WO2001078260A1 - Reference unit for a location system of a cellular network - Google Patents

Reference unit for a location system of a cellular network Download PDF

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Publication number
WO2001078260A1
WO2001078260A1 PCT/US2001/008557 US0108557W WO0178260A1 WO 2001078260 A1 WO2001078260 A1 WO 2001078260A1 US 0108557 W US0108557 W US 0108557W WO 0178260 A1 WO0178260 A1 WO 0178260A1
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WO
WIPO (PCT)
Prior art keywords
signals
btss
snap
satellite
gps
Prior art date
Application number
PCT/US2001/008557
Other languages
French (fr)
Inventor
Joseph Nir
Baruch Shayevits
Hanoch Cohen
Original Assignee
Cellguide Ltd.
Friedman, Mark, M.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cellguide Ltd., Friedman, Mark, M. filed Critical Cellguide Ltd.
Priority to AU2001245825A priority Critical patent/AU2001245825A1/en
Publication of WO2001078260A1 publication Critical patent/WO2001078260A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/24Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2662Arrangements for Wireless System Synchronisation
    • H04B7/2671Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
    • H04B7/2678Time synchronisation
    • H04B7/2687Inter base stations synchronisation
    • H04B7/2696Over the air autonomous synchronisation, e.g. by monitoring network activity

Definitions

  • the present invention relates generally to location systems of mobile transceivers. More specifically, the invention is in the field of location systems for mobile units of unsynchronized cellular systems.
  • Ranging methods based on radio channels measure the time it takes for a radio signals to travel from a radio source to a receiver. The longer it takes for the signal to travel the way, the farther the receiver is displaced from the emitter.
  • a set of radio sources emitting signals received by a receiver can potentially provide enough physical information of time of travel for such a receiving unit to determine its own location relative to the radio stations. Practically however, the speed of light being extremely high, about 3 X 10 8 m/sec, requires compatible clock for providing meaningful measurements of the time of arrival of the respective signals to the receiver of the radio sources.
  • the emitted signals of the radio sources must be structured in such a way as to facilitate timing references of the signal to be clearly discerned by the receiver.
  • Base stations of the GSM network do not supply time of emission of signals, which complicates the process for determination of location.
  • a way to overcome the lack of data as incicated earlier is by providing timing references which mutually synchronize base stations.
  • WO - 99- 21028 the contents of which are incorporated herewith by reference, is disclosed a method for calculating a location of a mobile receiver (MU) in which at least one extra receiver of the unsynchronized cellular network is employed in order to provide time reference to base stations.
  • Another method, disclosed in WO - 99 - 61934 uses navigation satellite ranging signals, in addition to base station signals.
  • GSM cellular networks operate along the principles of the TDMA (time division multiple access) and FDMA (frequency division multiple access) technology and associated standards.
  • the time division principle allows many subscribers to use the radio channel concomitantly by occupying each a small portion of the time resources available for the communication medium.
  • the mobile stations (MUs) communicating with a certain base station (BTS) are rendered mutually synchronized.
  • the BTSs communicates with each mobile unit by sending a sequence of discrete structures called time slots, allocated exclusively for data bits to or from the active subscriber, uplink or downlink oriented.
  • GSM and other unsynchronized cellular network systems do not provide however mutual base station synchronization. This implies that whereas each MU is fully synchronized with the BTS with which they are actively engaged, there is no concomitant synchronization of a mobile station with other base stations of the same network. This lack of mutual time synchronization among the BTSs of a network, precludes the possibility of a MU to synchronize with signals originating in BTSs other than the one within the cell boundary of which it is operative. Accurate ranging methods for locating
  • LMU LMA
  • location measurement unit is such a GSM network elements that
  • the LMUs are classified into two classes: first, a class containing
  • a GPS - correlating LMU is inherently more accurate than a
  • system clock has a much higher stability (10 "12 sec/sec deviation) as compared
  • An object of the present invention is to provide a method for mutually
  • NRU network
  • the respective signals of the BTSs are identical to each other reference unit ( reference unit) of the invention.
  • the respective signals of the BTSs are identical to each other reference unit ( reference unit) of the invention.
  • a further object of the present invention is to provide a system for time - synchronizing signals of individual BTSs (base transceiver stations) of an unsynchronized cellular network with the time system of the GPS system of navigation satellites.
  • the system of the invention contains receiving circuits for satellite navigation signals and for BTS signals.
  • the system contains sufficient DTA (digital to analog devices to facilitate fast parallel sampling of all received signals, the rate of which is set by a local clock, and the resulting digital numbers are stored in a snap memory preferably capable of storing two snaps.
  • the system of the invention provides for a triggering circuit and a communication line for receiving and transferring data to and from the network.
  • Fig. 1A is a block diagram illustrating the main functional elements of a prior art LMU of a GSM cellular network
  • Fig. 1 B is block diagram illustrating the interconnectivity of the functional elements of a prior art LMU as in Fig. 1 A;
  • Fig. 2A is a block diagram illustrating schematically the architecture of
  • NRU network reference unit
  • Fig. 2B is a block diagram illustrating schematically the architecture of
  • NRU network reference unit
  • Fig. 3 is a schematic illustration of the sequence of events performed
  • Fig. 4 is a graphic illustration describing the timing signal structures of
  • Fig. 5. is a graphic illustration describing the timing signal structures of
  • Fig. 6 is a block diagram classifying the groups of data which
  • Fig. 7 is a schematic illustration describing the sequence of events of
  • a fully operational GPS receiver 14 is coupled to
  • the data obtained is sent to the BTS through a link
  • a precise clock 15, of better stability characteristics than mobile unit clock, provides frequency for the ATD (analog to digital) circuit of the cellular receiver 20, and timing reference to the TMC (time measuring circuit) 16.
  • the TMC measures time between the precise trigger pulse supplied by the GPS receiver 14 and one or more identifiable timing references of the of the BTSs received.
  • the timing references are sent to the BTS through a link 18 to network.
  • present invention relates also to third generation networks, for example UMTS networks, that are scheduled to succeed the GSM networks.
  • third generation networks for example UMTS networks
  • GPS antenna 13 is connected to a fully operational
  • GPS receiver 14 that sends a triggering pulse, known as 1PPS (one pulse per
  • the GPS receiver can also
  • An RF receiver 22 receives BTS signals
  • Analog to digital converter 34 demodulates the signal and
  • the TMC 16 calculates the time difference between the triggering pulse and the reception of the identifiable time references of the BTSs, typically SCHs (synchronization channels).
  • the time difference between the triggering pulse and the timing references may be long enough to cause deterioration of the timing accuracy, which necessitates the employment of a high quality clock 42.
  • Communication channel 44 sends to the network respective time matching data of each of the BTS signals as referenced to the 1 PPS pulse, through a physical A-bis connection or through wireless connection.
  • Controller 48 regulates the output link with the network.
  • Ancillary data obtained by the GPS receiver, from the individual satellites (ephemeris) or system time are also transferred to the network through any of the two links, A - bis 46, or wireless transmitter 38.
  • RF receiver 64 receives through antenna 62 at
  • the signal is downconverted in
  • Triggering circuit 69 triggers the snap memory which sets off a data collection and processing stage as will be elaborated later on.
  • the sampling rate is determined by local clock 78.
  • a parallel circuit triggered by the same triggering signal as above, cellular BTSs are received through antenna 70, which may be the same as antenna 62, and the received signal is
  • Processor 80 receives therefore a digitized output of digitizers 68 and 76 collected in one snap, and processes the signals. Processor 80 sends the resulting data to communication channel 82.
  • the transmission is carried out by wireless link, or by a physical A -bis link to the network 84.
  • wireless link or by a physical A -bis link to the network 84.
  • a commercial GPS receiver 65 is
  • a first task is obtaining satellite ephemeris data independently, and another reason is for triggering the snap through the 1PPS mentioned above.
  • Other tasks of the adjunct GPS receiver will be discussed later on.
  • the adjunct receiver 65 is optionally connected to the existing antenna 62 at the front end,
  • a trigger is set off at a predetermined rate and for a predetermined period of time, typically for 0.1 second every 30 seconds.
  • the trigger sets off a process which aims at achieving mutual synchronization of cellular BTS signals and a reference to the GPS system time.
  • Snap is triggered at step 108, collecting data from both a plurality of GPS
  • step 110 Data processing begins
  • step 112 within reception of enough data to start a procedure, as will be
  • step 114 the BTSs are mutually synchronized and referenced to the GPS system time.
  • the processor of a NRU of the invention performs the necessary calculations for calibrating the local clock.
  • the principles of the calibration procedure for the local clock are explained with reference to Fig. 4.
  • the local clock time axis is indicated in the figure by arrow 120.
  • start designated by arrow 122 occurs receiving the two signals: satellite and BTS.
  • two respective repetitive signal structures are discerned, one of each radio source.
  • the contiguous repetitive GPS code periods are discerned, by correlating the received signal code with a stored replica code within the processor.
  • Discrete GSM frames are discerned by identifying specific burst periods, such that the total number of frames is calculated until a synchronization frame is identified.
  • a first beginning of a GPS code period 130, marked by arrow 118 is measured in local
  • the processor calculates the number of frames having been counted since snap start 122.
  • the method of the invention takes into consideration measurement elements much shorter than GSM frames, and the example portrayed in Fig. 4 puts line 126 in a frame start, for convenience of illustration but sub- frame structures, i.e. time slots, bits and sub- bit accuracy can be attained.
  • a snap start designated by arrow 160 indicates, on the local clock time axis and on the satellite time axis, the initiation of data collection and loading into the snap memory. Collected are frames of a first BTS signal 162, and of a second BTS 164. In addition, the
  • BTSs such as frame 170 of BTS 162 are shadowed to distinguish them from other frames.
  • a s.frame is encountered, it is identified by its internal structure, and the identification number it bears is registered, then, the number pf frames elapsed between this frame and the snap start (arrow 160) are counted, including fractions of a frame), thereby finding the time between the snap start and the s: frame, in sub-frame resolution.
  • the same is performed for the signal of BTS 164, until all available BTSs have mutually correlated their timing, referencing to the same snap start. It should be noted that this entire process is performed with corrected local clock bias.
  • the compensation for drift is implemented for every sample in the snap, assuming a linear drift model.
  • Group 242 is the information related to the satellite system. This group includes:
  • Differential correction parameters for each satellite received is optionally provided.
  • Group 244 contains the location parameters of the NRU itself, in units and
  • Group 246 contains the information carried by the signals of the BTSs, which include the transmitted signals of all available BTSs, at preset frequencies.
  • Table 1 describes the above information types and the alternative sources for their acquisition.
  • determining the location of the NRU can be achieved by either obtaining
  • the determination can be used to determine whether the NRU is based on received satellite data.
  • the determination can be used to determine whether the NRU is based on received satellite data.
  • step 250 the receiver locks on to every available
  • step 252 to calculate ranges to each of the available satellites.
  • step 256 a mean is calculated with respect to all of the satellites.
  • T re the time of reception of a signal
  • the satellite navigation message there is contained information for compensating for satellite clock offset and drift. This information is used for correcting the system time synchronization, and local clock bias and drift.
  • the transmitter in each BTS contains a clock that provides a reference for the production of the discrete signals subsequently received by the individual mobile receivers localized within the particular cell.
  • the procedure of the invention includes determining the clock drift of each BTS timing signals received, with reference to the more stable satellite system clock.
  • two separate snaps are executed, registering in each snap a nominal of a synchronization frame, matched to a snap start. The entire procedure for determining BTS clock drift is explained schematically by reference to Fig. 5, to which reference is again being made.
  • BTS signal 162 is
  • digitized and synchronization frame 170 is identified, its identity registered.
  • Arrow 112 designates the point in time on the local clock's time axis at which a first period start is encountered. Thence, the start time of synchronization frame
  • the resulting parameter is used by mobile units for calculating location, based on ranging to BTSs.
  • This aspect of synchronization of the BTSs is to correlate between their timing and the GPS system time. This procedure is implemented mainly for facilitating so called hybrid location procedures, involving pseudoranging to satellites as well as to BTSs.
  • Each code period lasts exactly 1 msec
  • the entire navigation data message of the satellite is a 30 seconds long
  • Each sub-frame divides into 10 words each
  • TLM time division multiplexer
  • a snap start designated by arrow 160 indicates, on the local
  • BTSs such as frame 170 of BTS 162 are shadowed to distinguish them from other frames.
  • a synchronization frame is encountered, it is identified by its internal structure, and the identification number it bears is registered, then, the number pf frames elapsed between this frame and the
  • snap start (arrow 160) are counted, including fractions of a frame, thereby finding the time between the snap start and the synchronization frame, in sub-frame resolution.
  • the arrow 112 indicates the first code period start encountered during since snap start. This timing indicator is also registered with respect to snap start 160 so all BTSs synchronization frames are also registered with respect to code periods of the satellite.

Abstract

A system is described which provides a timing reference for a plurality of BTSs (base transceiver stations), of an unsynchronized cellular network. The system receives and processes two types of radio sources, namely BTSs signals and navigation satellite signals. It employs internal triggering for snap starts. One embodiment of the system incorporates commercial GPS receiver (65) for executing some of the tasks otherwise performed by the processor and triggering circuit. A local clock (78) determines the rate at which signals of the radio sources are sampled. In the method of the invention, regular satellite positioning is performed out of which local clock bias is calculated, and local clock drift is calculated by the ratio between observed Doppler offset and calculated Doppler offset. Mutual BTSs signals are matched, providing mutual synchronization by referencing the timing of identifiable timing structures of each BTSs to the snap start. The BTSs signals are also referenced to satellite system time in order to facilitate the use of hybrid navigation techniques.

Description

REFERENCE UNIT FOR A LOCATION SYSTEM OF A CELLULAR
NETWORK
FIELD OF THE INVENTION
The present invention relates generally to location systems of mobile transceivers. More specifically, the invention is in the field of location systems for mobile units of unsynchronized cellular systems.
BACKGROUND OF THE INVENTION
Ranging methods based on radio channels measure the time it takes for a radio signals to travel from a radio source to a receiver. The longer it takes for the signal to travel the way, the farther the receiver is displaced from the emitter. A set of radio sources emitting signals received by a receiver, can potentially provide enough physical information of time of travel for such a receiving unit to determine its own location relative to the radio stations. Practically however, the speed of light being extremely high, about 3 X 108 m/sec, requires compatible clock for providing meaningful measurements of the time of arrival of the respective signals to the receiver of the radio sources.
There are additional requisites that must be fulfilled in order to make the ranging technique practical. The emitted signals of the radio sources must be structured in such a way as to facilitate timing references of the signal to be clearly discerned by the receiver. Base stations of the GSM network do not supply time of emission of signals, which complicates the process for determination of location. A way to overcome the lack of data as incicated earlier is by providing timing references which mutually synchronize base stations. In WO - 99- 21028, the contents of which are incorporated herewith by reference, is disclosed a method for calculating a location of a mobile receiver (MU) in which at least one extra receiver of the unsynchronized cellular network is employed in order to provide time reference to base stations. Another method, disclosed in WO - 99 - 61934 uses navigation satellite ranging signals, in addition to base station signals.
GSM cellular networks operate along the principles of the TDMA (time division multiple access) and FDMA (frequency division multiple access) technology and associated standards. The time division principle allows many subscribers to use the radio channel concomitantly by occupying each a small portion of the time resources available for the communication medium. To achieve that, the mobile stations (MUs) communicating with a certain base station (BTS), are rendered mutually synchronized. The BTSs communicates with each mobile unit by sending a sequence of discrete structures called time slots, allocated exclusively for data bits to or from the active subscriber, uplink or downlink oriented.
GSM and other unsynchronized cellular network systems do not provide however mutual base station synchronization. This implies that whereas each MU is fully synchronized with the BTS with which they are actively engaged, there is no concomitant synchronization of a mobile station with other base stations of the same network. This lack of mutual time synchronization among the BTSs of a network, precludes the possibility of a MU to synchronize with signals originating in BTSs other than the one within the cell boundary of which it is operative. Accurate ranging methods for locating
mobile units based on network radio channels, cannot be sustained under
these circumstances unless a synchronization element mutually synchronizing
base stations is made operative to that effect. A network element called LMU
(location measurement unit) is such a GSM network elements that
synchronizes between different BTS (ETSI MOBILE NEWS, SPECIAL
EDITION - 2000 GSM WORLD CONGRESS). With regards to the reference
methods, the LMUs are classified into two classes: first, a class containing
mutually synchronizing BTS signals on a real time basis, in that the correlation
between identifiable timing structures of the different BTS signals are made in
real time furnished by the real time clock of the LMU. A second LMU class,
correlates the received identifiable timing structures of the BTSs with the GPS
timing structures. A GPS - correlating LMU is inherently more accurate than a
non GPS correlating LMU. The reason for that stems from the fact that a GPS
system clock has a much higher stability (10 "12 sec/sec deviation) as compared
to network clock stability (10 "8 sec/sec deviation).
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for mutually
time - synchronizing signals of BTSs. According to the method of the invention,
all available BTSs of a cellular network are received by a NRU (network
reference unit) of the invention. The respective signals of the BTSs are
processed in a single snap. They are digitized, and the individual discrete frames are discerned. Identifiable timing frames of each respective BTS signal are matched with the equivalent timing frames of all other BTS signals, thus providing mutual calibration. Navigation satellites (typically of the GPS system) are received, providing for bias corrections to be made to the local clock of the NRU. Code periods of the satellite system are digitized and matched with the BTS frames in the same snap indicate earlier.
A further object of the present invention is to provide a system for time - synchronizing signals of individual BTSs (base transceiver stations) of an unsynchronized cellular network with the time system of the GPS system of navigation satellites. The system of the invention contains receiving circuits for satellite navigation signals and for BTS signals. The system contains sufficient DTA (digital to analog devices to facilitate fast parallel sampling of all received signals, the rate of which is set by a local clock, and the resulting digital numbers are stored in a snap memory preferably capable of storing two snaps. The system of the invention provides for a triggering circuit and a communication line for receiving and transferring data to and from the network.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1A is a block diagram illustrating the main functional elements of a prior art LMU of a GSM cellular network;
Fig. 1 B is block diagram illustrating the interconnectivity of the functional elements of a prior art LMU as in Fig. 1 A; Fig. 2A is a block diagram illustrating schematically the architecture of
a NRU (network reference unit) in accordance with a preferred embodiment of
the invention.
Fig. 2B is a block diagram illustrating schematically the architecture of
a NRU (network reference unit) having additional GPS receiver unit.
Fig. 3 is a schematic illustration of the sequence of events performed
for achieving mutual synchronization of BTSs.
Fig. 4 is a graphic illustration describing the timing signal structures of
the satellite with respect to the BTS signals within the frame work of a single
snap in the processor.
Fig. 5. is a graphic illustration describing the timing signal structures of
the satellite with respect to signals of two BTSs as being matched in the
processor, mutually and with respect to the satellite time system.
Fig. 6 is a block diagram classifying the groups of data which
contribute to the synchronization process of the invention.
Fig. 7 is a schematic illustration describing the sequence of events of
calculating the local clock bias with respect to satellite system clock.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
GPS referenced commercial LMUs employed in GSM networks
contain the functional components as are illustrated schematically in Fig. 1A, to
which reference is now made. A fully operational GPS receiver 14 is coupled to
a time measuring circuit 16. The data obtained is sent to the BTS through a link
18. A precise clock 15, of better stability characteristics than mobile unit clock, provides frequency for the ATD (analog to digital) circuit of the cellular receiver 20, and timing reference to the TMC (time measuring circuit) 16. The TMC measures time between the precise trigger pulse supplied by the GPS receiver 14 and one or more identifiable timing references of the of the BTSs received.
The timing references are sent to the BTS through a link 18 to network. The
present invention relates also to third generation networks, for example UMTS networks, that are scheduled to succeed the GSM networks.
In Fig. 1B such an LMU is described in more details and in reference
to the functionality thereof. GPS antenna 13 is connected to a fully operational
GPS receiver 14 that sends a triggering pulse, known as 1PPS (one pulse per
second) to the TMC (time measurement circuit) 16. The GPS receiver can also
send system time data to the TMC. An RF receiver 22 receives BTS signals
through antenna 33, the signal is downconverted by a circuit 36 to IF, and burst periods extracted. Analog to digital converter 34 demodulates the signal and
frames of the BTS signals are then extracted. The TMC 16 calculates the time difference between the triggering pulse and the reception of the identifiable time references of the BTSs, typically SCHs (synchronization channels). The time difference between the triggering pulse and the timing references may be long enough to cause deterioration of the timing accuracy, which necessitates the employment of a high quality clock 42. Communication channel 44 sends to the network respective time matching data of each of the BTS signals as referenced to the 1 PPS pulse, through a physical A-bis connection or through wireless connection. Controller 48 regulates the output link with the network. Optionally, Ancillary data, obtained by the GPS receiver, from the individual satellites (ephemeris) or system time are also transferred to the network through any of the two links, A - bis 46, or wireless transmitter 38.
In Fig. 2A to which reference is now made, is described in general the architecture of a NRU (network reference unit), in accordance with a preferred embodiment of the invention. RF receiver 64, receives through antenna 62 at
least one GPS satellite navigation signals. The signal is downconverted in
circuit 66, and the resulting IF signal is digitized by the ATD (analog to digital)
converter 68. Triggering circuit 69 triggers the snap memory which sets off a data collection and processing stage as will be elaborated later on. The sampling rate is determined by local clock 78. In a parallel circuit, triggered by the same triggering signal as above, cellular BTSs are received through antenna 70, which may be the same as antenna 62, and the received signal is
downconverted in circuit 74. IF signal is sampled in ATD converter 76, the
sampling rate of which is set by local clock 78. When sampling is finished, snap memory 79 transfers the information into signal processor 80. Signal processor
80 receives therefore a digitized output of digitizers 68 and 76 collected in one snap, and processes the signals. Processor 80 sends the resulting data to communication channel 82.
The transmission is carried out by wireless link, or by a physical A -bis link to the network 84. In another embodiment of the invention, described generally in
Fig 2B to which reference is now made, a commercial GPS receiver 65 is
integrated into a network NRU of the invention, for performing several tasks. A first task is obtaining satellite ephemeris data independently, and another reason is for triggering the snap through the 1PPS mentioned above. Other tasks of the adjunct GPS receiver will be discussed later on. The adjunct receiver 65 is optionally connected to the existing antenna 62 at the front end,
and to the processor 80.
Mutually synchronizing the BTS signals
To achieve the end of mutual synchronization of cellular BTSs signals and their common reference to the GPS system time, the following steps are followed, as depicted generally in Fig. 3 to which reference is now made. In accordance with the present invention, a trigger is set off at a predetermined rate and for a predetermined period of time, typically for 0.1 second every 30 seconds. The trigger sets off a process which aims at achieving mutual synchronization of cellular BTS signals and a reference to the GPS system time.
Snap is triggered at step 108, collecting data from both a plurality of GPS
system satellites and a plurality of BTSs, in step 110. Data processing begins
in step 112 within reception of enough data to start a procedure, as will be
explained later on. In step 114 the BTSs are mutually synchronized and referenced to the GPS system time.
The processor of a NRU of the invention performs the necessary calculations for calibrating the local clock. The principles of the calibration procedure for the local clock are explained with reference to Fig. 4. The local clock time axis is indicated in the figure by arrow 120. When triggered, a snap
start designated by arrow 122 occurs receiving the two signals: satellite and BTS. In the processing stage, two respective repetitive signal structures are discerned, one of each radio source. The contiguous repetitive GPS code periods are discerned, by correlating the received signal code with a stored replica code within the processor. Discrete GSM frames are discerned by identifying specific burst periods, such that the total number of frames is calculated until a synchronization frame is identified. In more detail, a first beginning of a GPS code period 130, marked by arrow 118 is measured in local
clock time terms. When the first synchronization frame 124, hereinafter referred to as s.frame of a certain BTS signals is encountered, the processor calculates the number of frames having been counted since snap start 122. The method of the invention takes into consideration measurement elements much shorter than GSM frames, and the example portrayed in Fig. 4 puts line 126 in a frame start, for convenience of illustration but sub- frame structures, i.e. time slots, bits and sub- bit accuracy can be attained.
Two calculation results are subsequently obtained, in local clock
terms: A. Tsatreference ~ ' snap start 3Hd B. Ts.frarne start — Tsnap start • The local Clock IS
used only for the short period of time between snap start and the GPS code period, and s.frame, whichever comes last. For this short period of time it is required to compensate the measurement system for inaccuracies cause by the local clock bias and drift. This compensation is effected by using the timing and Doppler data derived from the GPS system with reference to the local clock. In Fig. 5 to which reference is now made, the synchronization of two cellular BTS channels are described schematically. A snap start designated by arrow 160 indicates, on the local clock time axis and on the satellite time axis, the initiation of data collection and loading into the snap memory. Collected are frames of a first BTS signal 162, and of a second BTS 164. In addition, the
code periods of GPS navigation transmission 166 are collected. S.frames of the
BTSs, such as frame 170 of BTS 162 are shadowed to distinguish them from other frames. Thus, when a s.frame is encountered, it is identified by its internal structure, and the identification number it bears is registered, then, the number pf frames elapsed between this frame and the snap start (arrow 160) are counted, including fractions of a frame), thereby finding the time between the snap start and the s: frame, in sub-frame resolution. The same is performed for the signal of BTS 164, until all available BTSs have mutually correlated their timing, referencing to the same snap start. It should be noted that this entire process is performed with corrected local clock bias. The compensation for drift is implemented for every sample in the snap, assuming a linear drift model.
Compensating for local clock bias
In each snap, data is collected in order to provide a set of parameters required for repeatedly correcting the measurements performed using the local clock as a reference. Data from optional sources are collected and submitted for processing by a processor of the unit of the invention in. In Fig. 6 to which
reference is now made, the data collected for providing to processor 240 of the NRU of the invention are classified into three groups. Group 242 is the information related to the satellite system. This group includes:
1. Ephemeris data for each satellite received
2. Differential correction parameters for each satellite received is optionally provided.
3. Satellite system time (TOW)
Group 244 contains the location parameters of the NRU itself, in units and
terms compatible with the geographical notation used by the unit. This Information need not be updated once the unit is positioned, but should be updated if the unit is moved. Group 246 contains the information carried by the signals of the BTSs, which include the transmitted signals of all available BTSs, at preset frequencies.
Table 1 describes the above information types and the alternative sources for their acquisition.
Table t
Figure imgf000013_0001
In accordance with a preferred embodiment of the invention, the
sequence of events leading to calibration of the local clock begins with
determining the location of the NRU. Such can be achieved by either obtaining
the information from a data base within the network or by calculating within the
NRU, based on received satellite data. Within the NRU, the determination can
be carried out by the processor of the unit, or by the adjunct receiver, if present.
In Fig. 7 to which reference is now made, the steps for determining the
described are described. In step 250, the receiver locks on to every available
satellite, extracting from each of them navigation information, which allows in
step 252 to calculate ranges to each of the available satellites. In step 254,
from the range parameters calculated for each satellite, the local clock bias for
each satellite, as will be explained later on. Bias obtained for each satellite, in
step 256 a mean is calculated with respect to all of the satellites.
The functional relationship between local clock bias and the range is
explained as follows. The difference in time of transmission (Ttr ) from the
satellite and the time of reception of a signal (Tre) is the time it takes to a signal
to pass the distance from the satellite to a receiver. Theoretically , this time,
multiplied by the speed of light ( C ) is the distance (Range) between the two
objects. Theoretically:
1. (Ttr - Tre )XC = R
In reality, this range is not absolute because the parameter Tre is measured by a relatively inaccurate local clock, and the measured distance is called therefore
pseudorange (PR). In real world therefore: 2. (Ttr - Tre)XC = PR A parameter representing the local clock bias is inserted in the equation as follows:
3. (Ttr - Tre - clock_bias)XC = R From a set of equations formed by the measurements performed with respect to each satellite, R given as distance between the geographical location of the NRU, and the satellite's position as derived from the ephemeris data, Ttr extracted, Tre provided, clock_bias is calculated. Clock bias is thus calculated for each satellite received, and a mean is calculated. The clock bias obtained is used for correcting the local clock bias at the snap start (advance or retard). As regards the clock drift, Doppler frequency is used in the assessment of the variable. The local clock drift is calculated as follows:
- . - . _ measured Doppler offset - calculated Doppler offset
Local _ clock _ drift = = — — — = = — — — =
No min al _ frequency
Compensating for satellite clock bias
Within the ephemeris of the satellite navigation message, there is contained information for compensating for satellite clock offset and drift. This information is used for correcting the system time synchronization, and local clock bias and drift.
Determining BTS clock drift
The transmitter in each BTS contains a clock that provides a reference for the production of the discrete signals subsequently received by the individual mobile receivers localized within the particular cell. Although the clock of the BTS is more stable than that of the NRU, the procedure of the invention includes determining the clock drift of each BTS timing signals received, with reference to the more stable satellite system clock. In order to determine a BTS clock drift, two separate snaps are executed, registering in each snap a nominal of a synchronization frame, matched to a snap start. The entire procedure for determining BTS clock drift is explained schematically by reference to Fig. 5, to which reference is again being made. BTS signal 162 is
digitized and synchronization frame 170 is identified, its identity registered.
Arrow 112 designates the point in time on the local clock's time axis at which a first period start is encountered. Thence, the start time of synchronization frame
170 with respect to arrow 112, is registered as ΔTsnapl. In other words, the
difference in time (corrected local clock time), between code period start and synchronization frame start is registered. Subsequently, in the consecutive
snap, the same procedure is repeated, registering ΔTsnap2.
The difference ΔTsnapl- ΔTsnap2, for a given nominal time difference between
the respective snap starts, is considered a function of the BTS clock drift. The resulting parameter is used by mobile units for calculating location, based on ranging to BTSs.
Synchronizing BTSs clocks with satellite system time
The purpose of this aspect of synchronization of the BTSs is to correlate between their timing and the GPS system time. This procedure is implemented mainly for facilitating so called hybrid location procedures, involving pseudoranging to satellites as well as to BTSs. The C/A code used for
regular pseudoranging positioning tasks of GPS receivers is transmitted in code
periods as explained above. Each code period lasts exactly 1 msec
(millisecond) and repeats itself perpetually and contiguously. Each sequence of
20 code periods is structured into a data bit and each 30 bits are structured into
a word. The entire navigation data message of the satellite is a 30 seconds long
entity, divided into 5 sub-frames. Each sub-frame divides into 10 words each
one 600 msec long, the first of which in a cycle is a telemetry message (known
as TLM) which is an identifiable timing structure. Following the TLM word is a
HOW (hand over word) that contains the TOW (time of week) information.
There exists a synchronization between a beginning of a data bit and a
beginning of a code period. A more elaborate explanation is found in
UNDERSTANDING GPS: PRINCIPLES AND APPLICATIONS, Elliott D.
Kaplan, ed., Artech House Publications, Boston - London.1996, pp. 186 -
189, the contents of which are incorporated herein by reference. In order to
keep the system of the invention synchronized with the system time, the snap
must be performed at such a time as the HOW word, containing the TOW
data is received. This is performed by orderly scanning of the navigation
message, until such a time as identification of a TLM word is achieved.
Reference is again made to Fig. 5, now describing schematically in a
snap performed during a HOW word, BTSs signals and satellite code periods
are received. A snap start designated by arrow 160 indicates, on the local
clock time axis and on the satellite time axis, the initiation of data collection
and loading into the snap memory. Collected are frames of a first BTS signal 162, and of a second BTS 164. In addition, the code periods of GPS
navigation transmission 166 are collected. Synchronization frames of the
BTSs, such as frame 170 of BTS 162 are shadowed to distinguish them from other frames. Thus, when a synchronization frame is encountered, it is identified by its internal structure, and the identification number it bears is registered, then, the number pf frames elapsed between this frame and the
snap start (arrow 160) are counted, including fractions of a frame, thereby finding the time between the snap start and the synchronization frame, in sub-frame resolution. The arrow 112 indicates the first code period start encountered during since snap start. This timing indicator is also registered with respect to snap start 160 so all BTSs synchronization frames are also registered with respect to code periods of the satellite.

Claims

1. A network reference unit for providing time reference for unsynchronized cellular network, wherein identifiable time references of respective signals of a plurality of BTSs (base stations) are mutually synchronized, comprising:
• a receiver for receiving a plurality of BTS signals,
• at least one receiver for GPS satellite navigation signals,
• a local clock for providing rate for sampling said BTS signals and said GPS satellite navigation signals,
• at least one ATD (analog to digital) converter for each receiver;
• a snap memory for storing BTS and satellite data of at least one snap, and
• a processor for processing data received at least from said snap memory.
2. A network reference unit for providing time reference for unsynchronized cellular network as in claim 1 , comprising two receivers for GPS signals.
A method for mutually synchronizing respective signals of a plurality of BTSs of an unsynchronized cellular network, and for synchronizing said plurality of BTS with GPS system time, whereby a reference unit receives said plurality of BTSs and matches identifiable timing references of said signals, comprising the steps of:
• receiving signals of said plurality of BTSs signals in a single snap,
• receiving identifiable timing references of at least one
GPS navigation satellite signal in said snap,
• compensating a local clock of said reference unit for offset and drift with respect to GPS clock,
• sampling simultaneously said at least one satellite signal and said plurality of BTSs signals,
• measuring time difference between identifiable timing references of each respective signal and a snap start, and
• matching between said identifiable timing references and satellite system time.
4. A method for mutually synchronizing signals of a plurality of BTSs
of an unsynchronized cellular network, as in claim 3, and wherein
at least ephemeris data for calculating said compensating of said
local clock is obtained from said cellular network.
PCT/US2001/008557 2000-04-07 2001-03-19 Reference unit for a location system of a cellular network WO2001078260A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007022361A1 (en) * 2005-08-16 2007-02-22 Sirf Technology, Inc. Synchronizing a radio network with end user radio terminals

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997023785A1 (en) * 1995-12-22 1997-07-03 University Of Technology, Sydney Location and tracking system
EP0803994A2 (en) * 1996-04-22 1997-10-29 Italtel s.p.a. Method to obtain and synchronize the radio multiframe number in DECT cordless systems
WO1998052376A1 (en) * 1997-05-09 1998-11-19 Nokia Telecommunications Oy A method for determining timing differences between radio transmitters and a radio network incorporating the same
WO1999021028A1 (en) * 1997-10-22 1999-04-29 Cambridge Positioning Systems Ltd. Positioning system for digital telephone networks

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997023785A1 (en) * 1995-12-22 1997-07-03 University Of Technology, Sydney Location and tracking system
EP0803994A2 (en) * 1996-04-22 1997-10-29 Italtel s.p.a. Method to obtain and synchronize the radio multiframe number in DECT cordless systems
WO1998052376A1 (en) * 1997-05-09 1998-11-19 Nokia Telecommunications Oy A method for determining timing differences between radio transmitters and a radio network incorporating the same
WO1999021028A1 (en) * 1997-10-22 1999-04-29 Cambridge Positioning Systems Ltd. Positioning system for digital telephone networks

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7925210B2 (en) 2001-05-21 2011-04-12 Sirf Technology, Inc. Synchronizing a radio network with end user radio terminals
WO2007022361A1 (en) * 2005-08-16 2007-02-22 Sirf Technology, Inc. Synchronizing a radio network with end user radio terminals

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