Multiple-Access CE-OFDM Carrier Rotation for Inter-User Interference
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Solution Overview
Problem
The high peak-to-average power ratio (PAPR) of traditional OFDM waveforms reduces power amplifier efficiency and causes inter-user interference due to subcarrier overlap in OFDMA systems, affecting wireless communication systems.
Innovation Solution
A multiple access method for CE-OFDMA that rotates user carriers by different phases to reduce inter-user interference through phase modulation, employing a transmitter and receiver process involving digital modulation, conjugate symmetric mapping, phase modulation, and frequency-domain shifting to maintain orthogonality among subcarriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional OFDM waveforms are used, then high data transmission capability is achieved, but peak-to-average power ratio increases reducing power amplifier efficiency
Solution Approach 1:
The patent applies parameter changes by transforming the OFDM signal from complex envelope representation to constant envelope representation through phase modulation. The key parameter change is converting the signal model from x(t) = Σa_k·g(t−kT) to s(t) = A·exp(jφ(t)) where A is constant amplitude. This parameter transformation maintains data transmission capability while reducing PAPR to improve power amplifier efficiency.
2Loss of energy
If phase modulation is applied to reduce PAPR, then power amplifier efficiency improves, but orthogonality between subcarriers is destroyed causing inter-user interference
Solution Approach 1:
The patent applies segmentation by dividing the frequency spectrum into orthogonal subcarriers and assigning different subsets of subcarriers to different users. Each user's signal is segmented in the frequency domain, and through careful design of subcarrier allocation and phase modulation, inter-user interference is reduced while maintaining power amplifier efficiency.
Solution Approach 2:
The patent employs feedback mechanisms in the receiver to compensate for phase distortion and maintain orthogonality. The receiver uses channel state information and phase tracking to correct phase errors introduced by non-linear power amplifiers, thereby reducing inter-user interference while allowing the transmitter to operate in constant envelope mode.
3Productivity
If multiple users access the system simultaneously, then system capacity increases, but data aliasing and inter-user interference increase
Solution Approach 1:
The patent resolves multi-user interference by transitioning from time-domain separation to frequency-domain separation. Users are separated in the frequency dimension through orthogonal subcarrier allocation, while phase modulation operates in the time domain. This dimensional separation allows multiple users to access simultaneously without data aliasing, increasing system capacity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Reduces inter-user interference and improves system performance by minimizing data aliasing and interference between users, enhancing power amplifier efficiency and communication efficiency.
Implementation Method 1
a4. A phase modulation module in the transmitter performs a phase modulation on the time-domain orthogonal frequency division multiplexing (OFDM) symbol xi of user i to obtain a discrete time-domain constant envelope OFDM (CE-OFDM) signal si
Data Source
AI summary
A multiple-access constant envelope orthogonal frequency division multiplexing (OFDM) method and wireless communication system are disclosed. The method and system include a transmitter that sequentially processes the information and/or information bits of each user by digital modulation, symmetric mapping, frequency-domain to time-domain transformation, phase modulation, time-domain to frequency-domain transformation, frequency domain offsetting, frequency-domain to time-domain transformation, and cyclic prefix addition to obtain a baseband transmission signal, which is then sent to one or more receivers through a channel, and a receiver that sequentially processes the received signal by time-domain to frequency-domain transformation, user signal separation, equalization offsetting, frequency-domain to time-domain transformation, phase demodulation, another time-domain to frequency-domain transformation, demapping, and decision-making to obtain detection results for the corresponding user. The present method and system reduce data overlap between users and decrease inter-user interference by applying different phase rotations and/or different offsets to different users, thereby enhancing system performance.