COMPRESSION OF BASEBAND SIGNALS IN BASE TRANSCEIVER SYSTEMS

• US 20110280209A1
• Filed: 07/26/2011
• Published: 11/17/2011
• 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.
• Granted Patent: US 8,705,634 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• 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. A base transceiver system, comprising:

a base station processor, an RF unit, and a data transfer link between the base station processor and the RF unit;

the RF unit being connected to the data transfer link, and to an antenna to receive an analog uplink signal having one or more carriers, the RF unit being configured to translate each of said one or more carriers from the analog uplink signal into one or more uplink digital baseband antenna-carrier channels, each uplink digital baseband antenna-carrier channel having a sequence of uplink signal samples that are sent to the data transfer link, wherein each uplink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, and the RF unit also being configured to translate one or more downlink digital baseband antenna-carrier channels received from the data transfer link and having a sequence of downlink signal samples, wherein each downlink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, into an analog downlink signal having one or more carriers for transmission by an antenna;

the base station processor being connected to the data transfer link, and including a communication interface adapted for connection to a source of downlink signals, and to a destination for uplink signals, the base station processor being configured to translate the downlink signal from the communications interface to one or more downlink digital baseband antenna-carrier channels and having a sequence of downlink signal samples, wherein each downlink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, and to transmit the sequence of downlink digital baseband antenna-carrier channels across the data transfer link to the RF unit, and to process one or more uplink digital baseband antenna-carrier channels received from the RF unit across the data transfer link to produce uplink data for delivery across the communications interface; and

further including

compression and decompression logic at the RF unit and at the base station processor arranged for transfer of compressed versions of the uplink and downlink digital baseband antenna-carrier channels across the data transfer link.

2. The base transceiver system of claim 1, wherein the compression and decompression logic includes

logic at the RF unit to compress the signal samples of the one or more uplink digital baseband antenna-carrier channels to form compressed uplink samples, to format the compressed uplink samples for transfer over the data transfer link, and to transfer the compressed uplink samples over the data transfer link from the RF unit to the base station processor;

logic at the base station processor to decompress the compressed uplink samples corresponding to each uplink digital baseband antenna-carrier channel to form decompressed uplink signal samples of the corresponding uplink digital baseband antenna-carrier channel;

logic at the base station processor to compress the signal samples corresponding to each downlink digital baseband antenna-carrier channel to form compressed downlink samples, to format the compressed downlink samples for transfer over the data transfer link, and to transfer the compressed downlink samples over the data transfer link to the RF unit; and

logic at the RF unit to decompress the compressed downlink samples to form decompressed downlink signal samples corresponding to each downlink digital baseband antenna-carrier channel.

3. The base transceiver system of claim 1, wherein the data transfer link comprises a serial link.

4. The base transceiver system of claim 1, wherein the one or more downlink digital baseband antenna-carrier signals includes at least one digital baseband antenna-carrier signal comprised of signal samples for a composite of signals to be transmitted to multiple wireless subscribers.

5. The base transceiver system of claim 1, wherein the one or more uplink digital baseband antenna-carrier signals for uplink includes at least one digital baseband antenna-carrier signal comprised of signal samples for a composite of signals received from multiple wireless subscribers.

6. The base transceiver system of claim 1, wherein the data transfer link is compliant with one of a Common Public Radio Interface (CPRI) standard and an Open Base Station Architecture Initiative (OBSAI) standard.

7. The base transceiver system of claim 1, including at least one additional RF unit connected to the data transfer link, and including compression and decompression logic arranged for transfer of compressed versions of uplink and downlink digital baseband antenna-carrier channels across the data transfer link.

8. The base transceiver system of claim 7, wherein the data transfer link comprises one or more hubs.

9. The base transceiver system of claim 7, wherein the data transfer link comprises a physical layer link between one of said at least one additional RF units and said RF unit, and a physical layer link between said RF unit and the base station processor.

10. The base transceiver system of claim 1, including at least one additional RF unit connected to the base station processor by at least an additional data transfer link, and including compression and decompression logic arranged for transfer of compressed versions of uplink and downlink digital baseband antenna-carrier channels across the at least one additional data transfer link.

11. The base transceiver system of claim 1, wherein the analog uplink signal includes a plurality of carriers, and wherein the compression and decompression logic includes logic for compression and decompression of each of the plurality of carriers individually, and a multiplexer at the RF unit and a de-multiplexer at the base station processor arranged for interleaving the transfer of compressed versions of the uplink digital baseband antenna-carrier channels for the individual carriers across the data transfer link.

12. The base transceiver system of claim 1, wherein the compression and decompression logic is configurable in response to one or more of sample rate, a sample width, a bandwidth and a modulation type for the antenna carrier channels.

13. A base transceiver system, comprising:

a base station processor, a plurality of antenna nodes, and a data transfer network connected to the base station processor and the plurality of antenna nodes;

each of the plurality of antenna nodes including an antenna and an RF unit connected to the antenna, the RF unit arranged to receive an analog uplink signal having one or more carriers, the RF unit being configured to translate each of said one or more carriers from the analog uplink signal into one or more uplink digital baseband antenna-carrier channels, each uplink digital baseband antenna-carrier channel having a sequence of uplink signal samples that are sent to the data transfer network, wherein each uplink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, and the RF unit also being configured to translate one or more downlink digital baseband antenna-carrier channels received from the data transfer network and having a sequence of downlink signal samples, wherein each downlink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, into an analog downlink signal having one or more carriers for transmission by an antenna;

the base station processor being connected to the data transfer network, and including a communication interface adapted for connection to a source of downlink signals, and to a destination for uplink signals, the base station processor being configured to translate the downlink signal from the communications interface to a plurality of downlink digital baseband antenna-carrier channels each having a sequence of downlink signal samples, wherein each downlink signal sample includes an in-phase (I) sample and a quadrature (Q) sample, and to transmit the sequences of downlink digital baseband antenna-carrier channels across the data transfer network to RF units of the plurality of antenna nodes, and to process one or more uplink digital baseband antenna-carrier channels received from the plurality of antenna nodes across the data transfer network to produce uplink data for delivery across the communications interface; and

further including

compression and decompression logic at the RF units of the plurality of antenna nodes and at the base station processor arranged for transfer of compressed versions of the uplink and downlink digital baseband antenna-carrier channels across the data transfer network.

14. The base transceiver system of claim 13, wherein the compression and decompression logic includes

logic at the RF units to compress the signal samples of the one or more uplink digital baseband antenna-carrier channels to form compressed uplink samples, to format the compressed uplink samples for transfer over the data transfer network, and to transfer the compressed uplink samples over the data transfer network from the RF unit to the base station processor;

logic at the base station processor to decompress the compressed uplink samples corresponding to each uplink digital baseband antenna-carrier channel to form decompressed uplink signal samples of the corresponding uplink digital baseband antenna-carrier channel;

logic at the base station processor to compress the signal samples corresponding to each downlink digital baseband antenna-carrier channel to form compressed downlink samples, to format the compressed downlink samples for transfer over the data transfer network, and to transfer the compressed downlink samples over the data transfer network to the RF unit; and

logic at the RF units to decompress the compressed downlink samples to form decompressed downlink signal samples corresponding to each downlink digital baseband antenna-carrier channel.

15. The base transceiver system of claim 13, wherein the data transfer network comprises one or more serial links.

16. The base transceiver system of claim 13, wherein the plurality of downlink digital baseband antenna-carrier signals includes at least one digital baseband antenna-carrier signal comprised of signal samples for a composite of signals to be transmitted to multiple wireless subscribers.

17. The base transceiver system of claim 13, wherein the one or more uplink digital baseband antenna-carrier signals for uplink at each of the plurality of antenna nodes includes at least one digital baseband antenna-carrier signal comprised of signal samples for a composite of signals received from multiple wireless subscribers.

18. The base transceiver system of claim 13, wherein the data transfer network is compliant with one of a Common Public Radio Interface (CPRI) standard and an Open Base Station Architecture Initiative (OBSAI) standard.

19. The base transceiver system of claim 13, wherein the data transfer network comprises one or more hubs.

20. The base transceiver system of claim 13, wherein the data transfer network comprises a physical layer link between first and second RF units of the plurality of antenna nodes, and a physical layer link between said second RF unit and the base station processor.

21. The base transceiver system of claim 13, wherein the data transfer network comprises a first physical layer link between a first RF unit of the plurality of antenna nodes and the base station processor, and a second physical layer link between a second RF unit of the plurality of antenna nodes and the base station processor.

22. The base transceiver system of claim 13, wherein the analog uplink signal includes a plurality of carriers, and wherein the compression and decompression logic includes logic for compression and decompression of each of the plurality of carriers individually, and a multiplexer at the RF units and a de-multiplexer at the base station processor arranged for interleaving the transfer of compressed versions of the uplink digital baseband antenna-carrier channels for the individual carriers across the data transfer network.

23. The base transceiver system of claim 13, wherein the compression and decompression logic is configurable in response to one or more of sample rate, a sample width, a bandwidth and a modulation type for the antenna carrier channels.

24. In a base transceiver system of a wireless communication network, a method for transferring signal data from a radio frequency (RF) unit to a baseband processor 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, and wherein the baseband processor performs signal processing operations on the signal samples received from the RF unit, the method comprising:

compressing the signal samples of each baseband channel at the RF unit 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;

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

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

receiving the compressed samples at the baseband processor;

decompressing the compressed samples corresponding to each baseband channel in accordance with a decompression control parameter to form decompressed signal samples of the corresponding baseband channel, wherein each decompressed signal sample includes a decompressed I sample and a decompressed Q sample, wherein the baseband processor applies the signal processing operations to the decompressed signal samples for each baseband channel.

25. The method of claim 24, wherein the step of compressing further comprises one of the following steps:

applying block floating point encoding to the signal samples to form the compressed samples; and

applying Huffman encoding to the signal samples to form the compressed samples.

26. The method of claim 24, 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.

27. The method of claim 26, wherein the step of encoding includes block floating point encoding or Huffman encoding applied to the difference samples.

28. The method of claim 24, wherein the compression control parameter is based on one or more characteristics of the signal samples.

29. The method of claim 28, wherein the characteristic includes at least one of a sample rate, a sample width, a bandwidth and a modulation type of the signal samples.

30. The method of claim 24, wherein the step of compressing is performed in a compression subsystem implemented in a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) of the RF unit.

31. The method of claim 24, 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.

32. The method of claim 24, wherein the step of formatting further comprises:

mapping a sequence of the compressed samples 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 the data structures corresponding to the plurality of baseband channels to form a sequence of multiplexed data structures representing the compressed samples for the step of transferring.

33. The method of claim 32, wherein the step of mapping further comprises:

mapping the sequence of the compressed samples corresponding to each baseband 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 channel.

34. The method of claim 32, 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.

35. The method of claim 25, wherein the step of decompressing further comprises one of the following:

applying block floating point decoding to the compressed samples to form the decompressed signal samples; and

applying Huffman decoding to the compressed samples to form the decompressed signal samples.

36. The method of claim 26, 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.

37. The method of claim 36, wherein the step of decoding further comprises applying block floating point decoding or Huffman decoding to the compressed samples.

38. The method of claim 24, 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 baseband processor.

39. The method of claim 32, 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 channels; and

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

40. The method of claim 33, 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 channels;

reconstructing the sequence of Ethernet MAC frames from the sequence of data structures corresponding to each baseband channel; and

extracting the sequence of the compressed samples corresponding to each baseband channel from the corresponding sequence of Ethernet MAC frames.

41. The method of claim 24, 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, each RF unit performing the steps of compressing the signal samples, formatting the compressed samples and transferring the compressed samples over the serial data link to the baseband processor, wherein the baseband processor applies the step of decompressing to the compressed samples received from each of the RF units to form corresponding decompressed signal samples.