Uplink Power Control for LTE Random Access
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Solution Overview
Problem
In wireless communication systems, particularly in LTE (E-UTRAN), there is a challenge in transitioning from full path loss compensated preamble transmissions to fractional power control for uplink shared channels, as the eNB lacks initial power control information for PUSCH transmissions, leading to potential interference and detection issues due to unequal signal strengths from UEs with varying path losses.
Innovation Solution
A method involving a processor to initialize power control states for uplink control and shared channels, using an initial transmit power based on preamble power with full path loss compensation, and adjusting power control formulas to ensure accurate power control for subsequent uplink messages, including using specific formulas for PUSCH and PUCCH to account for open loop errors and power control commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full path loss compensation is used for preamble transmissions, then all UEs can be detected equally regardless of path loss, but the eNB lacks power control information for subsequent PUSCH transmissions
Solution Approach 1:
The patent applies preliminary action by having the UE include power control information in the random access preamble transmission itself. The UE calculates and transmits power control commands (PC commands) along with the preamble, so that the eNB receives this information before needing to configure power control for subsequent PUSCH transmissions. This eliminates the information loss problem while maintaining the reliability benefits of full path loss compensation for preamble detection.
2Measurement precision
If fractional power control is used for PUSCH transmissions, then power control precision is improved, but the eNB cannot accurately control initial power without path loss information
Solution Approach 1:
The patent implements feedback by having the UE transmit power control commands in the preamble, which then feed back to the eNB the necessary power control information. The eNB uses this feedback information to accurately configure fractional power control for subsequent PUSCH transmissions, achieving both precision and accuracy in power control.
3Ease of operation
If UEs with varying path losses transmit preambles at equal power, then detection is simplified, but signal strength equality cannot be maintained for all UEs
Solution Approach 1:
The patent applies local quality by allowing different power control strategies for different transmission types. For preambles, full path loss compensation is used to ensure equal signal strength at the eNB regardless of UE location. For subsequent PUSCH transmissions, fractional power control is applied with locally adjusted power levels based on individual UE path loss conditions, optimizing detection for each specific transmission scenario.
Data Source
AI summary
A first power control adjustment state g(i) and a second power control adjustment state f(i) are initialized for i=0 to each reflect an open loop power control error. An initial transmit power for a shared uplink channel is computed using full pathloss compensation. The computed initial transmit power depends on a preamble power of a first message sent on an access channel, and the initial transmit power is initialized with the second power control adjustment state f(0). A third message is sent from a transmitter on an uplink shared channel at the initial transmit power. In various implementations, the power for i=0 on the uplink control channel is also initialized similar to the initial transmit power for the third message and using full pathloss compensation, and after the third message (and retransmissions of it), subsequent messages sent on the uplink shared channel are sent at a power that is computed using fractional pathloss compensation.