Random Access Channel Preamble Timing in TDD Wireless Systems
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Solution Overview
Problem
In wireless communication systems, particularly in LTE's TDD mode, the transmission of signals on a random access channel faces interference issues between the preamble and subsequent uplink data, and the coverage area of the random access channel is limited due to timing delays, which can be exacerbated by multi-path effects.
Innovation Solution
A method where a terminal transmits a cyclic prefix and a preamble on the random access channel with a specific time length ahead of the uplink pilot time slot, with the preamble length being two symbols without a cyclic prefix, and the cyclic prefix length is optimized to avoid interference and enhance coverage by considering the largest delay extension on multi-path channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the start position of the RACH is moved forward to increase the set time length, then the coverage area of the random access channel is improved, but the previous downlink signal is interfered
Solution Approach 1:
The patent applies preliminary action by moving the RACH start position forward in time, allowing the random access signal to be transmitted earlier. This increases the set time length (Tgt) and improves coverage area for cell-edge users, while carefully managing the timing to avoid interfering with downlink signals.
Solution Approach 2:
The patent changes the timing parameter of the RACH start position and optimizes the set time length (Tgt) to balance coverage improvement with downlink signal protection. By adjusting these parameters, the system achieves better coverage without causing harmful interference.
2Area of stationary object
If the set time length is increased to improve coverage, then the transmitting time delay of the signal on the random access channel is increased, but the previous downlink signal will be interfered
Solution Approach 1:
The patent uses preliminary action by transmitting the random access signal earlier with an increased set time length, which improves coverage for users with large transmitting time delays. The forward positioning of the RACH start allows signals from cell-edge users to reach the base station within the available time window.
3Reliability
If a CP is added in front of the preamble to handle multi-path effects, then the signal and multi-path of UE on a border of a cell fall within a search window, but the timing alignment becomes more complex
Solution Approach 1:
The patent applies preliminary action by adding a cyclic prefix (CP) in front of the preamble before transmission. This CP serves as a buffer that accommodates multi-path delays and ensures that both the direct signal and reflected signals fall within the receiver's search window, improving reliability in multi-path environments.
Data Source
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AI summary
A transmitting method of a signal on a random access channel in a wireless communication system, comprises the steps that: a terminal transmits a preamble on the random access channel with a set time length ahead of the end position of an uplink pilot time slot, and the length of the preamble is the length of two symbols without a cyclic prefix. Another transmitting method of a signal on a random access channel in a wireless communication system, comprises the steps that: a terminal transmits a cyclic prefix and a preamble on the random access channel with a set time length ahead of the end position of an uplink pilot time slot, and the length of the preamble is the length of two symbols without a cyclic prefix. The methods can avoid the interference of the preamble to the data of the uplink subframe, and can improve the coverage area of the random access channel and the work efficiency of the time division duplex system.