Patent Application
20250007555
Aspects herein relate generally to ultra-low-power wireless communication by means of reflection of signals. More particularly, aspects herein relate to a method for receiving an analog, information-bearing signal that modulates a radio frequency carrier signal that impinges on an antenna. The modulation of said analog, information-bearing signal is performed by an impedance modulator that modulates the impedance of said antenna. The method disclosed in the present invention relates to recovering the backscattered signal from said antenna and recovering the analog information that is modulated on it, using commercial, digital, embedded radio receiver devices.
Recent advances in the field of wireless communication by means of reflecting a RF signal, have enabled the development of ultra-low-power, wireless sensing devices [Bletsas et al 18]. A sensing device can transmit information related to a measured quantity without the need for a power amplifier or a mixer. An externally provided carrier signal impinging on the antenna of said sensing device, can be modulated using backscatter radio principles [Stockman 48].
In a conventional transmitting device, a baseband signal containing analog or digital information is upconverted using a high frequency oscillator and a mixer. Then, a gain stage (e.g., a power amplifier) amplifies the signal. The amplified signal subsequently drives an antenna that radiates said signal into the environment. Using backscatter radio principles, in a backscattering device, an appropriately designed information-bearing baseband signal, controls an impedance modulator that is coupled to an antenna. Provided RF illumination to said antenna and by appropriate modulation of said antenna's impedance, reflections occur that contain said information, which propagate and can be received by an appropriate device.
Recent studies and inventions have demonstrated that low-complexity circuits can exploit either modulated ambient [Smith et al 13], [Smith et al 17], [Bletsas et al 17], [Vougioukas et al 19] or unmodulated [Reynolds et al 20] illumination signals to convey analog or digital information towards an appropriate receiver. Analog backscattering techniques are used to convey sensor information towards software defined [Bletsas et al 13] or analog radio receivers [Vougioukas et al 19]. Information of a sensor modulates the frequency of a baseband waveform that in turn controls an impedance modulator resulting in the backscattering of analog information (i.e., said frequency) [Baldwin et al 78], [Bletsas et al 13b], [Bletsas et al 14].
Backscattering devices for transmitting digital information in a packet format, can transmit their information under modulated or unmodulated illumination by a carrier [Bletsas et al 08], [Smith et al 13], [Bletsas et al 14]. Appropriate receivers can either be designed using software defined radios and accompanying demodulation and detection software [Bletsas et al 14] or appropriately configured embedded radio systems [Bletsas et al 16], [Reynolds et al 20].
A need exists to provide a method for wirelessly interfacing backscattering devices that transmit analog frequency information, with digital packet-based, embedded radio systems. That way the need for a dedicated analog receiver or a software defined radio receiver with accompanying demodulation software (amplitude demodulation, frequency demodulation, phase demodulation or combinations thereof, is omitted in favor for the lower-cost alternative of an embedded receiver module.
The inventors have devised a method for receiving analog information that is frequency modulated (and transmitted by a backscattering device) from an embedded radio module, designed for digitally modulated signals. More specifically this invention offers a method for estimating the fundamental frequency of a signal that modulates the frequency of subcarriers, generated by means of backscattering a continuous wave signal impinging on the antenna of a backscattering device. Any commercially available embedded radio module/receiver of FSK or OOK modulated signals, able to configure the communication bit rate and the packet structure by means of external or embedded control, can be used for the proposed estimation method.
The objective of the present invention is achieved by an embedded receiver of FSK or OOK modulated signals connected to an external or embedded controller able to control and configure said receiver. The external or embedded controller sequentially configures the embedded receiver to a bit rate from a set of bit rates. For each bit rate, said controller polls the receiver for a successful detection of a packet or parts of a packet of data. If a packet or parts of a packet are detected, the controller reports the target bit rate for which the detection occurred. The objective is also achieved in conjunction with a backscattering device that is illuminated by an externally provided unmodulated signal. As a result of its backscattering operation, the backscattering device generates subcarriers that are frequency modulated by a signal whose frequency is estimated by dividing said target bit rate by two.
Voltage controlled oscillator 130 produces a squarewave signal 132 having a variable fundamental frequency that is configured according to the squarewave input signal 131. In an example implementation, the squarewave input signal 131 has two distinct states, state A and state B; voltage controlled oscillator 130 produces the squarewave signal 132 having a fundamental frequency equal to FH when the squarewave input signal 131 attains state A; voltage controlled oscillator 130 produces the squarewave signal 132 having a fundamental frequency equal to FL when the squarewave input signal 131 attains state B.
RF switch 120 implements an impedance modulator, modulating the termination impedance of the antenna 170. In an example implementation, RF switch 120 alters the termination impedance of antenna 170 between two impedance loads according to the squarewave signal 132 of the voltage controlled oscillator 130.
The source of unmodulated RF signals emits an unmodulated RF carrier signal 102 having carrier at a frequency of FC. The unmodulated carrier signal 102 impinges on the antenna 170 of the backscattering device 100. In an example implementation of the backscattering device 100, due to its backscattering operation, subcarriers 103 will be transmitted at FC+FH when the squarewave input signal 131 attains state A, or at FC+FL when the squarewave input signal 131 attains state B. Backscattering device 100 transmits the subcarriers 103 at FC+FH or FC+FL, each for a duration of TS/2 seconds. Duration TS/2 is the duration of each state of the squarewave input signal 131. An example of the process is depicted in
In an example implementation of the deployment depicted in
The embedded receiver 104 is further configured to receive binary-FSK modulated signals, for which the FSK subcarrier corresponding to signaling logic zero is located at a frequency of FC+FL and FSK subcarrier corresponding to signaling logic one is located at a frequency of FC+FH. In another example of the invention, the embedded receiver 104 can be configured to receive binary-FSK modulated signals, for which the FSK subcarrier corresponding to signaling logic zero is located at a frequency of FC−FH and FSK subcarrier corresponding to signaling logic one is located at a frequency of FC−FL.
In other configurations of the embedded receiver 104, frequency deviation and receiver bandwidth adjustments can be made to increase the reception performance. Said adjustments are performed while also tuning the FL and FH frequencies in the VCO 130 of the backscattering device 100.
Due to the state alternation of the squarewave input 131 in backscattering device 100, the upper sideband subcarriers transmitted by the backscattering device 100 alternatively at FC+FL or FC+FH, or the lower sideband subcarriers transmitted by the backscattering device 100 alternatively at FC−FH or FC−FL, resemble a binary FSK-modulated signal that is modulated by a continuous sequence of alternating bits. If the embedded receiver 104 is configured to receive packets having a bit duration of TS/2, then the embedded receiver 104 will report the detection of a packet or parts of a packet containing a continuous stream of alternating bits.
The aforementioned detection occurs only when the packet structure is configured at the embedded receiver to include a preamble sequence of alternating bits. The transmissions of the backscattering device 100 resemble a digitally modulated binary FSK packet transmission where the contents of said packets include a sequence of continuously alternating bits. Thus, in order for the embedded receiver 104 to successfully detect the FSK-resembling transmission, said embedded receiver 104 must be configured to detect such a packet of alternating bits. Thus the preamble sequence expected by the embedded receiver at the start of a packet, must be configured to be a preamble sequence of alternating bits.
When a successful detection event is logged by the controller, the controller reports the bit rate from the plurality of bit rates for which the successful detection event at the receiver occurred. Due to the resemblance of the backscattered subcarriers/signal 103 with binary FSK modulated signals, the frequency of the squarewave input signal 131 can be then estimated by dividing the bit rate for which successful detection occurred by 2.
In another example implementation, the embedded receiver 104 can be configured to demodulate and detect OOK modulated signals following the same packet structure described in previous implementation examples. In that example implementation of the invention, one of either of the fundamental frequencies (FH or FL) of the square wave 132, must be equal to zero. In another example implementation, one of either of FH or FL, can be set to zero even if the embedded receiver 104 is configured for the reception of FSK modulated signals.
While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed.
