CN113630209A - WiFi to low-power-consumption Bluetooth (BLE) cross-technology communication method based on narrow-band decoding - Google Patents

Abstract

Translated fromChinese

本发明提出一种基于窄带解码的WiFi到低功耗蓝牙(BLE)跨技术通信方法‑‑NBee。其特征在于：当WiFi发送的802.11b信号通过BLE接收端的低通滤波器(LPF)时，虽然WiFi信号产生了失真，但是接收端滤波后的信号幅值包含有WiFi所发出信息的部分特征。利用这一特征，我们可以通过在WiFi发送端选择合适的数据内容，构造出符合BLE接收端解码条件的相位差，使接收端准确解码；本发明不需要修改发送端和接收端的任何硬件或固件，在不影响设备对标准信号收发的情况下，实现WiFi到BLE全信道的高速，可靠的跨技术通信。The present invention proposes a WiFi-to-Bluetooth Low Energy (BLE) cross-technology communication method--NBee based on narrowband decoding. It is characterized in that: when the 802.11b signal sent by WiFi passes through the low-pass filter (LPF) of the BLE receiving end, although the WiFi signal is distorted, the signal amplitude filtered by the receiving end contains part of the characteristics of the information sent by WiFi. Using this feature, we can construct a phase difference that meets the decoding conditions of the BLE receiving end by selecting the appropriate data content at the WiFi sending end, so that the receiving end can decode accurately; the present invention does not need to modify any hardware or firmware of the sending end and the receiving end. , to achieve high-speed and reliable cross-technology communication from WiFi to BLE full channel without affecting the standard signal transmission and reception of the device.

Description

WiFi to low-power-consumption Bluetooth (BLE) cross-technology communication method based on narrow-band decoding

Technical Field

The invention relates to a heterogeneous equipment cross-technology communication method based on narrow-band decoding. Specifically, when the WiFi transmits 802.11b signals by utilizing DQPSK modulation or DBPSK modulation, the phase difference between adjacent sampling points at intervals of 1us of the WiFi signals passing through a 1MHz low pass filter of a BLE receiving end can meet BLE decoding conditions by reasonably selecting the transmitted data content, so that the technical-information transmission across WiFi to BLE full channels is realized, and the method belongs to the technical field of wireless communication.

Background

The explosive growth of wireless internet of things devices has made our wireless ecosystems more and more diverse. For example, more than 40 billion Bluetooth devices and more than 15 billion WiFi devices co-exist in the ISM band at 2.4 GHz. Such coexisting heterogeneous devices cause severe cross-technology interference (CTI) and have become a major obstacle to improving network scalability and spectral efficiency.

Several studies have been presented to alleviate CTI, wherein cross-technology communication (CTC) as a very promising field of research, enables direct communication between heterogeneous devices. As an emerging technology, CTC may bring many benefits to internet of things applications. First, legacy gateways incur additional hardware cost, deployment complexity, and data ingress and egress to these gateways incur additional latency, while CTCs avoid these disadvantages. Second, CTCs enable cross-technology collaboration between heterogeneous wireless devices. Thirdly, CTC helps to reduce CTI and improve spectrum utilization.

Physical layer CTC (PHY-CTC) which has appeared in recent years achieves high throughput communication through signal simulation, which closely simulates the waveform of a signal at a receiving end by selecting an appropriate payload at a transmitting end. However, these simulation-based CTC technologies also face their own challenges. First, they are less reliable and OFDM-based simulations are easily distorted by inherent errors (e.g., simulation error due to cyclic prefix) and thus lose nearly half of the CTC packets. Secondly, due to the existence of quantization error during simulation, the target waveform can only be simulated by adopting a high-order modulation scheme such as 64QAM, which limits the use of the signal simulation method in many application occasions. Third, physical layer cross-technology communication can support only a few channels due to the strict limitations of the simulation process. For example, in WEBee, one WiFi channel can only support two ZigBee channels, while many other ZigBee channels cannot enable cross-technology communication.

These shortcomings of signal simulation based CTCs severely limit its application in many scenarios. Take WiFi to Bluetooth Low Energy (BLE) CTC as an example. For a BLE receiver, it has no fault tolerance like ZigBee, and therefore cannot tolerate any bit errors within a frame. Even if error correction codes are used, BLE loses an entire analog frame when an analog error occurs in its preamble or Access Address (AA). Furthermore, since BLE employs Adaptive Frequency Hopping (AFH) to prevent interference, when a BLE device hops to a channel that is not supported by the CTC, it cannot receive any CTC data packets. For these reasons, current signal simulation methods have not been able to well achieve reliable full-channel physical layer CTCs from WiFi to BLE.

Disclosure of Invention

The invention provides a narrow-band decoding-based WiFi-to-low-power-consumption Bluetooth (BLE) cross-technology communication method-NBee. The method can realize high-speed and high-reliability direct communication from WiFi to BLE full channels.

The invention comprises the following contents:

1. implementation of CTC using DQPSK modulation

When an 802.11b signal sent by a WiFi single path (an I path or a Q path) passes through a 1MHz low-pass filter of a BLE receiving end, the output signal has three modes: (a) when WiFi transmits alternating bits '1' and '0', the amplitude of the bit '1' filtered signal is almost always positive, and the amplitude of the bit '0' filtered signal is almost always negative. (b) When WiFi transmits continuous bit '1', the signal amplitude after the receiving end filters is always positive. (c) When WiFi transmits continuous bit '0', the signal amplitude after the receiving end filters is always negative. Therefore, when we use DQPSK modulation to transmit WiFi signals, a very special phenomenon can be obtained: although the received signal is significantly distorted after passing through the low-pass filter of BLE, the original WiFi symbol (QPSK) and its corresponding BLE sampling point are still actually in the same quadrant in the constellation diagram.

According to the above characteristics, given a WiFi symbol, we can deduce the quadrant where it is located at the BLE receiving end corresponding to the sampling point. Therefore, given two consecutive WiFi symbols, we can determine whether the phase difference between two consecutive sampling points at the receiving end is positive or negative. In other words, if we choose to transmit the proper WiFi symbol sequence, the phase difference required for correct decoding can be obtained at the BLE receiving end.

2. Implementation of CTC using DBPSK modulation

Because the DBPSK signal only has a real part, the phase difference of adjacent sampling points after BLE filtering can only be 0 or pi. This phase difference is not accurately decodable by BLE, so we need to adjust the receiving end phase difference under DBPSK modulation.

First, after passing through an ADC module at a BLE receiving end, a value of an nth sampling point used for calculating a phase difference is calculated:

s[n]＝(w(nTs)ej2π(fw-fB)nTs)*h (1)

wherein s [ n ] is the nth sampling point used by the BLE receiving end to calculate the phase difference. w (t) is a WiFi transmitting end baseband analog signal, fw is a WiFi carrier frequency, and fB is a BLE carrier frequency. Ts is the sample interval (1us) — denoted convolution, h denotes the effect of the channel and filter on the signal. Since the BLE demodulator compares the phase difference between two adjacent sampling points, we substitute n-1 intoequation 1 to obtain the value of the n-1 th sampling point as:

s[n-1]＝(w((n-1)Ts)ej2π(fw-fB)(n-1)Ts)*h

＝(w((n-1)Ts)ej2π(fw-fB)nTs ej2π(fB-fW)Ts)*h (2)

by comparing s [ n ] and s [ (n-1) ], we find that the phase difference between these two sampling points consists of two parts: (1) the phase difference between the transmit end sideband signals w (nTs) and w ((n-1) Ts) (i.e., π or 0), (2) s [ n-1] the additional phase difference due to Carrier Frequency Offset (CFO) (i.e., 2 π (fw-fB) Ts). Therefore, we can select an appropriate CFO (i.e., fw-fB) to construct a phase difference that can be accurately decoded at the BLE receiver.

Inequation 2, when the carrier frequency offset of the WiFi transmitting end/BLE receiving end is adjusted to 250KHz (i.e., fw-fB is 250KHz), the n-1 th sampling point has an additional phase difference of pi/2 (2 pi is250KHz 1/1 MHz). In this case, when WiFi transmits alternating bits, the phase difference between two consecutive sampling points at the receiving end is pi/2 (═ pi-pi/2). Similarly, when WiFi transmits the same bit, the receiving end phase difference is-pi/2 (═ 0-pi/2). These two phase differences enable the BLE decoder to accurately decode bit '1' and bit '0', respectively.

In order not to interfere with normal reception by WiFi or BLE devices, the CFO cannot be set too large. The maximum limit of CFO specified by the 802.11 standard is 232KHz, and some BLE chips have carrier frequency allowed offset values up to 250KHz, which has enough redundancy to achieve correct decoding at the BLE receiving end. Considering the versatility of the chip and the inherent CFO, we set fw-fB to 125 KHz. Such CFO values have little effect on adjacent channels due to the presence of guard bands between channels.

3. Full channel communication

According to the IEEE 802.11 and BLE4.0 standards, the center frequency of the WiFi channel and the center frequency of the BLE channel are not always coincident. For example, center frequencies of BLE channel 6(2416MHz) and WiFi channel 2(2417MHz) are offset by 1 MHz. However, we have found that even if there is a frequency offset, the NBee signal can still be correctly decoded by the BLE receiver as long as its operating channel is within the coverage of the WiFi channel. The reason for this is as follows: as can be seen from equation (1), since the CFO between WiFi and BLE (i.e., fw-fB) is an integer multiple of 1MHz, the phase change due to the presence of CFO (i.e., 2 pi (fw-fB) nTs) will be an integer multiple of 2 pi. For example, if CFO is nMHz, the phase of the nth sample point will be rotated counterclockwise by 2 pi xnMHz 1/1MHz 2n pi. When a phase is rotated by an integer multiple of 2 pi, the position of the phase in the constellation diagram does not change, so that the phase difference between adjacent sampling points does not change. Therefore, even if the transmitting end and the receiving end have carrier center frequency offset, as long as the BLE channel is in the coverage range of the WiFi channel, the decoding of the receiving end cannot be influenced.

Since the WiFi channel is 22MHz and the BLE channel is 1MHz, one WiFi channel can cover 10 or 11 BLE channels. This means that each BLE channel can be covered by one or more WiFi channels. Based on the characteristic, for a BLE device on any channel, a WiFi sending end can find a channel to communicate with the BLE device.

The WiFi-to-BLE cross-technology communication method based on narrow-band decoding has the following advantages:

(1) transparency: NBee does not need to change the hardware and firmware of the commercial chip, only the payload of the WiFi frame needs to be carefully selected. This mechanism can ensure that neither the WiFi device nor the BLE device has an effect on the reception of their respective normal signals. In contrast, other CTCs (e.g., DopplerFi) need to modify at least the firmware of WiFi or BLE.

(2) High throughput: because BLE receives NBee frames as standard BLE frames, the transmission rate of BLE can reach 1Mbps, which is 3400 times higher than that of the existing WiFi-to-BLE cross-technology communication technology.

(3) High reliability: since this method does not require signal simulation, inherent simulation errors are avoided and the reliability of NBee is much higher than that of simulation-based physical-level CTCs.

(4) Full channel communication: NBee supports inter-technology communication of all channels WiFi to BLE, with which WiFi devices can remain connected at all times regardless of which channel BLE hops to operate.

According to the invention, a physical-level WiFi-to-BLE cross-technology communication method is designed by utilizing narrow-band decoding, so that high-speed and reliable information transmission of all channels from WiFi to BLE is realized, and the limitation caused by gateway communication among heterogeneous devices is effectively avoided. The invention provides new possibility for the application of cross-technology communication in the Internet of things, and opens up a new idea for gateway-free direct communication between other heterogeneous devices.

Drawings

FIG. 1 is a design framework of NBee proposed by the present invention.

Fig. 2 is a comparison graph of a narrowband filtered signal at a receiving end and an original WiFi signal.

Figure 3 shows the characteristics of BLE filtered signals when WiFi transmits different signals.

Fig. 4 shows a phase difference suitable for decoding by a BLE receiving end, constructed by DQPSK modulation.

Fig. 5 shows a phase difference suitable for decoding at a BLE receiving end constructed by DBPSK modulation.

Fig. 6 is a diagram of full channel communication.

FIG. 7 shows an experimental setup in an embodiment of the present invention.

Figure 8 is a graph comparing the transmission rate of the present invention with prior art WiFi to BLE inter-technology communications.

Fig. 9 is a graph of frame reception rate at different transmission powers and transmission distances in accordance with the present invention.

Figure 10 is a graph of frame reception rate for all BLE channels in accordance with the present invention.

Detailed Description

In order to make the objects, technical solutions, and the like of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings.

(1) Design framework for NBee: as shown in fig. 1, NBee implements high-speed inter-technology communication from WiFi to BLE by using narrowband decoding, and its principle is to select appropriate data packet content at WiFi end for transmission, and then BLE can implement correct decoding according to appropriate phase difference between sampling points after receiving signals passing through narrowband filter. The header and the trailer of the WiFi frame cannot be selected manually, but the header and the trailer of the WiFi frame can be automatically ignored by the BLE end as noise and cannot influence the receiving of the BLE frame.

(2) Comparing the signal subjected to BLE receiving end narrow band filtering with the original WiFi signal: according to the 802.11 protocol and the BLE4.0 protocol, the bandwidth of WiFi is 22MHz, but the bandwidth of BLE is only 1 MHz. The broadband WiFi signal is necessarily distorted after passing through the narrow-band filter of BLE, but the distorted signal still has some characteristics for transmitting information, and a receiving end can extract the information. According to the DSSS specification in 802.11b, the WiFi signal is spread with bits '1' spread to 10110111000(Barker code) and bits '0' spread to 01001000111. Notably, the two sequences are complementary, and are symmetric about the x-axis in the time domain. Furthermore, the duration of each sequence is 1us, and the throughput of BLE is 1Mbps (═ 1/1us), which means that the BLE receiving end performs one phase difference calculation for decoding at each barker sequence. When two continuous sequences transmitted by WiFi are complementary, the sampling point values of BLE receiving end every 1us are opposite numbers, i.e. the phase difference is pi (as shown in fig. 2, the phase difference between sampling points s [ n-1] and s [ n ] is pi). When two continuous sequences sent by the WiFi sending end are the same, the phase difference between sampling points of the receiving end is 0. This difference in phase enables us to transfer information from WiFi to BLE.

(3) Characteristics of BLE filtered signals when WiFi sends different signals: as shown in fig. 3, we find that, no matter what the bit sequence transmitted by WiFi is, after passing through a low-pass filter of 1MHz at the BLE receiving end, the amplitude of the '1' bit portion in the signal is almost always positive, and the amplitude of the '0' bit portion is almost always negative. We can take advantage of this feature to achieve cross-technology information transfer.

(4) Constructing a phase difference suitable for decoding by a BLE receiving end by utilizing DQPSK modulation: as shown in fig. 4, if WiFi transmission is signed by '11' (located in the first quadrant), then the sample point for BLE will also be in the first quadrant (see red at time t 1). This is because the bits of the in-phase (I) branch and the quadrature (Q) branch of the WiFi transmitting end are both '1', and the I-path amplitude and the Q-path amplitude of the sampling point after filtering by the receiving end are both positive values. According to the characteristic that the symbol sent by the WiFi and the sampling point of the BLE receiving end are in the same quadrant of a constellation diagram, as long as one WiFi symbol is given, the quadrant of the sampling point corresponding to the BLE receiving end can be deduced. Therefore, given two consecutive WiFi symbols, we can determine whether the phase difference between two consecutive sampling points at the receiving end is positive or negative. In other words, if we choose to transmit the proper WiFi symbol sequence, the phase difference required for correct decoding can be obtained at the BLE receiving end.

For example, in fig. 4, when the I path of the WiFi transmitting end transmits '1, 0, 1', and the Q path transmits '1, 1, 1' (i.e. the WiFi transmits symbols '11', '01', '11') in sequence, after passing through the 1MHz low-pass filter of the BLE receiving end, the sampling points t1 and t2 are located in the first and second quadrants of the constellation diagram respectively according to the amplitude of the I/Q signal. Therefore, the phase difference between sample points t1 and t2(1us interval) is greater than 0 and less than pi, which the BLE receiving end decodes as bit '1'. Similarly, the phase difference between the sampling points t2 and t3(1us interval) is larger than-pi and smaller than 0, and the BLE receiving end can decode bit '0'.

(5) Constructing a phase difference suitable for decoding by a BLE receiving end by utilizing DBPSK modulation: fig. 5 shows the phase difference change before and after the addition of the 125KHz carrier frequency offset. In fig. 5a, WiFi transmits bit '1' and bit '0' in turn by DBPSK modulation. When the frequency offset of the loading wave is not generated, the phase difference between two adjacent sampling points of the BLE receiving end is pi, and correct decoding cannot be achieved. After a CFO of 125KHz is added to the WiFi transmitter/BLE receiver (fB-fW ═ 125KHz), the s [ n-1] sampling point is additionally rotated counterclockwise by pi/4 than the s [ n ] sampling point. Therefore, the phase difference between the two sampling points is changed from pi to 3 pi/4, and the BLE receiving end can accurately decode the bit '1'. In fig. 5b, WiFi transmits the same bits consecutively by DBPSK modulation. When no CFO is added, the phase difference between adjacent sampling points at the receiving end is 0, and correct decoding cannot be performed. But when a CFO of 125KHz is added, the phase difference changes from 0 to-pi/4, and BLE can accurately decode bit '0'.

(6) Full channel communication schematic: as shown in fig. 6,WiFi channel 6 covers 10 BLE channels, andWiFi channel 11 covers 11 BLE channels. Each BLE channel is within the coverage of one or more WiFi channels, so WiFi can maintain communication with it regardless of which channel BLE hops to.

(7) Experimental equipment in the embodiment of the invention: the NBee transmitting end is USRP N210 working under 802.11b/g protocol. The NBee receiving end is a TI CC2650 chip and works in a BLE mode. In the experiment, each CTC BLE frame consists of a preamble of one byte (10101010b), an Access Address (AA) of four bytes (0x8E89BED6), a PDU of variable length and a CRC of three bytes. The WiFi sending end respectively uses DBPSK (1Mbps) and DQPSK (2Mbps) to modulate and send signals. We set the default BLE channel to 39 (broadcast channel) and the default WiFi channel to 13. Experimental evaluation results include Bit Error Rate (BER), Frame Reception Rate (FRR), and throughput. To ensure the validity of the statistics, each data is the average result of 10 times of the same experimental scene. Under the setting of various experimental conditions such as indoor/corridor, short-distance/long-distance and mobile scenes, 1000 NBee data packets are transmitted in each experiment. The experimental platform set-up is shown in figure 7.

(8) In contrast to the prior art transmission rates: as shown in fig. 8, the data rate of freebe is only 31.5bps, which is slow because it uses the periodicity of WiFi beacons to transfer information. The data rates of DCTC and C-Morse are 41bps and 50.4bps, respectively, which use packet time to carry information. DopplerFi is a recently proposed WiFi-to-BLE CTC that utilizes Carrier Frequency Offset (CFO) to transmit information, increasing throughput to 250 bps. NBee as a physical layer CTC from WiFi to BLE can reach a transmission rate of 1Mbps, the same as the standard BLE rate. NBee throughput is more than 3400x higher than other WiFi-to-BLE CTC schemes because other schemes are packet-level and can only carry a small amount of bit data in one or more packets.

(9) Frame reception rate at different transmission power and transmission distance: we analyzed the FRR of NBee as a function of transmission distance and transmission power. In the experimental process, the distance between the WiFi sending end and the BLE receiving end is increased to 20m from 5m, and the power of the sending end is increased to 20dBm from 0 dBm. Fig. 9 shows the FRR of NBee at different transmission distances and transmission powers. When the transmission distance is close (e.g., 5m), the change in the transmission power has little effect on the FRR (always remains above 95%). When the distance is increased to 20m, FRR drops sharply with decreasing transmission power, which is only 20% at a transmission power of 0 dBm. This indicates that the transmit power of NBee has a large influence on the frame reception rate when the transmission distance is greater than 10 m. However, WiFi typically has a transmit power greater than 10dbm (e.g., for a handset), so the FRR of NBee is higher than 80% even at a distance of 20 m.

(10) Frame reception rate under all BLE channels: to verify that NBee supports full channel communication, we tested NBee performance on 40 BLE channels. During the test, WiFi works onchannel 1,channel 5,channel 9, andchannel 13 in sequence. These four WiFi channels may cover all BLE channels. As can be seen from the results of figure 10, NBee works stably on all BLE channels (FRR > 95%), even when BLE is located on the broadcast channel (channel 37,channel 38, channel 39). This is because the WiFi transmit side is much more powerful than the BLE devices, so other BLE signals on the broadcast channel have less impact on the NBee signal.

The experiments prove that: the WiFi-to-BLE cross-technology communication method based on narrowband decoding can realize reliable transmission of the WiFi-to-BLE full channel. The frame receiving rate can reach more than 95%, and the throughput can reach 1Mbps, which is 3400 times of that of the prior art at present.

Claims (3)

Translated fromChinese

1.一种基于窄带解码的WiFi到低功耗蓝牙(BLE)物理层级跨技术通信方法，其特征在于：通过合理选择WiFi发送端的数据内容，构造出经过BLE接收端1MHz低通滤波器后符合解码器解码条件的相位差，在全部BLE信道都可以实现BLE接收端的正确解码。1. a kind of WiFi based on narrowband decoding to low power bluetooth (BLE) physical level cross-technical communication method, it is characterized in that: by rationally selecting the data content of the WiFi transmitting end, after constructing the BLE receiving end 1MHz low-pass filter to meet the The phase difference of the decoding conditions of the decoder can realize the correct decoding of the BLE receiver in all BLE channels.2.根据权利要求1所述的WiFi发送端，其特征在于：发送经DQPSK调制或DBPSK调制的802.11b信号，当发送DQPSK信号时，其I/Q两路选择发送的相邻比特在经过BLE接收端1MHz滤波器后，能够使接收端相邻采样点间的相位差符合解码条件；当发送DBPSK信号时，在WiFi/BLE加上合适的载波中心频率偏移后，其选择发送的相邻比特在经过BLE接收端低通滤波器后，对应的相邻采样点相位差符合BLE解码条件。2. The WiFi transmitter according to claim 1, characterized in that: the 802.11b signal modulated by DQPSK or DBPSK is sent, and when the DQPSK signal is sent, the adjacent bits sent by its I/Q two-way selection are passed through BLE. After the 1MHz filter at the receiving end, the phase difference between adjacent sampling points at the receiving end can meet the decoding conditions; when sending a DBPSK signal, after adding the appropriate carrier center frequency offset to WiFi/BLE, it selects the adjacent sampling point to send. After the bits pass through the low-pass filter at the BLE receiving end, the phase difference between the corresponding adjacent sampling points meets the BLE decoding conditions.3.根据权利要求1所述的BLE接收端，其特征在于：当发送端选择合适的WiFi发送比特后，不论是采用DQPSK调制方式还是DBPSK调制方式，经过接收端1MHz的低通滤波器后，失真后的WiFi信号每间隔1us的相邻采样点间的相位差都满足BLE解码器的解码条件(即相位差为正时解码为比特‘1’，相位差为负时解码为比特‘0’)。3. The BLE receiver according to claim 1, characterized in that: after the transmitter selects a suitable WiFi transmission bit, whether it adopts DQPSK modulation or DBPSK modulation, after a low-pass filter of 1MHz at the receiver, The phase difference between adjacent sampling points of the distorted WiFi signal every 1us meets the decoding conditions of the BLE decoder (that is, when the phase difference is positive, it is decoded as bit '1', and when the phase difference is negative, it is decoded as bit '0'. ).

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