Low-power-consumption Internet of Things equipment access method

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a low-power-consumption Internet of Things equipment access method. The method comprises the following steps: a base station sends cellular information to a receiver, and a reflection device collects energy by using a base station signal; when the energy collected by the reflection equipment meets a set condition, the reflection equipment enters an active state, and the active reflection equipment modulates information to be transmitted by using a predefined spreading code and loads the information to a base station signal for reflection transmission; and the receiver jointly demodulates the information of the base station and the information of the active reflection equipment. According to the access scheme provided by the invention, low-power-consumption interference-free access of large-scale Internet of Things equipment can be realized by virtue of a cellular system, and the access method has important application value and development potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a low-power consumption Internet of Things device access method. Background Art

[0002] With the widespread application of IoT in smart cities, smart transportation, and industrial Internet, the number of IoT devices and connections has shown explosive growth. According to Ericsson's latest IoT report released in 2024, the number of global IoT connections will reach 38.8 billion by 2029. Existing IoT technologies (such as LTE-M and NB-IoT) rely on active communication architectures, have high transmission power consumption, and usually require dedicated batteries. However, frequent battery replacement not only generates huge operation and maintenance costs, but many IoT devices are limited by size and environmental factors and are difficult to rely on batteries for power or charging. Passive IoT (Ambient Internet of Things) technology integrates backscatter communication technology with energy harvesting technology to achieve near-zero power communication, and has received great attention from academia and industry in recent years. However, traditional backscatter communication technology has direct link interference problems, which limits the transmission performance of IoT reflective devices, further limiting the large-scale application of passive IoT.

[0003] Symbiotic Radio technology is a new type of backscatter communication technology. By introducing collaborative transmission between cellular and IoT devices and utilizing joint demodulation technology, the transmission performance of IoT devices is significantly improved. In scenarios that support access to a large number of devices, it is crucial to study efficient access mechanisms for symbiotic wireless communications. However, most existing access solutions use a relatively simple time division multiple access (TDMA) method, which cannot support concurrent transmission of multiple devices at the same time. In addition, these solutions rarely take into account the energy collection requirements of IoT reflective devices, making it difficult to directly apply them to passive IoT scenarios. Summary of the invention

[0004] The main content of the present invention is to propose a low-power IoT 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 present invention is:

[0006] A low-power Internet of Things device access method, the system includes a cellular base station configured with a single antenna, K passive Internet of Things reflection 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 for energy harvesting;

[0008] When the energy collected by the reflection device meets the set conditions, it enters the active state. The active reflection device modulates the information to be transmitted using the 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 reflector devices.

[0010] Furthermore, the specific method of the reflection device using the base station signal to collect energy is: setting the time length for the reflection device to use the base station signal to collect energy to be τ0, and 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, and 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 reflection device is T, the duration of information transmission after the reflection device collects enough energy is T-τ0. The total power consumption of the reflection device in the data transmission stage is defined as:

[0015]

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

[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 spread spectrum code is:

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

[0020]

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

[0022]

[0023] Multiply the L active reflector device transmission symbols by the spreading code to obtain the transmission information of the reflector device, which is expressed as b l c l (n), where l is the lth reflection device among the L active reflection devices.

[0024] Furthermore, the specific method for the receiver to jointly demodulate the base station information and the information of the active reflection device is:

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

[0026]

[0027] Where s(n) represents the normalized base station transmission signal, h l represents the channel from the base station to the lth reflection device, g l represents the channel from the lth reflection device to the receiver, and u(n) represents the complex Gaussian noise of the receiver;

[0028] The receiver first treats the reflected link as interference to demodulate the base station signal s(n);

[0029] After demodulating s(n), the receiver uses serial interference cancellation to eliminate the direct link signal and then demodulates the transmitted symbol b of the reflected device. l , the signal after serial interference elimination is:

[0030]

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

[0032]

[0033] When demodulating the transmitted symbol of reflecting device k (1≤k≤L), the receiver converts the signal Multiply by the known spreading code And use maximum ratio combining to demodulate b k The signal-to-noise ratio is:

[0034]

[0035] The beneficial effect of the present invention is that the access scheme proposed by the present invention can realize low-power and interference-free access of large-scale Internet of Things devices with the help of cellular systems, and has important application value and development potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the system composition of the present invention;

[0037] Figure 2 This is a schematic diagram of the energy collection-information transmission frame structure;

[0038] Figure 3 It is a schematic diagram of symbol period relationship;

[0039] Figure 4 This is a graph showing the relationship between IoT transmission rate and energy collection time under different transmission SNRs;

[0040] Figure 5 The relationship between IoT transmission rate and energy collection time for different systems. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings:

[0042] The present invention proposes a low-power Internet of Things reflective device access design method. The system composition is as follows Figure 1 As shown, it includes a cellular base station with a single antenna, K passive IoT reflector devices, and a single-antenna receiver. The base station sends cellular information to the receiver, and the reflector uses the base station signal to collect energy. When the reflector collects enough energy, it enters the active state. The active reflector uses a predefined spread spectrum code to modulate the information to be transmitted 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 reflector device.

[0043] The frame structure of the reflective device for energy collection and information transmission is as follows: Figure 2 As shown, τ0 represents the time period for energy collection, and T-τ0 represents the time period for information transmission. The period for the base station to send symbols s(n) is T s , the period of the reflection device sending symbols is T b , the spread spectrum code length used by the reflection device is N, and its period is T c , the symbol period relationship of the three satisfies T b =NT c =NT s ,like Figure 3 The channel from the base station to the kth reflection device is denoted as h k , the channel from the kth reflection 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 reflection device k is

[0044]

[0045] Where s(n) represents the normalized base station transmission signal, and p represents the transmission power. In the energy collection phase, the reflection device only collects energy without reflection. The average power of energy collected by the reflection device k is

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

[0047] Where h∈[0,1] is the energy collection efficiency. The energy collected by the reflector k in time τ0 is

[0048] E k =P k τ0=hτ0ph k 2 . (3)

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

[0050]

[0051] Among them, E0 represents the energy consumption of adjusting the reflection coefficient once, P c Represents the power consumption of the circuit. When the energy collected by the reflective device exceeds the energy required to be consumed, that is, when the following conditions are met, the reflective device becomes active.

[0052] hτ0p|h k | 2 ≥E c . (5)

[0053] Consider that the channels all obey complex Gaussian distribution The probability that the reflective device is active is

[0054]

[0055] The probability that L of the K reflective devices are active is

[0056]

[0057] Let b i represents the transmission symbol of reflection device i. To avoid interference between reflection devices, reflection device i multiplies the transmission symbol with its own spreading code c i(n), n = 0, L, N-1. The received signal at the receiver consists of the direct link signal from the base station and the reflected link signal from the active reflection device. Assuming that there are L reflection devices active, the received signal at the receiver is

[0058]

[0059] Among them, u(n) represents the distribution at the receiver 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 the base station symbol. The receiver treats the reflected link as interference when demodulating s(n). At this time, the signal-to-interference-plus-noise ratio (SIR) of demodulated s(n) is

[0060]

[0061] After demodulating s(n), the receiver uses serial interference cancellation to eliminate the direct link signal and then demodulates the transmitted symbol b of the reflected device. l The signal after serial interference elimination is

[0062]

[0063] The receiver first multiplies the received signal y(n) by s * (n), and then divided by |s(n)| 2 , we can get

[0064]

[0065] When demodulating the transmitted symbol of the reflecting device k, the receiver converts the signal Multiply by the known spreading code Then, by combining the maximum ratio from the time dimension, we can get

[0066]

[0067] Assume that the spread spectrum codes used by different reflection devices are mutually orthogonal, that is, satisfying

[0068]

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

[0070]

[0071] in, 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, we can know that the reflective device can achieve interference-free information transmission. When s(n) is modulated by phase-shift keying, The signal-to-noise ratio at this time is When s(n) uses other non-constant amplitude modulation, such as 16QAM, the noise power will be amplified and the signal-to-noise ratio is

[0076]

[0077] Considering the impact of energy harvesting of reflective devices, the throughput of reflective device k can be expressed as

[0078]

[0079] Where I(·) represents the indicative function. The total throughput of IoT transmission is

[0080]

[0081] The following simulation will verify the beneficial effects of the present invention. The simulation parameters are set as follows: the symbol period ratio N is set to 16, the bandwidth is set to 20 kHz, and the symbol period T is set to 16. s = 0.005ms, the total duration is T = 1s. The number of IoT 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 The energy required to adjust the reflection coefficient each time is set to -10 dBm, and E0 = 0.1 μJ. For comparison, the solution in which the reflection device does not use a spread spectrum code is used as a benchmark solution and compared with the access solution based on code division multiple access proposed in the present invention.

[0082] Figure 4 The figure shows the relationship between the total throughput of IoT transmission and the energy collection time under different transmission SNR conditions, where s(n) uses BPSK modulation. As can be seen from the figure, as the energy collection time increases, the total throughput increases first and then decreases, indicating that there is an optimal energy collection time. can maximize the total throughput. This reveals the trade-off between energy harvesting and data transmission time. In addition, as the transmit SNR increases, the optimal For example, when the transmit SNR is 10dB, it takes about 30ms of energy collection time to achieve the maximum throughput. When the SNR is 10dB, it only takes about 10ms to achieve the maximum throughput. This shows that under high transmit power conditions, the reflective device needs less time to complete energy collection, so that more time is used for data transmission.

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

[0084] In summary, the simulation results show that the access design method proposed in the present invention can not only achieve efficient utilization of energy and time resources, but also significantly improve the total throughput of IoT devices, which has important practical application value and theoretical significance.

Claims

1. A low-power IoT device access method, the system includes a cellular base station configured with a single antenna, K passive IoT reflective devices and a single-antenna receiver; characterized in that: The access method is: The base station sends cellular information to the receiver, and the reflector uses the base station signal for energy harvesting; When the energy collected by the reflection device meets the set conditions, it enters the active state. The active reflection device modulates the information to be transmitted using the 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 reflector devices.

2. A low-power Internet of Things device access method according to claim 1, characterized in that: The specific method of the reflection device using the base station signal to collect energy is: set the time length for the reflection device to use the base station signal to collect energy as τ0, and the energy collected by the reflection device k within the time τ0 is: E k =P k τ0=hτ0p|h k | 2 Among them, h∈[0,1] is the energy collection efficiency, p represents the base station transmission power, and h k is the channel from the base station to the kth reflection device.

3. A low-power Internet of Things device access method according to claim 2, characterized in that: The specific method by which the energy collected by the reflection device meets the set conditions is: Assuming the duration of each frame signal of the reflection device is T, the duration of information transmission after the reflection device collects enough energy is T-τ0. The total power consumption of the reflection device in the data transmission stage is defined as: Among them, T b is the period of symbol transmission by the reflection device, N is the length of the spread spectrum code used by the reflection device, E0 represents the energy consumption of adjusting the reflection coefficient once, P c Indicates the circuit power consumption. When the following conditions are met, the reflective device is judged to enter the active state: hτ0p|h k | 2 ≥E c 。 4. A low-power Internet of Things device access method according to claim 3, characterized in that: The method in which the active reflector modulates the information to be transmitted using a predefined spreading code is: Assume that the channels all obey complex Gaussian distribution where λ h Denotes the variance, and the probability of the reflective device being active is calculated as: Therefore, the probability that L out of K reflection devices are active is: Multiply the L active reflector device transmission symbols by the spreading code to obtain the transmission information of the reflector device, which is expressed as b l c l (n), where l is the lth reflection device among the L active reflection devices.

5. A low-power Internet of Things device access method according to claim 4, characterized in that: The specific method for the receiver to jointly demodulate the base station information and the information of the active reflection device is: The received signal at the receiver is defined as: Where s(n) represents the normalized base station transmission signal, h l represents the channel from the base station to the lth reflection device, g l represents the channel from the lth reflector to the receiver, and u(n) represents the distribution at the receiver. Complex Gaussian noise; The receiver first treats the reflected link as interference to demodulate the base station signal s(n); After demodulating s(n), the receiver uses serial interference cancellation to eliminate the direct link signal and then demodulates the transmitted symbol b of the reflected device. l , the signal after serial interference elimination is: The receiver first receives the signal Multiply by s * (n), and then divided by |s(n)| 2 ,get: When demodulating the transmitted symbol of the reflecting device k, 1≤k≤L, the receiver converts the signal Multiply by the known spreading code And use maximum ratio combining to demodulate b k The signal-to-noise ratio is: The throughput of reflection device k is obtained as: Where I(·) represents the indicator function.

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