The present invention relates generally to communications networks, and more specifically, to the use of fiber optic links in a radio location system as a replacement to RF coaxial cable links.
A multitude of wireless communications systems are in common use today. Mobile telephones, pagers and wireless-connected computing devices such as personal digital assistants (PDAs) and laptop computers provide portable communications at virtually any locality. Wireless local area networks (WLANs) and wireless personal area networks (WPANs) according to the Institute of Electrical and Electronic Engineers (IEEE) specifications 802.11 (WLAN) (including 802.11a, 802.11b, 802.11g, 802.11n, etc.), 802.15.1 (WPAN) and 802.15.4 (WPAN-LR) also provide wireless interconnection of computing devices and personal communications devices, as well as other devices such as home automation devices.
Within the above-listed networks and wireless networks in general, in many commercial and industrial applications it is desirable to know the location of wireless devices and RFID tags. The above-incorporated patent applications describe a system for location finding in a wireless area network.
Techniques that may be used to determine location are disclosed in the above-incorporated patent applications. The techniques include loop delay measurement for distance determination or received signal strength measurement (RSSI), time-difference-of-arrival techniques (TDOA), and angle-of-arrival techniques (AOA) for location finding.
A typical deployment of such a location system includes a plurality of WLAN transceivers and/or access points, each unit connected to one or two antennas to receive and transmit wireless signals. According to different deployment alternatives, the antennas of those transceivers and/or access points can be directly connected to the unit or through a suitable RF coaxial cable.
Typical uses of RF coaxial cables include many cases where the antenna shall be mounted on a mast or pole to ensure proper coverage while the transceiver or access point unit needs to be mounted on the ground or in a covered area far away from its antenna. In those cases, the length of the coaxial cable is a critical factor since it directly affects the system performance. A long RF coaxial cable (e.g. >10-15 m) may have a significant attenuation (e.g. >3 dB) that will degrade the overall system performance.
This problem has already been identified and fiber optic solutions have been proposed and commercially implemented. This solution consists of replacing the RF coaxial cable with a fiber optic link and two transponders which convert the RF signal to a light signal and vice versa. Since the fiber optic cable has very low signal attenuation over distance, a very long link between the antenna and the transceiver or access point can be deployed while still maintaining a good system performance.
In many communication systems, those fiber optic links operating as a replacement to RF links are already available from several vendors. In those cases, knowing the overall delay of the link with a high precision (e.g. ˜1 nsec or less) is not important since this delay does not affect the received or transmitted signal.
However, when using those links in a TDOA location system, knowing those link delays is critical to ensure proper operation of the system. In addition, those fiber optic links enable several advantages which are specifically beneficial to location systems.
For example, US20080194226 discloses a method and system for providing. E911 services for a distributed antenna system uses a lookup table including round trip delay (RTD) ranges for a number of nodes of the distributed antenna system. The system has a lookup table based on the values of the fiber delays and air delays for each node on the distributed antenna system to determine the exact location of the wireless unit generating the E911 call.
U.S. Pat. No. 5,457,557 discloses a fiber optic RF signal distribution system which has a plurality of antenna stations, each station including an RF antenna. A central RF signal distribution hub receives and transmits signals external to the system. A pair of optical fibers connects each antenna station directly to the distribution hub with the connections being in a star configuration.
Similar systems are disclosed in U.S. Pat. No. 6,812,905, U.S. Pat. No. 5,936,754, U.S. Pat. No. 6,801,767, U.S. Pat. No. 6,597,325, U.S. Pat. No. 7,469,105 and U.S. Pat. No. 6,826,164.
Other implementations including optical fibers include conversion of RF signals to digital signals and their transmission over fibers. U.S. Pat. No. 7,366,150 discloses an indoor local area network (LAN) system using an ultra wide-band (UWB) communication system. The system comprises access point adapted to receive the analog signal of the ultra wide-bandwidth transmitted from the remote terminal and convert the received analog signal into an optical signal.
A common problem of TDOA location systems is the receiver time synchronization which is essential to allow a correct TDOA calculation when a wireless signal is time stamped by two or more receivers. This synchronization can be achieved by providing a common clock to all the receivers through cables connected between them and the common clock source or by using wireless methods. Both techniques are well known and widely used in the industry.
Although clock distribution solves the problem of the continuous drifts between the clocks in the different receivers, the initial offset of the time counters is a problem that requires special solutions.
Using fiber optic links enables one to concentrate in a single place all the transceivers used to locate in a specific area thus significantly simplifying the clock distribution and also providing several solutions to the initial offsets of the TOA counters used to time stamp the received signals.
Therefore, it would be desirable to provide a method and system for using fiber optic links in a TDOA location system, said fiber optic link having the properties and functionality required to solve common problems found in TDOA location systems and to ensure their proper system operation.
The above objectives of using fiber optic links in a location system are achieved in a method, system and related elements.
The method is embodied in a system that determines the physical location of a first mobile wireless device coupled to a wireless network by processing the measured characteristics of signals received from the first wireless device by one or more other wireless transceiver devices deployed in the location area.
More specifically, this invention applies to a TDOA (time difference of arrival) location system, in which mobile wireless devices broadcast wireless signals which are received by two or more transceivers deployed in the vicinity of said mobile wireless device. Each transceiver measures the TOA (time of arrival) of the received broadcasted signal and reports the TOA to a central server. Said server then calculates the mobile device position using multi-lateration of TDOA values.
This patent further refers to the use of fiber optic links between the antennas and the transceivers deployed in the location area to provide unique advantages that could not be achieved using RF coaxial cables. Those advantages are specifically useful in TDOA location systems.
In one preferred embodiment of this invention, the wireless transceivers used to receive wireless signals from the mobile wireless device are installed in one central place and the antennas of each of said transceivers are mounted on poles, walls, buildings, etc in the located area.
Each of said transceivers is connected to its antenna(s) using a fiber optic link including at least three main components: A local transponder connected to the transceiver which converts RF signals from the transceiver to light signals and vice versa, a fiber optic cable to transmit those light signals to long distances (e.g. from tens of meters to few kilometers) and a remote transponder which converts the light signals from the fiber optic cable to RF signals and vice versa. This remote transponder is also connected to the antenna(s).
In such a system, the transceivers are timed synchronized using wireless synchronization. The delay of the fiber optic link is automatically cancelled during the process of offset correction of the TOA counters used for time stamping.
In another preferred embodiment, part or all of the transceivers are replaced by receivers (without transmitter) thus simplifying the fiber optic link and the transponders.
Since all the transceivers associated to a specific location area can now be concentrated in one single place, there are several advantages as follows:
Other preferred embodiments include the integration of multiple transceivers in one single enclosure sharing a common data bus and a common TOA counter.
Other embodiments include means for self calibration of the RF and fiber optic link delay, integration of the remote transponder into the antenna and providing power to the remote transponder using a copper cable which is bundled in the fiber optic cable.
The foregoing and other objectives, features, and advantages of the invention will be apparent from the following and more particular, descriptions of the preferred embodiments of the invention, as illustrated in the accompanying drawings.
The present invention provides TDOA location of a mobile wireless device (e.g. tag, laptop, VoIP phone, bar code reader. etc.) within a wireless network such as a WLAN (e.g. IEEE 802.11a/b/g/a/n) or other any other suitable wireless network for TDOA location such as networks using UWB technology.
As described in the above-incorporated patent applications, the TDOA location system may include wireless synchronization as well as other improvements to reduce the synchronization offsets that may be caused by such synchronization method.
In said TDOA location system, multiple (two or more) receivers or transceivers are used to calculate the time-difference-of-arrival (TDOA) of wireless signals received from a transmitting source. Some or all the transceivers and/or receivers are connected to their respective antennas using a fiber optic link thus providing the capability to install those units far from their antennas without degrading the system performance as typically caused by long RF coaxial cables.
The location of the transmitting source (e.g. RFID tag or mobile station) can be determined by triangulation, based on the difference between the signal arrivals at the multiple receivers. Angle of arrival methods (AOA) may also be used to locate a unit by intersecting the line of position from each of the receivers. Those and other techniques for providing wireless device location information are well known to those skilled in the art and may be used within the method and system of the present invention taking advantage of the special architecture and benefits provided by this invention.
Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
Some embodiments of the invention are herein described, by way of example only, with reference to the associated drawings. With specific reference now to the drawings in detail, it is stressed that the details shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.
The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to”. The term “consisting of” means “including and limited to”.
The term “location transceiver” means any wireless communication unit which is part of a location system, and used to communicate with tags or any other wireless mobile devices being located by the location system. The term “location transceiver” includes WLAN Access Points (e.g. APs compliant to IEEE 802.11a/b/g/n), location receivers (in those cases where there is no need for 2-way communication), location transceivers, combinations of the above and other wireless location devices operating in the unlicensed frequency bands (e.g. ISM bands), UWB bands or any other radio frequency band (licensed or unlicensed) applicable to a location system.
The term “tag” means any portable wireless device being located by the location system, including unidirectional or bidirectional communication means, stand alone or integrated into other devices, battery powered or externally powered by any other source, passive, semi-passive or active RFID tags and also portable wireless devices including other communication means in addition to the one used to communicate with the location transceivers (e.g. ultrasound, infrared, low frequency magnetic interface, wired serial interface, etc.).
The term “transponder” means an electronic unit able to convert RF signals (e.g. signals in the 2.4 GHz, 5.7 GHz ISM bands or UWB signals) to light signals and vice versa. The transponder may be adapted to different types of fiber optic cables used to transmit and receive the light signals as well as to different kinds of RF signals. RF-Fiber optic transponders are commercially used for many applications. According to this invention, the transponder unit may also comprise other functions which enhance its functionality in accordance to some preferred embodiments.
The term “antenna” means any RF antenna used to transmit and/or receive RF signals. It includes both omni-directional and directional antennas of any type and gain.
The term “fiber optic” means a fiber optic cable used for communication (RF and/or digital) including single mode and multi-mode fibers.
Referring now to the figures and in particular to
In this location system as depicted in
The location system further comprises a wireless sync source 27 transmitting beacons 29 which are received by the location transceivers 3-6. By measuring the time of arrival (TOA) of those beacons 29 at each location transceiver 3-6 and reporting the TOA values to the server 2, it is possible to estimate the continuous TOA counter offset between all the location transceivers 3-6 and synchronize the whole location system to perform TDOA location. As previously mentioned, this synchronization technique is described in U.S. Pat. No. 6,968,194, entitled “METHOD AND SYSTEM FOR SYNCHRONIZING LOCATION FINDING MEASUREMENTS IN A WIRELESS LOCAL AREA NETWORK”, issued on Nov. 22, 2005 and United States Patent Application, entitled “METHOD AND SYSTEM FOR SYNCHRONIZATION OFFSET REDUCTION IN A TDOA LOCATION SYSTEM”, filed on Oct. 24, 2006, having a Ser. No. 11/552,211.
Also according to the preferred embodiment depicted in
Therefore and according to this preferred embodiment, the location system includes two location transceivers 4-5 which can be deployed far from their antennas 12-13. As can be easily understood, another preferred embodiment of the location system may include location transceivers which all of them are far from their antennas and connected to the antennas with fiber optic links.
In the depicted embodiment, the fiber optic links 21, 22 enables to concentrate two location transceivers 4, 5 in a single place (together or not with other equipment) thus providing several advantages to the user as easier maintenance, lightning protection (due to the fiber link), protection against hard environmental conditions, etc.
As can be easily understood, the location transceivers 3-6 can also be replaced by receivers only, since in some location system architectures they are not required to transmit any message. As already explained and for the sake of simplicity, in any case where a location transceiver is mentioned in this invention, it can be optionally replaced by a location receiver if that unit is not required to transmit messages as part of its normal operation.
Optionally, in another preferred embodiment, the sync source is one of the location transceivers 3-6 which transmit beacons 29 used for the location system synchronization.
Referring now to
In this location system as depicted in
Also according to this preferred embodiment as depicted in
According to this preferred embodiment, all the four location transceivers 3-6 are installed in one single place, close each to other. Two location transceivers 4-5 are deployed far from their antennas 12-13 while the other two location transceivers 3, 6 are connected relatively close to their antennas 10-11 through RF coaxial cables 15-16 (e.g. antennas mounted on a roof or wall close to the location transceiver installation). As can be easily understood, another preferred embodiment of the location system may include location transceivers which all of them are far from their antennas and connected to the antennas with fiber optic links.
In the depicted embodiment, and taking advantage of the concentrated deployment of the location transceivers 3-6, additional advantages can be provided in addition to the already mentioned advantages as easier maintenance, lightning protection (due to the fiber link), protection against hard environmental conditions, etc.
The location system further comprises a central timing source 40 which provides a wired timing signal 41 to all the location transceivers 3-6. According to a preferred embodiment, this timing signal may be a clock at frequencies in the range of 10-100 MHz. This timing signal 41 or a synchronized derivative of it is used in each location transceiver to clock the TOA counter which is used to timestamp the received wireless signals. Since the location transceivers 3-6 are all deployed in a single place, providing this timing signal 41 to all the transceivers is very simple since it can be performed with very short cables and without having the limitations normally found when providing fast clocks over long lines.
Optionally and still taking advantage of the transceivers being close each to other, a common TOA counter reset signal 42 can be provided by one transceiver 3 to the other transceivers 4-6. Since the distances between the units are short and can be fully controlled, it is possible to reset the TOA counters of all the transceivers 3-6 almost simultaneously thus providing a time synchronization between all the transceivers.
Since each of the transceivers 3-6 may have a different time delay of the received signals from the antenna to the time stamp section in the transceiver itself, it is possible to cancel this fixed offset by an initial calibration.
According to this preferred embodiment, a wireless sync source unit 27 transmits periodic beacons 29 which are received by each of the location transceivers 3-6. By measuring the time of arrival (TOA) of those beacons 29 at each location transceiver 3-6 and reporting them to the server 2, it is possible to estimate the time offset between all the location transceivers 3-6 and synchronize the whole location system to perform TDOA location. Since all the transceivers are clocked from a common timing signal 41 there is no drift between the TOA counters (one TOA counter in each location transceiver) and the TOA offsets due to different cable lengths remain fixed so far the cables connecting the antennas to the transceivers 15-16 and 21-22 are not modified. Even if one or more of the location transceivers are powered off and on, there is no need to recalibrate the system since the time offsets calculated during the calibration process are still valid and can be used.
Comparing this embodiment to the embodiment in
Optionally, the TOA counter reset signal 42 can be combined with the timing signal itself thus providing both functions directly from the timing source 40 and using a single signal. This feature will be further described in other embodiments of this invention.
Although it is possible to use this synchronization technique when the location transceivers are installed close to their antennas and far from each other, the distribution of the timing signal is problematic and requires high quality shielded cables.
In another preferred embodiment, all (or part) the location transceivers installed in one place are enclosed in a single enclosure. For example, a motherboard including several slot connectors where each location transceiver is connected to the motherboard through one of said slot connectors. In this preferred embodiment a very easy and reliable distribution of the clock and TOA counter initialization can be implemented. The common clock may be generated internally on the motherboard and distributed through the motherboard to all the location transceiver boards. Optionally, all the location transceivers may share a single TOA counter thus eliminating the need for any distributed sync timing signal. In addition, it is also possible to have one central processor used to process the signals received from all the receivers enclosed in the same case.
In another embodiment the fiber cables 21-22 are bundled into a single cable which is chained from antenna to antenna. Since the location transceivers 4-5 are located in the same place, it is convenient to connect those units to a single cable with multiple fibers which is chained to both antennas 12-13. Other preferred embodiments may include cable chaining to a plurality of antennas.
Referring now to
According to this preferred embodiment as depicted in
The received signal is demodulated by the WLAN receiver 53 and converted to baseband signals I and Q 67. Those signals are decoded by the baseband controller 51 and in parallel sampled by two A/D converters included in the A/D, MF, RAM and TOA counter function 50. The sampled signals (e.g. with a resolution of 8-10 bits) are passed through a matched filter (ME) of the A/D, MF, RAM and TOA counter function 50 and the results stored in a dedicated RAM of the A/D, MF, RAM and TOA counter function 50. As an example, a typical IEEE 802.11b at 1 Mbps BPSK signal will be sampled at a rate of 22 MHz. The RAM of the A/D, MF, RAM and TOA counter function 50 stores the matched filter output of around 128 bits (2816 I and Q matched filter results). For the skilled in the art, it shall be obvious that a hardware implementation of the matched filter is just one preferred embodiment. Fast digital signal processors (DSP) can perform the same function by reading directly the I and Q samples 67. In order to calculate the time of arrival of the received signal, a TOA counter of the A/D, MF, RAM and TOA counter function 50 is used to time stamp the samples. The timing of the TOA counter is controlled by a timing function 54 which provides the clock for this TOA counter of the A/D, MF, RAM and TOA counter function 50. The master clock of this timing function 54 may be provided from an internal clock (e.g. TCXO or OCXO) or from an external signal 64 which can also be supplied to other location transceivers. The final TOA of the received signal is calculated by the controller 51 which reads the I&Q matched filter results and the TOA counter data 66 from the A/D, MF, RAM and TOA counter function 50. The final TOA calculation may optionally include fine interpolation and sophisticated algorithms to reduce the effects of noise, multipaths and other interference conditions which may cause an error in the TOA calculation. Many of those algorithms are well known and beyond the scope of this invention.
Optionally the TOA counter can be initialized from the controller 51 or from an external signal 65. Initializing the TOA counter of the A/D, MF, RAM and TOA counter function 50 from an external signal enables a controlled and synchronized initialization of those TOA counters in multiple location transceivers.
According to the preferred embodiment as depicted in
The remote transponder 62 converts the light signal back to an RF signal and amplifies it to get the required signal power (e.g. +20 dBm). The amplified RF signal is transmitted using the location transceiver antenna 63.
Also according to this preferred embodiment, the transmitted I&Q signals 68 are also sampled using the same function 50 used to sample the received signals. This sampling enables the controller 51 to calculate the time of transmission with the same level of accuracy as done with the received signals. Having this capability, the location transceiver can synchronize itself when transmitting beacons for wireless synchronization or when performing a distance measurement. This capability will be described in more detail when describing a method which allows self calibration of the fiber cable length. The controller 51 has an Ethernet interface 69 which allows communication to a server or to any other unit connected to the network.
In another preferred embodiment, the location transceiver operates as a receiver only. In that case, all the functions related to the transmission of signals can be saved including the relevant functions in the local and remote transponders. Also according to this preferred embodiment and referring to
Referring now to
In addition, and according to this preferred embodiment the initialization of the TOA counter of the A/D, MF, RAM and TOA counter function 50 used for time stamping of the received and/or transmitted signals is provided by the timing function 54. The advantage of this approach is the fact that this initialization signal 71 can be directly derived from a periodic marker in the external timing signal 64. A simple and common method to generate this marker in the timing signal is by masking one cycle of the timing signal (e.g. the timing signal amplitude will remain constant for one cycle) without changing the timing signal frequency. Preferably, this marker shall have a repetition period long enough to avoid TOA ambiguity of the time stamped signals. For example a repetition period of 1 every 106 cycles of a 50 MHz clock, will create a marker every 20 msec, time which is long enough to avoid any TOA ambiguity in typical WLAN location systems.
According to this preferred embodiment, a location system including location transceivers having the functionality as depicted in
Referring now to
According to this preferred embodiment as depicted in
The received RF signals 84 and 85 are connected to a diversity switch 86 and then a selected signal is connected to a low noise amplifier 55 part of the receiver chain. In many cases the received signals 84 and 85 are strong enough (due to the LNA in the remote transponder 82) so there is no need for an LNA 55 and it can be avoided. The selected signal from the diversity switch 86 can be fed directly to the WLAN receiver 53. Note that also this embodiment has no T/R switch as the embodiment described in
The received signal selected by the diversity switch 86 is demodulated by the WLAN receiver 53 and converted to baseband signals I and Q 67. Those signals are decoded by the baseband controller 51 and in parallel sampled by two A/D converters included in the A/D, MF, RAM and TOA counter function 50. The sampled signals (e.g. with a resolution of 8-10 bits) are passed through a matched filter (MF) of the A/D, MF, RAM and TOA counter function 50 and the results stored in a dedicated RAM of the A/D, MF, RAM and TOA counter function 50. The RAM of the A/D, MF, RAM and TOA counter function 50 stores the matched filter output of around 128 bits (2816 I and Q matched filter results). For the skilled in the art, it shall be obvious that a hardware implementation of the matched filter is just one preferred embodiment. Fast digital signal processors (DSP) can perform the same function by reading directly the I and Q samples 67. In order to calculate the time of arrival of the received signal, a TOA counter of the A/D, MF, RAM and TOA counter function 50 is used to time stamp the samples. The timing of the TOA counter is controlled by a timing function 54 which provides the clock for this TOA counter of the A/D, MF, RAM and TOA counter function 50. The master clock of this timing function 54 maybe provided from an internal clock (e.g. TCXO or OCKO) or from an external signal 64 which can also be supplied to other location transceivers. The final TOA of the received signal is calculated by the controller 51 which reads the I&Q matched filter results and the TOA counter data 66 from the A/D, MF, RAM and TOA counter function 50. As previously mentioned, the final TOA calculation may optionally include fine interpolation and sophisticated algorithms to reduce the effects of noise, multipaths and other interference conditions which may cause an error in the TOA calculation.
Optionally the TOA counter can be initialized from the controller 51 or from an external signal 65. Initializing the TOA counter of the A/D, MF, RAM and TOA counter function 50 from an external signal enables a controlled and synchronized initialization of those counters in multiple location transceivers.
According to the preferred embodiment as depicted in
The remote transponder 82 converts the light signal back to an RF signal and amplifies it to generate the required signal power (e.g. +20 dBm). The amplified RF signal is then transmitted using one of the location transceiver antennas 63.
Also according to this preferred embodiment, the transmitted I&Q signals 68 are also sampled using the same function 50 used to sample the received signals. This sampling enables the controller 51 to calculate the time of transmission with the same level of accuracy as done with the received signals. Having this capability, the location transceiver can synchronize itself when transmitting beacons for wireless synchronization or perform a distance measurement.
The controller 51 has an Ethernet interface 69 which allows communication to a server or any other unit connected to the network.
Referring now to
The transmitted I&Q signals 105-106 and the received I&Q signals 107-108 are connected to two analog switches (multiplexers) 103-104 in a way that enables unique functionality.
In normal operation during signal reception, both I&Q components 107-108 of the received signal are sampled by two parallel A/D converters 101-102. Switch 103 is set to position 1 by the controller 51 through control lines 109. The received 1-signal 107 is then sampled by A/D 101. Switch 104 is set to position 1 by the controller 51 through control lines 109. The received Q-signal 108 is then sampled by A/D 102.
In normal operation during signal transmission, both I&Q components 105-106 of the transmitted signal are sampled by the two A/D converters 101-102. Switch 103 is set to position 2 by the controller 51 through control lines 109. The transmitted I-signal 105 is then sampled by A/D 101. Switch 104 is set to position 2 by the controller 51 through control lines 109. The transmitted Q-signal 106 is then sampled by A/D 102.
In addition to this normal operation, the location transceiver can perform a self measurement of the RF and fiber optic link delay thus allowing a self calibration process.
Referring now to
In another preferred embodiment this local power source is a solar power unit mounted in the same pole as the antenna and the remote antenna unit 132.
A transmitted signal 142 is converted by the local transponder 130 to a light signal and sent to the remote transponder 131 through a fiber optic 145. The remote transponder 131 converts the light signal back to an RF signal 139 which drives the power amplifier 141. In addition, the transmitted signal 139 is connected to two T/R switches 135-136 which send this signal back to the remote transponder 131. Therefore the transmitted signal 139 is received back by the local transponder 130 after it passed through two fibers 146-147.
Note that the remote transponder automatically controls the T/R switches 135-136. When a signal is transmitted, the remote transponder senses the presence of energy of signal 139 and automatically sets both T/R switches 135-136 to transmit mode. In this mode, the transmitted signal is sent back to the local transponder 130. When there is no signal being transmitted (absence of energy), the remote transponder 131 sets the T/R switches 135-136 to their normal receive mode thus allowing the reception of signals from antennas 137-138.
When a signal is being transmitted by the location transceiver, the remote transponder also sets T/R switch 140 to transmit mode thus allowing the transmission of the signal through antenna 137. When there is no signal being transmitted, the remote transponder 131 sets T/R switch 140 to its normal receive mode thus allowing the reception of signals from antenna 137.
According to a preferred embodiment of a location transceiver as depicted in
The transmitted signal is looped back by the remote transponder 131 and fed back to the location transceiver by the local transponder 130. One of the received signals 143-144 is selected using a diversity switch 86 (e.g. as depicted in
The overall delay (receive +transmit) of the RF and fiber optic link including the transponders 130-131 can be measured by measuring the delay between the transmitted signal 105 and one or both of the received signals 107-108. In this mode, switch 103 is set to position 1 and therefore A/D 101 samples the transmitted signal 105 while at the same time switch 104 is set to either position 1 or 3 to allow a simultaneous sampling of either one of the received signals 107-108 by A/D 102. Since the delay of this link is unknown, also the phase of the received signal is unknown. Therefore the received signal energy may be either concentrated in one of its I&Q components only or split in both I&Q components 107-108.
For this reason, the delay measurement may include two steps. In the first step the transmitted signal 105 is sampled together with the I-component 107 of the looped back signal and in the second step the same procedure is repeated with the Q component 108.
Having the matched filter output of the sampled data of both transmitted 110 and received 111 signals, the controller 51 can calculate the overall delay using the TOA functions 50 which are normally used for the TOA measurement of the transmitted or received signals.
This delay measurement operation can be performed for each of the receive paths 143-144 thus providing a better accuracy of the overall delay since both receive fibers 146-147 are bundled in the same cable.
In principle, the overall signal delay (from the A/D′s 101-102 to the antennas 137-138) include a small additional delay consisting of the power amplifier, the LNAs and the short RF coaxial cable. Those delays are fixed and easily calculated or measured and can be taken in account in the overall self calibration process. Since the fiber optic delay is very stable, this self calibration process is not required very often.
Knowing the overall delay of the RF link and optical link is very useful for the following reasons:
In addition, the same mechanism can be used to provide additional advantages as follows:
In another preferred embodiments, the measurement of the link delay can be done with other known techniques as transmission of very short pulses or phase delay variations using frequency hopping techniques.
Referring now to
In this preferred embodiment the power to the integrated antenna unit is provided through the local transponder 130 (e.g. from the location transceiver). The fiber optic cable includes also a copper cable 151 used to provide the DC power to the integrated antenna unit 150. Since the power consumption of this integrated antenna unit is relatively low (typically 1-2 watts), the requirements for the copper cable 151 are not severe. Typically the integrated antenna unit will also include a voltage regulator (not shown) to provide a stable and clean power to the integrated antenna unit 150.
The fiber optic or the copper cables connecting between the location transceiver and the remote antenna unit can also be used to send digital commands to the remote antenna unit and receive digital messages from it.
In another preferred embodiment, the remote antenna unit includes a small micro controller able to receive commands from the location transceiver or a central unit. Those commands can be used to control the remote transponder and perform diagnostics. This microcontroller can also send back status messages. In chained configuration, it is possible to use also multicast and/or broadcast commands sent to multiple remote antenna units.
Other preferred embodiments comprise using the same antenna for a location transceiver and a WLAN Access Point located in the same place. This technique is well known and commercially available.
Large location systems may include several groups of location transceivers each group concentrated in a different place and synchronized by a different timing source. In a preferred embodiment of such location system it may be necessary to synchronize between two or more of said timing sources. This synchronization can be achieved by having a connection between those timing sources and defining one of them as a master timing source. This master timing source will provide the clock to each of the other slave timing sources connected to said master timing source. The connection between those synchronized timing sources may be implemented using a CAT5/CAT6 cable or a fiber optic.
The principles of this invention can also be applied to a TDOA location system also capable to locate using Angle of Arrival (AOA).
It may be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that many alternatives, modifications and variations and other changes in form, and details may be made therein without departing from the spirit and scope of the invention.
The present application claims the benefit of U.S. Provisional Patent Application entitled “LOCATION SYSTEM AND METHOD WITH FIBER OPTIC LINK”, filed Oct. 27, 2008, having Ser. No. 61/108, in the name of the same inventor. The present application is further related to U.S. Patent Application entitled “METHOD AND SYSTEM FOR LOCATION FINDING IN A WIRELESS LOCAL AREA NETWORK”, filed on Aug. 20, 2002, having a Ser. No. 10/225,267; U.S. Pat. No. 6,968,194, entitled “METHOD AND SYSTEM FOR SYNCHRONIZING LOCATION FINDING MEASUREMENTS IN A WIRELESS LOCAL AREA NETWORK”, issued on Nov. 22, 2005; and United States Patent Application, entitled “METHOD AND SYSTEM FOR SYNCHRONIZATION OFFSET REDUCTION IN A TDOA LOCATION SYSTEM”, filed on Oct. 24, 2006, having a Ser. No. 11/552,211; the specifications of which are herein incorporated by reference.