A method for enabling multiple access of low power devices in wireless communication

Abstract

The invention is related to a method for modulating and separating the signals of different devices such as ambient power-enabled Internet of Things devices, backscatter devices (BDs), tags or reconfigurable intelligent surface (RIS).

Description

[0001] DESCRIPTION

[0002] A METHOD FOR ENABLING MULTIPLE ACCESS OF LOW POWER DEVICES IN WIRELESS COMMUNICATION

[0003] Technical Field

[0004] The invention is related to a method for separating the signals coming from different devices such as ambient power-enabled loT devices, also referred to as tags or backscatter devices (BDs).

[0005] Prior Art

[0006] Conventional communication systems rely on some sort of resource allocation (in time, frequency, space, or code domains) to identify the source of any data reaching the receiver. Alternatively, some extra communication resources are used to carry information about the source, such as its identity of MAC / IP address, to ensure the receiver knows where the data originates from.

[0007] The focus of wireless communications has shifted from providing connectivity between people to connectivity between things. Internet-of-things (loT) and massive machine type connectivity (mMTC) applications are examples of applications where a massive number of low-end devices and / or sensors are connected to each other or to a network for functionalities such as inventory, positioning, sensor information transfer, and command. One of the challenges that arises with this massive connectivity is the increased power usage, which goes against the sustainable development goals. Consequently, there has been a push towards devising “green” communication technologies which do not rely on extraneous power sources to exchange information.

[0008] Ambient power-enabled loT (A-IoT) technology, ambient backscatter communication (AmBC), or symbiotic radio (SRad) capitalize on environmental signals, such as radio waves or ambient RF energy to enable wireless data transfer. These devices can operate without conventional power sources, relying on ambient or harvested energy. This reduces the need for batteries and facilitates prolonged device lifespans, making it ideal for energy-constrained applications like loT. Additionally, this technology supports the seamless integration of a myriad of devices into wireless networks, crucial for the proliferation of loT in smart healthcare, smart cities, smart agriculture and so on. Its ability to harness energy from ambient signals also enhances coverage and penetration, crucial for consistent connectivity in urban environments and buildings. Finally, the absence of any active RF sources at the device means minimal hardware leading to cost-efficient and simple networks.

[0009] Given that the number of communicating A-IoT devices also known as backscatter devices (BDs) / Tag, is expected to increase manifold in beyond 5G networks, one of the major issues is to enable backscatter communication considering multiple BDs. The current invention is related to the same problems, i.e., multiple accessing of A-IoT device / BDs / Tags.

[0010] Given that backscatter communication systems operate on scarce resources, mostly ambient radio frequency (RF) signals, it is not possible to have a sophisticated resource allocation solution. Consequently, it is difficult to distinguish between the signals received from different BDs, which greatly reduces the multiple accessing capability of the system.

[0011] The method disclosed in EP3794497A1 involves providing RFID readers that are synchronized to a baseband frequency and assigned orthogonal codes for code division multiple access (CDMA). The readers transmit CDMA-encoded signals to RFID tags and receive response signals encoded with the orthogonal codes. The data in the response signals is decoded using a known set of orthogonal codes. The collaborative RFID reader system includes transmitters, receivers, and processors for encoding, transmitting, receiving, and decoding the CDMA-encoded signals. Additionally, the RFID tags store unique identification codes and sets of mutually orthogonal RFID reader codes, and utilize antennas, receivers, energy-harvesting circuits, and frequency conversion units for signal reception and backscattering.

[0012] US2010060424A1 discloses a method in which one or more readers transmit radio frequency (RF) beacons to be electronically reflected by tags. Data transmitted via modulated backscatter from RFID tags is encoded so as to permit reliable demodulation of simultaneous transmissions from multiple tags. This includes the use of spreading sequences as in direct sequence spread spectrum, where the spreading sequences may be a function of the tag ID or may be randomly chosen. Backscattered signals from multiple tags may be detected using well-known receiver techniques for code division multiple access (CDMA) systems. Readers may be equipped with transmit and / or receive antenna arrays. A receive antenna array permits a reader to estimate directions of arrival for received signals, as well as to enhance range by performing receive beamforming. CN112202535A discloses a multi-user symbiotic communication system and method based on backscattering, and the method comprises the steps: compiling a leading part and a carrier part of transmitting frame information, transmitting the compiled leading part and carrier part to a passive user, analyzing the received transmitting frame information through the passive user, obtaining control signaling information, and according to the access sequence of the passive user, allocating different product factors to different passive users respectively; enabling a passive user multiply received and analyzed control signaling information by an obtained product factor to obtain a chip length and a chip transmission rate required by the passive user during encoding, so that the orthogonality among a plurality of passive users is ensured, and the respective backscatter communication is not interfered by other users; symbiotic communication with main transmission is realized by randomly accessing a passive user, the synchronization requirement of a multiple access technology in traditional multi-user access is weakened, and a passive communication link is realized.

[0013] EP0915573A2 discloses a modulated backscatter (MBS) system that provides a processing gain over MBS background noise by using a wideband uplink signal and a narrowband downlink signal. The wideband uplink signal is generated by controlling the reflection of a narrowband downlink signal using a wideband data signal. The wideband data signal is generated by modulating a pseudo random signal with an information signal, where the chip rate of the pseudo random signal is higher than the bit or symbol rate of the information signal.

[0014] CN114492488A discloses an ICA (independent component analysis)-based environment backscattering multi-label signal separation detection method, which comprises the following steps that: each same-frequency interference user in an environment backscattering system performs spectrum spreading on a data signal to be sent by utilizing a random sequence in a random sequence codebook, and then sends the data signal to a reader in a mode of reflecting an environment radio frequency signal; according to the method, signals received by a reader are separated on the basis of the ICA algorithm, the signals obtained through separation are recognized through spread spectrum sequences of different labels, ICA-based environment backscattering multi-label signal separation detection is completed, separation detection of the signals is achieved. CN110289938 A discloses a multi-passive reflection label access system based on code division multiple access and a control method. The multi-passive reflection label access system comprises a plurality of passive reflection labels, an excitation source and a receiver, wherein each passive reflection tag sends a backscattering signal of an excitation source to the receiver after sequentially carrying out frame sealing, coding and modulation on the sent data, and each code contains a unique PN sequence of the corresponding passive reflection tag; and the receiver can decode and distinguish the coded data sent by different passive reflection labels according to PN sequences obtained by decoding. The system realizes simultaneous transmission of a plurality of nodes by code division multiple access in a passive reflection communication system comprising a plurality of passive reflection tags.

[0015] CN103747521 A discloses a real-time location method and a system based on radio frequency identification of a mobile communication terminal. A transmitting function of a radio frequency identification locating signal extends in the mobile communication terminal, a reading function of the radio frequency identification locating signal is realized in an identification locating reader, the mobile communication terminal is communicated with the identification locating reader through wired and wireless communication networks and a network server, by adopting subcarrier modulation, direct sequence spread spectrum, code division multiple access, time division collision prevention and multi-system parameter calibration technologies, the interference between a multipath signal and multiple terminals of multiple readers, and the interference of the other wireless communication system can be effectively inhibited, the remote high-precision radio frequency identification location is realized, and the network server is utilized to carry out distributed interactive processing fusion of data information and network dynamic optimization configuration of communication parameters, so that the convenient, reliable, economic and flexible real-time location service application based on the mobile communication terminal can be provided for a user.

[0016] In study of Mi et. al [1], a coded-backscatter multiple access (CBMA) scheme was proposed for high-capacity, distributed control of large-scale networks. CBMA utilizes a direct sequence spread spectrum and a correlation-based detector to support simultaneous transmissions. Asynchronous transmission impacts the spread sequence's orthogonality, but CBMA addresses this challenge. The scheme enables tags to adjust their antenna impedance for power control, compensating for the weak backscatter signal affected by tag-reader distance. CBMA employs pseudo-noise (PN) codes similar to asynchronous code division multiple access (CDMA) for encoding tag data. The power control scheme adaptively adjusts the tag impedance to optimize system capacity. The tag performs framing, encoding, power selection, on / off modulation, and frequency shifting. The reader decodes data using the orthogonality of PN sequences.

[0017] The proposed solution in the previous documents exploits the codes / sequences transmitted by the reader and some require the backscatter devices to transmit orthogonal codes which can be detected at the backscatter receiver / reader. Besides, some other solutions also require the backscatter devices to control the power of the backscattered signals to avoid the near-far problem. Most of the methods are designed considering RFID systems in which one or multiple readers are deployed only to support the communication of the BDs / tags, which require dedicated resources and deployment cost. Deployment of multiple readers adds additional cost to the backscatter system design. Moreover, the number of orthogonal codes / sequences are limited because of that only a small number of backscatter devices may be supported. Exploiting the power control by changing impedance at the backscatter devices has limitations as the power difference between different backscattered signals is very little. Therefore, power control may also not provide high gains.

[0018] As a result, all of the problems mentioned above has made it necessary to provide a novelty in the related field.

[0019] Objects of the Invention

[0020] The main object of the present invention is to provide a method for multiplexing communicating reflectors such as a A-IoT backscatter device, to enable that a receiver distinguishes between the signals coming from different communicating reflectors, thereby providing multiple accessing capability to the A-IoT system.

[0021] Another object of the present invention is to avoid the collision or interference of the signals meant for (or sent by) different users / BDs / Tags.

[0022] Another object of the present invention is to eliminate requirements of some extra communication resources such as codes to distinguish between the signals coming from different communicating reflectors. Another object of the present invention is to provide a method for device identification, positioning, sensing, sensors information transfer, and command purposes.

[0023] Description of the Figures of the Invention

[0024] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0025] Figure 1. An illustration of a wireless network comprising a transmitter, environmental scatterers, communicating reflectors such as reconfigurable intelligent surface (RIS) and backscatter devices (BDs) and a receiving node.

[0026] Figure 2. An illustration of another embodiment of wireless network comprising a transmitter, environmental scatterers, backscatter devices (BDs), a receiving node, and a normal user terminal.

[0027] Figure 3. An illustration of a wireless communication system comprising of co-located transmitter and receiver in the presence of environmental scatterers and backscatter devices (BDs).

[0028] Figure 4. An illustration of another embodiment of a wireless network comprising a transmitter, a relay node, environmental scatterers, and backscatter devices (BDs).

[0029] Figure 5. A flowchart of the proposed approach from the transmitter and backscatter devices (BDs) perspective.

[0030] Figure 6. A flowchart of the reception process of the proposed approach.

[0031] Figure 7a. A graphical illustration that represents channel impulse response (CIR) when the BD path is un-identifiable.

[0032] Figure 7b. A graphical illustration that represents channel impulse response (CIR) when the BD is identifiable.

[0033] Figure 8a. A graphical illustration that represents transmission of symbol “1” by the BD.

[0034] Figure 8b. A graphical illustration that represents transmission of symbol “0” (b) by the BD. Reference Numbers

[0035] The parts and components are given in the figures are referenced for the subject matter of the invention to be understood better.

[0036] 110. Transmitter

[0037] 111. Signal

[0038] 112. Second signal

[0039] 113. Forward link signal

[0040] 120. Environmental scatterers

[0041] 130. Communicating reflectors

[0042] 131. Reflector link signal

[0043] 135. Reconfigurable intelligent surface

[0044] 140. Receiver

[0045] 150. User terminal

[0046] 160. Relay node

[0047] AP. Access point

[0048] BS. Base station

[0049] UE. User equipment

[0050] AP. Access point

[0051] Detailed Description of the Invention

[0052] The invention is related to a method for separating the signals coming from different communicating reflectors (130) such as backscatter devices, also referred to as tags.

[0053] The term “communicating reflector” (130) defines a device for wireless communication that may contain single or multiple antennas and it may transmit, receive, modulate, and reflect the incident radio frequency signals that maybe ambient or dedicated to transmitting its information. Preferably, communicating reflector (130) is device that is not limited backscatter device (BD), reconfigurable intelligent surfaces (RIS), ambient-power enabled loT device, user equipment (UE). Figure 1 is an embodiment of a wireless network comprising a transmitter (110), environmental scatterers (120), communicating reflectors (130) such as A-IoT devices / backscatter devices / Tags, reconfigurable intelligent surfaces (RISs) (135) and a receiver (140).

[0054] Referring to Figure 1; The transmitter (110) may be a base station (BS), an access point (AP), a user equipment (UE) or any other device capable of transmitting wireless signals. The signal (111) may propagate directly between transmitter (110) and receiver (140). The receiver (140) is assumed to be any device capable of decoding the signal of communicating reflectors (130) preferably, a signal of backscatter device. The propagation environment can contain a plurality of environmental scatterers (120) such as buildings, trees, cars, humans and any other objects that can reflect, refract, absorb or scatter the signal (111) and creates a second signal (112). This embodiment also includes the transmitter (110) transmitting a forward link signal (113) towards a plurality of communicating reflectors (130) preferably a plurality of backscatter device. The communicating reflectors (130) may have single or multiple antennas. The communicating reflectors (130) modulate the forward link signal (113) with their data and send the reflector link signal (131) to the receiver (140). In an embodiment of the invention, reconfigurable intelligent surfaces (135) can also be considered in place of or in addition to the communicating reflectors (130). The reflector link signal (131) can also be used to achieve diversity gains at the receiver (140).

[0055] Figure 2 is an illustration of a wireless network comprising a transmitter (110), environmental scatterers (120), communicating reflectors (130), a receiver (140), and a normal user terminal (150).

[0056] Referring to Figure 2; The transmitter (110) may be a base station (BS), an access point (AP), a user equipment (UE) or any other device capable of transmitting wireless signals. The signal (111) may propagate directly between transmitter (110) and receiver (140). The receiver (140) is assumed to be any device capable of decoding the signal of communicating reflectors (130) preferably, a signal of backscatter device. The propagation environment can contain a plurality of environmental scatterers (120) such as buildings, trees, cars, humans and any other objects that can reflect, refract, absorb or scatter the signal (111) and creates a second signal (112). This embodiment also includes the transmitter (110) transmitting a forward link signal (113) towards a plurality of a communicating reflector (130) preferably a plurality of backscatter devices. The communicating reflector (130) may have single or multiple antennas. The communicating reflector (130) modulates the forward link signal (113) with their data and sends the reflector link signal (131) to the receiver (140). In this embodiment of the invention, a conventional user terminal (150) is also present and has ongoing communication with the transmitter (110).

[0057] Figure 3 is an embodiment of a wireless network comprising a transmitter (110), environmental scatterers (120), communicating reflectors (130), and a receiver (140).

[0058] Referring to Figure 3; The transmitter (110) may be a base station (BS), an access point (AP), a user equipment (UE) or any other device capable of transmitting wireless signals. The propagation environment can contain a plurality of environmental scatterers (120) such as buildings, trees, cars, humans and any other objects that can reflect, refract, absorb or scatter the signal (111) and create a second signal (112). This embodiment includes the transmitter (110) transmitting a forward link signal (113) towards a plurality of communicating reflectors (130) preferably a plurality of backscatter device. The communicating reflector (130) may have single or multiple antennas. The communicating reflector (130) modulates the forward link signal (113) with their data and sends the reflector link signal (131) to the receiver (140). The receiver (140) is any device capable of decoding signal of communicating reflectors (130) preferably, a signal of backscatter device. In this embodiment, the receiver (140) is assumed to be collocated with the transmitter (110) or both functionalities are part of the same device. In another embodiment, this setup may also be used localization, positioning or sensing of the communicating reflectors (130). For instance, the communicating reflector (130) may be localized based on its incorporated delay to the signal at the receiver.

[0059] Figure 4 is an illustration of a wireless network comprising a transmitter (110), a relay node (160), environmental scatterers (120), communicating reflectors (130), and a receiver (140).

[0060] Referring to Figure 4; The transmitter (110) may be a base station (BS), an access point (AP), a user equipment (UE) or any other device capable of transmitting wireless signals. The propagation environment can contain a plurality of environmental scatterers (120) such as buildings, trees, cars, humans and any other objects that can reflect, refract, absorb or scatter the signal (111) and creates a second signal (112). This embodiment includes the transmitter (110) communicating with a relay node (160) over a bidirectional link (114). The relay node (160) may be a base station (BS), an access point (AP), a user equipment (UE) or any other device capable of transmitting wireless signals which transmits a forward link signal (113) a plurality of communicating reflectors (130) preferably a plurality of backscatter device. The communicating reflectors (130) may have single or multiple antennas. The communicating reflectors (130) modulate the forward link signal (113) with their data and send the reflector link signal (131) to the relay (160). In this embodiment, the relay node (160) is assumed to have both transmission and reception capabilities.

[0061] Figure 5 shows the flowchart of the proposed approach from the transmission perspective. In step first, all the communicating reflectors (130) preferably backscatter devices are turned off. After that, the channel between the transmitter (110) and receiver (140) is estimated including the maximum excess delay, gains, phases, and delays of the different channel taps. In case of a relay node (160) being used, this step involves relay node (160) in the channel estimation process. After that, a single communicating reflector (130) is turned on. In next step, the receiver (140) compares the observed channel to the one obtained in step that estimated including the maximum excess delay, gains, phases, and delays of the different channel taps. If the forward link signal (113) coming from the communicating reflector (130) is identified at the receiver (140), the channel response is updated in this step. If the signal coming from the communicating reflector (130) overlaps with the other channel taps, the receiver (240) identifies the overlapped channel tap. Then, an appropriate delay is added at the communicating reflector (130) so that the forward link signal (113) is identifiable at the receiver (140) and the channel estimate is updated. After that, it is checked that all the communicating reflectors (130) have been identified. If identification is completed, the algorithm terminates. If there is still an unidentified communicating reflector (130), then all the steps from the step where a single communicating reflector (130) is turned on to the step where all the communicating reflector (130) is identified.

[0062] Figure 6 is a flowchart of the reception part of the proposed approach. In the first step, the receiver (140) identifies the delays of all the participating communicating reflectors (130). After that, the signal is transmitted by the transmitter (110) or relay node (160). The transmitted forward link signal (113) consists of a time-domain spread-spectrum sequence. However, in another embodiment, a signal spread in any other domain can also be considered. In the next step, the communicating reflector (130) modulates its data over the received signal. In this embodiment, on-off keying (OOK) modulation is considered. However, other embodiments may use any other modulations including binary phase-shift keying (BPSK). After modulation, the communicating reflector (130) transmits the reflector link signal (131). In the last step, the receiver (140) demodulates the received signal (131) using at least spread spectrum techniques.

[0063] Figure 7 shows the two cases of step where the receiver (140) compares the observed channel to the one obtained in step that estimated including the maximum excess delay, gains, phases, and delays of the different channel taps. In this step, the receiver (140) evaluates whether the communicating reflector (130) is identifiable from the estimated channel. Specifically, Figure 7a shows the case where the signal from reflector link signal (131) falls in the same chip duration as one of the environmental scatterers (120). In this case, the reflector link signal (131) from communicating reflector (130) is not identified. Figure 7b shows the case where the signal from reflector link signal (131) falls in an empty chip duration meaning it is distinguishable. It should be noted that Figure 7b may also be obtained after step, where delay addition is carried out, once the appropriate delay has been added at the communicating reflector (130).

[0064] Figure 8 shows the transmission of communicating reflector (130) and how it is observed at the receiver (140). Figure 8a illustrates the case where the reflector link signal (131) is received as a multipath component of the signal transmitted by the transmitter (110). This is demodulated as a “1” by the receiver (140). Figure 8b shows the case where no signal is received at the corresponding delay as Figure 8a. This is interpreted to be a “0” transmitted by the communicating reflector (130) to the receiver (140). Here it should be noted that is an embodiment of on-off keying (OOK) modulation. Other embodiments of the invention may leverage different modulation schemes as well.

[0065] REFERENCES

[0066] [1] N. Mi, X. Zhang, X. He, J. Xiong, M. Xiao, X.-Y. Li, and P. Yang, “CBMA: Coded- backscatter multiple access,” in Proc. IEEE 39th Int. Conf. Distrib. Comput. Syst. (ICDCS), Jul. 2019, pp. 799-809.

Claims

CLAIMS1. A method for separating and identifying signals coming from different single or plurality of communicating reflectors (130) that are wireless communication devices and operate by modulating and reflecting incident radio frequency signals to transmit information, in wireless transmission among a transmitter (110), a receiver (140) and the plurality of communicating reflectors (130), characterized by a) Estimating a channel between the transmitter (110) and receiver (140) with at least one parameter of channel impulse responses of the different channel taps, b) Turning on single or multiple communicating reflector (130), c) Observing the channel to find a forward link signal (113) coming from the communicating reflector (130) to identify the communicating reflector (130) by and d) Updating channel impulse response according to the identified communicating reflector (130), e) Repeating step b to d for at least one more communicating reflector (130).

2. A method according to Claim 1, characterized by parameter of channel impulse response are the maximum excess delay, gains, phases, and delays of the different channel taps.

3. A method according to Claim 1 or 2, characterized by further comprising step of controlling whatever the forward link signal (113) coming from the communicating reflector (130) overlaps with the channel taps estimated in step c.

4. A method according to Claim 3, characterized by further comprising step of adding delay at the communicating reflector (130) when the forward link signal (113) coming from the communicating reflector (130) overlaps with the channel taps estimated in step c.

5. A method according to Claim 1, wherein communicating reflectors (130) are devices that may not generate their own signal and rely on only incident radio frequency signals.

6. A method according to Claim 1, wherein communicating reflectors (130) are at least ambient power-enabled Internet of Things devices, backscatter devices, tags, and / or reconfigurable intelligent surface (RIS).

7. A method for wireless communication among a plurality of communicating reflectors (130) that are wireless communication devices and operates by modulating and reflecting incident radio frequency signals to transmit information, and a transmitter (110), and a receiver (140), characterized by a) Transmitting a signal ( 101 ) by the transmitter (110), b) Modulating the data according to the signal (101) by the communicating reflector (130) that separated and identified by method according to any of Claim 1 to 6, c) Transmitting a reflector link signal (131) by the communicating reflector (130), d) Demodulating and detecting the reflector link signal (131) by the receiver (1 0).

8. A method according to Claim 7, characterized by parameter the modulation is carried out by on off keying (OOK) modulation or any other modulations scheme.

9. A system for wireless communication comprises a single or plurality of communicating reflectors (130) that are wireless communication devices and operates by modulating and reflecting incident radio frequency signals to transmit information, and a transmitter (110), a receiver (140) and means adapted to execute the steps of the method of any of claim 7 to 9.

10. A computer program [product] comprising instructions to cause the system of claim 10 to execute the steps of the method of any of claim 7 to 9.

11. A computer-readable medium having stored there on the computer program of claim

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