A method for OFDM based wake up signals and a system thereof

Abstract

A method performed by a system comprising at least an OFDM (orthogonal frequency-division multiplexing) based base station (100) and at least an OFDM based user equipment (200) comprising a main radio (202) which is configured to operate in a sleep mode and in an operating mode where the main radio (202) performs main communication with the base station (100); and a wake up radio (201) which is configured to transmit a trigger signal to main radio (202) for triggering the operating mode; the base station (100) is configured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (201) to trigger main radio (202).

Description

[0001] DESCRIPTION

[0002] A METHOD FOR OFDM BASED WAKE UP SIGNALS AND A SYSTEM THEREOF

[0003] TECHNICAL FIELD

[0004] Invention relates to a method performed by a system comprising at least an OFDM (orthogonal frequency-division multiplexing) based base station and at least an OFDM based user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs main communication with the base station; and a wake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base station is configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio, and the system thereof.

[0005] PRIOR ART

[0006] A wake-up radio and a main radio are components in user equipment (UE) used to optimize energy efficiency in wireless communication systems. The wake-up radio is a low-power receiver designed to continuously monitor the wireless environment for specific signals or triggers. It operates in an energy-efficient manner, consuming minimal power while remaining active to detect a predefined wake-up signal. This signal is typically transmitted by a base station, access point, or another device in the network.

[0007] Once the wake-up radio detects the wake-up signal, it activates the main radio. The main radio is the primary communication module of the UE and is responsible for handling high-bandwidth tasks such as data transmission and reception. However, the main radio consumes significantly more power compared to the wake-up radio. To conserve energy, the main radio remains in a low-power or dormant state until it is triggered by the wake-up radio.

[0008] This arrangement ensures that the UE efficiently balances power consumption and communication readiness. The wake-up radio monitors the channel for incoming signals, and when a wake up signal (WUS) is received, the main radio transitions to an active state to perform its communication functions. This system is particularly useful in battery-powered devices, such as loT nodes, smartphones, and wireless sensors, where energy conservation is essential.Numerous studies have investigated the design of WUS waveforms that are compatible with OFDM systems. One approach involves directly mapping the On-Off Keying (OOK)-modulated WUS onto OFDM symbols through the inverse fast Fourier transform (IFFT) [1], While this technique preserves orthogonality, it faces challenges when dealing with variable carrier spacing and symbol rates.

[0009] Another method utilizes high and low power constellation points to modulate OFDM symbols, with each symbol representing a single bit, as specified in the IEEE 802.11 ah protocol [2], This scheme has been successfully validated on a Wake-Up Radio (WUR) prototype. Building on this foundation, a Peak-Flat amplitude-based modulation technique has been proposed to ensure compatibility with existing OFDM systems while achieving satisfactory sensitivity [3].

[0010] In the time domain, attention has been given to minimizing the distortion between the desired OOK WUS symbol and the constructed OFDM symbols [4], taking into account constraints on signal energy distribution and leakage. An alternating minimization approach has been proposed to optimize the WUS waveform, with its performance assessed under fading channel conditions and Manchester coding.

[0011] To address the challenge of varying OFDM symbol rates, another approach suggests dividing the WUS into sections and embedding each within the OFDM frame [5]. This strategy ensures full orthogonality between the transmitted WUS and concurrent OFDM transmissions on other subcarriers.

[0012] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0013] [1] R. S. M. Park, S. Azizi, and J. Liu. Low-Power Wake-Up Receiver for 802.11. Accessed: May 14, 2023. [Online]. Available: https: / / mentor.ieee.Org / 802.11 / dcn / 15 / 11-15-1307-00-0wng-low-powerwake-up-receiver-for-80211.pptx

[0014] [2] H. Zhang, C. Li, S. Chen, T. Xi, N. Yan, and H. Min, “A low-power OFDM-based wake-up mechanism for loE applications,” IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 65, no. 2, pp.

[0015] 181-185, Feb. 2018.[3] M. C. Caballe, A. C. Auge, E. Lopez-Aguilera, E. Garcia-Villegas, I. Demirkol, and J. P. Aspas, “An alternative to IEEE 802.11 ba: Wakeup radio with legacy IEEE 802.11 transmitters,” IEEE Access, vol. 7, pp. 48068-48086, 2019.

[0016] [4] A. Sahin and R. Yang, “Sequence-based OOKfor orthogonal multiplexing of wake-up radio signals and OFDM waveforms,” in Proc. IEEE Global Commun. Conf. (GLOBECOM), Dec.

[0017] 2018, pp. 1-6.

[0018] [5] N. Mazloum and O. Edfors, “Interference-free OFDM embedding of wake-up signals for low-power wake-up receivers,” IEEE T rans. Green Commun. Netw., vol. 4, no. 3, pp. 669-677, Sep. 2020.

[0019] BRIEF DESCRIPTION OF THE INVENTION

[0020] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.

[0021] An object of the invention is to transmit wake up signal and data using OFDM framework and reduce the resources spent transmitting wake up signal.

[0022] Another object of the invention is to increase accuracy of wake up signal detection.

[0023] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method performed by a system comprising at least an OFDM (orthogonal frequency-division multiplexing) based base station and at least an OFDM based user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs main communication with the base station; and a wake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base station is configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio. Accordingly, it is characterized by comprising the steps of: acquiring, by the base station, data to be transmitted; generating, by the base station, an OFDM symbol having multiple sub-symbols, using data to be transmitted where at least a predetermined subcarrier of each sub-symbol is in “on” state or in “off” state representing each bit of an on-off keying (OOF) sequence representing a wake up signal; adding, by the base station, a cyclic prefix to OFDM symbol and generating at least one OFDMmessage; transmitting, by the base station, the at least one OFDM message; receiving, by the user equipment, the at least one OFDM message; applying, by the user equipment, band pass filtering to the OFDM message for filtering out the data signal; performing, by the user equipment, energy detection, on filtered OFDM message and determining OOF sequence; determining a wake up signal from OOF sequence; triggering, by the wake up radio of the user equipment, the main radio to operate in operation mode. Thus, Data and the wake up signal are sent using same OFDM message. Thanks to this method, OOK is transmitted using reduced resources. Further, the method provides increased accuracy.

[0024] A possible embodiment of the invention is characterized in that enveloping, by the base station, the OFDM symbol with one cyclic prefix and generating an OFDM message.

[0025] Invention also relates to a system comprising at least an OFDM (orthogonal frequency-division multiplexing) based base station and at least an OFDM based user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs main communication with the base station; and awake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base station is configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio. It is characterized in that the system is configured to perform one of the above method and wherein the wake up radio comprising a low power filter.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a drawing illustrating top schematic view of the system.

[0028] Figure 2 is a drawing illustrating the wake up radio of the user equipment.

[0029] Figure 3 is a drawing illustrating multiple symbols encapsulated by a single prefix.

[0030] Figure 4 illustrates an example of the generated OOK time sequence based on the disclosed method without data transmission,

[0031] Figure 5 illustrates an example of the generated OOK time sequence based on the disclosed method withFigure 6 illustrates an example of the transmitted signal and processed signal at user equipment.

[0032] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0033] 100 Base station

[0034] 200 User equipment

[0035] 201 Wake up radio

[0036] 202 Main radio

[0037] 210 Analog front end

[0038] 211 Band pass filter

[0039] 212 Second band pass filter

[0040] 213 Envelope detector

[0041] 214 DC blocker

[0042] 215 Low pass filter

[0043] 220 OOK detector

[0044] 221 Energy detector

[0045] 222 Threshold unit

[0046] 230 WUS detector

[0047] 300 OFDM symbol

[0048] 310 Sub-symbol

[0049] 320 Cyclic prefix

[0050] 330 Repeated part

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0053] Referring to figure 1, invention is a method realized by a system comprising at least base station (100) and at least user equipment (200). The base station (100) is capable of performing OFDM (orthogonal frequency-division multiplexing) communication. Base station (100) transmits communication signals and wake up signals and for the user equipment (200) trigger its main radio (202). The base station (100) generates OFDM messages and embeds on-off keying (OOF) sequences into OFDM messages. On-Off Keying (OOK) is a binary modulation technique where the presence of a carrier signal represents a binary "1 and itsabsence represents a binary "0," enabling energy-efficient and straightforward signal transmission. Predetermined pattern of the OOF sequence defines a wake up signal.

[0054] The user equipment (200) comprises a main radio (202) configured to operate in a sleep (idle) mode and an operating mode where it performs main communication with a base station (100). The user equipment (200) further includes a main radio antenna operably connected to the main radio (202) for transmitting and receiving communication signals, and a wake-up radio configured to process wake-up signals dedicated to activating the main radio (202). The wakeup radio is operably connected to a wake-up radio antenna for receiving low-power signals and is configured to trigger the main radio (202) to transition from the sleep mode to the operating mode upon receiving a dedicated wake-up signal. Therefore, when the user equipment (200) detects the OOF sequence it can determine that it represents a wake-up signal, and triggers its main radio (202) to operate in operation mode.

[0055] Essentially, base station (100) embeds OOK sequence into an OFDM message and user equipment (200) filters the OFDM message and detects OOK sequence from OFDM message. Then user equipment’s (200) wake up radio (201) triggers main radio (202) if OOK sequence corresponds to a predetermined wake up signal, or keeps main radio (202) in sleep mode.

[0056] In more detail, the base station acquires data to be transmitted. The base station (100) accesses to the OOK sequence that represents a wake up signal. Referring to figure 3, the base station (100) generates one multi-symbol encapsulated (MSE)-OFDM symbol (300) wherein shorter OFDM sub-symbols (310) (i.e., of higher numerologies) are sent back to back protected by a single cyclic prefix (CP). Here, each sub-symbol (310) of the MSE OFDM symbol (300) determines a single chip of the OOK sequence, such that a predetermined subcarrier / subcarriers of each sub-symbol (310) is “on” state or in “off” state based on OOK sequence. For instance, subcarrier may be “0” for representing “0” of the OOK sequence. And subcarrier may be “1” for representing “1” of the OOK sequence.

[0057] In other words, base station (100) selects specific number of subcarrier / subcarriers jvR£with frequency indices / G [0, K] from all the OFDM symbol (300) and set them “On” (by assigning power to this subcarrier) or “Off” (by transmitting no power over that subcarrier), where K is the inverse Fourier transform size (FFT) size.

[0058] Note that for NRE= i the OOK sequence generation is straight forward. For example, if a the OOK sequence c = [1 0 1 1] is intended to be generated then, Ncode= 4 OFDM sub-symbols(310) are used. Let NRE= i and 1 = 5. Then, the frequency domain representation of the i-th sub-symbol (310) is expressed as

[0059]

[0060] Note that for NRE= 1, if a the OOK sequence c = [1 0 1 1] is intended to be generated then,Ncode =4OFDM sub-symbols (310) are used. Let NRE= 1 and 1 = 5. Then, the frequency domain representation of the i-th sub-symbol (310) is expressed as

[0061]

[0062] Where xpis a random complex number. Figure 3 and 4 represents time domain OFDM signal when data is not present in OFDM signal and when data is present.

[0063] Note that Ncode= 27where j e N, However, due to the cyclic prefix (320) the last code word of each OFDM is repeated at the cyclic prefix (320). One way of solving this issue is using OOK sequences of 27- 1 words while the last code word is always set to a fixed known value “On” or “Off”.

[0064] The CP of the OFDM symbol (300) can also be used to increase the reliability of the detection and for improving synchronization. On example of doing that is, selecting the last OOK sequence value to be equal to the first. Thus, creating double code pattern along the WuS due to the cyclic prefix (320) repetition. This method can also be used for grouping different WuRs. In this case, the double bits are may be selected based on the WuRs groups.

[0065] Referring to figure 2, wake up radio (201 ) of the user equipment (200) comprises a band pass filter (211) for filtering out data in the OFDM. Then wake up radio (201 ) performs generic power detection methods in order to determine the OOK sequence from filtered OFDM signal.

[0066] Furthermore, the wake-up radio comprises a second band-pass filter (212) for isolating the desired frequency band of the filtered OFDM signal; an envelope detector (213) for extracting cyclic prefix (320) of the signal; a DC blocker (214) for removing any direct current offset or low-frequency noise; a low-pass filter for smoothing the envelope signal; an energy detector (221) for measuring the energy of the filtered signal; a threshold unit (222) for comparing the detected energy to a predefined threshold; and a WUS detector (230) for identifying the presence of the wake-up signal based on the On-Off Keying (OOK) pattern. Then it triggers the main radio (202) if wake up signal is identified.Figure 6 depicts transmitted signal and the form of received OFDM signal before OOK determination step.

[0067] The design of Wake-Up Radio (WUR) is well-aligned with the current 3GPP standardization efforts, particularly those outlined in Release 19 and subsequent studies focusing on energy efficiency and network optimization. According to 3GPP specifications, WUR technology integrates with the 5G architecture by leveraging advancements in wake-up signaling and low-power communication, as detailed in 3GPP TR 38.869 [3GPP TR 38.869, “Study on low-power Wake-up Signal and Receiver for NR),” Dec. 2023]. This compatibility ensures that WUR can operate seamlessly within the 5G ecosystem while preparing for future 6G requirements. As 3GPP's studies on 6G emphasize ultra-low latency, enhanced energy efficiency, and advanced loT connectivity, WUR becomes increasingly important. It enables devices to remain in a low-power sleep mode while responding to wake-up signals, thus significantly extending battery life and optimizing network resource usage. This capability supports the realization of next-generation applications envisioned in 6G, such as ubiquitous connectivity and pervasive sensing, making WUR a key technology in achieving these ambitious goals.

[0068] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A method performed by a system comprising at least an OFDM (orthogonal frequencydivision multiplexing) based base station (100) and at least an OFDM based user equipment (200) comprising a main radio (202) which is configured to operate in a sleep mode and in an operating mode where the main radio (202) performs main communication with the base station (100); and a wake up radio (201) which is configured to transmit a trigger signal to main radio (202) for triggering the operating mode; the base station (100) is configured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (201) to trigger main radio (202) characterized in that comprising the steps of:- acquiring, by the base station (100), data to be transmitted;- generating, by the base station (100), an OFDM symbol (300) having multiple subsymbols (310), (300) using data to be transmitted where at least a predetermined subcarrier of each sub-symbol (310) is in “on” state or in “off” state representing each bit of an on-off keying (OOF) sequence representing a wake up signal;- adding, by the base station (100), a cyclic prefix (320) to OFDM symbol (300) and generating at least one OFDM message;- transmitting, by the base station (100), the at least one OFDM message;- receiving, by the user equipment (200), the at least one OFDM message;- applying, by the user equipment (200), band pass filtering to the OFDM message for filtering out the data signal;- performing, by the user equipment (200), energy detection, on filtered OFDM message and determining OOF sequence;- determining a wake up signal from OOF sequence;- triggering, by the wake up radio (201 ) of the user equipment (200), the main radio (202) to operate in operation mode.

2. A system comprising at least an OFDM (orthogonal frequency-division multiplexing) based base station (100) and at least an OFDM based user equipment (200) comprising a main radio (202) which is configured to operate in a sleep mode and in an operating mode where the main radio (202) performs main communication with the base station (100); and a wake up radio (201 ) which is configured to transmit a trigger signal to main radio (202) for triggering the operating mode; the base station (100) isconfigured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (201 ) to trigger main radio (202) characterized in that the system is configured to perform the method of claim 1 ; the wake up radio (201) comprising a band pass filter.

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