Multiple-access constant envelope orthogonal frequency division multiplexing method and system

Patent metadata

Field	Value
Publication number	US-12362969-B2
Application number	US-202318517215-A
Country	US
Kind code	B2
Filing date	Nov 22, 2023
Priority date	Jul 25, 2022
Publication date	Jul 15, 2025
Grant date	Jul 15, 2025

Abstract

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.

First claim

What is claimed is:

1. A method of constant envelope orthogonal frequency division multiple access (CE-OFDMA) based on constant envelope orthogonal frequency division multiplexing for multi-user access, where a number of subcarriers in the method is N, a total number of users is U, and an oversampling factor is Q, wherein each of the users occupies a subset of the subcarriers N i =N/U, an effective number of the subcarriers is N c =N i /2, and a user identifier i is i=1, 2, . . . , U, comprising:
using a transmitter, generating and transmitting a baseband transmission signal by:
using a digital modulation module in the transmitter, mapping information bits of a user i to M-ary QAM modulation symbols, resulting in a modulation signal X i of length N c , where X i =[0, X i (1), X i (2), . . . , X i (N c −1)] T , M is a number of digital or binary bits transmitted per QAM modulation symbol, X i (q) represents the q-th symbol of the modulation signal X i , and q=1, . . . , N−1;
using a mapping module in the transmitter, mapping or placing the modulation signal X i according to a preset conjugate symmetric format, resulting in a frequency-domain symbol {tilde over (X)} i of length N FFT =N×Q;
using a frequency-domain to time-domain transformation module in the transmitter, generating a time-domain orthogonal frequency division multiplexing (OFDM) symbol x i for a user i among the users by performing an inverse fast Fourier transform (IFFT) on the frequency-domain symbol {tilde over (X)} i , wherein the IFFT transform includes a number of points N FFT ;
using a phase modulation module in the transmitter, performing a phase modulation on the time-domain OFDM symbol x i of the user i to obtain a discrete time-domain constant envelope OFDM (CE-OFDM) signal s i , where the signal s i includes N FFT sampling points, a signal s i [n] at an n-th sampling point is given by a formula s i [n]=Ae jϕ i , A is a carrier signal amplitude, ϕ i is a phase and ϕ i =2πhC N x i [n], 2πh is a preset modulation index, C N is a normalization constant factor, and x i [n] is a signal at the n-th sampling point of the time-domain OFDM symbol x i ;
using a time-domain to frequency-domain transformation module in the transmitter, performing an N FFT -point FFT transform on s i to generate the frequency-domain signal S i for user i;
using a frequency-domain shifting module in the transmitter, shifting the signal S i by NS i subcarriers to obtain a signal S′ i , where NS i is related to the subset of the subcarriers N i and the user identifier i;
using the frequency-domain to time-domain transformation module, performing an N FFT -point IFFT transform on the signal S′ i to obtain a time-domain signal s′ i ; and
using a cyclic prefix module in the transmitter, adding a cyclic prefix of length N CP to the time-domain signal s′ i , resulting in the baseband transmission signal s′ cp i ;

using a receiver, receiving a signal through or from a channel and processing the signal to obtain detection results of or for each user, including:
using a time-domain to frequency-domain transformation module in the receiver, removing the cyclic prefix from the signal, then performing an N FFT -point FFT transform to obtain a frequency-domain received signal Y;
using a user separation module in the receiver, separating the frequency-domain received signal Y to obtain a signal Y i for each user;
using an equalization offset module in the receiver, equalizing the signal Y i to obtain an equalized symbol Y i , and then inverse-shifting the equalized symbol Y i by NS i subcarriers to obtain a symbol {tilde over (Y)} i ;
using a phase adjustment module in the receiver, performing a phase demodulation on the symbol {tilde over (Y)} i to produce a phase-demodulated symbol, and using a time-domain to frequency-domain transformation module in the receiver, processing the phase-demodulated symbol by an FFT transform to obtain the data {circumflex over (X)} i and transform the data {circumflex over (X)} i to the time domain, and
using a demapping module in the receiver, demapping the data {circumflex over (X)} i to obtain effective data {tilde over (X)} i for user i, and using a decision module in the receiver, making a decision on the effective data {tilde over (X)} i to obtain one of the detection results {circumflex over (X)} i for user i.

2. The method as claimed in claim 1 , wherein the frequency-domain symbol {tilde over (X)} i is defined as:
{tilde over (X)} i =[0, X i (1), X i (2), . . . , X i ( N c −1),0 1×(N/2-N c ) ,0 1×N zp 0,0 1×(N/2-N c ) ,X i *( N c −1), . . . , X i *(2), X i *(1)] T

where N zp =N(Q−1), an asterisk (*) denotes a complex conjugate, and 0 1×N represents a zero vector of size 1×N.

3. The method as claimed in claim 1 , wherein the normalization constant factor C N =√{square root over (N FFT 2 /[(N−2)σ I 2 ])}, where σ I 2 =2(M−1)/3, and M represents an order of QAM modulation.

4. The method as claimed in claim 1 , wherein the signal S′ i is defined as:

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Assignees

• Univ Electronic Science And Tech Of China
• Univ Electronic Sci & Tech China

Inventors

• Dan Lilin
• Hu Yuanjie
• Ji Haimeng

Classifications

• H04L5/0007 Primary

  the frequencies being orthogonal, e.g. OFDM(A) or DMT · CPC title

• H04L2025/03414

  Multicarrier · CPC title

• H04L25/03159

  operating in the frequency domain (H04L25/03165, H04L25/03178 take precedence) · CPC title

• Y02D30/70

  in wireless communication networks · CPC title

• H04L27/22

  Demodulator circuits; Receiver circuits · CPC title