Methods and arrangements for peak to average power ratio reduction
View Patent ↗The present invention relates to a transmitter and to a receiver and methods thereof wherein the PAPR is reduced by applying a set of different phase rotations to the output of each DFT of the transmitter. A corresponding set of inverse phase rotations are applied to the input of the IDFT of the receiver. The set of phase rotations applied to the subcarriers at the output of the DFT precoder of the transmitter results in a circular time shift of the corresponding time domain at the output of the IDFT modulator. If the phase rotations are properly selected for each DFT precoder, the probability that signal peaks sum in a constructive way at the output of the IDFT modulators is reduced, with a consequent reduction of the PAPR.
1. An Orthogonal Frequency Division Multiplexing (OFDM) transmitter comprising:
a plurality of modulators configured to apply multicarrier OFDM modulation to generate a plurality of modulated data streams, wherein the number of modulated data streams corresponds to the number of carriers of the applied multi carrier OFDM modulation;
a plurality of Discrete Fourier Transformers (DFTs) configured to transform the plurality of modulated data streams into the frequency domain;
a plurality of phase rotation blocks each configured to apply a specific phase rotation to each output of a respective DFT, wherein the value of that specific phase rotation is a linear function of a subcarrier index;
a plurality of subcarrier mappers configured to map the output of the DFTs, as phased rotated by the phase rotation blocks, onto subcarriers;
at least one Inverse DFT (IDFT) configured to transform the output of the DFTs, as mapped onto the subcarriers, back to the time domain; and
at least one power amplifier configured to amplify the output of the at least one IDFT
wherein the OFDM transmitter is configured to transmit at least one power amplified data stream from the at least one power amplifier; and
wherein the value of the specific phase rotation applied to each output of the respective DFT depends at least on the number of carriers of the multicarrier OFDM modulation applied, the length of the at least one IDFT, the distance of a first mapped subcarrier of the DFT from the first input of the at least one IDFT, and the length of the DFT.
2. The OFDM transmitter according to claim 1 , wherein parameters defining the value of a specific phase rotation are specific to each DFT.
3. The OFDM transmitter according to claim 1 , wherein the output of a phase rotation block is configured to be input to a subcarrier mapper.
4. The OFDM transmitter according to claim 1 , further comprising one or more antennas configured to wirelessly transmit the at least one power amplified data stream.
5. The OFDM transmitter according to claim 4 , wherein the one or more antennas comprise a plurality of antennas configured for wireless Multiple Input Multiple Output (MIMO) transmission, wherein the number of said antennas corresponds to the number of modulated data streams.
6. The OFDM transmitter according to claim 5 , wherein the at least one IDFT comprises a plurality of IDFTs that are each antenna specific, and wherein the OFDM transmitter further comprises a spatial processing block configured to combine the output of the DFTs, as phased rotated by the phase rotation blocks, and to deliver the combined output to the plurality of IDFTs, via said plurality of subcarrier mappers.
7. The OFDM transmitter according to claim 5 , wherein the value of a specific phase rotation depends at least on the number of power amplified data streams to be transmitted.
8. The OFDM transmitter according to claim 1 , further comprising a number of digital-to-analogue converters and analogue processing circuits configured to transmit the at least one power amplified data stream via wired Multiple Input Multiple Output (MIMO) transmission, wherein the number of digital-to-analogue converters and analogue processing circuits corresponds to the number of modulated data streams.
9. The OFDM transmitter according to claim 1 , wherein the specific phase rotations are defined according to a predefined function in the OFDM transmitter.
10. The OFDM transmitter according to claim 1 , further configured to send information indicating the specific phase rotations in a control message.
11. An Orthogonal Frequency Division Multiplexing (OFDM) receiver configured to receive at least one OFDM modulated data stream and comprising:
a number of analogue-to-digital converters and analogue processing circuits configured to receive the at least one OFDM modulated data stream via wired Multiple Input Multiple Output (MIMO) reception, wherein the number of analogue-to-digital converters and analogue processing circuits corresponds to the number of received OFDM modulated data streams;
at least one Discrete Fourier Transformer (DFT) configured to transform the at least one OFDM modulated data stream into the frequency domain;
a plurality of subcarrier demappers configured to demap the output of the at least one DFT onto subcarriers;
a plurality of phase correction blocks each configured to apply a specific phase correction to each output of a respective subcarrier demapper, wherein the value of that specific phase correction is a linear function of a subcarrier index; and
a plurality of inverse DFTs (IDFTs) each configured to transform the output of a respective phase correction block back to the time domain;
wherein the value of the specific phase correction depends at least on the number of received OFDM modulated data streams, the length of the at least one IDFT, the distance of a first mapped subcarrier of the IDFT from the first input of the at least one DFT, and the length of the IDFT.
12. The OFDM receiver according to claim 11 , wherein parameters defining the value of a specific phase correction are specific to each IDFT.
13. The OFDM receiver according to claim 11 , wherein the OFDM receiver is configured for multicarrier OFDM.
14. The OFDM receiver according to claim 11 , further comprising one or more antennas configured to wirelessly receive the at least one OFDM modulated data stream.
15. The OFDM receiver according to claim 14 , wherein the one or more antennas comprise a plurality of antennas configured for wireless Multiple Input Multiple Output (MIMO) reception, wherein the number of said antennas corresponds to the number of OFDM modulated data streams received.
16. The OFDM receiver according to claim 11 , wherein the specific phase corrections are defined according to a predefined function in the OFDM transmitter.
17. The OFDM receiver according to claim 11 , further configured to receive information indicating the specific phase corrections in a control message.
18. A method implemented by an Orthogonal Frequency Division Multiplexing (OFDM) transmitter, comprising:
applying multicarrier OFDM modulation using a plurality of modulators to generate a plurality of modulated data streams, wherein the number of modulated data streams corresponds to the number of carriers of the applied multi carrier OFDM modulation;
transforming at a plurality of Discrete Fourier Transformers (DFTs) the plurality of modulated data streams into the frequency domain;
applying a specific phase rotation to each output of a respective DFT, wherein the value of that specific phase rotation is a linear function of a subcarrier index;
mapping the output of the DFTs, as phased rotated, onto subcarriers;
transforming at one or more inverse DFTs (IDFTs) the output of the DFTs, as mapped onto the subcarriers, back to the time domain;
amplifying the output of the one or more IDFTs to obtain at least one power amplified data stream; and
transmitting the at least one power amplified data stream;
wherein the value of the specific phase rotation applied to each output of the respective DFT depends at least on the number of carriers of the multicarrier OFDM modulation applied, the length of the at least one IDFT, the distance of a first mapped subcarrier of the DFT from the first input of the at least one IDFT, and the length of the DFT.
19. A method implemented by an Orthogonal Frequency Division Multiplex (OFDM) receiver, comprising:
receiving at least one OFDM modulated data stream via wired Multiple Input Multiple Output (MIMO) reception using a number of analogue-to-digital converters and analogue processing circuits, wherein the number of analogue-to-digital converters and analogue processing circuits corresponds to the number of received OFDM modulated data streams;
transforming at one or more Discrete Fourier Transformers (DFTs) the at least one OFDM modulated data stream into the frequency domain;
mapping at a plurality of subcarrier demappers the output of the one or more DFTs onto subcarriers;
applying at each of a plurality of phase correction blocks a specific phase correction to each output of a respective subcarrier demapper, wherein the value of that specific phase correction is a linear function of a subcarrier index; and
transforming the output of each phase correction block back to the time domain;
wherein the value of the specific phase correction depends at least on the number of received OFDM modulated data streams, the length of the at least one IDFT, the distance of a first mapped subcarrier of the IDFT from the first input of the at least one DFT, and the length of the IDFT.