PRACH Repetition Level Selection for MTC Coverage
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Solution Overview
Problem
Low complexity User Equipment (UE) in cellular communications networks, particularly Machine-to-Machine (M2M) devices, face challenges in decoding system information blocks due to high path loss and signal attenuation, requiring enhanced coverage techniques and efficient resource allocation for reliable random access signals.
Innovation Solution
A method for determining the number of resources needed by a wireless device to decode information blocks, including code rate and transmit power, to adjust the number of PRACH repetitions for reliable random access signal transmission based on coverage scenarios, optimizing resource usage and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coverage enhancing techniques are employed to improve signal reception in challenging scenarios, then reliability of random access procedures is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic adaptation of PRACH repetition levels based on measured downlink signal quality (RSRP). The wireless device adjusts the number of repetitions upward when signal quality is poor and downward when signal quality is good, creating a dynamic system that optimizes power consumption while maintaining reliable random access procedures across varying coverage conditions
Solution Approach 2:
The patent changes the parameter of PRACH repetition level based on measured RSRP values. By mapping RSRP measurements to specific repetition levels (e.g., RSRP thresholds determining between 1, 2, 4, or 8 repetitions), the system adapts its transmission strategy to match actual coverage conditions, resolving the contradiction between reliability and power consumption
2Reliability
If PRACH repetition level is increased to ensure reliable signal transmission in poor coverage, then reliability is improved, but resource usage increases
Solution Approach 1:
The system dynamically adjusts PRACH repetition levels based on real-time RSRP measurements rather than using a fixed high repetition level for all devices. This dynamic approach ensures reliable signal transmission only when and where actually needed, optimizing resource usage across the network
Solution Approach 2:
The patent applies different repetition levels to different wireless devices based on their local coverage conditions as indicated by their RSRP measurements. Devices in poor coverage areas use higher repetition levels while devices in good coverage areas use lower repetition levels, ensuring reliable transmission locally without wasting network resources
3Device complexity
If downlink bandwidth is reduced to 1.4 MHz for low complexity UE, then device complexity and cost are reduced, but decoding capability deteriorates
Solution Approach 1:
The patent employs periodic transmission of downlink information blocks (such as system information blocks) to allow low complexity UEs with reduced bandwidth capability to accumulate sufficient signal energy over multiple periods for successful decoding. This periodic repetition compensates for the reduced decoding capability inherent in 1.4 MHz bandwidth devices
Solution Approach 2:
The network performs preliminary assessment of the UE's downlink bandwidth capability and configures appropriate repetition levels before the UE attempts to decode critical information. This preliminary configuration ensures that low complexity UEs are given sufficient transmission repetitions to successfully decode information despite their reduced bandwidth capability
Data Source
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AI summary
Systems and methods are disclosed herein that relate to determining a coverage scenario of a wireless device and determining an amount of resources to be used by the wireless device for transmission of a random access signal based on the coverage scenario of the wireless device. In some embodiments, a method of operation of a wireless device for random access to a cellular communications network comprises determining a number of resources needed for the wireless device to successfully decode an information block received from a radio access node. The method further comprises determining at least one of: a code rate and a transmit power used for transmission of the information block by the radio access node. The method further comprises determining an amount of resources to be used by the wireless device when transmitting a random access signal for a random access procedure based on the aforementioned information.