Patent Application
20150382237
This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2014-0080012, filed on Jun. 27, 2014, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.
1. Field
The following description relates to network technology based on orthogonal frequency-division multiplexing (OFDM), and more particularly, a technology for reducing the bandwidth of an interface signal that is transmitted through a digital interface.
2. Description of the Related Art
Orthogonal frequency-division multiplexing (OFDM) method is widely used for wired/wireless communications due to the ease in which data may be transmitted at high speeds and bandwidth expandability. OFDM technology can be applied to a passive optical network (PON).
A sharp increase in traffic demands is expected between network transmitting nodes in network infrastructure such as distributed cloud-RAN (C-RAN). Thus, a technology is required which can reduce up to the several times or ten times compared to the present bandwidth of an interface signal that handles large-scale traffic between the transmitting devices. For example, in a case in which a wireless base station uses a serial interface e.g., a common public radio interface (hereinafter referred to as CPRI), a transmission bandwidth of an interface signal needs to be drastically reduced in consideration of expansion of wireless base stations for telecom service providers or device manufacturers.
Provided is an apparatus and method for increasing usage efficiency of transmission bandwidth through compression and recovery of interface signals, which are transmitted between network devices over a wired/wireless network based on orthogonal frequency-division multiplexing (OFDM).
In one general aspect, an OFDM-based network apparatus includes compressors to compress raw digital signals by using compressed sensing (CS), and a modulator to modulate the raw digital signals that have been compressed by the compressors.
In another general aspect, an OFDM-based network apparatus includes a demodulator to receive a modulated compressed signal that was once a raw digital signal, and to demodulate the modulated compressed signal, and recoverers to recover the compressed signal to the raw digital signal by decompressing the compressed signal, which has been demodulated through the demodulator, by using compressed sensing (CS).
In another general aspect, the data compression and recovery method of an OFDM-based network apparatus includes compressing raw digital signals by using compressed sensing (CS); modulating and transmitting the compressed raw digital signals; receiving and demodulating the modulated raw digital signals; and recovering the raw digital signals by decompressing, by using CS, the demodulated raw digital signals.
Other features and aspects may be apparent from the following detailed description, the drawings, and the claims.
Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.
The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness.
Referring to
The transmitter 1 and the receiver 2 may be base stations, exchange stations, or personal terminals. For example, the relationship between the transmitter 1 and the receiver 2 may be that of base station-base station, exchange station-personal terminal, or base station-personal terminal, each of which is connected through a network transmission medium. The transmitter 1 and the receiver 2 are distributed wireless base stations, which are located in a passive optical network (OFDM-PON) based on orthogonal frequency-division multiplexing; hence, as examples, transmitter 1 is a digital unit (DU), and the receiver 2 is a radio unit (RU).
The network transmission medium that connects the transmitter 1 and the receiver 2 may be a digital interface that transmits and receives a serial signal of a digital type. As demands for network infrastructure such as distributed cloud-RANs sharply increase, the bandwidth of an interface signal handling large-scale traffic between network devices needs to be reduced. The present disclosure aims to maximally reduce the bandwidth of an interface signal transmitted through the digital interface by applying compressed sensing (CS) technology and OFDM at the same time.
Referring to
A signal to be compressed by a compressor 10, is a ‘sparse signal’, which when converted to a specific domain, is a signal whose elements are not all zeros, but rather a signal whose elements sparsely show non-zero values. When illustrated on a graph, a sparse signal has a zero value at several coordinates and a very small number of non-zero values at others. The sparsity indicates that there is the very small number of non-zero values at a sparse signal. Thus, the signal that has a non-zero value may be much shorter than the length of data that a user wanted to originally transmit, and in such a case, the sparse signal may be successfully compressed through CS. Furthermore, a sparse signal that has been compressed into a compressed signal may be successfully recovered with a high probability by using a specific algorithm.
If a signal vector has numerous zeros, CS may recover the raw signal using a higher compression ratio than that of Nyquist sampling. Generally, Nyquist sampling is capable of recovering the raw signal only when sampling a signal at a rate higher than the Nyquist rate. However, through CS, the raw signal may be recovered completely even when sampling a signal at a rate lower than the Nyquist rate. Here, the measurement number of signals required for signal processing may be reduced using the sparsity of the sparse signal.
The modulator 12 modulates signals that have been compressed by the compressors 10. The modulator 12 modulates general OFDM signal, and the modulated compressed signals are transmitted to the receiver 2 through a digital interface.
The receiver 2 includes a demodulator 20 and recoverers 22. The demodulator 20 can demodulate an OFDM signal that has been received through a digital interface. The recoverers 22 recover OFDM data that is in a compressed state, and produces the characteristics of the raw digital signals. The recovery of the signal may be to a level wherein the characteristics of the raw signal have been restored; if at this time, this restored signal has an error vector magnitude (EVM) that is below the error threshold, then said signal may be construed a recovered signal; furthermore, if at this time, the loss between the compression and recovery processes of a signal is less than 3%, the recovered signal may be construed the same as the raw signal.
Referring to
Based on standardization and requests of industries, etc., the short-term prediction is that interface bandwidth sizes of network devices will be reduced by more than half, while the long-term, theoretical prediction proposes that bandwidth sizes may be reduced to an eighth of the original size when OFDM-based multiplexing is doubled. The present invention is capable of reducing the bandwidth size of an interface signal that is transmitted by a digital interface, by applying both CS technology and OFDM-based multiplexing at the same time, to an eighth of its original size.
Referring to
The compressors 10 may refer to multiple compressors 10-1, . . . , 10-n. These compressors are divided into compression blocks 10-1, . . . , 10-n according to the modulation method (e.g., a quadrature amplitude modulation (QAM) method) of the modulator 12, and compresses the raw digital signal by way of compressing each of its divided compression blocks.
First, the S/P converters 14-1, . . . , 14-n convert serial data, which is based on the serial interface, such as a common public radio interface (CPRI), into parallel data, and transmit the parallel data to the compressors 10. The parallel data consist of several bits e.g., two to seven bits. Each of the compressors 10-1, . . . , 10-n may include a multiplexer (MUX) 100, a time-to-frequency domain converter 102, and further include filters 104.
To apply compressed sensing to the parallel data that has been converted at each of the S/P converters 14-1, . . . , 14-n, the MUX 100 multiplexes two or more channel signals to one (for example, 2×1, 3×1, and 4×1) and outputs the combined signal to the time-to-frequency domain transformer 102. The time-to-frequency domain converter 102 converts the signal, which has been received from the MUX 100, from a time domain to a frequency domain, and compresses the converted signal. Such is a basic and essential technology for compressed sensing, which is performed to increase sparsity in converting to a frequency domain. The sparsity indicates a data share that shows zero or a value close to zero out of the entire data. For example, the time-to-frequency domain converter 102 may convert the domain using a fast Fourier transform (FFT), a discrete cosine transform (DCT), and a discrete wavelet transform (DWT), etc., and compress a signal by using such.
The filters 104 may be low pass filters (LPF). The filters 104 receive signals that have been output from the time-to-frequency domain converter 102, samples the data at a value that is set according to standardization of a communications protocol service, and removes unnecessary data components but only to a degree that does not go beyond the error threshold.
The modulator 12 receives the signal compressed by each of the compressors 10-1, . . . , 10-n and performs a general OFDM model modulation function. The modulator 12 includes a mapper 120, an inverse fast Fourier transform (FFT) module 122 (hereinafter referred to as IFFT module), a cyclic prefix (CP) inserter 124, and a parallel-to-serial converter 126 (hereinafter referred to as P/S converter).
The mapper 120 receives the signals compressed by the compressors 10-1, . . . , 10-n, maps the compressed signals into symbols, inserts a pilot symbol signal into each of the mapped signals, and provides the result to the IFFT module 122. The IFFT module 122 modulates, including IFFT, the symbols that have been received from the mapper 120, converts signals to a time domain, and outputs them. The output signals are carried on each different carrier, which is orthogonal to each other. The CP inserter 124 inserts cyclic prefixes to the signals so as to prevent interference between channels. The P/S converter 126 converts a low-speed parallel signal into a high-speed serial signal and transmits the converted signal to the DAC 16. The DAC 16 converts a signal of the serially-converted digital data type into an analog signal. The light sources 17 optically transmit the converted analog signal which is carried therein.
Referring to
The photodiode 24 detects an analog signal that has been transmitted optically, and the ADC 26 converts the detected analog signal into a digital signal and then outputs the digital signal to the demodulator 20.
The demodulator 20 includes a synchronizer 200, an S/P converter 201, a CP remover 202, a fast Fourier transform (FFT) module 203, a channel estimator 204, an equalizer (EQ) 205, and a demapper 206.
The synchronizer 200 synchronizes the digital signal that has been converted in the ADC 26, and the S/P converter 201 converts the synchronized digital signal from its serial form into a parallel form. The CP remover 202 removes the cyclic prefix that was inserted into the parallel signal converted in the S/P converter 201. The FFT module 203 performs an FFT on the signal from which the cyclic prefix has been removed and then converts said signal from a time domain to a frequency domain. The EQ 205 equalizes the channel for the signal coming from the FFT module 203. Here, the EQ 205 performs the equalization required for digital signal decompression that is to be conducted by the recoverers 22. Since the EQ 205 is substituting the equalization function of the recoverers 22 at this time, block configuration may be simple. Then, the demapper 206 demaps the signal that has been output from the EQ 205 and transmits the demapped signal to a recoverer in 22. The channel estimator 204 may estimate a channel between the transmitter and the receiver according to the signal that has been converted by the FFT module 203 using a fast Fourier transform.
The recoverers 22 may refer to multiple recoverers 22-1, . . . , 22-n. These recoverers are divided into decompression blocks 22-1, . . . , 22-n according to a demodulation method (e.g., QAM method) of the demodulator 20 and recovers the compressed signals by way of decompressing each of its decompression blocks. Each of the recoverers 22, 22-1, . . . , 22-n includes decompressors 220, a frequency-to-time domain converter 222, and a demultiplexer (DEMUX) 224.
The decompressor 220 decompresses the compressed signal through a recovery method using L1 minimization that is used as CS technique. The L1 minimization is a method of recovering the original raw signal that has been compressed to be below the Nyquist rate, whereby the recovery process is repeated until the error value is below the error threshold so as to recover the desired data. Then, the frequency-to-time domain converter 222, corresponding to the time-to-frequency domain converter 102 of the compressors 10 in
What has been described above is the background of the present invention along with examples of its application in in-phase/quadrature (I/Q) data that follows transmission protocols between distributed wireless base station devices. However, the application of the present invention is not limited to distributed wireless base stations but may be applied to other areas in the field of network communications (e.g., access networks or backbone networks). Alternatively, as a network transmission medium, the present invention may be applied to a wired/wireless system, the system using coaxial cables, or the combined system using both wired and wireless communications. Alternatively, the present invention may be applied to a network device as a multiplexing system in which time division, frequency division, wavelength division, code division, Orthogonal Frequency-Division Multiple Access (OFDMA), etc. are applied. As a network device, the present invention may be applied to a router, switch, and terminal, or to satellite communications, fixed wireless communications, and wireless mobile communications systems. Furthermore, the present invention may be widely applied to the hardware or software of various communications systems that need to be able to conduct compression and recovery to the data to be transmitted through the networks.
Referring to
According to an exemplary embodiment, in a case of transmitting and receiving an OFDM signal using a digital interface, all types of capital expenditures (hereinafter referred to as CAPEX) and operating expenditure (hereinafter referred to as OPEX) may be dramatically reduced as a bandwidth of an interface signal transmitted through the digital interface is reduced. Particularly, in distributed base station markets, next generation mobile communications markets to be developed in the future, especially in cases where the digital interface is connected between an exchange station and a personal terminal, or a digital interface is connected between a base station and a personal terminal, the CAPEX and OPEX of communications service providers may be reduced dramatically. In such a case, it is predicted that a technology, which coexists communications enterprises, device manufacturing enterprises, content and service providing enterprises, consumers, etc., may be developed.
A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0080012 | Jun 2014 | KR | national |
