Method and apparatus for high-order PAPR reduction of an OFDM signal

• US 20050286648A1
• Filed: 08/24/2004
• Published: 12/29/2005
• Est. Priority Date: 06/28/2004
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Feng, Chih-Chun, Wang, Chih-Yaw
• Granted Patent: US 7,315,580 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2621 Reduction thereof using phase offsets between subcarriers

Abstract

A method and apparatus for high-order peak-to-average power ratio reduction of an OFDM signal are disclosed. The method partitions time-domain input data x[n] of length N into M disjoint subblocks in time domain, and a complete N-point transmitted signal {tilde over (x)}[n], n=0, 1, . . . , N−1, is composed after transformation, complex multiplication, and phase optimization, where M is a power of 2, M≧8 and N/M>1 is an integer. Accordingly, the apparatus comprises an N-point inverse fast Fourier transform (N-IFFT), a de-multiplexer, a transformer, two sets of memories, a plurality of complex multipliers, and an adder. This invention uses only one N-IFFT, whereby it achieves significant computation reduction. As M=8, the number of complex multiplications and that of memory units required are less than or equal to (N/2)log₂N+(3N/4) and 3N/2, respectively. The invention also preserves the inherent property as well as advantages of an OFDM system.

Claims

1. A method for high-order peak-to-average power ration (PAPR) reduction for an OFDM signal, comprising:

(a) transforming a frequency domain signal X[k] of length N by an N-IFFT into a time domain signal x[n] of length N, where N is the number of useful data in an OFDM symbol, n=0, 1, . . . , N−

1;

(b) partitioning said sequence x[n] of length N into M disjoint subblocks, M being a power of 2 and greater or equal to 8, and N/M being an integer greater than 1;

(c) transforming said subblocks into sub-sequences z[n], each having the length N/M, l=1, 2, . . . , M and n=0, 1, . . . , (N/M)−

1; and

(d) each said sub-sequence zl [n] being processed using complex multiplication followed by phase rotation or directly using phase rotation, then addition to form a complete N-point transmitted signal {tilde over (x)}[n].

2. The method as claimed in claim 1, wherein said transformation in said step (c) is equivalent to an M-point inverse fast Fourier transform (IFFT).

3. The method as claimed in claim 1, wherein said M is equal to 8.

4. The method as claimed in claim 1, wherein said transformation in said step (c) further comprises addition, imagery multiplication or complex multiplication.

5. The method as claimed in claim 1, wherein said complex multiplication in said step (d) is e^j(2π

/M)

6. The method as claimed in claim 1, wherein said method requires less than or equal to (N/2)log₂N+(3N/4) complex multiplications.

7. The method as claimed in claim 1, wherein said step (d) further comprises the steps of:

(d1) a part of said M sub-sequences zl[n] being processed using complex multiplication e<sup>j(2π

/M)</sup> to form another sub-sequence z_l[n], l being between 1 and M, and n=0, 1, . . . , (N/M)−

1; and

(d2) using different time period to select sub-sequence z[n] or {tilde over (z)}_l[n] for phase rotation, and adding to form a complete N-point transmitted signal {tilde over (x)}[n].

8. The method as claimed in claim 1, wherein in said step (d), said phase rotation parameter is of the four possibilities {+1, −

1, +j, −

j}.

9. An apparatus for PAPR reduction of an OFDM signal, comprising:

an N-point inverse fast Fourier transform (N-IFFT) for transforming N-length frequency domain signal X[k] into N-length time domain signal x[n], where N is the number of useful data in an OFDM symbol, n=0, 1, . . . , N−

1;

a de-multiplexer for partitioning said time domain signal x[n] of length N into M disjoint subblocks of identical length N/M, where n=0, 1, . . . , N−

1, N is an integer greater than 1, M is a power of 2 and greater than or equal to 8, and N/M is an integer greater than 1;

a transformer transforming said M disjoint subblocks into M N/M-length sub-sequences z[n], where l=1, 2, . . . , M and n=0, 1, . . . , (N/M)−

1, for further complex multiplication or phase rotation;

at most M complex multipliers executing said complex multiplication on a part of said sub-sequences zl[n] to form another sub-sequence {tilde over (z)}_l[n], where l is between 1 and M, and n=0, 1, . . . , (N/M)−

1;

two sets of memories, one said memory storing said M disjoint subblocks and said M sub-sequences z[n], and the other said memory storing said sub-sequences z[n]; and

an adder for adding said sub-sequences zl[n] and {tilde over (z)}_l[n], after phase rotation, to obtain a complete N-point transmitted signal {tilde over (x)}[n].

10. The apparatus as claimed in claim 9, wherein said M is 8, and said transformer is implemented with 24 adders, 3 imagery j multipliers and 2 complex multipliers.

11. The apparatus as claimed in claim 9, wherein said M is 8, and said transformer is implemented with 16 adders, 1 imagery j multipliers and 4 real multipliers.

12. The apparatus as claimed in claim 9, wherein said apparatus only uses an N-point inverse fast Fourier transform (N-IFFT).

13. The apparatus as claimed in claim 9, wherein said two sets of memories require less than or equal to 3N/2 units of memory.