MULTIPLE-ACCESS CONSTANT ENVELOPE ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING METHOD AND SYSTEM

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.

Claims

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.sup.i=N/U, an effective number of the subcarriers is N.sub.c=N.sup.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.sup.i of length N.sub.c, where X.sup.i=[0, X.sup.i(1), X.sup.i(2), . . . , X.sup.i(N.sub.c?1)].sup.T, M is a number of digital or binary bits transmitted per QAM modulation symbol, X.sup.i(q) represents the q-th symbol of the modulation signal X.sup.i, and q=1, . . . , N?1; using a mapping module in the transmitter, mapping or placing the modulation signal X.sup.i according to a preset conjugate symmetric format, resulting in a frequency-domain symbol {tilde over (X)}.sup.i of length N.sub.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.sup.i for a user i among the users by performing an inverse fast Fourier transform (IFFT) on the frequency-domain symbol {tilde over (X)}.sup.i, wherein the IFFT transform includes a number of points N.sub.FFT; using a phase modulation module in the transmitter, performing a phase modulation on the time-domain OFDM symbol x.sup.i of the user i to obtain a discrete time-domain constant envelope OFDM (CE-OFDM) signal s.sup.i, where the signal s.sup.i includes N.sub.FFT sampling points, a signal s.sup.i[n] at an n-th sampling point is given by a formula s.sup.i[n]=Ae.sup.j?.sup.i, A is a carrier signal amplitude, ?.sup.i is a phase and ?.sup.i=2?hC.sub.Nx.sup.i[n], 2?h is a preset modulation index, C.sub.N is a normalization constant factor, and x.sup.i[n] is a signal at the n-th sampling point of the time-domain OFDM symbol x.sup.i; using a time-domain to frequency-domain transformation module in the transmitter, performing an N.sub.FFT-point FFT transform on s.sup.i to generate the frequency-domain signal S.sup.i for user i; using a frequency-domain shifting module in the transmitter, shifting the signal S.sup.i by NS.sup.i subcarriers to obtain a signal S.sup.i, where NS.sup.i is related to the subset of the subcarriers N.sup.i and the user identifier i; using the frequency-domain to time-domain transformation module, performing an N.sub.FFT-point IFFT transform on the signal S.sup.i to obtain a time-domain signal s.sup.i; and using a cyclic prefix module in the transmitter, adding a cyclic prefix of length N.sub.CP to the time-domain signal s.sup.i, resulting in the baseband transmission signal s.sub.cp.sup.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.sub.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.sup.i for each user; using an equalization offset module in the receiver, equalizing the signal Y.sup.i to obtain an equalized symbol Y.sup.i, and then inverse-shifting the equalized symbol Y.sup.i by NS.sup.i subcarriers to obtain a symbol {tilde over (Y)}.sup.i; using a phase adjustment module in the receiver, performing a phase demodulation on the symbol {tilde over (Y)}.sup.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)}.sup.i and transform the data {circumflex over (X)}.sup.i to the time domain, and using a demapping module in the receiver, demapping the data {circumflex over (X)}.sup.i to obtain effective data {tilde over (X)}.sup.i for user i, and using a decision module in the receiver, making a decision on the effective data {tilde over (X)}.sup.i to obtain one of the detection results {circumflex over (X)}.sup.i for user i.

2. The method as claimed in claim 1, wherein the frequency-domain symbol {tilde over (X)}.sup.i is defined as:
{tilde over (X)}.sup.i=[0,X.sup.i(1),X.sup.i(2), . . . ,X.sup.i(N.sub.c?1),0.sub.1?(N/2-N.sub.c.sub.),0.sub.1?N.sub.zp0,0.sub.1?(N/2-N.sub.c.sub.),X.sup.i*(N.sub.c?1), . . . ,X.sup.i*(2),X.sup.i*(1)].sup.T where N.sub.zp=N(Q?1), an asterisk (*) denotes a complex conjugate, and 0.sub.1?N represents a zero vector of size 1?N.

3. The method as claimed in claim 1, wherein the normalization constant factor C.sub.N=?{square root over (N.sub.FFT.sup.2/[(N?2)?.sub.I.sup.2])}, where ?.sub.I.sup.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.sup.i is defined as: $S^i=\{\begin{array}{cc}{\left[S^i\left(1\right),.Math.,S^i\left(N_{FFT}\right)\right]}^T,& i=1\\ \begin{array}{c}[S^i\left(N_{FFT}-N{S}^i+1\right),.Math.,S^i\left(N_{FFT}\right),\\ {S^i\left(1\right),.Math.,S^i\left(N_{FFT}-N{S}^i\right)]}^T\end{array},& 2?i?U\end{array}$ where S.sup.i(j) represents the signal S.sup.i at given j-th sampling point of signal S.sup.i.

5. The method as claimed in claim 1, wherein the baseband transmission signal sc is defined as:
s.sub.cp.sup.i=[s.sup.i[N.sub.FFT?N.sub.CP+1], . . . ,s.sup.i[N.sub.FFT?1],s.sup.i[0],s.sup.i[1], . . . ,s.sup.i[N.sub.FFT?1]].sup.T where s.sup.i[?] represents the baseband transmission signal at a given sampling point of the baseband transmission signal s.sub.cp.sup.i.

6. The method as claimed in claim 1, wherein the signal Y.sup.i for user i is defined as: $Y^i=\{\begin{array}{c}\begin{array}{c}[Y\left(1\right),.Math.,Y\left(N_c\right),0_{1?\left(N_{FFT}-N^i\right)},\\ {Y\left(N_{FFT}-N_c+1\right),.Math.,Y\left(N_{FFT}\right)]}^T\end{array},i=1\\ \begin{array}{c}[0_{1?N_c},0_{1?K_i},Y\left(K_i+N_c+1\right),.Math.,\\ {Y\left(K_{i+1}+N_c\right),0_{1?\left(N_{FFT}-N_c-K_{i+1}\right)}]}^T\end{array},2?i?U\end{array}$ where 0.sub.1?N represents a zero vector of size 1?N, Y(?) represents the frequency-domain received signal Y at a given sampling point of the frequency-domain received signal Y, and K.sub.i=(i?2)N.sup.i.

7. The method as claimed in claim 1, wherein the symbol {tilde over (Y)}.sup.i is represented as: ${\tilde{Y}}^i=\{\begin{array}{cc}{\left[{\stackrel{?}{Y}}^i\left(1\right),.Math.,{\stackrel{?}{Y}}^i\left(N_{FFT}\right)\right]}^T,& i=1\\ \left[{\stackrel{?}{Y}}^i\left(N{S}^i+1\right),.Math.,{\stackrel{?}{Y}}^i\left(N_{FFT}\right),{\stackrel{?}{Y}}^i\left(1\right),.Math.,{\stackrel{?}{Y}}^i\left(N{S}^i\right)\right],& 2?i?U\end{array}$ where Y.sup.i(?) represents the symbol at a given sampling point of the equalized symbol Y.sup.i for user i.

8. The method as claimed in claim 1, wherein NS.sup.i is a result of a mathematical operation performed on the subset of the subcarriers N.sup.i and the user identifier i.

9. The method as claimed in claim 8, wherein NS.sup.i=N.sup.i(i?1).

10. A constant envelope orthogonal frequency division multiple access (CE-OFDMA) communication system having multi-user access, where a number of subcarriers in the system 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.sup.i=N/U, an effective number of the subcarriers is N.sub.c=N.sup.i/2, and a user identifier i is i=1, 2, . . . , U, comprising: a transmitter configured to generate and transmit a baseband transmission signal, the transmitter comprising: a digital modulation module configured to map information bits of a user i to M-ary QAM modulation symbols, resulting in a modulation signal X.sup.i of length N.sub.c, where X.sup.i=[0, X.sup.i(1), X.sup.i(2), . . . , X.sup.i(N.sub.c?1)].sup.T, M is a number of digital or binary bits transmitted per QAM modulation symbol, X.sup.i(q) represents the q-th symbol of the modulation signal X.sup.i, and q=1, . . . , N.sub.c?1; a mapping module configured to map or place the modulation signal X.sup.i according to a preset conjugate symmetric format, resulting in a frequency-domain symbol {tilde over (X)}.sup.i of length N.sub.FFT=N?Q. a frequency-domain to time-domain transformation module configured to generate a time-domain orthogonal frequency division multiplexing (OFDM) symbol x.sup.i for a user i among the users by performing an inverse fast Fourier transform (IFFT) on the frequency-domain symbol {tilde over (X)}.sup.i, wherein the IFFT transform includes a number of points N.sub.FFT; a phase modulation module configured to perform a phase modulation on the time-domain OFDM symbol x.sup.i of the user i to obtain a discrete time-domain constant envelope OFDM (CE-OFDM) signal s.sup.i, where the signal s.sup.i includes N.sub.FFT sampling points, a signal s.sup.i[n] at an n-th sampling point is given by a formula s.sup.i[n]=Ae.sup.j?.sup.i, A is a carrier signal amplitude, ?.sup.t is a phase and ?.sup.i=2?hC.sub.Nx.sup.i[n], 2?h is a preset modulation index, C.sub.N is a normalization constant factor, and x.sup.i[n] is a signal at the n-th sampling point of the time-domain OFDM symbol x.sup.i; a time-domain to frequency-domain transformation module configured to perform an N.sub.FFT-point FFT transform on s.sup.i to generate the frequency-domain signal S.sup.i for user I; a frequency-domain shifting module configured to shift the signal S.sup.i by NS.sup.i subcarriers to obtain a signal S.sup.i, where NS.sup.i is related to the subset of the subcarriers N.sup.i and the user identifier i, wherein the frequency-domain to time-domain transformation module is further configured to perform an N.sub.FFT-point IFFT transform on the signal S.sup.i to obtain a time-domain signal s.sup.i; and a cyclic prefix module configured to add a cyclic prefix of length N.sub.CP to the time-domain signal s.sup.i, resulting in the baseband transmission signal s.sub.cp.sup.i; and a receiver configured to receive a signal through or from a channel and process the signal to obtain detection results of or for each user, including: a time-domain to frequency-domain transformation module configured to remove the cyclic prefix from the signal, then perform an N.sub.FFT-point FFT transform to obtain a frequency-domain received signal Y; a user separation module configured to separate the frequency-domain received signal Y to obtain a signal Y.sup.i for each user; an equalization offset module configured to equalize the signal Y.sup.i to obtain an equalized symbol Y.sup.i, and then inverse-shift the equalized symbol Y.sup.i by NS.sup.i subcarriers to obtain a symbol {tilde over (Y)}.sup.i; a phase adjustment module configured to perform a phase demodulation on the symbol {tilde over (Y)}.sup.i to produce a phase-demodulated symbol; a time-domain to frequency-domain transformation module configured to process the phase-demodulated symbol by an FFT transform to obtain the data {circumflex over (X)}.sup.i and transform the data {circumflex over (X)}.sup.i to the time domain; a demapping module configured to demap the data {circumflex over (X)}.sup.i to obtain effective data {tilde over (X)}.sup.i for user i; and a decision module configured to make a decision on the effective data {tilde over (X)}.sup.i to obtain one of the detection results {circumflex over (X)}.sup.i for user i.

11. The system as claimed in claim 10, wherein the frequency-domain symbol {tilde over (X)}.sup.i is defined as:
{tilde over (X)}.sub.i=[0,X.sup.i(1),X.sup.i(2), . . . ,X.sup.i(N.sub.c?1),0.sub.1?(N/2-N.sub.c.sub.),0.sub.1?N.sub.zp,0,0.sub.1?(N/2-N.sub.c.sub.),X.sup.i*(N.sub.c?1), . . . ,X.sup.i*(2),X.sup.i*(1)].sup.T where N.sub.zp=N(Q?1), an asterisk (*) denotes a complex conjugate, and 0.sub.1?N represents a zero vector of size 1?N.

12. The system as claimed in claim 10, wherein the normalization constant factor C.sub.N=?{square root over (N.sub.FFT.sup.2/[(N?2)?.sub.I.sup.2])}, where ?.sub.I.sup.2=2(M?1)/3, and M represents an order of QAM modulation.

13. The system as claimed in claim 10, wherein the signal S.sup.i is defined as: $S^i=\{\begin{array}{cc}{\left[S^i\left(1\right),.Math.,S^i\left(N_{FFT}\right)\right]}^T,& i=1\\ \begin{array}{c}[S^i\left(N_{FFT}-N{S}^i+1\right),.Math.,S^i\left(N_{FFT}\right),\\ {S^i\left(1\right),.Math.,S^i\left(N_{FFT}-N{S}^i\right)]}^T\end{array},& 2?i?U\end{array}$ where S.sup.i(j) represents the signal S.sup.i at given j-th sampling point of signal S.sup.i.

14. The system as claimed in claim 10, wherein the baseband transmission signal s.sub.cp.sup.i is defined as:
s.sub.cp.sup.i=[s.sup.i[N.sub.FFT?N.sub.CP+1], . . . ,s.sup.i[N.sub.FFT?1],s.sup.i[0],s.sup.i[1], . . . ,s.sup.i[N.sub.FFT?1]].sup.T where s.sup.i[?] represents the baseband transmission signal at a given sampling point of the baseband transmission signal s.sub.cp.sup.i.

15. The system as claimed in claim 10, wherein the signal Y.sup.i for user i is defined as: $Y^i=\{\begin{array}{c}\begin{array}{c}[Y\left(1\right),.Math.,Y\left(N_c\right),0_{1?\left(N_{FFT}-N^i\right)},\\ {Y\left(N_{FFT}-N_c+1\right),.Math.,Y\left(N_{FFT}\right)]}^T\end{array},i=1\\ \begin{array}{c}[0_{1?N_c},0_{1?K_i},Y\left(K_i+N_c+1\right),.Math.,\\ {Y\left(K_{i+1}+N_c\right),0_{1?\left(N_{FFT}-N_c-K_{i+1}\right)}]}^T\end{array},2?i?U\end{array}$ where 0.sub.1?N represents a zero vector of size 1?N, Y(?) represents the frequency-domain received signal Y at a given sampling point of the frequency-domain received signal Y, and K.sub.i=(i?2)N.sup.i.

16. The system as claimed in claim 10, wherein the symbol {tilde over (Y)}.sup.i is represented as: ${\tilde{Y}}^i=\{\begin{array}{cc}{\left[{\stackrel{?}{Y}}^i\left(1\right),.Math.,{\stackrel{?}{Y}}^i\left(N_{FFT}\right)\right]}^T,& i=1\\ \left[{\stackrel{?}{Y}}^i\left(N{S}^i+1\right),.Math.,{\stackrel{?}{Y}}^i\left(N_{FFT}\right),{\stackrel{?}{Y}}^i\left(1\right),.Math.,{\stackrel{?}{Y}}^i\left(N{S}^i\right)\right],& 2?i?U\end{array}$ where Y.sup.i(?) represents the symbol at a given sampling point of the equalized symbol Y.sup.i for user i.

17. The system as claimed in claim 10, comprising a mathematical operator configured to perform a mathematical operation on the subset of the subcarriers N.sup.i and the user identifier i to obtain NS.sup.i.

18. The system as claimed in claim 17, wherein the mathematical operator comprises (i) an adder or subtractor configured to reduce the user identifier i by 1, and (ii) a multiplier configured to multiply the subcarriers N.sup.i by the user identifier i minus 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0031] FIG. 1 shows a block diagram of an exemplary system and/or the functionality therein in accordance with the present invention.

DETAILED DESCRIPTION

[0032] In order to clarify the objectives, technical solutions, and advantages of the present invention, a detailed description of embodiments of the present invention will be given in conjunction with the accompanying drawing.

Example 1

[0033] In a first example, an uplink CE-OFDM system has a total number of subcarriers N=32, a total number of users U=2, and an oversampling factor Q=2, each user occupying N.sub.i=N/U=16 subcarriers and having N.sub.c=N.sub.i/2=8 effective subcarriers, where i=1, 2, and QPSK modulation is employed. As shown in FIG. 1, an exemplary embodiment of the present invention provides a method for multiple access in a constant envelope orthogonal frequency division multiplexing system, comprising the following. In the transmitter, the information bits of each user are, in sequence, digitally modulated, symmetrically mapped, transformed from the frequency domain to the time domain, phase-modulated, transformed from the time domain back to the frequency domain, offset in the frequency domain, and transformed from the frequency domain back to the time domain. A cyclic prefix is added to the processed information in the time domain to obtain the baseband transmission signal, which is then sent to the receiver via the channel. In the receiver, the cyclic prefix is removed from the signal received from the channel, and the resulting signal is sequentially processed by time-domain to frequency-domain transformation, user separation (e.g., separating the different signals for each user in the CE-OFDM system), equalization offset, frequency-domain to time-domain transformation, phase demodulation, time-domain to frequency-domain transformation, demapping, and decision-making to obtain the detection results (e.g., the information or information bits processed and transmitted by the transmitter) for the corresponding user.

[0034] To illustrate with User 2, the method of the embodiment of the present invention specifically includes the following:

[0035] In the transmitter:

[0036] Step 1, Digital Modulation: The transmitted bit sequence of User 2 is mapped to QPSK symbols, resulting in the modulation signal X.sup.(2)?:

X.sup.(2)=[0,0.7+0.7j,0.7+0.7j,?0.7?0.7j,0.7+0.7j,0.7?0.7j,?0.7?0.7j,?0.7?0.7j].sup.T

X.sup.i=[0,X.sup.i(1),X.sup.i(2), . . . ,X.sup.i(N.sub.c?1)].sup.T

[0037] Step 2, Symmetric Mapping: X.sup.(2) is placed in a conjugate symmetric format as follows:

{tilde over (X)}.sup.(2)=[0,0.7+0.7j, . . . ,?0.7?0.7j,0.sub.1?49,?0.7+0.7j, . . . ,0.7?0.7j].sup.T

resulting in a frequency-domain symbol {tilde over (X)}.sup.(2)? with a length of N.sub.FFT=NQ=64. Different users may be mapped to different frequency domains.

[0038] Step 3, Frequency Domain to Time Domain Transformation: {tilde over (X)}.sup.(2) is transformed by an N.sub.FFT=64 IFFT to generate the OFDM symbol x.sup.(2)? in the time domain for the second user:

x.sup.(2)=[0.021,0.054,0.082, . . . ,0.009,?0.005,?0.001].sup.T

[0039] Step 4, Phase Modulation: The time-domain OFDM symbol x.sup.(2) for User 2 obtained above is phase-modulated to obtain the discrete-time CE-OFDM signal s.sup.(2)?, where A=1, 2?h=0.7 and the calculated values are ?.sub.I.sup.2=2 and C.sub.N=8.2624. Hence, s.sup.(2) is represented as:

s.sup.(2)=[0.992+0.126j,0.950+0.310j,0.888+0.458j, . . . ,0.998+0.055j,0.999?0.315j,1.00?0.007j].sup.T

[0040] Step 5, Time Domain to Frequency Domain Transformation: The signal s.sup.(2) is transformed by an N.sub.FFT=64 point FFT to generate the frequency domain signal S.sup.(2)? for User 2, where S.sup.(2) is expressed as:

S.sup.(2)=[7.56+0.019j,?0.472+0.615j,?0.446+0.446j, . . . ,?0.547?0.486j,0.568+0.506j,0.472+0.369j].sup.T

[0041] Step 6, Frequency Domain Offset: S.sup.(2) is shifted to the right by NS.sup.(2)=16 subcarriers to obtain S.sup.(2)?:

S.sup.(2)=[ . . . ,?0.547?0.486j,0.568+0.506j,0.472+0.369j,7.56+0.019j,?0.472+0.615j,?0.446+0.446j, . . . ].sup.T

The offset frequency domain signal S.sup.(i) for other users (in this example, User 1) may be offset by different amounts, and for one of the users, the offset frequency domain signal S.sup.(i) may not be offset (e.g., offset by zero [0] subcarriers). For example, S.sup.(1) may be shifted (e.g., to the right) by NS.sup.(1)=0 subcarriers to obtain the offset frequency domain signal S.sup.(1) for User 1.

[0042] Step 7, Frequency Domain to Time Domain Transformation: S.sup.(2) is transformed by an N.sub.FFT=64 point IFFT to obtain the time-domain signal s.sup.(2)?:

s.sup.(2)=[0.124+0.015j,?0.038+0.118j,?0.111?0.057j, . . . ,?0.007+0.124j,?0.124+0.003j,?0.001?0.125j].sup.T

[0043] Step 8, Setting N.sub.CP=2, add a cyclic prefix to obtain the baseband transmission signal s.sub.cp.sup.(2)?:

s.sub.cp.sup.(2)=[?0.124+0.003j,?0.001?0.125j,0.124+0.015j,?0.038+0.118j, . . . ,?0.124+0.003j,?0.001?0.125j].sup.T

[0044] In the receiver:

[0045] Assuming there is no fading or noise in the channel, the signal Y=S is received in the frequency domain at the receiver, where S represents the frequency-domain signal of all users transmitted by the transmitter.

[0046] Step 9, Time Domain to Frequency Domain Transformation at the Receiver: Remove the cyclic prefix from the received signal and transform it through N.sub.FFT=64 point IFFT to obtain the frequency-domain received signal Y?.

[0047] Step 10, User Separation: Separate the received signal Y in the frequency domain for User 2 to obtain the received signal Y.sup.(2)? for User 2.

[0048] Step 11, Equalization Offset: Since the channel response H=1.sub.N.sub.FFT.sub.?1 at this point, then we can conclude or assume that Y.sup.(2)=Y.sup.(2)=S.sup.(2). Y.sup.(2) is then inversely offset (e.g., to the left) by NS.sup.(2) subcarriers to obtain {tilde over (Y)}.sup.(2):

{tilde over (Y)}.sup.(2)=[7.56+0.019j,?0.472+0.615j,?0.446+0.446j, . . . ,?0.547?0.486j,0.568+0.506j,0.472+0.369j].sup.T

The inverse offset function is also performed for other users (in this example, User 1), but by the complementary amount in the offset preformed in the transmitter (e.g., Step 6 above). For example, Y.sup.(1) may be shifted (e.g., to the left when the transmitter offsets to the right, or to the right when the transmitter offsets to the left, or not at all when the transmitter does not offset Y.sup.(1)) by NS.sup.(1) subcarriers to obtain the signal {tilde over (Y)}.sup.(1) for User 1.

[0049] Step 12, Obtain Detection Results (e.g., the transmitted bit sequence of User 2): Transform {tilde over (Y)}.sup.(2) obtained from Step 11 by an IFFT to the time domain, then phase-demodulate the resulting data sequence in the time domain using an arctangent function, and further transform it using an FFT to obtain data {circumflex over (X)}.sup.i for User 2 in the frequency domain. Finally, make a decision on the effective data of the i-th user to obtain the detection result {circumflex over (X)}.sup.(2) for that user:

{circumflex over (X)}.sup.(2)=[0,0.7+0.7j,0.7+0.7j,?0.7?0.7j,0.7+0.7j,0.7?0.7j,?0.7?0.7j,?0.7?0.7j].sup.T

[0050] The present method and system reduces interference between users by applying different frequency domain offsets to different users. In this example, in step 2, if different users are mapped to different frequency domains, but no offset is applied in step 6, it represents a conventional uplink CE-OFDM multiple access method. From step 7, it can be observed that in the present invention, the DC components of the data and/or signals for different users are separated, resulting in less interference between users compared to traditional uplink CE-OFDM systems.

[0051] Finally, it should be noted that the above embodiments are only intended to illustrate the technical solution(s) of the present invention, and not to limit it. Although a detailed description of the present invention has been provided with reference to the aforementioned embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the aforementioned embodiments, or some technical features can be equivalently replaced. Such modifications or replacements do not depart from the essence of the technical solutions of the various embodiments of the present invention.

[0052] The above are only some embodiments of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the creative concept of the present invention, all of which are within the scope of protection of the present invention.