Orthogonal frequency division multiplexing-code division multiple access system
View Patent ↗An orthogonal frequency division multiplexing (OFDM)-code division multiple access (CDMA) system is disclosed. The system includes a transmitter and a receiver. At the transmitter, a spreading and subcarrier mapping unit spreads an input data symbol with a complex quadratic sequence code to generate a plurality of chips and maps each chip to one of a plurality of subcarriers. An inverse discrete Fourier transform is performed on the chips mapped to the subcarriers and a cyclic prefix (CP) is inserted to an OFDM frame. A parallel-to-serial converter converts the time-domain data into a serial data stream for transmission. At the receiver, a serial-to-parallel converter converts received data into multiple received data streams and the CP is removed from the received data. A discrete Fourier transform is performed on the received data streams and equalization is performed. A despreader despreads an output of the equalizer to recover the transmitted data.
1. A transmitting device, comprising:
a sequence generator circuit to spread a data symbol with a spreading code having a quadratic phase sequence code and an orthogonal sequence, wherein the first sequence is derived by shifting a second sequence having a plurality of phases, wherein for a spreading factor of 2 m , the spreading code has 2 m chips and codes used by different users are different in the quadratic phase sequence code part;
a mapping circuit coupled with the sequence generator to map a combined result to a plurality of subcarriers; and
a transmission circuit coupled with the mapping circuit to process the mapped plurality of subcarriers and transmit a result of the processing as a radio frequency signal.
2. The transmitting device of claim 1 , wherein the second sequence is a four phase sequence having constant amplitude.
3. The transmitting device of claim 1 , wherein the radio frequency signal is further derived from a third sequence.
4. The transmitting device of claim 3 , wherein the third sequence reduces intercellular interference.
5. The transmitting device of claim 3 , wherein the third sequence is a masking code.
6. The transmitting device of claim 1 , wherein the orthogonal sequence is assigned to the transmitting device.
7. The transmitting device of claim 1 , wherein the first circuit is further configured to use orthogonal sequences of different lengths for spreading.
8. The transmitting device of claim 1 , wherein the mapped plurality of subcarriers are transmitted as an orthogonal frequency division multiplexed (OFDM) based signal.
9. A method, comprising:
spreading, by a sequence generator, a data symbol with a spreading code having a quadratic phase sequence code and an orthogonal sequence, wherein the first sequence is derived by shifting a second sequence having a plurality of phases, wherein codes used by different users are different in the quadratic phase sequence code part;
mapping, by the sequence generator, a combined result to a plurality of subcarriers;
processing, by the sequence generator, the mapped plurality of subcarriers; and
transmitting a result of the processing as a radio frequency signal.
10. The method of claim 9 , wherein the second sequence is a four phase sequence having a constant amplitude.
11. The method of claim 9 , wherein the radio frequency signal is further derived from a third sequence.
12. The method of claim 11 , wherein the third sequence reduces intercellular interference.
13. The method of claim 11 , wherein the third sequence is a masking code.
14. The method of claim 9 , wherein the orthogonal sequence is assigned to the transmitting device.
15. The method of claim 9 , wherein the mapped plurality of subcarriers are transmitted as an orthogonal frequency division multiplexed (OFDM) based signal.
16. A receiving device, comprising:
at least one circuit configured to receive a radio frequency signal and determine a data symbol from the radio frequency signal;
wherein the at least one circuit including at least one equalizer circuit to process combined data for subcarriers, wherein the combined data is mapped to a plurality of subcarriers and codes used by different users are different in a quadratic phase sequence code part,
wherein the at least one circuit including at least a Fourier transform circuit to recover a data symbol resulting from combining the data symbol with a first sequence and an orthogonal sequence, the first sequence being derived by shifting a second sequence having a plurality of phases.
17. The receiving device of claim 16 , wherein the second sequence is a four phase sequence having constant amplitude.
18. The receiving device of claim 16 , wherein the radio frequency signal is further derived from a third sequence.
19. The receiving device of claim 18 , wherein the third sequence reduces intercellular interference.
20. The receiving device of claim 18 , wherein the third sequence is a masking code.
21. The receiving device of claim 16 , wherein the orthogonal sequence is assigned to the transmitting device.