Patent Application
20220345235
The technology of the disclosure relates to broadcasting (i.e., transmission) and reception of television (TV) signals, and more particularly to supporting location services in TV signal compatible receivers.
Television (TV) broadcasters use high-power, high tower, terrestrial antennas to broadcast TV signals. The TV signals are modulated onto a radio frequency carrier and radiated from an antenna as over-the-air signals. The broadcast TV signals can then be received through a reception antenna of a TV signal-compatible receiver device as over-the-air signals. For example, TV broadcasters may broadcast TV signals according to the Advanced Television Systems Committee (ATSC) 3.0 standards. Alternatively, a receiver device may receive the TV signals as re-transmitted signals through a different physical transmission medium, such as a cable network or wired or wireless Internet, as examples. In either case, the TV signals can be decoded and display as visual and audio content by TV signal-compatible display devices or compatible receivers.
Satellite signal transmission is also employed in the global positioning system (GPS) for providing timing and location services. In GPS, a GPS receiver can determine its location through trilateration or multilateration based on receiving multiple satellite signals from known satellites that have known locations. The GPS receiver can calculate its position based on the differences in time-of-arrival (TOA) (and thus relative delay) in signal reception from the multiple satellites determined based on use of synchronized clocks. TV broadcasters have an advantage over satellite transmission systems by being capable of signal transmission in certain situations that may not be available, reliable, or possible for satellite signal transmission. TV broadcast signals can travel long distances and can penetrate obstacles, including man-made structures, that satellite signals cannot or may not. Weather events, such as strong winds, rain, and snow, can interfere with transmitted satellite signals and thus their reception. Moreover, TV transmission facilities are designed to operate during natural disasters. Also, most areas in the United States, for example, are in the broadcast range of multiple TV broadcaster's transmission systems and thus can receive multiple TV broadcast signals from these multiple TV broadcasters. GPS signals can also be spoofed by fake GPS transmitters that can cause a GPS receiver to incorrectly determine its position based on the spoofed GPS signals.
It may be desired for TV signal receivers to determine their position for providing location services without requiring such TV receivers to also include a GPS receiver. Even if a TV signal receiver includes a GPS receiver capable of determining position through received GPS satellite signals, it may also be desired for such TV signal receivers to have a secondary and/or fallback method of determining location without use of GPS satellite signals.
Exemplary aspects disclosed herein include broadcast positioning systems supporting location services through over-the-air (wireless) television (TV) signals. The broadcast positioning system includes a TV signal transmitter that is capable of transmitting broadcast TV signals through an antenna, including a terrestrial antenna, over-the-air to be received by compatible TV signal receivers. The transmitted TV signals can include TV-based content that is demodulated and processed by a TV signal receiver receiving the broadcast TV signals to be displayed on a visual display. The TV signal receiver can be a mobile device or a non-mobile device. In exemplary aspects disclosed herein, to support the ability of the TV signal receiver to also determine the time and its position and location without the requirement of also including a GPS receiver or other positioning system as examples, the broadcast positioning system supports inclusion of a broadcast TV signal format that includes a transmission time (e.g., a timestamp) that the broadcast TV signal is transmitted. The transmission time of the broadcast TV signal is used by the TV signal receiver to determine the time of arrival, and thus the propagation delay of the broadcast TV signal between the TV signal transmitter and its reception at the TV signal receiver. The broadcast TV signal can also include clock information used by the TV signal receiver to synchronize its clock to the TV broadcaster so that an accurate propagation delay can be calculated based on the timing information included in the received broadcast TV signal. The TV signal receiver is also configured to receive multiple broadcast TV signals from multiple TV broadcasters, wherein the same time delay of arrivals for those broadcast TV signals can be determined. The positions of the antennas of the multiple TV broadcasters that transmitted their respective broadcast TV signals are known and can be programmed to be known by the TV signal receiver. In this manner, the TV signal receiver can use the determined multiple time delays of arrival from the multiple received broadcast TV signals as multiple time-of-arrival (TOA) and the known locations of the antenna radiating these multiple broadcast TV signals to perform a trilateration or multilateration calculation to determine its position to provide location services.
However, note that the transmission time of the broadcast TV signal may be affected by a group delay (e.g., signal processing delay and delay in further downstream signal processing of the broadcast TV signal) that occurs in the TV signal transmitter after generation and insertion of the transmission time into a communication frame. Notably, a group delay refers generally to an actual transit time of a signal through multiple circuits in a device (e.g., a TV signal transmitter) as a function of respective processing frequencies (e.g., clock rate) of the multiple circuits. Specifically, in the context of the present disclosure, the group delay refers to a total delay between a time at which the transmission time is generated and inserted into the communication frame in the broadcast TV signal and a time at which the broadcast TV signal is emitted over-the-air through an antenna in the TV signal transmitter. For example, after a broadcast TV signal is framed and the transmission time is generated and inserted in the communications frame, the framed broadcast TV signal may be converted to a waveform (e.g., in-phase and quadrature (IQ) signals) at a radio frequency (or frequency band) of a broadcaster according to their TV transmission license to be transmitted as a radio-frequency (RF) signal as an over-the-air signal. This conversion incurs a signal processing delay as part of the group delay. As another example, further delay in the transmission of the broadcast TV signal can occur as another part of the group delay when the broadcast TV signal is processed by an RF transmitter circuit to create a transmission-ready RF signal. For example, the broadcast TV signal may be further processed by digital-to-analog converters (DACs), filters, amplifiers, and waveguides before being ultimately transmitted over an antenna. Thus, the group delay may include this additional signal processing delay, which differs from a propagation delay that only occurs after the broadcast TV signal is transmitted through the antenna, if the transmission time is generated before this further signal processing occurs. Thus, in other exemplary aspects disclosed herein, the transmission time can be compensated to account for an estimation of the additional signal processing delay between when the transmission time is generated and the broadcast TV signal is actually transmitted from the antenna. The group delay between when the transmission time is determined and when the broadcast TV signal is ultimately transmitted over-the-air through the antenna is compensated so that the TV signal receiver does not have to determine a propagation delay for the broadcast TV signal that includes the group delay in the TV signal transmitter, which is not truly part of the propagation delay. As another example, the transmission time included in the communication frame can be generated based on an estimate of the signal processing delay when the transmission time is generated and before the additional signal processing of the communication frame is performed to generate the broadcast TV signal.
In this manner, the broadcast positioning system allows the TV signal receiver to provide location services without the requirement to include a GPS receiver or other positioning system. The TV signal broadcaster antenna towers act like satellites in a GPS system that are in known locations and where the propagation delay of its transmitted TV signals can be used by a TV signal receiver to perform a trilateration or multilateration calculation to determine its position. As an alternative, the TV signal receiver can receive clock information from another source to synchronize its clock with the clock of the TV broadcaster. The broadcast positioning system can allow a TV signal receiver to determine its position as a secondary or backup method to other methods, such as through the GPS. For example, the TV signal receiver may be configured to determine location using the broadcast positioning system and also using the GPS through received signals in a GPS receiver. The TV signal receiver can compare the positioning calculations through both systems to determine if a significant enough disagreement between calculated positions exists to note an issue. For example, the position determined by the GPS receiver may have been based on spoofed GPS satellite signals.
In exemplary aspects disclosed herein, the broadcast positioning system and the location services made available through the same TV signal receiver may be provided through a particular TV broadcast signal format that can include delay timing information to determine delay in time of arrival. For example, the TV broadcast signal format may be according to the Advanced Television Systems Committee (ATSC) 3.0 standard as a non-limiting example. The ATSC 3.0 standard specifies delivery of content (i.e., payload) through a broadcast signal according to an ATSC 3.0 communication frame. The ATSC 3.0 communication frame includes a preamble that includes fields that allow inclusion of the transmission time, which can be edited to account for the group delay.
In another exemplary aspect, a TV signal transmitter is provided. The TV signal transmitter includes a frame circuit. The frame circuit is configured to receive communications data and generate a plurality of communication frames. Each of the plurality of communication frames includes a preamble configured to indicate a transmission time of a respective one of the plurality of communication frames. Each of the plurality of communication frames also includes a payload subframe comprising the communications data. The TV transmitter also includes a transmitter circuit. The transmitter circuit is configured to determine a group delay between a time at which the preamble is generated and a time at which the respective one of the plurality of communication frames is transmitted. The transmitter circuit is also configured to update the transmission time in the preamble in each of the plurality of communication frames to include the determined group delay. The transmitter circuit is also configured to generate a broadcast TV signal comprising the plurality of communication frames.
In another exemplary aspect, a method performed by a TV signal transmitter for support broadcast positioning service (BPS) is provided. The method includes generating a plurality of communication frames. Each of the plurality of communication frames includes a preamble configured to indicate a transmission time of a respective one of the plurality of communication frames. Each of the plurality of communication frames also includes a payload subframe comprising a communications data. The method also includes determining a group delay between a time at which the preamble is generated and a time at which the respective one of the plurality of communication frames is transmitted. The method also includes updating the transmission time in the preamble in each of the plurality of communication frames to include the determined group delay. The method also includes generating a broadcast TV signal comprising the plurality of communication frames.
In another exemplary aspect, a TV signal receiver is provided. The TV signal receiver includes a radio-frequency (RF) receiver circuit. The RF receiver circuit is configured to receive a plurality of broadcast TV signals. The TV signal receiver also includes a control circuit. The control circuit is configured to determine a plurality of propagation delays for the received plurality of broadcast TV signals, respectively. The control circuit is also configured to determine a location of the TV signal receiver based on a TDOA of the plurality of broadcast TV signals and the plurality of propagation delays, respectively.
In another exemplary aspect, a method performed by a TV signal receiver for supporting BPS is provided. The method includes receiving a plurality of broadcast TV signals. The method also includes determining a plurality of propagation delays for the received plurality of broadcast TV signals, respectively. The method also includes determining a location of the TV signal receiver based on a TDOA of the plurality of broadcast TV signals and the plurality of propagation delays, respectively.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred aspects in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.
Aspects disclosed herein include broadcast positioning systems supporting location services through over-the-air (wireless) television (TV) signals. The broadcast positioning system includes a TV signal transmitter that is capable of transmitting broadcast TV signals through an antenna, including a terrestrial antenna, over-the-air to be received by compatible TV signal receivers. The transmitted TV signals can include TV-based content that is demodulated and processed by a TV signal receiver receiving the broadcast TV signals to be displayed on a visual display. The TV signal receiver can be a mobile device or a non-mobile device. In exemplary aspects disclosed herein, to support the ability of the TV signal receiver to also determine the time and its position and location without the requirement of also including a GPS receiver or other positioning system as examples, the broadcast positioning system supports inclusion of a broadcast TV signal format that includes a transmission time (e.g., a timestamp) that the broadcast TV signal is transmitted. The transmission time of the broadcast TV signal is used by the TV signal receiver to determine the time of arrival, and thus the propagation delay of the broadcast TV signal between the TV signal transmitter and its reception at the TV signal receiver. The broadcast TV signal can also include clock information used by the TV signal receiver to synchronize its clock to the TV broadcaster so that an accurate propagation delay can be calculated based on the timing information included in the received broadcast TV signal. The TV signal receiver is also configured to receive multiple broadcast TV signals from multiple TV broadcasters, wherein the same time delay of arrivals for those broadcast TV signals can be determined. The positions of the antennas of the multiple TV broadcasters that transmitted their respective broadcast TV signals are known and can be programmed to be known by the TV signal receiver. In this manner, the TV signal receiver can use the determined multiple time delays of arrival from the multiple received broadcast TV signals as multiple time-of-arrival (TOA) and the known locations of the antenna radiating these multiple broadcast TV signals to perform a trilateration or multilateration calculation to determine its position to provide location services.
In this regard,
With continuing reference to
With continuing reference to
With reference to
However, note that the transmission time of the broadcast TV signal 106 may include additional signal processing delay that occurs in the TV signal transmitter between generation of the transmission time and its insertion into a communication frame, and delay in further downstream signal processing of the broadcast TV signal 106. For example, after the broadcast TV signal 106 is framed and the transmission time is generated and inserted in the communications frame, the framed broadcast TV signal 106 may be converted to a waveform (e.g., IQ signals) at a radio frequency (or frequency band) of broadcast station 102 according to their TV transmission license to be transmitted as a radio-frequency (RF) signal as an over-the-air signal. This conversion incurs delay. As another example, further delay in the transmission of the broadcast TV signal 106 can occur when the broadcast TV signal is processed by an RF circuit to create a transmission-ready RF signal. For example, the framed broadcast TV signal 106 may be further processed in the TV signal transmitter 104 by digital-to-analog converters (DACs), filters, amplifiers, and waveguides, such as in the waveform generation circuit 124 and the RF transmitter circuit 126, before being ultimately transmitted over an antenna. Thus, the transmission time will include this additional signal processing delay that is not truly propagation delay, only after the broadcast TV signal 106 is transmitted through the antenna if the transmission time is generated before this further signal processing occurs.
Thus, in exemplary aspects, the transmission time can be compensated by the TV signal transmitter 104 to account (e.g., remove) for an estimation of the additional signal processing time between when the transmission time is generated and the actual transmission time of the broadcast TV signal 106 over the antenna 112. The signal processing delay between when the transmission time is determined and when the broadcast TV signal 106 that is ultimately transmitted over-the-air through the antenna 112 is compensated so that the TV signal receiver 108 does not determine a propagation delay for the broadcast TV signal 106 that includes signal processing time in the TV signal transmitter 104, not truly part of the propagation delay. As another example, the transmission time included in the communication frame of the broadcast TV signal 106 can be generated based on an estimate of the signal processing delay when the transmission time is generated before the additional signal processing of the communication frame is performed to generate the broadcast TV signal 106.
In this manner, the broadcast positioning system 100 allows the TV signal receiver 108 to provide location services without the requirement to include a GPS receiver or other positioning system. The TV signal broadcaster antenna 112 towers act like satellites in a GPS system that are in known locations and where the propagation delay of its transmitted broadcast TV signals 106 can be used by the TV signal receiver 108 to perform a trilateration calculation to determine its position. As an alternative, the TV signal receiver 108 can receive clock information from another source to synchronize its clock with the clock of the TV broadcast station 102. The broadcast positioning system 100 can allow the TV signal receiver 108 to determine its position as a secondary or backup method to other methods, such as through the GPS. For example, the TV signal receiver 108 may be configured to determine location using the broadcast positioning system 100 and also using the GPS through received signals in a GPS receiver. The TV signal receiver 108 can compare the positioning calculations through both systems to determine if a significant enough disagreement between calculated positions exists to note an issue. For example, the position determined by the GPS receiver may have been based on spoofed GPS satellite signals.
In this regard, in one example, the frame circuit 122 of the TV signal transmitter 104 can be configured to receive communications data for the content 110 and generate a communication frame. As will be discussed in more detail below, by example, the communication frame can include a preamble that includes a transmission time field configured to store a transmission time indicating a time of generation of the preamble. The communication frame can also include a payload subframe comprising the communications data. A transmitter circuit 127 in the TV signal transmitter 104 can be configured to generate the broadcast TV signal 106 based on the communication frame over a signal processing time indicative of a signal processing delay in the transmitter circuit 127. The transmitter circuit 127 can be configured to transmit the broadcast TV signal 106 over the antenna 112. The frame circuit 122 is configured to generate the transmission time in a transmission time field of the communication frame based on the time of generation of the preamble and an estimate of the signal processing delay in the transmitter circuit 127.
The TV signal receiver 108 in
The communications standard used to format the broadcast TV signal 106 can be ATSC 3.0 as a non-limiting example. The ATSC 3.0 (NEXTGEN TV) system, when properly calibrated and populated with the correct information, can transmit waveforms that an ATSC 3.0 TV signal receiver can use to calculate its position and time. The system can provide the following services:
Since the ATSC 3.0 system can transmit data, TV towers can also provide the following information to augment GPS service.
Equations 802 illustrate how the group delay (τ) in the digital transmission chain 700 can be calculated such that it can be compensated in the transmission time so as to exclude the group delay from the propagation delay as perceived by a TV signal receiver. In a non-limiting example, a measurement device 804 is placed in LOS from the antenna 112 in a TV tower 806. The measurement device 804 receives the preamble at time tm, which is equal to a sum of tg, τd, τa, and τp according to a first one of the equations 802. The measurement device 804 can also calculate the propagation delay (τp) based on a third one of the equations 802. Accordingly, the measurement device 804 can determine the group delay (τ) according to a second one of the equations 802. Although the group delay (τ) is expected to be fairly constant over a period of time, practical implementations of the system will need to monitor the timing alignment continuously because timing accuracy is critical to the overall system performance For example, the measurements from the measurement device 804 can be used to automatically and continuously adjust the timing so that the emission time of the first sample of the first symbol of the bootstrap always matches the timing information carried in the preamble within the desired accuracy. The concept of a closed-loop timing error tracking and automatic timing adjustment system is discussed next in reference to
The measurement device 804 in
The BPS service can be enabled with either an existing bootstrap 202 of major and minor version 0 as defined in the ATSC 3.0 standards, or with a new bootstrap with a new set of major and minor versions. In the first instance, the solution can be a part of the NEXTGEN TV service, whereas in the second instance, with new major and minor versions, the solution will be an independent service delivered on the same frequency or channel. An advantage of the overlay broadcast positioning system discussed above to compensate for transmission time in a broadcast TV signal on existing NEXTGEN TV service is that it may be simpler to implement within regulatory constraints. However, depending on another service may mean less freedom in choosing the parameters. In contrast, an independent broadcast positioning system service using a new bootstrap can be optimized without being subject to the restrictions imposed by the ATSC 3.0 standards.
At a minimum, every TV station needs to transmit its location (e.g., World Geodetic System 1984 (WGS 84), WGS 84 XYZ, or other geodetic coordinates of latitude, longitude, and altitude) to the receiver via a PLP so that the receiver knows when and where the bootstrap was transmitted. However, the signal detection at the receiver can be made more efficient and resilient if additional information about the transmitting antenna of the TV station and its neighboring TV stations can be transmitted to the receiver. Herein, a first TV station is said to be neighboring with a second TV station if a signal(s) emitted by a respective antenna(s) of the first TV station can be received by a respective antenna(s) of the second TV station in a respective coverage area of the second TV station, regardless of whether the first TV station and the second TV station are configured to operate in same or different radio frequencies. For example, the first TV station can be configured to operate with just one transmitter and/or antenna at frequency f1 and the second TV station can be configured based on a single frequency network (SFN) configuration to operate with three transmitters and/or antennas at frequency f2. In this regard, the first TV station will still be considered by the second TV station as the neighboring TV station as long as the signal(s) emitted at frequency f1 can be received by the respective antenna(s) of the second TV station. Likewise, the three transmitters and/or antennas of the second TV station will each be considered by the first TV station as the neighboring TV station as long as the signal(s) emitted at frequency f2 can be received by the respective antenna(s) of the first TV station. Further, each of the three transmitters and/or antennas at frequency f2 will consider any other two of the three transmitters and/or antennas at frequency f2 as neighbors. In addition to the time information embedded in the preamble, the following is a desired set of data fields that will be transmitted in the PLP that is carried by subframes.
Among the parameters listed above, the SFN transmitter IDs, the timing offset, the frequency offsets, and the TDCFSs are only required for the SFN operation, while the reported bootstrap transmission time of the previous frame and the measured time-stamp reporting error of the previous frame are only required if a history of neighbor measurement errors is desired. These parameters will be further explained later in the description. All of the above values may be somewhat static except the relative bootstrap timing offset, which will need to be continually measured at the transmitting antenna.
The BPS may be utilized to provide GPS enhancement data to help speed up GPS satellite acquisition. It takes at least 12.5 minutes for a GPS receiver to retrieve a satellite's complete navigation messages, commonly known as a Master Frame. A Master Frame, which is 37500 bits long, contains satellite ephemeris, almanac, clock corrections, health indicators, etc. There is an opportunity for the TV towers to transmit information that will help the GPS receiver to lock the GPS satellites faster. The GPS almanac would be most useful in determining which satellites the GPS receiver should search for. The reference point could be the location of the TV antenna. As an additional service, the TV broadcaster can also transmit the Master Frames or parts of Master Frames.
The BPS may also be utilized to provide navigation data, such as local maps and real-time traffic information, periodically.
Notably, the transmission system needs to be synchronized with an accurate clock. Using GPS is an easy option, but it also means reliance on the GPS service. Alternatively, the transmission facility can use an accurate, independent clock. Another practical solution would be to use an accurate, free-running clock that periodically synchronizes with national atomic clocks. Using a clock that does not rely on GPS makes the broadcast positioning service more resilient when the GPS signal is compromised.
To enable BPS, a TV signal receiver can include the following capabilities:
One example of a typical receiver may include multiple tuners, one for each frequency or channel, followed by a timestamped buffer to collect the baseband samples. The receiver will demodulate the frames and extract the positioning, timing, and navigation-related information. By correlating the buffered and timestamped samples against a replica of the bootstrap, the time of arrival (TOA) of the 1st bootstrap symbol can be determined.
Since the TOA of the neighboring station would be known, the number of required tuners can be reduced by tuning to a given frequency only when a signal is expected. Another approach would be to capture the RF or I/Q samples of multiple frequency bands using a wideband receiver. Each channel can then be extracted by known digital signal processing techniques. Neighbor timing information will be helpful in this type of implementation.
Position and time in BPS can be computed using TOA and pseudo-range-based multilateration or by time difference of arrival (TDOA) based hyperbolic positioning. Although the theoretical constructs of these methods are based on the same measurements, the imperfections in system behavior and system components can make one method more accurate or efficient than the other. An RF finger-printing-based location estimation, which has a different construct than trilateration or hyperbolic positioning, is also possible.
As discussed above, the TV signal transmitter 104 is configured to compensate for the group delay incurred in the digital transmission chain 700 in
The hyperbolic positioning method can be further explained with reference to
t
1
′=t
1
+d
1
/c+Δt
t
2
′=t
2
+d
2
/c+Δt
d
2
−d
1
=c[(t2′−t1′)−(t2−t1)
The above TDOA equations involve two transmitting antennas. The set of equations for n number of transmitting antennas follows in the equations 1100 in
Since the antenna height, frequency, antenna pattern, and transmission power of the TV towers will be known, there is an opportunity to compute the location of the receiver based on electromagnetic propagation characteristics. One approach is to use a suitable propagation model that indicates the signal strength as a function of distance. Comparing the values with received signal strength will lead to approximate ranges from the TV antennas. There are other heuristic approaches that provide reasonably good estimates. For example, weighted average, based on the received signal strength level, of the coordinates of the TV tower will also provide reasonable estimates.
Accuracy of an RF fingerprinting method will be lower than trilateration or hyperbolic positioning. Position calculated by the RF fingerprinting method can be used to validate location computed by other methods.
Location computation can be optimized by using additional information that one of the methods may require.
√{square root over ((x1−x)2+(y1−y)2)}−√{square root over ((x2−x)2+(y2−y)2=cΔt12)}
√{square root over ((x1−x)2+(y1−y)2)}−√{square root over ((x3−x)2+(y3−y)2=cΔt13)}
The above equations, mathematically, will have two sets of (x, y) solutions, which means that the hyperbolas may intersect at two points A and B, as shown in
Other heuristics based on the neighbor data can also be used. For example, it is possible to choose the point closest to the centroid, which could be either geographical average ((x1+x2+x3)/3, (y1+y2+y3)/3) or weighted geographical average ((P1x1+P2x2+P3x3)/3, (P1y1+P2y2+P3y3)/3), where P1, P2, and P3 are weights computed using the transmit power levels of the TV antennas at Tower1, Tower2, and Tower3. Point A will be more likely with this approach.
In an embodiment, BPS can also be used to verify that GPS position and time are not being spoofed. This will be a basic sanity check of the GPS locations. For example, if a location computed by GPS is 90 miles away from the location computed by BPS, or if the time computed by GPS is 500 μs apart from BPS time, it can be inferred that one of the systems has been compromised.
The RF signal characteristics transmitted as neighbor data in the BPS can also be used as an additional validation method. If the surrounding tower locations, antenna patterns, bootstrap timing offsets, and transmit power levels do not agree with what is observed by the BPS receiver at the GPS computed location, it can be inferred that the GPS satellite signal has been compromised.
The detailed neighbor information transmitted in BPS can also serve as self-validation. Location computed by triangulation method can be validated with RF characteristics such as tower locations, antenna patterns, bootstrap timing offsets, and transmit power levels. Since TV service is offered by different companies on different channels, spoofing all of these pieces of interdependent information in real-time is challenging.
If the GPS signal is corrupted or spoofed in a small geographic area, the broadcast signal emitted from far away towers can be used as the validating signal even if those towers use GPS themselves. Such validation is possible because the TV towers will be outside the spoofed GPS signal area. If the TV towers use a clock reference independent of GPS, location validation will be more resilient and will work in the event of widespread GPS outage.
In addition, BPS location can also be a fallback solution when GPS is unavailable or is compromised.
The timing information transmitted by the TV antenna can be a good reference of time when two-way communication, which is required for PTP protocol, is unavailable. Below are two examples for establishing and maintaining a timescale in the receiver.
In a first example, it is possible to compute an approximate position of the receiver with 300-meter accuracy. The propagation delay between the TV antenna and the receiver can be computed, and the timing offset can be adjusted in the receiver. With 300-meter position uncertainty, the timescale will be about 1 μs accurate.
In a second example, it is possible to compute an approximate position of the receiver in case only the TV antenna coverage area is known. If the triangulated position of the receiver is unknown, the proximity of the TV station can be used for establishment of a timescale. Say a TV station's coverage area is defined by a 50-mile radius. If the receiver assumes that it is 25 miles (half of the radius) away from the TV antenna, the maximum propagation error will be 135 μs.
The BPS may also be utilized to help achieve faster GPS acquisition and more accurate position estimation by RTK. In addition, mapping, navigation, and traffic update are also possible.
The BPS aspects as described above can be extended to single frequency network (SFN) configuration, which is a kind of distributed antenna system that allows multiple geographically separated transmitters to transmit in the same channel/frequency to improve service coverage with the existing frequency resource. Notably, an SFN deployment with three or more transmitters opens up an opportunity for the operator to provide BPS service using only one frequency channel.
Although the service-related information (e.g., video and audio) transmitted from the geographically diverse towers may be the same, the control signals and the physical waveform transmitted from each tower can be different. The difference in waveforms provides an opportunity for a receiver to differentiate signals from each SFN tower and use the TOA information in location calculation. More specifically, the signals transmitted from different transmitters in the same channel/frequency can be differentiated based on timing offset, frequency offset, and/or TDCFS techniques. Notably, the SFN may be deployed based on any one or any combination of the timing offset, the frequency offset, and the TDCFS techniques.
With respect to the timing offset technique, the bootstrap transmit times of SFN transmitters can be staggered so that the bootstrap signals transmitted on the same frequency from different transmitters do not interfere with each other. Thus, a receiver can potentially measure the bootstrap TOA of all the transmitters in the SFN system. Armed with the SFN transmitters' IDs (xmtr_id) and bootstrap timing data (tx_time_offset), which can be sent to the receiver along with the tower locations, a receiver can find out the transmitter locations corresponding to the TOA values and thus compute its location.
With respect to the frequency offset technique, transmitting on the same channel/frequency with a small frequency offset is another technique to mitigate co-channel interference. Just like the timing offset, the frequency offset (tx_carrier_offset) at the transmitter acts as a differentiator of the emitted signal. If the transmitter IDs, carrier offsets, and the transmitter location are made available to the receiver, the receiver can distinguish the TOAs of different transmitters and thus can compute the location. Current ATSC 3.0 standard does not recommend the use of frequency offset for SFN configurations, but the technique can be used if the standard recommends such configuration in the future.
With respect to the TDCFS technique, it is a predistortion technique applied to the data part of a frame excluding the bootstrap and preamble. Signals emitted from each SFN tower can be predistorted using one of the predefined all-pass filters. These TDCFS filters are defied by the num_miso_filt_codes and miso_filt_code_index parameters in the ATSC Standard, A/324, Scheduler/Studio to Transmitter Link. If the mapping of TDCFS and SFN tower is made available to the receiver, the receiver can figure out which TDCFS is the most likely one for the channel, and hence it can identify the corresponding transmitter. This method, however, is less reliable than other above-mentioned methods, but it can be used as a validation of other methods.
Although the transmitter IDs, timing offsets, frequency offsets, and TDCFS codes should be adequate to identify a transmitter, the receiver can additionally use the intelligence gathered from the neighbor tower measurements to identify the SFN towers. If multiple neighboring TV towers report the bootstrap emission time of a stand-alone or SFN transmitter, a receiver can compute an approximate location of that transmitter using observed time difference of arrival (OTDOA) technique. The receiver can then identify the matching transmitter location mentioned in the neighbor measurement report and associate a TOA with it. This method can also be applied by the receiver to cross-check and validate the integrity of the neighbor measurement reports.
In an embodiment, it is possible to employ a directional antenna at the receiver to help the receiver to effectively scan for different bootstrap signals transmitted from different SFN antennas. Since the SFN towers will be geographically separated, directional antennas at the receiver can help mitigate the co-channel interference while measuring TOAs of the bootstrap signals transmitted on the same frequency. A smart antenna that is capable of beam steering can be effectively used to scan for the different bootstrap signals that impinge on the receiver from different directions.
In an embodiment, it is possible to improve accuracy of a location calculation by taking into consideration a history of neighbor measurement errors. Although the calibration of the transmission chain and the error compensation by the tracking loop will help reduce the error between the actual transmission of the bootstrap and the transmission time reported in the preamble, there will be some residual error which will directly impact the accuracy of the location calculation. One way to mitigate the inaccuracy is to report previous frame's time reporting error to the receiver. The receiver can apply this correction to the previous set of measurements and compute a more accurate location after receiving the next frame.
As an example, say the transmission time-stamps reported in the preambles of signals from 4 towers have +100 ns, −150 ns, −200 ns, and +250 ns errors. Assume that there is no multipath and that the receiver is able to detect the TOAs within 20 ns accuracy. In this scenario, the time reporting error will introduce location inaccuracies which is much greater than the inaccuracy introduced by the 20 ns TOA uncertainty. Based on the tower geometry and geometric dilution of precision (GDOP), let us say the location error is 180 meters instead of the expected bound of 18 meters. However, if the time reporting error of the previous frame is reported in the next frame after 250 ms, assuming 250 ms frame length, the receiver can recompute the location and achieve 18 meters of accuracy. However, the receiver, in this case, has to wait for the next frame to compute the more accurate location. In this sort of operation, the receiver will be able to compute a less accurate location immediately but will be able to compute a more accurate location for the same set of TOA measurements a frame later.
Although the measurement report is assumed to be delivered via the broadcast chain, the BPS solution as described herein can also work if the measurement report is delivered to the receiver via the Internet. For the internet implementation, the individual towers will send the measurement report to a server. A receiver will retrieve the relevant measurement reports from the server in case the receiver is connected to the Internet. The broadcast plus internet implementation will provide higher yield in location computation. The bootstrap signal, which is used for TOA measurement, is detectable around −12 dB SNR, but the measurement report requires at least −6 dB SNR to be delivered on the broadcast chain. For example, a receiver detects 3 bootstrap TOA values at −7 dB SNR. Since preambles can be detected and decoded around −9 dB SNR, the receiver will also be able to decode the time-stamps of the bootstrap transmission times. However, the receiver will not have the location of the transmitting antennas as the signal that delivers that information will be too weak to decode. Without internet connection, the receiver will be unable to compute a location. However, if the measurement reports are delivered over the Internet, the receiver will be able to compute a location. Further, the broadcast plus internet implementation will be more resilient to spoofing because of the redundancy.
The TV signal transmitter 102 in
The TV signal transmitter 102 is configured to generate a plurality of communication frames each including a preamble configured to indicate a transmission time of a respective one of the plurality of communication frames and a payload subframe that includes a communications data (block 1302). The TV signal transmitter 102 is also configured to determine a group delay (τ) between a time at which the preamble is generated and a time at which the respective one of the plurality of communication frames is transmitted (block 1304). The TV signal transmitter 102 is also configured to update the transmission time in the preamble in each of the plurality of communication frames to include the determined group delay (τ) (block 1306). The TV signal transmitter 102 is further configured to generate a broadcast TV signal including the plurality of communication frames (block 1308).
The TV signal receiver 108 in
The TV signal receiver 108 is configured to receive a plurality of broadcast TV signals (block 1402). The TV signal receiver 108 is also configured to determine a plurality of propagation delays for the received plurality of broadcast TV signals, respectively (block 1404). Accordingly, the TV signal receiver 108 is further configured to determine a location of the TV signal receiver 108 based on a TDOA of the plurality of broadcast TV signals and the plurality of propagation delays, respectively (block 1406).
The processor-based system 1500 may be a circuit or circuits included in an electronic board card, such as a printed circuit board (PCB), a server, a personal computer, a desktop computer, a laptop computer, a personal digital assistant (PDA), a computing pad, a mobile device, or any other device, and may represent, for example, a server, or a user's computer. In this example, the processor-based system 1500 includes the processor 1502. The processor 1502 represents one or more processing circuits, such as a microprocessor, central processing unit, or the like. The processor 1502 is configured to execute processing logic in instructions for performing the operations and steps discussed herein. Fetched or prefetched instructions from a memory, such as from a system memory 1510 over a system bus 1512, are stored in an instruction cache 1508. The instruction processing circuit 1504 is configured to process instructions fetched into the instruction cache 1508 and process the instructions for execution. These instructions fetched from the instruction cache 1508 to be processed can include loops that are detected by the loop buffer circuit 1506 for replay based on prediction of one or more loop characteristics as loop characteristic predictions.
The processor 1502 and the system memory 1510 are coupled to the system bus 1512 and can intercouple peripheral devices included in the processor-based system 1500. As is well known, the processor 1502 communicates with these other devices by exchanging address, control, and data information over the system bus 1512. For example, the processor 1502 can communicate bus transaction requests to a memory controller 1514 in the system memory 1510 as an example of a slave device. Although not illustrated in
Other devices can be connected to the system bus 1512. As illustrated in
The processor-based system 1500 in
While the non-transitory computer-readable medium 1532 is shown in an exemplary embodiment to be a single medium, the term “computer-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that stores the one or more sets of instructions. The term “computer-readable medium” shall also be taken to include any medium that is capable of storing, encoding, or carrying a set of instructions for execution by the processing device and that causes the processing device to perform any one or more of the methodologies of the embodiments disclosed herein. The term “computer-readable medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical medium, and magnetic medium.
The embodiments disclosed herein include various steps. The steps of the embodiments disclosed herein may be formed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, the steps may be performed by a combination of hardware and software.
The embodiments disclosed herein may be provided as a computer program product or software that may include a machine-readable medium (or computer-readable medium) having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the embodiments disclosed herein. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes a machine-readable storage medium (e.g., ROM, random access memory (“RAM”), a magnetic disk storage medium, an optical storage medium, flash memory devices, etc.); and the like.
Unless specifically stated otherwise and as apparent from the previous discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing,” “computing,” “determining,” “displaying,” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data and memories represented as physical (electronic) quantities within the computer system's registers into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission, or display devices.
The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatuses to perform the required method steps. The required structure for a variety of these systems will appear from the description above. In addition, the embodiments described herein are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the embodiments as described herein.
Those of skill in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the embodiments disclosed herein may be implemented as electronic hardware, instructions stored in memory or in another computer-readable medium and executed by a processor or other processing device, or combinations of both. The components of the distributed antenna systems described herein may be employed in any circuit, hardware component, integrated circuit (IC), or IC chip, as examples. Memory disclosed herein may be any type and size of memory and may be configured to store any type of information desired. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. How such functionality is implemented depends on the particular application, design choices, and/or design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. Furthermore, a controller may be a processor. A processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).
The embodiments disclosed herein may be embodied in hardware and in instructions that are stored in hardware and may reside, for example, in RAM, flash memory, ROM, Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a remote station. In the alternative, the processor and the storage medium may reside as discrete components in a remote station, base station, or server.
It is also noted that the operational steps described in any of the exemplary embodiments herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the exemplary embodiments may be combined. Those of skill in the art will also understand that information and signals may be represented using any of a variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips, that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields, or particles, optical fields, or particles, or any combination thereof.
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since modifications, combinations, sub-combinations, and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 63/180,345, filed Apr. 27, 2021, and U.S. Provisional Patent Application Ser. No. 63/242,618, filed Sep. 10, 2021, the disclosures of which are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 63242618 | Sep 2021 | US | |
| 63180345 | Apr 2021 | US |
