Random Access Procedure in Unlicensed Bands
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Solution Overview
Problem
In wireless communication, especially in unlicensed bands, the interference from coexisting communication protocols like WLAN and the challenge of ensuring quality of service and mobility due to contention-based channel access hinder efficient random access procedures in LTE-U and LAA systems.
Innovation Solution
A method for performing a random access procedure in an unlicensed band, involving transmission timing adjustments and flexible bandwidth allocation using Zadoff-Chu sequences, with repeated RAP transmission and frequency hopping to enhance channel access and reduce interference, allowing for wider bandwidth utilization while adhering to power spectral density limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If random access procedure is performed using predetermined radio resource at predetermined timing in unlicensed band, then channel access procedure is simplified, but interference from coexisting protocols like WLAN increases and quality of service cannot be guaranteed
Solution Approach 1:
The patent applies dynamics by making the random access procedure adaptable to unlicensed band conditions. The base station dynamically determines whether to receive a random access preamble based on downlink signal detection results, and the user equipment dynamically adjusts its transmission based on feedback. This dynamic adaptation allows the system to respond to changing channel conditions and interference levels, resolving the contradiction between simplified procedure and reliable QoS.
Solution Approach 2:
The patent changes key parameters of the random access procedure: instead of using fixed predetermined timing and resources, the system uses downlink signal quality metrics (RSRP, SINR) to dynamically determine preamble reception. The base station can adjust its reception behavior based on measured signal parameters, and the UE adapts its random access attempts based on feedback about channel conditions. This parameter-based adaptation resolves the contradiction by allowing the procedure to simplify under good conditions while maintaining reliability under poor conditions.
2Adaptability or versatility
If contention-based channel access (CSMA/CA) is used in unlicensed band, then channel sharing with WLAN is enabled, but interference phenomenon becomes serious and mobility cannot be supported
Solution Approach 1:
The patent introduces the downlink signal quality measurement as an intermediary mechanism between the contention-based access and the random access procedure. The base station measures downlink signal quality (RSRP, SINR) as an intermediate step to determine whether to accept random access preambles. This intermediary measurement allows the system to share the channel with WLAN (maintaining adaptability) while filtering out excessive interference (reducing harmful factors) by making informed decisions about preamble reception based on the intermediate measurement results.
3Device complexity
If random access preamble is transmitted at predetermined timing without timing adjustment, then transmission procedure is simplified, but uplink synchronization cannot be achieved in unlicensed band with varying channel conditions
Solution Approach 1:
The patent applies preliminary action by having the base station perform downlink signal quality measurements and determine reception decisions before the random access preamble transmission. The base station prepares by measuring RSRP and SINR of downlink signals, and decides in advance whether it will be able to receive preambles at upcoming random access opportunities. This preliminary preparation allows the system to maintain simple predetermined timing (low complexity) while achieving reliable synchronization (high reliability) because the base station is already prepared to handle the preamble transmission based on pre-assessed channel conditions.
Data Source
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AI summary
Provided are a method of performing a random access procedure in an unlicensed band and a device using the method. The device performs a clear channel assessment (CCA) during a random access preamble (RAP) window in the unlicensed band. If the CCA succeeds, the wireless device transmits a plurality of RAPs. The plurality of RAPs are repeatedly transmitted in a frequency domain or a time domain.