Radio Channel Quality Indicator via Decorrelated Pilot Signals
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Solution Overview
Problem
Current cellular networks face challenges in accurately determining the Channel Quality Indicator (CQI) due to intercellular interference, leading to sub-optimal bit rate selection and increased transmission delays or inefficiencies, particularly in sporadic and real-time services like voice transmission and network video games.
Innovation Solution
The method involves transmitting a reference pilot signal with a total load pilot and an effective load pilot signal on orthogonal subcarriers, allowing for the measurement of channel quality under full and effective load conditions, enabling a more precise CQI determination by calculating the difference between these indicators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single CQI indicator is used for link adaptation, then the system is simple to operate, but the CQI may be inaccurate due to sporadic interference from neighboring cells
Solution Approach 1:
The pilot signal is segmented into two distinct parts: a first part (total load pilot) that experiences interference from all neighboring cells regardless of their data transmission state, and a second part (effective load pilot) that experiences interference only when neighboring cells are actively transmitting data. This segmentation allows separate measurement of total interference and effective interference, improving CQI accuracy without requiring complex additional signaling.
Solution Approach 2:
The first part of the pilot signal is transmitted in advance during a period when data transmission has not yet started, allowing the mobile terminal to measure the total interference level before data transmission begins. This preliminary measurement of total interference (including both active and inactive neighboring cells) provides a baseline that can be combined with the effective load measurement to derive accurate CQI.
2Productivity
If the CQI indicator is overestimated, then the data rate can be increased, but transmission delays increase due to retransmissions
Solution Approach 1:
The system uses feedback from two separate measurements (total load CQI and effective load CQI) to determine the final CQI indicator. By comparing the difference between these two measurements, the base station can assess the level of sporadic interference and adjust the data rate selection accordingly, ensuring both high productivity and transmission reliability.
Solution Approach 2:
The invention changes the parameter measurement approach by introducing a time-based differentiation in pilot signal transmission. The first pilot part is measured during a period with no data transmission (higher interference), while the second part is measured during active data transmission (lower interference). This parameter change allows the system to capture interference variations and select appropriate data rates that maintain reliability while maximizing throughput.
3Reliability
If the CQI indicator is underestimated, then transmission reliability is maintained, but system efficiency decreases due to sub-optimal data rate selection
Solution Approach 1:
The system dynamically adjusts the CQI indicator based on the measured difference between total load and effective load conditions. Rather than using a fixed conservative estimate, the CQI is adapted in real-time according to the actual interference environment, allowing the system to maintain reliability while optimizing data rate selection for each transmission opportunity.
Data Source
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AI summary
The invention relates to a method for establishing a quality indicator (CQI) of a radio transmission channel in a first cell of a cellular network using a plurality of orthogonal frequency-division multiplexed subcarriers for transmitting data, said method including: a first transmitter device (NB1) located in the first cell transmitting (11) a reference control signal (SP1) including a total-load control signal (SPCT) modulating one or more of said orthogonal subcarriers, during one or more first symbol times dedicated to the transmission of symbols other than data symbols, and a useful-load control signal (SPCE) modulating one or more orthogonal subcarriers during at least one second symbol time dedicated to the transmission of data symbols; for every cell adjacent to the first cell in the cellular network, a transmitting device (NB2) located in said adjacent cell transmitting (13) an interfering control signal (SP2) modulating, during the first symbol time(s) during which the total-load control signal (SPCT) modulates one or more subcarriers, said subcarrier modulated by the total-load control signal (SPCT); a receiving device (M) located in the first cell measuring (20) a quality indicator of the channel under the total load (CQICT) using the total-load control signal (SPCT) and a quality indicator of the channel under the useful load (CQICE) using the useful-load control signal (SPCE); and determining (30) the quality indicator (CQI) of the radio transmission channel according to the quality indicator of the channel under the useful load (CQICE) and the quality indicator of the channel under the total load (CQICT).