WO2013084058A1 - Method for compressing/decompressing multi -carrier modulation signal and corresponding compressor/decompressor - Google Patents

Method for compressing/decompressing multi -carrier modulation signal and corresponding compressor/decompressor

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Publication number
WO2013084058A1
WO2013084058A1 PCT/IB2012/002678 IB2012002678W WO2013084058A1 WO 2013084058 A1 WO2013084058 A1 WO 2013084058A1 IB 2012002678 W IB2012002678 W IB 2012002678W WO 2013084058 A1 WO2013084058 A1 WO 2013084058A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
domain
signal
carrier modulation
modulation signal
Prior art date
Application number
PCT/IB2012/002678
Other languages
French (fr)
Inventor
Zhaojun Xu
Gang A. SHEN
Xiobing LENG
Wu Zheng
Francis Dominique
Dragan Samardzija
Original Assignee
Alcatel Lucent
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcatel Lucent filed Critical Alcatel Lucent
Publication of WO2013084058A1 publication Critical patent/WO2013084058A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2634—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
    • H03M7/3059—Digital compression and data reduction techniques where the original information is represented by a subset or similar information, e.g. lossy compression
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
    • H03M7/3068—Precoding preceding compression, e.g. Burrows-Wheeler transformation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2634—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
    • H04L27/26362—Subcarrier weighting equivalent to time domain filtering, e.g. weighting per subcarrier multiplication

Definitions

  • the present invention relates to a mobile communication technology, and more specifically, to a method for compressing/decompressing a multi-carrier modulation signal and a compressor/decompressor.
  • the baseband processing unit (BBU) and a remote radio-frequency head (RRH) are separate geographically, which may be connected via a wired network such as an optical network or Ethernet network and perform data exchange via an open base station architecture protocol (OBSAI) or a common public radio interface (CPRI), so as to transmit original time-domain baseband signals over these wired connections.
  • OBSAI open base station architecture protocol
  • CPRI common public radio interface
  • LTE Long Term Evolution
  • LTE-A Long Term Evolution-Advanced
  • a multi-carrier modulation signal in a wireless communication system for example, of an orthogonal frequency division multiplexing (OFDM) or DFT-spread OFDM (DFT-S-OFDM) modulation adopted in an LTE/LTE-A system, it would be more effective to compress in a frequency domain.
  • OFDM orthogonal frequency division multiplexing
  • DFT-S-OFDM DFT-spread OFDM
  • a higher compression ratio can be achieved through a compression algorithm designed for characteristics of a received uplink multi-carrier modulation signal.
  • the received uplink multi-carrier modulation signal has a wide dynamic range in time domain, while a small dynamic range in frequency domain; therefore, it would be more advantageous to perform compression in the frequency domain.
  • the received signal would have noise loss.
  • a quantization with an over high accuracy would not bring any gain; thus, a low bit width quantization may be adopted.
  • a frequency-domain compression may be performed to independently quantize the signal over the different sub-carriers, and they do not affect each other.
  • user signal over the different sub-carriers would mix and overlap with each other; further, a user signal with a high-power has a greater impact on the quantization operation, thereby impairing a low-power user signal. Therefore, in this case, the frequency-domain compression is also more advantageous over the time-domain compression.
  • the present invention effectively utilizes the characteristics of a multi-carrier modulation signal, such as independence between sub-carriers, frequency selectivity channels, etc., and provides a method for compressing/decompressing a multi-carrier modulation signal and a compressor/decompressor.
  • the multi-carrier modulation signal is first subjected to a time-frequency domain transformation to be transformed to a frequency-domain signal and then a low- loss compression in the frequency domain, and thereby a bandwidth required for transmitting the compressed signal is greatly reduced.
  • a signal transmitted over a wired network has to be first subjected to frequency-domain decompression and then a conventional baseband signal processing.
  • a method for compressing a multi-carrier modulation signal comprising: transforming a time-domain multi-carrier modulation signal to a frequency domain multi-carrier modulation signal through a time-frequency domain transformation processing; compressing the frequency-domain multi-carrier modulation signal; packaging and transmitting the compressed multi-carrier modulation signal.
  • the compressing the frequency-domain multi-carrier modulation signal comprises removing a null sub-carrier.
  • the compressing the frequency-domain multi-carrier modulation signal comprises performing low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
  • the compressing the frequency-domain multi-carrier modulation signal comprises extracting a common factor per group for the frequency-domain multi-carrier modulation signal.
  • the performing low-order bit truncation on the frequency-domain multi-carrier modulation signal comprises: performing noise level estimation on the multi-carrier modulation signal; determining an appropriate truncation bit number based on the noise level estimation and in the case of guaranteeing that performance loss caused by the low-order bit truncation is acceptable, and truncating the truncation bit number of low-order bits.
  • the performing high-order bit truncation on the frequency-domain multi-carrier modulation signal comprises: performing signal dynamic range statistics per group on the frequency-domain multi-carrier modulation signal; determining a high-order bit truncation number based on a maximal value of each group of signal levels or an average value of each group of signal levels, and truncating the bit truncation number of high-order bits.
  • the process of transforming a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through a time- frequency domain transformation processing comprises: frequency band moving for moving the RACH preamble signal to a center of a frequency band; decimating and filtering for filtering the time-domain multi-carrier modulation signal and decimating samples; time- frequency domain transformation processing for determining an appropriate FFT window, performing an FFT operation, and obtaining a RACH sequence of the frequency domain.
  • the null sub-carrier comprises a signal on a guard band, a direct current (DC) sub-carrier, or an unscheduled resource block.
  • a method for decompressing a multi-carrier modulation signal comprising: parsing a received compression packet to obtain a compressed signal; performing frequency-domain decompression on the compressed signal.
  • the frequency-domain decompression comprises performing sign bit extension on the compressed truncated signal over each sub-carrier.
  • the performing frequency-domain decompression comprises performing amplification by multiplying the compressed signal on each group of sub-carriers by a common factor.
  • a frequency-domain compressor comprising: a time- frequency domain transformation processing unit configured to transform a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through an FFT processing; a compression processing unit configured to compressing the frequency-domain multi-carrier modulation signal; a signal package and transmission unit configured to package and transmit the compressed multi-carrier modulation signal.
  • the compression processing unit comprises a null sub-carrier removal processing unit configured to remove a null sub-carrier in the frequency-domain multi-carrier modulation signal.
  • the compression processing unit comprises a bit truncation unit configured to perform low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
  • the compression processing unit comprises a common factor extraction unit configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal.
  • the bit truncation unit comprises a level estimation unit configured to perform noise level estimation on the multi-carrier modulation signal; a low-order truncation bit number determination unit configured to determine an appropriate low-order truncation bit number based on the estimated noise level outputted from the level estimation unit and in the case of guaranteeing performance loss caused by low-order bit truncation is acceptable; a low-order bit truncation unit configured to truncate, based on the determined low-order truncation bit number, the low-order truncation bit number of low-order bits.
  • the bit truncating unit comprises: a signal dynamic range statistics unit configured to perform signal dynamic range statistics per group on the multi-carrier modulation signal; a high-order truncation bit number determination unit configured to determine an appropriate high-order truncation bit number based on a maximal value of each group of signal levels or an average value of each group of signal levels; a high-order bit truncation unit configured to truncate, based on the high-order truncation bit number, the high-order truncation bit number of high-order bits.
  • the time- frequency domain transformation processing unit further comprises: a frequency band movement unit configured to move a RACH preamble signal to a center of a frequency band; a decimation and filtering unit configured to filter the time-domain multi-carrier modulation signal and decimate samples;
  • the null sub-carrier comprises a signal on a guard band, a DC sub-carrier, or an unscheduled resource block.
  • the compressor is configured on a remote radio frequency head device.
  • a frequency domain decompressor comprising: a parsing unit configured to parse a received compression packet to obtain a compressed signal; and a frequency-domain decompression unit configured to perform frequency-domain decompression on the compressed signal outputted from the parsing unit.
  • the frequency-domain decompression unit comprises a common factor per group multiplication amplification unit configured to perform amplification by multiplying the compressed signal over each group of sub-carriers by a common factor.
  • the frequency-domain decompression unit comprises a sign bit extension unit configured to perform sign bit extension on the compressed truncated signal over each sub-carrier.
  • the frequency-domain decompressor is configured on a baseband processing device.
  • a system for processing an uplink multi-carrier modulation signal comprising: a remote radio frequency head, RRH, device comprising a frequency-domain compressor; a baseband processing device comprising a frequency-domain decompressor; and an optical network or an Ethernet network for transmitting a signal between the remote radio frequency head, RRH, device and the baseband processing device.
  • FIG. 1 shows a schematic diagram of a method for compressing a time-domain signal in LightRadio of the prior art
  • FIG. 2 shows a schematic diagram of a compression method of Samplify Corporation in the prior art
  • FIG. 3 shows a schematic diagram of a system for processing an uplink multi-carrier modulation signal according to embodiments of the present invention
  • Figs. 4a, 4b , 4c, 4d, 4e, and 4f show schematic flow charts of a frequency-domain compression of different compression schemes according to embodiments of the present invention, respectively;
  • Fig. 5 shows a schematic diagram of RACH sequence extraction according to embodiments of the present invention.
  • Fig. 6 shows a principle diagram of common factor extraction
  • Fig. 7 shows a schematic diagram of an adaptive quantization principle for bit truncation according to embodiments of the present invention
  • FIGs. 8a and 8b show schematic diagrams of low-order bit truncation and high-order bit truncation according to embodiments of the present invention, respectively;
  • FIGs. 9a and 9b show schematic diagrams of package formats of a compressed signal according to embodiments of the present invention.
  • Figs. 10a and 10b show schematic flow charts of frequency-domain decompression of different decompression schemes according to embodiments of the present invention, respectively;
  • FIGs. 11a, l ib, 11c, l id, l ie and l lf show structural schematic diagrams of frequency-domain compressors of different compression schemes according to embodiments of the present invention, respectively;
  • Figs. 12a, 12b and 12c show structural schematic diagrams of frequency-domain decompressors of different decompression schemes according to embodiments of the present invention
  • Table 1 shows sampling coefficients for different system bandwidths
  • Table 2 shows determining low-order truncation bit numbers based on different noise levels
  • Table 3 shows a performance simulation result according to embodiments of the present invention.
  • Fig. 3 shows a schematic diagram of a system for processing an uplink multi-carrier modulation signal.
  • a time-frequency domain transformation processing unit 31 1 of a frequency compressor 310 first performs time-frequency domain transformation on the received uplink multi-carrier modulation signal, and then a compression processing unit 312 performs signal compression in the frequency domain; the compressed signal is transmitted to a BBU via a wired network and then subjected to baseband signal processing after frequency-domain decompression at a frequency-domain decompressor 320 of the BBU.
  • Figs. 4 a, 4b , 4 c , 4 d, 4 e , and 4 f show s chematic flow charts of frequency-domain compression of different compression schemes, wherein Fig. 4a shows a schematic flow chart in general.
  • the time- frequency domain transformation unit is implemented on a remote radio head (RRH) instead of a baseband processing unit (BBU), i.e., at step S401, the time- frequency domain signal transformation is performed on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • RRH remote radio head
  • BBU baseband processing unit
  • an appropriate FFT Fast Fourier Transformation
  • PUSCH Physical Uplink Shared Channel
  • PUCCH Physical Uplink Control Channel
  • SRS Sounding Reference Symbol
  • the time-frequency domain signal transformation may be implemented by RACH front-end processing, comprising the following steps.
  • Frequency band moving moving the RACH preamble signal to a center of a frequency band which is a pass band of the following decimation filter.
  • the offset information of the frequency band occupied by the RACH preamble signal may be notified by the BBU.
  • (c) 2048-point FFT determining an appropriate FFT window, performing a 2048-point FFT operation, and obtaining a RACH sequence with a length of 839 after transformation.
  • the RACH sequence with a length of 839 may be extracted as shown in Fig. 5.
  • the frequency-domain compression may adopt a method of removing a null sub-carrier, a method of extracting a common factor per group, or a method of high-order and/or low-order bit truncation, or a combination of the method of removing a null sub-carrier and the method of extracting a common factor per group, or a combination of removing a null sub-carrier and the method of high-order and/or low-order bit truncation.
  • Fig. 4b adopts the method of removing a null sub-carrier, specifically, removing the signal on a guard band, a direct current (DC) sub-carrier, and an unscheduled resource block to perform frequency-domain compression.
  • Some sub-carriers do not bear any information:
  • (b) unscheduled sub-carriers the base station schedules radio resources based on traffic requirements, and these sub-carriers are not used.
  • RRH using a simple bitmap based on resource scheduling information. For example, an LTE system with a bandwidth of 20MHz divides available sub-carriers into 100 resource blocks, thus a 100-bit bitmap may be used to indicate the scheduling condition of these resource blocks.
  • the RRH removes the signals on the unscheduled sub-carriers based on the received bitmap indication and then further compresses the remaining useful signal. By removing the unscheduled sub-carrier signals, the compression ratio under a low load condition can be improved.
  • frequency-domain compression is performed by the method of extracting a common factor per group.
  • the signal on each sub-carrier within each resource block adopts the same modulation modes, they will have a common factor; both the real part and the imaginary part of the quotient of the signal divided by this common factor are very small integers that may be represented by a few bits during quantization; in order to guarantee a lossless performance, the common factor may be represented in a full precision (for example 16 bits).
  • the principle diagram of the common factor extraction is shown in Fig.
  • the common factor of each subcarrier is 1623; all sub-carrier signals are divided by 1623, and thus the real parts and the virtual parts of the sub-carriers after the common factor extraction are all very small integers which may be represented with a few bits.
  • frequency domain compression is performed by the method of high-order and/or low-order bit truncation, wherein based on system requirements, frequency-domain compression may be performed by adopting either high-order bit truncation or low-order bit truncation, or both high-order bit truncation and low-order bit truncation.
  • Fig. 7 shows an adaptive quantization principle diagram for bit truncation. By adaptively truncating low order and high order of digital signals based on the noise level estimation and received signal strength estimation, the received signal may be represented with a few bits, which merely brings little performance loss. The noise level may be estimated based on the signal on the guard band.
  • low-order bits are truncated based on the estimated noise level.
  • An appropriate truncation bit number (NL) should be selected so as to guarantee that the performance loss caused by low-order bit truncation is acceptable.
  • Table 2 shows an embodiment of determining low-order truncation bit numbers based on different noise levels.
  • high-order bits are truncated based on the maximum value of the received signal levels.
  • statistics are performed on dynamic ranges of the signals on 12 sub-carriers within each resource block, i.e., the maximum values of the real parts and imaginary parts of all complex signals, thereby determining the locations of effective sign bits and truncating the remaining high-order bits, because they are only simple repetition of effective sign bits.
  • this step may also be implemented by other means, for example, truncating the high-order bits based on the average level of the received signal.
  • Fig. 4e shows a schematic flow chart of frequency-domain compression by a combination of the method of removing null sub-carriers and the method of extracting a common factor per group.
  • the frequency-domain signal is subjected to null sub-carrier removing, and then a common factor is extracted by group.
  • the frequency-domain signals are grouped, and then a common factor is calculated and extracted.
  • the methods of removing null sub-carriers and extracting the common factor are as described above.
  • Fig. 4f shows a schematic diagram of performing frequency-domain compression by a combination of the method of removing null sub-carriers and the method of high-order and/or low-order bit truncation.
  • the methods of removing null sub-carriers and the method of high-order and/or low-order bit truncation have been described in detail above, which will not be detailed here; however, it should be noted that when combining the two methods, noise level estimation and/or receives signal strength estimation must be performed first, and then frequency-domain compression is performed by removing null sub-carriers and truncating high-order and/or low-order bits.
  • baseband signals via wired transmission for example, over a remote optical network
  • the bandwidth requirements of wired transmission for example, over a remote optical network will be greatly reduced, such that the access network deployment based on centralized processing becomes more convenient with a far lower cost.
  • step S403 After frequency-domain compression, at step S403, the compressed signal is packaged and the packaged compression packet is sent to the BBU.
  • the compressed signal after the null sub-carrier removal it may be packaged by general I/Q signals.
  • the common factor may be quantized in a full precision (for example 16 bits); the real parts and the imaginary parts of the signals after the common factor extraction may be respectively quantized by selecting an appropriate number of bits based on the modulation mode. For example, a 2-bit quantization is adopted for QPSK modulation; a 3 -bit quantization is adopted for 16QAM, and a 4-bit quantization is adopted for 64QAM.
  • the method and format for packaging are similar to that for packaging a signal after extracting the common factor per group (Fig. 9a), while for the solution of combining the method of removing a null sub-carrier and the method of high-order and/or low-order bit truncation to perform frequency-domain compression, the method and format for packaging are similar to that for packaging a signal after bit truncation (Fig. 9b).
  • the uplink signal processing does not need accurate timing synchronous information. Because the RRH has an accurate reference timing signal originated from GPS, it may control framing timing and send the compressed uplink data to the BBU at the exact time. Thus, the uplink data processing of the BBU may be set as a data driving mode such that upon the reception of the compressed data packet, the uplink data processing is initiated immediately to perform operations such as frequency-domain decompression, signal demodulation, decoding, etc.
  • Fig. 10 shows a schematic flow chart of frequency-domain decompression at the BBU side, wherein Fig. 10a corresponds to the schematic flow chart of frequency-domain decompression through performing amplification by multiplication with the common factor per group, and Fig. 10b corresponds to a schematic flow chart of frequency-domain decompression through sign-bit extension.
  • step S I 001 signal depackaging is performed to parse the received compression packet to obtain the compressed signal.
  • Fig. 10a shows a decompression scheme for frequency-domain compression through the method comprising extracting a common factor per packet.
  • each group of signals are respectively multiplied with a common factor to recover the original signal.
  • Fig. 10b shows a decompression scheme for a frequency-domain compression through the method comprising bit truncation.
  • step S1012 for truncated signals over each sub-carrier within each resource block, their sign bits are extended.
  • the number of extended bits is determined based on the specific implementation of the BBU. For example, the bits may be extended to 16 bits.
  • a decompression scheme which corresponds to frequency-domain compression adopting a combination of removing a null sub-carrier and extracting a common factor per group may be implemented with reference to the decompression scheme as shown in Fig. 10a.
  • a decompression scheme which corresponds to frequency-domain compression adopting a combination of removing null sub-carrier and truncating bits may be implemented with reference to the decompression scheme as shown in Fig. 10b.
  • uplink data processing such as signal demodulation, decoding, etc.
  • uplink signals for example, on PUSCH, PUCCH, SRS, RACH, etc., respectively.
  • Figs. 11a, l ib, 1 1c, l id, l ie, and l lf respectively show structural schematic diagrams of frequency-domain compressors representing different compression schemes according to embodiments of the present invention. Moreover, the individual frequency-domain compressor structures as shown in Fig. 11 correspond to respective frequency-domain compression flows of Fig. 4. Detailed description will be provided below.
  • Fig. 11a shows a structural schematic diagram of a general frequency-domain compressor, corresponding to 3 10 of Fig. 3.
  • the frequency-domain compressor 1 100 comprises a time-frequency domain transformation processing unit 1 101 , a compression processing unit 1102, a signal package and transmission unit 1103.
  • the time- frequency domain transformation processing unit 1101 is configured to perform time-frequency domain signal transformation on a received time domain signal to transform the time-domain signal to a frequency-domain signal.
  • a general uplink multi-carrier signal for example, on PUSCH, PUCCH, SRS, etc.
  • an appropriate FFT (fast Fourier transformation) window is determined through timing information, and then a corresponding FFT operation is performed based on system parameters.
  • the time-frequency domain transformation processing unit 1101 further comprises a frequency band movement unit and decimation and filtering unit for processing the RACH channel, wherein the frequency band movement unit is configured to move a RACH preamble signal to a center of a frequency band; and the decimation and filtering unit is configured to filter the time-domain multi-carrier modulation signal and decimate samples. Then, the decimated and filtered RACH signal is transformed to the frequency-domain signal through the FFT transformation.
  • the specific implementation structure and function of the time- frequency domain transformation processing unit 1101 correspond to step S401, which will not be detailed here.
  • the compression processing unit 1 120 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, corresponding to step S402.
  • 1 1 f show structural schematic diagrams of frequency-domain compressors for implementing a frequency-domain compression function, respectively comprising a null sub-carrier removal processing unit 1 104, a common factor per group extraction unit 1105 or a bit truncating unit 1106, or a combination of the null sub-carrier removal processing unit 1 104 and the common factor per group extraction unit 1 105, or a combination of the null sub-carrier removal processing unit 1 104 and the bit truncation unit 1106.
  • a null sub-carrier removal processing unit 1 104 a common factor per group extraction unit 1105 or a bit truncating unit 1106, or a combination of the null sub-carrier removal processing unit 1 104 and the common factor per group extraction unit 1 105, or a combination of the null sub-carrier removal processing unit 1 104 and the bit truncation unit 1106.
  • the signal package and transmission unit 1 103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the function as implemented by this unit corresponds to the step as described in step S403.
  • the package functions configured to the signal package and transmission unit 1 103 are also different, which have been described in detail at step S403 and Figs. 9a and 9b, which will not be detailed here.
  • the frequency-domain compressor 1110 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 121, and a signal package and transmission unit 1 103. Similar to the embodiment as shown in Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • the signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the compression processing unit 1 121 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 configured to implement the frequency-domain compression function by removing signals on a guard band, DC sub-carriers, and unscheduled resource blocks.
  • the null sub-carrier removal processing has been specifically described above, which will not be detailed here.
  • the frequency-domain compressor 1120 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 122, and a signal package and transmission unit 1 103. Similar to the embodiment as shown in Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • the signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the compression processing unit 1122 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a common factor per group extraction unit 1 105 configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal to implement the frequency-domain compression function.
  • a common factor per group extraction unit 1 105 configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal to implement the frequency-domain compression function.
  • the frequency-domain compressor 1 120 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 123, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11 a, the time- frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • the signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the compression processing unit 1 123 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a bit truncating unit 1 106 configured to perform low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal so as to implement the frequency-domain compression function.
  • the bit truncation unit may implement the low-order bit truncation function or the high-order bit truncation function, or be simultaneously configured with the high-order and low-order bit truncation functions.
  • bit truncation unit 1 106 when configured to implement the low-order bit truncation function, it further comprises a level estimation unit configured to perform noise level estimation on the multi-carrier modulation signal; a low-order truncation bit number determination unit configured to determine an appropriate low-order truncation bit number based on an estimated noise level outputted by the level estimation unit and in the case of guaranteeing that the performance loss caused by the low-order bit truncation is acceptable; a low-order bit truncation unit is configured to truncate, based on the determined low-order truncation bit number, the low-order truncation bit number of low-order bits.
  • bit truncation unit 1106 When the bit truncation unit 1106 is configured to implement the high-order bit truncation function, it further comprises a signal dynamic range statistical unit configured to perform signal dynamic range statistics per group on the multi-carrier modulation signal; a high-order truncation bit number determination unit configured to determine an appropriate high-order truncation bit number based on a maximum value of each group of signal levels or an average value of each group of signal values; and a high-order bit truncation unit configured to truncate, based on the determined high-order truncation bit number, the high-order truncation bit number of high-order bits.
  • the specific high-order and/or low-order bit truncation processing have been specifically described above, which will not be detailed here.
  • the frequency-domain compressor 1 130 comprises a time- frequency domain transformation processing unit 1101 , a compression processing unit 1 124, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11 a, the time- frequency domain transformation processing unit 1 101 is configured to perform the time- frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • the signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the compression processing unit 1 124 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 and a common factor per group extraction unit 1105 .
  • the frequency-domain compression function is implemented by adopting a combination of null sub-carrier removing processing and common factor per group extracting processing.
  • the specific implementations of the null sub-carrier removal processing unit 1104 and the common factor per group extraction unit 1105 have been specifically described above, which will not be detailed here.
  • Fig. l lf corresponds to the embodiment of Fig. 4f.
  • the frequency-domain compressor 1 130 comprises a time-frequency domain transformation processing unit 1 101, a compression processing unit 1 124, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform the time- frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal.
  • the signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU.
  • the compression processing unit 1124 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 and a bit truncation unit 1 106.
  • the specific implementation of the frequency-domain compression function by adopting the combination of null sub-carrier removal processing and bit truncation processing may refer to the embodiments as provided above in Figs. 1 lb and l id.
  • the specific implementations of the null sub-carrier removal processing unit 1104 and the bit truncation unit 1106 have been specifically described above, which will not be detailed here.
  • Figs. 12a, 12b, and 12c show schematic structural diagrams representing a frequency-domain decompressor for different decompression schemes according to the embodiments of the present invention.
  • the frequency-domain decompressor 1200 comprises a parsing unit 1201 and a frequency-domain decompression unit 1202.
  • the parsing unit 1201 is configured to parse the received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1202 is configured to perform frequency-domain decompression on the compressed signal outputted by the parsing unit.
  • the frequency-domain decompressor 1210 comprises a parsing unit 1201 and a frequency-domain decompression unit 1212.
  • the parsing unit 1201 is configured to parse the received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1212 is configured to perform frequency-domain decompression on the compressed signal outputted by the parsing unit.
  • the frequency-domain decompression unit 1202 comprises a common factor per group multiplication amplification unit 1204 configured to perform amplification by multiplying the compressed signal on each group of sub-carriers by the common factor.
  • the frequency-domain decompressor 1210 comprises a parsing unit 1201 and a frequency-domain decompression unit 1222.
  • the parsing unit 1201 is configured to parse a received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1222 is configured to perform the frequency-domain decompression on the compressed signal outputted by the parsing unit.
  • the frequency-domain decompression unit 1222 comprises a sign bit extension unit 1205 configured to perform sign bit extension on the compressed truncated signal over each sub-carrier.
  • the number of extended bits is determined based on the specific implementation of the BBU. For example, the bits may be extended to 16 bits.
  • a frequency-domain decompressor corresponding to performing frequency-domain compression by jointly adopting null sub-carrier removal and common factor per group extraction may refer to the frequency-domain decompressor structure as shown in Fig. 12b to implement decompression.
  • a frequency-domain decompressor corresponding to p erforming frequency-domain compression by jointly adopting the null sub-carrier removal and bit truncation may refer to the frequency-domain decompressor as shown in Fig. 12c to implement decompression.
  • the error vector amplitudes after compression which are calculated through simulation are provided below.
  • the error vector amplitudes in the case of no compression are also simulated.
  • a 6-path channel as defined by the LTE evaluation method is adopted. Table 3 lists the simulation results. Adopting the solution provided by the present invention may obtain a 3.1 times compression ratio and meanwhile obtain an error vector amplitude close to that in the case of no compression.
  • the present invention nearly has no any impact in terms of timing accuracy, probability of undetection, and probability of false alarm.
  • the present invention may be implemented by hardware, software, firmware, as well as their combination. Those skilled in the art should be aware that the present invention may also be embodied on a statistical machine program product set on a signal bearer medium available to any data processing system.
  • signal bearer medium may be a transmission medium or a recordable medium for machine-readable information, comprising a magnetic medium, optical medium or other appropriate medium. Examples of recordable mediums include: magnetic disk or floppy disk in hard disk driver, an optical disc or magnetic tape for an optical driver, and other medium that can be contemplated by those skilled in the art.
  • any communication device with a proper programming device can execute the steps of the present invention methods as embodied in the program products.

Abstract

The present invention provides a new compression/decompression method and compressor/decompressor for a multi-carrier modulation signal. According to the present invention, the multi-carrier modulation signal is first subjected to a time-frequency domain transformation to be transformed to a frequency-domain signal and then a low-loss compression in the frequency domain, and thereby a bandwidth required for transmitting the compressed signal is greatly reduced. Correspondingly, a signal transmitted over a wired network has to be first subjected to frequency-domain decompression and then a conventional baseband signal processing. Applying the present invention may achieve a higher compression ratio, thereby reducing the bandwidth requirements of a remote optical network in an access network based on centralized processing.

Description

METHOD FOR COMPRESSING/DECOMPRESSING MUL I - CARRIER MODULATION SIGNAL AND CORRESPONDING COMPRESSOR/DECOMPRESSOR
FIELD OF THE INVENTION
[0001] The present invention relates to a mobile communication technology, and more specifically, to a method for compressing/decompressing a multi-carrier modulation signal and a compressor/decompressor.
BACKGROUND OF THE INVENTION
[0002] With rapid increase of mobile Internet traffic, costs of a traditional access network deployment are more and more expensive for a mobile operator to maintain its competitive advantage. In order to decrease costs of network construction and meanwhile to provide quality services to subscribers, many mobile operators and equipment providers start to consider adoption of a more attractive solution. Recently, all popular solutions are based on distributed antennas and centralized baseband processing architecture, for example, the cloud access network (C-RAN) of China Mobile, LightRadio of Alcatel Lucent, etc. By employing the access network architecture with centralized baseband processing, demands on base station sites may be greatly reduced, and a baseband processing device (or baseband processing unit, BBU) may be shared between multiple virtual base stations. Compared with a traditional access network, such architecture may dramatically reduce operation costs and construction costs. Further, advanced scheduling and signal processing techniques such as inter-cell interference cancellation and multi-point coordination can be implemented more easily, such that such architecture may provide a greater capacity, a wider coverage, and a better user experience.
[0003] In such centralized processing systems, the baseband processing unit (BBU) and a remote radio-frequency head (RRH) are separate geographically, which may be connected via a wired network such as an optical network or Ethernet network and perform data exchange via an open base station architecture protocol (OBSAI) or a common public radio interface (CPRI), so as to transmit original time-domain baseband signals over these wired connections. Such architecture brings a huge challenge to an optical network or Ethernet network in terms of requirements on wired transmission bandwidth. For example, an 8-antenna 3GPP LTE (Long Term Evolution) system with a bandwidth of 20 MHz requires a 9.8304 Gbps wired transmission bandwidth, and the bandwidth requirement of LTE-A (LTE-Advanced) under standardized study increases dramatically to 49.152 Gbps.
[0004] To address the issue of the too high bandwidth requirements as described above, a few compression algorithms have been currently adopted to compress baseband signals. Two typical solutions are: time-domain signal compression algorithm adopted in LightRadio of Alcatel Lucent (Fig. 1) and the compression algorithm of Samplify (Fig. 2). These algorithms may provide a twice to thrice of a compression ratio with less performance loss, such that they can effectively reduce the bandwidth requirement of wired transmission. Compared with a non-compression transmission, only less than a half of optical resources are required if these effective compression algorithms are adopted.
[0005] However, for a multi-carrier modulation signal in a wireless communication system, for example, of an orthogonal frequency division multiplexing (OFDM) or DFT-spread OFDM (DFT-S-OFDM) modulation adopted in an LTE/LTE-A system, it would be more effective to compress in a frequency domain. A higher compression ratio can be achieved through a compression algorithm designed for characteristics of a received uplink multi-carrier modulation signal. These characteristics comprise the following aspects.
[0006] 1. The received uplink multi-carrier modulation signal has a wide dynamic range in time domain, while a small dynamic range in frequency domain; therefore, it would be more advantageous to perform compression in the frequency domain.
[0007] 2. The received signal would have noise loss. In the case of a low signal-to-noise ratio, a quantization with an over high accuracy would not bring any gain; thus, a low bit width quantization may be adopted.
[0008] 3. Because a wideband signal experiences a frequency selectivity channel or because the distance between a transmitter and a receiver is near or far, strengths of the received signal would change dramatically over different sub-carriers. A more reasonable solution should be quantizing the signal over different sub-carriers using an adaptive bit width.
[0009] In addition, when a base station serves multiple users simultaneously, signal powers over neighboring sub-carriers would differ greatly, which is caused by respective signal to interference-plus-noise ratios of the users or channel fading. A frequency-domain compression may be performed to independently quantize the signal over the different sub-carriers, and they do not affect each other. However, in the case of adopting a time-domain compression technique, user signal over the different sub-carriers would mix and overlap with each other; further, a user signal with a high-power has a greater impact on the quantization operation, thereby impairing a low-power user signal. Therefore, in this case, the frequency-domain compression is also more advantageous over the time-domain compression. SUMMARY OF THE INVENTION
[0010] In order to solve the above drawbacks in the prior art, the present invention effectively utilizes the characteristics of a multi-carrier modulation signal, such as independence between sub-carriers, frequency selectivity channels, etc., and provides a method for compressing/decompressing a multi-carrier modulation signal and a compressor/decompressor. According to the present invention, the multi-carrier modulation signal is first subjected to a time-frequency domain transformation to be transformed to a frequency-domain signal and then a low- loss compression in the frequency domain, and thereby a bandwidth required for transmitting the compressed signal is greatly reduced. Correspondingly, a signal transmitted over a wired network has to be first subjected to frequency-domain decompression and then a conventional baseband signal processing.
[0011] Specifically, according to one embodiment of the present invention, there is provided a method for compressing a multi-carrier modulation signal, comprising: transforming a time-domain multi-carrier modulation signal to a frequency domain multi-carrier modulation signal through a time-frequency domain transformation processing; compressing the frequency-domain multi-carrier modulation signal; packaging and transmitting the compressed multi-carrier modulation signal.
[0012] According to one specific embodiment of the present invention, the compressing the frequency-domain multi-carrier modulation signal comprises removing a null sub-carrier.
[0013] According to one specific embodiment of the present invention, the compressing the frequency-domain multi-carrier modulation signal comprises performing low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
[0014] According to one specific embodiment of the present invention, the compressing the frequency-domain multi-carrier modulation signal comprises extracting a common factor per group for the frequency-domain multi-carrier modulation signal.
[0015] According to one specific embodiment of the present invention, the performing low-order bit truncation on the frequency-domain multi-carrier modulation signal comprises: performing noise level estimation on the multi-carrier modulation signal; determining an appropriate truncation bit number based on the noise level estimation and in the case of guaranteeing that performance loss caused by the low-order bit truncation is acceptable, and truncating the truncation bit number of low-order bits.
[0016] According to one specific embodiment of the present invention, the performing high-order bit truncation on the frequency-domain multi-carrier modulation signal comprises: performing signal dynamic range statistics per group on the frequency-domain multi-carrier modulation signal; determining a high-order bit truncation number based on a maximal value of each group of signal levels or an average value of each group of signal levels, and truncating the bit truncation number of high-order bits.
[0017] According to one specific embodiment of the present invention, for a RACH preamble signal, the process of transforming a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through a time- frequency domain transformation processing comprises: frequency band moving for moving the RACH preamble signal to a center of a frequency band; decimating and filtering for filtering the time-domain multi-carrier modulation signal and decimating samples; time- frequency domain transformation processing for determining an appropriate FFT window, performing an FFT operation, and obtaining a RACH sequence of the frequency domain.
[0018] According to one specific embodiment of the present invention, the null sub-carrier comprises a signal on a guard band, a direct current (DC) sub-carrier, or an unscheduled resource block.
[0019] According to another embodiment of the present invention, there is provided a method for decompressing a multi-carrier modulation signal, comprising: parsing a received compression packet to obtain a compressed signal; performing frequency-domain decompression on the compressed signal.
[0020] According to one specific embodiment of the present invention, the frequency-domain decompression comprises performing sign bit extension on the compressed truncated signal over each sub-carrier.
[0021] According to one specific embodiment of the present invention, the performing frequency-domain decompression comprises performing amplification by multiplying the compressed signal on each group of sub-carriers by a common factor.
[0022] According to a further embodiment of the present invention, there is provided a frequency-domain compressor, comprising: a time- frequency domain transformation processing unit configured to transform a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through an FFT processing; a compression processing unit configured to compressing the frequency-domain multi-carrier modulation signal; a signal package and transmission unit configured to package and transmit the compressed multi-carrier modulation signal.
[0023] According to one specific embodiment of the present invention, the compression processing unit comprises a null sub-carrier removal processing unit configured to remove a null sub-carrier in the frequency-domain multi-carrier modulation signal.
[0024] According to one specific embodiment of the present invention, the compression processing unit comprises a bit truncation unit configured to perform low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
[0025] According to one specific embodiment of the present invention, the compression processing unit comprises a common factor extraction unit configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal.
[0026] According to one specific embodiment of the present invention, the bit truncation unit comprises a level estimation unit configured to perform noise level estimation on the multi-carrier modulation signal; a low-order truncation bit number determination unit configured to determine an appropriate low-order truncation bit number based on the estimated noise level outputted from the level estimation unit and in the case of guaranteeing performance loss caused by low-order bit truncation is acceptable; a low-order bit truncation unit configured to truncate, based on the determined low-order truncation bit number, the low-order truncation bit number of low-order bits.
[0027] According to one specific embodiment of the present invention, the bit truncating unit comprises: a signal dynamic range statistics unit configured to perform signal dynamic range statistics per group on the multi-carrier modulation signal; a high-order truncation bit number determination unit configured to determine an appropriate high-order truncation bit number based on a maximal value of each group of signal levels or an average value of each group of signal levels; a high-order bit truncation unit configured to truncate, based on the high-order truncation bit number, the high-order truncation bit number of high-order bits.
[0028] According to one specific embodiment of the present invention, the time- frequency domain transformation processing unit further comprises: a frequency band movement unit configured to move a RACH preamble signal to a center of a frequency band; a decimation and filtering unit configured to filter the time-domain multi-carrier modulation signal and decimate samples;
[0029] According to one specific embodiment of the present invention, the null sub-carrier comprises a signal on a guard band, a DC sub-carrier, or an unscheduled resource block.
[0030] According to one specific embodiment of the present invention, the compressor is configured on a remote radio frequency head device.
[0031] According to a yet further embodiment of the present invention, there is provided a frequency domain decompressor, comprising: a parsing unit configured to parse a received compression packet to obtain a compressed signal; and a frequency-domain decompression unit configured to perform frequency-domain decompression on the compressed signal outputted from the parsing unit.
[0032] According to one specific embodiment of the present invention, the frequency-domain decompression unit comprises a common factor per group multiplication amplification unit configured to perform amplification by multiplying the compressed signal over each group of sub-carriers by a common factor.
[0033] According to one specific embodiment of the present invention, the frequency-domain decompression unit comprises a sign bit extension unit configured to perform sign bit extension on the compressed truncated signal over each sub-carrier.
[0034] According to one specific embodiment of the present invention, the frequency-domain decompressor is configured on a baseband processing device.
[0035] According to a yet further embodiment of the present invention, there is provided a system for processing an uplink multi-carrier modulation signal, comprising: a remote radio frequency head, RRH, device comprising a frequency-domain compressor; a baseband processing device comprising a frequency-domain decompressor; and an optical network or an Ethernet network for transmitting a signal between the remote radio frequency head, RRH, device and the baseband processing device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Other objectives and effects of the present invention will become more apparent and comprehensible with more thorough understanding of the present invention through the following description with reference to the accompanying drawings, wherein:
[0037] Fig. 1 shows a schematic diagram of a method for compressing a time-domain signal in LightRadio of the prior art;
[0038] Fig. 2 shows a schematic diagram of a compression method of Samplify Corporation in the prior art;
[0039] Fig. 3 shows a schematic diagram of a system for processing an uplink multi-carrier modulation signal according to embodiments of the present invention;
[0040] Figs. 4a, 4b , 4c, 4d, 4e, and 4f show schematic flow charts of a frequency-domain compression of different compression schemes according to embodiments of the present invention, respectively;
[0041] Fig. 5 shows a schematic diagram of RACH sequence extraction according to embodiments of the present invention;
[0042] Fig. 6 shows a principle diagram of common factor extraction;
[0043] Fig. 7 shows a schematic diagram of an adaptive quantization principle for bit truncation according to embodiments of the present invention;
[0044] Figs. 8a and 8b show schematic diagrams of low-order bit truncation and high-order bit truncation according to embodiments of the present invention, respectively;
[0045] Figs. 9a and 9b show schematic diagrams of package formats of a compressed signal according to embodiments of the present invention;
[0046] Figs. 10a and 10b show schematic flow charts of frequency-domain decompression of different decompression schemes according to embodiments of the present invention, respectively;
[0047] Figs. 11a, l ib, 11c, l id, l ie and l lf show structural schematic diagrams of frequency-domain compressors of different compression schemes according to embodiments of the present invention, respectively;
[0048] Figs. 12a, 12b and 12c show structural schematic diagrams of frequency-domain decompressors of different decompression schemes according to embodiments of the present invention;
[0049] Table 1 shows sampling coefficients for different system bandwidths;
[0050] Table 2 shows determining low-order truncation bit numbers based on different noise levels;
[0051] Table 3 shows a performance simulation result according to embodiments of the present invention.
[0052] In all of the above accompanying drawings, the same reference numbers indicate same, similar or corresponding features or functions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [0054] Fig. 3 shows a schematic diagram of a system for processing an uplink multi-carrier modulation signal. In an RRH, a time-frequency domain transformation processing unit 31 1 of a frequency compressor 310 first performs time-frequency domain transformation on the received uplink multi-carrier modulation signal, and then a compression processing unit 312 performs signal compression in the frequency domain; the compressed signal is transmitted to a BBU via a wired network and then subjected to baseband signal processing after frequency-domain decompression at a frequency-domain decompressor 320 of the BBU.
[0055] Figs. 4 a, 4b , 4 c , 4 d, 4 e , and 4 f show s chematic flow charts of frequency-domain compression of different compression schemes, wherein Fig. 4a shows a schematic flow chart in general. According to the present invention, first, the time- frequency domain transformation unit is implemented on a remote radio head (RRH) instead of a baseband processing unit (BBU), i.e., at step S401, the time- frequency domain signal transformation is performed on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. For most uplink signals, for example, on PUSCH (Physical Uplink Shared Channel), PUCCH (Physical Uplink Control Channel), and SRS (Sounding Reference Symbol) in the LTE/LTE-A system, an appropriate FFT (Fast Fourier Transformation) window may be determined through timing information, and then a corresponding FFT operation is performed based on system parameters to transform the time-domain signal to the frequency domain signal.
[0056] For a RACH (Random Access Channel) preamble signal of LTE/LTE-A, according to one embodiment of the present invention, the time-frequency domain signal transformation may be implemented by RACH front-end processing, comprising the following steps.
[0057] (a) Frequency band moving: moving the RACH preamble signal to a center of a frequency band which is a pass band of the following decimation filter. The offset information of the frequency band occupied by the RACH preamble signal may be notified by the BBU.
[0058] (b) Decimating and filtering: filtering the received signal and decimating sampling points, and reducing the sampling rate to 2.56MHz. Table 1 provides sampling coefficients under different system bandwidth conditions.
[0059] (c) 2048-point FFT: determining an appropriate FFT window, performing a 2048-point FFT operation, and obtaining a RACH sequence with a length of 839 after transformation. For the RACH preamble signal, the RACH sequence with a length of 839 may be extracted as shown in Fig. 5.
[0060] Next, at step S402, frequency-domain compression is performed on the frequency-domain signal after time-frequency domain transformation. According to the present invention, the frequency-domain compression may adopt a method of removing a null sub-carrier, a method of extracting a common factor per group, or a method of high-order and/or low-order bit truncation, or a combination of the method of removing a null sub-carrier and the method of extracting a common factor per group, or a combination of removing a null sub-carrier and the method of high-order and/or low-order bit truncation.
[0061] The embodiment of Fig. 4b adopts the method of removing a null sub-carrier, specifically, removing the signal on a guard band, a direct current (DC) sub-carrier, and an unscheduled resource block to perform frequency-domain compression. Some sub-carriers do not bear any information:
(a) a guard band and a DC sub-carrier;
(b) unscheduled sub-carriers: the base station schedules radio resources based on traffic requirements, and these sub-carriers are not used.
[0062] Since they have no help to the processing at the BBU end, it is unnecessary to send these signals to the BBU end for processing.
[0063] Because both the BBU and the RRH have known the locations of sub-carriers of Type (a), no extra information interaction is required to process such type of sub-carriers.
[0064] For sub-carriers of Type (b), its scheduling condition may be informed to the
RRH using a simple bitmap based on resource scheduling information. For example, an LTE system with a bandwidth of 20MHz divides available sub-carriers into 100 resource blocks, thus a 100-bit bitmap may be used to indicate the scheduling condition of these resource blocks.
The RRH removes the signals on the unscheduled sub-carriers based on the received bitmap indication and then further compresses the remaining useful signal. By removing the unscheduled sub-carrier signals, the compression ratio under a low load condition can be improved.
[0065] In the embodiment of Fig. 4c, frequency-domain compression is performed by the method of extracting a common factor per group. Specifically, because the signal on each sub-carrier within each resource block adopts the same modulation modes, they will have a common factor; both the real part and the imaginary part of the quotient of the signal divided by this common factor are very small integers that may be represented by a few bits during quantization; in order to guarantee a lossless performance, the common factor may be represented in a full precision (for example 16 bits). The principle diagram of the common factor extraction is shown in Fig. 6, wherein for sub-carriers of the 16QAM resource block, the common factor of each subcarrier is 1623; all sub-carrier signals are divided by 1623, and thus the real parts and the virtual parts of the sub-carriers after the common factor extraction are all very small integers which may be represented with a few bits.
[0066] In the embodiment of Fig. 4d, frequency domain compression is performed by the method of high-order and/or low-order bit truncation, wherein based on system requirements, frequency-domain compression may be performed by adopting either high-order bit truncation or low-order bit truncation, or both high-order bit truncation and low-order bit truncation. Specifically, Fig. 7 shows an adaptive quantization principle diagram for bit truncation. By adaptively truncating low order and high order of digital signals based on the noise level estimation and received signal strength estimation, the received signal may be represented with a few bits, which merely brings little performance loss. The noise level may be estimated based on the signal on the guard band.
[0067] (a) For all digital signals, their low order is impaired by additive noise. Truncating a part of low-order bits may not cause signal deterioration as long as the resulted quantization noise does not exceed the noise floor.
[0068] (b) Due to great differences between the powers of received signals over different sub-carriers, the dynamic ranges of the signals on respective resource blocks are also different; however, the signals over neighboring sub-carriers within a resource block will have a simlilar dynamic range. In the present invention, statistics is performed on maximum or average values of signal levels on 12 sub-carriers within each resource block, and therewith its high-order bits are truncated. In this way, for each resource block, signal level estimation and high-order bit truncation are performed respectively. This operation nearly causes no performance loss.
[0069] As shown in Fig. 8(a), low-order bits are truncated based on the estimated noise level. An appropriate truncation bit number (NL) should be selected so as to guarantee that the performance loss caused by low-order bit truncation is acceptable. Table 2 shows an embodiment of determining low-order truncation bit numbers based on different noise levels.
[0070] As shown in Fig. 8(b), high-order bits are truncated based on the maximum value of the received signal levels. In the present invention, statistics are performed on dynamic ranges of the signals on 12 sub-carriers within each resource block, i.e., the maximum values of the real parts and imaginary parts of all complex signals, thereby determining the locations of effective sign bits and truncating the remaining high-order bits, because they are only simple repetition of effective sign bits. Here, only one embodiment of high-order truncation is provided, and this step may also be implemented by other means, for example, truncating the high-order bits based on the average level of the received signal.
[0071] Fig. 4e shows a schematic flow chart of frequency-domain compression by a combination of the method of removing null sub-carriers and the method of extracting a common factor per group. In this solution, first, the frequency-domain signal is subjected to null sub-carrier removing, and then a common factor is extracted by group. Based on the definition on resource blocks in the communication system standard, the frequency-domain signals are grouped, and then a common factor is calculated and extracted. The methods of removing null sub-carriers and extracting the common factor are as described above.
[0072] Fig. 4f shows a schematic diagram of performing frequency-domain compression by a combination of the method of removing null sub-carriers and the method of high-order and/or low-order bit truncation. The methods of removing null sub-carriers and the method of high-order and/or low-order bit truncation have been described in detail above, which will not be detailed here; however, it should be noted that when combining the two methods, noise level estimation and/or receives signal strength estimation must be performed first, and then frequency-domain compression is performed by removing null sub-carriers and truncating high-order and/or low-order bits.
[0073] Through the above frequency-domain compression, baseband signals via wired transmission, for example, over a remote optical network, can be greatly compressed with a controllable performance loss. In this way, the bandwidth requirements of wired transmission, for example, over a remote optical network will be greatly reduced, such that the access network deployment based on centralized processing becomes more convenient with a far lower cost.
[0074] After frequency-domain compression, at step S403, the compressed signal is packaged and the packaged compression packet is sent to the BBU.
[0075] For the compressed signal after the null sub-carrier removal, it may be packaged by general I/Q signals.
[0076] With respect to the solution of performing frequency-domain compression by extracting a common factor per group, in order to correctly recover the original signal in decompressing, after the common factor is extracted, it is required to package the common factor and the signal after the common factor extraction together into the compression packet. The packaging format is shown in Fig. 9a, wherein the common factor may be quantized in a full precision (for example 16 bits); the real parts and the imaginary parts of the signals after the common factor extraction may be respectively quantized by selecting an appropriate number of bits based on the modulation mode. For example, a 2-bit quantization is adopted for QPSK modulation; a 3 -bit quantization is adopted for 16QAM, and a 4-bit quantization is adopted for 64QAM.
[0077] For the solution of performing frequency-domain compression by high-order bit truncation, because the high-order truncation bit numbers of the signal on the sub-carriers within different resource blocks are not equal, the final quantization bit numbers are also different; thus, it is required to indicate the quantization bit number in the compression packet. The packaging format is shown in Fig. 9b, wherein the maximal quantization bit number is 15, which may be represented by a 4-bit digit.
[0078] For the solution of combining the method of removing a null sub-carrier and the method of extracting a common factor to perform frequency-domain compression, the method and format for packaging are similar to that for packaging a signal after extracting the common factor per group (Fig. 9a), while for the solution of combining the method of removing a null sub-carrier and the method of high-order and/or low-order bit truncation to perform frequency-domain compression, the method and format for packaging are similar to that for packaging a signal after bit truncation (Fig. 9b).
[0079] From the perspective of the BBU, the uplink signal processing does not need accurate timing synchronous information. Because the RRH has an accurate reference timing signal originated from GPS, it may control framing timing and send the compressed uplink data to the BBU at the exact time. Thus, the uplink data processing of the BBU may be set as a data driving mode such that upon the reception of the compressed data packet, the uplink data processing is initiated immediately to perform operations such as frequency-domain decompression, signal demodulation, decoding, etc. Fig. 10 shows a schematic flow chart of frequency-domain decompression at the BBU side, wherein Fig. 10a corresponds to the schematic flow chart of frequency-domain decompression through performing amplification by multiplication with the common factor per group, and Fig. 10b corresponds to a schematic flow chart of frequency-domain decompression through sign-bit extension.
[0080] At step S I 001 , signal depackaging is performed to parse the received compression packet to obtain the compressed signal.
[0081] Fig. 10a shows a decompression scheme for frequency-domain compression through the method comprising extracting a common factor per packet. At step SI 002, each group of signals are respectively multiplied with a common factor to recover the original signal.
[0082] Fig. 10b shows a decompression scheme for a frequency-domain compression through the method comprising bit truncation. At step S1012, for truncated signals over each sub-carrier within each resource block, their sign bits are extended. The number of extended bits is determined based on the specific implementation of the BBU. For example, the bits may be extended to 16 bits.
[0083] A decompression scheme which corresponds to frequency-domain compression adopting a combination of removing a null sub-carrier and extracting a common factor per group may be implemented with reference to the decompression scheme as shown in Fig. 10a.
[0084] A decompression scheme which corresponds to frequency-domain compression adopting a combination of removing null sub-carrier and truncating bits may be implemented with reference to the decompression scheme as shown in Fig. 10b.
[0085] After implementation of frequency-domain decompression, conventional uplink data processing, such as signal demodulation, decoding, etc., are performed on uplink signals, for example, on PUSCH, PUCCH, SRS, RACH, etc., respectively.
[0086] Figs. 11a, l ib, 1 1c, l id, l ie, and l lf respectively show structural schematic diagrams of frequency-domain compressors representing different compression schemes according to embodiments of the present invention. Moreover, the individual frequency-domain compressor structures as shown in Fig. 11 correspond to respective frequency-domain compression flows of Fig. 4. Detailed description will be provided below.
[0087] Fig. 11a shows a structural schematic diagram of a general frequency-domain compressor, corresponding to 3 10 of Fig. 3. The frequency-domain compressor 1 100 comprises a time-frequency domain transformation processing unit 1 101 , a compression processing unit 1102, a signal package and transmission unit 1103.
[0088] Specifically, the time- frequency domain transformation processing unit 1101 is configured to perform time-frequency domain signal transformation on a received time domain signal to transform the time-domain signal to a frequency-domain signal. For a general uplink multi-carrier signal, for example, on PUSCH, PUCCH, SRS, etc., an appropriate FFT (fast Fourier transformation) window is determined through timing information, and then a corresponding FFT operation is performed based on system parameters. Further, the time-frequency domain transformation processing unit 1101 further comprises a frequency band movement unit and decimation and filtering unit for processing the RACH channel, wherein the frequency band movement unit is configured to move a RACH preamble signal to a center of a frequency band; and the decimation and filtering unit is configured to filter the time-domain multi-carrier modulation signal and decimate samples. Then, the decimated and filtered RACH signal is transformed to the frequency-domain signal through the FFT transformation. The specific implementation structure and function of the time- frequency domain transformation processing unit 1101 correspond to step S401, which will not be detailed here.
[0089] The compression processing unit 1 120 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, corresponding to step S402. Correspondingly, according to different embodiments of the present invention, Fig. 1 lb, Fig. 11c, Fig. l id, Fig. l ie, and Fig. 1 1 f show structural schematic diagrams of frequency-domain compressors for implementing a frequency-domain compression function, respectively comprising a null sub-carrier removal processing unit 1 104, a common factor per group extraction unit 1105 or a bit truncating unit 1106, or a combination of the null sub-carrier removal processing unit 1 104 and the common factor per group extraction unit 1 105, or a combination of the null sub-carrier removal processing unit 1 104 and the bit truncation unit 1106. Detailed description will be provided below.
[0090] The signal package and transmission unit 1 103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The function as implemented by this unit corresponds to the step as described in step S403. Corresponding to different frequency-domain compression schemes, the package functions configured to the signal package and transmission unit 1 103 are also different, which have been described in detail at step S403 and Figs. 9a and 9b, which will not be detailed here.
[0091] Embodiments shown in Figs, l ib, 1 1c, l id, l ie, and 1 I f will be described below respectively.
[0092] The embodiment as shown in Fig. 1 lb corresponds to the embodiment of Fig. 4b. According to Fig. 1 lb, the frequency-domain compressor 1110 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 121, and a signal package and transmission unit 1 103. Similar to the embodiment as shown in Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. The signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The compression processing unit 1 121 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 configured to implement the frequency-domain compression function by removing signals on a guard band, DC sub-carriers, and unscheduled resource blocks. The null sub-carrier removal processing has been specifically described above, which will not be detailed here.
[0093] The embodiment as shown in Fig. 1 1c corresponds to the embodiment of Fig. 4c. According to Fig. 11c, the frequency-domain compressor 1120 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 122, and a signal package and transmission unit 1 103. Similar to the embodiment as shown in Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. The signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The compression processing unit 1122 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a common factor per group extraction unit 1 105 configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal to implement the frequency-domain compression function. The processing of extracting a common factor per group has been specifically described above, which will not be detailed here.
[0094] The embodiment shown in Fig. l id corresponds to the embodiment of Fig. 4d. According to Fig. l id, the frequency-domain compressor 1 120 comprises a time- frequency domain transformation processing unit 1 101, a compression processing unit 1 123, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11 a, the time- frequency domain transformation processing unit 1 101 is configured to perform time-frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. The signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The compression processing unit 1 123 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a bit truncating unit 1 106 configured to perform low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal so as to implement the frequency-domain compression function. Based on different system configurations, the bit truncation unit may implement the low-order bit truncation function or the high-order bit truncation function, or be simultaneously configured with the high-order and low-order bit truncation functions. Thus, further, when the bit truncation unit 1 106 is configured to implement the low-order bit truncation function, it further comprises a level estimation unit configured to perform noise level estimation on the multi-carrier modulation signal; a low-order truncation bit number determination unit configured to determine an appropriate low-order truncation bit number based on an estimated noise level outputted by the level estimation unit and in the case of guaranteeing that the performance loss caused by the low-order bit truncation is acceptable; a low-order bit truncation unit is configured to truncate, based on the determined low-order truncation bit number, the low-order truncation bit number of low-order bits. When the bit truncation unit 1106 is configured to implement the high-order bit truncation function, it further comprises a signal dynamic range statistical unit configured to perform signal dynamic range statistics per group on the multi-carrier modulation signal; a high-order truncation bit number determination unit configured to determine an appropriate high-order truncation bit number based on a maximum value of each group of signal levels or an average value of each group of signal values; and a high-order bit truncation unit configured to truncate, based on the determined high-order truncation bit number, the high-order truncation bit number of high-order bits. The specific high-order and/or low-order bit truncation processing have been specifically described above, which will not be detailed here.
[0095] The embodiment of Fig. 1 l e corresponds to the embodiment of Fig. 4e. According to Fig. l ie, the frequency-domain compressor 1 130 comprises a time- frequency domain transformation processing unit 1101 , a compression processing unit 1 124, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11 a, the time- frequency domain transformation processing unit 1 101 is configured to perform the time- frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. The signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The compression processing unit 1 124 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 and a common factor per group extraction unit 1105 . The frequency-domain compression function is implemented by adopting a combination of null sub-carrier removing processing and common factor per group extracting processing. The specific implementations of the null sub-carrier removal processing unit 1104 and the common factor per group extraction unit 1105 have been specifically described above, which will not be detailed here.
[0096] The embodiment of Fig. l lf corresponds to the embodiment of Fig. 4f.
According to Fig. l lf, the frequency-domain compressor 1 130 comprises a time-frequency domain transformation processing unit 1 101, a compression processing unit 1 124, and a signal package and transmission unit 1 103. Similar to the embodiment of Fig. 11a, the time-frequency domain transformation processing unit 1 101 is configured to perform the time- frequency domain signal transformation on a received time-domain signal to transform the time-domain signal to a frequency-domain signal. The signal package and transmission unit 1103 is configured to package the compressed multi-carrier modulation signal and transmit the packaged compression packet to the BBU. The compression processing unit 1124 is configured to perform compression processing on the frequency-domain multi-carrier modulation signal, comprising a null sub-carrier removal processing unit 1 104 and a bit truncation unit 1 106. The specific implementation of the frequency-domain compression function by adopting the combination of null sub-carrier removal processing and bit truncation processing may refer to the embodiments as provided above in Figs. 1 lb and l id. The specific implementations of the null sub-carrier removal processing unit 1104 and the bit truncation unit 1106 have been specifically described above, which will not be detailed here. Likewise, when the two functions are combined to implement frequency-domain compression, it is necessary to first perform noise level estimation and/or received signal strength estimation, and then remove the null sub-carriers and truncate high-order and/or low-order bits so as to perform frequency-domain compression.
[0097] Figs. 12a, 12b, and 12c show schematic structural diagrams representing a frequency-domain decompressor for different decompression schemes according to the embodiments of the present invention.
[0098] In Fig. 12a, the frequency-domain decompressor 1200 comprises a parsing unit 1201 and a frequency-domain decompression unit 1202. The parsing unit 1201 is configured to parse the received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1202 is configured to perform frequency-domain decompression on the compressed signal outputted by the parsing unit.
[0099] In Fig. 12b, the frequency-domain decompressor 1210 comprises a parsing unit 1201 and a frequency-domain decompression unit 1212. The parsing unit 1201 is configured to parse the received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1212 is configured to perform frequency-domain decompression on the compressed signal outputted by the parsing unit. In this embodiment, corresponding to the embodiment of Fig. 10a, the frequency-domain decompression unit 1202 comprises a common factor per group multiplication amplification unit 1204 configured to perform amplification by multiplying the compressed signal on each group of sub-carriers by the common factor.
[00100] In Fig. 12c, the frequency-domain decompressor 1210 comprises a parsing unit 1201 and a frequency-domain decompression unit 1222. The parsing unit 1201 is configured to parse a received compression packet to obtain the compressed signal; and the frequency-domain decompression unit 1222 is configured to perform the frequency-domain decompression on the compressed signal outputted by the parsing unit. In this embodiment, corresponding to the embodiment of Fig. 10b, the frequency-domain decompression unit 1222 comprises a sign bit extension unit 1205 configured to perform sign bit extension on the compressed truncated signal over each sub-carrier. The number of extended bits is determined based on the specific implementation of the BBU. For example, the bits may be extended to 16 bits.
[00101] A frequency-domain decompressor corresponding to performing frequency-domain compression by jointly adopting null sub-carrier removal and common factor per group extraction may refer to the frequency-domain decompressor structure as shown in Fig. 12b to implement decompression.
[00102] A frequency-domain decompressor corresponding to p erforming frequency-domain compression by jointly adopting the null sub-carrier removal and bit truncation may refer to the frequency-domain decompressor as shown in Fig. 12c to implement decompression.
[00103] In order to verify the performance of the compression/decompression method and compressor/decompressor for a multi-carrier modulation signal according to the present invention, the error vector amplitudes after compression which are calculated through simulation are provided below. As a reference for comparison, the error vector amplitudes in the case of no compression are also simulated. In simulation, a 6-path channel as defined by the LTE evaluation method is adopted. Table 3 lists the simulation results. Adopting the solution provided by the present invention may obtain a 3.1 times compression ratio and meanwhile obtain an error vector amplitude close to that in the case of no compression.
[00104] For a RACH preamble signal detection, the present invention nearly has no any impact in terms of timing accuracy, probability of undetection, and probability of false alarm.
[00105] In the simulation, it is supposed that the system operates under full load. In an actual system, most cells bear different loads. Considering statistical multiplexing in a remote optical network, application of the present invention may achieve a higher compression ratio. For example, when the system operates under half load, a compression ratio as high as 5 times can be achieved, thereby reducing the bandwidth requirement of the remote optical network in a centralized processing-based access network. Due to the high compression ratio, the present invention enables the signal transmission in the remote optical network to be more effective, the deployment of the centralized processing-based access network to be more convenient and low-cost. For a mobile operator that rents a trunk network, a low data rate also means a low rental cost.
[00106] The present invention may be implemented by hardware, software, firmware, as well as their combination. Those skilled in the art should be aware that the present invention may also be embodied on a statistical machine program product set on a signal bearer medium available to any data processing system. Such signal bearer medium may be a transmission medium or a recordable medium for machine-readable information, comprising a magnetic medium, optical medium or other appropriate medium. Examples of recordable mediums include: magnetic disk or floppy disk in hard disk driver, an optical disc or magnetic tape for an optical driver, and other medium that can be contemplated by those skilled in the art. Those skilled in the art should appreciate that any communication device with a proper programming device can execute the steps of the present invention methods as embodied in the program products.
[00107] It should be understood from the above description that modifications and variations can be made to various embodiments of the present invention without departing from the spirit of the present invention. For example, although the embodiments of the present invention are described with an uplink multi-carrier signal as an example, the description in the present description is only for illustration and should not be understood as limitation. Those skilled in the art would understand from the description of the present description that the present invention may also be applied to a multi-carrier signal in other scenarios. The scope of the present invention is merely limited by the appending claims.

Claims

What Is Claimed Is:
1. A method for compressing a multi-carrier modulation signal, comprising:
transforming a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through time- frequency domain transformation processing; compressing the frequency-domain multi-carrier modulation signal; and
packaging and transmitting the compressed multi-carrier modulation signal.
2. The method according to claim 1 , wherein said compressing the frequency-domain multi-carrier modulation signal comprises removing a null sub-carrier.
3. The method according to claim 1 or 2 , wherein said compressing the frequency-domain multi-carrier modulation signal comprises performing low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
4. The method according to claim 1 or 2 , wherein said compressing the frequency-domain multi-carrier modulation signal comprises:
extracting a common factor per group for the frequency-domain multi-carrier modulation signal.
5. The method according to claim 3, wherein said performing low-order bit truncation on the frequency-domain multi-carrier modulation signal comprises:
performing noise level estimation on the multi-carrier modulation signal;
based on the noise level estimation and in the case that performance loss caused by the low-order bit truncation is acceptable, determining an appropriate truncation bit number and truncating the truncation bit number of low-order bits.
6. The method according to claim 3, wherein said performing high-order bit truncation on the frequency-domain multi-carrier modulation signal comprises:
performing signal dynamic range statistics per group on the multi-carrier modulation signal;
based on a maximal value of each group of signal levels or an average value of each group of signal levels, determining a high-order truncation bit number and truncating the truncation bit number of high-order bits.
7. The method according to claim 1, wherein for a RACH preamble signal, the process of transforming a time-domain multi-carrier modulation signal to a frequency domain multi-carrier modulation signal through time-frequency domain transformation processing comprises:
frequency band moving for moving the RACH preamble signal to a center of a frequency band;
decimating and filtering for filtering the time-domain multi-carrier modulation signal and decimating sampling points; and
time-frequency domain transformation processing for determining an appropriate FFT window, performing an FFT operation, and obtaining a RACH sequence in the frequency domain.
8. The method according to claim 2, wherein the null sub-carrier comprises a signal on a guard band, a direct current sub-carrier or an unscheduled resource block.
9. A method for decompressing a multi-carrier modulation signal, comprising:
parsing a received compression packet to obtain a compressed signal;
performing frequency-domain decompression on the compressed signal; and
performing data processing on the decompressed data.
10. The method according to claim 9, wherein said performing frequency-domain decompression comprises performing sign bit extension on compressed truncated signal on each sub-carrier.
1 1 . The method according to claim 9, wherein said performing frequency-domain decompression comprises performing amplification by multiplying the compressed signal on each group of sub-carriers by a common factor.
12. A frequency-domain compressor, comprising:
a time- frequency domain transformation processing unit configured to transform a time-domain multi-carrier modulation signal to a frequency-domain multi-carrier modulation signal through Fast Fourier Transformation (FFT) processing;
a compression processing unit configured to compressing the frequency-domain multi-carrier modulation signal; and
a signal package and transmission unit configured to package and transmit the compressed multi-carrier modulation signal.
13. The frequency-domain compressor according to claim 12, wherein the compression processing unit comprises a null sub-carrier removal processing unit configured to remove a null sub-carrier in the frequency-domain multi-carrier modulation signal.
14. The frequency-domain compressor according to claim 12 or 13, wherein the compression processing unit comprises:
a bit truncation unit configured to perform low-order bit and/or high-order bit truncation on the frequency-domain multi-carrier modulation signal.
15. The frequency-domain compressor according to claim 12 or 13, wherein the compression processing unit comprises:
a common factor extraction unit configured to extract a common factor per group for the frequency-domain multi-carrier modulation signal.
16. The frequency-domain compressor according to claim 14, wherein the bit truncation unit comprises:
a level estimation unit configured to perform noise level estimation on the multi-carrier modulation signal;
a low-order truncation bit number determination unit configured to determine an appropriate low-order truncation bit number based on the estimated noise level outputted by the level estimation unit and in the case that performance loss caused by the low-order bit truncation is acceptable;
a low-order bit truncation unit configured to truncate, based on the determined low-order truncation bit number, the low-order truncation bit number of low-order bits.
17. The frequency-domain compressor according to claim 14, wherein the bit truncation unit comprises:
a signal dynamic range statistical unit configured to perform signal dynamic range statistics per group on the multi-carrier modulation signal;
a high-order truncation bit number determination unit configured to determine an appropriate high-order truncation bit number based on a maximal value of each group of signal levels or an average value of each group of signal levels;
a high-order bit truncation unit configured to truncate, based on the determined high-order truncation bit number, the high-order truncation bit number of high-order bits.
18. The frequency-domain compressor according to claim 12, wherein the time- frequency domain transformation processing unit further comprises:
a frequency band movement unit configured to move a RACH preamble signal to a center of a frequency band; and
a decimation and filtering unit configured to filtering the time-domain multi-carrier modulation signal and decimating sampling points.
19. The frequency-domain compressor according to claim 13, wherein the null sub-carrier comprises a signal on a guard band, a direct current sub-carrier or an unscheduled resource block.
20. The frequency-domain compressor according to claim 12, wherein the compressor is configured on a remote radio frequency head (RRH) device.
21. A frequency-domain decompressor, comprising: a parsing unit configured to parse a received compression packet to obtain a compressed signal; and
a frequency-domain decompression unit configured to perform frequency-domain decompression on the compressed signal;
22. The frequency-domain decompressor according to claim 21, wherein the frequency-domain decompression unit comprises a common factor per group multiplication amplification unit configured to perform amplification by multiplying the compressed signal on each group of sub-carriers by a common factor.
23. The frequency-domain decompressor according to claim 2 1 , wherein the frequency-domain decompression unit comprises a sign bit extension unit configured to perform sign bit extension on the compressed truncated signal on each sub-carrier.
24. The frequency-domain decompressor according to claim 21 , wherein the frequency-domain decompressor is configured on a baseband processing device.
25. A system for processing an uplink multi-carrier modulation signal, comprising: a remote radio frequency head (RRH) device comprising a frequency-domain compressor according to any one of claims 12-20;
a baseband processing device comprising a frequency-domain decompressor according to any one of claims 21-24; and
an optical network or an Ethernet network for transmitting a signal between the RRH device and the baseband processing device.
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