Compression of baseband signals in base transceiver systems

• US 8,005,152 B2
• Filed: 05/21/2008
• Issued: 08/23/2011
• Est. Priority Date: 05/21/2008
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Samplify Systems Incorporated
• Inventors: Wegener, Albert W
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): PATEL, DHAVAL V
• Application Number:
  US12/124,382
• Publication Number:
  US 20110135013A1
• Time in Patent Office: 1,189 Days
• Field of Search: 375/140, 375/150, 375/256, 375/260, 375/341, 375/340
• US Class Current: 375/241
• CPC Class Codes: H03M 7/40 Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

A signal compression method and apparatus for a base transceiver system (BTS) in a wireless communication network provides efficient transfer of compressed signal samples over serial data links in the system. For the uplink, an RF unit of the BTS compresses baseband signal samples resulting from analog to digital conversion of a received analog signal followed by digital downconversion. The compressed signal samples are transferred over the serial data link to the baseband processor then decompressed prior to normal signal processing. For the downlink, the baseband processor compresses baseband signal samples and transfers the compressed signal samples to the RF unit. The RF unit decompresses the compressed samples prior to digital upconversion and digital to analog conversion to form an analog signal for transmission over an antenna. Compression and decompression can be incorporated into operations of conventional base stations and distributed antenna systems, including OBSAI or CPRI compliant systems.

Claims

1. In a base transceiver system of a wireless communication network, a method for transferring communication data for transmission to wireless subscribers, including generating signal samples of a plurality of baseband antenna-carrier channels in a baseband processor for transfer to a radio frequency (RF) unit over a serial data link, the plurality of baseband antenna-carrier channels including at least one particular baseband antenna-carrier channel comprised of signal samples for a composite of signals to be transmitted to multiple wireless subscribers, each signal sample associated with one of the plurality of baseband antenna-carrier 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 the plurality of baseband antenna-carrier channels to a plurality of upconverted antenna-carrier channels to form a single upconverted digital signal comprised of upconverted signal samples from the plurality of upconverted antenna-carrier channels, 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 upconverted antenna-carrier channels, the method comprising:

compressing the signal samples corresponding to each baseband antenna-carrier channel, including the at least one particular baseband antenna-carrier channel, to form compressed samples in accordance with a compression control parameter wherein each compressed sample includes a compressed I sample and a compressed Q sample, wherein the compressed samples for the particular baseband antenna-carrier channel represent the composite of signals to be transmitted to the multiple wireless subscribers;

formatting the compressed samples for transfer over the serial data link;

transferring the compressed samples over the serial data link to the RF unit;

receiving the compressed samples at the RF unit; and

decompressing the compressed samples in accordance with a decompression control parameter to form decompressed signal samples corresponding to each baseband antenna-carrier channel, wherein each decompressed sample includes a decompressed I sample and a decompressed Q sample, wherein the decompressed signal samples for the at least one particular baseband antenna-carrier channel reconstruct the composite of signals to be transmitted to the multiple wireless subscribers, and wherein the decompressed signal samples are provided to the DUC for forming the upconverted digital signal.

2. The method of claim 1, wherein the step of compressing further comprises:

applying block floating point encoding to the signal samples to form the compressed samples.

3. The method of claim 1, wherein the step of compressing further comprises:

calculating first or higher order differences of the signal samples to form a sequence of difference samples in accordance with the compression control parameter; and

encoding the difference samples to form the compressed samples.

4. The method of claim 3, wherein the step of encoding includes block floating point encoding.

5. The method of claim 1, wherein the compression control parameter is based on one or more characteristics of the signal samples.

6. The method of claim 5, wherein the characteristic includes at least one of a sample rate, a sample width, a bandwidth and a modulation type of the signal samples.

7. The method of claim 1, wherein the step of compressing is performed in a compression subsystem implemented in programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) of the baseband processor.

8. The method of claim 1, wherein the steps of formatting, transferring and receiving are performed in accordance with one of the following industry standards:

an Open Base Station Architecture Initiative (OBSAI) standard; and

a Common Public Radio Interface (CPRI) standard.

9. The method of claim 1, wherein the step of formatting further comprises:

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

multiplexing the plurality of sequences of data structures corresponding to the plurality of baseband antenna-carrier channels to form a sequence of multiplexed data structures representing the compressed samples for the step of transferring.

10. The method of claim 9, wherein the step of mapping further comprises:

mapping the sequence of the compressed samples corresponding to each baseband antenna-carrier channel to a sequence of Ethernet MAC frames; and

mapping the sequence of Ethernet MAC frames to the sequence of data structures corresponding to each baseband antenna-carrier channel.

11. The method of claim 9, wherein the data structures are formed in accordance with one of the following:

an Open Base Station Architecture Initiative (OBSAI) standard, wherein the data structures are in accordance with a Reference Point 3(RP3) message protocol; and

a Common Public Radio Interface (CPRI) standard wherein the data structures are in accordance with an antenna-carrier (AxC) container protocol.

12. The method of claim 2, wherein the step of decompressing further comprises:

applying block floating point decoding to the compressed samples to form the decompressed signal samples in accordance with the decompression control parameter.

13. The method of claim 3, wherein the step of decompressing further comprises:

decoding the compressed samples to form decoded difference samples; and

integrating the decoded difference samples to form the decompressed signal samples.

14. The method of claim 1, wherein the step of decoding further comprises applying block floating point decoding.

15. The method of claim 1, wherein the step of decompressing is performed in a decompression subsystem implemented in a programmable processor, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) of the RF unit.

16. The method of claim 9, wherein the step of receiving further comprises the following steps:

demultiplexing the sequence of multiplexed data structures to reconstruct the plurality of sequences of data structures corresponding to the plurality of baseband antenna-carrier channels; and

extracting the sequence of the compressed samples from the sequence of data structures corresponding to each baseband antenna-carrier channel.

17. The method of claim 10, wherein the step of receiving further comprises the following steps:

demultiplexing the sequence of multiplexed data structures to reconstruct the plurality of data structures corresponding to each baseband antenna-carrier channel;

reconstructing the plurality of Ethernet MAC frames from the plurality of data structures; and

extracting the compressed samples corresponding to each baseband antenna-carrier channel from the corresponding plurality of Ethernet MAC frames.

18. The method of claim 1, wherein the base transceiver system includes a plurality of RF units in communication with the baseband processor via a plurality serial data links in a distributed antenna system, wherein the baseband processor transfers the compressed samples over the corresponding serial data link to each RF unit, each RF unit applying the step of decompressing to the compressed samples received from the baseband processor to form corresponding decompressed signal samples, wherein each RF unit provides the corresponding decompressed signal samples to the DUC to form the upconverted digital signal.

19. In a base transceiver system of a wireless communication network, including a radio frequency (RF) unit coupled to an antenna to transmit an analog signal and a baseband processor coupled to the RF unit by a serial data link, the baseband processor providing a plurality of signal samples for a plurality of baseband antenna-carrier channels derived from communication data for transmission to wireless subscribers, each signal sample associated with one of the plurality of baseband antenna-carrier channels, wherein each signal sample includes an in-phase (I) sample and a quadrature (Q) sample, the plurality of baseband antenna-carrier channels including at least one particular baseband antenna-carrier channel comprised of signal samples for a composite of signals to be transmitted to multiple wireless subscribers, the RF unit including a digital up converter (DUC) that upconverts the signal samples of the plurality of baseband antenna-carrier channels to a plurality of upconverted 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 upconverted antenna-carrier channels, an apparatus for data transfer from the baseband processor to the RF unit, comprising:

a plurality of compressors, each compressor compressing signal samples of a corresponding baseband antenna-carrier channel in accordance with a compression control parameter to form compressed samples, wherein each compressed sample includes a compressed I sample and a compressed Q sample, one of the plurality of compressors compressing signal samples of the at least one particular baseband antenna-carrier channel, and wherein the compressed samples for the particular baseband antenna-carrier channel represent the composite of signals to be transmitted to the multiple wireless subscribers;

a formatter coupled to the plurality of compressors and formatting the compressed samples in accordance with a data transfer protocol;

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

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

a plurality of decompressors at the RF unit, each decompressor receiving the compressed samples of the corresponding baseband antenna-carrier channel and forming decompressed signal samples, wherein each decompressed signal sample includes a decompressed I sample and a decompressed Q sample, wherein the decompressed signal samples for the at least one particular baseband antenna-carrier channel reconstruct the composite of signals to be transmitted to the multiple wireless subscribers, and wherein the decompressed signal samples are provided to the DUC for forming the upconverted digital signal.

20. The apparatus of claim 19, wherein the compressor further comprises:

a block floating point encoder applied to the signal samples to produce the compressed samples.

21. The apparatus of claim 19, wherein the compressor further comprises:

a difference operator that calculates first or higher order differences of the signal samples to form a sequence of difference samples in accordance with the compression control parameter; and

an encoder applied to the difference samples to produce the compressed samples.

22. The apparatus of claim 21, wherein the encoder further comprises:

a block floating point encoder applied to the difference samples to produce the compressed samples.

23. The apparatus of claim 19, wherein the compression control parameter is based on one or more characteristics of the signal samples.

24. The apparatus of claim 23, wherein the characteristic includes at least one of a sample rate, a sample width, a bandwidth and a modulation type of the signal samples.

25. The apparatus of claim 19, wherein the plurality of compressors is implemented in a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) in a compression subsystem of the baseband processor.

26. The apparatus of claim 19, wherein the base transceiver system is compatible with one of the following industry standards:

an Open Base Station Architecture Initiative (OBSAI) standard; and

a Common Public Radio Interface (CPRI) standard.

27. The apparatus of claim 19, wherein the formatter further comprises:

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

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

28. The apparatus of claim 27, wherein the mapper further comprises:

an Ethernet frame mapper that maps the sequence of the compressed samples to a sequence of Ethernet MAC frames; and

a second mapper that maps the sequence of Ethernet MAC frames to the sequence of data structures.

29. The apparatus of claim 27, wherein the data structures are formed in accordance with one of the following:

an Open Base Station Architecture Initiative (OBSAI) standard, wherein the data structures are formed in accordance with a Reference Point 3(RP3) message protocol; and

a Common Public Radio Interface (CPRI) standard wherein the data structures are formed in accordance with an antenna-carrier (AxC) container protocol.

30. The apparatus of claim 20, wherein the decompressor further comprises:

a block floating point decoder applied to the compressed samples to produce the decompressed signal samples.

31. The apparatus of claim 21, wherein the decompressor further comprises:

a decoder applied to the compressed samples to produce decoded difference samples; and

an integration operator applied to the decoded difference samples to form the decompressed signal samples.

32. The apparatus of claim 31, wherein the decoder further comprises a block floating point decoder applied to the compressed samples.

33. The apparatus of claim 19, wherein the decompressor is implemented in a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or a programmable processor in a decompression subsystem of the RF unit.

34. The apparatus of claim 27, wherein the RF unit further comprises:

a demultiplexer that receives the sequence of multiplexed data structures representing the compressed samples and reconstructs the plurality of sequences of data structures corresponding to the plurality of baseband antenna-carrier 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 samples of the corresponding baseband antenna-carrier channel, wherein the plurality of demappers provides the plurality of sequences of the compressed samples to the plurality of decompressors.

35. The apparatus of claim 28, further comprising:

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

a plurality of Ethernet frame demappers, each Ethernet frame demapper receiving a corresponding sequence of data structures from the demultiplexer and reconstructing the sequence of Ethernet MAC frames of the corresponding baseband antenna-carrier channel; and

a plurality of demappers, each demapper receiving the corresponding sequence of Ethernet MAC frames and extracting the sequence of the compressed samples of the corresponding baseband antenna-carrier channel, wherein the plurality of demappers provides the plurality of sequences of the compressed samples to the plurality of decompressors.

36. The apparatus of claim 19, wherein a first serial data link couples the baseband processor to an intermediate hub, the intermediate hub being coupled by a second serial data link to another hub or to the RF unit, wherein the intermediate hub transfers the compressed samples from the first serial data link to the second serial data link.

37. The apparatus of claim 19, wherein the base transceiver system includes a plurality of the RF units coupled to communicate via a plurality of serial data links with the baseband processor to form a distributed antenna system, each RF unit including the plurality of decompressors to decompress corresponding compressed samples received from the baseband processor and providing the corresponding decompressed signal samples to the DUC for forming the upconverted digital signal.