Multi-channel low power wake-up system
A wake-up system includes an instigator for transmitting a wake-up message from a primary node to a receiver at a secondary node. The instigator sends a wake-up on either first RF channel or a second RF channel having respective frequencies such that the second RF channel is an image of the first RF channel at a local oscillator frequency of the receiver. The receiver includes an RF filter that passes both the image and non-image channels, a frequency generator for generating a local oscillator signal at the local oscillator frequency, and a mixer for mixing the filtered modulated RF signal with said local oscillator signal to generate a modulated intermediate frequency (IF) signal. The receiver monitors both the image and non-image channels simultaneously for a valid wake-up message. A wake-up message detector indicates a wake-up condition in response to the reception of a valid wake-up message.
1. A wake-up system for use in a communications network wherein communications are established between a primary node and one or more secondary nodes over one or more RF communications channels, wherein the secondary nodes are placed in a sleep state in the absence of active communications and are responsive to a wake-up message transmitted from the primary node to enter a wake-up state to permit the establishment of active communications, the wake-up system comprising an instigator for transmitting the wake-up message from a primary node to a receiver at a secondary node, said receiver being configured to sniff said communications channels at intervals for a valid wake-up message, and wherein:
the instigator comprises:
a wake-up message generator for generating a wake-up message;
a channel selector for generating a select signal to select either first RF channel or a second RF channel having respective frequencies such that the second RF channel is an image of the first RF channel at a local oscillator frequency of the receiver; and
a transmitter responsive to said select signal to transmit the wake-up message as a modulated RF signal over the selected RF channel; and wherein
the receiver comprises:
an RF filter for receiving and filtering a modulated RF signal and being configured to pass both said first and second RF channels;
a frequency generator for generating a local oscillator signal at said local oscillator frequency;
a mixer for mixing the filtered modulated RF signal with said local oscillator signal to generate a modulated intermediate frequency (IF) signal;
a demodulator for extracting data from the modulated IF signal; and
a wake-up message detector for indicating a wake-up condition in response to a determination that the extracted data represents a valid wake-up message.
2. A wake-up system as claimed in claim 1 , comprising an inverter at the transmitter responsive to a data inversion control signal from the channel selector to invert the wake-up message when the second RF channel is selected.
3. A wake-up system as claimed in claim 2 , wherein said wake-up message comprises a predetermined bit pattern and said inverter is an exclusive OR gate controlled by said select signal.
4. A wake-up system as claimed in claim 1 , comprising an inverter at the receiver configured to invert an incoming wake-up message on the second RF channel.
5. A wake-up system as claimed in claim 4 , wherein the receiver is configured to invert the data in the received RF signal based on the sign of a recognized correlation or preamble information.
6. A wake-up system as claimed in claim 1 , wherein the frequency generator is configured to vary said local oscillator frequency in alternate sniffs by +/−f IF where f IF is the intermediate frequency.
7. A wake-up system as claimed in claim 1 , wherein the receiver is responsive to multiple pairs of RF channels, and is configured to check each pair of channels in sequence for a valid wake-up message during each sniff.
8. A wake-up system as claimed in claim 7 , wherein each sniff comprises a sequence of sub-sniffs in which the receiver checks a different pair of RF channels for a valid wake-up message, and wherein in successive sniffs the pairs of RF channels checked in each sub-sniff are offset from the pairs of RF channels checked in each sub-sniff of a preceding sniff.
9. A wake-up system as claimed in claim 8 , wherein in successive sniffs the pairs of channels are offset by one channel relative to the pairs of channels in the preceding sniff.
10. A wake-up system as claimed in claim 1 , wherein said receiver comprises an upstream IF section configured to perform real signal processing, and a downstream baseband section including a complex mixer for generating a complex baseband representation of a wake-up message signal, and said downstream baseband section comprises a bank of complex mixers, filters and demodulators operating at different IF frequencies.
11. A method of establishing communications between a primary node and one or more secondary nodes over one or more RF communications channels, wherein the secondary nodes are placed in a sleep state in the absence of active communications and are responsive to a wake-up message transmitted from the primary node to enter a wake-up state, method comprising:
at the instigator:
generating a wake-up message;
selecting either a first RF channel or a second RF channel having respective frequencies such that the second RF channel is an image of the first RF channel at a local oscillator frequency of the receiver; and
transmitting the wake-up message as a modulated RF signal over the selected RF channel; and
at the receiver:
receiving and filtering a modulated RF signal while passing both said first and second RF channels;
generating a local oscillator signal at said local oscillator frequency;
mixing the filtered modulated RF signal with said local oscillator signal to generate a modulated intermediate frequency (IF) signal;
demodulating the modulated IF signal to extract data therefrom; and
indicating a wake-up condition in response to a determination that the extracted data represents a valid wake-up message.
12. A method as claimed in claim 11 , further comprising:
inverting data in the wake-up message at the instigator when the second RF channel is selected.
13. A method as claimed in claim 12 , wherein said wake-up message comprises a predetermined bit pattern that is inverted when said second RF channel is selected.
14. A method as claimed in claim 11 , further comprising:
inverting data in the wake-up message at the receiver when the second RF channel is selected.
15. A method as claimed in claim 14 , wherein the data in the incoming wake-up message is inverted based on the sign of a recognized correlation or preamble information.
16. A method as claimed in claim 11 , further comprising:
varying the local oscillator frequency in alternate sniffs by +/−f IF where f IF is the intermediate frequency.
17. A method as claimed in claim 11 , wherein multiple pairs of RF channels are pre-determined frequencies are available, the method further comprising:
setting the local oscillator frequency to check each pair of channels in sequence for a valid wake-up message during each sniff, and wherein each sniff comprises a sequence of sub-sniffs in which the receiver checks a different pair of RF channels for a valid wake-up message, and wherein in successive sniffs the pairs of RF channels checked in each sub-sniff are offset from the pairs of RF channels checked in each sub-sniff of a preceding sniff.
18. A method as claimed in claim 17 , wherein in successive sniffs the pairs of channels are offset by one channel relative to the pairs of channels in the preceding sniff.
19. A receiver for use in a communications network wherein communications are established between a primary node and one or more secondary nodes over one or more RF communications channels, wherein the secondary nodes are placed in a sleep state in the absence of active communications and are responsive to a wake-up message transmitted from the primary node to enter a wake-up state to permit the establishment of active communications, the wake-up system comprising an instigator for transmitting the wake-up message from a primary node to a receiver at a secondary node, said receiver being configured to sniff said communications channels at intervals for a valid wake-up message, the receiver comprising:
a generator arranged to generate a local oscillator signal at a local oscillator frequency;
an RF filter for receiving and filtering a modulated RF signal and being configured to pass both a first and a second RF channels, said first and second RF channels being mirrors of each other about said local oscillator frequency;
a mixer for mixing the filtered modulated RF signal with said local oscillator signal to generate a modulated intermediate frequency (IF) signal;
a demodulator for extracting data from the modulated IF signal; and
a wake-up message detector for indicating a wake-up condition in response to a determination that the extracted data represents a valid wake-up message.
20. A receiver as claimed in claim 19 , further comprising an inverter configured to invert an incoming wake-up message on the second RF channel.
21. A receiver as claimed in claim 19 , wherein the receiver is responsive to multiple pairs of RF channels, and is configured to check each pair in of channels in sequence for a valid wake-up message during each sniff.
22. A receiver as claimed in claim 21 , wherein each sniff comprises a sequence of sub-sniffs in which the receiver checks a different pair of RF channels for a valid wake-up message, and wherein in successive sniffs the pairs of RF channels checked in each sub-sniff are offset from the pairs of RF channels checked in each sub-sniff of a preceding sniff.
23. A receiver as claimed in claim 19 , further comprising an upstream IF section configured to perform real signal processing, and a downstream baseband section including a complex mixer for generating a complex baseband representation of a wake-up message signal.