System and method for data scrambling to reduce the crest factor in an OFDM waveform
A method is provided for reducing the peak power level in a combination of orthogonal frequency division multiplexed (OFDM) tones. The method is particularly effective when the information to be communicated is digital data consisting of long patterns of “1”s or “0”s. The digital data of the message is combined with a scrambling vector before the data is modulated. The randomization of data patterns, in turn, leads to a more random combination of OFDM tone amplitude being transmitted. The message is recovered at the receiver by removing the scrambling vector. An OFDM communication system using the above-described method is also provided.
1. An apparatus comprising:
a transmitter comprising:
a scrambler configured to generate scrambled data based on a scrambling vector calculated according to a formula;
a modulator configured to generate modulated data based on the scrambled data; and
a mapper configured to map the modulated data into orthogonal frequency division multiplexed tones for transmission,
wherein the scrambler generates the scrambled data by combining the scrambling vector with digital data of a message.
2. The apparatus, as recited in claim 1 , wherein all data transmitted in a single time slot of a frame of orthogonal frequency division multiplexed tones for transmission uses the scrambling vector only once.
3. The apparatus, as recited in claim 1 , wherein the scrambler is configured to rescramble the digital data to generate the scrambled data further based on a second scrambling vector calculated according to the formula in response to clipping by a power amplifier of a signal based on the orthogonal frequency division multiplexed tones.
4. The apparatus, as recited in claim 1 , further comprising:
a receiver comprising:
a de-mapper configured to de-map received modulated data from the orthogonal frequency division multiplexed tones;
a demodulator configured to generate received scrambled data based on the modulated data; and
a descrambler configured to recover the digital data from the received scrambled data using the scrambling vector,
wherein the descrambler recovers the digital data by combining the scrambling vector with the received scrambled data.
5. A transmitter comprising:
a scrambler configured to generate scrambled data using a scrambling vector based on a slot number in a frame;
a modulator configured to generate modulated data based on the scrambled data;
a mapper configured to map the modulated data into orthogonal frequency division multiplexed tones for transmission,
wherein the scrambler generates the scrambled data by combining the scrambling vector with digital data of a message.
6. The transmitter, as recited in claim 5 , wherein the scrambler is configured to generate the scrambling vector from a formula as the scrambling vector is used.
7. The transmitter, as recited in claim 5 , wherein the scrambler is configured to select the scrambling vector from a scrambling vector table by directing a pointer to a row in the scrambling vector table using an algorithm responsive to the slot number.
8. The transmitter, as recited in claim 5 , wherein the scrambler is configured to regenerate the scrambled data based on a second scrambling vector calculated in response to clipping by a power amplifier of a signal based on the orthogonal frequency division multiplexed tones.
9. The transmitter, as recited in claim 5 , wherein the slot number is a frequency slot number corresponding to a group of tones of a plurality of groups of tones that comprise the orthogonal frequency division multiplexed tones.
10. The transmitter, as recited in claim 5 , wherein the slot number corresponds to one or more time division multiple access frames.
11. A receiver comprising:
an antenna configured to receive orthogonal frequency division multiplexed tones;
a de-mapper configured to de-map orthogonal frequency division multiplexed tones into modulated data;
a demodulator configured to generate scrambled data based on the modulated data; and
a descrambler configured to recover data from the scrambled data using a scrambling vector based on a slot number in a frame,
wherein the descrambler recovers the data by combining the scrambling vector with the scrambled data.
12. The receiver, as recited in claim 11 , wherein the descrambler calculates the scrambling vector from a formula as the scrambling vector is used.
13. The receiver, as recited in claim 11 , wherein the descrambler selects the scrambling vector from a scrambling vector table by directing a pointer to a row in the scrambling vector table using an algorithm responsive to the slot number.
14. The receiver, as recited in claim 11 , wherein the slot number is a frequency slot number corresponding to a group of tones of a plurality of groups of tones that comprise the orthogonal frequency division multiplexed tones.
15. The receiver, as recited in claim 11 , wherein the slot number corresponds to one or more time division multiple access frames.
16. An apparatus comprising:
a transmitter comprising:
a scrambler configured to generate scrambled data based on a scrambling vector calculated according to a formula, wherein the scrambler generates the scrambled data by combining the scrambling vector with digital data of a message; and
a modulator configured to generate modulated data based on the scrambled data, wherein the transmitter is configured to transmit orthogonal frequency division multiplexed tones based on the modulated data.
17. An apparatus comprising:
a receiver comprising:
a demodulator configured to provide scrambled data based on modulated data, the modulated data being based on received orthogonal frequency division multiplexed tones; and
a descrambler configured to recover digital data based on a scrambling vector calculated according to a formula, wherein the descrambler recovers the digital data by combining the scrambling vector with the scrambled data.