Uplink Scheduling for Random Access Coverage and Data Rates
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Solution Overview
Problem
In mobile radio communications, there is a trade-off between uplink coverage and peak transmission rates, with high rise over thermal (RoT) values limiting coverage and causing difficulties in random access, while lowering the RACH preamble threshold leads to erroneous detections and power issues.
Innovation Solution
Implementing a time division multiplexing (TDM)-based uplink scheduling scheme that allocates radio resources differently based on uplink load targets, with two repeating time periods for random access and active connections, allowing greater resource use during one period and restricted resource use during another, to enhance coverage and data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high rise over thermal (RoT) values are used to support high uplink data rates, then peak transmission rates are improved, but uplink coverage is worsened and random access becomes difficult
Solution Approach 1:
The uplink transmission time is segmented into multiple subframes, with specific subframes designated for high-rate transmission and others for coverage-critical transmission. This temporal segmentation allows the system to achieve high data rates in some subframes while maintaining coverage in others, resolving the contradiction between peak power and coverage reliability.
Solution Approach 2:
The system dynamically adjusts the RoT target value based on the current uplink load and transmission requirements. When the uplink is lightly loaded, higher RoT targets enable peak data rates; when load is high, lower RoT targets ensure coverage and random access reliability. This dynamic adaptation resolves the static trade-off between power and coverage.
2Reliability
If the RACH preamble detection threshold is lowered to improve coverage, then random access coverage is improved, but erroneous preamble detections increase
Solution Approach 1:
The system performs preliminary power control adjustments before random access transmission. By ensuring that preambles are transmitted at sufficiently high power levels in advance, the system maintains a high detection threshold that filters out thermal noise while still allowing coverage extension. This preliminary power management resolves the contradiction between coverage and detection precision.
3Reliability
If mobile terminals gradually increase transmission power over RACH to ensure detection, then access reliability is improved, but interference in the cell increases and Ec/Io decreases
Solution Approach 1:
The system implements periodic random access opportunities rather than continuous power ramping. Terminals transmit preambles at discrete, scheduled intervals with controlled power levels, rather than continuously increasing power. This periodic transmission pattern reduces cumulative interference while maintaining access reliability through repeated attempts at appropriate power levels.
Data Source
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AI summary
Random access coverage is assured while at the same time supporting high uplink data rates in a same service area served by a base station. A set of radio resources are shared by multiple mobile terminals for transmitting uplink to the base station including requests for access to service from the base station and transmissions for active connections with the base station. A first repeating time period and a second different repeating time period are defined. Uplink transmission grants are scheduled for active connections that permit use of a greater amount of the radio resources during the first repeating time period. Uplink transmission grants are also scheduled for active connections that permit use of a smaller amount of those resources during the second repeating time period. At least some random access requests to the base station are controlled to occur only during the second repeating time period.