Downlink OFDMA DFT-Precoding for Lower PAPR in 6G PA Output
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Solution Overview
Problem
The efficiency of power amplifiers (PAs) in super-high-frequency bands, such as terahertz bands considered in 6G communication systems, is degraded due to high peak-to-average power ratios (PAPRs) of signals, leading to increased power backoff and decreased output efficiency.
Innovation Solution
A method involving DFT-precoding is applied in downlink OFDMA to adjust the number and size of DFT-precoding chunks, allowing the base station to determine the appropriate PA power backoff and output power based on the communication environment, thereby optimizing PA efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If single carrier modulation scheme is used, then implementation is simple, but spectral efficiency is limited
Solution Approach 1:
The invention segments the modulation process into two distinct stages: first applying DFT precoding to convert time-domain signals to frequency-domain components, then applying subcarrier mapping and OFDM modulation. This segmentation allows the system to achieve SC-FDA's spectral efficiency while maintaining implementation simplicity by reusing existing OFDM components.
Solution Approach 2:
The invention introduces DFT precoding as an intermediary step between the input signal and the OFDM modulation process. This intermediary transformation converts the single carrier signal into frequency-domain components that can be efficiently transmitted using OFDM's parallel subcarrier structure, thereby improving spectral efficiency without complicating the overall system architecture.
2Reliability
If DFT precoding is applied to achieve frequency domain equalization, then frequency selective fading is compensated, but PAPR increases
Solution Approach 1:
The invention applies local quality by performing DFT precoding only on the data symbols that require frequency domain equalization, while keeping the pilot symbols and other control signals in their original form. This selective application provides frequency selective fading compensation where needed without unnecessarily increasing PAPR across the entire signal.
Solution Approach 2:
The invention changes the modulation parameter by using a cyclic prefix length that is optimized for the specific channel conditions and DFT precoding configuration. By adjusting the cyclic prefix length parameter, the system can mitigate PAPR increase while maintaining the frequency domain equalization benefits.
3Reliability
If SC-FDA with DFT precoding is used, then frequency diversity gain is achieved, but system complexity increases
Solution Approach 1:
The invention achieves universality by designing the DFT precoding structure to be compatible with existing OFDM systems. The same DFT matrix and subcarrier mapping algorithms used in OFDM can be reused for SC-FDA, allowing the system to achieve frequency diversity gain without requiring completely new hardware or processing architectures.
Solution Approach 2:
The invention applies preliminary action by pre-calculating and storing the DFT transformation matrices before actual data transmission. This pre-computation allows the system to achieve frequency diversity gain through DFT precoding without increasing real-time processing complexity, as the heavy computational burden is shifted to offline matrix generation.
Data Source
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AI summary
The disclosure relates to a 5G or 6G communication system for supporting a higher data transfer rate beyond a 4G communication system, such as LTE. A method by a base station in a communication system according to an embodiment may include: determining the number of DFT-precoding chunks on which DFT precoding is performed; determining a power backoff value of a power amplifier (PA) of the base station; transmitting information indicating the number of DFT-precoding chunks to a terminal; transmitting downlink control information (DCI) including a resource allocation field, configured based on the number of DFT-precoding chunks, to the terminal; and transmitting data to the terminal according to the resource allocation field included in the DCI.