WO2017149965A1

WO2017149965A1 - Receiver, transmitter, and signal decoding method

Info

Publication number: WO2017149965A1
Application number: PCT/JP2017/001456
Authority: WO
Inventors: 正裕青野
Original assignee: 株式会社日立製作所
Priority date: 2016-03-01
Filing date: 2017-01-18
Publication date: 2017-09-08

Abstract

The purpose of the present invention is to improve frequency utilization efficiency and increase communication speed of wireless communication. A receiver (2) is provided with: a receive unit which receives a signal obtained by modulating each of a plurality of subcarriers differing by a predetermined frequency with transmission data at a modulation speed not lower than the predetermined frequency; a Fourier transform computing unit (24) which, with respect to an output signal from the receive unit, performs a discrete Fourier transform in which the frequencies after transformation are limited to the frequencies of the subcarriers; and a data acquisition unit (25) which acquires reception data from each of the subcarriers computed by the Fourier transform computing unit (24).

Description

Receiver, transmitter, and signal decoding method

The present invention relates to a receiver, a transmitter, and a signal decoding method.

In conventional cellular phone communication, digital modulation of orthogonal frequency division multiplexing may be employed. This orthogonal frequency division multiplexing is multicarrier modulation in which data is carried on a number of subcarriers. Since these subcarriers are orthogonal to each other, they do not interfere with each other even though there is an overlap on the frequency axis, and each subcarrier can be distinguished by fast Fourier transform processing.

Patent Document 1 states that “a 2N-channel baseband pulse amplitude modulation signal synchronized with each other with a clock period of T seconds, a frequency difference between adjacent carriers is 1 / T cycle, and carriers are in phase or quadrature with each other. In a quadrature multiplexed signal transmission / reception system in which N is converted to N quadrature amplitude modulation signals by 2N carriers whose phases are set so as to maintain the same, and then these signals are multiplexed and transmitted, two in-phase channels adjacent to each other in the frequency domain And at the identification time of each baseband signal demodulated at the receiving side by giving a delay difference of T / 2 seconds between the transmitting side baseband pulse amplitude modulation signals corresponding to these two orthogonal channels only. Transmission and reception of orthogonal multiplexed signals characterized by almost zero intersymbol interference and interchannel interference It has been described as expressions ".

JP-A-52-151510

Patent Document 1 describes a method of performing frequency multiplex communication using a plurality of orthogonal carrier waves. However, this method limits the frequency utilization efficiency and limits the communication speed of wireless communication.
Therefore, an object of the present invention is to provide a receiver, a transmitter, and a signal decoding method that can improve the frequency utilization efficiency and improve the communication speed of wireless communication.

In order to solve the above-described problem, the receiver of the present invention receives a signal that is modulated with transmission data at a modulation speed equal to or higher than the predetermined frequency for each of a plurality of subcarriers that differ by a predetermined frequency. A Fourier transform calculation unit that performs a discrete Fourier transform on the output signal of the reception unit, the frequency after conversion being limited to the frequency of the subcarrier, and reception from each subcarrier calculated by the Fourier transform calculation unit A data acquisition unit for acquiring data.
Other means will be described in the embodiment for carrying out the invention.

According to the present invention, it is possible to increase the frequency utilization efficiency and improve the communication speed of wireless communication.

It is an example of the transmitter in 1st Embodiment. It is an example of a transmission signal generation part. It is an example of the receiver which performs discrete Fourier transform which restricted the frequency after conversion in a 1st embodiment. It is an example of the transmission signal production | generation part which performs on-off modulation. It is the simulation result of the discrete Fourier transform which restrict | limited the frequency after conversion. It is a simulation result of a fast Fourier transform. It is an example of the transmitter in the case of performing frequency conversion in the second embodiment. It is an example of the receiver in the case of performing frequency conversion in 2nd Embodiment. It is an example of the transmission signal generation part which performs phase shift keying. It is a flowchart in the case of adjusting a sampling frequency automatically.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(First embodiment)
1st Embodiment is an example of the radio equipment provided with the receiver which performs the Fourier transformation which restrict | limited the frequency after conversion.
It is assumed that the frequency of the carrier used is f _c , the frequency difference between the sub-carriers is f _b , and the number of sub-carriers is n. The frequency of the kth subcarrier is (f _c + f _b · k). The frequency difference f _b is smaller than the frequency at which the subcarriers f _c are orthogonal to each other.

FIG. 1 shows the configuration of the transmitter 1.
The transmitter 1 includes a transmission signal generation unit 11, a D / A converter (Digital Analog Converter) 12, and a radio frequency (RF) circuit 13, and a transmission antenna 10 is connected thereto.
The transmission signal generated by the transmission signal generation unit 11 is converted into an analog signal by the D / A converter 12. This analog signal is amplified by the high frequency circuit 13 and band-limited, and transmitted from the transmitting antenna 10. The D / A converter 12 and the high frequency circuit 13 are transmission units that transmit the output of the transmission signal generation unit 11 as a signal.

FIG. 2 shows a configuration of the transmission signal generation unit 11.
The transmission signal generation unit 11 includes a first carrier wave generation unit 14a to a fifth carrier wave generation unit 14e, a first carrier wave modulation unit 15a to a fifth carrier wave modulation unit 15e, a transmission data generation unit 16, and a transmission data parallelization unit 17 And an adder 18 and a transmission signal normalization unit 19.

The data to be transmitted to the receiver is generated by the transmission data generation unit 16. The generated data is parallelized by the transmission data parallelization unit 17 into five pieces equal to the number of subcarriers. The five pieces of parallel data are simultaneously transmitted using the frequency multiplexing communication method. Note that the number of subcarriers is not limited to five, and may be any natural number n.

In the first carrier generation unit 14a to the fifth carrier generation unit 14e, a sine wave is generated as a digital signal. Each carrier generation unit is required by the number of subcarriers to be used. The first carrier wave generation unit 14a generates a sine wave having a frequency (f _c + f _b ). The second carrier wave generation unit 14b generates a sine wave having a frequency (f _c + f _b · 2). The third carrier wave generation unit 14c generates a sine wave having a frequency (f _c + f _b · 3). The fourth carrier wave generation unit 14d generates a sine wave having a frequency (f _c + f _b · 4). The fifth carrier wave generation unit 14e generates a sine wave having a frequency (f _c + f _b · 5).
Each generated sine wave is modulated by the first carrier modulation unit 15a to the fifth carrier modulation unit 15e, respectively. Each carrier modulation unit is required as many as the number of subcarriers to be used in the same manner as the carrier generation unit. For the modulation, data parallelized by the transmission data parallelization unit 17 is used.

The modulated five carrier waves are added by the adder 18 and then normalized by the transmission signal normalization unit 19 and output. Normalization is signal processing that amplifies and attenuates a signal so that the amplitude of the output signal is kept constant.

FIG. 3 shows the configuration of the receiver 2.
The receiver 2 includes a high frequency circuit 22, an A / D converter (Analog Digital Converter) 23, a Fourier transform calculation unit 24, and a data acquisition unit 25 connected to the reception antenna 21.
A reception signal received by the reception antenna 21 via the wireless communication path is amplified and band-limited by the high frequency circuit 22 and converted into a digital signal by the A / D converter 23. This digital signal is Fourier-transformed by the Fourier transform calculation unit 24 and becomes reception data by the data acquisition unit 25. In the Fourier transform calculation unit 24, Fourier transform is performed by limiting the frequency after the transform.
The reception antenna 21, the high frequency circuit 22, and the A / D converter 23 receive a signal that is modulated at a modulation speed equal to or higher than a predetermined frequency by transmission data for each of a plurality of subcarriers that differ by a predetermined frequency. Part. The Fourier transform calculation unit 24 performs a discrete Fourier transform on the output signal of the reception unit in which the frequency after conversion is limited to the frequency of the subcarrier. The data acquisition unit 25 acquires reception data from each subcarrier calculated by the Fourier transform calculation unit 24.

Each of the following equations shows a transmission signal with a limited frequency. Let the transmission signal be f (t). When limited to a time shorter than the modulation period, the transmission signal f (t) is the sum of subcarriers used for transmission, as shown in Equation (1). Here, D ₀ is a constant component. Ideally, there are no constant components, but they are included in equation (1) to increase the accuracy of the Fourier transform.

A sine wave of phase α _k can be separated into a sine wave and a cosine wave with no phase difference. When the amplitude of the sine wave component is A _k and the amplitude of the cosine wave component is B _k , the transmission signal f (t) is expressed by Equation (2).

Sine and cosine waves can be represented by complex exponential functions. As a result, the transmission signal can be expressed as in Expression (3).

C _k is defined as in equation (4).

E _k (t) is defined as in equation (5).

From these equations (4) and (5), the transmission signal can be expressed as equation (6).

When Expression (6) is converted, it can be expressed as Expression (7). This is a Fourier transform calculation method in which the frequency after conversion is limited.

For the Fourier transform, the received signal needs to be sampled over (2n + 1) points, and the sampling points are (t _k, v _k ) (where −n ≦ k ≦ n). t _k is the time of the sampling point. This may be relative time. That is, t ₀ = 0. This is because the difference between relative time and absolute time can be included in α _k as a phase difference. v _k is the value of the sampled signal.

A Fourier transform matrix M is defined as in equation (8). This matrix M depends only on the time of the sampling point, and if the time is determined, the matrix M can be uniquely determined.

A column vector of C _k is defined as C as shown in Equation (9).

A column vector of v _k is defined as V as shown in Expression (10).

Since the received signal is Equation (7), Equation (11) is established.

and f _b << f _c, the period for sampling if sufficiently shorter than the period of f _b, the Fourier transform matrix M exists the inverse matrix M ^-1. When the inverse matrix M ⁻¹ is multiplied by the equation (11) from the left side, the equation (12) is obtained. That is, the column vector C can be obtained from the sampling points by calculating the inverse matrix of M.

From the condition of k = 0 in the equation (4), the following equation (13) can be derived.

From the condition of k> 0 and the condition of k <0 in the expression (4), the following expression (14) can be derived.

From Equation (3), the following Equation (15) can be derived. That is, the amplitude D _k of each subcarrier can be obtained. The data acquisition unit 25 can acquire data from the amplitude D _k of each subcarrier.

From the equation (3), the following equation (16) can be derived. That is, the phase α _k of each subcarrier can be obtained. The data acquisition unit 25 can acquire data from the phase α _k of each subcarrier.

By using this Fourier transform, it is theoretically possible to increase the frequency utilization efficiency by reducing f _b and increasing n. However, in reality, there are limits to these due to the resolution and noise of the A / D converter 23. More specifically, the modulation method is on-off keying (OOK), f _c = 920 MHz, f _b = 15 kHz, n = 5, the modulation speed for each carrier is 50 kbps, and the resolution of the A / D converter 23 is In the case of 12 bits, the transmission speed is 250 kbps.

FIG. 4 shows the configuration of the transmission signal generation unit 11 under the above-described conditions.
The transmission signal generation unit 11 includes switches 151a to 151e that function as the first carrier modulation unit 15a to the fifth carrier modulation unit 15e, and is otherwise configured in the same manner as the transmission signal generation unit 11 shown in FIG. Yes.

The transmission data generation unit 16 generates data to be transmitted to the receiver 2 (see FIG. 3). The generated data is parallelized by the transmission data parallelization unit 17 into five pieces equal to the number of subcarriers. The five pieces of parallel data are simultaneously transmitted using the frequency multiplexing communication method. Since five subcarriers are used and each carrier is modulated by 1 bit, the transmission data parallelization unit 17 converts the transmission data into 5-bit parallel data. The transmission data parallelization unit 17 parallelizes the data so as to avoid only zero data. Note that the number of subcarriers is not limited to five, and may be any natural number n.

In the first carrier generation unit 14a to the fifth carrier generation unit 14e, a sine wave is generated as a digital signal. For example, the first carrier generation unit 14a generates a carrier of 920.015 MHz. Each generated sine wave is modulated by switches 151a to 151e, which are carrier wave modulation units. For the modulation, 5-bit data parallelized by the transmission data parallelization unit 17 is used. The carrier wave is modulated by turning on the corresponding switch when the data is “1” and turning off the corresponding switch when the data is “0”. The five modulated carrier waves are added by the adder 18 and then normalized by the transmission signal normalization unit 19 and output. In the transmission signal normalization unit 19, the output amplitude is normalized to 1. For example, when all the switches 151a to 151e are ON, the signal is set to 1/5, and when only 3 are set, the signal is set to 1/3.

Since the modulation speed is 50 kHz, the modulation period is 20 ms, and since there are five subcarriers, 11 sampling points are required. Therefore, the sampling period of the A / D converter 23 is (20/11) = 1.82 ms, and the sampling frequency is 550 kHz.

The data acquisition unit 25 (see FIG. 3) determines a threshold value, and obtains a received signal assuming that the subcarrier amplitude D _k is greater than or equal to the threshold value is “1”, and that below the threshold value is “0”. When all the five carriers are “1”, D _k is about 0.2, so that the received data can be suitably obtained when the threshold is 0.1 to 0.15.

FIG. 5 shows a simulation result of Fourier transform in which the frequency after conversion is limited.
For each of the five subcarriers, the value of the amplitude D _k is shown. The data related to the first, second, and fifth subcarriers is received as “1”, and the data related to the third and fourth subcarriers is received as “0”. As shown in FIG. 5, the frequency difference between the subcarriers is smaller than the frequency at which the subcarriers are orthogonal to each other.
In this simulation, the bit error rate was 10 ⁻⁶ or less.

FIG. 6 shows a simulation result when the received signal having the above-described condition is subjected to Fourier transform by normal FFT (Fast Fourier Transform). However, at a sampling frequency of 550 kHz, a 920 MHz signal cannot be Fourier transformed from the Nyquist theorem. Therefore, the sampling frequency is specifically set to 10 GHz. However, for f _b = 15 kHz, the sampling time is 20 ms and the frequency resolution is 50 kHz. Therefore, as can be seen from FIG. 6, each carrier wave cannot be decomposed. That is, under the conditions of the first embodiment, a received signal cannot be obtained by normal FFT, and therefore data cannot be transmitted / received by orthogonal frequency division multiplexing.
As described above, the use efficiency of the frequency can be improved by using the wireless device including the receiver 2 that performs the Fourier transform in which the frequency after the conversion in the first embodiment is limited. In addition, since the matrix is low-dimensional compared to normal FFT, the received wave can be demodulated from short-time sampling data. Furthermore, since the fundamental frequency becomes the frequency resolution, a high frequency resolution can be realized by fixing the fundamental frequency in advance.
The transmitter and receiver of the first embodiment are suitable for a large capacity wireless communication system of several Mbps inside a substation, a wireless communication system for a factory, a traffic system, a short-range wireless communication system, and the like.

In the second embodiment, an example in which frequency conversion is used in addition to the first embodiment will be described.
FIG. 7 shows the configuration of the transmitter 1A.
In the transmission signal generation unit 11A, a transmission signal is generated with the carrier frequency f _c = 0, and is converted into an analog signal by the D / A converter 12. This analog signal is multiplied by the carrier wave generated by the oscillator 32 in the high frequency circuit 13, amplified and band-limited by the high frequency circuit 13, and then transmitted from the transmission antenna 10.
With this frequency conversion, the operating frequency of the D / A converter 12 can be lowered. Therefore, an inexpensive one can be used for the D / A converter 12.

FIG. 8 shows a carrier modulation unit when phase modulation (Phase Shift Keying, PSK) is used. A first carrier modulation unit 15a (see FIG. 2) is realized by a combination of the inverter 152a and the switch 153a. The same applies to the inverters 152b to 152e and the switches 153b to 153e.

When the data is “1”, the switch 153a outputs the carrier wave as it is, and when the data is “0”, the inverter 152a outputs the carrier wave whose phase is shifted by 180 degrees. As a result, the amplitude of the transmission signal does not change, so signal normalization is not necessary.

The receiver 2 of the first embodiment uses the amplitude D _k as received data. The receiver 2A of the second embodiment uses the phase α _k . However, since the sampling time t _k is relative, inversion of “1” and “0” can occur. Therefore, a method of determining “1” and “0” using a pilot signal before communication, time synchronization between the transmitter 1A and the receiver 2A, and a sampling point time t _k as an absolute time. It is necessary to use the method to do.

It is also possible to perform multilevel modulation. For example, if quaternary quadrature amplitude modulation (QAM) is used, each of the amplitude D _k and the phase α _k takes four values. The data acquisition unit 25 needs to set a threshold value for each to obtain data.
As described above, it is possible to simplify the circuit and improve the communication speed by using the modulation method of the second embodiment.

FIG. 9 shows the configuration of the receiver 2A.
A carrier wave is reproduced by the carrier wave reproduction circuit 26 from the reception signal output from the high frequency circuit 22. The reproduced carrier wave and the received signal are multiplied by a multiplier 27, filtered by a low-pass filter 28, and down-converted. It is possible to use a detection circuit instead of the carrier wave recovery circuit 26.
The down-converted received signal is then digitally converted by the A / D converter 23 and Fourier-transformed by the Fourier transform calculation unit 24 with f _c = 0. This frequency conversion can be a f _c = 0, it is easy to matrix calculation of the Fourier transform. Further, since the down-converted signal is A / D converted, an inexpensive A / D converter 23 can be employed.
By using the wireless device of the second embodiment, the band utilization efficiency can be increased with a slower circuit / calculation.

In the first embodiment, the sampling rate is 550 kHz. This is the minimum sampling rate for performing the Fourier transform. When this sampling rate is doubled, the sampling points are also doubled, and received data can be obtained using two different sets of data. By obtaining and averaging a plurality of received data, communication with few errors can be performed.

FIG. 10 is a flowchart of processing for determining the sampling rate.
First, the receiver 2A sets the smallest value as the initial value of the sampling frequency (step S10). Next, the receiver 2A sets a variable f to 0 (step S11), and then transmits a pilot signal transmission start request to the transmitter 1A (step S12).

The receiver 2A receives the pilot signal (step S13) and calculates a bit error rate (BER) (step S14). If the bit error rate satisfies the regulation (step S15 → Yes), after substituting the sampling frequency into the variable f (step S16), the sampling frequency is lowered by one step (step S17), and the process of step S13 is performed. Return to.

If the bit error rate does not satisfy the regulation (step S15 → No), it is determined whether the variable f is 0 or not. If the variable f is 0 (step S18 → Yes), the sampling frequency is increased by one level (step S19), and the process returns to step S13.

If the variable f is not 0 (step S18 → No), a sampling frequency at which the pit error rate satisfies the regulation has been found. At this time, the receiver 2A transmits a pilot signal transmission stop request to the transmitter 1A (step S20), sets the sampling frequency (sampling speed) to the value of the variable f, and ends the flowchart of FIG. Thereafter, the A / D converter 23 samples the signal at the frequency f and demodulates it into a digital signal.

In addition, when communication is not possible at any sampling frequency, the number of carrier waves and the frequency difference can be made variable. The processing for determining the sampling rate shown in FIG. 10 may be performed only once before the session is established, or may be performed depending on the communication situation such as when the communication error rate deteriorates.
According to the processing for determining the sampling rate of this embodiment, it is possible to select a sampling rate according to the communication environment.

(Modification)
The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

The above-described configurations, functions, processing units, processing means, etc. may be partially or entirely realized by hardware such as an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by a processor interpreting and executing a program that realizes each function.

In each embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.
Examples of modifications of the present invention include the following (a) to (e).
(A) The communication path between the transmitter and the receiver is not limited to wireless, but may be wired. Application examples may be digital television, broadcasting, broadband internet connection, and the like. According to the present invention, since clock synchronization is not necessary, data communication can be speeded up.
(B) The number of subcarriers is not limited to five.
(C) Subcarrier modulation is not limited to 1-bit modulation of transmission data, and multi-level modulation such as 256QAM (256 Quadrature Amplitude Modulation) may be used. As a result, the data communication can be further speeded up.
(D) The sampling frequency adjustment process is not limited to the process according to the flowchart of FIG.
(E) The transmission wave may be calculated by directly adding and subtracting each carrier wave without being limited to the inverse Fourier transform.

1, 1A Transmitter 10

Transmitting antenna

11, 11A Transmission signal generator 12 D / A converter 13 High-frequency circuit 14a First carrier wave generator ...
14e 5th carrier generation part 15a 1st carrier modulation part ...
15e 5th carrier wave modulation part 16 transmission data generation part 17 transmission data parallelization part 18 adder 19 transmission

signal normalization part

2, 2A receiver 21 reception antenna 22 high frequency circuit 23 A / D converter 24 Fourier transform calculation part 25 data Acquisition unit 26 Carrier wave recovery circuit 27 Multiplier 28 Low-pass filter 151a to 151e Switch 152a to 152e Inverter 153a to 153e Switch

Claims

For each of a plurality of subcarriers that differ by a predetermined frequency, a receiving unit that receives a signal modulated by transmission data at a modulation speed equal to or higher than the predetermined frequency;
A Fourier transform calculation unit that performs a discrete Fourier transform on the output signal of the reception unit, in which the frequency after conversion is limited to the frequency of the subcarrier;
A data acquisition unit for acquiring reception data from each subcarrier calculated by the Fourier transform calculation unit;
A receiver comprising:
The data acquisition unit acquires received data from the intensity of each subcarrier calculated by the Fourier transform calculation unit,
The receiver according to claim 1.
The data acquisition unit acquires received data from the phase of each subcarrier calculated by the Fourier transform calculation unit,
The receiver according to claim 1.
The receiving unit changes a sampling period according to an error rate of received data acquired by the data acquiring unit,
The receiver according to any one of claims 1 to 3, wherein
The receiving unit samples a signal received via a communication path with an A / D converter,
5. The receiver according to any one of claims 1 to 4, wherein:
The reception unit samples the frequency of a signal received via a communication channel after down-conversion with an A / D converter,
5. The receiver according to any one of claims 1 to 4, wherein:
A combination of a plurality of carrier generation units that generate a plurality of subcarriers that differ by a predetermined frequency, and a plurality of carrier modulation units that modulate the subcarriers generated by the carrier generation unit based on data;
An adder for adding subcarriers modulated by each of the carrier modulators;
A transmission unit that transmits the output of the addition unit as a signal;
With
The predetermined frequency is smaller than a frequency difference in which each subcarrier is orthogonal to each other.
A transmitter characterized by that.
A normalization unit for normalizing the output of the addition unit;
Each carrier modulation unit performs on-off modulation on the subcarrier generated by each carrier generation unit based on data,
The transmitter according to claim 7.
Each of the carrier modulation units performs phase shift keying on the subcarrier generated by each of the carrier generation units based on data.
The transmitter according to claim 7.
The transmission unit converts the output of the addition unit into an analog signal by a D / A converter, and transmits the analog signal through a communication path.
The transmitter according to any one of claims 7 to 9, characterized by the above.
The transmission unit converts the output of the addition unit into an analog signal by a D / A converter, up-converts the frequency, and transmits the signal via a communication path.
The transmitter according to any one of claims 7 to 9, characterized by the above.
Receiving a signal modulated by transmission data at a modulation speed equal to or higher than the predetermined frequency for each of a plurality of subcarriers different from each other by a predetermined frequency;
Performing a discrete Fourier transform on the received signal with the transformed frequency limited to the frequency of the subcarrier;
Decoding received data from each subcarrier calculated by the discrete Fourier transform;
A signal decoding method comprising: