WO2024022736A1

WO2024022736A1 - Low-power wireless end node

Info

Publication number: WO2024022736A1
Application number: PCT/EP2023/068050
Authority: WO
Inventors: Wolfgang Bruchner
Original assignee: Cascoda Ltd
Priority date: 2022-07-28
Filing date: 2023-06-30
Publication date: 2024-02-01
Also published as: GB202211077D0; GB2620982A

Abstract

The present invention relates to a wireless end node, that comprises a Direct Sequence Spread Spectrum (DSSS) demodulator, wherein the DSSS demodulator is based on a double correlation algorithm, a data communications module configured to receive, via a first wireless receiver, an incoming DSSS coded data communication signal from a network, a sensor module configured to receive, via a second wireless receiver, a DSSS coded signal from a sensor, wherein the sensor measures an environmental variable; and the DSSS demodulator is configured to demodulate the received DSSS coded signal from the sensor during a first time period, and to demodulate the received DSSS coded data communication signal from the network during a second time period. The present invention also relates to a corresponding method and computer program product.

Description

LOW-POWER WIRELESS END NODE

Technical Field

The present invention relates to an improved wireless end node and, in particular, to combined baseband processing for processing radio data communications and a received sensor signal.

Background

Wireless end nodes in wireless sensor networks, such as those deployed in homes, offices, industrial plants etc., typically utilise batteries and/or energy harvesting devices as a power source. Therefore, the end nodes typically have stringent requirements on power consumption. The end nodes may include, or be operatively coupled to, one or more sensors for measuring an environmental variable that use stimulus or interrogation signals and/or essentially modulate the information relating to the measured environmental variable on the frequency response of the sensor, such as Surface Acoustic Wave (SAW) sensors, Electro-Mechanical Resonant Sensors (EMRS), and so on.

Figure 1 shows a conventional wireless end node 101 which includes a separate sensor system 102. A wireless communications transceiver 103 is used to connect to a data communications network with a microcontroller (MCU) 104 controlling the data communications. The sensor system 102 includes a sensor 105 to sense an environmental variable 106 and transfers the sensed data to the MCU 104 to be communicated back to the network.

The wireless communications transceiver 103 of the wireless end node 101 typically includes a transmitter (Tx) 107 and a receiver (Rx) 108.

On the transmit side the data from the microcontroller 104 is pre-processed and modulated with Direct-Sequence-Spread-Spectrum (DSSS) codes by the DSSS modulator 109 in the baseband processing section 110. The pre-processed and modulated signal is then up-modulated to the radio frequency (RF) and amplified in a radio frontend 111 for emission over an antenna 112 to a receiving device on the network.

On the receive side the radio frontend 111 is amplifying an incoming signal from the antenna 112 received from a device on the network and down-modulating the received signal with a quadrature mixer. The resulting complex signal is then processed in the baseband DSSS demodulator 113, correlated to the DSSS codes, in order to extract the data from the received signal. A Local Oscillator (LO) 114 provides the radio-frequency (RF) signal to both Tx and Rx, and a Medium Access Control (MAC) interface 115 interfaces with the MCU 104 to control the data flow.

In Figure 1, the sensor 102, converts an environmental variable 106 into an electrical signal. This electrical signal is then converted to a digital signal by an Analog-to-Digital Converter (ADC) 116 and communicated to the microcontroller 104 via a standard digital data and control interface 117.

It is also known to separate the sensor from the wireless end node such that the sensor itself is also wireless and can communicate wirelessly with the wireless end node in order to provide a signal indicative of the sensed environmental variable to the wireless end node.

However, by implementing a wireless sensor the wireless end node will typically require an additional receiver along with additional circuitry and an additional controller in order to perform the required processing of the signal received from the wireless sensor.

The conventional wireless end nodes that include a sensor or operatively communicate with a wireless sensor require a significant amount of power and increases the size, cost and complexity of the wireless end node.

The present invention seeks to address, at least in part, any or all of the disadvantages described above.

Summary of the Invention

According to a first aspect of the present invention there is provided a wireless end node comprising: a Direct Sequence Spread Spectrum (DSSS) demodulator, wherein the DSSS demodulator is based on a double correlation algorithm; a data communications module configured to receive, via a first wireless receiver, an incoming DSSS coded data communication signal from a network; a sensor module configured to receive, via a second wireless receiver, a DSSS coded signal from a sensor, wherein the sensor measures an environmental variable; and the DSSS demodulator is configured to demodulate the received DSSS coded signal from the sensor during a first time period, and to demodulate the received DSSS coded data communication signal from the network during a second time period.

In some embodiments, the sensor is a Surface Acoustic Wave (SAW) sensor.

In some embodiments, the wireless end node may further comprise a first wireless transmitter; and the sensor module is further configured to transmit, via the first wireless transmitter, an impulse excitation signal to the sensor.

In some embodiments, the impulse excitation signal may be a burst impulse excitation signal. In some embodiments, the burst impulse excitation signal may be a short cosine burst excitation signal.

In some embodiments, the DSSS demodulator may be configured to demodulate the received DSSS coded signal from the sensor using the double correlation algorithm to extract one or more data components.

In some embodiments, the one or more data components may include one or more of a sensor identification component and a frequency deviation component.

In some embodiments, the frequency deviation component may be indicative of a value of the environmental variable measured by the sensor. In some embodiments, the environmental variable may be one of temperature, pressure, humidity, strain, stress, or torque.

In some embodiments, the wireless end node may be configured to sleep during a third time period.

In some embodiments, the wireless node may further comprise: a second wireless transmitter; and a DSSS modulator configured to modulate an outgoing DSSS coded data communication signal during a fourth time period; wherein the data communications module may be configured to transmit, via the second wireless transmitter, the outgoing DSSS coded data communication signal to the network. In some embodiments, the outgoing DSSS coded data communication signal may include, at least, data extracted by the demodulation of the received DSSS coded signal from the sensor. In some embodiments, the first wireless receiver and the second wireless receiver may be the same wireless receiver.

In some embodiments, the first wireless transmitter and the second wireless transmitter may be the same wireless transmitter.

In some embodiments, the first time period and the second time period may be between 1 and 10 milliseconds.

According to a second aspect of the present invention there is provided a method of operating a wireless end node comprising: receiving, via a first wireless receiver, an incoming DSSS coded data communication signal from a network; receiving, via a second wireless receiver, a DSSS coded signal from a sensor, wherein the sensor measures an environmental variable; and demodulating, via a Direct Sequence Spread Spectrum (DSSS) demodulator using a double correlation algorithm, the received DSSS coded signal from the sensor during a first time period, and demodulating the received DSSS coded data communication signal from the network during a second time period.

In some embodiments, the sensor may be a Surface Acoustic Wave (SAW) sensor.

In some embodiments, the method may further comprise: transmitting, via a first wireless transmitter, an impulse excitation signal to the sensor.

In some embodiments, demodulating the received DSSS coded signal from the sensor using the double correlation algorithm may extract one or more data components.

In some embodiments, the method may further comprise causing the wireless end node to sleep during a third time period.

In some embodiments, the method may further comprise: modulating, via a DSSS modulator, an outgoing DSSS coded data communication signal during a fourth time period; and transmitting, via a second wireless transmitter, the outgoing DSSS coded data communication signal to the network. In some embodiments, the outgoing DSSS coded data communication signal may include, at least, data extracted by the demodulation of the received DSSS coded signal from the sensor.

In some embodiments, the first wireless receiver and the second wireless receiver may be the same wireless receiver.

According to a third aspect of the present invention there is provided a computer program product comprising computer readable executable code for implementing a method according to any one of the features of the second aspect.

It will be appreciated that any features described herein as being suitable for incorporation into one or more aspects or embodiments of the present disclosure are intended to be generalizable across any and all aspects and embodiments of the present disclosure. Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure. The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claims. Drawings

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows a traditional wireless end node including a sensor.

Figure 2 shows a conventional wireless SAW sensor operatively coupled to a wireless end node.

Figure 3 shows an arrangement of a typical SAW sensor that can be used in one or more embodiments of the present invention.

Figure 4 shows example waveforms for a transmitted impulse signal as excitation (Tx) and the returned signal (Rx) from a SAW sensor that can be used in one or more embodiments of the present invention.

Figure 5 shows a Wireless Sensor Node operatively coupled to a SAW Sensor with combined Baseband Processing according to one or more embodiments of the present invention.

Figure 6 shows a simplified schematic of a DSSS demodulator implementing a double correlation algorithm that can be used in one or more embodiments of the present invention.

Figure 7 shows a modified DSSS demodulator according to one or more embodiments of the present invention.

Figure 8 shows a processing cycle according to one or more embodiments of the present invention.

Figure 9 shows a combined wireless frontend according to one or more embodiments of the present invention.

Detailed Description

In the following embodiments, a wireless end node that includes a sensor, or is operatively coupled with one or more wireless sensors, will be described in which the power consumption, size, cost and complexity of the wireless end node are reduced. The sensor may be any suitable sensor that uses stimulus or interrogation signals, and wherein information or data indicative of a measured environmental variable is modulated on or coded in the frequency and/or phase of the output high frequency signal of the sensor, such that the measured environmental variable is obtainable from the frequency and/or phase of the output high frequency signal of the sensor. As the excitation signal transmitted to the sensor and/or the output signal of the sensor received by the wireless end node is, by nature, a high frequency radio signal then, even for an integrated sensor in the wireless end node, a radio frequency frontend would be required.

A suitable sensor may include, for example, a Surface Acoustic Wave (SAW) sensor, an Electro-Mechanical Resonant Sensor (EMRS), and so on.

The sensors (e.g. SAW sensor, EMRS, and so on) may be used to sense and measure a multitude of environmental variables (for example, temperature, pressure, humidity, mechanical variables, such as torque, strain or stress, chemical variables etc.).

In the following embodiments the sensor is a SAW sensor which is wirelessly connected to the wireless end node in operation. However, as will be appreciated, the wireless end node of the present invention is equally applicable to other similar types of sensor, such as an EMRS, that are wirelessly or operatively coupled to the wireless end node.

SAW sensors may be stimulated and interrogated wirelessly, making them suitable for harsh environments. The operation of a SAW sensor is based on the sensor converting an electrical input signal into a mechanical wave. The velocity of this wave is influenced by the environmental property to be sensed, which is then time-delayed and reflected, and subsequently converted back into an electrical signal. The interface of a SAW sensor typically includes circuitry that comprises a transmitter and a receiver. The transmitter of a SAW sensor typically transmits an interrogation signal to the sensor and the receiver of a conventional SAW sensor typically receives a corresponding response from the sensor.

An example of a conventional wireless SAW sensor 202 operatively coupled to a wireless end node 201 is shown in Figure 2. The wireless end node wireless communications transceiver 103 is the same as shown in Figure 1. However, in order to implement a wireless SAW sensor 202, the wireless end node 201 additionally requires a SAW sensor Readout Interface 204. The SAW sensor Readout Interface 204 would typically include a separate radio frontend 205 that includes a receiver 206, a Local Oscillator (LO) 207, and a transmitter 208. The receiver 206 receives the SAW sensor output signal and the transmitter 208 transmits an excitation signal to the SAW sensor, for example, a burst impulse excitation signal, wherein the burst impulse excitation signal may be a short cosine burst. The SAW sensor Readout Interface 204 would typically also include an MCU 209 to perform baseband data processing where the MCU 209 typically has to run complex algorithms such as Fourier transforms. However, this requires a significant amount of power and therefore is not practical for a wireless end node with form factor and power constraints.

Figure 3 shows an arrangement of a typical SAW sensor 301, in a reflective delay line configuration. The SAW sensor 301 converts an electromagnetic interrogation signal into a mechanical SAW wave via an interdigital transducer (IDT) 302. This wave propagates across the surface of the substrate of the sensor at a much reduced velocity compared to the electromagnetic wave. The wave is reflected by one or more reflectors 303, typically a plurality of reflectors 303, located on the substrate, and converted back to an electromagnetic signal in the IDT 302.

Depending on the number and location of the reflectors 303 the signal returned by the SAW sensor 301 can contain specific coding information. For example, the reflector locations may be spaced apart by a predetermined distance. The predetermined distance may be dependent on a propagation speed (or frequency), wherein the propagation speed (or frequency) may be dependent on the SAW sensor material, and the time delay between the reflected pulses, wherein the time delay is a design parameter of the SAW sensor. Thus, the predetermined distance between reflector locations is effectively a variable that is optimised and predetermined for a given SAW sensor 301, and which may be optimised to achieve a desired time delay.

In order to receive an impulse response signal with, for example, an 8-chip DSSS code then the SAW sensor may include an array of 8 reflector locations. If a reflector is positioned at a reflector location (RL) then it may be interpreted as a "1", whilst no reflector positioned at a reflector location may be interpreted as a "0" (or vice-versa). For example, as shown in Figure 3 there are reflectors positioned at reflector location RL1, RL3, RL4, RL5, RL7 and RL8, and no reflectors positioned at reflector locations RL2 and RL6, thereby providing an impulse response signal (as shown in Figure 4) that includes an 8-chip DSSS code of 10111011. As will be appreciated, the number of reflector locations will correspond to x for an x-chip DSSS code. The code may enable the wireless end node to identify the SAW sensor ID, as the SAW sensor ID corresponds to the code formed by the positions of reflectors in the given reflector locations.

The delay T between 2 reflections in the response of the SAW sensor can be expressed as:

where L is the distance between the reflectors, v is the velocity of the surface acoustic wave, and A. is the wavelength. Environmental variables such as temperature, humidity, pressure, strain, stress, torque, and so on, can change the wave velocity v and/or the relative distance L depending on the application and environmental variable being measured. For example, the relative distance L may change in applications where the SAW sensor material is getting stretched/compressed, e.g. when measuring torque, stress, and so on, and the wave velocity v may change in applications where the SAW sensor is measuring temperature, humidity, and so on.

The relative frequency deviation of the signal may therefore be proportional to the relative change in velocity and/or relative distance L. As such, the environmental variable being measured by the SAW sensor can be determined based on the relative frequency deviation from the sensors resonance frequency. In other words, the environmental variable being measured causes a shift in the resonance frequency of the sensor and the amount of shift (e.g. the frequency deviation) is caused by, and indicative of, the value of the environmental variable being measured. As can be seen form the expression given above, a change in the velocity (Av) may cause a change in either or both of the frequency (Af) and the time delay (AT).

Figure 4 shows example waveforms for a transmitted impulse signal as excitation (Tx) and the returned signal (impulse response) from the SAW sensor (Rx). The excitation signal is typically in the form of an impulse or a cosine burst approximating an impulse. The velocity of the SAW wave, and therefore the delay between the returned code pulses by the reflectors, is influenced by the environmental variable to be measured which causes a frequency deviation in the returned signal. Furthermore, the SAW sensors can be manufactured with different orthogonal codes for each sensor via a suitable arrangement of the reflectors, therefore allowing Code-Division-Multiple-Access (CDMA) multiplexing for the identification of the sensors.

Returning to Figure 2, the signal output by the SAW sensor 202 is received and processed by the SAW sensor Readout Interface 204 of the wireless end node 201. Traditionally SAW readout interfaces are complex systems similar to those used in RADAR, employing Chirp (e.g. frequency-sweep) pulses for excitation and complex signal processing involving Fourier Transforms on the receiver side, which increases the power consumption and the complexity of the wireless end node.

As it has been identified that a SAW sensor can advantageously be used to provide coding information, e.g. by using a particular arrangement of the reflectors located within the SAW sensor as discussed above, the coding information, which can be imparted onto the returned signal, can be similar to, or imitate, DSSS codes as used in data communications. Therefore, the signal received by a SAW sensor readout interface of the wireless end node can be similar to a radio data communication DSSS encoded radio signal but at the resonance frequency of the SAW sensor.

As the SAW sensor can be arranged to output a signal comprising coded information substantially similar to DSSS codes as used in wireless data communications then the DSSS demodulator of the wireless end nodes can also be used to demodulate the received signal from the SAW sensor in order to extract one or more data components from the received signal.

For example, the data components may include one or more of a sensor identification component and a frequency deviation component wherein the frequency deviation component is the frequency deviation from the resonance frequency of the SAW sensor which is indicative of a value of the measurement of the environmental variable being measured by the SAW sensor. With reference to Figure 5, a wireless SAW sensor 502 senses an environmental variable and is operatively coupled, via a wireless communication means, to a wireless end node 501. The wireless end node include a wireless communications transceiver 503, a radio frontend 504, MAC Data and Control circuitry 505, a microcontroller 506, a SAW sensor readout interface 507, a readout RF frontend 508, Sensor Data and Control circuitry 509, and a Baseband Processing module 510.

The Baseband Processing module 510 is advantageously shared between the Wireless Transceiver 503 and the SAW Sensor Readout Interface 508 as the signal received from the wireless SAW sensor 502 is coded in a similar manner to the DSSS coded radio data communication received from the network. The Baseband Processing module 510 may include a DSSS modulator 511, a DSSS demodulator 512 and transmitter control circuitry 513.

The DSSS demodulator 512 can advantageously be used to demodulate the signal received from the wireless SAW sensor 502 in order to extract the relevant data components from the received SAW sensor signal and also to demodulate any received radio data communications by the wireless end node transceiver 503 from one or more devices on the network, which advantageously eliminates the need for complex data processing circuitry in the wireless end node, making the system suitable for integration into a low-power wireless sensor end node and decreasing the size, cost and complexity of the wireless end node.

The DSSS demodulator 512 may implement any known DSSS demodulator algorithms, for example, a double correlation algorithm. The double correlation algorithm conforms to, and is used for the demodulation of an IEEE 802.15.4 standard signal, specifically correlating the IEEE 802.15.4 DSSS spreading codes. However, as will be appreciated, any DSSS coded communications standard can be decoded using one or more embodiments of the present invention.

Figure 6 shows a simplified schematic of a DSSS demodulator implementing a double correlation algorithm, which can be used to demodulate a received DSSS coded radio data communications signal received from a device on the network. As shown in Figure 6, a sampler 601 samples and stores (or delays) the incoming complex signal, which is then correlated to a finite amount of s DSSS symbol codes stored in a DSSS Code Look-Up-Table memory 602 in the double-correlation core 603. The correlation results C(s) for each symbol are then compared and a maximum decision is taken 604. Synchronisation and frequency correction are performed post-correlation 605, 606.

Double correlation result for a specific symbol s:

Received baseband signal y_n: y_n = Issn + jQsBn

Pseudo-random noise (PN) DSSS chip code of symbol s: s_s = Sl_s + jSQs

Parameters: Number of symbols: s = 0 - NS

Number of chips per symbol: n = 1 - N

Lag delay: d = 1 - D

A detailed description of the demodulator or the double correlation algorithm is not provided in detail herein as a detailed description of a conventional demodulator for implementing the double correlation algorithm can be found in GB2511079B1, and a detailed description of the double correlation algorithm can be found in GB2472774B1.

So that the DSSS demodulator can be used for demodulating both the signal received from the SAW sensor and the radio data communications the DSSS demodulator as shown in Figure 6 is modified, and the modified DSSS demodulator is shown in Figure 7.

The DSSS demodulator, as shown in Figure 7, is modified to further include a first multiplexer 701 connected to the sampler 704 and an input data signal, such that an input data signal, i.e. an input radio communication signal or an input SAW sensor signal, is multiplexed into the sampler 704 depending on whether the wireless end node is processing radio communications data or SAW sensor data. The DSSS demodulator further includes a second multiplexer 702 connected between a double correlation core 703 and a DSSS code look-up table 705 and a Sensor Identification look-up table 706, wherein the look-up tables comprise the spreading codes relevant to the DSSS radio communication and the sensor identification respectively. The second multiplexer 702 multiplexes the respective spreading codes to the Double Correlation core 703 depending on whether the wireless end node is processing radio communications data or SAW sensor data.

The double correlation core 703 may be parametrisable to allow for a different number of required number of symbols (s), number of DSSS code bits (chips) per symbol (N), and lag delays (D) used in the double correlation algorithm which can be configured depending on whether communications data or sensor data is currently being processed by the double correlation core. For example, for the demodulation of an IEEE 802.15.4 radio communication signal the typical configuration is s=16, and N=32, which is dictated by the relevant IEEE standard. The lag delay is typically D=3, which empirically gives the best compromise between high performance (high D) and low complexity (low D). For the SAW sensor interface these parameters may be determined, but generally s will reflect the number of sensors to be distinguished by Code Division Multiple Access (CDMA), wherein CDMA is a form of, or based on, DSSS. N may indicate the length of the spreading code, which may be proportional to the number of reflectors.

As discussed above, the signal received from the sensor may include various data components, wherein the data components may include a sensor Identification component (e.g. the CDMA code), and a frequency deviation component, wherein the frequency deviation component is the frequency deviation from the resonance frequency component of the SAW sensor, which is indicative of the environmental variable being measured by the SAW sensor.

The Sensor identification component may be extracted and subsequently matched in the sensor ID block 707, similar to a data symbol decision for the radio communications, by comparing the correlation results for each possible symbol s. As described above, for the sensor ID component, s is the number of different sensors to be distinguished by CDMA. The strongest correlation for the code s will identify a specific sensor.

The frequency deviation component of the incoming signal may be determined from an intermediate result of the correlation process. The signals CF(s,d) are the complex correlation results for the symbols before summation over the lag delays d. These are used to determine the phase angle of the signals and subsequently the frequency deviation component in the sensor frequency estimator block 708.

Signals used for the extraction of signal phase in order to determine the change in frequency with respect to reference frequency, i.e. the frequency deviation, are:

The complex signals c/(s,d) are the results of the double correlation, which may be taken before summation over lag delays and determination of magnitude. The signals may be taken before the lag delay summation and processed individually for frequency determination, as the individual phases are rotating at different speeds due to the difference in delays between samples.

The individual signals can then be used to determine the momentary phase change:

The frequency deviation for each s and d can then be determined from the individual phases:

where T_C is the nominal delay between the code chips and fo is the nominal frequency (e.g. the frequency of the LO).

The value of the measured environmental variable may then be determined based on the frequency deviation, for example, a predefined programmable look-up may be used in order to determine the value of the measured environmental variable based on the determined frequency deviation, where the look-up table provides a mapping between frequency deviation and a value of the measured environmental variable. Alternatively a scalable linear conversion formula may be used for the SAW sensors, as the dependency between the frequency deviation and the value of the measured environmental variable is likely to be linear in the range of interest. Methods to determine the frequency deviation are known in the art and therefore further detailed explanations of the frequency deviation determination is not replicated here. For example, suitable methods for determining the frequency deviation can be found in M. J. Ammer and J. Rabaey, "Frequency offset estimation with improved convergence time and energy consumption," Eighth IEEE International Symposium on Spread Spectrum Techniques and Applications - Programme and Book of Abstracts (IEEE Cat. No.04TH8738), 2004, pp. 596-600, doi: 10.1109/ISSSTA.2004.1371770, and in I. Perisa and J. Lindner, "Frequency offset estimation based on phase offsets between sample correlations," 2005 13th European Signal Processing Conference, 2005, pp. 1-4.

A separate control block 709 may be implemented in order to control the signal acquisition and read timing when sensor data is processed.

The embodiments of the present invention advantageously enable the wireless end node radio data communications transceiver and the SAW sensor readout interface to effectively and efficiently share the same circuitry for processing both the received sensor data and received radio data communications. In order to ensure there are no conflicts between the radio data communication processing and the SAW sensor data processing, these two functions are not performed at the same time and therefore may be performed during different time periods. The processing of the received SAW sensor data is performed during a first time period T1 and the processing of the received radio data communications is performed at a second time period T2, and an example processing cycle is shown in Figure 8.

The first time period may precede the second time period, or vice-versa. The wireless end node may sleep during a third time period T3, which may be of a longer or shorter duration than the first time period T1 and the second time period T2 for power saving reasons. Periodically the wireless end node may wake up, read the data from the sensor, and communicate the data wirelessly to one or more devices on the network that the wireless end node is connected to, or receive communications from the network. The processing of the transmission of the radio data communication may be performed during the second time period or may be performed during a fourth time period T4 (not shown in Figure 8). The first, second and/or fourth time period may be any suitable time period, for example, the time periods may be in the range of 1 to 10 milliseconds. The third time period may be any suitable time period for the wireless end node to be asleep, and the wireless end node my wake up periodically (e.g. a predetermined third time period), variably (e.g. a random or variable third time period), or in response to an event (e.g. on request from a controller/device).

In order to further reduce the power consumption and complexity of the wireless end node, the wireless frontend for the radio data communications may also be shared with the SAW sensor readout interface, as shown in Figure 9. In Figure 9, a combined frontend 901 includes a receiver 902 for the radio data communications and the SAW sensor signal, a Local Oscillator (LO) 903, and a transmitter 904 for the radio data communications and the SAW sensor signal. A combined frontend 901 for both the radio data communications and the SAW sensor may be achieved if they share one or more of the same properties, for example, the same centre frequencies (e.g. resonant frequency for the sensor) and the required bandwidth. In respect of the shared transmitter, the channel centre frequency (or frequencies for multiple channels) should match between the wireless end node and the SAW sensor. The bandwidth should also be of similar magnitude. Pulse shaping and On/Off switching times should also be met for both the wireless end node and the SAW sensor.

In respect of the shared receiver, the channel centre frequency (or frequencies for multiple channels) should match between the wireless end node and the SAW sensor. The bandwidth should be of similar magnitude or can be programmable to the correct bandwidths for the wireless end node and the SAW sensor. Acquisition times should also be met for both the wireless end node and the SAW sensor. The signal received by the receiver should also be compatible for l/Q demodulation.

Embodiments of the present invention are therefore advantageous over the conventional wireless end nodes that include, or are operatively connected to, one or more sensors, as one or more of the complexity, cost, size and power consumption are significantly reduced. The embodiments take advantage of sharing the baseband processing circuitry and/or the frontend circuitry between the radio data communication processing and the received sensor signal processing.

The embodiments and examples of the wireless end node have been described in relation to SAW sensors, however, as will be appreciated the wireless end node can equally be operatively connected to any suitable sensor, in which the output of the sensor is a high frequency radio signal so as to enable sharing the received sensor signal processing with the wireless communications system processing of the wireless end node. For example, ElectroMechanical Resonant Sensors (EMRS) are based on a small conductive elastic element with low damping rate and therefore a high Q fundamental mode of frequency, meaning that EMRS can be used with the wireless end node of the present invention.

In the foregoing embodiments, features described in relation to one embodiment may be combined, in any manner, with features of a different embodiment in order to provide a more efficient and effective wireless end node. Note that, the above description is for illustration only and other embodiments and variations may be envisaged without departing from the scope of the invention as defined by the appended claims.

Claims

1. A wireless end node comprising: a Direct Sequence Spread Spectrum (DSSS) demodulator, wherein the DSSS demodulator is based on a double correlation algorithm; a data communications module configured to receive, via a first wireless receiver, an incoming DSSS coded data communication signal from a network; a sensor module configured to receive, via a second wireless receiver, a DSSS coded signal from a sensor, wherein the sensor measures an environmental variable; and the DSSS demodulator is configured to demodulate the received DSSS coded signal from the sensor during a first time period, and to demodulate the received DSSS coded data communication signal from the network during a second time period.

2. The wireless end node of claim 1, in which the sensor is a Surface Acoustic Wave (SAW) sensor.

3. The wireless end node of claim 1 or 2, further comprising: a first wireless transmitter; and the sensor module is further configured to transmit, via the first wireless transmitter, an impulse excitation signal to the sensor.

4. The wireless end node of claim 3, in which the impulse excitation signal is a burst impulse excitation signal; and preferably wherein the burst impulse excitation signal is a short cosine burst excitation signal.

5. The wireless end node of any one of the preceding claims, in which the DSSS demodulator is configured to demodulate the received DSSS coded signal from the sensor using the double correlation algorithm to extract one or more data components.

6. The wireless end node of claim 5, in which the one or more data components include one or more of a sensor identification component and a frequency deviation component.

7. The wireless end node of claim 6, in which the frequency deviation component is indicative of a value of the environmental variable measured by the sensor; and preferably wherein the environmental variable is one of temperature, pressure, humidity, strain, stress, or torque.

8. The wireless end node of any one of the preceding claims, in which the wireless end node is configured to sleep during a third time period.

9. The wireless node of any one of the preceding claims, further comprising: a second wireless transmitter; and a DSSS modulator configured to modulate an outgoing DSSS coded data communication signal during a fourth time period; wherein the data communications module is configured to transmit, via the second wireless transmitter, the outgoing DSSS coded data communication signal to the network; preferably wherein the outgoing DSSS coded data communication signal includes, at least, data extracted by the demodulation of the received DSSS coded signal from the sensor.

10. The wireless end node of any one of the preceding claims, in which the first wireless receiver and the second wireless receiver are the same wireless receiver.

11. The wireless end node of claims 9 or 10, in which the first wireless transmitter and the second wireless transmitter are the same wireless transmitter.

12. The wireless end node of any one of the preceding claims, in which the first time period and the second time period is between 1 and 10 milliseconds.

13. A method of operating a wireless end node comprising: receiving, via a first wireless receiver, an incoming DSSS coded data communication signal from a network; receiving, via a second wireless receiver, a DSSS coded signal from a sensor, wherein the sensor measures an environmental variable; and demodulating, via a Direct Sequence Spread Spectrum (DSSS) demodulator using a double correlation algorithm, the received DSSS coded signal from the sensor during a first time period, and demodulating the received DSSS coded data communication signal from the network during a second time period.

14. The method of claim 13, in which the sensor is a Surface Acoustic Wave (SAW) sensor.

15. The method of claim 13 or 14, further comprising: transmitting, via a first wireless transmitter, an impulse excitation signal to the sensor.

16. The method of claim 15, in which the impulse excitation signal is a burst impulse excitation signal; and preferably wherein the burst impulse excitation signal is a short cosine burst excitation signal.

17. The method of any one of claims 13 to 16, in which demodulating the received DSSS coded signal from the sensor using the double correlation algorithm extracts one or more data components.

18. The method of claim 17, in which the one or more data components include one or more of a sensor identification component and a frequency deviation component.

19. The wireless end node of claim 18, in which the frequency deviation component is indicative of a value of the environmental variable measured by the sensor; and preferably wherein the environmental variable is one of temperature, pressure, humidity, strain, stress, or torque.

20. The method of any one of claims 13 to 19, further comprising: causing the wireless end node to sleep during a third time period.

21. The method of any one of claims 13 to 20, further comprising: modulating, via a DSSS modulator, an outgoing DSSS coded data communication signal during a fourth time period; and transmitting, via a second wireless transmitter, the outgoing DSSS coded data communication signal to the network; preferably wherein the outgoing DSSS coded data communication signal includes, at least, data extracted by the demodulation of the received DSSS coded signal from the sensor.

22. The method of any one of claims 13 to 21, in which the first wireless receiver and the second wireless receiver are the same wireless receiver.

23. The method of claims 21or22, in which the first wireless transmitter and the second wireless transmitter are the same wireless transmitter.

24. The method of any one of claims 13 to 23, in which the first time period and the second time period is between 1 and 10 milliseconds.

25. A computer program product comprising computer readable executable code for implementing a method according to any one of claims 13 to 24.