COMPRESSION OF SIGNALS IN BASE TRANSCEIVER SYSTEMS

• US 20090290632A1
• Filed: 05/21/2008
• Published: 11/26/2009
• 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 8,174,428 B2
• Time in Patent Office: Days
• US Class Current: 375/240
• 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: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H
• CPC Class Codes: H04B 1/40 Circuits

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 signal samples resulting from analog to digital conversion of an analog signal received via an antenna. The RF unit transfers the compressed signal samples over the serial data link to the base station processor where they are decompressed prior to the normal signal processing operations. For the downlink, the base station processor compresses signal samples and transfers the compressed signal samples over the serial data link to the RF unit. The RF unit decompresses the compressed samples and converts the decompressed samples to an analog signal for transmission over an antenna. Compression and decompression can be incorporated into operations of conventional base stations and distributed antenna systems.

Claims

1. In a base transceiver system of a wireless communication network, a method for transferring signal data from a radio frequency (RF) unit to a base station processor over a serial data link, wherein the RF unit is coupled to an antenna to receive an analog signal modulated based on communication data and includes an analog to digital converter (ADC) that converts the analog signal to a plurality of signal samples, wherein the base station processor performs signal processing operations on the signal samples received from the RF unit, the method comprising:

compressing the signal samples output from the ADC at the RF unit to form compressed samples in accordance with a compression control parameter;

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 base station processor;

receiving the compressed samples at the base station processor; and

decompressing the compressed samples to form decompressed signal samples in accordance with a decompression control parameter, wherein the base station processor applies the signal processing operations to the decompressed signal samples.

2. The method of claim 1, 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.

3. The method of claim 1, further comprising:

calculating a sum or difference of a pair of signal samples separated by a predetermined number of sample intervals in accordance with the compression control parameter to produce a modified sample, wherein a plurality of modified samples is calculated from a plurality of pairs of signal samples; and

encoding the modified samples to form the compressed samples.

4. The method of claim 3, wherein the step of encoding includes block floating point encoding or Huffman encoding applied to the modified samples.

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 center frequency, 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 a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) of the RF unit.

8. The method of claim 2, 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.

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

decoding the compressed samples to form decoded modified samples;

reconstructing the decompressed signal samples by adding or subtracting a corresponding decoded modified sample to a first decompressed signal sample to calculate a second decompressed signal sample, the first and second decompressed signal samples corresponding to the pair of signal samples separated by the predetermined number of sample intervals, in accordance with the decompression control parameter.

10. The method of claim 9, wherein the step of decoding applies block floating point decoding or Huffman decoding to the compressed samples.

11. 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 base station processor.

12. The method of claim 1, wherein the signal processing operations comprise applying at least one of the following functions to the decompressed signal samples or to processed samples derived from the decompressed signal samples, in accordance with a modulation format of the wireless communication network:

demodulating symbols, channel decoding, despreading, diversity processing, interference cancelling, equalizing, time synchronizing, frequency synchronizing, downconverting, demultiplexing, and discrete Fourier transforming.

13. The method of claim 1, wherein the signal processing operations recover the communication data from the decompressed signal samples in accordance with a modulation format of the wireless communication network.

14. The method of claim 1, wherein the base transceiver system includes a plurality of RF units in communication with the base station 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 base station processor, wherein the base station processor applies the step of decompressing to the compressed samples received from each of the RF units to form corresponding decompressed signal samples.

15. In a base transceiver system of a wireless communication network, a method for transferring signal samples representing modulated communication data from a base station processor to an RF unit over a serial data link, the RF unit having a digital to analog converter (DAC) for converting the signal samples to an analog signal, wherein the RF unit is coupled to an antenna to transmit the analog signal, the method comprising:

compressing the signal samples at the base station processor to form compressed samples in accordance with a compression control parameter;

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

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

receiving the compressed samples at the RF unit; and

decompressing the compressed samples to form decompressed signal samples in accordance with a decompression control parameter, wherein the decompressed signal samples are provided to the DAC for conversion to the analog signal.

16. The method of claim 15, 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.

17. The method of claim 15, wherein the step of compressing further comprises:

calculating a sum or difference of a pair of signal samples separated by a predetermined number of sample intervals in accordance with the compression control parameter to produce a modified sample, wherein a plurality of modified samples is calculated from a plurality of pairs of signal samples; and

encoding the modified samples to form the compressed samples.

18. The method of claim 17, wherein the step of encoding includes block floating point encoding or Huffman encoding applied to the modified samples.

19. The method of claim 15, wherein the compression control parameter is based on one or more characteristics of the signal samples.

20. The method of claim 19, wherein the characteristic includes at least one of a center frequency, a sample rate and a modulation type of the signal samples.

21. The method of claim 15, 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 base station processor.

22. The method of claim 16, 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.

23. The method of claim 17, wherein the step of decompressing further comprises:

decoding the compressed samples to form decoded modified samples;

reconstructing the decompressed signal samples by adding or subtracting a corresponding decoded modified sample to a first decompressed signal sample to calculate a second decompressed signal sample, the first and second decompressed signal samples corresponding to the pair of signal samples separated by the predetermined number of sample intervals, in accordance with the decompression control parameter.

24. The method of claim 23, wherein the step of decoding applies block floating point decoding or Huffman decoding to the compressed samples.

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

26. The method of claim 15, wherein the signal processing operations comprise at least one of the following functions performed in accordance with a modulation format of the wireless communication network prior to said compressing the signal samples:

modulating symbols, channel coding, spreading, diversity processing, time synchronizing, frequency synchronizing, upconverting, multiplexing and inverse discrete Fourier transforming.

27. The method of claim 15, wherein the signal processing operations include modulating communication data to form the signal samples in accordance with a modulation format of the wireless communication network prior to said compressing the signal samples.

28. The method of claim 15, wherein the base transceiver system includes a plurality of RF units in communication with the base station processor via a plurality serial data links in a distributed antenna system, wherein the base station 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 base station processor to form corresponding decompressed signal samples, wherein each RF unit provides the corresponding decompressed signal samples to the DAC for conversion to the analog signal.

29. In a base transceiver system of a wireless communication network, including an RF unit coupled to an antenna to receive an analog signal modulated based on communication data and a base station processor coupled to the RF unit by a serial data link, the RF unit including an analog to digital converter (ADC) for converting the analog signal into a plurality of signal samples, wherein the base station processor performs signal processing operations on the signal samples received from the RF unit, an apparatus for data transfer from the RF unit to the base station processor, comprising:

a compressor at the RF unit coupled to receive the signal samples from the ADC and producing compressed samples in accordance with a compression control parameter;

a formatter coupled to the compressor and formatting the compressed samples for transfer over the serial data link;

the serial data link coupled to the formatter for transferring the compressed samples to the base station processor;

the base station processor coupled to the serial data link to receive the compressed samples; and

a decompressor integrated into the base station processor for decompressing the received compressed samples to form decompressed signal samples, wherein the base station processor applies the signal processing operations to the decompressed signal samples.

30. The apparatus of claim 29, wherein the compressor further comprises one of the following:

a block floating point encoder applied to the signal samples to form the compressed samples; and

a Huffman encoder applied the signal samples to form the compressed samples.

31. The apparatus of claim 29, wherein the compressor further comprises:

an arithmetic operator that add or subtracts a pair of signal samples in accordance with the compression control parameter to form a modified sample, wherein the signal samples in the pair are separated by a predetermined number of sample intervals, the arithmetic operator calculating a plurality of modified samples from a plurality of pairs of signal samples; and

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

32. The apparatus of claim 31, wherein the encoder further comprises one of the following:

a block floating point encoder applied to the modified samples to produce the compressed samples; and

a Huffman encoder applied to the modified samples to produce the compressed samples.

33. The apparatus of claim 29, wherein the compression control parameter is based on one or more characteristics of the signal samples.

34. The apparatus of claim 33, wherein the characteristic includes at least one of a center frequency, a sample rate and a modulation type of the signal samples.

35. The apparatus of claim 29, wherein the compressor is implemented in a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) coupled to receive the signal samples from the ADC.

36. The apparatus of claim 30, wherein the decompressor further comprises one of the following:

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

a Huffman decoder applied to the compressed samples to produce the decompressed signal samples.

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

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

an inverse arithmetic operator that performs inverse operations of the arithmetic operator to calculate the decompressed signal samples by adding or subtracting a corresponding decoded modified sample to a first decompressed signal sample to calculate a second decompressed signal sample, the first and second decompressed signal samples corresponding to the pair of signal samples separated by the predetermined number of sample intervals, in accordance with the decompression control parameter.

38. The apparatus of claim 37, wherein the decoder further comprises a block floating point decoder or a Huffman decoder applied to the compressed samples.

39. The apparatus of claim 29, 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 base station processor.

40. The apparatus of claim 29, wherein the base station processor applies at least one of the following signal processing operations to the decompressed signal samples or to processed samples derived from the decompressed signal samples, in accordance with a modulation format of the wireless communication network:

symbol demodulation, channel decoding, despreading, diversity processing, interference cancellation, equalization, time synchronization, frequency synchronization, downconversion, demultiplexing, and discrete Fourier transformation.

41. The apparatus of claim 29, wherein the signal processing operations recover the communication data from the decompressed signal samples in accordance with a modulation format of the wireless communication network.

42. The apparatus of claim 29, wherein a first serial data link couples the RF unit to an intermediate hub, the intermediate hub being coupled by a second serial data link to another hub or to the base station processor, wherein the intermediate hub transfers the compressed samples from the first serial data link to the second serial data link.

43. The apparatus of claim 29, wherein the base transceiver system includes a plurality of RF units in communication with the base station processor via a plurality serial data links in a distributed antenna system, each RF unit including the compressor and the formatter to provide corresponding compressed samples for transfer over the serial data links to the base station processor, the base station processor decompressing the compressed samples received from each of the RF units to form corresponding decompressed signal samples.

44. 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 base station processor coupled to the RF unit by a serial data link, the base station processor providing a plurality of signal samples representing modulated communication data to the RF unit, the RF unit including a digital to analog converter (DAC) for converting the plurality of signal samples to the analog signal, wherein the base station processor performs signal processing operations on the signal samples, an apparatus for data transfer from the base station processor to the RF unit, comprising:

a compressor integrated into the base station processor for compressing the signal samples in accordance with a compression control parameter to form compressed samples;

a formatter coupled to the compressor and formatting the compressed samples for transfer over the serial data link;

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 decompressor integrated into the RF unit for decompressing the received compressed samples to form decompressed signal samples, wherein the decompressed signal samples are provided to the DAC for conversion to the analog signal.

45. The apparatus of claim 44, wherein the compressor further comprises one of the following:

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

a Huffman encoder applied to the signal samples to produce the compressed samples.

46. The apparatus of claim 44, wherein the compressor further comprises:

an arithmetic operator that add or subtracts a pair of signal samples in accordance with the compression control parameter to form a modified sample, wherein the signal samples in the pair are separated by a predetermined number of sample intervals, the arithmetic operator calculating a plurality of modified samples from a plurality of pairs of signal samples; and

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

47. The apparatus of claim 46, wherein the encoder further comprises one of the following:

a block floating point encoder applied to the modified samples to produce the compressed samples; and

a Huffman encoder applied to the modified samples to produce the compressed samples.

48. The apparatus of claim 44, wherein the compression control parameter is based on one or more characteristics of the signal samples.

49. The apparatus of claim 48, wherein the characteristic includes at least one of a center frequency, a sample rate and a modulation type of the signal samples.

50. The apparatus of claim 44, wherein the compressor 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 base station processor.

51. The apparatus of claim 45, wherein the decompressor further comprises one of the following:

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

a Huffman decoder applied to the compressed samples to produce the decompressed signal samples.

52. The apparatus of claim 46, wherein the decompressor further comprises:

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

an inverse arithmetic operator that performs inverse operations of the arithmetic operator to calculate the decompressed signal samples by adding or subtracting a corresponding decoded modified sample to a first decompressed signal sample to calculate a second decompressed signal sample, the first and second decompressed signal samples corresponding to the pair of signal samples separated by the predetermined number of sample intervals, in accordance with the decompression control parameter.

53. The apparatus of claim 52, wherein the decoder further comprises a block floating point decoder or a Huffman decoder applied to the compressed samples.

54. The apparatus of claim 44, wherein the decompressor is implemented in a programmable processor, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) in a decompression subsystem of the RF unit.

55. The apparatus of claim 44, wherein the base station processor applies at least one of the following signal processing operations in accordance with a modulation format of the wireless communication network prior to applying the compressor to the signal samples:

symbol modulation, channel coding, spreading, diversity processing, time synchronization, frequency synchronization, upconversion and inverse discrete Fourier transformation.

56. The apparatus of claim 44, wherein the base station processor applies signal processing operations for modulating communication data to form the signal samples in accordance with a modulation format of the wireless communication network prior to applying the compressor to the signal samples.

57. The apparatus of claim 44, wherein a first serial data link couples the base station 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.

58. The apparatus of claim 44, wherein the base transceiver system includes a plurality of the RF units coupled to communicate via a plurality of serial data links with the base station processor to form a distributed antenna system, each RF unit including the decompressor to decompress corresponding compressed samples from the base station processor and providing the corresponding decompressed signal samples to the DAC.