METHODS FOR DATA TRANSMISSION

Abstract

This invention relates to methods for data transmission in OFDM (Orthogonal Frequency Division Multiplexed) communication systems. More particularly, it relates to data transmission in multi-band OFDM (MB-OFDM) systems. The method of generating an OFDM signal for transmission, comprises the steps of: dividing a plurality of subcarriers into two or more groups of subcarriers, minimising the peak-average power ratio (PAPR) of an OFDM signal, and enhancing the transmission of said OFDM signal by further repeating transmission of said OFDM signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described with reference to the accompanying drawings, wherein:

FIG. 1 shows subcarriers of an OFDM signal spectrum, with frequency on the x-axis, and power on the y-axis (in an arbitrary scale);

FIG. 2 is a schematic diagram of an example communication device;

FIGS. 3 a and 3b are schematic diagrams showing a transmitter and a receiver respectively according to Task Group 3a of the IEEE 802.15 standards setting body;

FIG. 3 c is a schematic diagram of a transmitter in accordance with a specific embodiment of the invention;

FIG. 4 shows grouping of the first 13 subcarriers for input to a 128-point IFFT in accordance with an embodiment of the present invention;

FIG. 5 shows grouping of the inner nine subcarriers shown spectrally in accordance with an embodiment of the present invention;

FIG. 6 a shows the probability distribution functions (PDF) of PAPR obtained in accordance with an embodiment of the present invention and the PDF of PAPR obtained in accordance with the method disclosed in the prior art;

FIG. 6 b shows the cumulative frequency distribution (CDFs) of PAPR obtained in accordance with an embodiment of the present invention and the CDF of PAPR obtained in accordance with the method disclosed in the prior art;

FIG. 7 a shows the complimentary CDFs (CCDFs) of PAPR for competing schemes when using QPSK and 128 subcarriers obtained in accordance with the method of the present invention;

FIG. 7 b shows the CCDFs of PAPR for competing schemes when using 16 QAM and 128 subcarriers obtained in accordance with the method of the present invention;

FIG. 8 shows the CCDFs of PAPR for competing schemes demonstrating how relative performance gains increase as the number of tones decreases, which could provide performance gains for an OFDMA scheme obtained in accordance with the method of the present invention;

Claims

1. A method of generating an OFDM signal for transmission, the signal being intended for transmission over a plurality of subcarriers, the method comprising the steps of: allocating said plurality of subcarriers into two groups of subcarriers, and: allocating information for transmission to a first of said groups;transposing said allocated information by means of a transposition algorithm; andallocating to a second of said groups said transposed allocated information.

2. A method in accordance with claim 1 wherein said subcarriers are designated in the frequency domain.

3. A method in accordance with claim 2 wherein the first and second groups of subcarriers are disposed symmetrically about a DC baseband carrier in the frequency domain.

4. A method in accordance with claim 1 wherein said step of transposing comprises allocating to one of the subcarriers in the second group of subcarriers the information allocated to a first one of the subcarriers in the first group.

5. A method in accordance with claim 4 wherein the step of transposing said information from said first subcarrier comprises the step of rendering said information into its negative.

6. A method in accordance with claim 5 wherein said step of transposing comprises allocating to another of the subcarriers in the second group of subcarriers information derived from a combination of the information allocated to more than one of the subcarriers in the first group.

7. A method in accordance with claim 6 wherein said step comprises the step of combining the information allocated to two subcarriers of the first group into information suitable for allocation to a subcarrier of the second group.

8. A method in accordance with claim 7 wherein said step of combining comprises determining from said two subcarriers the respective signs of the real and imaginary components of the symbols allocated to these subcarriers, to form a mutual polarity function from the signs of the respective real and imaginary components of the symbols on the two said subcarriers.

9. A method in accordance with claim 8 and further comprising using said mutual polarity function to modify a copy of a symbol applied to one of the two subcarriers to form a transposed symbol that is allocated to the second group of subcarriers.

10. A method in accordance with claim 8 wherein said mutual polarity function comprises the algebraic sign of the product of the real and imaginary parts of the information allocated to said first and second subcarriers.

11. A method in accordance with claim 1 wherein said subcarriers are considered in groups of four, with two subcarriers being allocated information symbols and the remaining two being allocated symbols derived from the first two symbols.

12. OFDM transmission apparatus comprising information allocation means for allocating information to a plurality of subcarriers, said allocation means being operable to allocate said plurality of subcarriers into two groups of subcarriers, each group comprising an even number of subcarriers and, for each group, said allocation means being operable to allocate information for transmission to a first half of said subcarriers, and including information transposition means for transposing said allocated information by means of a transposition algorithm, said allocation means being operable to allocate said transposed allocated information to a second half of the subcarriers in the group.

13. Apparatus in accordance with claim 12 wherein said allocation means is operable to allocate said plurality of subcarriers into said first and second groups of subcarriers such that said groups are disposed symmetrically about a DC baseband carrier in the frequency domain.

14. Apparatus in accordance with claim 12 wherein said allocation means is operable to allocate to one of the subcarriers in the second group of subcarriers the information allocated to a first one of the subcarriers in the first group.

15. Apparatus in accordance with claim 14 wherein said allocation means is operable to combine the information allocated to two subcarriers of the first group into information suitable for allocation to a subcarrier of the second group.

16. Computer program product bearing computer executable program means operable to cause a computer to become configured to perform the method of any of claims 1 to 11.