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

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 Ni=N/U, an effective number of the subcarriers is Nc=Ni/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 Xi of length Nc, where Xi=[0, Xi(1), Xi(2), . . . , Xi(Nc−1)]T, M is a number of digital or binary bits transmitted per QAM modulation symbol, Xi(q) represents the q-th symbol of the modulation signal Xi, and q=1, . . . , N−1;
• using a mapping module in the transmitter, mapping or placing the modulation signal Xi according to a preset conjugate symmetric format, resulting in a frequency-domain symbol {tilde over (X)}i of length NFFT=N×Q;
• using a frequency-domain to time-domain transformation module in the transmitter, generating a time-domain orthogonal frequency division multiplexing (OFDM) symbol xi 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 NFFT;
• using a phase modulation module in the transmitter, performing a phase modulation on the time-domain OFDM symbol xi of the user i to obtain a discrete time-domain constant envelope OFDM (CE-OFDM) signal si, where the signal si includes NFFT sampling points, a signal si[n] at an n-th sampling point is given by a formula si[n]=Aejϕi, A is a carrier signal amplitude, ϕi is a phase and ϕi=2πhCNxi[n], 2πh is a preset modulation index, CN is a normalization constant factor, and xi[n] is a signal at the n-th sampling point of the time-domain OFDM symbol xi;
• using a time-domain to frequency-domain transformation module in the transmitter, performing an NFFT-point FFT transform on si to generate the frequency-domain signal Si for user i;
• using a frequency-domain shifting module in the transmitter, shifting the signal Si by NSi subcarriers to obtain a signal S′i, where NSi is related to the subset of the subcarriers Ni and the user identifier i;
• using the frequency-domain to time-domain transformation module, performing an NFFT-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 NCP to the time-domain signal s′i, resulting in the baseband transmission signal s′cpi;
• 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 NFFT-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 Yi for each user;
• using an equalization offset module in the receiver, equalizing the signal Yi to obtain an equalized symbol Yi, and then inverse-shifting the equalized symbol Yi by NSi 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.