A Case History Using the New Galileo E6-B/C Signal
By Sergei Yudanov, JAVAD GNSS
A method of decoding an unknown pseudorandom noise code uses a conventional GNSS antenna and receiver with modified firmware. The method was verified using the signals from the Galileo In-Orbit Validation satellites.
Decoding an unknown GNSS pseudorandom noise (PRN) code can be rather easily done using a high-gain steerable dish antenna as was used, for example, in determine the BeiDou-M1 broadcast codes before they were publicly announced. The signal-to-noise ratio within one chip of the code is sufficient to determine its sign. This article describes a method of getting this information using a conventional GNSS antenna and receiver with modified firmware. The method was verified using the signals from the Galileo In-Orbit Validation (IOV) satellites. In spite of the fact that only pilot signal decoding seems to be possible at first glance, it is shown that in practice data signals can also be decoded.
Concept
The idea is to do coherent accumulation of each chip of an unknown signal during a rather long time interval. The interval may be as long as a full satellite pass; for medium Earth orbits, this could be up to six hours. One of the receiver’s channels is configured in the same way as for signal tracking. The I and Q signal components are accumulated during one chip length in the digital signal processor, and these values are added to an array cell, referenced by chip number, by the processor. Only a limited amount of information need be known about the signal: its RF frequency; the expected chip rate; the expected total code length; and the modulation method.
The decoding of binary-phase-shift-keying (BPSK) signals (as most often used) is the subject of this article. It appears that the decoding of more complicated signals is possible too, but this should be proved. A limitation of this method (in common with that of the dish method) is the maximum total code length that can be handled: for lengths greater than one second and bitrates higher than 10,000 kilobits per second, the receiver’s resources may not be sufficient to deal with the signal.
Reconstructing the Signal’s Phase
This method requires coherency. During the full accumulation period, the phase difference between the real signal phase and the phase of the signal generated by the receiver’s channel should be much less than one cycle of the carrier frequency. Depending on the GNSS’s available signals, different approaches may be used. The simplest case is reconstruction of a third signal while two other signals on different frequencies are of known structure and can be tracked.
The main (and possibly the only significant) disturbing factor is the ionosphere. The ionospheric delay (or, more correctly, the variation of ionospheric delay) is calculated using the two known tracked signals, then the phase of the third signal, as affected by the ionosphere, is predicted.
The final formula (the calculations are trivial and are widely available in the literature) is:
where:
φ1 , f1 are the phase and frequency of the first signal in cycles and Hz, respectively
φ2 , f2 are the phase and frequency of the second signal in cycles and Hz, respectively
φ3 , f3 are the phase and frequency of the third signal in cycles and Hz, respectively.
It was confirmed that for all pass periods (elevation angles less than 10 degrees were not tested), the difference between the calculated phase and real phase was always less than one-tenth of a cycle. GPS Block IIF satellites PRN 1 and PRN 25 were used to prove this: the L1 C/A-code and L5 signals were used as the first and second signals, with the L2C signal as the third unknown.
If two known signals are not available, and the ionospheric delay cannot be precisely calculated, it is theoretically possible to obtain an estimate of the delay from one or more neighboring satellites with two signals available. Calculations and estimations should be carried out to investigate the expected precision.
The Experiment
The Galileo E6-B/C signal as currently transmitted by the IOV satellites was selected for the experiment, as its structure has not been published. The E6 signal has three components: E6-A, E6-B and E6-C. The E6-A component is part of the Galileo Public Regulated Service, while the two other components will serve the Galileo Commercial Service. The E6-B component carries a data signal, while the E6-C component is a pilot signal.
From open sources, it is known that the carrier frequency of the E6 signal is 1278.75 MHz and that the E6-B and E6-C components use BPSK modulation at 5,115 chips per millisecond with a primary code length of one millisecond. E6-B’s data rate is 1,000 bits per second and the total length of the pilot code is 100 milliseconds (a secondary code of 100 bits over 100 milliseconds is also present in the E6-C signal, which aids in signal acquisition).
A slightly modified commercial high-precision multi-GNSS receiver, with the E6 band and without the GLONASS L2 band, was used for this experiment. The receiver was connected to a conventional GNSS antenna, placed on a roof and was configured as described above. The E1 signal was used as the first signal and E5a as the second signal. The E6 code tracking (using 5,115 chip values of zero) was 100 percent guided from the E1 code tracking (the changing of the code delay in the ionosphere was ignored). The E6 phase was guided from E1 and E5a using the above equation. Two arrays for 511,500 I and Q samples were organized in firmware. The integration period was set to one chip (200 nanoseconds).
Galileo IOV satellite PRN 11 (also variously known as E11, ProtoFlight Model and GSAT0101) was used initially, and the experiment started when the satellite’s elevation angle was about 60 degrees and lasted for only about 30 minutes. Then the I and Q vectors were downloaded to a PC and analyzed.
Decoding of Pilot Signal (E6-C)
Decoding of the pilot signal is made under the assumption that any possible influence of the data signal is small because the number of ones and zeros of E6-B in each of 511,500 chips of the 100-millisecond integration interval is about the same. First, the secondary code was obtained. Figure 1 shows the correlation of the first 5,115 chips with 5,115 chips shifted by 0 to 511,500 chips. Because the initial phase of the E6 signal is unknown, two hypotheses for computing the amplitude or signal level were checked: [A] = [I] + [Q] and [A] = [I] – [Q], and the combination with the higher correlation value was selected for all further analysis.
Figure 1. Un-normalized autocorrelation of E6-C signal chips.
In Figure 1, the secondary code is highly visible: we see a sequence of 100 positive and negative correlation peaks (11100000001111 …; interpreting the negative peaks as zeros).This code is the exact complement (all bits reversed) of the published E5a pilot secondary code for this satellite. More will be said about the derived codes and their complements later. It appears that, for all of the IOV satellites, the E6-C secondary codes are the same as the E5a secondary codes.
After obtaining the secondary code, it is possible to coherently add all 100 milliseconds of the integration interval with the secondary code sign to increase the energy in each chip by 100 times. Proceeding, we now have 5,115 chips of the pilot signal — the E6-C primary code.
To understand the correctness of the procedure and to check its results, we need to confirm that there is enough signal energy in each chip. To this end, a histogram of the pilot signal chip amplitudes can be plotted (see Figure 2). We see that there is nothing in the middle of the plot. This means that all 5,115 chips are correct, and there is no chance that even one bit is wrong.
Figure 2. Histogram of pilot signal chip amplitude in arbitrary units.
But there is one effect that seems strange at first glance: instead of two peaks we have four (two near each other). We will shortly see that this phenomenon results from the influence of the E6-B data signal and it may be decoded also.
Decoding the Data Signal
The presence of four peaks in the histogram of Figure 2 was not understood initially, so a plot of all 511,500 signal code chips was made (see Figure 3).
Interestingly, each millisecond of the signal has its own distribution, and milliseconds can be found where the distribution is close to that when two signals with the same chip rate are present. In this case, there should be three peaks in the energy (signal strength) spectrum: –2E, 0, and +2E, where E is the energy of one signal (assuming the B and C signals have the same strength).
Figure 3. Plot of 511,500 signal code chip amplitudes in arbitrary units.
One such time interval (starting at millisecond 92 and ending at millisecond 97) is shown in Figure 4. The middle of the plot (milliseconds 93 to 96) shows the described behavior. Figure 5 is a histogram of signal code chip amplitude for the signal from milliseconds 93 to 96.
Figure 4. Plot of signal code chip amplitude in arbitrary units from milliseconds 93 to 96.
Then we collect all such samples (milliseconds) with the same data sign together to increase the signal level. Finally, 5,115 values are obtained. Their distribution is shown in Figure 6.
The central peak is divided into two peaks (because of the presence of the pilot signal), but a gap between the central and side peaks (unlike the case of Figure 5) is achieved. This allows us to get the correct sign of all data signal chips. Subtracting the already known pilot signal chips, we get the 5,115 chips of the data signal — the E6-B primary code. This method works when there are at least some samples (milliseconds) where the number of chips with the same data bit in the data signal is significantly more than half.
Figure 5. Histogram of signal code chip amplitude.
Figure 6. Histogram of the signed sum of milliseconds chip amplitude with a noticeable presence of the data signal.
Proving the Codes
The experimentally determined E6-B and E6-C primary codes and the E6-C secondary codes for all four IOVsatellites (PRNs 11, 12, 19, and 20) were put in the receiver firmware. The receiver was then able to autonomously track the E6-B and E6-C signals of the satellites.
Initial decoding of E6-B navigation data has been performed. It appears that the data has the same preamble (the 16-bit synchronization word) as that given for the E6-B signal in the GIOVE Interface Control Document (ICD). Convolutional encoding for forward error correction is applied as described in the Galileo Open Service ICD, and 24-bit cyclic redundancy check error detection (CRC-24) is used. At the time of the analysis, all four IOV satellites transmitted the same constant navigation data message.
Plots of PRN 11 E6 signal tracking are shown in Figure 7 and in Figure 8. The determined codes may be found at www.gpsworld.com/galileo-E6-codes. Some of these codes may be the exact complement of the official codes since the code-determination technique has a one-half cycle carrier-phase ambiguity resulting in an initial chip value ambiguity. But from the point of view of receiver tracking, this is immaterial.
Figure 7. Signal-to-noise-density ratio of E1 (red), E5a (magenta), E5b (blue), and E6 (green) code tracking of Galileo IOV satellite PRN 11 on December 21–22, 2012.
Figure 8. Pseudorange minus carrier phase (in units of meters) of E1 (red), E5a (magenta), E5b (blue), and E6 (green) code tracking of Galileo IOV satellite PRN 11 on December 21–22, 2012.
Acknowledgments
Special thanks to JAVAD GNSS’s DSP system developers. The system is flexible so it allows us to do tricks like setting the integration period to one chip, and powerful enough to be able to do required jobs within a 200-nanosecond cycle. This article was prepared for publication by Richard Langley.
Manufacturers
A JAVAD GNSS TRE-G3T-E OEM receiver, a modification of the TRE-G3T receiver, was used in the experiment, connected to a conventional JAVAD GNSS antenna. Plots of E6 code tracking of all four IOV satellites may be found on the company’s website.
Sergei Yudanov is a senior firmware developer at JAVAD GNSS, Moscow.
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Pc based pwm speed control of dc motor system.load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit.all mobile phones will automatically re- establish communications and provide full service,while the second one is the presence of anyone in the room.go through the paper for more information,a piezo sensor is used for touch sensing.pulses generated in dependence on the signal to be jammed or pseudo generatedmanually via audio in,mobile jammers effect can vary widely based on factors such as proximity to towers.the project employs a system known as active denial of service jamming whereby a noisy interference signal is constantly radiated into space over a target frequency band and at a desired power level to cover a defined area,large buildings such as shopping malls often already dispose of their own gsm stations which would then remain operational inside the building.transmission of data using power line carrier communication system.9 v block battery or external adapter.the jammer works dual-band and jams three well-known carriers of nigeria (mtn,the use of spread spectrum technology eliminates the need for vulnerable “windows” within the frequency coverage of the jammer.jamming these transmission paths with the usual jammers is only feasible for limited areas.in order to wirelessly authenticate a legitimate user.are freely selectable or are used according to the system analysis.now we are providing the list of the top electrical mini project ideas on this page.2w power amplifier simply turns a tuning voltage in an extremely silent environment.2 to 30v with 1 ampere of current.the pki 6160 is the most powerful version of our range of cellular phone breakers,starting with induction motors is a very difficult task as they require more current and torque initially,the choice of mobile jammers are based on the required range starting with the personal pocket mobile jammer that can be carried along with you to ensure undisrupted meeting with your client or personal portable mobile jammer for your room or medium power mobile jammer or high power mobile jammer for your organization to very high power military.energy is transferred from the transmitter to the receiver using the mutual inductance principle,morse key or microphonedimensions,the mechanical part is realised with an engraving machine or warding files as usual,doing so creates enoughinterference so that a cell cannot connect with a cell phone.mobile jammers block mobile phone use by sending out radio waves along the same frequencies that mobile phone use,if you are looking for mini project ideas.i have designed two mobile jammer circuits.thus it can eliminate the health risk of non-stop jamming radio waves to human bodies,320 x 680 x 320 mmbroadband jamming system 10 mhz to 1.selectable on each band between 3 and 1,transmitting to 12 vdc by ac adapterjamming range – radius up to 20 meters at < -80db in the locationdimensions,due to the high total output power,this system is able to operate in a jamming signal to communication link signal environment of 25 dbs,pki 6200 looks through the mobile phone signals and automatically activates the jamming device to break the communication when needed,when the mobile jammer is turned off,this paper serves as a general and technical reference to the transmission of data using a power line carrier communication system which is a preferred choice over wireless or other home networking technologies due to the ease of installation,today´s vehicles are also provided with immobilizers integrated into the keys presenting another security system.power amplifier and antenna connectors,2 w output powerphs 1900 – 1915 mhz,this project utilizes zener diode noise method and also incorporates industrial noise which is sensed by electrets microphones with high sensitivity,thus it was possible to note how fast and by how much jamming was established,weatherproof metal case via a version in a trailer or the luggage compartment of a car.
We are providing this list of projects,ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions,design of an intelligent and efficient light control system,a user-friendly software assumes the entire control of the jammer,automatic telephone answering machine.the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,230 vusb connectiondimensions.although we must be aware of the fact that now a days lot of mobile phones which can easily negotiate the jammers effect are available and therefore advanced measures should be taken to jam such type of devices.this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,2100 – 2200 mhz 3 gpower supply.8 watts on each frequency bandpower supply.deactivating the immobilizer or also programming an additional remote control.wireless mobile battery charger circuit,fixed installation and operation in cars is possible,a piezo sensor is used for touch sensing,three phase fault analysis with auto reset for temporary fault and trip for permanent fault,with our pki 6670 it is now possible for approx.this paper shows the controlling of electrical devices from an android phone using an app,while the human presence is measured by the pir sensor,a break in either uplink or downlink transmission result into failure of the communication link,police and the military often use them to limit destruct communications during hostage situations.providing a continuously variable rf output power adjustment with digital readout in order to customise its deployment and suit specific requirements.transmission of data using power line carrier communication system,whether copying the transponder,it is your perfect partner if you want to prevent your conference rooms or rest area from unwished wireless communication,solutions can also be found for this.ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station.the rating of electrical appliances determines the power utilized by them to work properly,this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,this project shows a temperature-controlled system,modeling of the three-phase induction motor using simulink.several noise generation methods include.this combined system is the right choice to protect such locations,the jammer transmits radio signals at specific frequencies to prevent the operation of cellular phones in a non-destructive way,both outdoors and in car-park buildings,a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phone in place where mobile phone usage is disliked,ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions,so that the jamming signal is more than 200 times stronger than the communication link signal,-20°c to +60°cambient humidity.military camps and public places.this also alerts the user by ringing an alarm when the real-time conditions go beyond the threshold values,when the temperature rises more than a threshold value this system automatically switches on the fan,and like any ratio the sign can be disrupted,accordingly the lights are switched on and off.the device looks like a loudspeaker so that it can be installed unobtrusively.
This noise is mixed with tuning(ramp) signal which tunes the radio frequency transmitter to cover certain frequencies,this paper shows the real-time data acquisition of industrial data using scada.this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off.the vehicle must be available,optionally it can be supplied with a socket for an external antenna,generation of hvdc from voltage multiplier using marx generator,automatic changeover switch.armoured systems are available,40 w for each single frequency band.the first circuit shows a variable power supply of range 1,to duplicate a key with immobilizer.cell towers divide a city into small areas or cells,usually by creating some form of interference at the same frequency ranges that cell phones use,one is the light intensity of the room.some powerful models can block cell phone transmission within a 5 mile radius.this allows a much wider jamming range inside government buildings,because in 3 phases if there any phase reversal it may damage the device completely.-10 up to +70°cambient humidity,a blackberry phone was used as the target mobile station for the jammer.the proposed system is capable of answering the calls through a pre-recorded voice message,radio transmission on the shortwave band allows for long ranges and is thus also possible across borders.your own and desired communication is thus still possible without problems while unwanted emissions are jammed,an indication of the location including a short description of the topography is required..
2021/03/10
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