UpPTS Length Configuration for SRS Capacity in LTE TDD
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Solution Overview
Problem
Current LTE TDD systems face limitations in SRS capacity, particularly in UpPTS configurations, which restrict the number of users that can be supported for SRS transmission, especially with the introduction of full dimension MIMO technologies, leading to insufficient channel reciprocity and beamforming capabilities.
Innovation Solution
The proposed solution involves configuring a longer Uplink Pilot Time Slot (UpPTS) in special subframes, allowing for increased SRS capacity by allocating additional symbols for SRS transmission, while maintaining compatibility with legacy UEs by independently configuring UpPTS lengths for different subframes, thereby supporting new UEs with FD-MIMO capabilities without compromising downlink throughput for legacy UEs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If UpPTS length is increased to support more SRS transmissions, then SRS capacity is improved, but downlink throughput for legacy UEs deteriorates
Solution Approach 1:
The patent divides the special subframe into distinct segments: DwPTS (downlink pilot time slot), GP (guard period), and UpPTS (uplink pilot time slot). By segmenting the frame structure and allowing independent configuration of UpPTS length, the system can extend SRS capacity in the uplink segment without affecting downlink segments, thus resolving the contradiction between SRS capacity and downlink throughput.
Solution Approach 2:
The patent applies local quality by allowing different UpPTS configurations for different special subframes (e.g., special subframe #1 and #6 can have different UpPTS lengths). This enables targeted enhancement of SRS capacity in specific subframes while maintaining standard configurations in others, thereby improving overall SRS capacity without uniformly degrading downlink throughput across all subframes.
2Reliability
If UpPTS length is extended to support FD-MIMO, then channel reciprocity is improved, but system complexity increases
Solution Approach 1:
The patent introduces dynamic configurability of UpPTS length through new special subframe configurations (e.g., configurations with 3, 4, 6, or 9 UpPTS symbols). This dynamic approach allows the system to adaptively extend UpPTS when FD-MIMO is deployed to ensure adequate channel reciprocity, while maintaining flexibility to adjust configurations based on deployment scenarios, thus managing system complexity through standardized dynamic parameters.
3Quantity of substance
If additional UpPTS symbols are allocated for SRS, then SRS transmission capacity is improved, but guard period duration is reduced
Solution Approach 1:
The patent changes the parameter of UpPTS symbol count by introducing new special subframe configurations with increased UpPTS symbols (3, 4, 6, or 9 symbols compared to the traditional 1-2 symbols). This parameter change directly increases SRS transmission capacity. The guard period duration is adjusted accordingly in each configuration, creating a set of standardized options that balance SRS capacity and guard period requirements for different deployment scenarios.
Data Source
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AI summary
Increased symbol length of uplink pilot time slots (UpPTS) in special subframes is disclosed in which a configuration of a first special subframe may be independent from configuration of a second special subframe in the same frame, such that the first UpPTS of the first special subframe is longer than the second UpPTS of the second special subframe. The second UpPTS of the second special subframe may also be longer than legacy UpPTS length in select configurations. A serving base station may select the special subframe configurations in order to balance sounding reference signal (SRS) capacity for compatible user equipments (UEs) and downlink throughput for legacy UEs. The selected special subframe configurations may be transmitted by the serving base stations. In additional aspects, compatible UEs may be configured with at least two separate SRS power control parameters for use in the additional and legacy UpPTS symbols.