Peak-to-average-power reduction for OFDM multiple access

1. An apparatus, comprising:

a code-division multiplexer configured to assign a different codeword set to each of a plurality of data streams, each codeword set comprising a different one of a plurality of spread-Discrete Fourier Transform (DFT) code division multiple-access channels;

a DFT spreader configured to spread the each of the plurality of data streams with its assigned codeword set to produce a plurality of DFT-spread data symbols;

a mapper configured to map the plurality of DFT-spread data symbols to a plurality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers;

an inverse discrete Fourier transform (IDFT) configured to modulate the plurality of DFT-spread data symbols onto the plurality of OFDM subcarriers to generate an OFDM signal; and

a cyclic-prefix appender configured to append a cyclic prefix to the OFDM signal to produce a transmission signal; wherein the code-division multiplexer and the DFT spreader configure the OFDM signal to have a low peak-to-average-power ratio (PAPR); and wherein the cyclic-prefix appender produces the cyclic prefix from the OFDM signal to provide the transmission signal with a low PAPR.

2. The apparatus of claim 1 , wherein the code-division multiplexer is configured to arrange the original data symbols in each of a plurality of length-N blocks to be spread by the DFT spreader, such that each of the plurality of data streams is spread with a code set corresponding to its spread-DFT code division multiple access channel.

3. The apparatus of claim 1 , wherein the DFT spreader comprises the code-division multiplexer.

4. The apparatus of claim 1 , further comprising a scheduler communicatively coupled to the code-division multiplexer and configured to assign each spread-DFT code division multiple access channel to one of a plurality of User Equipments (UEs).

5. The apparatus of claim 1 , wherein the DFT spreader employs at least one of a set of orthogonal codes and a set of quasi-orthogonal codes to spread the multiplexed original data symbols.

6. The apparatus of claim 1 , wherein the plurality of SC-FDMA symbols comprises a sequence of SC-FDMA symbols.

7. The apparatus of claim 1 , wherein the mapper maps the plurality of DFT-spread data symbols to contiguous or non-contiguous OFDM subcarriers.

8. The apparatus of claim 1 , further comprising a scheduler configured to assign multiple ones of the plurality of data streams to a common Physical Resource Block (PRB) based on at least one of similarity in modulation scheme and similarity in scaling factor.

9. The apparatus of claim 8 , further comprising a layer mapper configured to map each PRB to at least one of a different layer and a different power amplifier.

10. A method, comprising:

multiplexing each of a plurality of data streams into a different one of a plurality of spread-Discrete Fourier Transform (DFT) code division multiple-access channels by assigning a different DFT codeword set to each of the plurality of data streams;

spreading the each of the plurality of data streams with its assigned DFT codeword set to produce a plurality of DFT-spread data symbols;

mapping the plurality of DFT-spread data symbols to a plurality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers;

modulating the plurality of DFT-spread data symbols onto the plurality of OFDM subcarriers to generate an OFDM signal; and

appending a cyclic prefix to the OFDM signal to produce a transmission signal; wherein the multiplexing and the spreading configure the OFDM signal to have a low peak-to-average-power ratio (PAPR); and wherein the appending produces the cyclic prefix from the OFDM signal to provide the transmission signal with a low PAPR.

11. The method of claim 10 , wherein each of the plurality of DFT-spread data symbols is a single-carrier frequency division multiple access (SC-FDMA) symbol comprising a plurality of sub-symbols that comprises the original data symbols code-division multiplexed into the plurality of spread-DFT code division multiple-access channels.

12. The method of claim 10 , wherein the multiplexing arranges the original data symbols in each of a plurality of length-N blocks for spreading, such that each of the plurality of data streams is spread with a code set corresponding to its spread-DFT code division multiple access channel.

13. The method of claim 10 , wherein the OFDM transmission signal is a downlink signal.

14. The method of claim 10 , wherein the multiplexing further comprises assigning each spread-DFT code division multiple access channel to one of a plurality of User Equipments (UEs).

15. The method of claim 10 , wherein the spreading employs at least one of a set of orthogonal codes and a set of quasi-orthogonal codes to spread the multiplexed original data symbols.

16. The method of claim 10 , wherein the plurality of SC-FDMA symbols comprises a sequence of SC-FDMA symbols.

17. The method of claim 10 , wherein the mapping is configured to map the plurality of DFT-spread data symbols to contiguous or non-contiguous OFDM subcarriers.

18. The method of claim 10 , further comprising assigning multiple ones of the plurality of data streams to a common Physical Resource Block (PRB) based on at least one of similarity in modulation scheme and similarity in scaling factor.

19. The method of claim 18 , further comprising mapping each PRB to at least one of a different layer and a different power amplifier.

20. An Orthogonal Frequency Division Multiplexing (OFDM) transmitter apparatus configured to generate an OFDM multiple-access signal, the transmitter apparatus comprising at least one processor, at least one memory in electronic communication with the at least one processor, and instructions stored in the at least one memory, the instructions executable by the at least one processor to:

multiplex each of a plurality of data streams into a different one of a plurality of spread-Discrete Fourier Transform (DFT) code division multiple-access channels by assigning a different DFT codeword set to each of the plurality of data streams;

spread the each of the plurality of data streams with its assigned DFT codeword set to produce a plurality of DFT-spread data symbols;

map the plurality of DFT-spread data symbols to a plurality of OFDM subcarriers;

modulate on the plurality of DFT-spread data symbols onto the plurality of OFDM subcarriers to generate an OFDM signal; and

append a cyclic prefix to the OFDM signal to produce a transmission signal, wherein the instructions executable by the at least one processor to multiplex and spread configure the OFDM signal to have a low peak-to-average-power ratio (PAPR), and the cyclic prefix being produced from the OFDM signal to provide the transmission signal with a low PAPR.

21. The apparatus of claim 20 , wherein the instructions to multiplex provide for arranging the original data symbols in each of a plurality of length-N blocks for spreading, such that each of the plurality of data streams is spread with a code set corresponding to its spread-DFT code division multiple access channel.

22. The apparatus of claim 20 , wherein the instructions to multiplex provide for assigning each spread-DFT code division multiple access channel to one of a plurality of User Equipments (UEs).

23. The apparatus of claim 20 , wherein the instructions to spread provide for employing at least one of a set of orthogonal codes and a set of quasi-orthogonal codes to spread the multiplexed original data symbols.

24. The apparatus of claim 20 , wherein the plurality of SC-FDMA symbols comprises a sequence of SC-FDMA symbols.

25. The apparatus of claim 20 , wherein the instructions to map provides for mapping the plurality of DFT-spread data symbols to contiguous or non-contiguous OFDM subcarriers.

26. The apparatus of claim 20 , further comprising instructions to assign multiple ones of the plurality of data streams to a common Physical Resource Block (PRB) based on at least one of similarity in modulation scheme and similarity in scaling factor.

27. The apparatus of claim 26 , further comprising instructions to map each PRB to at least one of a different layer and a different power amplifier.