Dynamic Reference Symbol Bandwidth Allocation in OFDM Base Stations
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Solution Overview
Problem
In LTE cellular systems, the transmission of reference symbols across the full downlink channel bandwidth results in significant overhead in terms of transmission power and power consumption, especially when data traffic is low, as all subcarriers are used for reference symbols even when not all are necessary for data transmission.
Innovation Solution
The method involves determining the level of data traffic and adjusting the number and bandwidth of subcarriers used for reference symbols, restricting them to a central portion of the channel bandwidth or reducing the total number of subcarriers used for transmission, thereby optimizing power usage by matching the transmission bandwidth to the data traffic rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference symbols are transmitted over the full downlink channel bandwidth, then channel estimation accuracy is improved, but transmission power consumption increases
Solution Approach 1:
The downlink channel bandwidth is segmented into multiple subcarriers, and reference symbols are transmitted only on a subset of these subcarriers rather than all subcarriers. This segmentation allows the system to maintain channel estimation accuracy on the used subcarriers while reducing overall transmission power consumption by excluding unused subcarriers from reference symbol transmission.
Solution Approach 2:
The system applies local quality by transmitting reference symbols with higher density on subcarriers that are actively used for data transmission, while reducing or eliminating reference symbol transmission on unused subcarriers. This localized approach ensures sufficient channel estimation accuracy where needed while minimizing power consumption where not required.
2Use of energy by moving object
If the number of subcarriers used for reference symbols is reduced, then power consumption is decreased, but channel estimation capability deteriorates
Solution Approach 1:
The system dynamically adjusts the number and distribution of subcarriers used for reference symbol transmission based on current data traffic conditions. When data traffic is low, fewer subcarriers are allocated to reference symbols, reducing power consumption. When data traffic increases, more subcarriers are allocated to maintain channel estimation capability. This dynamic adaptation resolves the contradiction between power consumption and estimation capability.
Solution Approach 2:
The system changes the parameter of reference symbol transmission by adjusting the frequency spread and bandwidth allocation of reference symbols based on data traffic levels. This parameter change allows the system to optimize the balance between power consumption and channel estimation capability according to actual network conditions.
3Productivity
If reference symbol bandwidth is decreased, then transmission efficiency is improved, but handover measurement accuracy deteriorates
Solution Approach 1:
The reference symbol transmission system is designed to serve multiple functions: it provides channel estimation for active data transmission and simultaneously enables handover measurements by other base stations. By strategically positioning reference symbols on central subcarriers, the system achieves both transmission efficiency and adequate handover measurement capability, as central subcarriers are most relevant for both data transmission and inter-cell measurement.
Data Source
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AI summary
To reduce the number of subcarriers used for the transmission of reference symbols by base stations in an OFDM based cellular telecommunications network, the level of data for transmission from the base station to at least one subscriber station is determined and, when traffic levels are low and/or where the mobile station is unable to make efficient use of the full bandwidth, reference symbol data is transmitted from the base station using a number of the subcarriers less than the total number of subcarriers available. Thus the reference symbol frequency spread - the bandwidth between the lowest frequency subcarrier and the highest frequency subcarrier being used to transmit reference symbols - is made dependent upon the determined level of data for transmission.