Communication circuit and modulation method

Abstract

To reduce the cost and size of radio units in millimeter wave distributed antenna systems.SOLUTION: A communication circuit 1 performs n-bit (n is a natural number) band-pass delta-sigma modulation and includes a differentiator 11 that outputs the difference between an input signal and a feedback signal, an integrator 12 that integrates the output from the differentiator 11, a quantizer 13 that performs a 2n-level quantization operation on the output from the integrator 12 and outputs an output signal, a converter 15 that performs 2n-level conversion processing on the output from the quantizer 13, and a band-pass filter 14 that inputs a signal obtained by extracting a specific frequency band from the output from the converter 15 to the differentiator 11 as a feedback signal.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The technology described in this specification relates to a communication circuit and a modulation method.

Background Art

[0002] With the progress of the information society, the data traffic volume of both wired and wireless has been increasing.

[0003] In wireless communication, since the development of the millimeter wave band, which is a higher frequency band compiled with the microwave band, has been progressing since the 5G era. In millimeter waves, since the attenuation due to spatial propagation is larger than that in microwaves, an antenna arrangement mainly for line-of-sight propagation is used.

[0004] The adoption of distributed antennas is effective for obtaining a wide coverage area while maintaining the line of sight, but the size and cost of each distributed radio unit (RU) are important factors for realizing this.

[0005] In a distributed antenna system, the RU including the antenna and the distributed unit (DU) are connected using an optical fiber. As the standard for this optical fiber section, eCPRI is adopted. In this standard, the baseband signal is quantized to 8 bits or more and transmitted and received as digital data. Also, assuming the adoption of an active antenna system (AAS) that enables digital beamforming using a plurality of antenna elements, components such as digital / analog converters (DACs) and millimeter wave band mixers are required for each antenna element in the RU.

[0006] Therefore, an optical link using 1-bit delta-sigma modulation, which can be expected to miniaturize and reduce the cost of the distributed antenna system, has been proposed (Non-Patent Document 1).

[0007] In delta-sigma modulation, a millimeter wave band transmission signal can be obtained by simply photoelectrically converting the optical fiber output and passing it through a low-pass filter or a band-pass filter whose carrier frequency is included in the passband (Non-Patent Document 2).

[0008] One way to generate a direct RF signal from a digital signal is to filter the analog output generated in the first Nyquist zone of a high-speed n-bit DAC with a band-pass or low-pass filter and use it as the RF signal output.

[0009] Fig. 1(a) is a diagram illustrating an n-bit DAC transmitter 6 in the conventional example, and (b) is a diagram illustrating a 1-bit band-pass delta-sigma modulation transmitter 7 in the conventional example.

[0010] The n-bit DAC transmitter shown in Fig. 1(a) includes a modulator 61, and a modulator section includes an n-bit DAC 62 and a BPF 63 (band-pass filter).

[0011] The 1-bit band-pass delta-sigma modulation transmitter 7 shown in Fig. 1(b) includes a modulator 71, a 1-bit band-pass delta-sigma modulator 72, and a modulator section includes a 1-bit DAC 73 and a BPF 74.

[0012] Both transmitters in Fig. 1(a) and (b) generate RF signals in a frequency range below half of the sampling frequency.

[0013] In the case of the n-bit DAC 62, the spurious radiation power near the carrier including the signal-to-noise ratio (S / N) and the adjacent channel leakage power (ACP) depends on the resolution of the DAC 62.

[0014] On the other hand, in the 1-bit DAC 73, the dynamic range in terms of the amplitude after band-limiting is improved by the time resolution due to oversampling. Further, by 1-bit band-pass delta-sigma modulation, it is possible to generate an RF signal having a wide dynamic range while performing noise shaping at any frequency within the first Nyquist zone by filtering the periphery of the signal band in the feedback path.

[0015] When comparing the 1-bit DAC73 with the n-bit DAC62, since the amplitude resolution is unnecessary and the serial-to-parallel conversion is unnecessary, the operating clock frequency required for the 1-bit DAC73 can be increased.

[0016] Therefore, by using the 1-bit bandpass delta-sigma modulator 72, an RF signal with a higher frequency can be generated.

[0017] A method of generating an RF signal with a frequency exceeding the Nyquist frequency by using the image output of the DAC is called a direct digital RF transmitter.

[0018] An RF signal is generated in the first Nyquist zone by using the 1-bit bandpass delta-sigma modulator 72 using the 1-bit DAC73.

[0019] In delta-sigma modulation, oversampling is used to achieve a high dynamic range, and a much higher clock frequency is used than when using the n-bit DAC62. For this reason, the image frequency is also generated at a relatively high frequency.

[0020] In recent years, optical modules supporting 28 Gbps have been widely used in optical fiber communication, and devices having input / output ports (I / O) that support this are easily available for field-programmable gate arrays (FPGAs) used for digital signal processing.

[0021] By setting the sampling frequency to 28 GHz or a frequency close thereto, it has become easy to obtain a transmission signal with a carrier frequency of 40 GHz or higher as an image signal.

Prior Art Documents

Non-Patent Documents

[0022]

Non-Patent Document 1

[0023] In 1-bit bandpass delta-sigma modulation, by oversampling the input modulation signal, multi-level conversion can be achieved with 1 bit. In other words, increasing the oversampling rate (OSR) has the same effect as increasing the number of quantization bits of the DAC.

[0024] However, since the operating speed of optical modules that can be easily used for wired LAN (Local Area Network) communication devices is currently 28 Gbps, assuming that the baseband signal bandwidth is 100 MHz and its sampling frequency is 200 MHz, the OSR is approximately 140. When the bandwidth is 400 MHz, it is limited to approximately 35.

[0025] Due to the adoption of orthogonal frequency division multiplexing (OFDM) as a modulation method and the need to support multi-beams such as Multi Input Multi Output (MIMO) in a 5G communication system, a high peak-to-average power ratio (PAPR) and a wide dynamic range are required.

[0026] One solution is to increase the order of delta-sigma modulation, but this increases the computational complexity for digital signal processing and has limitations for real-time processing.

[0027] In one aspect, the technology described in this specification aims to reduce the cost and size of radio units in a millimeter-wave distributed antenna system.

Means for Solving the Problem

[0028] In one aspect, a communication circuit is a communication circuit that performs n-bit (n is a natural number) band-pass delta-sigma modulation, and includes a differentiator that outputs the difference between an input signal and a feedback signal, an integrator that integrates the output from the differentiator, a quantizer that performs a 2n-level quantization operation on the output from the integrator and outputs an output signal, a converter that performs the 2n-level conversion process on the output from the quantizer, and a band-pass filter that extracts a signal in a specific frequency band from the output from the converter and inputs it as the feedback signal to the differentiator.

Effect of the Invention

[0029] In one aspect, the cost and size of radio units in a millimeter-wave distributed antenna system can be reduced.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] Hereinafter, embodiments will be described with reference to the drawings. However, the embodiments shown below are merely examples, and there is no intention of excluding various modifications and applications of technologies not explicitly shown in the embodiments. That is, the present embodiment can be variously modified and implemented without departing from its gist.

[0032] Also, each drawing is not intended to include only the components shown in the drawing, but can include other components. Hereinafter, in the drawings, parts denoted by the same reference numerals indicate the same or similar parts unless otherwise specified.

[0033] 〔A〕Embodiment FIG. 2 is a diagram illustrating a delta-sigma modulator 1 according to an embodiment.

[0034] The n-bit (n is a natural number; 1 bit or 2 bits in the example shown in FIG. 2) bandpass delta-sigma modulator 1 shown in FIG. 2 is an example of a communication circuit provided in a radio unit in a millimeter-wave distributed antenna system for a 5G terrestrial network. The delta-sigma modulator 1 includes a differentiator 11, an integrator 12, a quantizer 13 with 2 levels (1, -1) or 4 levels (3, 1, -1, -3), a converter 14 with 2 levels (1, -1) or 4 levels (3, 1, -1, -3), and a bandpass filter 15.

[0035] The differentiator 11 outputs the difference between the input signal and the feedback signal.

[0036] The integrator 12 integrates the output from the differentiator 11.

[0037] The quantizer 13 performs a quantization operation of 2n levels on the output from the integrator 12 and outputs an output signal. In the example shown in FIG. 2, the quantizer 13 performs a quantization operation of 2 levels or 4 levels. The output signal from the quantizer 13 becomes 0, 1 or 0, 1, 2, 3.

[0038] The converter 14 performs a conversion process of 2n levels on the output from the quantizer 13. In the example shown in FIG. 2, the converter 14 performs a conversion process of 2 levels or 4 levels.

[0039] The band - pass filter 15 extracts a signal in a specific frequency band from the output of the converter 14 and inputs it as a feedback signal to the differentiator 11.

[0040] The 2 - bit conversion expands the dynamic range without increasing the OSR, and can suppress the reduction of the adjacent channel leakage power ratio (ACLR) and the reduction of the modulation accuracy (EVM).

[0041] By applying this, the delta - sigma modulation of the 2 - bit band - pass can be achieved relatively easily. Since it is possible to change to 2 - bit conversion only by using the delta - sigma modulation and its output, the transition from the delta - sigma modulation of the 1 - bit band - pass is easy.

[0042] When considering the application to a 5G terrestrial network by the band - pass delta - sigma modulation in the optical fiber link between DU and RU shown in FIG. 2, since it is necessary to support a wide base - band bandwidth and multiple beams, the sigma modulation of the 2 - bit band - pass can expand the dynamic range without increasing the oversampling rate. Also, the deterioration of the ACLR and EVM can be suppressed.

[0043] According to the communication circuit and modulation method in the above - described embodiment, the cost and size of the radio unit in the millimeter - wave distributed antenna system can be reduced.

[0044] 〔B〕Others The disclosed technology is not limited to the above-described embodiments, and various modifications can be made and implemented without departing from the spirit of each embodiment. Each configuration and each process of each embodiment can be selected as necessary or combined as appropriate.

[0045] In the above-described embodiments, the delta-sigma modulator 1 provided in the radio unit in the millimeter-wave distributed antenna system for 5G terrestrial network has been described. However, the delta-sigma modulator 1 may be used in other generations of networks such as 3G, 4G, and 6G and later, or may be used in addition to terrestrial networks such as satellite networks.

Explanation of Reference Numerals

[0046] 1: Delta-sigma modulator 11: Differentiator 12: Integrator 13: Quantizer 14: Converter 15: Band-pass filter 6: n-bit DAC transmitter 61, 71: Modulator 62, 73: DAC 63, 74: BPF 7: Delta-sigma modulation transmitter 72: Delta-sigma modulator

Claims

1. A communication circuit that performs n-bit (n is a natural number) bandpass delta-sigma modulation, comprising: a differentiator that outputs the difference between an input signal and a feedback signal; an integrator that integrates the output from the differentiator; a quantizer that performs a 2n-level quantization operation on the output from the integrator and outputs an output signal; a converter that performs the 2n-level conversion process on the output from the quantizer; a bandpass filter that extracts a signal with a specific frequency band from the output from the converter and inputs it as the feedback signal to the differentiator; A communication circuit comprising the above components.

2. The n bits are 2 bits, The communication circuit according to claim 1.

3. A modulation method that performs n-bit (n is a natural number) bandpass delta-sigma modulation, comprising: outputting the difference between an input signal and a feedback signal; integrating the output of the difference; performing a 2n-level quantization operation on the result of the integration and outputting an output signal; performing the 2n-level conversion process on the result of the quantization operation; using, as the input for outputting the difference, a signal obtained by extracting a specific frequency band from the result of the conversion process as the feedback signal; A modulation method in which a communication circuit performs the above processes.

4. The n bits are 2 bits, The modulation method according to claim 3.

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