OFDM signal processing in a base transceiver system

• US 8,989,088 B2
• Filed: 05/21/2012
• Issued: 03/24/2015
• Est. Priority Date: 01/07/2011
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Inventors: Ling, Yi
• Primary Examiner(s): Kao, Jutai
• Application Number:
  US13/476,862
• Publication Number:
  US 20120250740A1
• Time in Patent Office: 1,037 Days
• Field of Search: None
• US Class Current: 370/328
• CPC Class Codes: H03M 7/30 Compression speech analysis-synthesis for redundancy reduction G10L19/00; for image communication H04N; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/26524 Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation
• CPC Class Codes: H04L 27/26526 with inverse FFT [IFFT] or inverse DFT [IDFT] demodulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] receiver or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

A method and apparatus provides OFDM signal compression for transfer over serial data links in a base transceiver system (BTS) of a wireless communication network. For the uplink, an RF unit of the BTS applies OFDM cyclic prefix removal and OFDM frequency transformation of the baseband signal samples followed by frequency domain compression of the baseband signal samples, resulting from analog to digital conversion of received analog signals followed by digital downconversion, forming compressed coefficients. After transfer over the serial data link, the baseband processor applies frequency domain decompression to the compressed coefficients prior to further signal processing. For the downlink, the RF unit performs frequency domain decompression of the compressed coefficients and applies OFDM inverse frequency transformation of the decompressed coefficients and OFDM cyclic prefix insertion prior to digital upconversion and digital to analog conversion, generating the analog signal for transmission over the antenna.

Claims

1. In a base transceiver system of a wireless communication network, a method for transferring OFDM modulated signal data from a radio frequency (RF) unit to a baseband unit over a serial data link, wherein the RF unit is connected to an antenna to receive an analog signal, the analog signal representing a plurality of antenna-carrier channels, the RF unit including an analog to digital converter (ADC) that converts the analog signal to a digital signal and a digital down converter (DDC) that downconverts the digital signal to a plurality of baseband channels, each baseband channel corresponding to one of the antenna-carrier channels and having a sequence of signal samples, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, wherein a baseband processor of the baseband unit performs signal processing operations, the method comprising:

compressing the sequence of signal samples of each baseband channel at the RF unit, wherein for each baseband channel the compressing comprises;

computing an OFDM frequency domain transform of a plurality of the sequence of signal samples of each baseband channel at the RF unit to form a plurality of frequency domain coefficients, wherein the frequency domain coefficients include a real component and an imaginary component for each of a plurality of frequency bins and wherein a length of the OFDM frequency domain transform is equal to a symbol length of the OFDM modulated signal data;

attenuating one or more of the frequency domain coefficients in accordance with an attenuation profile to form a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the frequency bins; and

encoding the attenuated coefficients to form compressed coefficients;

formatting the compressed coefficients of the plurality of baseband channels for transfer over the serial data link;

transferring the compressed coefficients over the serial data link from the RF unit to the baseband unit;

receiving the compressed coefficients at the baseband unit; and

decompressing the compressed coefficients at the baseband unit, wherein for each baseband channel the decompressing comprises;

decoding the compressed coefficients to form reconstructed attenuated coefficients;

amplifying a plurality of the reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients corresponding to each baseband channel, wherein the gain profile corresponds to the attenuation profile and specifies gain levels for corresponding frequency bins; and

providing the decompressed coefficients to the baseband processor of the baseband unit to apply the signal processing operations to the decompressed coefficients.

2. The method of claim 1, wherein computing an OFDM frequency domain transform further comprises computing an OFDM frequency domain transform using a discrete Fourier transform (DFT), a fast Fourier transform (FFT), a discrete cosine transform (DCT), or a discrete sine transform (DST).

3. The method of claim 1, wherein formatting the compressed coefficients, transferring the compressed coefficients and receiving the compressed coefficients are performed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard or in accordance with a Common Public Radio Interface (CPRI) standard.

4. The method of claim 1, wherein formatting the compressed coefficients further comprises:

mapping a sequence of the compressed coefficients corresponding to each baseband channel to a sequence of data structures to form a plurality of sequences of data structures for the plurality of baseband channels; and

multiplexing the plurality of sequences of data structures corresponding to the plurality of baseband channels to form a sequence of multiplexed data structures containing the compressed coefficients prior to transferring the compressed coefficients.

5. The method of claim 4, wherein the data structures are formed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard using a Reference Point 3 (RP3) message protocol or with a Common Public Radio Interface (CPRI) standard using an antenna-carrier (AxC) container protocol.

6. The method of claim 1, wherein the compressing further comprises, removing an OFDM cyclic prefix from the plurality of the signal samples of each baseband channel at the RF unit prior to computing an OFDM frequency domain transform of a plurality of the signal samples of each baseband channel at the RF unit.

7. In a base transceiver system of a wireless communication network, a method for transferring OFDM modulated signal data from a baseband unit to a radio frequency (RF) unit over a serial data link, each signal sample associated with one of a plurality of baseband channels, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, the RF unit including a digital up converter (DUC) that upconverts a sequence of signal samples of each baseband channel to a corresponding one of a plurality of antenna-carrier channels to form a single upconverted digital signal and a digital to analog converter (DAC) that converts the upconverted digital signal to an analog signal, wherein the RF unit is coupled to an antenna to transmit the analog signal, the analog signal representing the plurality of antenna-carrier channels, the method comprising:

receiving a plurality of frequency domain coefficients for a plurality of baseband channels of the OFDM modulated signal data at the baseband unit, wherein the frequency domain coefficients include a real component and an imaginary component for each of a plurality of frequency bins;

compressing the frequency domain coefficients of each baseband channel at the baseband unit, wherein for each baseband channel the compressing comprises;

attenuating one or more of the frequency domain coefficients in accordance with an attenuation profile to form a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the frequency bins; and

encoding the attenuated coefficients to form compressed coefficients;

the method further comprising;

formatting the compressed coefficients of the plurality of baseband channels for transfer over the serial data link;

transferring the compressed coefficients over the serial data link from the baseband unit to the RF unit;

receiving the compressed coefficients at the RF unit; and

decompressing the compressed coefficients at the RF unit, wherein for each baseband channel the decompressing comprises;

decoding the compressed coefficients to form reconstructed attenuated coefficients;

amplifying a plurality of the reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients corresponding to each baseband channel, wherein the gain profile corresponds to the attenuation profile and specifies gain levels for corresponding frequency bins;

computing an OFDM inverse frequency domain transform of the plurality of decompressed coefficients to form a plurality of decompressed signal samples of the corresponding baseband channel, wherein each decompressed signal sample includes a decompressed I sample and a decompressed Q sample, wherein a length of the OFDM inverse frequency domain transform is equal to a symbol length of the OFDM signal data; and

providing the decompressed signal samples to the DUC for forming the upconverted digital signal.

8. The method of claim 7, wherein the OFDM inverse frequency domain transform comprises an inverse frequency domain transform using a discrete Fourier transform (DFT), a fast Fourier transform (FFT), discrete cosine transform (DCT), or a discrete sine transform (DST).

9. The method of claim 7, wherein formatting the compressed coefficients, transferring the compressed coefficients and receiving the compressed coefficients are performed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard or in accordance with a Common Public Radio Interface (CPRI) standard.

10. The method of claim 7, wherein formatting the compressed coefficients further comprises:

mapping a sequence of the compressed coefficients corresponding to each baseband channel to a sequence of data structures, to form a plurality of sequences of data structures for the plurality of baseband channels; and

multiplexing the plurality of sequences of data structures corresponding to the plurality of baseband channels to form a sequence of multiplexed data structures containing the compressed coefficients for the step of transferring.

11. The method of claim 10, wherein the data structures are formed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard using a Reference Point 3 (RP3) message protocol or a Common Public Radio Interface (CPRI) standard using an antenna-carrier (AxC) container protocol.

12. The method of claim 7, wherein the decompressing further comprises, inserting an OFDM cyclic prefix into the plurality of decompressed signal samples of each baseband channel at the RF unit after computing an OFDM inverse frequency domain transform of the plurality of decompressed coefficients to form a plurality of decompressed signal samples of the corresponding baseband channel at the RF unit.

13. The method of claim 7, wherein the decompressing further comprises, inserting an OFDM cyclic prefix into the sequence of decompressed signal samples prior to providing the decompressed signal samples to the DUC for forming the upconverted digital signal.

14. In a base transceiver system of an OFDM wireless communication network, including a radio frequency (RF) unit coupled to an antenna to receive an analog signal and a baseband unit coupled to the RF unit by a serial data link, the analog signal representing a plurality of antenna-carrier channels, the RF unit including an analog to digital converter (ADC) that converts the analog signal to a digital signal and a digital down converter (DDC) that downconverts the digital signal to a plurality of baseband channels, each baseband channel corresponding to one of the antenna-carrier channels and having a sequence of signal samples, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, wherein a baseband processor of the baseband unit performs signal processing operations, an apparatus for data transfer from the RF unit to the baseband unit over the serial data link, the apparatus comprising:

a plurality of compressors at the RF unit, each compressor coupled to receive the sequence of signal samples of a corresponding baseband channel output from the DDC, each of the plurality of compressors comprising;

logic to compute an OFDM frequency domain transform of a plurality of the sequence of signal samples of the corresponding baseband channel to form a plurality of frequency domain coefficients, wherein the frequency domain coefficients include a real component and an imaginary component for each of a plurality of frequency bins, wherein a length of the OFDM frequency domain transform is equal to a symbol length of the OFDM signal data;

an attenuator to adjust the frequency domain coefficients in accordance with an attenuation profile to form a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the frequency bins, wherein the attenuation profile is stored in a first memory coupled to the attenuator; and

an encoder coupled to the attenuator to encode the attenuated coefficients to form compressed coefficients;

a formatter coupled to the plurality of compressors to format the compressed coefficients of the plurality of baseband channels in accordance with a data transfer protocol;

the serial data link coupled to the formatter for transferring the compressed coefficients to the baseband processor;

the baseband unit coupled to the serial data link to receive the compressed coefficients; and

a plurality of decompressors at the baseband unit, each decompressor receiving the compressed coefficients of the corresponding baseband channel, each of the plurality of decompressors comprising;

a decoder to decode the compressed coefficients to form reconstructed attenuated coefficients;

an amplifier coupled to the decoder to increase magnitudes of a plurality of the reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients, wherein the gain profile corresponds to the attenuation profile and specifies gain levels corresponding to the frequency bins, wherein the gain profile is stored in a second memory coupled to the amplifier; and

a baseband processor of the baseband unit to apply the signal processing operations to the decompressed coefficients for each baseband channel.

15. The apparatus of claim 14, wherein the logic to compute the OFDM frequency domain transform comprises a discrete Fourier transform (DFT), a fast Fourier transform (FFT), a discrete cosine transform (DCT) or a discrete sine transform (DST).

16. The apparatus of claim 14, wherein the compressor is implemented in a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) at the RF unit.

17. The apparatus of claim 14, wherein the data transfer protocol is compatible with an Open Base Station Architecture Initiative (OBSAI) standard or a Common Public Radio Interface (CPRI) standard.

18. The apparatus of claim 14, wherein the formatter further comprises:

a plurality of mappers, each mapper receiving a sequence of the compressed coefficients from a corresponding compressor and mapping the sequence of the compressed coefficients to a sequence of data structures, the plurality of mappers producing a plurality of sequences of data structures corresponding to the plurality of baseband channels; and

a multiplexer that combines the plurality of sequences of data structures to form a sequence of multiplexed data structures representing the compressed coefficients of the plurality of baseband channels, wherein the multiplexer provides the sequence of multiplexed data structures to the serial data link.

19. The apparatus of claim 18, wherein the data structures are formed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard using a Reference Point 3 (RP3) message protocol or a Common Public Radio Interface (CPRI) standard using an antenna-carrier (AxC) container protocol.

20. The apparatus of claim 14, wherein the decompressor is implemented in a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or a programmable processor of the baseband processor.

21. The apparatus of claim 14, wherein the baseband unit further comprises:

a demultiplexer that receives the sequence of multiplexed data structures representing the compressed coefficients and reconstructs the plurality of sequences of data structures corresponding to the plurality of baseband channels; and

a plurality of demappers, each demapper receiving a corresponding sequence of data structures from the demultiplexer and extracting the sequence of the compressed coefficients of the corresponding baseband channel, wherein the plurality of demappers provides the plurality of sequences of the compressed coefficients to the plurality of decompressors.

22. The apparatus of claim 14, wherein each of the plurality of compressors further comprises, logic coupled to the output of the DDC to remove an OFDM cyclic prefix from the plurality of signal samples.

23. In a base transceiver system of an OFDM wireless communication network, including a radio frequency (RF) unit coupled to an antenna to transmit an analog signal and a baseband unit coupled to the RF unit by a serial data link, the baseband unit providing a plurality of signal samples to the RF unit, each signal sample associated with one of a plurality of baseband channels, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, the RF unit including a digital up converter (DUC) that upconverts a sequence of signal samples of each baseband channel to a corresponding one of a plurality of antenna-carrier channels to form a single upconverted digital signal and a digital to analog converter (DAC) that converts the upconverted digital signal to the analog signal, the analog signal representing the plurality of antenna-carrier channels, an apparatus for data transfer from the baseband unit to the RF unit, the apparatus comprising:

a plurality of compressors at the baseband unit, each compressor for receiving frequency domain coefficients for a plurality of baseband channels of the OFDM modulated signal data, wherein the frequency domain coefficients include a real component and an imaginary component for each of a plurality of frequency bins and for compressing frequency domain coefficients of a corresponding baseband channel, each of the plurality of compressors comprising;

an attenuator to adjust the frequency domain coefficients in accordance with an attenuation profile to form a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the frequency bins, wherein the attenuation profile is stored in a first memory coupled to the attenuator; and

an encoder coupled to the attenuator to encode the attenuated coefficients to form compressed coefficients;

a formatter coupled to the plurality of compressors to format the compressed coefficients in accordance with a data transfer protocol;

the serial data link coupled to the formatter for transferring the compressed coefficients to the RF unit;

the RF unit coupled to the serial data link to receive the compressed coefficients; and

a plurality of decompressors at the RF unit, each decompressor receiving the compressed coefficients of the corresponding baseband channel, each of the plurality of decompressors comprising;

a decoder to decode the compressed coefficients to form reconstructed attenuated coefficients;

an amplifier coupled to the decoder to increase magnitudes of a plurality of the reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients, wherein the gain profile corresponds to the attenuation profile and specifies gain levels corresponding to the frequency bins, wherein the gain profile is stored in a second memory coupled to the amplifier; and

logic coupled to the amplifier to compute an OFDM inverse frequency domain transform of the plurality of decompressed coefficients to form a plurality of decompressed signal samples of the corresponding baseband channel, wherein each decompressed signal sample includes a decompressed I sample and a decompressed Q sample, wherein a length of the OFDM frequency domain transform is equal to a symbol length of the OFDM signal data and wherein the decompressed signal samples are provided to the DUC for forming the upconverted digital signal.

24. The apparatus of claim 23, wherein the logic to compute the OFDM inverse frequency domain transform comprises an inverse frequency domain transform using a discrete inverse Fourier transform (IDFT), a inverse fast Fourier transform (IFFT), a discrete cosine transform (DCT) or a discrete sine transform (DST).

25. The apparatus of claim 23, wherein the compressor is implemented in a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) of the baseband processor.

26. The apparatus of claim 23, wherein the data transfer protocol is compatible with an Open Base Station Architecture Initiative (OBSAI) standard or a Common Public Radio Interface (CPRI) standard.

27. The apparatus of claim 23, wherein the formatter further comprises:

a plurality of mappers, each mapper receiving a sequence of the compressed coefficients from a corresponding compressor and mapping the sequence of the compressed coefficients to a sequence of data structures, the plurality of mappers producing a plurality of sequences of data structures corresponding to the plurality of baseband channels; and

a multiplexer that combines the plurality of sequences of data structures to form a sequence of multiplexed data structures representing the compressed coefficients of the plurality of baseband channels, wherein the multiplexer provides the sequence of multiplexed data structures to the serial data link.

28. The apparatus of claim 27, wherein the data structures are formed in accordance with an Open Base Station Architecture Initiative (OBSAI) standard using a Reference Point 3 (RP3) message protocol or a Common Public Radio Interface (CPRI) standard using an antenna-carrier (AxC) container protocol.

29. The apparatus of claim 23, wherein the decompressor is implemented in a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or a programmable processor at the RF unit.

30. The apparatus of claim 23, wherein the RF unit further comprises:

a demultiplexer that receives the sequence of multiplexed data structures representing the compressed coefficients and reconstructs the plurality of sequences of data structures corresponding to the plurality of baseband channels; and

a plurality of demappers, each demapper receiving a corresponding sequence of data structures from the demultiplexer and extracting the sequence of the compressed coefficients of the corresponding baseband channel, wherein the plurality of demappers provides the plurality of sequences of the compressed coefficients to the plurality of decompressors.

31. The apparatus of claim 23, wherein each of the plurality of decompressors further comprises, logic coupled to the OFDM inverse frequency domain transform to insert an OFDM cyclic prefix into the plurality of decompressed signal samples.

32. An integrated circuit device for compressing OFDM signal data for transmission over a serial data link in a base transceiver system of a wireless communication network, the integrated circuit device comprising:

logic to remove an OFDM cyclic prefix from a plurality of signal samples of the OFDM signal data;

an OFDM frequency transform unit to compute an OFDM frequency domain transform of the plurality of signal samples to generate a plurality of frequency domain coefficients for each of a plurality of frequency bins, wherein a length of the OFDM frequency domain transform is equal to a symbol length of the OFDM signal data;

an attenuator coupled to the frequency transform unit, the attenuator to adjust the plurality of frequency domain coefficients in accordance with an attenuation profile to generate a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the plurality of frequency bins; and

an encoder coupled to the attenuator, the encoder to encode the attenuated coefficients to form a plurality of compressed coefficients for transmission over the serial data link.

33. The integrated circuit device of claim 32, wherein the base transceiver system comprises at least one radio frequency (RF) unit and a baseband unit coupled to the at least one RF unit by the serial data link and wherein the integrated circuit for compressing the OFDM signal data is coupled to the at least one RF unit.

34. An integrated circuit device for decompressing a plurality of compressed coefficients received over a serial data link in a base transceiver system of a wireless communication network, the integrated circuit device comprising:

a decoder to decode the plurality of compressed coefficients to form a plurality of reconstructed attenuated coefficients;

an amplifier coupled to the decoder, the amplifier to increase a magnitude of at least one of the plurality of reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients, wherein the gain profile corresponds to an attenuation profile associated with the plurality of compressed coefficients and the gain profile specifies gain levels corresponding to a plurality of frequency bins of the compressed coefficients;

an OFDM inverse frequency domain transform unit coupled to the amplifier, the OFDM inverse frequency domain transform unit to compute an OFDM inverse frequency transform of the plurality of decompressed coefficients to generate a plurality of decompressed signal samples of the corresponding baseband channel, wherein a length of the OFDM inverse frequency domain transform is equal to a symbol length of the OFDM signal data; and

logic to insert an OFDM cyclic prefix into the plurality of decompressed signal samples.

35. The integrated circuit device of claim 34, wherein the base transceiver system comprises at least one radio frequency (RF) unit and a baseband unit coupled to the at least one RF unit by the serial data link and wherein the integrated circuit for decompressing the plurality of compressed coefficients is coupled to the at least one RF unit.

36. In a base transceiver system of a wireless communication network, a method for compressing OFDM modulated signal data at a radio frequency (RF) unit for transfer to a baseband unit over a serial data link, wherein the RF unit is connected to an antenna to receive an analog signal, the analog signal representing a plurality of antenna-carrier channels, the RF unit including an analog to digital converter (ADC) that converts the analog signal to a digital signal and a digital down converter (DDC) that downconverts the digital signal to a plurality of baseband channels, each baseband channel corresponding to one of the antenna-carrier channels and having a sequence of signal samples, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, wherein a baseband processor of the baseband unit performs signal processing operations, the method comprising:

compressing the sequence of signal samples of each baseband channel at the RF unit, wherein for each baseband channel the compressing comprises;

computing an OFDM frequency domain transform of a plurality of the sequence of signal samples of each baseband channel at the RF unit to form a plurality of frequency domain coefficients, wherein the frequency domain coefficients include a real component and an imaginary component for each of a plurality of frequency bins and wherein a length of the OFDM frequency domain transform is equal to a symbol length of the OFDM modulated signal data;

attenuating one or more of the frequency domain coefficients in accordance with an attenuation profile to form a plurality of attenuated coefficients, wherein the attenuation profile specifies attenuation levels corresponding to the frequency bins; and

encoding the attenuated coefficients to form compressed coefficients; and

formatting the compressed coefficients of the plurality of baseband channels for transfer over the serial data link.

37. In a base transceiver system of a wireless communication network, a method for decompressing OFDM modulated signal data transferred from a baseband unit over a serial data link and received at a radio frequency (RF) unit, each signal sample associated with one of a plurality of baseband channels, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, the RF unit including a digital up converter (DUC) that upconverts a sequence of signal samples of each baseband channel to a corresponding one of a plurality of antenna-carrier channels to form a single upconverted digital signal and a digital to analog converter (DAC) that converts the upconverted digital signal to an analog signal, wherein the RF unit is coupled to an antenna to transmit the analog signal, the analog signal representing the plurality of antenna-carrier channels, the method comprising:

receiving a plurality of compressed coefficients at the RF unit; and

decompressing the compressed coefficients at the RF unit, wherein for each baseband channel the decompressing comprises;

decoding the compressed coefficients to form reconstructed attenuated coefficients;

amplifying a plurality of the reconstructed attenuated coefficients in accordance with a gain profile to form a plurality of decompressed coefficients corresponding to each baseband channel, wherein the gain profile corresponds to the attenuation profile and specifies gain levels for corresponding frequency bins;

computing an OFDM inverse frequency domain transform of the plurality of decompressed coefficients to form a plurality of decompressed signal samples of the corresponding baseband channel, wherein each decompressed signal sample includes a decompressed I sample and a decompressed Q sample, wherein a length of the OFDM inverse frequency domain transform is equal to a symbol length of the OFDM signal data; and

providing the decompressed signal samples to the DUC for forming the upconverted digital signal.