Variable-Spreading-Factor CDM-OFDM for PAPR Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing CDM-OFDM communication systems face challenges in expanding coverage area due to high Peak to Average Power Ratio (PAPR) characteristics and wide variations in communication characteristics, particularly in wide frequency band applications, leading to decreased throughput and significant characteristic degradation.
Innovation Solution
A transmission apparatus using a variable-gain amplifier and a variable-spreading-factor spreading section with rotation orthogonal codes, which adjusts transmission power and spreading factor to minimize distortion and interference, allowing for flexible communication by increasing the spreading factor as amplification increases and selecting sub-carriers with low interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If CDM-OFDM transmission is used to improve coverage area, then transmission power can be increased, but signal distortion occurs due to high PAPR characteristics
Solution Approach 1:
The patent applies dynamics by making the spreading factor variable rather than fixed. The spreading factor is dynamically adjusted based on the required transmission power and channel conditions, allowing the system to adapt between high spreading factors (for low power/interference) and low spreading factors (for high power/coverage). This resolves the contradiction by enabling high transmission power for coverage expansion while controlling PAPR through appropriate spreading factor selection to prevent signal distortion.
Solution Approach 2:
The patent changes the parameter of spreading factor to resolve the contradiction. By varying the spreading factor as a control parameter, the system can adjust the balance between coverage area and signal distortion. High spreading factors reduce PAPR for coverage extension, while low spreading factors maintain signal integrity for high power transmission, thus resolving the technical contradiction through parameter optimization.
2Reliability
If spreading factor is increased to reduce PAPR, then transmission power margin is improved, but throughput decreases due to wider frequency band usage
Solution Approach 1:
The system dynamically adjusts the spreading factor based on real-time channel conditions and power requirements. When transmission power margin is needed, the spreading factor is increased; when throughput is prioritized, the spreading factor is decreased. This dynamic adaptation allows the system to optimize between reliability and productivity according to actual operational needs.
Solution Approach 2:
The patent applies partial action by using variable spreading factors that can be less than the maximum possible. Instead of always using high spreading factors to maximize power margin, the system uses only the necessary spreading factor level required for the current transmission conditions, thereby optimizing the balance between power margin and throughput.
3Device complexity
If fixed spreading factor is used in CDM-OFDM, then system complexity is reduced, but adaptability to different transmission power requirements is poor
Solution Approach 1:
The patent transforms the fixed spreading factor into a dynamic parameter that can be adjusted according to transmission power requirements and channel conditions. This adds adaptability to the system while maintaining relative simplicity by using a single controllable parameter (spreading factor) rather than multiple complex subsystems, thus resolving the contradiction between complexity and adaptability.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A transmission apparatus comprising: a spreading section configured to spread transmission data by discrete Fourier transform to generate a first multi-carrier signal; a data selection section configured to select, based on control information, one of the first multi-carrier signal and a second multi-carrier signal that is not spread by the spreading section; and an RF section configured to transmit one of the first and second multi-carrier signals simultaneously from each of a plurality of frequency channels. An OFDM transmission apparatus comprising: a variable-spreading-factor spreading section configured to perform discrete Fourier transform on data signals to generate at least one spread signal; a sub-carrier allocation section configured to allocate the at least one spread signal to a plurality of sub-carriers; an inverse discrete Fourier transform section configured to perform inverse discrete Fourier transform on the at least one spread signal allocated; and a control section configured to control, according to the number of the at least one spread signal, a limit of a power for transmitting the data signals.