Method and apparatus for efficient far-field wireless information and power transmission

Abstract

The WIPT system uses a synchronizable PPM waveform to transmit information and power from the ET to a distant far-field EH. In doing so, the solution proposed in this article reduces receiver complexity, optimizes power transfer, and meets information transmission requirements. The synchronizable PPM waveform includes a plurality of pulse modulation symbols, each of which includes one or more pulses that are position modulated in response to the information to be transmitted to the EH. The ET configures at least one pulse in each symbol of the synchronizable PPM waveform according to one or more synchronization constraints to enable symbol synchronization at the EH. The EH converts the RF power of the received synchronizable PPM waveform into a DC voltage and synchronizes the received PPM waveform to extract information in the PPM waveform.

Description

Technical Field

[0001] The solutions presented herein relate generally to wireless power transfer systems, and more particularly to improving the power and information transferred in wireless information and power transfer (WIPT) systems using pulse position modulation. Background Art

[0002] A far-field energy harvesting system includes an energy transmitter (ET) and an energy harvester (EH), which are far away from each other (far field) and coupled via radio frequency (RF) signals instead of inductive coupling. As used herein, far field refers to the distance separating the ET and the EH, which is greater than the size of the transmitter coil in the ET, and which may range, for example, from tens of centimeters to tens of meters. A wireless power transfer (WPT) system represents an example of such a far-field energy harvesting system, in which the ET sends RF power to the EH via an RF signal. A far-field wireless information and power transfer (WIPT) system represents another example, in which the ET sends RF power and information to the EH via an RF signal. Both the energy and information sent in such WIPT systems are limited by the RF to DC energy harvesting efficiency at the EH, which depends on the design of the rectifying antenna at the EH and the characteristics of the waveform sent by the ET. Ideally, the system optimizes energy and / or information transmission.

[0003] In-phase multi-sine wave signals represent the best waveforms for WPT systems because they have a flat response in the frequency domain, which is converted into a single pulse in the time domain (with proper sampling) and therefore has the highest possible crest factor (CF) or peak-to-average power ratio (PAPR). However, such in-phase multi-sine wave signals cannot transmit information and are therefore not suitable for WIPT systems. Although general orthogonal frequency division multiplexing (OFDM) signals can be used to transmit power and information, such signals are not the best choice for energy transmission, and are not the best choice for efficient power transmission on the ET side because such general OFDM signals have unpredictable peak-to-average power ratio (PAPR). In addition, OFDM demodulation requires accurate time and frequency synchronization, channel information, and highly complex signal processing, all of which are beyond the general power capabilities of EH. Therefore, there is still a need to improve RF signaling options for WIPT systems. Summary of the invention

[0004] The solution proposed in this paper provides an RF waveform that is not only suitable for power and information transmission from ET to the remote EH far field, but also synchronizable. The RF waveform of the solution proposed in this paper efficiently transmits energy to the EH and provides a low-complexity information signal, which reduces the demodulation / processing complexity at the EH. Therefore, the solution proposed in this paper improves the operating efficiency of the WIPT system in general, and the operating efficiency of the EH in particular.

[0005] According to an exemplary embodiment, a first wireless device of a wireless information and power transmission (WIPT) system includes an energy transmitter for simultaneously transmitting information and RF power to an energy harvester in a second wireless device in the WIPT system that is far-field from the first wireless device via a forward link. The transmitter includes a pulse modulation circuit and a transmission circuit. The pulse modulation circuit is configured to generate a synchronizable pulse position modulation (PPM) waveform including a plurality of pulse modulation symbols. Each of the pulse modulation symbols includes one or more pulses that are position modulated in response to information to be transmitted to the energy harvester. The transmission circuit is configured to send a synchronizable PPM waveform to the energy harvester via a forward link. At least one pulse in each symbol of the synchronizable PPM waveform is configured according to one or more synchronization constraints so that symbol synchronization can be achieved at the energy harvester.

[0006] According to an exemplary embodiment, a method simultaneously transmits information and RF power from an energy transmitter of a first wireless device in a wireless information and power transmission (WIPT) system to an energy harvester in a second wireless device in the WIPT system that is far field from the first wireless device via a forward link. The method includes generating a synchronizable pulse position modulation (PPM) waveform including a plurality of pulse modulation symbols. Each of the pulse modulation symbols includes one or more pulses that are position modulated in response to information to be transmitted to the energy harvester. The method further includes transmitting the synchronizable PPM waveform to the energy harvester via a forward link. At least one pulse in each symbol of the synchronizable PPM waveform is configured according to one or more synchronization constraints so that symbol synchronization can be achieved at the energy harvester.

[0007] According to an exemplary embodiment, a computer program product is used to simultaneously transmit information and RF power from an energy transmitter of a first wireless device in a wireless information and power transmission (WIPT) system to an energy harvester in a second wireless device in the WIPT system that is far field from the first wireless device. The computer program product includes software instructions that, when executed on at least one processing circuit in the energy transmitter, cause the energy transmitter to perform the energy transmitter method disclosed herein. In an exemplary embodiment, a computer readable medium includes the computer program product, wherein the computer readable medium may include a non-transitory computer readable medium.

[0008] According to an exemplary embodiment, a second wireless device of a wireless information and power transmission (WIPT) system includes an energy harvester including a rectifying antenna, a power supply circuit, and a processing circuit. The rectifying antenna is configured to receive a synchronizable pulse position modulation (PPM) waveform from an energy transmitter in a first wireless device in a far field of the second wireless device in the WIPT system via a forward link. The received synchronizable PPM waveform includes a plurality of pulse modulation symbols. Each of the pulse modulation symbols includes one or more pulses that are position modulated in response to information being transmitted by the first wireless device to the second wireless device. The power supply circuit is configured to generate a DC voltage in response to the RF power provided by the plurality of pulse modulation symbols in the received synchronizable PPM waveform. The processing circuit is powered by the power supply circuit in response to the generated DC voltage and is configured to synchronize the pulse modulation symbols of the received synchronizable PPM waveform to extract information from the received synchronizable PPM waveform.

[0009] According to an exemplary embodiment, a method harvests energy and retrieves information in an energy harvester of a second device of a wireless information and power transmission (WIPT) system. The method includes receiving a synchronizable pulse position modulation (PPM) waveform from an energy transmitter in a first wireless device in a far field from a second wireless device in the WIPT system via a forward link. The received synchronizable PPM waveform includes a plurality of pulse modulation symbols. Each of the pulse modulation symbols includes one or more pulses that are position modulated in response to information being transmitted by the first wireless device to the second wireless device. The method further includes generating a DC voltage in response to RF power provided by a plurality of pulse modulation symbols in the received synchronizable PPM waveform. The method further includes synchronizing the pulse modulation symbols of the received synchronizable PPM waveform to extract information from the received synchronizable PPM waveform in a processing circuit powered by a power supply circuit in response to the generated DC voltage.

[0010] According to an exemplary embodiment, a computer program product is used to control an energy harvester in a second wireless device of a wireless information and power transfer (WIPT) system. The computer program product includes software instructions that, when executed on at least one processing circuit in the energy harvester, cause the energy harvester to perform the energy harvester method disclosed herein. In an exemplary embodiment, a computer readable medium includes the computer program product, wherein the computer readable medium may include a non-transitory computer readable medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 An exemplary waveform structure is shown.

[0012] Figure 2An exemplary construction of modulation symbols with synchronization pulses at even and odd positions of a PPM waveform is shown.

[0013] Figure 3 A block diagram of an exemplary WIPT system is shown in accordance with an exemplary embodiment.

[0014] Figure 4 A block diagram of an exemplary ET and EH is shown according to an exemplary embodiment.

[0015] Figure 5 An exemplary ET method according to an exemplary embodiment is shown.

[0016] Figure 6 An exemplary EH method according to an exemplary embodiment is shown.

[0017] Figure 7 An exemplary Gabor pulse is shown.

[0018] Figure 8 Exemplary waveforms for time division duplexing for forward and reverse links are shown according to an exemplary embodiment of the solution proposed herein.

[0019] Fig. 9 An enlarged diode voltage-current characteristic is shown.

[0020] Fig.10 Back-to-back sync pulses due to even sign flips are shown. DETAILED DESCRIPTION

[0021] Because wireless information and power transmission (WIPT) systems transmit power and information, such systems are very different from traditional wireless communication systems that only focus on information transmission. Various factors, such as rectenna design, signal waveform design, etc., control the energy conversion efficiency of such WIPT systems. Even with advanced rectenna design, there is a basic trade-off between the effectiveness of energy transmission and the effectiveness of information transmission. Therefore, it is impossible to optimize both energy transmission and information transmission. Because the WIPT system is most limited by its energy transmission efficiency, for example, because the energy transmission efficiency defines how much energy can be used to power the EH, the solution proposed in this article seeks to optimize the RF energy transmission efficiency while keeping in mind the information transmission requirements. The solution proposed in this article also seeks to reduce the complexity of the signal processing required at the EH so as to indirectly improve the overall energy efficiency, for example, by reducing the energy demand / consumption of the EH. To this end, the solution proposed in this article uses pulse position modulation (PPM) to generate a forward link PPM waveform, which not only efficiently transmits RF energy, but also reduces the complexity of signal processing at the EH.

[0022] In order to better understand the details of the solution proposed in this paper, the PPM waveform is roughly explained below. Figure 1 As shown, the PPM waveform includes multiple frames, and the duration of each frame is T f seconds. Each frame has N s The duration is T s The symbol for seconds, where T f =N s T s . Each symbol has N c time slots (also called slices), with a time slot duration of T c seconds, where when D bits of information are transmitted, the symbol alphabet size is Q = 2 D When N c =2 D PPM places a single pulse in one of the time slots at a coded position corresponding to the information to be transmitted. Therefore, the resulting PPM waveform will have lower processing complexity.

[0023] It is known that PPM waveforms are prone to synchronization errors, which will reduce system performance. Therefore, the solution proposed in this article provides a synchronizable PPM waveform. The WIPT system can achieve synchronization at different levels of the waveform, such as frame synchronization, symbol synchronization, and / or time slot synchronization. With frame synchronization, the frame boundary is set so that the demodulation information will be in a predefined structure and semantics. With symbol synchronization, the symbol boundary is set so that the PPM waveform can be correctly demodulated. With time slot synchronization, the time slot boundary is set to maximize the signal-to-noise ratio (SNR) for demodulation. Although each of these synchronization levels is important, symbol synchronization has been proven to be the most critical and challenging. Therefore, the solution proposed in this article uses a synchronizable PPM waveform to transmit RF power and information, wherein at least one pulse in each symbol of the synchronizable PPM waveform is configured according to one or more synchronization constraints to enable at least symbol synchronization at the EH. As further discussed below, exemplary synchronization constraints include the use of guard symbols and the position of synchronization pulses in a specified synchronization slot in a PPM waveform (e.g., in slot zero of each symbol), and symbol flipping.

[0024] Figure 3A block diagram of a WIPT system 10 according to an exemplary embodiment disclosed herein is shown. The WIPT system 10 includes a first wireless device 100 and a second wireless device 200 in a far field from the first wireless device 100. The first wireless device 100 includes an energy transmitter (ET) 110 and a receiver 120, and the second wireless device 200 includes an energy harvester (EH) 210 and a transmitter 220. As further described below, the ET 110 acts as an information transmitter as well as an energy transmitter, and the EH 210 also acts as an information acquirer as well as an energy harvester. The ET 120 sends a synchronizable PPM waveform to the EH 210 via a forward link 20 (or downlink), and the transmitter 220 in the second wireless device 200 sends a waveform including information to the receiver 120 in the first wireless device 100 via a reverse link 30 (or uplink), for example, in response to information received from the ET 110. Although not required, it should be understood that the reverse link waveform sent on the reverse link 30 can have the same format as the PPM waveform sent on the forward link 20.

[0025] According to the solution proposed herein, ET 110 generates a synchronizable PPM waveform including a plurality of pulse modulation symbols. The amplitude of these symbols conveys RF power to EH 210, while the pulse modulation conveys information to EH 210. EH 210 receives the synchronized PPM waveform, generates a DC voltage from the RF power conveyed by the received PPM waveform, and synchronizes the received PPM waveform to extract information from the PPM waveform using the generated DC power.

[0026] Figure 4 1 shows a block diagram of an exemplary ET 110 and an exemplary EH 210 according to the solution proposed herein, and Figure 5 An exemplary method 300 implemented by ET 110 is shown, and Figure 6 An exemplary method 400 implemented by the EH 210 is shown. Figures 4 to 6 ET 110 includes a pulse modulation circuit 112 configured to generate a synchronizable PPM waveform (block 310). Each of the pulse modulation symbols in the synchronizable PPM waveform includes one or more pulses that are position modulated in response to information to be transmitted to EH 210. In addition, at least one pulse in each symbol of the synchronizable PPM waveform is configured according to one or more synchronization constraints to enable symbol synchronization at EH 210. Transmission circuit 114 sends the synchronizable PPM waveform to EH 210 via forward link 20 (block 320).

[0027] The EH 210 includes a rectifying antenna 212, a power supply circuit, and a processing circuit 216. The rectifying antenna 212 is configured to receive a synchronizable PPM waveform from the ET 110 via the forward link 20 (block 410). The received synchronizable PPM waveform includes a plurality of pulse modulation symbols, wherein each of the pulse modulation symbols includes one or more pulses position-modulated in response to information transmitted by the first wireless device 100 to the second wireless device 200. The power supply circuit 214 is configured to generate a DC voltage in response to RF power provided by the plurality of pulse modulation symbols in the received synchronizable PPM waveform (block 420). The processing circuit 216 is powered by the power supply circuit 214 in response to the generated DC voltage, and the processing circuit 216 is configured to synchronize the pulse modulation symbols of the received synchronizable PPM waveform to extract information from the received synchronizable PPM waveform (block 430).

[0028] Each element of the first wireless device 100 and the second wireless device 200 can be implemented in hardware (e.g., circuits, modules and / or units) and / or in software (including firmware, resident software, microcode, etc.), including an application-specific integrated circuit (ASIC). In addition, the solution proposed herein can take the form of a computer program product on a computer-usable or computer-readable storage medium, the medium having a computer-usable or computer-readable program code implemented in the medium for use by or in connection with an instruction execution system. In the context of this document, a computer-usable or computer-readable medium can be any medium that can contain, store, communicate, propagate or transport a program for use by or in connection with an instruction execution system, device or apparatus. A computer-usable or computer-readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device, apparatus or propagation medium. More specific examples of computer readable media (a non-exhaustive list) would include the following: an electrical connection having one or more wires, a portable computer disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), optical fibers, or a portable compact disc read-only memory (CD-ROM). Note that the computer usable or computer readable medium may even be paper or other suitable medium on which the program is printed, as the program may be captured electronically via, for example, optical scanning or paper or other medium, and then compiled, interpreted or otherwise processed (if necessary) in a suitable manner, and then stored in a computer memory.

[0029] Further details about exemplary PPM waveforms according to the solutions proposed herein are provided below, as well as synchronization details and details about reverse link waveforms. These details are exemplary; other implementations that fall within the scope of the general discussion above are also covered by the solutions proposed herein. It should be understood that exemplary embodiments may include one or more of these exemplary implementations.

[0030] As described above, it is preferred to optimize the energy provided by the forward link waveform. To this end, in some exemplary embodiments, the generated PPM waveform can be configured to have a high peak-to-average power ratio (PAPR) to improve energy conversion efficiency. For example, when the number of pulses in each pulse modulation symbol in the PPM waveform is less than or equal to 2, the generated PPM waveform will have a high PAPR. For example, when the alphabet size of the PPM is Q, a high PAPR means that the PAPR is greater than or equal to (Q+1) / 2, where R (the ratio of pulse slots to non-pulse slots) is 2 / (Q+1).

[0031] As also discussed above, it is preferable to reduce the complexity required to process the forward link waveform at the EH 210. To this end, the ET 110 may use Gabor pulses, such as Figure 7 As shown, each pulse modulation symbol in the pulse modulation symbols that can generate a synchronized PPM waveform in some exemplary embodiments. When Gabor pulses are used to generate a PPM waveform, the carrier and pulse width can be set independently. In addition, Gabor pulses simplify the demodulation required at the second wireless device 200.

[0032] The solution proposed herein also provides a synchronizable PPM waveform, wherein at least one pulse in each symbol of the synchronizable PPM waveform is configured according to one or more synchronization constraints to enable symbol synchronization at the EH 210. For example, each frame of the PPM waveform may include one or more pairs of composite symbols, wherein each composite symbol includes one or more guard symbols and pulse modulation symbols. At least one pulse in each composite symbol is configured according to (multiple) synchronization constraints to enable symbol synchronization at the EH 210. In an exemplary embodiment, the synchronization constraint includes including a synchronization pulse in a specified synchronization time slot in each composite symbol in the composite symbol. For example, the synchronization pulse may be included in time slot zero in each pulse modulation symbol. In another exemplary embodiment, the synchronization constraint includes appending a synchronization pulse to the corresponding pulse modulation symbol, for example, appending a synchronization pulse to the beginning of the corresponding pulse modulation symbol. Regardless of the particular constraints used, the synchronization constraints governing the synchronizable PPM waveform enable the EH 210 to synchronize the received PPM waveform, and thus demodulate and otherwise process the received PPM waveform.

[0033] In an exemplary embodiment, each composite symbol pair includes adjacent symbols, wherein one of the symbols in the composite symbol pair is an odd symbol and one of the symbols in the composite symbol pair is an even symbol. As used herein, the "even" and "odd" labels refer to the symbol numbering within a frame. Thus, symbols having even symbol numbers, e.g., 0, 2, 4, etc., represent "even" symbols in the composite symbol pair, while symbols having odd symbol numbers, e.g., 1, 3, 5, etc., represent "odd" symbols in the composite symbol pair.

[0034] One exemplary embodiment of the solution proposed herein is to order the symbols in one composite symbol of a composite symbol pair in a reversed order relative to the symbols in the other composite symbol of the pair. For example, an odd composite symbol of a composite symbol pair may include (one or more) pulse modulation symbols followed by (one or more) guard symbols, while an even composite symbol of the pair may include (one or more) guard symbols followed by pulse modulation symbols in a reversed order relative to the odd composite symbol. Figure 8 An exemplary implementation of a composite symbol pair in this embodiment is shown, the composite symbol pair includes an odd composite symbol followed by an even composite symbol, wherein the odd composite symbol includes a synchronization pulse followed by a modulation pulse and two guard symbols, and the subsequent even composite symbol starts with two guard symbols followed by a modulation pulse and a synchronization pulse. It should be understood that the solution proposed herein is not limited to Figure 8 In another exemplary embodiment, a composite symbol pair may include an even composite symbol followed by an odd composite symbol, wherein the even composite symbol includes a synchronization pulse followed by a modulation pulse and two guard symbols, and the subsequent odd composite symbol begins with two guard symbols followed by a flipped modulation pulse and then a synchronization pulse.

[0035] As described above, the second wireless device 200 transmits information to the first wireless device 100 via the reverse link 30. Such reverse link signaling may be time division duplexed with forward signaling from the first wireless device 100. For example, the transmitter circuit 220 in the second wireless device 200 may transmit a reverse link waveform via the reverse link 30, wherein the reverse link waveform is offset in time from the PPM waveform transmitted via the forward link 20 by an offset period (e.g., one or more of the odd numbers in the composite symbol). Figure 8An example of such an offset period between forward link and reverse link signaling is shown, where in this example, the offset period includes one composite symbol. Although not required, such a reverse link waveform can be configured to have the same frame structure as the PPM waveform of the forward link 20. The offset period will, for example, provide time for the first wireless device 100 to switch its antenna (not shown) between the energy transmitter 110 and the receiver 120. For example, as Figure 8 As shown, after ET 110 transmits the PPM waveform via forward link 20, first wireless device 100 may use the silent period in the offset to switch its antenna connection from ET 110 to receiver 120 to enable receiver 120 to receive the reverse link waveform.

[0036] In another exemplary embodiment, time division duplexing may be achieved by using complementary flipping, with an offset of zero or even composite symbols. For example, if the forward link uses an even flipping, e.g., the even composite symbols in the forward link composite symbol pair have pulse modulation and protection symbols in a flipped order relative to the pulse modulation and protection symbols in the odd composite symbols in the pair, then the reverse link may use an odd flipping for time division duplexing, e.g., the odd composite symbols in the reverse link composite symbol pair have pulse modulation and protection symbols in a flipped order relative to the pulse modulation and protection symbols in the even composite symbols in the pair. Similarly, if the forward link uses an odd flipping, e.g., the odd composite symbols in the forward link composite symbol pair have pulse modulation symbols in a flipped order relative to the pulse modulation symbols in the even composite symbols in the pair, then the reverse link may use an even flipping for time division duplexing, e.g., the even composite symbols in the reverse link composite symbol pair have pulse modulation symbols in a flipped order relative to the pulse modulation symbols in the odd composite symbols in the pair.

[0037] As described above, an important goal of RF energy transmission is to deliver sufficient power to the EH 210 so that the EH 210 can process the received information and send the information back to the first wireless device 100. Fig. 9 As shown, a simple diode-like nonlinear rectifier, such as may be used for rectifying antenna 212, will only be switched when the applied DC voltage exceeds a threshold voltage v TThe same concept also applies to the second wireless device 200, where the RF power provided by the PPM waveform must first be strong enough to activate the EH 210, for example, must exceed the activation threshold of the EH 210, and must further be strong enough to power the processing circuit 214 to process synchronization and extract information from the received PPM waveform, and to power the transmitter 220 to send information back to the first wireless device 100 via the reverse link 30. The solution proposed herein helps to relax the power requirements of the second wireless device 200, and therefore relax the power requirements of the WIPT system 10, because the PPM waveform disclosed herein is easy to demodulate. For example, the PPM waveform discussed herein can be processed using non-coherent or semi-coherent demodulation, which reduces the complexity associated with some processing operations, such as timing and channel estimation.

[0038] The solution proposed in this article provides multiple advantages over traditional WIPT systems. First, the disclosed synchronizable PPM waveform has a CF (or PAPR) that is closely close to the CF (or PAPR) of the in-phase multi-sinusoidal signal that is optimal for the WPT system in this article. In addition, as described above, the PPM waveform disclosed in this article uses a simple modulation / demodulation technique, which simplifies the receiver structure and thus reduces the power requirements of the EH 210. In addition, unlike traditional OFDM solutions, sending the PPM waveform disclosed in this article does not require a high linearity power amplifier in the transmitter. The PPM waveform disclosed in this article is also fully synchronizable and enables full time division duplex transmission between ET 110 and EH 210. Generating the PPM waveform disclosed in this article using Gabor pulses also simplifies carrier selection / migration and enables the EH 210 to use the received PPM waveform as a timing reference.

[0039] The following provides implementation examples consistent with the above description. It should be understood that the solutions proposed herein are not limited to these detailed examples.

[0040] An exemplary synchronizable PPM waveform is a GPPM waveform, which is constructed using Gabor pulses. The ET 110 may construct a GPPM waveform by modifying the PPM waveform according to the following constraints and extensions:

[0041] The GPPM waveform includes two types of symbols: pulse modulation symbols that carry information and energy, and non-pulse protection symbols that carry no information or energy.

[0042] The frame of the GPPM waveform contains an even number of modulation symbols.

[0043] • The duration of a modulation symbol with an alphabet size of Q extends from Q slots to (Q+1) slots.

[0044] The leading time slot in the modulation symbol, such as time slot 0, is a time slot used for synchronization pulses.

[0045] The modulation symbols in the GPPM waveform are modulated by Q-PPM following the synchronization pulse, for example, the PPM modulation pulse moves from {0, Q-1} to {1, Q}.

[0046] • Each modulation symbol is followed by two non-pulse guard symbols in a total of 2(Q+1) slots.

[0047] • The even-numbered (where counting starts at 0) modulation symbols in the GPPM waveform and the following two non-pulse guard symbols are time-reversed (flipped).

[0048] • There is an offset between the GPPM signals in the forward link and the reverse link, where the offset is two symbols, 2(Q+1) time slots.

[0049] • Due to the offset, there are (Q+1) slots of non-PPM guard symbols between the modulation symbols of the forward and reverse links, allowing sufficient silent gaps for radio switching (eg, with Rx / Tx shared antennas).

[0050] In the GPPM waveform, the modulation symbol plus the following two guard symbols can also be considered as a composite symbol, which implements a subset of the 2MPPM symbols of the alphabet 3(Q+1), where the constraints are set so that the pilot slot is always a pulse slot and the remaining 1 pulse is limited to the {1,Q} slot for modulation. The time-reversed even symbols include another mirrored subset of 2MPPM. Figure 8 Three GPPM modulation symbols are shown at alternating even and odd positions, along with a guard symbol. Note that a time flip for an even symbol flips its pulse position.

[0051] In addition to enabling full time division duplexing (TDD) between the forward and reverse links of the WIPT radio, the GPPM waveform constructed in this way is fully synchronizable due to the back-to-back synchronization pulses and protection symbols. Although the GPPM waveform is less efficient in terms of spectral efficiency for information transmission, it actually improves the RF-DC efficiency of the rectenna. This can be seen from the PAPR of the GPPM, which is 3(Q+1)=2>Q, where the PAPR of a pure (one pulse per symbol) PPM would have a PAPR of Q. In addition, the synchronization pulse pairs in the forward / reverse link GPPM waveform can also be used for timing calibration in the WIPT radio.

[0052] Due to the predictability of the discharge (two equal level pulses within a closed interval in a composite symbol), power efficient ET can be implemented using charge pump technology for GPPM waveforms with high PAPR. Figure 8 An example of time division duplexing of forward and reverse link signals is shown, where both the time aligned forward and reverse links are transmitting a sequence of symbols (Q-1) in a Q-GPPM modulation format, where Q=4.

[0053] At ET, the pulses can be generated with a Gaussian windowed carrier signal. At EH, a low complexity detector can be implemented with envelope detection or with a digital receiver combined with a narrowband oscillator filter and baseband sampling.

[0054] For PPM waveforms, the pulse duration is limited to avoid inter-symbol interference (ISI). For the relatively narrow-band GPPM waveform in WIPT systems, the maximum channel delay spread M < <T c . Nevertheless, we can still choose T p =T c =2. Then, the pulse signal in the time slot can be viewed as 2PPM modulation. This hierarchical view of the PPM waveform gives us an additional enhancement for reliable symbol synchronization due to the flipping of even symbols.

[0055] For all odd modulation symbols, the slot is encoded as 2PPM-0 pulses.

[0056] • For all even symbols, the slot is encoded as 2PPM-1 pulse.

[0057] Therefore, if Fig.10 As shown, the flipping or time reversal of the even symbols creates a unique back-to-back synchronization pulse pair. This synchronization pulse pair greatly reduces the synchronization complexity of the GPPM waveform.

[0058] Of course, the present invention can be carried out in other ways than those specifically described herein without departing from the basic characteristics of the present invention. The embodiments of the present invention should be considered illustrative and non-restrictive in all aspects, and all changes within the meaning and equivalent range of the appended claims are intended to be included therein.

Claims

1. A first wireless device of a wireless information and power transmission (WIPT) system, the first wireless device comprising an energy transmitter for simultaneously transmitting information and RF power to an energy harvester in a second wireless device in the WIPT system that is far away from the first wireless device via a forward link, the energy transmitter comprising: a pulse modulation circuit configured to generate a synchronizable pulse position modulated (PPM) waveform comprising a plurality of composite symbols, each of said composite symbols comprising at least one synchronization pulse and one or more pulses position modulated in response to said information to be transmitted to said energy harvester; as well as A transmission circuit is configured to send the synchronizable PPM waveform to the energy harvester via the forward link.

2. The first wireless device according to claim 1, wherein: The number of pulses in each of the plurality of complex symbols of the synchronizable PPM waveform is less than or equal to two.

3. The first wireless device according to claim 1: in, Each composite symbol further includes one or more guard symbols; wherein the synchronizable PPM waveform includes a plurality of frames; and Each of the multiple frames includes at least one composite symbol pair.

4. The first wireless device according to claim 3: in, Each composite symbol pair includes an odd composite symbol and an even composite symbol; wherein each even-numbered composite symbol in the corresponding composite symbol pair comprises one or more pulse modulation symbols followed by two guard symbols; and Each odd-numbered composite symbol in the corresponding composite symbol pair follows the corresponding even-numbered composite symbol and includes two guard symbols and one or more pulse modulation symbols in a reversed order relative to the even-numbered composite symbol.

5. The first wireless device according to claim 3: in, Each composite symbol pair includes an odd composite symbol and an even composite symbol; wherein each odd-numbered composite symbol in the corresponding composite symbol pair comprises one or more pulse modulation symbols followed by two guard symbols; and Each even-numbered composite symbol in the corresponding composite symbol pair follows the corresponding odd-numbered composite symbol and includes two guard symbols followed by one or more pulse modulation symbols in a reversed order relative to the odd-numbered composite symbol.

6. The first wireless device according to claim 3: further comprising a receiver circuit configured to receive a reverse link waveform from the second wireless device via a reverse link; in, The reverse link waveform includes a plurality of reverse link frames, each reverse link frame of the plurality of reverse link frames including at least one reverse link composite symbol pair; wherein, when the even composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform includes one or more of the pulse modulation symbols in an inverted order relative to the odd composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform in the forward link, the odd composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform includes one or more of the pulse modulation symbols in an inverted order relative to the even composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform; and Wherein, when the odd-numbered composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform includes one or more of the pulse modulation symbols in an inverted order relative to the even-numbered composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform in the forward link, the even-numbered composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform includes one or more of the pulse modulation symbols in an inverted order relative to the odd-numbered composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform.

7. The first wireless device according to claim 3: in, Each frame of the plurality of frames comprises the at least one composite symbol pair; as well as The at least one position modulated pulse and the at least one synchronization pulse in each composite symbol are configured according to one or more synchronization constraints so as to enable the symbol synchronization to be achieved at the energy harvester.

8. The first wireless device according to claim 7, wherein: The one or more synchronization constraints include including each of the at least one synchronization pulse in a designated synchronization time slot in each of the composite symbols.

9. The first wireless device according to claim 8, wherein: The designated synchronization time slot comprises time slot zero in each of the composite symbols.

10. The first wireless device according to claim 7, wherein: The one or more synchronization constraints include appending each of the at least one synchronization pulse to a pulse modulation symbol within a corresponding composite symbol.

11. The first wireless device according to any one of claims 1 to 10, further comprising a receiver circuit configured to receive a reverse link waveform from the second wireless device via a reverse link, wherein the reverse link waveform is offset in time from the transmitted synchronizable PPM waveform by an offset period, and the offset period includes one or more composite symbols of an odd number of the composite symbols.

12. The first wireless device according to claim 11, wherein: The reverse link waveform has the same frame structure as the transmitted synchronizable PPM waveform and a complementary flipped orientation relative to the orientation of the forward link.

13. The first wireless device of claim 11, further comprising an antenna shared between the energy transmitter and the receiver circuit and configured to switch from one of the energy transmitter and the receiver circuit to the other of the energy transmitter and the receiver circuit during the offset period.

14. The first wireless device according to any one of claims 1 to 10, wherein: The synchronizable PPM waveform is constructed using Gabor pulses.

15. A method for simultaneously transmitting information and RF power from an energy transmitter of a first wireless device in a wireless information and power transmission (WIPT) system to an energy harvester in a second wireless device in the WIPT system that is far-field from the first wireless device via a forward link, the method comprising: generating a synchronizable pulse position modulated (PPM) waveform comprising a plurality of composite symbols, each of said composite symbols comprising at least one synchronization pulse and one or more pulses position modulated in response to said information to be transmitted to said energy harvester; as well as The synchronizable PPM waveform is transmitted to the energy harvester via the forward link.

16. The method according to claim 15, wherein: The number of pulses in each of the plurality of complex symbols of the synchronizable PPM waveform is less than or equal to two.

17. The method according to claim 15: in, Each composite symbol further includes one or more guard symbols; wherein the synchronizable PPM waveform includes a plurality of frames; and Each of the multiple frames includes at least one composite symbol pair.

18. The method according to claim 17: in, Each composite symbol pair includes an odd composite symbol and an even composite symbol; wherein each even-numbered composite symbol in the corresponding composite symbol pair comprises one or more pulse modulation symbols followed by two guard symbols; and Each odd-numbered composite symbol in the corresponding composite symbol pair follows the corresponding even-numbered composite symbol and includes two guard symbols and one or more pulse modulation symbols in a reversed order relative to the even-numbered composite symbol.

19. The method according to claim 17: in, Each composite symbol pair includes an odd composite symbol and an even composite symbol; wherein each odd-numbered composite symbol in the corresponding composite symbol pair comprises one or more pulse modulation symbols followed by two guard symbols; and Each even-numbered composite symbol in the corresponding composite symbol pair follows the corresponding odd-numbered composite symbol and includes two guard symbols and one or more pulse modulation symbols in a reversed order relative to the odd-numbered composite symbol.

20. The method according to claim 17: in, The first wireless device further includes a receiver circuit configured to receive a reverse link waveform from the second wireless device via a reverse link; wherein the reverse link waveform comprises a plurality of reverse link frames, each reverse link frame of the plurality of reverse link frames comprises at least one reverse link composite symbol pair; wherein, when the even composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform includes one or more of the pulse modulation symbols in an inverted order relative to the odd composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform in the forward link, the odd composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform includes one or more of the pulse modulation symbols in an inverted order relative to the even composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform; and Wherein, when the odd-numbered composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform includes one or more of the pulse modulation symbols in an inverted order relative to the even-numbered composite symbol in each of the at least one composite symbol pair in the synchronizable PPM waveform in the forward link, the even-numbered composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform includes one or more of the pulse modulation symbols in an inverted order relative to the odd-numbered composite symbol in each of the at least one reverse link composite symbol pair in the reverse link waveform.

21. The method according to claim 17: in, Each frame of the plurality of frames comprises the at least one composite symbol pair; as well as The at least one position modulated pulse and the at least one synchronization pulse in each composite symbol are configured according to one or more synchronization constraints so as to enable the symbol synchronization to be achieved at the energy harvester.

22. The method according to claim 21, wherein: The one or more synchronization constraints include including each of the at least one synchronization pulse in a designated synchronization time slot in each of the composite symbols.

23. The method according to claim 22, wherein: The designated synchronization time slot comprises time slot zero in each of the composite symbols.

24. The method according to claim 21, wherein: The one or more synchronization constraints include appending each of the at least one synchronization pulse to a pulse modulation symbol within a corresponding composite symbol.

25. The method according to any one of claims 15 to 24, further comprising receiving a reverse link waveform from the second wireless device via a reverse link, wherein the reverse link waveform is offset in time from the transmitted synchronizable PPM waveform by an offset period, and the offset period includes one or more composite symbols of an odd number of the composite symbols.

26. The method according to claim 25, wherein: The reverse link waveform has the same frame structure as the transmitted synchronizable PPM waveform and a complementary flipped orientation relative to the orientation of the forward link.

27. The method of claim 25, further comprising: The antenna array is switched from one of the energy transmitter and the receiver circuit to the other of the energy transmitter and the receiver circuit during the offset period.

28. The method according to any one of claims 15 to 24, wherein: The synchronizable PPM waveform is constructed using Gabor pulses.

29. A computer program product for simultaneously transmitting information and RF power from an energy transmitter of a first wireless device in a wireless information and power transmission (WIPT) system to an energy harvester in a second wireless device in the WIPT system that is far away from the first wireless device, the computer program product comprising software instructions that, when executed on at least one processing circuit in the energy transmitter, cause the energy transmitter to perform a method according to any one of claims 15 to 28.

30. A computer readable medium comprising a computer program product according to claim 29.

31. The computer readable medium of claim 30, wherein: The computer readable medium includes a non-transitory computer readable medium.

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