System for, and the method for accurate and quick determination, in real time, of the true bearing of identification tag on radio frequency identification (RFID), connected with objects within the monitored area

PL 240 212 B1

Description of the invention

The disclosure relates generally to a system for and method for accurately and rapidly determining, in real time, a real bearing of radio frequency identification (RF) tags associated with items in a surveillance area, particularly locating and RFID tagged item tracking for inventory surveillance.

Radio frequency identification (RFID) technology is becoming increasingly important for logistics problems, material handling and inventory management in retail stores, warehouses, distribution centers, buildings and similar supervised areas. An RFID system typically includes an RFID reader, also known as an RFID developer, and preferably a plurality of such readers distributed around the surveillance area. Each RFID reader triggers one or more RFID tags in its coverage area. Each RFID tag is typically attached to or associated with a particular item, or to an item package, or to a pallet or multi-item container. Each RFID reader transmits the calling RF signal, and each RFID tag that detects the calling RF signal responds by transmitting the RF return signal. The RFID tag either optionally generates the reverse RF signal or reflects a portion of the causing RF signal in a process known as backscattering. The RF feedback signal may further encode data stored internally in the tag. The feedback signal is demodulated and decoded into data by each reader which thereby identifies, counts or otherwise interacts with the associated item. The decoded data can mean serial number, price, date, destination, other attribute (s) or any combination of attributes and so on.

An RFID tag typically includes an antenna, an energy management section, a radio section, and often a logical section, memory, or both. In earlier RFID tags, the energy management section included an energy storage device such as a battery. An RFID tag with an active transmitter is known as an active tag. An RFID tag with a passive emitter is known as a passive tag and backscatters. Advances in semiconductor technology have miniaturized electronics so much that an RFID tag can only be powered by the RF signal it receives. An RFID tag that is backscattered and provided by an embedded battery is known as a semi-passive tag.

An RFID system is often used to locate and track RFID tagged items in an inventory tracking application. For example, in order to take an inventory of RFID tagged items in a retail store, it is known to deploy at least one RFID reader in a surveillance area and then allow each reader to automatically read whether tagged items are within reach of each reader. For better RF coverage, it is known to equip each reader with an array of antenna elements which transmit the triggering RF signal as a primary transmitting beam which is electronically directed both in azimuth, e.g. 360 degrees, and elevated, e.g. about 90 degrees. and which receive the RF feedback signal as the primary receive beam from the tags.

While such known RFID inventory systems employing antenna arrays have been advantageous, it has proved difficult in practice to accurately determine, with a high degree of precision, the actual bearing, i.e. angular direction both in azimuth and elevation, of a specific tag relative to a specific reader. There is a practical limit to the number of antenna elements that can be used in each arrangement. This limitation of the antenna elements causes each primary transmission beam and each corresponding primary reception beam to have a relatively large beamwidth. In practice, it has also proved difficult to quickly determine the actual bearing of a specific tag against a specific reader in real time. The primary transmit beam is usually progressively shifted over successive periods and routed through the monitored area in the "seek" mode of operation until the reader finds the tag and takes a sample from it, with the highest or peak receive signal strength (RSS) of the primary beam receiving point by the original steering angle. Depending on the size of the monitored area, this may take a considerable amount of time as well as many primary transmit beam movements and multiple RSS samples to find each tag's peak RSS and hence the tag bearing. Determining the bearing, i.e. angular direction both in azimuth and pick up of each tag based on the peak RSS of the primary receiving beam, not only was imprecise due to the aforementioned limitation in the number of antenna elements and the relatively large beamwidth, but also slow. Row bearing errors

From 5 to 10 degrees, long delays, and limitations on the number of tags that can be located and tracked at a time have been reported and are not tolerated in many applications.

Accordingly, there is a need to more accurately determine the actual leads of RFID tags, determine the actual leads of the RFID tags faster, and reduce the delay in finding each tag with the highest RSS, and increase the number of tags that can be located and tracked at any given time.

SHORT DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING FIGURES

The accompanying figures, where like reference numerals refer to identical or functionally similar elements in all separate views, together with the detailed description below, are included and form part of the description, and serve to further illustrate the embodiments of the concepts which embody the invention as claimed and explain the various principles and principles. the benefits of these embodiments.

Fig. 1 is a schematic view of an exemplary radio frequency identification (RFID) tag reading system for accurately determining actual real-time RFID tag bearings according to the disclosure.

Fig. 2 is a perspective, schematic view of the system of Fig. 1 installed in an exemplary surveillance area, especially for inventory surveillance of RFID tagged items.

Fig. 3A is a diagram depicting the components of the overall system of Fig. 1 during transmission of the primary transmission beam.

Fig. 3B is a block diagram illustrating a detail of a weighting factor component for use in beam steering in a system.

Fig. 4 is a diagram illustrating the components of the overall system of Fig. 1 during reception of the primary receiver beam as well as additional secondary receiver beams.

Fig. 5 is a block diagram depicting signal processing of the primary and secondary reception beams depicted in Fig. 4 to obtain the actual bearing of each RFID tagged object.

Fig. 6 is a diagram illustrating bracketing for a tag bearing with the secondary receive beams in the sector of the monitored area.

Fig. 7 is a flowchart illustrating the steps performed according to the method of accurately determining the actual bearings of RFID tags associated with objects in a surveillance area in real time according to the disclosure.

Those skilled in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated with respect to other elements to help facilitate understanding of the embodiments of the invention.

The components of the system and method are represented as desired by conventional symbols in the figures, showing only those specific details which are relevant to an understanding of the embodiments of the invention so as not to obscure the disclosure with details which would be apparent to those of ordinary skill in the art using the description in this document.

DETAILED DESCRIPTION OF THE INVENTION

One object of this disclosure relates to a radio frequency (RF) identification (RFID) tag reading system for accurately and quickly determining, in real time, actual RFID tag bearings associated with items in a surveillance area. The supervised area can be a retail store, warehouse, or any other closed or open area where RFID tagged items are to be monitored. The surveillance area may be inside or outside and may be a single sector or a volume of space, or it may be, and often is, divided into multiple sectors. The system comprises an RFID reader having an array of antenna elements, e.g., a phase array; numerous RF transceivers; and a controller or programmed microprocessor operatively connected to the transceivers and operable to control the transceivers.

The controller activates a tag processing module operating to direct the primary transmit beam within a surveillance area by transmitting the primary transmit signal via the antenna elements to each tag and to direct the primary receive beam to the pier.

The target angle by receiving the original reception signal via the antenna elements from each tag. The controller also actuates a bearing processing module operable to substantially simultaneously direct a plurality of secondary yaw receive beams to a plurality of bearings in a surveillance area at multiple different secondary steering angles that deviate from the primary steering angle by receiving the plurality of secondary yaw receive signals via the antenna elements from the antenna elements. each tag. The controller processes secondary deviation receive signals to determine the true bearing for each tag in real time.

Preferably, the controller processes the signal powers of the secondary deviation receive signals to determine an approximate tag bearing for each tag in the monitored area, preferably by selecting a secondary deviation reception signal that has a peak processing signal power among all the secondary deviation reception signals. The controller selects a first pair of secondary yaw receive beams on opposite sides of the approximate tag bearing in a lift to obtain a pair of lift yaw signals, selects a second pair of secondary yaw beams on opposite sides of the approximate tag bearing in azimuth to obtain a pair of azimuth yaw signals, and then processes lift yaw signals and azimuth yaw signals, to determine the actual bearing for each tag in real time. Preferably, the bearing processing module processes the lift yaw signals by dividing their difference by their sum to obtain the lift error signal as an elevation correction for the original steering angle, and processes the azimuth deviation signals by dividing their difference by their sum to obtain the azimuth error signal as an azimuth correction for original steering angle.

In a preferred embodiment, the bearings processing module is operable to direct each secondary deviation receive beam by receiving the secondary deviation receive signals on multiple channels, e.g., four channels. A complex multiplier and a programmable complex factor determining device for the complex multiplier are provided on each channel to input a weighting factor for each channel to perform steering. All the secondary deviation receiving beams are directed to multiple leads in each sector at a time, each sector at a time. Preferably, each sector is approximately equal to the beamwidth for the original transmission beam. The system preferably comprises a server operatively connected to the RFID reader, and the beacons processing module is implemented in the RFID reader and / or the server. The RFID reader is preferably attached at the overhead location of the surveillance area and, depending on the application, multiple readers may be arranged in the surveillance area.

A method according to a further subject matter of this disclosure relates to a method of reading a radio frequency (RF) identification (RFID) tag for accurately and quickly determining, in real time, actual RFID tag bearings associated with items in a surveillance area. The method is performed by mounting an RFID reader having an array of antenna elements and a plurality of RF transceivers in a surveillance area; by controlling the transceivers by having the controller actuate a tag processing module operable to direct the primary transmit beam in a surveillance area by transmitting a primary transmit signal via antenna elements to each tag and to direct the primary receive beam to an original targeting angle by receiving the original signal receiving via the antenna elements from each tag; by controlling the transceivers by having the controller actuate a bearing processing module operable to substantially simultaneously direct a plurality of secondary yaw receive beams to a plurality of bearings in a surveillance area at multiple different secondary steering angles that deviate from the primary steering angle by receiving the plurality of secondary bias receiving signals via the antenna elements from each tag; and by processing the deviation secondary receive signals to determine the true bearing for each tag in real time. The method is preferably also performed by processing the signal power for the secondary yaw receive signals to determine an approximate tag bearing for each tag in the monitored area by selecting the first pair of secondary yaw receive beams on opposite sides of the approximate elevation tag bearing to obtain a pair of lift yaw signals. , by selecting a second pair of secondary yaw receive beams on opposite sides of the approximate tag bearing in azimuth to obtain a pair of azimuth yaw signals, and by processing the lift yaw signals and azimuth yaw signals to determine the actual bearing for each tag in real time.

PL 240 212 B1

Returning now to the figures, Fig. 1 shows a simplified illustration of a radio frequency (RF) identification (RFID) tag reading system 10 for accurately and quickly determining, in real time, actual RFID tag bearings associated with items to be tracked or monitored. System 10 has an RFID reader 20 coupled to the server or host 12 and user interface 14.

The RFID reader 20 has an array of antenna elements 1,2,3 ..., N, preferably a phase array. The RFID reader 20 also has a plurality of RF transceivers Tx / Rx 1, Tx / Rx 2, Tx / Rx 3, ... Tx / Rx N, one transceiver for each antenna element and for connection therewith. The number N is arbitrary and depends on the specific application. By way of non-limiting example, sixteen antenna elements and sixteen transceivers may be used. Although fig. 1 depicts one transceiver for each antenna element, this need not be the case. The number of transceivers may be different from the number of antenna elements. For example, a specific transceiver may be shared with two or more antenna elements.

A controller or programmed microprocessor 16 is operatively connected to the transceivers to control their operation. The controller 16 starts the software-based tag processing module 18 as well as starts the software-based bearing processing module 22. Modules 18 and 22 need not be software based, but either or both of them may be hardware based or may be implemented in both software and hardware. While the bearing processing module 22 is depicted in Fig. 1 as being implemented in the RFID reader 20, it should be understood that the bearing processing module 22, in whole or in part, may also be implemented in the server 12.

Fig. 2 is an exemplary depiction of an RFID reader 20 deployed in a retail level surveillance area 102 having a point of sell (POS) point 108 at which a server 12 and interface 14 having a fitting room 110 and a plurality of items may be provided. tagged with RFID tags, e.g., clothes 106, handbags 104, etc. arranged on shelves, hangers, racks, on the floor, etc. in the surveillance area 102. It should be understood that in some applications the server 12 is preferably located in a back office, away from the sales level. Each RFID tagged item 104, 106 is preferably associated with a passive RFID tag for cost reasons, although other types of RFID tags as described above may be used. It should further be understood that in certain applications, such as in a warehouse, each RFID tag is associated with a pallet or multi-item container. To simplify the figure, only one reader 20 is illustrated, with reader 20 being illustrated as preferably positioned above the ceiling in the surveillance area 102. It should further be understood that more than one reader 20 may be deployed in the surveillance area 102 and not necessarily distributed over the surveillance area 102. the ceiling. Each reader 20 may be AC ​​power, power over Ethernet (POE), or battery power.

The server 12 includes one or more computers and is in wired, wireless, direct, or network communication with the interface 14 and with the reader 20. The interface 14 provides a human / machine interface, e.g. presents information in picture and / or text form (e.g. representations of RFID tagged items 104, 106) for a human user and to initiate and / or alter the implementation of various processes that may be performed by the server 12 and / or by the controller 16. The server 12 and interface 14 may be separate hardware devices and include, for example, a computer, monitor, keyboard, mouse, printer, and various other hardware peripherals, or may be integrated into a single hardware device such as a mobile smartphone, portable tablet, or laptop computer. . Moreover, the user interface 14 may be on a smartphone or tablet etc., while the server 14 may be a computer or located in a surveillance area 102 (see Fig. 2) containing items 104, 106 tagged with RFID tags, either remotely at some other location or may be hosted on a cloud server. The server 12 may include a wireless RF transceiver that communicates with the reader 20. For example, Wi-Fi and Bluetooth® are open wireless standards for data exchange between electronic devices.

In operation, the controller 16 activates the tag processing module 18 by which the transceivers are commanded to act as a primary transmit beam steering unit operating to direct the primary transmit beam into surveillance area 102 by transmitting the primary transmit signal (X) via the antenna elements to each tag. As shown in Fig. 3A, the original transmission signal (X) is guided along different lines

Channels (four in this example) to a plurality of RF transceivers Tx / Rx 1, Tx / Rx 2, Tx / Rx 3 and Tx / Rx 4 and in turn to a plurality of antenna elements 1, 2, 3 and 4. Steering is accomplished by inputting a different weighting factor W1, W2, W3 and W4 on each channel. As shown in Fig. 3B, each weighting factor is generated by the complex multiplier 24 and a programmable device 26 that determines the complex factor for the complex multiplier 24 to perform baseband steering of the primary transmit beam. Baseband targeting of the primary transmit beam by setting a complex coefficient for each complex multiplier 24 is known in the art, and its details may be obtained, for example, by reference to US Patent 8,587,495 and / or to "A Primer on Digital Beamforming" by Toby Haynes, in Spectrum Signal Processing, March 26, 1998, and the entire contents of the patent and primer are hereby incorporated by reference.

In operation, the controller 16 also activates the tag processing module 18 by which the transceivers are instructed to act as primary receiver beam steering unit operating to direct the primary receiver beam to its original targeting angle by receiving the original receive signal (A) via the means antennas from each tag. As shown in Fig. 4, the antenna elements 1, 2, 3 and 4 receive feedback from each called tag along different channels (four in this example) and feedback signals from these four channels are respectively routed to a plurality of RF transceivers Tx / Rx 1, Tx / Rx 2, Tx / Rx 3, and Tx / Rx 4. Another weighting factor W1, W2, W3, and W4 is input on each channel before all weighted feedback signals are summed in an adder 28 to generate a primary receive signal (A). Each weighting factor is generated by the circuit of Fig. 3B. The directing of the primary receiver beam is accomplished by the weighting factors W1, W2, W3 and W4. As illustrated, the weighting factors (Fig. 4) used in primary receive beam steering are, in a preferred embodiment, the same as the weighting factors (Fig. 3A) used in primary transmit beam steering. As a result, the steering angle for both the primary transmitting beam and the primary receiving beam is the same or almost the same, i.e. they share a common antenna radiation axis or overall bearing. However, it should be understood that the weighting factors used in directing the primary transmit beam may be different from the weighting factors used in directing the primary transmit beam, in which case the targeting angle for the primary transmit beam is different from the targeting angle for the primary receive beam.

As described above, the practical limitation of the number of N antenna elements that can be used in the known arrangement causes each of the original transmission beam and the corresponding primary receiving beam to have a relatively large beamwidth, thus making it difficult in practice to accurately determine the actual bearing, i.e. angular direction in both azimuth and elevation for a specific tag relative to the reader. Bearing errors of the order of 5 to 10 degrees have been reported and are not tolerated in many applications. One object of this disclosure is to reduce such errors, preferably to less than one degree. As also described above, the primary transmit beam is typically progressively shifted over successive periods and routed through the surveillance area in the "seek" mode of operation until a reader finds the tag and takes a sample therefrom, with the highest or peak receive primary receive beam (RSS) power. at the original steering angle. Depending on the size of the monitored area, this may take a considerable amount of time as well as many primary transmit beam movements and multiple RSS samples to find each tag's peak RSS and hence the tag bearing. Long delays and limitations on the number of tags that can be localized and tracked at any given time have been reported and are not tolerated in many applications. A further object of this disclosure, therefore, is to reduce such delays and increase the number of tags that can be located and tracked at any given time.

According to this disclosure, and as further illustrated in Fig. 4, the feedback signals from each called tag from the antenna elements 1, 2, 3 and 4 are routed via respective RF transceivers Tx / Rx 1, Tx / Rx 2, Tx / Rx 3 , Tx / Rx 4, to the splitter 30, and then routed to a plurality of the N sub-circuits to simultaneously generate a plurality of different secondary reception signals 1 ... N to form a plurality of different secondary reception beams that are deviating from the primary reception beam. Thus, feedback signals are routed from the splitter 30 to the first set of weighting factors W11, W21, W31 and W41, before being added together at the first adder 32 to generate a first secondary reception signal 1 at the power of the first received signal RSS1; to a second set of weighting factors W12, W22, W32, and W42 before being summed

At a second adder 34 to generate a second secondary reception signal 2 with the power of the second received signal RSS2; and so on to additional sets of weighting factors and additional adders to generate additional secondary receive signals with the powers of the additional received signals until they are applied to the last set of weighting factors W1N, W2N, W3N and W4N before summing them in the last adder 38 to generate the last a secondary receive signal N with the strength of the last received signal RS SN.

Each set of weighting factors depicted in FIG. 4 for secondary receive signals is generated by a circuit identical to that depicted in FIG. 3B.

As best illustrated in Figure 6, each set of weighting factors for the secondary reception signals is selected to substantially simultaneously direct all the secondary receiving beams of the deviation to a plurality of bearings in representative sector 60 of the surveillance area at one point in time at multiple different secondary steering angles that are deflected. from the original steering angle. As shown by way of non-limiting example, sector 60 has a 4 x 5 pattern of twenty bearings at which the secondary deviation receive beams are simultaneously directed. Preferably, each sector is approximately equal to the beamwidth for the original transmission beam. Successively adjacent bearings along the azimuth are spaced approximately 10 °, and successively adjacent beams along the elevation are also spaced 10 °. The tag whose bearing is to be determined can be anywhere in sector 60 and, as shown by way of example, it is in the 4th row, 2nd column, in the approximate T tag bearing.

As described above, it is known to progressively move the primary transmit / receive beam from one bearing to the next in sector 60 to search for a tag bearing by measuring RSS at each bearing at subsequent times and then, after all these measurements have been made, determining which tag bearing had. the highest or peak RSS. Lots of movements and measurements are made, all of which increase a considerable amount of time to completion, thereby significantly delaying the final determination of the tag bearing. According to this disclosure, the primary transmit / receive beam is not progressively shifted from one bearing to the next in sector 60 at subsequent times to find a tag bearing. Instead, by simultaneously targeting all the deviation secondary receive beams at one point in time to all twenty leads in each sector 60, the RSS of all secondary receive signals can be measured, and may be the highest RSS, at any one time.

Returning to Fig. 4, all secondary receive signals 1 ... N having their respective received signal strengths RSS1, RSS2, ..., RS SN are routed to the corresponding plurality of inputs N of the multiplexer 36 having four outputs as described below. The controller 16 processes all received signal powers and selects the highest one, thus finding an approximate T tag bearing (see Fig. 6). After finding the approximate tag bearing T, the controller 16 selects a first pair of secondary deviation receive beams that define limits for raising the approximate tag bearing T to be derived from multiplexer 36, and also selects a second pair of secondary deviation receive beams that define limits for the azimuth of the approximate tag bearing T. to be output from the multiplexer 36. More specifically, one of the first pair of secondary receiver beams is formed by the secondary positive receive signal elevation (B) and is several degrees, e.g. ten degrees, in one direction from the pick-up of the approximate tag bearing, and the other of the first pair of secondary receive beams. the deviation is formed by the secondary negative receiving signal (C) of the lift and there are several degrees, e.g. ten degrees in the opposite direction from when the approximate bearing of the Tag is raised. Likewise, one of the other pair of deviation secondary receive beams is formed by the secondary positive azimuth receive signal (D) and is located a few degrees, e.g. ten degrees, in one direction from the azimuth of the approximate tag bearing, and the other from the other pair of secondary deviation receive beams. is formed by the secondary negative azimuth receiving signal (E) and has several degrees, e.g. ten degrees away from the azimuth of the approximate bearing of Tag.

Thus, as schematically shown in Fig. 6, four secondary deviation receive beams are formed. The yaw beams formed by the positive and negative lift signals (B) and (C) define the limits for the lift of the approximate bearing T tag. The yaw beams formed by the positive and negative lift signals (D) and (E) define the limits for the azimuth of the approximate bearing T tag. As shown in Fig. 4, the positive and negative elevation signals (B) and (C) and the positive and negative azimuth signals (D) and (E) are output from the multiplexer 36 and as shown in Fig. 5, the signals

The elevations (B) and (C) and the azimuth signals (D) and (E) are separately processed to obtain the azimuth bearing correction factors used to determine the actual bearing of each called tag.

Thus, the raise signals (B) and (C) are summed in the adder 40 and are subtracted from each other in the subtractor 42. The divisor 44 divides the difference (BC) from the subtractor 42 by the sum (B + C) of the adder 40, and the output from the divider 44, which is a voltage, is converted to an angle by converter 46, thereby obtaining an elevation angle error signal which is input to the bearing estimator 48. Furthermore, the azimuth signals (D) and (E) are summed in the adder 50 and are subtracted from each other in the subtractor unit 52. The divisor 54 divides the difference (DE) from the subtractor 52 by the sum (D + E) from the adder 50, and the output from the divider 54, which is a voltage, is converted to an angle by converter 56, thereby obtaining an azimuth angle error signal that is input to the bearing estimator 48. The bearing estimator 48 compares the two elevation and azimuth error signals with respect to the elevation and peak azimuth of the secondary receiving signal at the approximate T tag bearing and derives a true bearing for each called tag. This output may be logged or sent to server 12 or may be sent to tag processing module 18 for beam routing.

As described so far, four of the antenna elements are used to direct each of the deviation secondary receive beams around the primary transmit and receive beams. If sixteen antenna elements are used in the system, then a switch is used to switch the same four RF transceivers to four of the sixteen antenna elements. At any one time, four of the sixteen antenna elements are active, while the other twelve antenna elements are inactive. The four antenna elements are effective in one volume or sector 60 of space within the surveillance area 102. The remaining antenna elements in the array may operate, sequentially or simultaneously, in the same or different volumes or sectors of space in the surveillance area. The antenna elements operate in groups, typically four simultaneously, and preferably the antenna elements may overlap in different groups. It should be understood that this disclosure is not intended to be limited to a group of four antenna elements as a different number or group of antenna elements and a different number or group of secondary bias receiver beams may be used.

As described above and as shown in the flow diagram 200 of Fig. 7, starting from the exit step 202, the RFID system 10 accurately and quickly determines, in real time, the actual bearings of the RFID tags associated with the items 104, 106 in each sector 60 of the surveillance area 102, each sector 60 in turn, by directing (step 204) not only the primary transmitting beam and the primary receiving beam in all tags, but also substantially simultaneous directing of multiple secondary receiving beams of the deviation at steering angles, that are tilted in elevation and azimuth on tags in each sector or area monitored. The controller 16 processes the signal powers of the secondary deviation receive signals of the secondary deviation receive beams to determine an approximate tag bearing for each tag based on the highest RSS (step 206). The controller 16 selects a first pair of secondary yaw receive beams on opposite sides of the approximate tag bearing in the lift to obtain a pair of lift yaw signals (step 208) and selects a second pair of secondary yaw beams on opposite sides of the approximate tag bearing in azimuth to obtain a pair of yaw signals. azimuth (step 210). The controller 16 then processes the lift yaw signals and azimuth yoke signals to determine the true bearing for each tag in real time for each tag by calculating an elevation error correction to raise the peak steering angle of the secondary reception signal at the approximate tag bearing (step 212) by dividing the difference and sum of the lift yaw receive signals for the lift yaw beams. Similarly, for each tag, the controller 16 calculates an azimuth angle correction for the azimuth steering angle of the peak steering angle of the secondary reception signal at the approximate tag bearing T (step 214) by dividing the difference and sum of the azimuth deviation reception signals for the azimuth deviation beams. Then, the peak targeting angle of the secondary reception signal at the approximate bearing T tag is corrected for each tag (step 216) and steering angle corrected, i.e. the actual bearing for each such is derived (step 218). The method ends in step 220.

Specific embodiments have been described in the foregoing description. However, one of ordinary skill in the art will appreciate that various modifications and variations can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the description and figures should be considered

In an illustrative and not limiting sense, all such modifications are intended to be within the scope of the disclosure.

Benefits, advantages, solutions to problems, and any element (s) that may result in or accentuate any benefit, advantage or solution should not be interpreted as critical, required or necessary features or elements of any or all of the claims. The invention is defined only by the appended claims, including any amendments made in the course of the examination of this application and all equivalents of those claims as issued.

Moreover, in this document, relational terms such as first and second, top and bottom, and the like may only be used to distinguish one whole or action from another whole or action, without necessarily requiring or implying such an actual relationship or sequence between such wholes or actions. The terms "comprises", "comprising", "has", "having", "comprises", "comprising" or any other variations thereof are intended to include non-exclusive inclusion such that the method, method, article, or device that it comprises is intended to , contains a list of items, not only those items, but may contain other items that are not explicitly mentioned or inherent in the process, method, article or device. An item preceded by "includes ...", "has ..." or "includes" does not exclude, without limitation, additional identical items in the process, method, article or device that contains, has or includes the item. Terms declined in the singular are intended to include the singular or the plural unless expressly indicated otherwise herein. The terms "substantially," essentially "," approximately "," about "or any other version thereof are defined as conspicuous as understood by one of ordinary skill in the art and in one non-limiting embodiment the term is defined as falling within the scope of the present invention. %, in a further embodiment 5%, in another embodiment 1%, and in another embodiment 0.5%. The term "coupled" as used herein is defined as being coupled, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in some way is at least configured in this way, but may also be configured in ways not listed.

It should be noted that some embodiments may include one or more general or specialized processors (or "processing devices"), such as microprocessors, digital signal processors, customized processors, and programmable gate arrays (FPGAs). field-programmable gate array), and unique stored program instructions (including software and firmware) that control one or more processors to implement, in conjunction with some non-processor circuitry, some, most or all of the functions of the method described herein, and / or devices. Alternatively, some of all the functions may be implemented with a state machine that has no program instructions written, or in one or more application specific integrated circuits (ASICs) in which each function or some combination of some of the functions is implemented as custom logic. Of course, a combination of these two approaches can be used.

In addition, the embodiment may be implemented as a computer-readable storage medium having computer-readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed. Examples of such computer-readable storage media include, but are not limited to, hard disk, CDROM, optical storage device, magnetic storage device, ROM (read-only memory). read only memory), PROM (Programable Read Only Memory), EPROM (Eresable Programable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory) electrically eresable programable read only memory) and Flash memory. Furthermore, the average skilled person, regardless of potentially significant effort and many design choices motivated by, for example, available time, current technology and economic considerations, when guided by the concepts and principles disclosed herein, will be able to readily generate such instructions. software and programs and integrated circuits with minimal experimentation.

A summary of the disclosure has been provided to enable the reader to quickly ascertain the nature of the technical disclosure. It is provided with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Additionally, it will be appreciated in the above detailed description that various features are grouped together in the various examples