WO2021213553A2

WO2021213553A2 - Frequency-spectrum dynamic control method and system of ofdma backscatter network

Info

Publication number: WO2021213553A2
Application number: PCT/CN2021/100810
Authority: WO
Inventors: 朱丰源; 冯宇达; 李倩茹; 田晓华; 王新兵
Original assignee: 上海交通大学
Priority date: 2020-04-20
Filing date: 2021-06-18
Publication date: 2021-10-28
Also published as: CN111565393A; CN111565393B; WO2021213553A3

Abstract

The present invention provides a frequency-spectrum dynamic control method and system of an orthogonal frequency-division multiple access (OFDMA) backscatter network, comprising: step 1: a central control node obtaining network spectrum occupancy information, and reading the number of active nodes in the spectrum and the current total number of sub-channels; step 2: the central control node encoding the total number of sub-channels, and broadcasting the wireless channel after modulation; step 3: a backscatter tag decoding the broadcast modulated wireless channel by means of a demodulation circuit to obtain the total number of new sub-channels, and, taking the total number of sub-channels as a parameter, controlling the symbol rate in the backscatter communication process. The present invention solves the spectrum waste of a large-capacity OFDMA backscatter network in a situation where there is a small amount of equipment; can also be used to adjust the data rate of the network, and, in the case of poor network SNR, can improve the reliability of communication by means of reducing the symbol rate or increasing the symbol length.

Description

Frequency spectrum dynamic control method and system of OFDMA backscatter network

Technical field

The present invention relates to the field of communication technology, in particular to a method and system for dynamic spectrum control of OFDMA backscatter network.

Background technique

Backscatter communication has attracted widespread attention in the field of Internet of Things in recent years. Its main feature is to use external electromagnetic waves to modulate to realize its own communication. Since there is no need to actively generate electromagnetic waves, even if it is generated for Wi-Fi communication, the power consumption is very low, only tens of microwatts (see the 2016 paper by Bryce Kellogg et al. in NSDI). However, with the expansion of the scale of the Internet of Things, multiple access technologies have gradually changed from time division multiplexing to frequency domain multiplexing. In 2019, Renjie Zhao and others published "OFDMA-Enabled Wi-Fi Backscatter" on MobiCom, which uses 48 data subcarriers in the 802.11g protocol to be allocated to 48 different backscatter tags to achieve parallel uplinks. Solve the problem of network capacity. The network can reach a physical layer throughput of 12Mbps at full load; however, when the network load is low and only a few (less than 3) tags work, the physical layer throughput of the network is less than 1Mbps. In fact, in this case, although the entire 20MHz frequency band is occupied, the actually utilized frequency band is less than 1MHz. In a mobile network, the joining/leaving of devices is a common operation, so a small number of devices objectively exists. Therefore, it has become an important issue to improve the spectrum utilization in a large-capacity orthogonal frequency division multiple access OFDMA backscatter network.

Patent document CN103974408B (application number: 201410128764.9) discloses an OFDMA system based on a Mesh network, which includes a Mesh network and a number of orthogonal and non-overlapping data blocks divided according to the time domain and frequency domain. Each node is connected to one or more other nodes; the data block has a reserved gap before the time domain; and a control node is included in the several nodes, and the control node has access to all nodes The corresponding synchronization signal of the node synchronizes the signal of the node with the signal of the control node. The control node controls and coordinates the sending and scheduling of the data blocks of each node through the communication protocol; the control node is also used for control and management in the same time domain and frequency domain Commonly required data blocks and their arrangement in the Mesh network.

Summary of the invention

Aiming at the defects in the prior art, the purpose of the present invention is to provide a method and system for dynamic spectrum control of an OFDMA backscatter network.

The spectrum dynamic control method of OFDMA backscatter network provided according to the present invention includes:

Step 1: The central control node obtains network spectrum occupancy information, reads the number of active nodes in the spectrum and the current total amount of sub-channels;

Step 2: The central control node encodes the total amount of sub-channels, and broadcasts the wireless channel after modulation;

Step 3: The backscatter tag decodes the broadcast modulated wireless channel through the demodulation circuit to obtain the new total amount of subchannels, and uses the total amount of subchannels as a parameter to control the symbol rate in the backscatter communication process.

Preferably, the step 1 includes: if the number of active nodes is less than 50% of the total number of sub-channels, reducing the current total number of sub-channels to 50%; if the number of active nodes is saturated, then reducing the current sub-channels The total amount is doubled;

The central control node negotiates with the access point to obtain network spectrum occupancy information. The acquisition methods include wired, wireless, and direct acquisition with the access point into one device. After obtaining the spectrum occupancy information, the central control node broadcasts the symbol rate through the downlink. Modify all backscatter tags;

Downlink modulation methods include OOK signals or ASK or PSK/FSK/OFDM signals in the backscatter system.

Preferably, the step 2 includes: the modulation mode of the broadcast information corresponds to the demodulation circuit of the tag;

Demodulation occurs at the analog level, and decoding occurs at the digital level. When the demodulation circuit of the tag is an envelope detector circuit and a comparator, the broadcast information is modulated by ASK/OOK.

Preferably, the step 3 includes: activating a counter when each symbol rate starts to transmit, and when the counter counts to the end of the count, the counter is set to zero and the transmission of the next symbol rate is started; the value of the count end is the total number of subchannels plus The length of the upper cyclic prefix;

The access point obtains the sub-channel information of the network from the central control node and controls the window length of the fast Fourier transform FFT. The access point uses the same number of FFT points for sub-channel demodulation under different symbol rates.

Preferably, the sub-channel demodulation includes:

Step 3.1: When the number of sub-channels is lower than the upper limit of the number of FFT points, zero padded each original symbol to the maximum number of FFT points, and take the window according to the FFT of the maximum specification;

Step 3.2: Execute FFT;

Step 3.3: Convert the index of the sub-channel, and multiply the ratio of the original sub-channel index by the FFT size;

Step 3.4: Take out complex frequency domain data from the corresponding sub-channel according to the index, and perform demodulation.

The spectrum dynamic control system of OFDMA backscatter network provided according to the present invention includes:

Module M1: The central control node obtains network spectrum occupancy information, reads the number of active nodes in the spectrum and the current total amount of sub-channels;

Module M2: The central control node encodes the total number of sub-channels, and broadcasts the wireless channel after modulation;

Module M3: The backscatter tag decodes the broadcast modulated wireless channel through the demodulation circuit to obtain the total amount of new subchannels, and uses the total amount of subchannels as a parameter to control the symbol rate in the backscatter communication process.

Preferably, the module M1 includes: if the number of active nodes is less than 50% of the total number of sub-channels, reducing the total number of current sub-channels to 50%; if the number of active nodes is saturated, then reducing the current sub-channels The total amount is doubled;

Preferably, the module M2 includes: the modulation mode of the broadcast information corresponds to the demodulation circuit of the tag;

Preferably, the module M3 includes: activating a counter when each symbol rate starts sending, and when the counter counts to the end of the count, the counter is set to zero and the next symbol rate is sent; the value of the count end is the total number of subchannels plus The length of the upper cyclic prefix;

Preferably, the sub-channel demodulation includes:

Module M3.1: When the number of sub-channels is lower than the upper limit of the number of FFT points, zero padded each original symbol to the maximum number of FFT points, and take the window according to the FFT of the maximum specification;

Module M3.2: execute FFT;

Module M3.3: Convert the index of the sub-channel, and multiply the ratio of the original sub-channel index by the FFT size;

Module M3.4: Take out complex frequency domain data from the corresponding sub-channel according to the index, and perform demodulation.

Compared with the prior art, the present invention has the following beneficial effects:

1. The symbol rate control algorithm proposed by the present invention can make the frequency band occupancy of the network above 50% in most cases, and solves the spectrum waste of the large-capacity OFDMA backscatter network in the case of a small number of devices;

2. The method of the present invention can also be used to adjust the data rate of the network. In the case of poor network SNR, the communication reliability can be improved by reducing the symbol rate or increasing the symbol length.

Description of the drawings

By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more apparent:

Figure 1 is a system structure diagram of the OFDMA backscatter network in the present invention;

Fig. 2 is a schematic diagram of updating the local symbol rate of the backscatter tag in the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be pointed out that for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

The central control node of OFDMA network that supports dynamic spectrum control. Its characteristic is that it can broadcast different downlink control signaling according to the current spectrum status of the network so that all backscatter devices can adjust the symbol rate at the same time. The modulation mode of the downlink can be a common OOK signal in a backscatter system, or a PSK/FSK/OFDM signal. The present invention does not restrict the specific modulation mode, and any modulated downlink is within the protection scope of this patent.

Support rate control OFDMA backscatter tags. Its characteristic is that it can demodulate the control signaling of the central node, can perform sub-carrier modulation, and change the modulated symbol rate according to the control signaling in the wireless channel.

The access point (wireless gateway) of OFDMA network that supports dynamic spectrum control. Its characteristic is that it can coordinate with the central control node. Supports demodulation capabilities in a multi-symbol rate environment. The access point can be physically integrated with the central control node into one device.

Improving spectrum utilization is only an application of spectrum control technology. Anything that changes the symbol rate of devices in the network through broadcasting and realizes spectrum control of OFDMA backscatter network is within the protection scope of this patent.

The purpose of the present invention is to provide a technology for dynamically controlling the frequency spectrum, which can be used to improve the spectrum utilization rate of the OFDMA backscatter network, improve the communication reliability under the condition of low SNR, and other uses.

The backscatter system based on orthogonal frequency division multiple access technology provided according to the present invention includes the following parts:

Part 1: Central control node of OFDMA network supporting dynamic spectrum control

The central control node can negotiate with part 3 (access point) to obtain network spectrum occupancy information, which can be wired or wireless, or it can be combined with the access point to obtain it directly as a device. After obtaining the spectrum occupancy information, the node broadcasts the new network symbol rate through the downlink according to the situation, and requires all tags to be modified. The modulation mode of the downlink can be the common OOK signal in the backscatter system, or other ASK or PSK/FSK/OFDM signals.

Part 2: OFDMA backscatter tags supporting rate control

The backscatter tag needs to support the rate control signaling of the demodulation and decoding center control node, where demodulation occurs at the analog level and decoding occurs at the digital level. For example, when the demodulation circuit of the tag is an envelope detection circuit and a comparator, the broadcast information is modulated by ASK/OOK.

Part 3: Access point (wireless gateway) of OFDMA network supporting dynamic spectrum control

The access point obtains the sub-channel information of the network from the central control node and is used to control the window length of the FFT. The access point still uses the same number of FFT points for sub-channel demodulation under different symbol rates. The specific method is:

Step 1: When the number of subchannels is lower than the upper limit of the number of FFT points, zero padded each original symbol to the maximum number of FFT points. That is, take the window according to the FFT of the largest specification;

Step 2: Perform FFT;

Step 3: Convert the sub-channel index, that is, the ratio of the original sub-channel index multiplied by the FFT size.

Step 4: Take out complex frequency domain data from the corresponding sub-channel according to the index, and perform demodulation.

The specific process of updating the symbol rate of the entire OFDMA network (taking the improvement of spectrum utilization as an example) is as follows:

Step 1: The central control node reads the number of active nodes in the spectrum and the current total number of subchannels (that is, the number of FFT points, which is related to the symbol rate). If the number of active nodes is less than 50% of the total number of subchannels, the number of subchannels is reduced to 50% of the original number. If the current sub-channels of the network are saturated, the number of sub-channels is doubled.

Step 2: The central control node encodes the total amount of new sub-channels, and then modulates the radio channel to broadcast. The modulation method of the broadcast information corresponds to the specific design of the tag's demodulation circuit; for example, when the tag's demodulation circuit is an envelope detector circuit and a comparator, the broadcast information is modulated by ASK/OOK.

Step 3: The backscatter tag is decoded by the demodulation circuit to obtain the new total number of subchannels, which is used as a parameter to control the symbol rate in the backscatter communication process. The specific process is that the counter will be activated when each symbol starts to be sent, and when the counter reaches the end of the count, the counter will be set to zero and the next symbol will be sent. The value at the end of the count is the total number of sub-channels plus the length of the cyclic prefix.

Module M1: The central control node obtains network spectrum occupancy information, reads the number of active nodes in the spectrum and the current total number of sub-channels;

Those skilled in the art know that, in addition to implementing the system, device and various modules provided by the present invention in a purely computer-readable program code manner, it is completely possible to make the system, device and various modules provided by the present invention by logically programming method steps The same program is implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system, device and various modules provided by the present invention can be regarded as a hardware component, and the modules included in it for implementing various programs can also be regarded as the structure within the hardware component; The modules for realizing various functions can be regarded as both software programs for realizing methods and structures within hardware components.

The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

A dynamic spectrum control method of OFDMA backscatter network, which is characterized in that it comprises:

Step 1: The central control node obtains network spectrum occupancy information, reads the number of active nodes in the spectrum and the current total amount of sub-channels;

Step 2: The central control node encodes the total amount of sub-channels, and broadcasts the wireless channel after modulation;

Step 3: The backscatter tag decodes the broadcast modulated wireless channel through the demodulation circuit to obtain the new total amount of subchannels, and uses the total amount of subchannels as a parameter to control the symbol rate in the backscatter communication process.
The frequency spectrum dynamic control method of OFDMA backscatter network according to claim 1, wherein said step 1 comprises: if the number of active nodes is less than 50% of the total number of sub-channels, reducing the current total number of sub-channels It is 50% of the original; if the number of active nodes is saturated, the total number of current sub-channels will be doubled;

The central control node negotiates with the access point to obtain network spectrum occupancy information. The acquisition methods include wired, wireless, and direct acquisition with the access point into one device. After obtaining the spectrum occupancy information, the central control node broadcasts the symbol rate through the downlink. Modify all backscatter tags;

Downlink modulation methods include OOK signals or ASK or PSK/FSK/OFDM signals in the backscatter system.
The frequency spectrum dynamic control method of OFDMA backscatter network according to claim 1, characterized in that, said step 2 comprises: the modulation mode of the broadcast information corresponds to the demodulation circuit of the tag;

Demodulation occurs at the analog level, and decoding occurs at the digital level. When the demodulation circuit of the tag is an envelope detector circuit and a comparator, the broadcast information is modulated by ASK/OOK.
The frequency spectrum dynamic control method of the OFDMA backscatter network according to claim 1, wherein the step 3 comprises: activating a counter when each symbol rate starts to be transmitted, and setting the counter to zero when the counter reaches the end of the count And start the transmission of the next symbol rate; the value at the end of the count is the total number of subchannels plus the length of the cyclic prefix;

The access point obtains the sub-channel information of the network from the central control node and controls the window length of the fast Fourier transform FFT. The access point uses the same number of FFT points for sub-channel demodulation under different symbol rates.
The method for dynamic spectrum control of OFDMA backscatter network according to claim 4, wherein the sub-channel demodulation comprises:

Step 3.1: When the number of sub-channels is lower than the upper limit of the number of FFT points, zero padded each original symbol to the maximum number of FFT points, and take the window according to the FFT of the maximum specification;

Step 3.2: Execute FFT;

Step 3.3: Convert the index of the sub-channel, and multiply the ratio of the original sub-channel index by the FFT size;

Step 3.4: Take out complex frequency domain data from the corresponding sub-channel according to the index, and perform demodulation.
A dynamic spectrum control system of OFDMA backscatter network, which is characterized in that it comprises:

Module M1: The central control node obtains network spectrum occupancy information, reads the number of active nodes in the spectrum and the current total amount of sub-channels;

Module M2: The central control node encodes the total number of sub-channels, and broadcasts the wireless channel after modulation;

Module M3: The backscatter tag decodes the broadcast modulated wireless channel through the demodulation circuit to obtain the total amount of new subchannels, and uses the total amount of subchannels as a parameter to control the symbol rate in the backscatter communication process.
The spectrum dynamic control system of the OFDMA backscatter network according to claim 6, wherein the module M1 comprises: if the number of active nodes is less than 50% of the total number of subchannels, reducing the total number of subchannels It is 50% of the original; if the number of active nodes is saturated, the total number of current sub-channels will be doubled;

The central control node negotiates with the access point to obtain network spectrum occupancy information. The acquisition methods include wired, wireless, and direct acquisition with the access point into one device. After obtaining the spectrum occupancy information, the central control node broadcasts the symbol rate through the downlink. Modify all backscatter tags;

Downlink modulation methods include OOK signals or ASK or PSK/FSK/OFDM signals in the backscatter system.
The frequency spectrum dynamic control system of the OFDMA backscatter network according to claim 6, wherein the module M2 comprises: a modulation method of broadcast information corresponding to a demodulation circuit of the tag;

Demodulation occurs at the analog level, and decoding occurs at the digital level. When the demodulation circuit of the tag is an envelope detector circuit and a comparator, the broadcast information is modulated by ASK/OOK.
The frequency spectrum dynamic control system of the OFDMA backscatter network according to claim 6, wherein the module M3 includes: activate a counter when each symbol rate starts to transmit, and set the counter to zero when the counter reaches the end of the count And start the transmission of the next symbol rate; the value at the end of the count is the total number of subchannels plus the length of the cyclic prefix;

The access point obtains the sub-channel information of the network from the central control node and controls the window length of the fast Fourier transform FFT. The access point uses the same number of FFT points for sub-channel demodulation under different symbol rates.
The spectrum dynamic control system of an OFDMA backscatter network according to claim 9, wherein the sub-channel demodulation comprises:

Module M3.1: When the number of sub-channels is lower than the upper limit of the number of FFT points, zero padded each original symbol to the maximum number of FFT points, and take the window according to the FFT of the maximum specification;

Module M3.2: execute FFT;

Module M3.3: Convert the index of the subchannel, and multiply the ratio of the original subchannel index by the FFT size; Module M3.4: Take out complex frequency domain data from the corresponding subchannel according to the index, and perform demodulation.