CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional patent application claiming priority to European Patent Application No. 20150999.9, filed Jan. 9, 2020, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The disclosure relates to time reference generation in duty-cycled wireless communications, especially for generating wakeup time reference for duty-cycled wireless sensor nodes.

BACKGROUND

Wireless communication technology is gradually becoming popular in many new applications. For example, for implantable applications, sensors that are located inside a human body capture the biomedical metrics of the human body and send them out to external electronic equipment using wireless communication technology such as wireless radios. This greatly reduces the inconvenience for patients that is typically associated with conventional bulky equipment such as an endoscope. Furthermore, for disposable applications, a wireless device cannot be re-used and has to be thrown away afterwards.

In the above-mentioned applications, the wireless radio needs to be very small, namely in the millimeter scale, to be friendly to the human body. In addition, the cost of each tag needs to be very low. Moreover, a large link budget is desired due to high channel loss. Therefore, key requirements for those applications include but are not limited to extremely small Figure of Merit (FOM), extremely low cost, and adequate performance.

The requirements in implantable applications as well as in disposable applications raise challenges for a wireless radio because present wireless radios are much bigger and more expensive due to bulky off-chip components. For example, the most popular crystal quartz size is 3.2 mm by 2.5 mm, and the price for each crystal quartz is substantial enough to increase the overall cost of a radio. Generally, in a wireless radio, two crystal oscillators are required. One is for the system clock, which provides the frequency reference in order to define the communication channel. Other is for the wakeup timer, which performs the sleep/wakeup control for the whole chip, so that the chip operation is duty-cycled in order to reduce the power consumption and prolong battery lifetime.

Therefore, replacing the crystal-based oscillators with a less bulky arrangement or at least reducing the number of crystal quartz in a wireless radio is greatly demanded to make the wireless technology feasible for the aforementioned applications. For example, the document WO 2017/147591 A1 shows a crystal-less radio node operative as a slave node, where the system clock uses an RC oscillator. The frequency of the RC oscillator defines the RF carrier frequency. The slave node calibrates the RC oscillator and thus calibrates the RF carrier frequency of the slave node to the same of the master node. However, the crystal-less slave node does not comprise a wakeup timer to perform the sleep/wakeup control for the node. Without a wakeup timer, the slave node is required to be always active, which results in high power consumption and short battery lifetime.

SUMMARY

Accordingly, the disclosure includes a system and a method for generating wakeup time reference for duty-cycled wireless sensor nodes, which can help alleviate the aforementioned limitations.

According to a first aspect of the disclosure, a system is provided for generating time reference in duty-cycled wireless communications. The system comprises at least one master module comprising a master transceiver adapted to transmit data packets. The system further comprises at least one slave module comprising a slave transceiver adapted to receive the data packets. The slave module further comprises a signal generator adapted to generate a clock signal with a period equal to the time interval of two data packets transmitted by the master module. Moreover, the slave module further comprises a slave timer adapted to utilize the clock signal as a time reference in order to perform the sleep/wakeup control for the slave module.

Therefore, the disclosure includes a system comprising a slave module and its pair master module, where the slave module does not require crystal based oscillator to perform the sleep/wakeup control for the slave module. In order to enhance the precision of the wakeup timer without a crystal-based oscillator, the slave module generates a timing reference to control the frequency of the wakeup timer. Here, the slave module generates the timing reference indirectly corresponding to the master module by generating a clock signal based on the transmitted packet duration from the master module. Consequently, the system eliminates the requirement of having a crystal-based oscillator for the sleep/wakeup control for the slave module, thereby reducing the overall size and cost of the radio significantly.

According to a first implementation form of the first aspect of the disclosure, the slave module is implemented on a single integrated circuit whereby the slave timer comprises an on-chip oscillator. The on-chip oscillator can be implemented by means of a fully integrated complementary metal oxide semiconductor (CMOS) oscillator, for example, a fully integrated CMOS RC-oscillator. As such, the on-chip oscillator can alleviate the size and cost constraints for the radio.

According to a second implementation form of the first aspect of the disclosure, the master module is further adapted to transmit the data packet with a specific duty-cycle ratio and a specific time interval between two transmitted data packets. The duty cycled packet transmission facilitates effective sleep scheduling in order to mitigate the energy consumption due to idle listening and overhearing in the master and slave module.

According to a further implementation form of the first aspect of the disclosure, the master module further comprises a high precision clock such as a crystal oscillator or a microelectromechanical system (MEMS) based oscillator or a bulk acoustic wave (BAW) based oscillator, operating as a master timer. In this context, the master timer is adapted to generate a time reference in order to perform the sleep/wakeup control for the master module. Hence, the high precision clock in the master module generates a precise time reference for sleep/wakeup control for the master module. Since the slave module generates its sleep/wakeup time reference based on the time reference of the master module, the time reference in the slave module is also precise.

According to a further implementation form of the first aspect of the disclosure, the slave module is further adapted to detect the data packet by means of signal detection such as energy detection or preamble detection or synchronized frame detection. Therefore, the slave module detects the transmitted data packet through a signal detection technique depending on the nature of the application and that may or may not require a priori knowledge about the primary transmission.

According to a further implementation form of the first aspect of the disclosure, the signal generator is further adapted to set a flag signal to high if the data packet is detected and to reset the flag signal to zero upon completion, thereby generating the clock signal in a manner that the period equals the time interval of two data packets transmitted by the master module. Therefore, an accurate clock signal is generated in the slave module for sleep/wakeup control that indirectly corresponds to the high precision clock of the master module.

According to a further implementation form of the first aspect of the disclosure, the slave timer further comprises a calibration circuit adapted to calibrate the on-chip oscillator based on the flag signal. In other words, the accurate period of the flag signal is used as the time reference in order to calibrate the sleep/wakeup time control for the slave module.

According to a further implementation form of the first aspect of the disclosure, the frequency reference for the master module is defined by a high precision clock such as a crystal oscillator or a microelectromechanical system (MEMS) based oscillator or a bulk acoustic wave (BAW) based oscillator. The high precision clock precisely defines the RF carrier frequency for the master module.

According to a second aspect of the disclosure, a method is provided for generating time reference in duty-cycled wireless communications. The method comprises the act of transmitting data packets by at least one master module. The method further comprises the act of receiving the data packets by at least one slave module. Furthermore, the method comprises the act of generating a clock signal by a signal generator in the slave module with a period equal to the time interval of transmitting two data packets by the master module. Moreover, the method comprises the act of utilizing the clock signal by a slave timer in the slave module as a time reference in order to perform the sleep/wakeup control for the slave module. Therefore, the time reference to perform the sleep/wakeup control for the slave module is indirectly generated from the master module. The overall size and cost of the radio for the slave node are significantly reduced.

According to a first implementation form of the second aspect of the disclosure, the slave module is implemented on a single integrated circuit whereby the slave timer comprises an on-chip oscillator. The on-chip oscillator effectively addresses the size and cost constrains for the radio of the slave node.

According to a second implementation form of the second aspect of the disclosure, the method further comprises the act of transmitting the data packet from the master module with a specific duty-cycle ratio and a specific time interval between two transmitted data packets. Effective sleep scheduling can be performed for the master module and for the slave module thereby prolonging their operational lifetime.

According to a further implementation form of the second aspect of the disclosure, the method further comprises the act of generating a time reference by a high precision clock such as a crystal oscillator or a microelectromechanical system (MEMS) based oscillator or a bulk acoustic wave (BAW) based oscillator in the master module in order to perform the sleep/wakeup control for the master module. The time reference generated by the slave module is also precise since it is generated indirectly from the master module.

According to a further implementation form of the second aspect of the disclosure, the method further comprises the act of detecting the data packet by the slave module by means of signal detection such as energy detection or preamble detection or synchronized frame detection. The signal detection technique depends on the nature of application, which may or may not require a priori knowledge about the primary transmission.

According to a further implementation form of the second aspect of the disclosure, the method further comprises the act of setting a flag signal to high by the signal generator if the data packet is detected and an act of resetting the flag signal to zero upon completion, thereby generating the clock signal in a manner that the period equals to the time interval of two data packets transmitted by the master module. An accurate clock signal is generated in the slave module that indirectly corresponds to the high precision clock of the master module in order to perform the sleep/wakeup control for the slave module. In addition, the slave timer further comprises a calibration circuit and wherein the method further comprises the act of calibrating the on-chip oscillator by the calibration circuit with respect to the flag signal.

