SRS Bandwidth Alignment in TDD UpPTS for Resource Utilization
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Solution Overview
Problem
In time division duplex (TDD) wireless communication systems, the limited flexibility in sounding reference signal (SRS) bandwidths leads to unsounded resource blocks, which are not effectively utilized, especially in frequency selective channels, and the uplink pilot time slot (UpPTS) allocation does not allow for easy reuse of these unsounded blocks.
Innovation Solution
The SRS is transmitted in the uplink pilot time slot (UpPTS) with a maximum SRS bandwidth size that is an even number of resource blocks with prime factors from {2, 3, 5} and less than or equal to (NRBUL-6·NRA), where NRBUL is the uplink bandwidth and NRA is the number of Random Access Channel opportunities, allowing for a subset of resource blocks to be used for SRS transmission, excluding those for RACH opportunities and ensuring alignment with the uplink bandwidth center.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SRS bandwidth is restricted to multiples of 4 RBs, then signaling requirements are limited, but edge resource blocks are missed due to restricted flexibility
Solution Approach 1:
The SRS bandwidth is segmented into multiple possible sizes (4, 8, 12, 16, 20, 24, 32, 40, 48, 60, 64, 72, 80, 96 RBs) that can be selected based on channel conditions and system requirements. This segmentation allows the system to choose from discrete bandwidth options rather than being restricted to a single fixed size, thereby improving adaptability while maintaining manageable signaling overhead through standardized choices.
Solution Approach 2:
The SRS bandwidth is made dynamic by allowing different bandwidth configurations to be applied in different UpPTS occasions based on scheduling decisions and channel conditions. The system can adjust the SRS bandwidth size dynamically rather than using a fixed bandwidth, enabling better adaptation to varying system requirements while maintaining signaling efficiency through pre-defined bandwidth options.
2Area of stationary object
If maximum SRS bandwidth of 96 RBs is used, then more bandwidth is covered, but maximum unsounded resource blocks increase to 15 (2.7 MHz)
Solution Approach 1:
Instead of uniformly sounding the entire bandwidth or leaving large gaps, the system applies local quality by selectively sounding specific resource blocks within the available bandwidth. The SRS can be configured to sound particular RBs while leaving others unsounded, allowing the system to focus measurement resources on critical frequency regions while accepting that some edge RBs may remain unsounded in certain configurations.
Solution Approach 2:
The system changes the parameter of SRS bandwidth size across different UpPTS occasions rather than maintaining a fixed maximum bandwidth. By varying the SRS bandwidth parameter (selecting from available sizes), the system can adapt the sounding coverage to match actual system needs, reducing the number of unsounded RBs when smaller bandwidths are appropriate while still providing full coverage when larger bandwidths are configured.
3Adaptability or versatility
If SRS is transmitted in ordinary uplink sub-frames, then flexibility is maintained, but problems occur with PUCCH or data transmission
Solution Approach 1:
The uplink transmission resources are segmented into different types of sub-frames: ordinary uplink sub-frames for data and PUCCH transmission, and UpPTS for SRS transmission. This segmentation separates the functions to avoid conflicts, ensuring that SRS transmissions in UpPTS do not interfere with PUCCH or data transmissions in ordinary uplink sub-frames, thereby maintaining both flexibility and reliability.
Solution Approach 2:
The UpPTS is designed with multi-functionality to support both random access and SRS transmission. By making the UpPTS versatile and capable of supporting multiple functions, the system can allocate SRS to UpPTS without sacrificing the flexibility needed for random access operations, while avoiding the reliability issues that would arise from transmitting SRS in ordinary uplink sub-frames alongside PUCCH and data.
Data Source
AI summary
A wireless terminal operating in TDD mode transmits a plurality of sounding reference signals using an assigned maximum sounding reference signal (SRS) bandwidth (BW) size. At least one of the sounding reference signals is transmitted in a corresponding uplink pilot time slot (UpPTS) region of a special sub-frame of a radio frame wherein, in the frequency dimension, an uplink BW center is misaligned with a BW center of the SRS in the UpPTS region, a maximum SRS BW size in the UpPTS region is an even number of resource blocks with prime factors from a set of {2, 3, 5}, and the maximum SRS BW having a size in number of resource blocks less than or equal to (NRBUL−6·NRA) where NRA is a number of Random Access Channel (RACH) opportunities in the UpPTS region.