FIELD OF THE INVENTION

The present invention relates to controlling and synchronizing of wireless sensors and actuators, and in particular, the invention is directed to application of a weak signal detector using a nonlinear oscillator for controlling and synchronizing wireless sensors and actuators.

BACKGROUND OF THE INVENTION

Wireless sensor networks ("ubi networks") are in a central position in the applications of every day information technology. One of the most central challenges and study fields of wireless sensor networks is energy efficiency of sensor nodes. In commercial sensor network applications, a complete energy self- sufficiency or battery duration for several months to several years is typically required.

One-way wireless technologies supporting very low current operation which can be applied to transferring e.g. measuring data of independently operating sensor to central node with pre-determinated intervals, are known. These solutions do not apply to systems in which e.g. sample rate has to be set from central node dynamically or in which a large amount of sensors cause conflicts in dispatching and thus reduces the reliability of data transmission.

Furthermore, two-way wireless technologies (e.g. ZigBee) supporting low current operation in which control and measuring data is transferred with the same radio channel, are known. This requires that the sensor's relatively high current radio receiver is turned on even when the data is not transferred which increases the current consumption of sensor node, particularly when there are rapid response time demands relating to control data transmission. The fact that the minimization of energy consumption of these technologies is based on the "low duty cycle" operation of sensor nodes' radio circle and of controllers involves significant lengthening of communication response times which excludes the use of said technologies i.a. in several real-time control applications or in applications demanding a detailed mutual synchronizing of wireless sensor nodes.

Different kinds of methods have been developed wherein wireless sensor nodes can be induced by a separate radio channel. Data transfer channel used in these methods is, however, often not reliably enough in terms of the system operation for transmitting eventually critical control and synchronizing data, and therefore the same radio channel is used with measurement information for transmitting control and synchronizing data. The amount of false impulses due to erroneous detection in a troubled environment then increases which increases power consumption. Furthermore, synchronizing and control data can be transmitted to sensor nodes by a separate radio channel ("out-of-band management") and the received data can be detected with a circuit solution of very low power consumption. Then there will usually be a problem of achieving transmission range which is long enough, and of the reliability of data transmission. Tetsuya Asai, Yusuke Kanazawa, Masayuki Ikebe, Yoshihito Amemiya. "A Mos Circuit for the Lotka-Volterra Chaotic Oscillator" discloses the application of a detector based on a chaotic oscillator for the detection of weak periodic signals. A weak periodic signal supplied to a chaotic oscillator then changes its mode of oscillation from chaotic to periodic and a change of mode of oscillation back to chaotic mode is a result from the disappearance of a periodic signal, respectively. This change of mode between periodic and chaotic mode can be detected e.g. as a change of current consumption of a chaotic oscillator. The method of separating a chaotic and periodic signal is, however, sensitive for a certain type of periodic disturbing signals which can erroneously cause a change of mode from aperiodic mode to periodic mode. A method using two or more chaotic dispatches is clearly more robust against external disturbances.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a solution in which the aforesaid defects have been eliminated or are at least alleviated. In particular, the invention aims to solve how wireless sensor nodes can be controlled and synchronized quickly and reliably with a short response time and with a low power consumption in sensor nodes. The objective of the invention is met by the features defined in the independent claims.

A receiver according to the invention is characterized by the features disclosed in the characterizing part of the patent claim describing the independent apparatus claim 1.

A system according to the invention is characterized by the features disclosed in the characterizing part of patent claim describing the independent method claim 8.

According to one embodiment of the invention sensor nodes in the wireless network are controlled and/or synchronized by transmitting chaotic signals using a separate one-way data-communication channel and by receiving the signals in sensor nodes with a weak chaotic signal detector circuit based on low-power analogy implementation.

According to another embodiment the receiving head has been achieved by a weak chaotic signal detector circuit based on MEMS-technology (Micro Electro Mechanical System). According to an embodiment an energy harvester has been integrated to the same MEMS-technology implementation.

The usefulness of the system according to the present invention is based on several different matters. The technology of the invention applies e.g. to critical real time networks, to which the previous solutions do not apply adequately. By means of the invention it is possible to transmit control and synchronizing information authentically in a noisy environment with a rapid response time. Furthermore, a detector circuit of a receiving head can be extremely energy efficient. Compared to DSP-based solutions the invention is more energy efficient and compared to low- current analog solutions the present invention can be more sensitive and is better at tolerating disturbances.

The invention can easily be applied very widely to; e.g. as "wake-up radio" of wireless sensors and actuators; for synchronizing the afore said devices and transmitting the control data, for real time wireless control applications, for control applications, for military applications and for positioning on a cell-based accuracy. Preferred embodiments of the invention are also disclosed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

Next, the preferred embodiments of the invention are described in more detail with reference to the appended drawings, in which

FIG. 1 illustrates data transfer and controlling of wireless sensor nodes in network,

FIG. 2 illustrates a method of implementation of a chaotic control channel.

DETAILED DESCRIPTION OF THE EMBODIMENTS The following references are used in figures:

Central node 102

BCC transmitter 104

Sensor node 106

BCC receiver 108

WSN-transmitter-receiver 110

Generator of chaotic transmittals 1 12

Detector 1 14

Excitation circuit 116

Decoder 118 Figure 1 illustrates the data transfer and controlling of wireless sensor nodes in network. The operation of wireless sensor nodes 106 in network requires synchronizing and control operations of different level controlled from the outside of the sensor nodes 102, which can be handled in a most energy-effective and reliable way by a separate data transfer channel (BCC = Broadcast Control Channel) dedicated for this purpose. There is a BCC transmitter 1 10 in the central node and in every sensor node 106 there is a BCC receiver 108. The actual data transfer among sensor nodes and/or between central node occurs with own data transfer channel in a wireless network (WSN = Wireless Sensor Network) with a WSN-transmitter-receiver 1 10. The best possible combination of different qualities of a detector can be achieved by forming the realization of sensor nodes' BCC to chaotic transmittals and their analogy-circuit-based detection. Figure 2 presents an alternative embodiment for a chaotic control channel. In the central node 102 there is a generator 112 and a BCC transmitter 104 of chaotic transmittals. The generator 112 of chaotic transmittals generates chaotic signals, e.g. with an analogous chaotic oscillator or with a DSP-based solution which are modulated by bit stream to be transmitted, e.g. with an on/off switch of a chaotic signal or with a changeover switching of two independent chaotic signals. The signals can also be generated e.g. with computing unit. Transmitter 104 transmits the bit-modulated chaotic signal to data transfer channel either as such, e.g. with a low-frequency radio channel, or modulated, e.g. radio-modulated at 2,4 GHz AM frequency. The modulation of a chaotic signal can be implemented also with another technology, e.g. ultrasonic modulation, acoustic modulation, magnetic field or light modulation.

A signal receiver comprising a BCC receiver and a passive front head 108, a detector 114, an excitation circuit 1 16 and a decoder 118 are positioned in to the sensor node 106 or are at least functionally been connected in connection with it. The reception of a chaotic signal is usually sequenced. BCC receiver and passive front head 108 can be, e.g. a ferrite core antenna without down-converter or a dipole antenna with down-converted produced with diodes. The purpose of the antenna and the passive front head 108 is also the impedance matching of antenna with detector 114 and tuning the antenna to the used frequency range. BBC receiver and passive front head 108 are implemented without an external power supply or the power supply can be a very low-powered.

According to an embodiment of the present invention a detector 114 can be a chaotic oscillator based on low-power analogy connection, which chaotic oscillator has at least two chaotic oscillation modes (chaotic attractors corresponding to transmittals of a central node) or an own chaotic natural oscillation mode in on/off transmittal mode as well as an oscillation mode corresponding to the transmittal and to which a connection indicating different oscillation modes has been added. It is possible that the connection indicating different oscillation modes has been implemented by connection observing the oscillator's power consumption, e.g. by a comparator capable of separating different chaotic modes from each other according to deviating power consumption levels. The connection has been advantageously implemented in a way that the power consumption of different oscillation modes differs from each other sufficiently. In another embodiment the detector has been implemented with MEMS-technology. It is possible to integrate the energy harvester to the same MEMS implementation with chaotic detector.

According to an embodiment an excitation circuit 1 16 can be e.g. a space device clocked with a quick-starting RC oscillator inducing to the change of mode of input signal and induces the decoder 118 after having detected its address from the beginning of the received data packet. Decoder 118 can be e.g. a customized HW implementation of SW-based implementation with microcontroller. Decoder 118 induced by excitation circuit 116 can be configured to check from the received data packet if the data packet has been allocated exactly to this sensor node.

According to an embodiment a very low-current detection technology based on chaotic oscillators applied earlier to detecting of weak periodic signals is developed in a way that merely two or more chaotic transmittals can be used from wireless real-time measurement system for achieving a required robust level. The complex principals of chaotic communication technology are thus not applied but merely a simple detection technology of weak signals.

The ability of detectors to operate authentically with weak received signals can possibly replace a radio receiver positioned in front of detector and consuming active energy with a simpler and less current consuming receiver or even with a completely passive receiver. The total power consumption can this way be reduced significantly. By transmitting alternately chaotic signals possessing two different attractors from the central code, the first levels and zero levels of a narrowband baseband signal are transmitted to sensors. An alternate synchronization (bifurcation) detected from the changes in the own current consumption of sensors' low current detector detects the transmittal. The detector detects only the synchronizing mode. A low current and robust detector to be developed is "media- agnostic" applying also to the use of e.g. ultrasound and light as transmitters of control data.

It is possible to use the present invention for example in wake-up -radios, for transmitting synchronizing and control data in sensor networks from central node to sensor nodes, in real time wireless control applications and in positioning on a cell- based accuracy. Practical applications of the invention can be for example measuring applications and/or control/military applications wherein a wireless sensor or actuator can be in a release condition even for years but can be activated and/or configured very quickly, if required.

According to an embodiment the invention can be used to condition monitoring for example of buildings, products and/or environment. Measurements can be conducted at log intervals and/or at regular intervals, but when required, for example in a case when a damage is suspected, the measurements can be conducted very quickly. In another embodiment the invention can function as positioning device and/or as anti-theft device. A sensor node leaving the nearness of central node can release alarm when sensor node does not receive a signal from the central unit anymore, or a sensor node arriving to the circle of central node can declare its position. Sensor nodes of present invention can be placed e.g. in shipping containers which sensor nodes can carry out periodic measurements of the conditions of the container and transmit location information of the container, if required. According to another example, sensor nodes observing the condition of the building can receive their signals directly from the power supply in the real estate.

Embodiments in which the invention has been used for monitoring the boundary and/or for military applications may comprise signals that are underneath the noise level. It is very difficult, or even impossible, for an outsider then to detect a signal to be transmitted. The scope of the invention is defined in the following claims. It is, however, obvious for a man skilled in the art that the details of different features of the invention can alternate in certain amount within inventive overall idea subject to each embodiment of invention.