DC Sub-carrier Allocation in DFT-SOFDM Wireless Systems
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Solution Overview
Problem
Direct conversion transmitters and receivers in DFT-SOFDM systems introduce distortion on the DC sub-carrier, degrading receiver performance and worsening error vector magnitude (EVM) and cubic metric (CM)/peak to average power ratio (PAPR), which is not effectively addressed in existing wireless communication standards like 3GPP 25.814 v2.0.0 and IEEE 802.16.
Innovation Solution
The proposed solution involves allocating radio resources in wireless communication systems to exclude the DC sub-carrier from data transmission, using techniques such as time division multiplexing of pilot and data blocks, and frequency shifting to mitigate DC sub-carrier distortion, thereby preserving the low PAPR properties of IFDMA/DFT-SOFDM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the DC sub-carrier is used for DFT-SOFDM data transmission, then resource utilization is improved, but receiver performance and EVM degrade due to DC distortion
Solution Approach 1:
The patent extracts the DC sub-carrier from the set of data-bearing sub-carriers, dedicating it solely to pilot transmission. This separation removes the harmful DC distortion from the data transmission path while preserving the DC sub-carrier's utility for channel estimation, thereby resolving the contradiction between resource utilization and receiver performance.
Solution Approach 2:
The patent applies different functional qualities to different parts of the frequency spectrum: the DC sub-carrier is assigned exclusively to pilot transmission with high power to ensure accurate channel estimation, while other sub-carriers carry data. This local differentiation of function optimizes both pilot accuracy and data transmission quality.
2Productivity
If the DC sub-carrier is allocated for data transmission, then data rate is improved, but PAPR and CM worsen due to DC distortion
Solution Approach 1:
By extracting the DC sub-carrier from data transmission and assigning it solely to pilot signals, the patent eliminates the source of DC distortion that degrades PAPR and CM. This allows data transmission on remaining sub-carriers to maintain the low-PAPR advantage of DFT-SOFDM while achieving high data rates through efficient resource allocation.
3Productivity
If more sub-carriers are used for data transmission including DC, then resource efficiency is improved, but error vector magnitude increases due to DC distortion
Solution Approach 1:
The patent extracts the DC sub-carrier from the data transmission pool and dedicates it to pilot transmission. This resolves the contradiction by maintaining high resource efficiency through full utilization of available sub-carriers while eliminating DC distortion's harmful impact on EVM, thereby improving both resource efficiency and signal accuracy.
Data Source
AI summary
A method in a wireless communication terminal (103), including receiving a radio resource allocation comprising a plurality of sub-carriers that is a subset of available sub-carriers, wherein the available sub-carriers include a DC sub-carrier, wherein the DC sub-carrier and all but one edge-most sub-carrier of the plurality of sub-carriers are designated for transmission if the DC sub-carrier is between any two sub-carriers of the allocation, and all of the sub-carriers except the DC sub-carrier from the plurality of sub-carriers are designated for transmission if the DC sub-carrier is not between any two sub-carriers of the allocation.