PRACH Resource Configuration for Distinguishing MTC and Legacy UEs
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Solution Overview
Problem
Existing mobile communication technologies face challenges in supporting reduced bandwidth and coverage enhanced machine-type communication (MTC) devices, particularly in LTE Rel-13, due to issues with receiving PDCCH and PRACH channels, and identifying and reducing collisions between different device categories.
Innovation Solution
Implementing category-specific PRACH configurations with differentiated PRACH resources and preamble sequences for, and configuring a common search space based on these configurations to ensure efficient communication with MTC devices, including separate PRACH configurations for legacy, reduced bandwidth, and coverage enhanced UEs, and using PDCCH or EPDCCH for DCI transmission based on device category.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single PRACH configuration is used for all UEs, then system complexity is reduced, but collision probability increases between different device categories
Solution Approach 1:
The PRACH configuration is segmented into multiple configurations (first PRACH configuration and second PRACH configuration) tailored for different device categories. Legacy UEs use the first configuration while reduced bandwidth UEs use the second configuration, thereby reducing collision probability between these different device types while maintaining manageable system complexity through structured segmentation.
Solution Approach 2:
Different PRACH configurations are assigned to different device categories based on their specific requirements. The first PRACH configuration is optimized for legacy UEs with full bandwidth capability, while the second PRACH configuration is optimized for reduced bandwidth UEs. This local quality approach ensures each device type uses parameters suited to its capabilities, reducing collisions without requiring complex unified configuration.
2Device complexity
If reduced bandwidth UEs use the same bandwidth as legacy UEs, then resource allocation is simplified, but communication reliability deteriorates in coverage enhanced conditions
Solution Approach 1:
The bandwidth parameter is changed based on device category. Reduced bandwidth UEs are configured with a second PRACH configuration that specifies a reduced bandwidth smaller than the system bandwidth, while legacy UEs use the first configuration with full system bandwidth. This parameter change enables reduced bandwidth UEs to operate reliably in coverage enhanced conditions without requiring complex dynamic bandwidth adjustment mechanisms.
3Reliability
If coverage enhanced UEs use more repetitions, then reception reliability improves, but time delay increases
Solution Approach 1:
The number of repetitions is made dynamic and configurable based on coverage enhancement level. Coverage enhanced UEs can be configured with different numbers of repetitions (e.g., 2, 4, or 8 repetitions) depending on their specific coverage requirements. This dynamic approach allows the system to optimize between reliability and delay by adjusting repetitions only when and where needed, rather than applying a fixed high repetition count to all UEs.
Data Source
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AI summary
A communication system is disclosed in which a communications node allocates resources for potential use by any of a plurality of user communication devices, including first type (e.g. legacy) user communication devices and second type (e.g. machine-type) communication devices. Control data is sent, to the user communication devices, defining communication resources for potential use by any of the user communication devices. The control data includes information identifying a first PRACH resource configuration for a first type user communication device and a second PRACH resource configuration for a second type of device such that the user devices can be distinguished by the PRACH configuration used.