CN109586768B - Near field communication method based on magnetic sensor - Google Patents
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- CN109586768B CN109586768B CN201811391997.2A CN201811391997A CN109586768B CN 109586768 B CN109586768 B CN 109586768B CN 201811391997 A CN201811391997 A CN 201811391997A CN 109586768 B CN109586768 B CN 109586768B
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Abstract
The invention provides a near field communication mode based on a magnetic sensor, which utilizes a magnetic induction signal sent by a CPU and carries out communication through a magnetic intensity sensor on mobile equipment of a smart phone. Since the CPU and the magnetic strength sensor are already widely used components in smart mobile devices, the present invention eliminates the need for special hardware, provides additional bandwidth, and supplements existing near field communication protocols. The invention systematically analyzes the characteristics of the magnetic signals of the CPU and realizes one-way communication, full-duplex communication and multi-transmitter communication on common intelligent equipment in the market.
Description
Technical Field
The invention relates to the field of near field communication, in particular to a near field communication method based on a magnetic sensor.
Background
Near Field Communication (NFC) has attracted considerable attention in recent years because it has promoted the development of mobile-end applications for mobile payments, social networks, interactive games, and the like. However, at present, even though most of smart phones of mainstream brands are integrated with NFC near-field communication modules, due to the strict requirement of NFC chips, a large part of mobile devices do not have NFC. Current NFC implementations are based on the ISO-13157 standard, which requires dedicated hardware, i.e. an NFC chip module, including antennas and circuitry for encoding and decoding. However, the need for an NFC chip leads to additional costs, and a handset manufacturer has to increase the size of a handset in order to use the NFC chip, which greatly limits the applicability of NFC. On the other hand, even for NFC-enabled devices, NFC functionality is sometimes limited, e.g., NFC on an iPhone only supports Apple Pay. To address the problems with standard NFC implementations, the skilled person has devised many alternative approaches. Typical examples are bluetooth, acoustic, visible light, etc. Most of these methods rely on dedicated hardware or built-in sensors. Among them, bluetooth is a very popular technology suitable for short-range communication on mobile devices. However, these alternatives to NFC also face these various problems. First, they are susceptible to security issues. For example, bluetooth operates in a longer communication range than standard NFC, and it is easy for an attacker to eavesdrop on the transmitted information. Second, the communication channel is subject to noise and interference, e.g., bluetooth is very susceptible to interference with WiFi signals, let alone acoustic and visible light methods. Thus, existing alternative NFC implementations cannot meet both security and performance requirements. The present invention seeks to provide an NFC implementation that does not require dedicated hardware, while taking security and performance issues into account. Magnetic Induction (MI) signals emitted by the mobile device are used as a communication channel, and built-in magnetic field sensors are used for signal reception.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a near field communication method based on a magnetic sensor.
The invention provides a near field communication method based on a magnetic sensor, which comprises the following steps:
a signal generating step: a CPU of the first device sends out a magnetic induction signal;
a signal control step: modulating the magnetic induction signal by an operating system of the first device;
a signal receiving step: the magnetic sensor of the second device receives the modulated magnetic induction signal.
Preferably, the number of the core groups of the CPU is plural.
Preferably, the operating system comprises: windows system, Ubuntu system, MacOS X system or Android system.
Preferably, the operating system modulates the magnetic induction signal by pulse width-pulse amplitude modulation.
Preferably, the signal receiving step includes:
a lead code detection step: the lead code positions data contained in the magnetic induction signal;
a channel estimation step: performing channel estimation on the magnetic induction signals, and determining the amplitude and width information of each symbol in the magnetic induction signals;
and a data recovery step: the original data bits of the magnetic induction signal are recovered.
Preferably, the method further comprises the step of signal cancellation:
when the first device simultaneously transmits and receives the magnetic induction signal, the pulse width-pulse amplitude modulation symbol of the magnetic induction signal of the target magnetic induction signal is obtained by subtracting the pulse width-pulse amplitude modulation symbol of the transmitted magnetic induction signal from the pulse width-pulse amplitude modulation symbol of the received magnetic induction signal.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention utilizes the hardware facility of the magnetic sensor widely used on the mainstream mobile equipment and utilizes the magnetic induction signal emitted by the equipment to transmit information, thereby achieving the effect of near field communication;
2. the invention meets the safety and performance indexes, does not need to modify the existing hardware setting, and reduces the difficulty of popularization of near field communication.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a schematic diagram of an overall architecture of a near field communication method based on a magnetic sensor;
FIG. 2 is a schematic diagram of pulse width-pulse amplitude modulation of a near field communication method based on a magnetic sensor;
FIG. 3 is a data flow diagram of a near field communication method based on a magnetic sensor;
fig. 4 is a diagram of experimental results of a prototype system 1 based on a near field communication method of a magnetic sensor;
fig. 5 is a diagram of experimental results of a prototype system 2 based on a near field communication method of a magnetic sensor.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
As shown in fig. 1 to 5, the near field communication method based on a magnetic sensor according to the present invention includes two adjacent devices, wherein one device generates a magnetic induction signal through a CPU, encodes information into the magnetic induction signal by controlling the operating state of the CPU, and decodes the signal by using the magnetic sensor of the other device. By carefully adjusting the magnetic induction signal emitted from the CPU and sensing with a magnetic sensor on the device, the two devices can communicate in a near field manner. The invention can be divided into 3 layers, wherein the bottom layer is a physical layer which mainly modulates, transmits and demodulates magnetic induction signals; the middle is a data link layer, which comprises technologies of multi-transmitter, full duplex communication, active retransmission, error detection of a transmitting terminal and the like; the top layer is the application layer. The present invention develops this communication system into a full-duplex magnetic signal communication system using techniques such as pulse width, amplitude modulation, channel estimation, active retransmission, and self-signal cancellation of the magnetic signal.
More specifically, the magnetic induction signal generated by the CPU is scheduled by a job in the operating system, but due to the limitation of the scheduling itself, the generated magnetic induction signal is difficult to control, so that a complex modulation scheme such as the ofdm technique is basically not feasible. And the conventional magnetic sensor can only measure the working and idle states of the CPU core, so the intuitive way of embedding data in the magnetic induction signal is to use binary On-Off Keying (OOK). That is, one of the CPU cores is switched between an idle state and an operating state, which represent 0 and 1, respectively. Switching the CPU state every 5ms for a 200Hz magnetometer will bring the data transfer rate to 200 bps. However, in most practical cases, it is difficult to control the CPU in this manner. In addition, the modulation method of binary on-off keying is affected by noise generated by background programs. Therefore, Pulse Width and Amplitude Modulation (PWAM) is selected to modulate data on the magnetic induction signal, as opposed to binary on-off keying, to balance transmission speed and accuracy. Specifically, each data symbol has a period T and is presented using the proportion of CPU on time during that period. The data symbols consist of M + N data bits, where the M bits are converted to a set of predefined 2 of CPU magnetic induction signals (PAM)MAmplitude level, N bits are converted to a set of predefined 2NPer CPU Percent Work (PWM) level. Taking fig. 2 as an example, each data symbol is 30ms in length and consists of 4 bits. The amplitude of each symbol may be 1, 4, 3, 2, representing a data bit: 00. 11, 10 and 01. The CPU work percentage per symbol may be 40%, 60%, 20%, 80% for 01, 10, 01 and 11. We can getAdjust T, M, N based on current channel conditions, and control the accuracy of the CPU core. Modern operating systems optimize task scheduling specifically for multi-core CPUs to ensure efficiency in executing commands. The operating system maintains a global task queue that can be assigned to any idle core. Processor association may be used to bind a given process to a particular CPU core when controlling the particular CPU core to generate the required magnetic signal. To increase transmission range, multiple cores may be used to generate the same PWAM symbol or to generate different PWAM symbols for parallel communication. In the prototype implementation, operating systems such as Windows 7, 8, 10, Ubuntu14, MacOS X, and Android 6, 7 are used.
Furthermore, the simultaneous operations on the CPU may cause interference during transmission, thereby increasing the difficulty of detecting the CPU magnetic induction signal. In order to guarantee the transmission quality in a noisy environment, preamble detection is performed at the time of reception of the magnetic induction signal for synchronization and signal strength estimation. After the symbols are segmented, they are demodulated to extract the data bits. The preamble is used to locate the start of a data packet and a retransmission scheme that monitors real-time CPU usage and bit error distribution and retransmits previously corrupted data packets if necessary. The receiver applies cross-correlation to accurately locate the preamble pattern and must perform channel estimation before extracting the symbols. After the lead code detection, the data contained in the magnetic induction signal can be accurately positioned. The receiver can easily split the symbol with a fixed PWAM length known in advance after the preamble. After channel estimation, the receiver determines the amplitude and width information in each symbol so that the original data bits can be recovered.
In wireless communication, multipath and interference are generally cancelled efficiently by increasing the transmission bandwidth, and a multiple antenna system is preferable to a single antenna system. The same idea is adopted in the present invention and a multicore CPU is used as a plurality of transmitters. For example, in an eight core CPU notebook, one core group consisting of two cores may be considered a first transmitter, and another core group consisting of six cores may be considered a second transmitter. Two core groups may transmit data simultaneously to increase throughput. In the transmitter, we rely on using different CPU cores to generate the PWAM symbols. However, in the receiver, a mechanism is needed to distinguish PWAM symbols from different transmitters. The solution of the invention is based on a simple idea: each transmitter uses a different number of CPU cores so the amplitude values of the PWAM symbols from different transmitters are different.
The invention also designs a subtraction algorithm by utilizing the signal cancellation technology to realize full duplex communication. In particular, full duplex communication can be achieved when two mobile devices are equipped with magnetometers (i.e. communication between two mobile phones). A challenge in enabling full-duplex communication is that when the mobile device is simultaneously transmitting and receiving data, the received PWAM symbol is a linear combination of its own transmitted PWAM symbol and the target PWAM symbol. But since the device knows what it is transmitting and can estimate the amplitude of its own PWAM symbol, the device can subtract the transmitted PWAM symbol from the received PWAM symbol and recover the target PWAM symbol.
Considering that the magnetometer equipped on the smartphone is not sufficient to capture the MI signal of the other smartphone CPU, the invention uses two notebook computers equipped with DRV425 magnet sensors to verify the feasibility of full-duplex communication.
The first prototype transmitter was a laptop running Windows, Ubuntu or MacOS X, and the receiver was an Android handset. Notebook computers are equipped with Intel core CPUs (4 or 8 cores). The Android mobile phone is equipped with a Hall effect magnetometer, namely Nexus 6P, and the sampling frequency is 50 Hz. In this prototype, we implemented unidirectional communication that enabled multiple transmitters. Fig. 4 is an experimental result of the prototype system 1. The experimental scenes 1 to 4 correspond to nothing the user does, watching a video, browsing a website, and playing a game, respectively.
The second prototype used a transmitter and receiver on two notebook computers with an external magnetometer (DRV 425). In this system we used the same notebook computer as used in the first prototype. The magnetometer is a fluxgate sensor with a sampling rate of 200 KHz. This prototype enables full duplex communication with multiple transmitters. Fig. 5 is the experimental result of prototype system 2. The experimental scenario is the same as in fig. 4.
The invention utilizes the Magnetic Induction (MI) signal sent by the CPU and carries out communication through the magnetic intensity sensor on the mobile equipment of the smart phone. Since the CPU and the magnetic strength sensor are already widely used components in smart mobile devices, the present invention eliminates the need for special hardware, provides additional bandwidth, and supplements existing near field communication protocols. The invention systematically analyzes the characteristics of the magnetic signal of the CPU, and realizes one-way communication, full-duplex communication and multi-transmitter communication on common smart phone equipment in the market. We have created prototypes of the present invention on notebook computers and smart phones.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (4)
1. A near field communication method based on a magnetic sensor is characterized by comprising the following steps:
a signal generating step: a CPU of the first device sends out a magnetic induction signal;
a signal control step: modulating the magnetic induction signal by an operating system of the first device;
a signal receiving step: a magnetic sensor of the second device receives the modulated magnetic induction signal;
the signal receiving step includes:
a lead code detection step: the lead code positions data contained in the magnetic induction signal;
a channel estimation step: performing channel estimation on the magnetic induction signals, and determining the amplitude and width information of each symbol in the magnetic induction signals;
and a data recovery step: recovering original data bits of the magnetic induction signal;
the near field communication method further comprises the step of signal cancellation:
when the first device simultaneously transmits and receives the magnetic induction signal, the pulse width-pulse amplitude modulation symbol of the magnetic induction signal of the target magnetic induction signal is obtained by subtracting the pulse width-pulse amplitude modulation symbol of the transmitted magnetic induction signal from the pulse width-pulse amplitude modulation symbol of the received magnetic induction signal.
2. The magnetic sensor-based near field communication method of claim 1, wherein the number of the core groups of the CPU is plural.
3. A magnetic sensor-based near field communication method according to claim 1, wherein the operating system comprises: windows system, Ubuntu system, MacOS X system or Android system.
4. A method of near field communication based on a magnetic sensor as claimed in claim 1 wherein the operating system modulates the magnetic induction signal by pulse width-pulse amplitude modulation.
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| GB2585352A (en) * | 2019-05-08 | 2021-01-13 | Saralon Gmbh | Wireless communication via modulated magnetic field reception |
| CN114448523B (en) * | 2021-12-31 | 2022-12-30 | 上海交通大学 | Ultrasonic communication method and system based on frequency domain modulation PWAM |
| CN117580021B (en) * | 2023-11-22 | 2024-05-31 | 广州莲雾科技有限公司 | Bluetooth tag batch self-checking and configuring method and system |
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| CN103368889B (en) * | 2012-03-29 | 2016-06-29 | 上海贝尔股份有限公司 | The method and apparatus of the transmitting of filter bank multi-carrier signal and channel estimating |
| CN104113501B (en) * | 2014-06-19 | 2017-04-26 | 北京科技大学 | Modulator, demodulator, modulation method and demodulation method for low-frequency magnetic induction communication |
| KR20170050308A (en) * | 2015-10-30 | 2017-05-11 | 쌍용자동차 주식회사 | Output control apparatus for a vehicle with an near field audio |
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