WO2022065999A1

WO2022065999A1 - A method for power and signal directivity of a wireless sensor network

Info

Publication number: WO2022065999A1
Application number: PCT/MY2020/050178
Authority: WO
Inventors: Hafizal BIN MOHAMAD @ DIN; Nuzli BIN MOHAMAD ANAS; Ahmad Zaki BIN ABU BAKAR
Original assignee: Mimos Berhad
Priority date: 2020-09-25
Filing date: 2020-11-30
Publication date: 2022-03-31

Abstract

The present invention relates to a method for power and signal directivity of a wireless sensor network (1000). The method comprises the steps of determining an energy profile of at least one sensor node (10), determining the classification of channel condition between the sensor node (10) and a gateway (20), and determining a time slot for the transmission of sensor data from the sensor node (10) to the gateway (20). An optimized transmit power for the sensor node (10) is then determined and employed together with a signal directivity to establish an optimum transmission channel between the sensor node (10) and the gateway (20).

Description

A METHOD FOR POWER AND SIGNAL DIRECTIVITY OF A WIRELESS SENSOR NETWORK

FIELD OF INVENTION

The present invention relates to power management of at least one sensor node in a wireless sensor network. More particularly, the present invention relates to power management of at least one sensor node in a wireless sensor network based on a method for power and signal directivity of a signal transmission from the sensor node.

BACKGROUND OF THE INVENTION

Wireless sensor network is widely implemented as part of an Internet of Things or loT subsystem where a number of dispersed sensor nodes are interconnected through a wireless interface. The wireless sensor network is generally deployed during remote monitoring for the sensing of physical environment, where minimal computational and energy efficient capabilities are highly desirable due to limited resources. Therefore, various methods have been invented to improve the performance of the wireless sensor network by introducing various power management methods.

An example of power management method is disclosed in United States Patent Publication No. US 2018/0279221. The method involves determining a battery life of loT devices and associated the battery life with a power management profile, wherein the power management profile determines a wake-up frequency and time scheduling for data transmission by the loT devices.

However, such methods typically employ a sleeping and wake scheduling technique for the loT devices, which may result in missed events that could degrade the performance of the wireless sensor network especially for time - critical loT applications. Moreover, no further analysis is provided on how the condition of a wireless channel may impact the performance of data transmission from the loT devices. This may be necessary in order to identify the optimized power needed to reduce the power consumption of the loT devices. Power optimization for the wireless sensor network is important in order to prolong the lifetime of the sensor nodes, where the sensor nodes are expected to be operated over a long period of time to collect data from the physical environment without requiring a constant power source replacement. Therefore, there is a need to provide a method that addresses the abovementioned drawbacks.

SUMMARY OF INVENTION

According to one aspect of the present invention, a method for power and signal directivity of wireless sensor network (1000) is provided. The method is characterised by the steps of determining an energy profile of at least one sensor node (10) by an active module (11), wherein the energy profile indicates the amount of energy used to transmit a sensor data to a gateway (20); determining an optimized power coefficient by a controller module (21 ), wherein the optimized power coefficient is the classification of channel condition between the sensor node (10) and the gateway (20); determining a time slot for the transmission of the sensor data to the gateway (20) based on the optimized power coefficient; computing an optimized transmit power for the sensor node (10) by a manager module (22) using a current transmit power and the optimized power coefficient; determining if the transmit power remains optimized by a transmit controller (12); performing sensor data transmission from the sensor node (10) to a gateway (20) using the optimized transmit power in the determined time slot; and applying a signal directivity at the gateway (20) to receive the data transmission by the controller module (21).

Preferably, the step of determining the optimized power coefficient by the controller module (21) includes determining a distance between the sensor node (10) and the gateway (20); determining a channel impairment between the sensor node (10) and the gateway (20); determining a path loss exponent between the sensor node (10) and the gateway (20); normalizing the distance, the channel impairment, and the path loss exponent into a value ranging from zero to one; generating the optimized power coefficient by multiplying the normalized distance with the normalized channel impairment and the normalized path loss exponent; and classifying the optimized power coefficient into a category of channel condition. Preferably, the distance between the sensor node (10) and the gateway (20) is determined by using a ranging capability of a transmitter in the sensor node (10) and a receiver in the gateway (20).

Preferably, the channel impairment between the sensor node (10) and the gateway (20) is determined by measuring a bit error rate or BER.

Preferably, the path loss exponent between the sensor node (10) and the gateway (20) is determined by measuring an inherent channel quality indicator or CQL

Preferably, if the transmit power is determined to not remain optimized, the step includes computing a new optimized transmit power for the sensor node (10).

Preferably, the step of applying the signal directivity at the gateway (20) to receive the data transmission by the controller module (21) includes directing a signal beam width at the gateway (20) to the transmitting sensor node (10).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 illustrates a block diagram for power and signal directivity of wireless sensor network (1000) according to an embodiment of the present invention.

FIG. 2a illustrate a flowchart of a method for power and signal directivity of wireless sensor network according to an embodiment of the present invention.

FIG. 2b illustrates a flowchart of the sub-steps for determining the optimized power coefficient by a controller module (21 ) of the method of FIG. 2a.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. Referring to FIG. 1 , there is shown a block diagram for power and signal directivity of wireless sensor network (1000) according to an embodiment of the present invention. The wireless sensor network (1000) comprises at least one sensor node (10) and a gateway (20), wherein the sensor node (10) is connected to the gateway (20) via a wireless connection. The wireless sensor network (1000) is configured to transmit sensor data from the sensor node (10) by computing an optimized transmit power of the sensor node (10), wherein the optimized transmit power indicates the amount of transmit power that is needed to compensate for packet loss due to signal interference. The gateway (20) employs the optimized transmit power together with a signal directivity to establish an optimum transmission channel between the sensor node (10) and the gateway (20).

Each sensor node (10) is configured to collect sensor data from physical environment, wherein the sensor node (10) includes various type of sensor devices such as temperature sensor, pressure sensor, humidity sensor, and etc. The sensor node (10) may be powered by a power source such as battery, wherein the power source provides a total energy capacity for the sensor node (10). The sensor node (10) comprises an active module (11 ) which further comprises a transmit controller (12).

The active module (11 ) is configured to obtain an energy profile of the sensor node (10), wherein the energy profile indicates the amount of energy used to transmit the sensor data to the gateway (20). The energy profile of the sensor node is determined based on activity levels of the sensor node (10), wherein the activity levels may include but not limited to frequency of sensor data transmission and packet size of the sensor data. The active module (11) is also configured to manage the time slot allocated by the gateway (20). Based on the allocated time slot and the energy profile, the transmit controller (12) is configured to perform a time scheduled transmission of the sensor data to the gateway (20).

The gateway (20) is configured to receive the sensor data transmitted by the sensor node (10) and manage the connection of the sensor node (10) in the wireless sensor network (1000). The gateway (20) comprises a controller module (21 ) which further comprises a manager module (22). The controller module (21) is configured to allocate the time slot to the sensor node (10) for the transmission of sensor data to the gateway (20) and determine an optimized power coefficient of a channel, wherein the optimized power coefficient is the classification of channel condition between the sensor node (10) and the gateway (20). Based on the optimized power coefficient, the manager module (22) is configured to compute the optimized transmit power of the sensor node (10), wherein the optimized transmit power is computed by multiplying a current transmit power of the sensor node (10) with the optimized power coefficient. The manager module (22) is also configured to store critical parameters for the transmission of sensor data, wherein the critical parameters include but not limited to the optimized transmit power of the sensor node (10), and signal directivity and beam width applied at the gateway (20).

Referring now to FIG. 2a, there is shown a flowchart of a method for power and signal directivity of wireless sensor network (1000) according to an embodiment of the present invention. Initially, the active module (11 ) determines the energy profile of the sensor node (10) in step 100, wherein the energy profile indicates the amount of energy used to transmit the sensor data to the gateway (20). The energy profile of the sensor node (10) is determined based on the activity levels of the sensor node (10), wherein the activity levels may include but not limited to frequency of sensor data transmission and packet size of the sensor data. As the frequency of the sensor data transmission and packet size of the sensor data increases, the amount of the energy used to transmit the sensor data also increases.

In step 200, the controller module (21 ) determines the optimized power coefficient of the channel, wherein the optimized power coefficient is the classification of channel condition between the sensor node (10) and the gateway (20). The optimized power coefficient is determined by computing a distance, a channel impairment, and a path loss exponent between the sensor node (10) and the gateway (20). The optimized power coefficient is then used to classify the channel condition according to categories such as good channel condition, moderate channel condition, bad channel condition, and worst channel condition. The step of determining the optimized power coefficient will be described later in relation to FIG. 2b.

The optimized power coefficient is then used by the controller module (21 ) to determine a suitable time slot for the transmission of the sensor data to the gateway (20) as in step 300. As the channel condition may vary over time due to factors such as signal interference, different time slots may have different value of the optimized power coefficient. For example, the controller module (21 ) may schedule the transmission of the sensor data during a time slot that has a lower value of the optimized power coefficient, wherein the lower value of the optimized power coefficient may indicate a good channel condition with low signal interference.

Based on the optimized power coefficient, the optimized transmit power of the sensor node (10) is computed by the manager module (22) as in step 400. The optimized transmit power indicates the amount of transmit power that is needed to compensate for packet loss due to signal interference. If the channel is determined to be in good condition, the transmit power may be reduced. However, if the channel is in bad condition, the transmit power may be increased in order to receive the data packet from the sensor node (10). Preferably, the optimized transmit power is computed based on the equation below:

Optimized transmit power = current transmit power x (1+ optimized power coefficient)

For example, the optimized transmit power for the sensor node (10) with 10mW current transmit power is 14.5 mW. This indicates that the transmit power should be increased 45% to compensate for the packet loss due to signal interference. The controller module (21) then notifies the transmit controller (12) in the sensor node (10) to utilize the optimized transmit power for the transmission of sensor data to the gateway (20).

In step 500, the transmit controller (12) determines whether the transmit power of the sensor node (10) remains optimized according to the channel condition and the energy profiles of the sensor node (10). The transmit power is periodically checked based on hourly, daily or weekly basis depending on the time - interval of sensor data transmission by the sensor node (10). If the transmit power is not optimized, step 400 is repeated in order to determine a new optimized transmit power for the sensor node (10).

If the transmit power remains optimized, the sensor node (10) begins the sensor data transmission to the gateway (20) using the optimized transmit power in the scheduled time slot provided by the controller module (21) as in step 600. The controller module (21 ) then applies a signal directivity by directing a signal beam width at the gateway (20) to the transmitting sensor node (10) in order to receive the sensor data transmission as in step 700. The signal beam width may be directed to the sensor node (10) by using a wide or narrow beam. The combination of optimized transmit power and signal directivity is able to reduce the total amount of energy usage of the sensor node (10), where the life-time of the sensor node (10) operating in the physical environment may be increased.

Referring now to FIG. 2b, there is shown a flowchart of the sub-steps for determining the optimized power coefficient by the controller module (21 ) as in step 300 of the method of FIG. 2a. In step 301 , the distance between the sensor node (10) and the gateway (20) is determined by using a ranging capability of a transmitter in the sensor node (10) and a receiver in the gateway (20). An example of technique that may be used to determine the distance between the sensor node (10) and the gateway (20) is a time-of-flight technique, wherein the distance is measured based on a time difference between the emission of a signal and its return to the sensor node (10) after being reflected.

In step 302, the channel impairment between the sensor node (10) and the gateway (20) is determined by measuring a bit error rate or BER, wherein the BER indicates the number of bits error on the data received by the gateway (20) as compared to the data transmitted by the sensor node (10). The BER is measured based on an example equation below:

where E(t) is the number of bits received in error over time t, and N(t) is the total number of bits transmitted in time t.

In step 303, the path loss exponent between the sensor node (10) and the gateway (20) is determined by measuring an inherent channel quality indicator or CQI, wherein the CQI indicates the communication quality of the channel. The CQI is measured based on performance metrics such as Signal-to-Noise ratio or SNR, or Signal-to-lnterference-plus-Noise ratio or SINR. The values of the distance, the channel impairment, and the path loss exponent are then normalized into a value ranging between one to zero with respect to one-hour time duration sliding window as in step 304.

The normalized distance is then multiplied with the normalized channel impairment and normalized path loss exponent to generate the optimized power coefficient of the channel as in step 305, wherein the optimized power coefficient may be represented as a percentage value. The optimized power coefficient is then classified into a category of channel condition as in step 306. For example, the optimized power coefficient in a range between 0% - 25% is categorized as good channel condition, the optimized power coefficient in a range between 26% - 50% is categorized as moderate channel condition, the optimized power coefficient in a range between 51% - 75% is categorized as bad channel condition, and the optimized power coefficient in a range between 76% - 100% is categorized as worst channel condition.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specifications are words of description rather than limitation and various changes may be made without departing from the scope of the invention.

Claims

9 CLAIMS

1 . A method for power and signal directivity of wireless sensor network (1000) is characterised by the steps of: a) determining an energy profile of at least one sensor node (10) by an active module (11), wherein the energy profile indicates an amount of energy used to transmit a sensor data to a gateway (20); b) determining an optimized power coefficient by a controller module (21 ), wherein the optimized power coefficient is a classification of channel condition between the sensor node (10) and the gateway (20); c) determining a time slot for the transmission of the sensor data to the gateway (20) based on the optimized power coefficient by the controller module (21); d) computing an optimized transmit power for the sensor node (10) by a manager module (22); e) determining if the transmit power remains optimized by a transmit controller (12); f) performing sensor data transmission from the sensor node (10) to the gateway (20) using the optimized transmit power in the determined time slot; and g) applying a signal directivity at the gateway (20) to receive the data transmission by the controller module (21).

2. The method as claimed in Claim 1 , wherein the step of determining the optimized power coefficient by the controller module (21 ) includes: a) determining a distance between the sensor node (10) and the gateway (20); b) determining a channel impairment between the sensor node (10) and the gateway (20); c) determining a path loss exponent between the sensor node (10) and the gateway (20); d) normalizing the distance, the channel impairment, and the path loss exponent into a value ranging from zero to one; e) generating the optimized power coefficient by multiplying the normalized distance with the normalized channel impairment and the normalized path loss exponent; and f) classifying the optimized power coefficient into a category of channel condition. The method as claimed in Claim 2, wherein the distance between the sensor node (10) and the gateway (20) is determined by using a ranging capability of a transmitter in the sensor node (10) and a receiver in the gateway (20). The method as claimed in Claim 2, wherein the channel impairment between the sensor node (10) and the gateway (20) is determined by measuring a bit error rate or BER. The method as claimed in Claim 2, wherein the path loss exponent between the sensor node (10) and the gateway (20) is determined by measuring an inherent channel quality indicator or CQL The method as claimed in Claim 1 , wherein the optimized transmit power for the sensor node (10) is computed by multiplying a current transmit power of the sensor node (10) with the optimized power coefficient. The method as claimed in Claim 1 , wherein if the transmit power is determined to not remain optimized, the step includes computing a new optimized transmit power for the sensor node (10). The method as claimed in Claim 1 , wherein the step of applying the signal directivity at the gateway (20) to receive the data transmission by the controller module (21) includes directing a signal beam width at the gateway (20) to the transmitting sensor node (10).