demodulation for UEs that do not require UE-specific reference signals. This multi-functionality reduces the need for additional pilot symbols, as the CRS structure is leveraged to serve multiple purposes, thereby reducing overall pilot overhead
Data Source
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AI summary
The present invention relates to a method for transmitting a pilot signal in a downlink MIMO (Multi Input Multi Output) system that supports a first UE (User Equipment) supporting N number of transmission antennae out of a total of M transmission antennae and supports a second UE supporting said M (M>N) number of transmission antennae. Said method comprises a step wherein a pilot symbol is placed as an image in the resource block (RB) region on a subframe that enables the transmission of a user-specific pilot symbol to said second UE in a base station; and a step wherein the subframe whereon said pilot symbol has been placed as an image is transmitted, wherein said RB region includes a first region and a second region, and the first region and the second region each include a certain number of continuous OFDM symbols on a respective time axis, and on said first region is placed as an image a cell-specific pilot symbol with respect to the transmission antenna ports 0 to N-1 that can recognize both said first UE and said second UE, and on said second region is placed as an image a user-specific pilot symbol with respect to the transmission antenna ports 0 to M that can recognize said UE only.