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Title:
METHOD, NETWORK NODE AND COMPUTER PROGRAM FOR ALIGNING RANGE PERFORMANCE
Document Type and Number:
WIPO Patent Application WO/2019/170557
Kind Code:
A1
Abstract:
There is provided a network node, and a method therefor, for wirelessly transmitting a packet comprising two parts where a first part is modulated according to a first modulation scheme and a second part is modulated according to a second modulation scheme different from the first modulation scheme, and where the first part and the second part are arranged to provide information to different receivers. The receivers comprise a first set of receivers capable of receiving the first modulation scheme and another receiver capable of receiving the second modulation scheme and a first receiver of the first set of receivers and the another receiver are co-located. The method comprises acquiring a sensitivity difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part, determining a power offset based on the sensitivity difference for aligning coverage towards the co-located first and another receivers, where the power offset is a difference in average power of transmission of the first part and average power of transmission of the second part, forming the packet applying the power offset for the first and second parts, and transmitting the packet.

Inventors:
LOPEZ, Miguel (Fridensborgvägen 24, SOLNA, SE-170 69, SE)
SUNDMAN, Dennis (Turevägen 42 A, SOLLENTUNA, SE-191 47, SE)
WILHELMSSON, Leif (Lyftvägen 5, DALBY, SE-247 55, SE)
Application Number:
EP2019/055214
Publication Date:
September 12, 2019
Filing Date:
March 01, 2019
Export Citation:
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Assignee:
TELEFONAKTIEBOLAGET LM ERICSSON (PUBL) (S Stockholm, SE-164 83, SE)
International Classes:
H04W52/16; H04L27/10
Domestic Patent References:
WO2018038532A12018-03-01
Foreign References:
US20170094600A12017-03-30
Other References:
None
Attorney, Agent or Firm:
ERICSSON (Patent Development Torshamnsgatan 21-23, STOCKHOLM, 164 80, SE)
Download PDF:
Claims:
CLAIMS

1. A method, for a network node, of wirelessly transmitting a packet comprising two parts where a first part is modulated according to a first modulation scheme and a second part is modulated according to a second modulation scheme different from the first modulation scheme, and where the first part and the second part are arranged to provide information to different receivers, wherein the receivers comprise a first set of receivers capable of receiving the first modulation scheme and another receiver capable of receiving the second modulation scheme and wherein a first receiver of the first set of receivers and the another receiver are co-located, the method comprising

acquiring a sensitivity difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part;

determining a power offset based on the sensitivity difference for aligning coverage towards the co-located first and another receivers, where the power offset is a difference in average power of transmission of the first part and average power of transmission of the second part;

forming the packet applying the power offset for the first and second parts; and transmitting the packet.

2. The method of claim 1, wherein the forming of the packet by applying the power offset comprises adjusting power of the second part with respect to a power setting for the first part.

3. The method of claim 1, wherein the forming of the packet by applying the power offset comprises adjusting power of the first and second parts with respect to default power settings for the first and second part.

4. The method of claim 2 or 3, wherein the adjusting power of the second part comprises any of

changing signal amplitude of the second part digitally in a baseband circuit of the network node; or

changing signal envelope of the second part by adjusting power for the second part in a power amplifier of the network node.

5. The method of any one of claims 2 to 4, wherein the first part is arranged such that a first minimum output back-off is required and the second part is arranged such that a second minimum output back-off is required, wherein the second minimum output back-off is smaller than the first minimum output back-off, wherein the adjusting the power of the second part comprises to set an average output power of the second part such that the power is below a maximum output power of a power amplifier of the network node minus the second minimum output back-off

6. The method of claim 1, wherein the forming of the packet by applying the power offset comprises adjusting power of the first part with respect to a power setting for the second part.

7. The method of any one of claims 1 to 6, wherein the first modulation is suitable for coherent demodulation and the second modulation is suitable for non coherent demodulation.

8. The method of any one of claims 1 to 7, wherein the packet is a wake-up packet intended for a co-located receiver arrangement where the first receiver is a receiver of a primary communication radio and the another receiver is a wake-up receiver arranged to change a power mode of the first receiver upon detection of a wake-up signal of the second part.

9. The method of claim 8, wherein the first receiver is arranged to operate according to IEEE 802.11, and the first part comprises a legacy IEEE 802.11 preamble and the second part comprises amplitude shift keyed data for the wake-up receiver.

10. The method of claim 9, wherein the amplitude shift keyed data is on-off keyed or multi-carrier on-off keyed.

11. The method of any one of claims 1 to 10, wherein the acquiring of the sensitivity difference comprises retrieving stored data about difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part.

12. The method of any one of claims 1 to 11, wherein the acquiring of the sensitivity difference comprises any one of

receiving, prior the transmission, information about the sensitivity difference from the first receiver; or

determining based on measurements, prior the transmission, the sensitivity difference.

13. A network node arranged to wirelessly transmit a packet comprising two parts where a first part is modulated according to a first modulation scheme and a second part is modulated according to a second modulation scheme different from the first modulation scheme, and where the first part and the second part are arranged to provide information to different receivers, wherein the receivers comprise a first set of receivers capable of receiving the first modulation scheme and another receiver capable of receiving the second modulation scheme and wherein a first receiver of the first set of receivers and the another receiver are co-located, and where the network node comprises

a transmission power handler arranged to acquire a sensitivity difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part, determine a power offset based on the sensitivity difference for aligning coverage towards the co-located first and another receivers, where the power offset is a difference in average power of transmission of the first part and average power of transmission of the second part, and form the packet applying the power offset for the first and second parts; and

a transmitter arranged to transmit the packet.

14. The network node of claim 13, wherein the transmission handler applies the power offset by adjusting power of the second part with respect to a power setting for the first part.

15. The network node of claim 13, wherein the transmission handler applies the power offset by adjusting power of the first and second parts with respect to default power settings for the first and second part.

16. The network node of claim 14 or 15, wherein the transmitter is arranged to adjust the power of the second part by any of changing signal amplitude of the second part digitally in a baseband circuit of the transmitter; or

changing signal envelope of the second part by adjusting power for the second part in a power amplifier of the transmitter.

17. The network node of any one of claims 14 to 16, wherein the first part is arranged such that a first minimum output back-off is required and the second part is arranged such that a second minimum output back-off is required, wherein the second minimum output back-off is smaller than the first minimum output back-off, wherein the transmitter is arranged to adjust the power of the second part by setting an average output power of the second part such that the power is below a maximum output power of a power amplifier of the network node minus the second minimum output back-off

18. The network node of claim 13, wherein the transmission handler applies the power offset by adjusting power of the first part with respect to a power setting for the second part.

19. The network node of any one of claims 13 to 18, wherein the first modulation is suitable for coherent demodulation and the second modulation is suitable for non-coherent demodulation.

20. The network node of any one of claims 13 to 19, wherein the packet is a wake-up packet intended for a co-located receiver arrangement where the first receiver is a receiver of a primary communication radio and the another receiver is a wake-up receiver arranged to change a power mode of the first receiver upon detection of a wake-up signal of the second part.

21. The network node of claim 20, comprising an access point operating according to IEEE 802.11, and wherein the first receiver is arranged to operate according to IEEE 802.11, and the first part comprises a legacy IEEE 802.11 preamble and the second part comprises amplitude shift keyed data for the wake-up receiver.

22. The network node of claim 21, wherein the amplitude shift keyed data is on-off keyed or multi-carrier on-off keyed.

23. The network node of any one of claims 13 to 22, arranged to acquire the sensitivity difference by retrieving stored data about difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part.

24. The network node of any one of claims 13 to 23, arranged to acquire the sensitivity difference by any one of

receiving, prior the transmission, information about the sensitivity difference from the first receiver; or

determining based on measurements, prior the transmission, the sensitivity difference.

25. A computer program comprising instructions which, when executed on a processor of a network node, causes the network node to perform the method according to any of claims 1 to 12.

Description:
METHOD, NETWORK NODE AND COMPUTER PROGRAM FOR ALIGNING RANGE PERFORMANCE

Technical field

The present disclosure generally relates to a method for a network node, such a network node, and a computer program for implementing the method on a network node. In particular, the present disclosure relates to transmission of a packet including different modulations, and aligning range performance of different parts of the packet.

Background

Communication systems may be organised such that a network node which, at least locally, acts as a central node for a plurality of stations or terminals. For example, as illustrated in Fig. 1, the central network node may be an access point (AP) 100, e.g. operating under some variant of the IEEE 802.11 and often referred to as WiFi, which access point is in wireless operation with a plurality of stations 102. In this disclosure, WiFi will be used as example for explaining the contributions by this disclosure. However, it should be understood that the similar principles will be applicable also to other systems, e.g. cellular systems such as those specified by 3 rd Generation Partnership Project or professional mobile radio systems.

This disclosure relates to application of so called wake-up radio or wake-up receiver, often abbreviated as WUR, in stations or terminals, which implies that a dedicated radio unit or an operation mode of a radio which consumes only little energy is used for detecting a signal from a central node indicating that communication in some sense is about to commence. The idea with a WUR is that it can be based on a very relaxed architecture, as it only needs to be able to detect the presence of a wake-up signal, but will not be used for any data reception.

The station or terminal then changes from the low-energy mode operation and prepares for ordinary communication which often includes more complex signal processing etc. and thus consumes more energy. Fig. 2 schematically illustrates an example of an architecture of a station 200 where a WUR 202 and a primary communications radio (PCR) 204 applying some variant of IEEE 802.11, e.g. IEEE 802.1 lba, shares a common antenna 206. When the WUR 202 is turned on and waiting for a wake-up message, the IEEE 802.11 chipset of the PCR 204 can be switched off to preserve power. Once the wake-up message is received by the WUR 202, it wakes up the IEEE 802.11 main radio of the PCR 204 and starts Wi-Fi communication with the AP. The provision of the wake-up message is normally provided by the AP. The architecture for this may be that a single entity 300 provides both wake-up message to a WUR 302 and handles communication with the PCR 304, as illustrated in Fig. 3. Alternatively, a legacy AP 400 operates together with a separate WUR AP 402, where the legacy AP 400 provides communication with a PCR 404 and the WUR AP 402 provides the wake-up message for a WUR 406.

A commonly used modulation for a wake-up packet (WUP) comprising the wake-up message, i.e., the signal sent to the WUR, is on-off keying (OOK). OOK is a binary modulation type of amplitude shift keying (ASK), where a logical one is represented with sending a signal (ON) whereas a logical zero is represented by not sending a signal (OFF), or vice versa. In a 802.11 draft specification,“Proposed Draft WUR PHY Specification”, IEEE 802.1 Ul8/0l52r5x, the WUP is called WUR PPDU (PLCP (Physical Layer Convergence Procedure) Protocol Data unit).

Fig. 5 schematically illustrates an On-Off Keying, OOK, signal, which is a modulation scheme where the presence of a signal represents the ON part or state and the absence of the signal represents the OFF part or state. In Fig. 5, where the presence of a signal is labelled as ON part and the absence of a signal is labelled as OFF part. For example, the ON and OFF parts could represent binary digits, or the transition between ON to OFF state and OFF to ON state could represent binary digits. OOK is considered the simplest form of amplitude-shift keying, ASK, modulation that represents digital data at the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to unipolar encoding line code. OOK is more spectrally efficient than frequency-shift keying, FSK, but more sensitive to noise when using a regenerative receiver or a poorly implemented superheterodyne receiver. For a given data rate, the bandwidth of a Binary Phase Shift keying, BPSK, signal and the bandwidth of OOK signal are equal.

In order to decode OOK, the receiver has to estimate which signal level corresponds to the presence of a signal and which signal level corresponds to the absence of a signal. Manchester Coding is a modulation means used to simplify clock recovery and to simplify demodulation by ensuring that the average signal level of the signal carries no information. Fig. 6 illustrates a data bit with value one is represented by, i.e. encoded to, a logical one followed by a logical zero, whereas a data bit with value zero is represented by a logical zero followed by a logical one. Alternatively, the encoding can be swapped so that a data bit with value one is represented by a logical zero followed by a logical zero, etc.

Clock recovery is simplified because there will always be a transition from zero to one or vice versa in the middle of each symbol irrespectively of what the data is.

The decoding of the Manchester coded symbol is essentially done by comparing the first and the second half of the symbols and decide in favour of a logical one if the first half of the symbol is larger than the second half of the same symbol, or vice versa. Implementation-wise, a metric, m, is generated as m=ro-ri,

where ro and n represent the signal during the first and second half of the signalling interval, respectively. An estimate of the k ib information symbol, h, is then obtained by just considering the signal if the metric m, i.e., i =1 if m³ 0 and f=0 if m< 0.

Since the metric, m, is generated by subtracting the second half of the symbol from the first half, the average signal level will be removed and thus have no impact on the metric used for making the decision.

Because of the properties of the Manchester coding when it comes to being insensitive to the average signal level, it is an attractive approach when the alternative would be to estimate a decision threshold for when to decide in favour of a logical one or a logical zero.

For example, Manchester coded OOK is being standardized within the IEEE 802.1 lba task group (TG). TG 802.1 lba develops a standard for wake-up radios (WUR), targeting to significantly reduce the power consumption in devices based on the 802.11 standard. It is proposed to generate the wake-up signal (WUS) by using an inverse fast Fourier transform (IFFT), as this block is already available in Wi-Fi transmitters supporting e.g. 802.1 la/g/n/ac. Specifically, an approach discussed for generating the OOK is to use the 13 sub-carriers in the centre, and then populating these with some signal to represent ON and to not transmit anything at all to represent OFF.

As an alternative to textbook Manchester coded OOK as shown in Fig. 6, it is feasible to zero-pad a portion of the ON part of the signal to further improve the performance. Fig. 7 illustrates such an approach, where Tz and T NZ denote the time when the ON signal is zero and non-zero, respectively. The potential improvement comes from that the same energy is received during time T NZ , i.e., a shorter time than half the bit time, T b / 2, the duration of the ON signal in the classic OOK signal with duty cycle 0.5. Since the noise power is proportional to that time, the signal-to-noise ratio, SNR, is increased correspondingly. Hypothetically, the SNR can in this way be made infinite. This is impossible in practice though. There are technical and regulatory aspects that may prevent the SNR from becoming arbitrarily large.

It is feasible to generate the WUP by means of an inverse fast Fourier transform (IFFT), as this block is already available in Wi-Fi transmitters supporting e.g. 802.1 la/g/n/ac. Specifically, an approach discussed for generating the OOK is to use the 13 sub-carriers in the centre, and then populating these with some signal to represent ON and to not transmit anything at all to represent OFF. This approach differs slightly from traditional OOK in that multiple carriers are used to generate the ON part. Therefore, the OOK scheme being standardized in 802.1 lba is referred to as multicarrier OOK (MC-OOK). The IFFT has 64 points and is operating at a sampling rate of 20 MHz, and just as for ordinary orthogonal frequency division multiplexing (OFDM) a cyclic prefix (CP) is added after the IFFT operation in order to keep the OFDM symbol duration used in 802.1 la/g/n/ac. A further discussion is provided in Annex 1 of this disclosure.

Fig. 8 illustrates an example of a wake-up signal structure. The structure of a wake-up signal is proposed to include an 802.11 preamble, followed by a wake-up synchronization sequence, followed by a data signal using OOK.

Fig. 9 shows an example of a wake-up message packet format when the WUR works together with an IEEE 802.11 chip of the PCR. The legacy preamble fields L- STF (Short Training Field), L-LTF (Long Training Field) and L-SIG (Signal) fields are based on OFDM modulation and the payload part is based on On-Off Keying (OOK). The legacy IEEE 802.11 preamble is inserted at the beginning of the packet in order to provide a co-existence mechanism with IEEE 802.11 legacy stations. In this way legacy stations will be able to detect the WUP and correctly defer access to the wireless medium. Legacy IEEE 802.11 stations are not able to decode the OOK part of the WUP, but the legacy preamble provides a mechanism for carrier sensing. Within the payload part, there are a wake-up preamble for packet detection (and possibly other functions, e.g. to indicate the message type), a MAC header that indicates the device address and the frame body that could include some control message. The wake-up message is ended with a Frame Check Sequence (FCS) that validates the received message integrity.

The signal (or signals) that constitute an ON in the OOK part of the WUP may be chosen to have desirable properties at the transmitter or at the receiver. For example, a compact spectrum, low Peak to Average Power Ratio (PAPR), or low Cubic Metric (CM) are desirable at the transmitter, while constant envelope may be advantageous for the receiver. A compact spectrum is advantageous to fulfil out of band emission requirements, while low PAPR/CM may help control signal distortions such as clipping. A constant envelope signal may improve the performance of a matched filter at the receiver. In contrast, there is no flexibility in the design of the part of the WUP, which consists of a legacy preamble, comprising L-STF, L-LTF and SIG, and which must be exactly as required by the IEEE 802.11 standard. Fig 10 illustrates a WUP, where the OOK part is designed to have low PAPR and a restricted dynamic range.

A problem is that the different properties of signals, i.e. for the WUR and for the PCR, may provide for a mis-alignment of coverage. First it can happen that the WUR signal may have a longer range than the PCR signal. Then, after association, the station may be moved so that its PCR is out of the range of the AP but its WUR remains in coverage, although the WUR and the PCR are inherently co-located. This is not desirable because the station will be able to decode a WUP, wake up the PCR, but the PCR will not be able to communicate with AP. The net result is wasted energy at the station. A straightforward solution to this problem is to reduce the power of the WUP. When the AP decreases the WUP TX power, the range of the WUP is reduced, so that it does not exceed the range of the PCR. However, this implies reducing also the power of the legacy preamble. Since the legacy preamble is intended for all stations in the coverage area of the access point, it is undesirable to reduce its power. On the contrary, it is desired that all the STA’s in the coverage area of the AP can decode the legacy preamble part of a WUP, so that they defer from communication correctly, and independently of the location of the WUR. Second, there are concerns regarding the sensitivity of WUR. Typically, there is a trade-off between cost/energy consumption of the WUR and sensitivity. A very cheap, or very energy efficient WUR may have poor sensitivity and the result may be a station with a range of the WUR shorter than the range of the PCR. These stations can’t benefit from energy savings brought about by the WUR when they are located within range of the PCR but outside of range of the WUR.

Hence, methods and apparatuses that help reduce the range difference between the legacy preamble part of the WUP and the OOK part of the WUP are sought.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary

The disclosure is based on the understanding that misalignment in range where different modulations are used in a same packet may degrade performance.

According to a first aspect, there is provided a method, for a network node, of wirelessly transmitting a packet comprising two parts where a first part is modulated according to a first modulation scheme and a second part is modulated according to a second modulation scheme different from the first modulation scheme, and where the first part and the second part are arranged to provide information to different receivers. The receivers comprise a first set of receivers capable of receiving the first modulation scheme and another receiver capable of receiving the second modulation scheme and a first receiver of the first set of receivers and the another receiver are co-located. The method comprises acquiring a sensitivity difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part, determining a power offset based on the sensitivity difference for aligning coverage towards the co-located first and another receivers, where the power offset is a difference in average power of transmission of the first part and average power of transmission of the second part, forming the packet applying the power offset for the first and second parts, and transmitting the packet.

The forming of the packet by applying the power offset may comprise adjusting power of the second part with respect to a power setting for the first part. Alternatively, the forming of the packet by applying the power offset may comprise adjusting power of the first and second parts with respect to default power settings for the first and second part. The adjusting power of the second part may comprise any of changing signal amplitude of the second part digitally in a baseband circuit of the network node, or changing signal envelope of the second part by adjusting power for the second part in a power amplifier of the network node. The first part may be arranged such that a first minimum output back-off is required and the second part may be arranged such that a second minimum output back-off is required, wherein the second minimum output back-off is smaller than the first minimum output back-off, and the adjusting of the power of the second part may comprise to set an average output power of the second part such that the power is below a maximum output power of a power amplifier of the network node minus the second minimum output back-off

The forming of the packet by applying the power offset may comprise adjusting power of the first part with respect to a power setting for the second part. The first modulation may be suitable for coherent demodulation and the second modulation may be suitable for non-coherent demodulation.

The packet may be a wake-up packet intended for a co-located receiver arrangement where the first receiver is a receiver of a primary communication radio and the another receiver is a wake-up receiver arranged to change a power mode of the first receiver upon detection of a wake-up signal of the second part. The first receiver may be arranged to operate according to IEEE 802.11, and the first part comprises a legacy IEEE 802.11 preamble and the second part comprises amplitude shift keyed data for the wake-up receiver. The amplitude shift keyed data may be on-off keyed or multi-carrier on-off keyed.

The acquiring of the sensitivity difference may comprise retrieving stored data about difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part.

The acquiring of the sensitivity difference may comprise any one of receiving, prior the transmission, information about the sensitivity difference from the first receiver, or determining based on measurements, prior the transmission, the sensitivity difference.

According to a second aspect, there is provided a network node arranged to wirelessly transmit a packet comprising two parts where a first part is modulated according to a first modulation scheme and a second part is modulated according to a second modulation scheme different from the first modulation scheme, and where the first part and the second part are arranged to provide information to different receivers, wherein the receivers comprises a first set of receivers capable of receiving the first modulation scheme and another receiver capable of receiving the second modulation scheme and wherein a first receiver of the first set of receivers and the another receiver are co-located. The network node comprises a transmission power handler arranged to acquire a sensitivity difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part, determine a power offset based on the sensitivity difference for aligning coverage towards the co- located first and another receivers, where the power offset is a difference in average power of transmission of the first part and average power of transmission of the second part, and form the packet applying the power offset for the first and second parts, and a transmitter arranged to transmit the packet.

The transmission handler may apply the power offset by adjusting power of the second part with respect to a power setting for the first part. Alternatively, the transmission handler may apply the power offset by adjusting power of the first and second parts with respect to default power settings for the first and second part. The transmitter may be arranged to adjust the power of the second part by any of changing signal amplitude of the second part digitally in a baseband circuit of the transmitter, or changing signal envelope of the second part by adjusting power for the second part in a power amplifier of the transmitter. The first part may be arranged such that a first minimum output back-off is required and the second part may be arranged such that a second minimum output back-off is required, wherein the second minimum output back-off is smaller than the first minimum output back-off, and wherein the transmitter is arranged to adjust the power of the second part by setting an average output power of the second part such that the power is below a maximum output power of a power amplifier of the network node minus the second minimum output back-off

The transmission handler may apply the power offset by adjusting power of the first part with respect to a power setting for the second part.

The first modulation may be suitable for coherent demodulation and the second modulation may be suitable for non-coherent demodulation.

The packet may be a wake-up packet intended for a co-located receiver arrangement where the first receiver is a receiver of a primary communication radio and the another receiver is a wake-up receiver arranged to change a power mode of the first receiver upon detection of a wake-up signal of the second part. The network node may comprise an access point operating according to IEEE 802.11, and wherein the first receiver is arranged to operate according to IEEE 802.11, and the first part comprises a legacy IEEE 802.11 preamble and the second part comprises amplitude shift keyed data for the wake-up receiver. The amplitude shift keyed data may be on-off keyed or multi carrier on-off keyed.

The network node may be arranged to acquire the sensitivity difference by retrieving stored data about difference between sensitivity of the first receiver for receiving the first part and sensitivity of the another receiver for receiving the second part.

The network node may be arranged to acquire the sensitivity difference by any one of receiving, prior the transmission, information about the sensitivity difference from the first receiver, or determining based on measurements, prior the transmission, the sensitivity difference. According to a third aspect, there is provided a computer program comprising instructions which, when executed on a processor of a network node, causes the network node to perform the method according to the first aspect.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present disclosure, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present disclosure, with reference to the appended drawings.

Fig. 1 schematically illustrates elements of a communication system comprising a network node and stations.

Fig. 2 schematically illustrates an example of an architecture of a station.

Fig. 3 schematically illustrates an example setup for wake-up radio.

Fig. 4 schematically illustrates an example setup for wake-up radio.

Fig. 5 schematically illustrates an on-off keying signal.

Fig. 6 illustrates a data bit with value representation.

Fig. 7 schematically illustrates a modified value representation.

Fig. 8 illustrates an exemplary wake-up signal structure.

Fig. 9 illustrates an exemplary wake-up signal structure.

Fig. 10 is a power to time diagram illustrating preamble and wake-up signal.

Fig. 11 is a power to time diagram illustrating power levels after application of a power offset according to an embodiment.

Fig. 12 is a power to time diagram illustrating power levels after application of a power offset according to an embodiment.

Fig. 13 is a power to time diagram illustrating preamble and wake-up signal after application of a power offset according to an embodiment.

Fig. 14 is a flow chart illustrating a method according to an embodiment.

Fig. 15 is a block diagram schematically illustrating a network node according to an embodiment.

Fig. 16 schematically illustrates a computer-readable medium and a processing device.

Detailed description

It is proposed to introduce a power offset between the legacy preamble part of the WUP and the OOK part of the WUP. This offset controls the relative powers between the two parts of the WUP and can be tuned to reduce or eliminate the difference between the PCR and WUR ranges, without having undesired secondary effects such as reduced coverage for carrier sensing. The purpose is to alleviate the problem of range mismatch between the PCR and WUR. This in turn results in increased energy efficiency at the stations. This method is transparent to the receiving stations, which do not require any signalling, nor need to perform any additional processing to the WUP. The principle may also be used for other types of packets than WUPs where there is a misalignment in range, but for the sake of tangible examples and easier understanding, the disclosure below will use WUP for demonstrating the principles.

The WUP, shown in Figs 8 and 9, consists of two different parts. The first part uses OFDM and is intended for carrier sensing/packet detection by legacy IEEE 802.11 stations different from the WUR, to which the second part is addressed. Moreover, the WUR is unable to detect the first part of the WUP. The second part uses OOK, and can’t be decoded by legacy IEEE 802.11 stations. As a consequence, it is possible to use different average powers in the two parts, in order to reduce range differences between the PCR and WUR. Legacy stations can’t decode the OOK part, so that increasing or decreasing the power of the OOK part has no consequence for legacy stations. Similarly, a WUR does not detect the legacy preamble, so that increasing/decreasing its power, relative to the OOK part, has no consequence for the WUR.

In one embodiment of the disclosure, the WUP transmitter introduces a power offset to decrease the power of the OOK part relative to the power of the legacy preamble, as illustrated in Fig. 11. This decreases the range of the WUR relative to the PCR, without affecting the sensitivity of carrier sensing for other stations in the BSS.

In another embodiment of the disclosure, the WUP transmitter introduces a power offset to decrease the power of the legacy preamble part relative to the power of the OOK part, as illustrated in Fig. 12.

Note that as explained in the background section, the OOK part of the WUP may be designed to have lower PAPR or more restricted dynamic range than the legacy preamble part of the WUP. Therefore, the power of the OOK part can be increased without increasing out of band emissions due to e.g. clipping/compression at the PA, as shown in Fig. 13.

Generation of waveforms for the OOK can be made from an Orthogonal Frequency Division Multiplex symbol, normally referred to as Multi-Carrier-OOK (MC-OOK). A time-domain single carrier waveform can be generated using continuous phase modulation with constant envelope and for example a 4 MHz bandwidth. Transforming this waveform to frequency domain and quantizing Fourier coefficients to for example a 256-QAM (Quadrature Amplitude Modulation) symbol for an Inverse Fast Fourier Transform (IFFT) generation of a waveform to be used for the MC-OOK, where all inactive subcarriers are nulled. For example, nulling all subcarriers except 13 contiguous subcarriers, corresponding to the desired bandwidth, provides a waveform resembling the desired constant envelope waveform.

Here, for 4 ps symbols, a 64-point IFFT and a 0.8 ps cyclic prefix may be applied. Examples of achieved Fourier coefficients are given in Table 1.

Table 1. Examples of Fourier coefficients for 4 ps example

The provided on- symbol according to the respective examples has nearly constant envelope and is power distributed over the full desired bandwidth. Therefore, it can be transmitted with an output power which is higher than during a legacy preamble.

A corresponding example for 2 ps symbols may be to use a 32-point IFFT and a 0.4 ps cyclic prefix. Examples of achieved Fourier coefficients are given in Table 2.

Table 2. Example of Fourier coefficients for 2 ps example

The MC-OOK on- symbol according to this example has nearly constant envelope and power distributed over the full desired bandwidth. Therefore, it can be transmitted with an output power which is higher than during the legacy preamble.

Fig. 14 is a flow chart illustrating a method according to embodiments. The method is performed by the network node, e.g. an AP, and the method comprises acquiring 1400 a sensitivity difference. This is generally performed by accessing a memory where the sensitivity difference is stored. The information may have been stored in different ways. For example, a station provides the information when registering to the network node. The information may be implicitly provided to the network node, e.g. by the station providing information about a device class or the like, wherein the network node is able to determine the desired information. Another way is that the network node saves results of earlier measurements when communicating with the station. Based on experienced performance during operation, the network node may also update saved information.

From the acquired sensitivity difference, the network node is able to determine 1402 a suitable power offset according to the principles demonstrated above. And when forming the WUP, power adjustment 1404 is performed. The WUP is then transmitted 1406.

There may be cases where there is no or very little misalignment. In such cases, it may not be worth the effort of doing any adjustments. Thus, there may be one or more options where to determine that no adjustments should take place. For example, a check 1401 based on the acquired sensitivity difference may show that there is no severe misalignment in coverage, wherein the method proceeds directly to the transmission

been determined 1402. If the power offset is very small, e.g. below a threshold, the adjustment 1404 of power is bypassed and the method proceeds with the transmission 1406 of the packet.

Fig. 15 is a block diagram schematically illustrating a network node 1500 according to an embodiment. The network node 1500, which may be an AP or any other base station applying the principles demonstrated above, comprises an antenna arrangement 1502, a receiver 1504 connected to the antenna arrangement 1502, a transmitter 1506 connected to the antenna arrangement 1502, a processing element 1508 which may comprise one or more circuits, one or more input interfaces 1510 and one or more output interfaces 1512. A memory (not shown) comprising stored sensitivity differences for stations may be provided with the processing element 1508, or be accessed via the interfaces 1510, 1512. The interfaces 1510, 1512 can be operator interfaces and/or signal interfaces, e.g. electrical or optical. The network node 1500 is arranged to operate as a central node, at least locally, in communication network where low-energy solutions as demonstrated above are provided by WUR. In particular, by the processing element 1508 being arranged to perform the embodiments demonstrated with reference to Figs 1 to 14, the network node 1500 is capable of providing a WUP where misalignment in range is reduced. The processing element 1508 can also fulfil a multitude of tasks, ranging from signal processing to enable reception and transmission since it is connected to the receiver 1504 and transmitter 1506, executing applications, controlling the interfaces 1510, 1512, etc.

The methods according to the present disclosure is suitable for implementation with aid of processing means, such as computers and/or processors, especially for the case where the processing element 1508 demonstrated above comprises a processor handling alignment of range for the different parts of the WUP. Therefore, there is provided computer programs, comprising instructions arranged to cause the processing means, processor, or computer to perform the steps of any of the methods according to any of the embodiments described with reference to Fig.1 to 14. The computer programs preferably comprise program code which is stored on a computer readable medium 1600, as illustrated in Fig. 16, which can be loaded and executed by a processing means, processor, or computer 1602 to cause it to perform the methods, respectively, according to embodiments of the present disclosure, preferably as any of the embodiments described with reference to Figs 1 to 6. The computer 1602 and computer program product 1600 can be arranged to execute the program code sequentially where actions of the any of the methods are performed stepwise, or perform actions on a real-time basis. The processing means, processor, or computer 1602 is preferably what normally is referred to as an embedded system. Thus, the depicted computer readable medium 1600 and computer 1602 in Fig. 16 should be construed to be for illustrative purposes only to provide understanding of the principle, and not to be construed as any direct illustration of the elements.