Pilot Signal Transmission Using OFDM Symbol Segmentation
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Solution Overview
Problem
Grant-free multiple access schemes in 5G wireless communications face interference challenges due to collisions between uplink transmissions from different user equipments (UEs), which can lead to reduced channel estimation quality and increased latency, especially with the limited pilot sequence lengths in current LTE designs.
Innovation Solution
The implementation of new frame formats that support longer pilot sequences, allowing pilot values to be transmitted over multiple orthogonal frequency division multiplexed (OFDM) symbols, and the use of comb-type pilot symbol arrangements combining code division multiplexing and frequency division multiplexing to mitigate interference, along with phase shifts to generate diverse pilot sequences from a root Zadoff-Chu sequence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If grant-free multiple access schemes are used to reduce latency and overhead, then uplink transmission efficiency is improved, but collision between UEs occurs leading to reduced channel estimation quality
Solution Approach 1:
The patent segments the pilot sequence transmission across multiple OFDM symbols (first OFDM symbol and second OFDM symbol) rather than transmitting all pilot values in a single symbol. This segmentation allows the base station to receive pilot values from different UEs in different time slots, reducing collision impact and improving channel estimation quality while maintaining grant-free access efficiency
Solution Approach 2:
The patent introduces a time dimension by transmitting pilot sequences across multiple OFDM symbols vertically in the time domain. This dimensional expansion allows the system to handle multiple UEs simultaneously with the same frequency resources while maintaining distinguishable pilot signals through time separation, thus improving channel estimation quality without sacrificing uplink transmission efficiency
2Measurement precision
If longer pilot sequences are transmitted to improve channel estimation quality, then measurement precision is improved, but overhead increases
Solution Approach 1:
The patent divides the pilot sequence into multiple parts transmitted across different OFDM symbols. Each UE transmits a portion of the pilot sequence in the first OFDM symbol and another portion in the second OFDM symbol. This segmentation enables the system to achieve better channel estimation quality through longer effective pilot sequences while distributing the overhead across multiple symbols, reducing the burden on any single resource block
Solution Approach 2:
The patent employs periodic transmission of pilot sequences across multiple OFDM symbols with a defined pattern (first subset in first symbol, second subset in second symbol). This periodic structure allows the base station to accumulate channel estimation information from multiple time instances, improving estimation quality while maintaining a predictable and manageable overhead pattern that can be efficiently processed
3Productivity
If more UEs are supported on the same time-frequency resources to increase system capacity, then productivity is improved, but interference between UEs increases
Solution Approach 1:
The patent segments the pilot transmission resources in the time domain by using multiple OFDM symbols. Different UEs can be assigned to transmit their pilot sequences in different OFDM symbols or with different time offsets. This time-domain segmentation reduces pilot collision and interference between UEs while allowing more UEs to share the same frequency resources, thereby increasing system capacity
Solution Approach 2:
The patent adds a time dimension to pilot sequence transmission by utilizing multiple OFDM symbols. This dimensional expansion allows the system to accommodate more UEs on the same frequency resources by separating their pilot transmissions in time. The base station can distinguish between UEs based on their time-positioned pilot sequences, reducing interference while maintaining high system capacity
Data Source
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AI summary
Longer pilot sequences can be supported by transmitting pilot values of a given pilot sequence over different orthogonal frequency division multiplexed (OFDM) symbols of an uplink frame. The pilot values may be contiguous, or non-contiguous, with one another in the time domain. Consecutive pilot values in a pilot sequence may be transmitted in different OFDM symbols of the frame. For example, odd pilot values (e.g., P1, P3, P5…) in a pilot sequence may be transmitted over a different OFDM symbol than even pilot values (e.g., P2, P4, P6…) in the pilot sequence. Alternatively, a leading subset of pilot values in a pilot sequence is transmitted over a different OFDM symbol than a trailing subset of pilot values in the pilot sequence.