A low-power internet of things device access method

Abstract

The present application belongs to the technical field of wireless communication, and particularly relates to a low-power Internet of Things device access method. The method of the present application comprises: a base station sending cellular information to a receiver, and a reflecting device collecting energy by using the base station signal; when the energy collected by the reflecting device meets a set condition, the reflecting device enters an active state, the active reflecting device modulates to-be-transmitted information by using a predefined spread spectrum code, and loads the information onto the base station signal for reflection transmission; and the receiver jointly demodulates the base station information and the information of the active reflecting device. The access scheme proposed in the present application can realize low-power and interference-free access of a large-scale Internet of Things device by means of a cellular system, and has important application value and development potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication, and particularly relates to a low-power Internet of Things device access method. BACKGROUND

[0002] With the wide application of the Internet of Things in the fields of smart cities, intelligent transportation and industrial Internet, the number of Internet of Things devices and connections shows an explosive growth. According to the latest Internet of Things report released by Ericsson in 2024, the number of global Internet of Things connections will reach 38.8 billion by 2029. Existing Internet of Things technologies (such as LTE-M and NB-IoT) rely on active communication architecture, have high transmission power consumption, and usually need to be equipped with dedicated batteries. However, frequent battery replacement not only generates huge operation and maintenance costs, but also many Internet of Things devices are limited in size and environmental factors, making it difficult to rely on battery power supply or charging. Ambient Internet of Things technology can realize near-zero power consumption communication by integrating backscattering communication technology and energy harvesting technology, and has received high attention from the academic and industrial communities in recent years. However, traditional backscattering communication technology has the problem of direct link interference, which limits the transmission performance of Internet of Things reflective devices, further limiting the large-scale application of ambient Internet of Things.

[0003] Symbiotic Radio technology is a new type of backscattering communication technology that significantly improves the transmission performance of Internet of Things devices by introducing cooperative transmission of cellular and Internet of Things devices and using joint demodulation technology. In the scenario of supporting massive device access, it is crucial to study an efficient access mechanism for Symbiotic Radio. However, most existing access schemes use a relatively simple time division multiple access (TDMA) method, which cannot support concurrent transmission of multiple devices. In addition, these schemes rarely take into account the energy harvesting needs of Internet of Things reflective devices, so they cannot be directly applied to ambient Internet of Things scenarios. SUMMARY

[0004] The main content of the application is to propose a low-power Internet of Things device access design method, covering system architecture, frame structure design, and multi-device access scheme, aiming to solve the problems of high power consumption and low multi-device access efficiency in the prior art.

[0005] The technical solution adopted by the application is:

[0006] A low-power Internet of Things device access method, the system includes a single-antenna cellular base station, K ambient Internet of Things reflective devices, and a single-antenna receiver; the access method is:

[0007] The base station sends cellular information to the receiver, and the reflector uses the base station signal to harvest energy;

[0008] When the energy collected by the reflector meets the set conditions, it enters the active state. The active reflector modulates the information to be transmitted using a predefined spread spectrum code and loads the information onto the base station signal for reflection transmission.

[0009] The receiver jointly demodulates the base station information and the information of the active reflective devices.

[0010] Furthermore, the specific method for the reflection device to collect energy using the base station signal is: setting the time length for the reflection device to collect energy using the base station signal to τ0, the energy collected by the reflection device k within the time τ0 is:

[0011] E k =P k τ0=hτ0p|h k | 2 ,

[0012] Among them, h∈[0,1] is the energy collection efficiency, p represents the base station transmission power, h k is the channel from the base station to the kth reflection device.

[0013] Furthermore, the specific method for the energy collected by the reflection device to meet the set conditions is:

[0014] Assuming the duration of each frame signal of the reflector device is T, the duration of information transmission after the reflector device collects enough energy is T-τ0. The total power consumption of the reflector device during the data transmission phase is defined as:

[0015]

[0016] Among them, T b is the period of symbol transmission by the reflection device, N is the spread spectrum code length used by the reflection device, E0 represents the energy consumption of adjusting the reflection coefficient once, P c Indicates the circuit power consumption. The reflective device is considered active when the following conditions are met:

[0017] hτ0p|h k | 2 ≥E c .

[0018] Furthermore, the method in which the active reflective device modulates the information to be transmitted using the predefined spreading code is:

[0019] Let the channels obey the complex Gaussian distribution where λ h Denotes the variance, and the probability of the reflective device being active is calculated as:

[0020]

[0021] Thus, the probability that L out of K reflecting devices are active is:

[0022]

[0023] The transmitted information of the reflecting device is obtained by multiplying the transmitted symbol of the L active reflecting devices by the spreading code, denoted as b l c l (n), where l is the lth active reflecting device.

[0024] Further, the specific method of the receiver jointly demodulating the base station information and the information of the active reflecting device is:

[0025] The received signal at the receiver is defined as:

[0026]

[0027] where s(n) represents the normalized base station transmitted signal, h l represents the channel from the base station to the lth reflecting device, g l represents the channel from the lth reflecting device to the receiver, and u(n) represents the complex Gaussian noise of the receiver.

[0028] The receiver first demodulates the base station signal s(n) by regarding the reflecting link as interference.

[0029] After demodulating s(n), the receiver cancels the direct link signal by using serial interference cancellation, and then demodulates the transmitted symbol b l of the reflecting device. The signal after serial interference cancellation is:

[0030]

[0031] The receiver first multiplies the received signal y(n) by s * (n), and then divides by |s(n)| 2 , to obtain:

[0032]

[0033] When demodulating the transmitted symbol of the reflecting device k (1≤k≤L), the receiver multiplies the signal by the known spreading code and adopts maximum ratio combining to demodulate b k . The signal-to-noise ratio of b

[0034]

[0035] The access scheme can realize low-power and non-interference access of large-scale Internet of Things devices by means of a cellular system, and has important application value and development potential. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A system composition schematic diagram of the present application is shown in the figure;

[0037] Figure 2 A schematic diagram of an energy collection-information transmission frame structure is shown in the figure;

[0038] Figure 3 A schematic diagram of a symbol period relationship is shown in the figure;

[0039] Figure 4 A diagram of Internet of Things transmission and rate versus energy collection time under different transmission SNRs is shown in the figure;

[0040] Figure 5 A diagram of Internet of Things transmission and rate versus energy collection time under different systems is shown in the figure. DETAILED DESCRIPTION

[0041] The present application will be described in detail below with reference to the accompanying drawings:

[0042] The present application proposes a low-power Internet of Things reflective device access design method. The system composition is shown in the figure, Figure 1 which includes a cellular base station configured with a single antenna, K passive Internet of Things reflective devices, and a single-antenna receiver. The base station transmits cellular information to the receiver, and the reflective devices perform energy collection using the base station signal. When the reflective devices collect sufficient energy, they enter an active state. The active reflective devices modulate the information to be transmitted using a predefined spread spectrum code, and load the information onto the base station signal for reflection transmission. The receiver jointly demodulates the base station information and the information of the active reflective devices.

[0043] The frame structure for energy collection and information transmission of the reflective devices is shown in the figure, Figure 2 wherein τ0 represents a time period for energy collection, and T-τ0 represents a time period for information transmission. The period of a base station transmitted symbol s(n) is T s , the period of a reflective device transmitted symbol is T b , the length of a spread spectrum code used by the reflective device is N, and the period of the spread spectrum code is T c , and the symbol period relationship of the three satisfies T b = NT c = NT s , as shown in the figure. Figure 3 The channel from the base station to the kth reflective device is denoted as h k , and the channel from the kth reflective device to the receiver is denoted as g k, the channel from the base station to the receiver is denoted as h0. The received signal of the reflecting device k is

[0044]

[0045] where s(n) denotes the normalized base station transmitted signal and p denotes the transmit power. In the energy harvesting phase, the reflecting device only performs energy harvesting without reflection. The average power that the reflecting device k harvests is

[0046] P k = hph k 2 , (2)

[0047] where h ∈ [0, 1] is the energy harvesting efficiency. The energy that the reflecting device k harvests in time τ0is

[0048] E k = P k τ0= hτ0ph k 2 . (3)

[0049] In the data transmission phase, the total power consumption of the reflecting device can be expressed as

[0050]

[0051] where E0denotes the energy consumption for adjusting the reflection coefficient once, and P c denotes the circuit power consumption. When the energy that the reflecting device harvests exceeds the energy that it needs to consume, i.e., when the following condition is satisfied, the reflecting device becomes active.

[0052] hτ0p|h k | 2 ≥ E c . (5)

[0053] Consider that the channels are subject to complex Gaussian distribution The probability that the reflecting device is active is

[0054]

[0055] The probability that L reflecting devices out of K reflecting devices are active is

[0056]

[0057] Let b i denote the transmitted symbol of the reflecting device i. To avoid interference between reflecting devices, the reflecting device i multiplies its transmitted symbol by its exclusive spreading code c i(n), n = 0, L, N - 1. The received signal at the receiver is composed of the direct link signal from the base station and the reflected link signal from the active reflecting devices. Assuming there are L reflecting devices active, the received signal at the receiver is

[0058]

[0059] where u(n) represents the complex Gaussian noise at the receiver, which is subject to distribution The receiver first demodulates the base station signal s(n). Since the reflected link signal b l c l (n) is unknown at the receiver and its symbol period is consistent with that of the base station, the receiver treats the reflected link as interference when demodulating s(n). At this time, the Signal-to-Interference-plus-Noise Ratio (SINR) of demodulating s(n) is

[0060]

[0061] After demodulating s(n), the receiver cancels the direct link signal using successive interference cancellation and then demodulates the transmitted symbol b l of the reflecting devices. The signal after successive interference cancellation is

[0062]

[0063] The receiver first multiplies the received signal y(n) by s * (n) and then divides by |s(n)| 2 , which can obtain

[0064]

[0065] When demodulating the transmitted symbol of reflecting device k, the receiver multiplies the signal by the known spreading code and then combines in the time dimension using maximum ratio combining, which can obtain

[0066]

[0067] Assuming that the spreading codes used by different reflecting devices are mutually orthogonal, i.e., satisfying

[0068]

[0069] Using the orthogonality of the spreading codes, we can obtain

[0070]

[0071] where The noise power can be obtained by the following formula

[0072]

[0073] The signal-to-noise ratio of the receiver demodulation is

[0074]

[0075] From the above formula, the reflection device can realize interference-free information transmission. When s(n) adopts phase shift keying (PSK) modulation, The signal-to-noise ratio at this time is And when s(n) adopts other non-constant amplitude modulation, such as 16QAM, the noise power will be amplified, and the signal-to-noise ratio at this time is

[0076]

[0077] Considering the energy collection effect of the reflection device, the throughput of the reflection device k can be represented as

[0078]

[0079] Where I(·) represents an indicator function. The total throughput of the Internet of Things transmission is

[0080]

[0081] The beneficial effects of the present application will be verified by simulation. The simulation parameters are set as follows: the symbol period ratio N is set to 16, the bandwidth is set to 20 kHz, the symbol period T s = 0.005 ms, and the total duration is T = 1 s. The number of Internet of Things devices is K = 10. The energy collection efficiency is set to h = 0.6. The channel parameter is set to λ g = λ h = 1. In terms of power consumption parameters, the circuit power consumption P c is set to -10 dBm, and the energy required for each adjustment of the reflection coefficient is E0= 0.1 μJ. In order to make a comparison, the scheme in which the reflection device does not use a spread code is taken as a benchmark scheme, and the access scheme based on code division multiple access proposed by the present application is compared.

[0082] Figure 4 The relationship between the total throughput of the Internet of Things transmission and the energy collection time under different transmission SNR conditions is shown, where s(n) adopts BPSK modulation. As can be seen from the figure, with the increase of the energy collection time, the total throughput presents a trend of first increasing and then decreasing, indicating that there is an optimal energy collection time that can maximize the total throughput. This reveals the trade-off relationship between energy collection and data transmission time. In addition, with the increase of the transmission SNR, the optimal decreases. For example, when the transmit SNR is 10 dB, about 30 ms of energy harvesting time is needed to reach the maximum throughput. When the transmit SNR is 10 dB, only about 10 ms is needed to achieve the maximum throughput. This shows that under the condition of high transmit power, the reflection device needs less time to complete energy collection, so as to use more time for data transmission.

[0083] Figure 5 The relationship between the total throughput of the Internet of Things transmission in different systems and the energy collection time τ0 under the condition that s(n) adopts 16QAM modulation and the transmit SNR is 10 dB is shown. As can be seen from the figure, the proposed access scheme is significantly better than the benchmark scheme, and higher total throughput is achieved in all energy collection time ranges.

[0084] In summary, the simulation results show that the access design method proposed by the present application not only can realize efficient use of energy and time resources, but also significantly improves the total throughput of the Internet of Things device, and has important practical application value and theoretical significance.

Claims

1. A low-power Internet of Things device access method, the system comprising a single-antenna cellular base station, K passive Internet of Things reflecting devices, and a single-antenna receiver; characterized in that, The access method is: The base station sends cellular information to the receiver, and the reflecting device collects energy by using the base station signal; the specific method of the reflecting device collecting energy by using the base station signal is that the time length of the reflecting device collecting energy by using the base station signal is set as , and the energy collected by the reflecting device k within the time is ， wherein, is the energy harvesting efficiency, denotes the base station transmit power, is the channel from the base station to the k-th reflecting device; When the energy collected by the reflecting device meets the set condition, the active state is entered, the active reflecting device modulates the information to be transmitted by using a predefined spread spectrum code, and loads the information onto the base station signal for reflection transmission; The receiver jointly demodulates the base station information and the information of the active reflecting device, and the specific method is: The received signal at the receiver is defined as: ， in, is the channel from the base station to the receiver, represents the normalized base station transmitted signal, Indicates the base station to the channels of reflective devices, Indicates the The channel from the reflecting device to the receiver, Indicates that the transmission information of the reflector device is obtained by multiplying the transmission symbols of L active reflector devices by the spreading code. is the first of L active reflective devices A reflective device, Indicates that the receiver follows the distribution Complex Gaussian noise; The receiver first demodulates the base station signal treating the reflection link as interference ; demodulating After that, the receiver cancels the direct link signal using serial interference cancellation and demodulates the transmitted symbol of the reflecting device again The signal after serial interference cancellation is: ， The receiver first multiplies the received signal by , divides by , to obtain: ， In demodulating the transmitted symbols of reflection device k, , the receiver multiplies the signal by the known spreading code and demodulates with maximal ratio combining. The signal-to-noise ratio of the demodulated signal is ， The throughput of the reflecting device k is obtained as: ， wherein denotes an indicator function.

2. The method of claim 1, wherein, The specific method for the reflecting device to meet the set condition is: The time length of each frame signal of the reflection device is set as The time length of information transmission after the reflection device collects enough energy is The total power consumption of the reflection device in the data transmission stage is defined as ， wherein, N is the length of the spread spectrum code used by the reflecting device, represents the energy consumption for adjusting the primary reflection coefficient, represents the circuit power consumption, and when the following condition is met, the reflecting device is determined to enter the active state: 。 3. The method of claim 2, wherein, The method for the active reflecting device to modulate the information to be transmitted by using a predefined spread spectrum code is: Let the channel be complex Gaussian distributed where denotes the variance, and the probability that the reflecting device is active is calculated as ， Thus, the probability that L reflecting devices among the K reflecting devices are active is obtained as: ， The transmission information of the reflector device is obtained by multiplying the transmission symbols of the L active reflector devices by the spreading code, which is expressed as ,in is the first of L active reflective devices A reflective device.

Images