阅读说明：本技术 调制解调方法、物端节点、接收机、通信系统 (Modulation-demodulation method, object end node, receiver and communication system ) 是由 卢宁宁 熊志广 高杰 张海鹏 宋瑞良 于 2021-10-29 设计创作，主要内容包括：本发明公开了一种调制解调方法、物端节点、接收机、通信系统,涉及通信领域。利用电磁波后向散射原理,实现了一种新型的调制解调,在保证无线通信功耗较低的同时,提高了可靠性,增强了抗干扰能力,降低了误码率,受噪声影响小,对信道特性变化不敏感,有利于节点移动,可以应用于物联网领域。(The invention discloses a modulation and demodulation method, an object end node, a receiver and a communication system, and relates to the field of communication. Utilize electromagnetic wave backscattering principle, realized a neotype modem, when guaranteeing that the wireless communication consumption is lower, improved the reliability, strengthened the interference killing feature, reduced the bit error rate, it is little influenced by the noise, it is insensitive to channel characteristic change, be favorable to the node to remove, can be applied to the thing networking field.)

1. A modulation method, comprising:

object end node N receives single-frequency electromagnetic signal r₂(t)，r₂(t) a single frequency electromagnetic signal c (t) transmitted from a radio frequency source F;

the object end node N transmits a bit sequence a to be transmitted_nTransformed into a differential code b_n；

The object end node N transmits the differential code b_nEach symbol of (a) is converted into a unipolar square wave signal b (t);

the object end node N uses a unipolar square wave signal b (t) to control the on-off state of the radio frequency switch K, adjust the reflection coefficient, and parasitically modulate the generated unipolar square wave signal b (t) on a single-frequency electromagnetic signal r₂(t) and reflected off.

2. Method according to claim 1, characterized in that the object node N is arranged to transmit a bit sequence a_nTransformed into a differential code b_nThe method comprises the following steps:

object end node N is according toOrBit sequence a to be transmitted_nTransformed into a differential code b_n，

Wherein n is 0,1,2，...，b_n-1Is b is_nThe previous symbol of (2), differential code b_nInitial bit b of_-1Can be preset to be 0 or 1,which means that the addition of the modulo 2,^-representing a binary negation.

3. Method according to claim 1, characterized in that the object node N transmits the differential code b_nTo a unipolar square wave signal b (t) comprises:

the object end node N is according to b (t) sigma_nb_ng(t-nT_B) Differential code b_nEach symbol of (a) is converted into a unipolar square wave signal b (t),

wherein g (T) is amplitude of 1 and duration of T_BRectangular pulse of (1), T_BIs the bit duration.

4. The method of claim 1,

the load impedance of the antenna at the object end node N is Z_a，A₂Is amplitude, w₀In order to be the angular frequency of the frequency,in order to be the phase position,

when the unipolar square wave signal b (t) is 0, the radio frequency switch K is connected to the load Z₀Coefficient of reflectionAt the moment, the electromagnetic wave s reflected by the object end node₀(t)＝Γ₀r₂(t)；

When the unipolar square wave signal b (t) is 1, the radio frequency switch K is connected to the load Z₁Coefficient of reflectionAt the moment, the electromagnetic wave s reflected by the object end node₁(t)＝F₁r₂(t)。

5. The method of claim 4,

when Z is₀＝0Ω，Z₁Infinity Ω, Γ₀＝-1，Γ₁＝+1，

Electromagnetic wave reflected by object end node

6. A demodulation method, comprising:

the receiver R receives an electromagnetic signal R (t) which comes from an electromagnetic wave s (t) reflected by an object end node N and acquires a corresponding in-phase component y_I2(t) and the orthogonal component y_Q2(t)；

Receiver R respectively corresponding to in-phase components y_I1(t) and the orthogonal component y_Q1(t) squaring and adding the results of the squaring to obtain a signal y₄(t) adding y₄(t) after DC cut-off, a sum-of-squares signal y is obtained₅(t)；

The receiver R will sum the squares signal y₅(T) delay time T_BObtaining a delayed signal y₆(t)，T_BFor bit duration, will y₅(t) and y₆(t) multiplication or division to obtain the signal y₇(t)；

Receiver R at nT_BTime, pair y₇(t) sampling to obtain a sampling value y₇(nT_B)；

Receiver R pair sample value y₇(nT_B) Making a decision with the result of e_nWherein, according to y₇(nT_B) Greater than 0 or less than 0, decision e_nIs 0 or 1, e_nI.e. the binary bit sequence finally demodulated by the receiver R.

7. Method according to claim 6, characterized in that the receiver R obtains the corresponding in-phase component y_I2(t) and the orthogonal component y_Q2(t) comprises:

the receiver R uses a band-pass filter to filter the received electromagnetic signal R (t) to obtain a signal y (t);

the receiver R generates a coherent carrier comprising an in-phase carrier c_I(t) and orthogonal carrier c_Q(t)；

The receiver R using signals y (t) and c_I(t) multiplying to obtain a signal y_I1(t) then passing through a low-pass filter to obtain an in-phase component y_I2(t)；

The receiver R using signals y (t) and c_Q(t) multiplying to obtain a signal y_Q1(t) then passing through a low pass filter to obtain the quadrature component y_Q2(t)。

8. Method according to claim 7, characterized in that the receiver R generates the in-phase carrier c of the coherent carrier_I(t) and orthogonal carrier c_Q(t) are respectively:

wherein the content of the first and second substances,for the phase of the coherent carrier, for characterizing the frequency shift of the coherent carrier, the magnitude of which varies slowly with time τ, w₀Is the angular frequency and a is the amplitude.

9. The method of claim 6 wherein the receiver R pairs the sample values y₇(nT_B) A decision is made as to whether or not to make a decision,the decision result is e_nThe method comprises the following steps:

when employing mark differential codes:

when null number differential codes are employed:

10. an object node configured to perform the modulation method of any one of claims 1-5.

11. A receiver configured to perform the mediation method of any one of claims 6-9.

12. A communication system for the internet of things, comprising:

the object end node of claim 10, and

the receiver of claim 11.

Technical Field

The invention relates to the field of communication, in particular to an ultra-low power consumption modulation and demodulation method, an object end node, a receiver and a communication system for the Internet of things based on electromagnetic wave backscattering.

Background

With the proposition of concepts such as smart cities, smart agriculture, smart medical treatment, smart wearable and the like, the Internet of things is applied more and more in social life and becomes one of the major industries for domestic and overseas development. The object end node is a necessary component of the Internet of things, belongs to a perception layer of the Internet of things, is positioned at the tail end of a topological structure of the Internet of things, is generally embedded into a human body or an object for use, serves as a perception organ and an executive organ of objective objects, and is a key ring for realizing an intelligent network and constructing network intelligence. However, the problems of excessive communication power consumption and the like are not properly solved, and the milliwatt-level communication power consumption can quickly exhaust the battery power, which seriously restricts the application of the internet of things.

Disclosure of Invention

The invention realizes a novel modulation and demodulation by using the electromagnetic wave back scattering principle, improves the reliability, enhances the anti-interference capability, reduces the error rate, is less influenced by noise, is insensitive to the change of channel characteristics, is beneficial to node movement and can be applied to the field of the Internet of things while ensuring that the power consumption of wireless communication is lower.

Some embodiments of the present invention provide a modulation method, including:

object end node N receives single-frequency electromagnetic signal r₂(t)，r₂(t) a single frequency electromagnetic signal c (t) transmitted from a radio frequency source F;

the object end node N transmits a bit sequence a to be transmitted_nTransformed into a differential code b_n；

The object end node N transmits the differential code b_nEach symbol of (a) is converted into a unipolar square wave signal b (t);

the object end node N uses a unipolar square wave signal b (t) to control the on-off state of the radio frequency switch K, adjust the reflection coefficient, and parasitically modulate the generated unipolar square wave signal b (t) on a single-frequency electromagnetic signal r₂(t) and reflected off.

In some embodiments, the articleThe end node N will send a bit sequence a_nTransformed into a differential code b_nThe method comprises the following steps:

object end node N is according toOrBit sequence a to be transmitted_nTransformed into a differential code b_n，

Wherein n is 0,1,2_n-1Is b is_nThe previous symbol of (2), differential code b_nInitial bit b of_-1Can be preset to be 0 or 1,representing modulo-2 addition, -representing binary negation.

In some embodiments, the object node N transmits the differential code b_nTo a unipolar square wave signal b (t) comprises:

the object end node N is according to b (t) sigma_nb_ng(t-nT_B) Differential code b_nEach symbol of (a) is converted into a unipolar square wave signal b (t),

wherein g (T) is amplitude of 1 and duration of T_BRectangular pulse of (1), T_BIs the bit duration.

In some embodiments, the load impedance of the antenna at the object node N is Z_a， A₂Is amplitude, w₀In order to be the angular frequency of the frequency,in order to be the phase position,

when the unipolar square wave signal b (t) is 0, the radio frequency switch K is connected to the load Z₀Coefficient of reflectionAt the moment, the electromagnetic wave s reflected by the object end node₀(t)＝Γ₀r₂(t)；

When the unipolar square wave signal b (t) is 1, the radio frequency switch K is connected to the load Z₁Coefficient of reflectionAt the moment, the electromagnetic wave s reflected by the object end node₁(t)＝Γ₁r₂(t)。

In some embodiments when Z₀＝0Ω，Z₁Infinity Ω, Γ₀＝-1，Γ₁+1, electromagnetic wave reflected from object end node

Some embodiments of the present invention provide a demodulation method, including:

the receiver R receives an electromagnetic signal R (t) which comes from an electromagnetic wave s (t) reflected by an object end node N and acquires a corresponding in-phase component y_I2(t) and the orthogonal component y_Q2(t)；

Receiver R respectively corresponding to in-phase components y_I1(t) and the orthogonal component y_Q1(t) squaring and adding the results of the squaring to obtain a signal y₄(t) adding y₄(t) after DC cut-off, a sum-of-squares signal y is obtained₅(t)；

The receiver R will sum the squares signal y₅(T) delay time T_BObtaining a delayed signal y₆(t)，T_BFor bit duration, will y₅(t) and y₆(t) multiplication or division to obtain the signal y₇(t)；

Receiver R at nT_BTime, pair y₇(t) sampling to obtain a sampling value y₇(nT_B)；

Receiver R pair sample value y₇(nT_B) Making a decision with the result of e_nWherein, according toy₇(nT_B) Greater than 0 or less than 0, decision e_nIs 0 or 1, e_nI.e. the binary bit sequence finally demodulated by the receiver R.

In some embodiments, the receiver R obtains a corresponding in-phase component y_I2(t) and the orthogonal component y_Q2(t) comprises:

the receiver R uses a band-pass filter to filter the received electromagnetic signal R (t) to obtain a signal y (t);

the receiver R generates a coherent carrier comprising an in-phase carrier c_I(t) and orthogonal carrier c_Q(t)；

The receiver R using signals y (t) and c_I(t) multiplying to obtain a signal y_I1(t) then passing through a low-pass filter to obtain an in-phase component y_I2(t)；

The receiver R using signals y (t) and c_Q(t) multiplying to obtain a signal y_Q1(t) then passing through a low pass filter to obtain the quadrature component y_Q2(t)。

In some embodiments, the in-phase carrier c of the coherent carrier generated by the receiver R_I(t) and orthogonal carrier c_Q(t) are respectively:

wherein the content of the first and second substances,for the phase of the coherent carrier, for characterizing the frequency shift of the coherent carrier, the magnitude of which varies slowly with time τ, w₀Is the angular frequency and a is the amplitude.

In some embodiments, the receiver R pairs the sample values y₇(nT_B) Making a decision with the result of e_nThe method comprises the following steps:

when employing mark differential codes:

when null number differential codes are employed:

some embodiments of the present invention provide an object node configured to perform a modulation method.

Some embodiments of the invention propose a receiver configured to perform a mediation method.

Some embodiments of the present invention provide a communication system for internet of things, including: an object node, and a receiver.

Compared with the prior art, the invention has the following advantages:

the invention ensures lower power consumption of wireless communication, improves reliability, enhances anti-interference capability, reduces bit error rate, is less influenced by noise, is insensitive to channel characteristic change, and is beneficial to node movement.

Drawings

Fig. 1 illustrates an ultra-low power modulation and demodulation method based on electromagnetic wave backscattering.

Fig. 2 shows a block diagram of a backscatter-like DBPSK system.

Fig. 3 shows a backscatter-like DBPSK modulation method.

Fig. 4 shows the generation of a backscattered DBPSK-like modulated signal.

Fig. 5 shows a backscatter-like DBPSK demodulation process.

Detailed Description

The invention designs an ultra-low power consumption modulation and demodulation method based on electromagnetic wave backscattering, and the principle is shown in figure 1. Wherein A is the antenna (antenna impedance Z)_a) B is an ambient radio frequency source, C is a radio frequency switch, Z_LIs a load, and Z_L＝Z_a. The specific working process is as follows:

1. the object end node converts the acquired data into a unipolar square wave signal through a baseband processing method such as channel coding and the like, and then uses the square wave signal to control the state (on or off) of the radio frequency switch C to realize signal modulation: (1) when bit 1 needs to be transmitted (as shown in the left half of fig. 1), a high level appears at control CTRL, causing switch K to be turned on₁Closed, A and load Z_LIs turned on because of Z_L＝Z_aThe radio frequency circuit is matched with the antenna, so that the reflection coefficient is 0, and ideally, the electromagnetic signal is completely absorbed, and the power of the reflected signal is 0. (2) When it is desired to transmit bit 0 (as shown in the right half of fig. 1), a low level appears at CTRL causing switch K to be turned on₁Open, antenna a and load Z_LNot connected, at this time, the load impedance is infinite for the antenna, and the reflection coefficient is 1. Ideally, the signal is totally reflected, with the reflected signal having the greatest power.

2. The receiving end can recover the bit data sent by the object end node by distinguishing the strength of the reflected signal, specifically: sampling and judging a received electromagnetic wave signal, (1) when the energy of the electromagnetic wave signal in a symbol period is greater than a threshold value, indicating that original data sent by an object end node is bit 0; (2) when the energy of the electromagnetic wave signal in one symbol period is less than the threshold value, it indicates that the original data sent by the object end node is bit 1.

As can be seen from fig. 1, in the transmitter there is only one active device of the radio frequency switch. For example, the radio frequency switch ADG901 produced by AD has power consumption less than or equal to 2.75 microwatts, which is far lower than the milliwatt-level power consumption of communication chips of the Internet of things such as ZigBee, Bluetooth, LoRa, NB-IoT and the like.

However, the scheme shown in fig. 1 essentially utilizes the electromagnetic wave backscattering principle to implement modulation similar to OOK (On-off keying), and while solving the problem of excessive power consumption of wireless communication, there are many disadvantages: the method is greatly influenced by noise, weak in anti-interference capability, high in error rate, poor in reliability, sensitive to channel change, not beneficial to node movement and the like.

In order to solve the above problems, embodiments of the present invention further provide a novel modulation and demodulation technique, which utilizes an electromagnetic wave backscattering principle to implement modulation and demodulation similar to DBPSK (Binary Differential Phase Shift Keying), and improves reliability, enhances anti-interference capability, reduces an error rate, is less influenced by noise, is insensitive to channel characteristic changes, and is beneficial to node movement while ensuring that wireless communication power consumption is low. Description will be made below with reference to the first to fourth embodiments.

First embodiment

1) System components

As shown in fig. 2, the whole system mainly comprises three network elements, namely a radio frequency source F, an object end node N and a receiver R. Their functions are:

(1) radio frequency source F

Sending out a single-frequency electromagnetic signal c (t).

(2) Object end node N

Is the sender of the digital message. Different from the traditional transmitter, N does not generate carrier waves, and when a message needs to be transmitted, the binary bit sequence to be transmitted is parasitically modulated on the single-frequency electromagnetic signal transmitted by F by using the electromagnetic wave backscattering principle, so that the communication power consumption is reduced.

(3) Receiver R

Is the recipient of the digital message. And the system is responsible for recovering the binary bit sequence sent by the output end node N from the received electromagnetic signal to finally obtain the original digital message.

2) Modulation method

The method can be divided into three steps of precoding, pulse shaping, back scattering similar to DBPSK modulation and the like:

(1) precoding

When digital information needs to be sent by an object end node N, firstly, pre-coding operation is carried out, and a binary bit sequence a to be sent is transmitted_nTransformed into a differential code b_n. The transformation method can adopt mark number differential code transformation or space number differential code transformation. In any transformation method, the initial bit of the differential code can be arbitrarily preset to be 0 or 1, and only the transmitting side and the receiving side need to be configured in advance to be consistent.

(2) Pulse shaping

The object-side node N transforms each symbol of the differential code into a unipolar square wave signal b (t).

(3) Modulation process

As shown in fig. 3, the unipolar square wave signal b (t) may be used to control the on/off state (open or closed) of the radio frequency switch K, and adjust the reflection coefficient, so that the generated unipolar square wave signal is parasitically modulated on the single-frequency electromagnetic signal sent by F and reflected.

The specific working process is as follows:

it is assumed that a single-frequency electromagnetic signal c (t) transmitted by the rf source F is transmitted to the node N of the object end via the path 1 in fig. 2, and may be represented as

Wherein A is₂Is amplitude, w₀In order to be the angular frequency of the frequency,is the phase.

Assume that the load impedance of the antenna is Z_aAnd then:

(1) when the unipolar square wave signal b (t) is 0, the switch K is connected to the load Z₀At this time, the reflection coefficient Γ₀＝(Z₀-Z_a)/(Z₀+Z_a) The electromagnetic wave reflected by the object end node is as follows:

(2) when the unipolar square wave signal b (t) is 1, the switch K is connected to the load Z₁At this time, the reflection coefficient Γ₁＝(Z₁-Z_a)/(Z₁+Z_a) The electromagnetic wave reflected by the object end node is as follows:

let Z₀0 Ω (i.e. short circuit), Z₁∞ Ω (i.e. short circuit), then:

Γ₀＝(Z₀-Z_a)/(Z₀+Z_a)＝-1 (4)

Γ₁＝(Z₁-Z_a)/(Z₁+Z_a)＝+1 (5)

by substituting equations (4) and (5) into equations (2) and (3), the modulated signal s (t) can be expressed as:

it can be seen that this is effectively a binary differential phase shift keying, with bit 0 of the differential code corresponding to phase pi and bit 1 of the differential code corresponding to phase 0. Let Z₀＝∞Ω，Z₁Another binary differential phase shift keying may be obtained, with bit 0 of the differential code corresponding to phase 0 and bit 1 of the differential code corresponding to phase pi.

Fig. 4 shows a bit sequence a to be transmitted_nA transformation relation to the modulated signal s (t).

3) Demodulation method

The demodulation process is shown in fig. 5, and mainly includes five steps of band-pass filtering, coherent low-pass, square summation, differential multiplication, and sampling decision.

1) Band pass filtering

An electromagnetic signal received by the receiver R is represented as R (t), and the signal y (t) is obtained by filtering the R (t) by using a band-pass filter.

The center frequency of the band-pass filter is w₀Its bandwidth may be determined according to the transmission rate.

2) Coherent low pass

The receiver R generates a coherent carrier comprising an in-phase carrier c_I(t) and orthogonal carrier c_Q(t)：

Wherein, w₀For angular frequency, a is amplitude, e.g. a-2,for the phase of the coherent carrier, a frequency offset characterizing the coherent carrier, the magnitude of which varies slowly with time τ, may be compared withDifferent. It can be seen that one of the advantages of the demodulation method of the present invention is that the requirement for carrier synchronization at the receiving end is reduced, and carrier synchronization with the transmitting end does not need to be strictly implemented at the receiving end.

Using signals y (t) and c_I(t) multiplying to obtain a signal y_I1(t) then passing through a low-pass filter to obtain an in-phase component y_I2(t)。

Using signals y (t) and c_Q(t) multiplying to obtain a signal y_Q1(t) then passing through a low pass filter to obtain the quadrature component y_Q2(t)。

3) Sum of squares

Respectively for in-phase component y_I1(t) and the orthogonal component y_Q1(t) squaring and adding the results of the squaring to obtain a signal y₄(t), namely:

will y₄(t) after DC cut-off, a sum-of-squares signal y is obtained₅(t)。

4) Differential multiplication

Sum of squares signal y₅(T) delay time T_B(T_BBit duration) to obtain a delayed signal y₆(t) adding y₅(t) and y₆(t) multiplying to obtain a signal y₇(t)。

At nT_BTime, pair y₇(t) sampling to obtain a sampling value y₇(nT_B)。

5) To the sampling value y₇(nT_B) Making a decision with the result of e_n。

When employing mark differential codes:

when null number differential codes are employed:

e_ni.e. the binary bit sequence finally demodulated by the receiver R.

Second embodiment

The object node may perform a mark-difference code conversion operation according to equation (12) to obtain a difference code. Space-number differential code conversion may also be performed according to equation (13).

Wherein, a_n,b_nIs 0 or 1. a is_nBinary bit sequence to be transmitted for the object node N, b_nIs a differential code, b_n-1Is b is_nThe previous symbol of (1), first b_-1Can be arbitrarily preset to be 0 or 1, but the transmitting and receiving parties are consistent,representing modulo-2 addition, -representing binary negation.

Third embodiment

The object end node uses a digital-to-analog conversion device to convert b_nConversion into unipolar square wave signal b (t):

b(t)＝∑_nb_ng(t-nT_B) (14)

wherein g (T) is an amplitude of 1 and a duration of T_BThe square pulse of (2).

Fourth embodiment

The 'difference multiplication' in the demodulation method can be modified into 'difference division', and then sampling judgment is carried out to obtain a binary bit sequence. The method comprises the following specific steps:

1) differential phase division

Sum of squares signal y₅(T) delay time T_B(T_BBit duration) to obtain a delayed signal y₆(t) adding y₅(t) and y₆(t) dividing to obtain the signal y₇(t)。

At nT_BTime, pair y₇(t) sampling to obtain a sampling value y₇(nT_B)。

2) To the sampling value y₇(nT_B) Making a decision with the result of e_n。

When employing mark differential codes:

when null number differential codes are employed:

e_ni.e. the binary bit sequence finally demodulated by the receiver R.

As will be appreciated by one skilled in the art, embodiments of the present disclosure may be provided as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present disclosure may take the form of a computer program product embodied on one or more non-transitory computer-readable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer program code embodied therein.

The above description is only exemplary of the present disclosure and is not intended to limit the present disclosure, so that any modification, equivalent replacement, or improvement made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.