Peak to Average Power Ratio Reduction Apparatus and Method for a Wireless OFDM transmitter

• US 20090103639A1
• Filed: 10/19/2007
• Published: 04/23/2009
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Redpine Signals Incorporated (Silicon Laboratories Incorporated)
• Inventors: Sankabathula, Dharani Naga Sailaja, Murali, Partha Sarathy
• Granted Patent: US 7,986,738 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2618 Reduction thereof using auxiliary subcarriers

Abstract

An OFDM symbol comprises information subcarriers which carry the information to be transmitted, accompanied by edge subcarriers, which are selected to minimize the PAPR of the transmitted signal. The selection of edge subcarriers which minimizes PAPR enables either higher power transmission for the same information content, or lower power consumption for the same transmitted symbol power.

Claims

1. ) A process for generating a reduced peak to average power ratio (PAPR) symbols for a communications system using a first plurality of information subcarriers and a second plurality of null subcarriers, where said first plurality of information subcarriers and said second plurality of null subcarriers are subject to frequency domain magnitude limitations, the process comprising:

a first step of computing the peak to average power ratio for said first plurality of information subcarriers;

a second step of computing the peak to average power ratio for a plurality of combinations of said second plurality of null subcarriers within said magnitude limitations, and selecting the combination of said null subcarriers which produce a reduced said peak to average power ratio.

2. ) The process of claim 1 where said first plurality of information subcarriers includes 48 information subcarriers, a pilot subcarrier, and 4 edge subcarriers.

3. ) The process of claim 1 where said second plurality of null subcarriers includes 11 subcarriers.

4. ) The process of claim 1 where said second plurality of null subcarriers includes at least subcarriers −

27, −

28, 27, and 28.

5. ) A process for the selection of reduced peak to average power ratio subcarriers for a symbol S comprising a plurality of information subcarriers, the process having the steps:

a first step of identifying the maximum time-domain peaks of said symbol and the times at which said maximum peaks occur, optionally also measuring the peak to average power ratio of said symbol S;

a second step of comparing said maximum peak or alternatively with said peak to average power ratio of said symbol S with a threshold and also with a maximum iteration count, transmitting said symbol if said maximum peak is below said threshold or above said maximum iteration count and processing further otherwise;

a third step of kernel iteration whereby a correction kernel Ki is selected and a kernel iteration plurality of values Ki(T) is selected from said correction kernel, said values substantially comprising the kernel value at each said first step times;

a fourth step of phase iteration whereby each fourth step kernel ki(T) is multiplied by a phase rotation value, thereby forming Ki(T)′

;

a fifth step of adding each said Ki(T)′

to said S for each said phase iteration and each said kernel iteration, thereby forming a merit vector, said merit vector with a maximum value being said maximum merit vector;

a sixth step of selecting a minimum said maximum merit vector having the minimum value of said maximum merit vectors;

an seventh step of adding all values of corresponding said kernel Ki(T)′

to said symbol S and incrementing said feedback iteration, thereafter executing said first step.

6. ) The process of claim 5 whereby said maximum feedback iteration count is one of 1, 2, or 3.

7. ) The process of claim 5 whereby said number of kernel Ki is 5;

8. ) The process of claim 5 whereby said phase iterations are multiplication of said kernel Ki by {1, j, −

1, −

j}.

9. ) The process of claim 5 whereby said maximum time-domain peaks is the maximum 4 said peaks.

10. ) The process of claim 5 where said T1 corresponds to the maximum said peak.

11. ) The process of claim 5 where a set of merit vectors is formed from {Ki(T1)+S(T1),Ki(T2)+S(T2),Ki(T3)+S(T3),Ki(T4)+S(T4)}*(said iteration phase), said maximum merit vector being the one having the maximum value in the set elements {Ki(T1)+S(T1),Ki(T2)+S(T2),Ki(T3)+S(T3),Ki(T4)+S(T4)}*(said iteration phase) where:

Ki is a said correction kernel;

T1, T2, T3, T4 are the time positions of said symbol maximum amplitudes;

Ki(T1),Ki(T2),Ki(T3),Ki(T4) are the amplitude values of said correction kernel at said T1, said T2, said T3, and said T4;

said iteration phase is each of {1, j, −

1, −

j};

said Ki(T)′

being the kernel corresponding to the kernel having the minimum said maximum merit vector.

12. ) The process of claim 5 where each said fifth step merit vector has a merit vector maximum value which is formed from the maximum magnitude of said merit vector {Ki(T1)+S(T1),Ki(T2)+S(T2),Ki(T3)+S(T3),Ki(T4)+S(T4)}, said minimum maximum merit vector is the merit vector associated with said merit vector having the minimum said merit vector maximum value.