U.S. patent application number 12/494715 was filed with the patent office on 2009-10-22 for synchronization of timing advance and deviation.
This patent application is currently assigned to INTERDIGITAL TECHNOLOGY CORPORATION. Invention is credited to Stephen E. Terry.
Application Number | 20090262713 12/494715 |
Document ID | / |
Family ID | 22719998 |
Filed Date | 2009-10-22 |
United States Patent
Application |
20090262713 |
Kind Code |
A1 |
Terry; Stephen E. |
October 22, 2009 |
SYNCHRONIZATION OF TIMING ADVANCE AND DEVIATION
Abstract
Apparatus and method for reducing the latency from timing
deviation (TD) measurement to time advance (TA) adjustment. A
deterministic procedure to coordinate time advance (TA) commands
and timing deviation (TD) measurements is used so that failed
transmissions or mobile terminals signal propagation changes can be
recognized and corrected much more rapidly. Radio resource
efficiency is maximized by minimizing signaling overhead through
effectively reducing the frequency of time advance commands. This
is accomplished by using TA command signals which include a Connect
Frame Number (CFN) to specify particular radio frames for time
advance (TA) adjustment. The potential for timing deviation (TD)
measurements to be incorrectly processed in conjunction with
adjusting a physical reception window and calculating mobile
termination location is minimized, without excessive command
signaling requirements.
Inventors: |
Terry; Stephen E.;
(Northport, NY) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600, 30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
INTERDIGITAL TECHNOLOGY
CORPORATION
Wilmington
DE
|
Family ID: |
22719998 |
Appl. No.: |
12/494715 |
Filed: |
June 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10082844 |
Feb 25, 2002 |
7573913 |
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12494715 |
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09826464 |
Apr 5, 2001 |
7023835 |
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10082844 |
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60195087 |
Apr 6, 2000 |
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Current U.S.
Class: |
370/336 ;
370/350 |
Current CPC
Class: |
H04W 56/001 20130101;
H04J 3/0682 20130101; H04W 56/00 20130101; H04W 92/10 20130101;
H04W 56/0045 20130101; H04W 56/0005 20130101; H04B 7/2681
20130101 |
Class at
Publication: |
370/336 ;
370/350 |
International
Class: |
H04J 3/06 20060101
H04J003/06 |
Claims
1. An apparatus for wireless communication comprising: a
transmitter configured to transmit selectively formatted
communication data to mobile terminals within system radio frames;
a receiver configured to receive communication data from mobile
terminals within system radio frames; a controller configured to
measure timing deviation of received mobile terminal transmissions
in identified radio frames in which communication data is received
from a selected mobile terminal; the transmitter configured to
transmit timing advance command signals which include: timing
advance data which is calculated based upon measured timing
deviation in an identified radio frame for a selected mobile
terminal, and information specifying a particular radio frame for
effectuating a timing adjustment by the selected mobile terminal;
and the controller configured to measure the timing deviation for
communication data received from a selected mobile terminal to
which a timing advance command signal had been transmitted in the
particular radio frame specified by the transmitted timing advance
command signal.
2. The apparatus according to claim 1 wherein the controller is
configured to generate timing advance command signals that include
a Connect Frame Number as the information specifying a particular
radio frame.
3. The apparatus according to claim 2 wherein the controller is
configured to only generate a timing advance command signal for a
selected mobile terminal when a measured timing deviation of a
transmission received from the selected mobile terminal is not
within a selected timing synchronization range.
4. The apparatus according to claim 1 further comprising a
geographic locator configured to calculate a geographic location of
the selected mobile terminal during the specified time frame in
conjunction with the timing advance data of a most recent
successful timing advance command signal transmitted to the
selected mobile terminal.
5. The apparatus of claim 4 including a base station coupled with a
radio network controller wherein the base station includes the
transmitter and receiver and the radio network controller includes
the controller and the geographic locator.
6. The apparatus of claim 1 including a base station coupled with a
radio network controller wherein the base station includes the
transmitter and receiver and the radio network controller includes
the controller.
7. A method for synchronizing signals in wireless communications
comprising: transmitting a timing advance command signal to a
selected mobile terminal that includes: timing advance data
calculated based upon measured timing deviation in an identified
radio frame from the selected mobile terminal, and information
specifying a particular radio frame for effectuating a timing
adjustment by the selected mobile terminal.
8. The method according to claim 7 wherein the timing advance
command signals include a Connect Frame Number as the information
specifying the particular radio frame.
9. The method according to claim 7 further comprising: receiving
communication data from the selected mobile terminal in the
particular radio frame specified by the transmitted timing advance
command signal; and measuring timing deviation for communication
data received from the selected mobile terminal in the particular
radio frame specified by the transmitted timing advance command
signal to determine if further timing adjustment is required for
the selected mobile terminal.
10. The method according to claim 9 further comprising: generating
a timing advance command signal when a measured timing deviation of
a transmission received from the selected mobile terminal is not
within a selected timing synchronization range.
11. The method according to claims 10 further comprising: using
measured timing deviation with respect to communication data
received from the selected mobile terminal in a specified time
frame to calculate a geographic location of the selected mobile
terminal during the specified time frame in conjunction with the
timing advance data of a most recent successful timing advance
command signal transmitted to the selected mobile terminal.
12. The method according to claim 10 wherein the timing advance
command signals include a Connect Frame Number as the information
specifying the particular radio frame.
13. The method according to claim 12 wherein the transmitting and
receiving is performed by a base station and the measuring and
generating is performed by a radio network controller
14. The method according to claim 7 further comprising: receiving
communication data from the selected mobile terminal in the
particular radio frame specified by the transmitted timing advance
command signal.
15. The method according to claim 14 performed by a base
station.
16. The method according to claim 7 performed by a base
station.
17. A base station comprising: a transmitter configured to transmit
selectively formatted communication data to mobile terminals within
system radio frames; a receiver configured to receive communication
data from mobile terminals within system radio frames; and the
transmitter configured to transmit timing advance command signals
which include: timing advance data which is calculated based upon
measured timing deviation in an identified radio frame for a
selected mobile terminal, and information specifying a particular
radio frame for effectuating a timing adjustment by the selected
mobile terminal.
18. The base station according to claim 15 wherein the transmitter
is configured to transmit timing advance command signals which
include a Connect Frame Number as the information specifying a
particular radio frame.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. application Ser.
No. 10/082,844, filed Feb. 25, 2002, which is a continuation of
U.S. application Ser. No. 09/826,464, filed Apr. 5, 2001, now U.S.
Pat. No. 7,023,835, which claims priority from U.S. Provisional
Application No. 60/195,087, filed Apr. 6, 2000, which applications
are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to digital
communication systems. More specifically, the invention relates to
a system and method for synchronizing uplink and downlink
transmissions for time division duplex and time division multiple
access protocols to compensate for radio propagation delays. As an
additional benefit, the systems facilitate geographic location of
mobile terminals.
BACKGROUND OF THE INVENTION
[0003] In the proposed 3.sup.rd generation (3G) wireless protocols,
time division duplex (TDD) and time division multiple access (TDMA)
methods divide an allocated radio spectrum into repetitive time
periods known as radio frames which are uniquely identified by a
sequential cell frame number (FN). Each radio frame is further
subdivided into a plurality of unique, numbered time slots (TS)
which are individually assigned for uplink (UL) or downlink (DL)
transmission.
[0004] Radio transmissions incur a propagation delay relative to
the distance from a transmitter to a receiver. In mobile cellular
communication systems, these delays vary over time as the distance
between a mobile terminal (MT) and a base station (BS) changes. In
order to receive communication transmissions without error, the
time of reception must be known to the receiver.
[0005] To compensate for varying propagation delays and to maintain
a known time of reception, the time of transmission is periodically
adjusted. The transmission timing adjustment is performed in the MT
rather than the BS since many MT's are supported by a common BS and
the propagation delay for each MT is different depending upon
distance. The BS downlink radio frame transmissions do not vary
over time and are used by an MT to synchronize uplink radio frame
transmissions.
[0006] The MT synchronizes to a BS downlink transmission that has
incurred a propagation delay. The MT uplink transmission also
incurs a propagation delay approximately equal to the downlink
propagation delay. The uplink transmission received in the BS is
the sum of the downlink and uplink propagation delays. Radio frame
reception (DL) and reply transmission (UL) at a MT before any
timing adjustment is performed is shown in FIG. 1a. FIG. 1a
illustrates a BS transmitted DL time slot (TS) received by the MT
immediately followed by a MT transmitted UL time slot (TS). Radio
frame transmission (DL) and reception (UL) at a base station before
any timing adjustment is performed is shown in FIG. 1b. FIG. 1b
illustrates one MT transmitted UL time slot immediately followed by
a BS transmitted DL time slot.
[0007] As reflected in FIG. 1a, the MT synchronizes on the downlink
time slot reception at a time T1 and initiates its uplink
transmission immediately thereafter. As shown in FIG. 1b, the start
of the downlink time slot (TS) transmission by the BS occurs at
time T2 and the end of a preceding uplink time slot (TS) received
by the BS occurs at time T3. The difference between times T3 and T2
is referred to as timing deviation (TD) and is equal to the sum of
the uplink and downlink propagation delays.
[0008] The TD can be identified and used to command the MT to
adjust the uplink time slot transmission time in order to
synchronize uplink transmission with downlink reception at the BS.
Since the MT is synchronized to a received downlink time slot that
has already incurred a downlink propagation delay, the MT must
advance transmission of uplink time slots by the TD sum of uplink
and downlink propagation delays. This is referred to as timing
advance (TA) defined as:
T3-T2=TD=UL propagation delay+DL propagation delay=TA Equation
1
[0009] Radio frame reception (DL) and reply transmission at an MT
after the TA adjustment is shown in FIG. 2a. FIG. 2a shows a BS
transmitted DL time slot followed by a time advanced MT transmitted
UL time slot at the MT. Radio frame transmission (DL) and reception
(UL) at the base station after TA adjustment of the transmission is
shown in FIG. 2b. FIG. 2b shows one BS transmitted DL time slot
immediately followed by a time advanced MT transmitted UL time slot
as received at the BS.
[0010] The MT has advanced the UL time slot transmission according
to the TA command from time T5 to time T4. Since the received time
slot at time T5 has already incurred the DL propagation delay, the
new MT time slot transmission time T4 synchronizes the reception
time T6 of the BS received UL time slot advanced by the expected UL
propagation delay.
T4=T5-TA(sum of UL and DL propagation delays) Equation 2
T5=T6(BS next time slot)+DL propagation delay Equation 3
T4=T6(BS next time slot)-UL propagation delay Equation 4
[0011] Accordingly, the TA adjustment of the MT transmissions
results in synchronization of UL and DL time slots at the BS.
[0012] A BS controller is responsible for instructing the MT to
adjust the uplink transmission according to the calculated TA. MT
commands for TA adjustment generated by the BS controller may
require considerable physical resources, it is important for the BS
controller to generate TA adjustment commands as infrequently as
possible to minimize signaling overhead.
[0013] This is facilitated by using small guard period (GP) with
respect to the time slot duration, within each radio frame between
transmitted data of each time slot. A conventional time slot
structure is shown in FIG. 3. The GP avoids simultaneous
transmission and reception in either the BS or MT. A "physical
reception window" of operation, which is substantially smaller than
the GP, dictates the allowed timing deviation. The physical
reception window shifts within the GP as MT propagation delay
changes.
[0014] The measured TD reflects the location of the physical
reception window within the GP. The TA provides a corrective shift
of the physical reception window within the GP. It is important to
synchronize the TA adjustment in the MT and BS, since the BS
reception window shifts as well. Conventionally, the BS controller
continuously monitors the TD for each MT independently and
generates TA commands in advance of the allowed physical reception
window being exceeded.
[0015] The logic used to generate TA commands infrequently must
also take into account the possibility that radio transmission
failures can cause TA commands not to be received by the MT. This
requires a fast and deterministic way to recognize when the MT has
not performed the TA adjustment.
[0016] The TD and TA can additionally be used to determine the
location of MTs. Since the propagation delay is equatable to the
distance between an MT and a BS, the TDs from several BSs for a
particular MT can be used to calculate by triangulation the MT
location.
[0017] In order to produce accurate TA signals in connection with
maintaining the reception window, minimizing signaling overhead and
geolocation, it is important to know the TA for the time slot the
TD was measured. Applicant has recognized that one method to
accomplish this is only to allow the TA to take affect in the MT on
specifically identified frames.
[0018] The need to coordinate TA adjustment in the MT and TD
measurement in the BS to a specific sequential radio frame is
difficult since the time of reception and processing in the MT of
the BS generated TA command is not known to the BS controller. One
conventional method is to only allow adjustments on periodic frame
boundaries. Since the radio frames are sequentially numbered,
periodic sequential frame numbers are conventionally used. However,
the period needs to be excessively large to guarantee that the TA
command can be processed in advance of the next periodic TD
measurement.
[0019] To determine the TA frame number period necessary to
coordinate the process, the worst case latency between BS
controller generation of the TA command to MT processing must be
used. This is the minimum period necessary to guarantee TA
adjustment on the next TA frame number. For this case, the BS
controller needs to initiate the procedure immediately following
the previous TA frame number period. This effectively results in a
TA adjustment delay of up to two TA sequential frame number
periods.
[0020] As shown in FIG. 4, the worst case latency from BS
generation to MT processing of the TA adjustment command is the
time between TA frame numbers. The BS may determine a TA command
needs to be generated some time (T1) after TA frame number 1 and a
time (T2) before TA frame number 2. To guarantee coordination of
the time the TA will take effect between the MT and BS, the BS must
wait for the previous TA frame number period to expire to generate
the request at time (T3). The result is when the TA requirement is
recognized at time T1 the delay to coordinate the TA adjustment is
greater than one frame number TA period, and at time T2 the delay
is less the two frame number TA periods.
(FN TA period)<(actual time to adjust TA)<(2(FN TA period))
Equation 5
[0021] Applicant has recognized that this methodology for TA
coordination using specified frame number TA periods results in
excessive TA delays that can be avoided. For example, excessive
delays can arise due to the potential for failed radio
transmissions. In this case it is necessary to recognize the failed
transmission in the BS controller as quickly as possible so that a
new TA adjustment command can be regenerated. Using the frame
number TA period method, the BS Controller will wait for subsequent
TD measurements following an expected TA adjustment to determine if
a TA command needs to be regenerated. This case is shown in FIG.
5.
[0022] In this prior art example, the BS controller, after
receiving a TD for correction at a time T0, must wait for a
subsequent TD measurement at time T1 that indicates the TA
adjustment did not take effect. The difficulty with this signaling
method is that the BS controller does not know exactly which TD
measurement identifies the TA adjustment failure. As a result, the
BS controller in order to minimize TA commands must wait for the
worst case TA adjustment delay before regenerating a TA command
base on the received TD measurement.
[0023] Another prior art solution has the MT confirm each TA
command as shown in FIG. 6. For this example, a timeout on the TA
confirmation will result in retransmission of the TA command. The
TA adjustment failure will be recognized faster then waiting for
the TA frame number period to expire. However, this faster recovery
requires approximately twice as much signaling since every command
is confirmed. This is undesirable, since a primary objective is to
reduce the TA command frequency.
[0024] Accordingly, there exists a need for a system and method
that allows for fast and efficient radio frame timing adjustment
without excessive command signaling requirements.
SUMMARY OF THE INVENTION
[0025] The present invention is directed to a system and method for
reducing the latency from timing deviation (TD) measurement to time
advance (TA) adjustment. The invention uses a deterministic
procedure to coordinate time advance (TA) commands and timing
deviation (TD) measurements so that failed transmissions or mobile
terminals signal propagation changes can be recognized and
corrected much more rapidly. Radio resource efficiency is maximized
by minimizing signaling overhead through effectively reducing the
frequency of time advance commands. This is accomplished by
specifying particular radio frames for time advance (TA) adjustment
by including a Connect Frame Number (CFN) in TA commands. The
potential for timing deviation (TD) measurements to be incorrectly
processed is then minimized since the TD measurement made in the BS
for the CFN specified radio frame, in which the TA adjustment was
to be made by the MT, will reflect whether or not the TA was
actually adjusted.
[0026] A preferred communication system supports base station
(BS)/mobile terminal (MT) wireless bi-directional communications
via the utilization of a radio frame format having sequentially
numbered system radio frames. System BSs have a transmitter for
transmitting selectively formatted communication data to MTs within
system radio frames and a receiver for receiving communication data
from MTs within system radio frames. The BS receivers have an
associated processor for measuring timing deviation (TD) in
identified radio frames of communication data received from a
selected MT.
[0027] Typically, TD measurement is monitored for all radio frames.
The BS processor associates the respective sequential frame number
with each TD measurement of transmissions received in a radio frame
thereby establishing a time associated with each measurement.
Timing advance (TA) commands are generated by a base station
controller that is associated with the BSs for providing TA
adjustment commands for transmission by the BSs to the MTs. The TA
adjustment command generator generates TA adjustment commands which
include the TA adjustment value, calculated based upon the most
recent successful TA command's adjustment and a measured TD for a
selected MT. TA adjustment commands also include a Connection Frame
Number (CFN) specifying a particular radio frame in which the
selected MT is to make the timing adjustment.
[0028] It is preferred that the TA signal generator only generates
a TA signal for a selected MT when the measured TD of a
transmission received from the selected MT does not fall within a
selected timing synchronization range, i.e. a TD threshold. Such a
TD threshold is preferably selected to correlate with the physical
reception window of the MTs and BSs.
[0029] After the BS controller transmits a TA adjustment command to
a selected MT, the TD measured for communication data received from
the selected MT in the frame specified in the CFN of the
transmitted TA command signal is analyzed to determine if the TA
adjustment has been made or if a new TA command is required.
Normally, a new TA command will be immediately required only if the
prior TA command did not successfully TA adjust the selected MT.
Otherwise the TD measurement for the CFN frame should be changed by
substantially the same amount which the TA command was to effect
and should fall within the TD threshold.
[0030] Preferred mobile terminals (MTs) have a transmitter and an
associated MT processor for transmitting selectively formatted
communication data to the BSs within system radio frames
synchronized by the MT processor and a receiver for receiving
communication data from the BSs within system radio frames. The MT
processor adjust the timing of the transmissions of the associated
MT transmitter in response to TA data in a received TA adjustment
command commencing in the radio frame specified in the CFN of the
received TA command.
[0031] The communication system preferably also includes a
geographic locator associated with the BSs for determining the
physical location of the MTs. In using conventional triangulation,
two or more BSs measures TDs with respect to communication data
received from a selected MT in a specified system radio frame.
However, using the TD measurements alone to calculate MT geographic
location will not produce an accurate result if the MT signal has
been TA adjusted. With the present invention, the TA of the MTs'
transmissions are known for virtually all radio frames, since the
actual TA is the TA of the most recent TA command signal
successfully sent to the MT. Since the TD for each CFN specified
radio frame is evaluated, failure of a TA command is known as soon
as the measured TD for the CFN frame is checked which is nearly
instantaneously. For a successful TA command, its TA value is used
in geolocation calculations for the frame specified by its CFN and
all subsequent frames until a CFN identified frame of the next
successful TA command. Thus, geographic location calculations may
be made with respect to any radio frame based on TA command data
which is known to have been effectuated.
[0032] The invention also provides a method of synchronizing
communication data at the BSs. Timing Deviation (TD) is measured in
identified radio frames in which communication data is received
from a selected MT by a BS. If the measured TD of a transmission
received from the selected MT does not fall within a selected
timing synchronization range, a TA command signal is generated. The
TA command signal includes TA data calculated based upon the
measured TD. The TA command signal also includes a Connect Frame
Number CFN specifying a particular radio frame for effectuating a
timing adjustment by the selected MT. The TA command signal is
transmitted to the selected MT. If the TA signal is then received
by the selected MT, the timing of the communication data
transmissions of the selected MT is adjusted based on the TA data
and commencing in the CFN specified radio frame of the received TA
command signal. The TD for data received from the selected MT to
which the TA command signal had been transmitted is checked for the
radio frame specified in the CFN of the transmitted TA command
signal to assure the TA command was effected in the selected MT.
Preferably, the TA command signal generation, transmission and the
associated TD checking is repeated when the TD of a transmission
received from the selected MT in the CFN radio frame does not fall
within a selected timing synchronization range or is not changed by
an amount virtually equal to the TA adjustment, since this would
indicate a failure of the selected MT to implement the previously
transmitted TA command.
[0033] The invention also facilitates a method of geographically
locating a mobile terminal (MT) in a communication system. The
method comprises effecting MT timing adjustments by communicating
timing advance (TA) command signals to a selected MT, when a
measured TD of a signal received by a BS from the selected MT
exceeds a TD threshold. The TA command signals including TA data
and a Connect Frame Number CFN specifying a particular radio frame.
Timing Adjustment of communication data transmissions by the
selected MT are made based on the TA data of a TA command signal in
the CFN specified radio frame. The TD for communication data
received from the selected MT in the CFN specified radio frame of a
TA command signal is checked to determine whether the respective TA
command signal was successfully effected by the selected MT,
thereby assuring the actual TA of the selected MT is known.
Measured timing deviation (TD) of a transmission received for a
selected radio frame from a selected MT one or more BSs is
collected. The TA data of the most recent successful TA command
signal and the TD measurements by the BSs for the selected radio
frame are used to calculate the geographic location of the selected
MT.
[0034] Other objects and advantages of the system and method will
become apparent to those skilled in the art after reading the
detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0035] FIG. 1a is a schematic timing diagram of radio frame
reception and transmission at a mobile terminal without any timing
adjustment.
[0036] FIG. 1b is a schematic timing diagram of radio frame
reception and transmission at a base station without any timing
adjustment.
[0037] FIG. 2a is a schematic timing diagram of radio frame
reception and transmission at a mobile terminal with timing
advance.
[0038] FIG. 2b is a schematic timing diagram of radio frame
reception and transmission at a base station with a timing advance
adjustment.
[0039] FIG. 3 is an illustration of a conventional time slot data
and guard period structure.
[0040] FIG. 4 is a timing diagram of a conventional time adjustment
method based on periodic frame number.
[0041] FIG. 5 is a timing diagram of timing adjustment command
failure and retransmission under the conventional method
illustrated in FIG. 4.
[0042] FIG. 6 is a timing diagram of an alternative conventional
method of timing adjustment utilizing command confirmation
signaling.
[0043] FIG. 7 is a timing diagram of frame number synchronized time
delay measurement and timing adjustment in accordance with the
teachings of the present invention.
[0044] FIG. 8 is a timing diagram of recovery from failed timing
adjustment in accordance with the teachings of the present
invention
[0045] FIG. 9 is a schematic diagram of a communicating system made
in accordance with the teachings of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0046] The embodiments will be described with reference to the
drawing figures where like numerals represent like elements
throughout.
[0047] Referring to FIG. 9, there is illustrated a communication
system 10 comprising a plurality of base stations (BSs) 12 which
conduct wireless communication with mobile terminals (MTs) 14. Each
BS conducts wireless communications with MTs in a geographic cell,
which cell areas normally have some overlap. Where an MT 14 is in
an overlap area, bi-directional communication is generally
conducted by the BS having the strongest signal link with the MT.
Where a second BS begins to have a stronger signal link, "hand off"
of the communication occurs. Desired parameters and procedures for
effectuating "hand off" are well known in the art.
[0048] In a preferred system such as in accordance with 3G wireless
protocols, node Bs 16 are provided in a physical or logical
connection with the one or more BSs. A radio network controller
(RNC) 17, to which the node Bs 16 are connected, controls the BSs
and coordinates communications over the communication system 10.
Multiple RNC's 17 coordinate communications for different BS groups
in an extended system. The RNC 17 includes a BS controller which
controls the BSs within the node Bs. Preferably the RNC 17 includes
an MT geographic locator, but it is not required that the
geographic locator be implemented in the RNC 17.
[0049] Each BS 12 preferably includes a transceiver 20 with an
associated antenna system 22 and BS signal processing circuitry 24.
Each MT 14 preferably includes a transceiver 26 with an associated
antenna 27 and MT signal processing circuitry 28. In lieu of
transceivers, BS and MT transmitters and receivers may be embodied
as separate components.
[0050] Downlink communications (DL) are processed by the BS
processing circuitry 24 and transmitted via the BS transceivers 20
from the BS antenna systems 22 for reception by the MTs 14. Uplink
communications (UL) are transmitted from the MTs 14 and received
via the BS antenna systems 22 and BS transceivers 20 of the base
stations 12.
[0051] The BS processing circuitry 24 implements the formatting of
wireless BS/MT communications into a selected radio frame format
having multiple time slots, which format is used on a system wide
basis for all BSs controlled by the RNC 17. Preferably, the RNC and
node Bs coordinate this implementation.
[0052] Within the radio frame format, each radio frame is assigned
a sequential number which enables the processing circuitry to
identify specific system frames in the wireless BS/MT
communications. The BS circuitry 24 is configured to measure
received time delays (TDs) such that each TD measurement is
identified with the respective radio frame of a received MT
transmissions, i.e. uplink communications. The sequential frame
numbers of the radio frames are used for this purpose.
[0053] The BSs provide TD data to the BS controller of the RNC 17
which preferably includes TD measurement data recorded at the BSs,
identification of the MT which made the measured UL transmission
and the system radio frame number in which the measured UL
transmission was received. When the TD measurement data exceeds a
specified threshold, the BS controller generates a TA command for
the respective MT. A conventional intelligent algorithm is used to
determine direction and speed of the MT with respect the measuring
BS based upon TD measurement.
[0054] Preferably, the communication time slots have a guard period
of a predetermined length within which a physical reception window
moves. The TD threshold is preferably slightly shorter than the
physical reception window and takes into account failed adjustments
and time to detect failure and retry adjustment.
[0055] An initial TD measurement TD.sub.0 reflects the initial
position of the physical reception window within the GP for a
particular MT before any TA adjustment. An initial TA, TA.sub.0, is
made at the MT which, assuming TA.sub.0 is successful, relocates
the physical reception window to a desired location reflected by a
new timing deviation measurement TD.sub.1. The initial TA,
TA.sub.0, was successful if TD.sub.1+TA.sub.0 is virtually equal to
TD.sub.0.
[0056] The TA of the MT transmission remains constant until the
next successful TA adjustment as reflected by the measured TD. For
example, an initial successful command TA.sub.0 could set the frame
advance of the MT transmission to 8 units, a next TA command
TA.sub.1 could command the advance the MT transmission to be
changed to 3 units. The success of TA.sub.1 would be reflected in a
retardation of the measured TD of a received MT transmission of 5
units. If TA.sub.1 was not successfully implemented, the TA of the
MT transmissions would remain at 8 units.
[0057] To establish the time when TA adjustments take place, TA
commands according to the invention specify a particular radio
frame when the TA adjustment is to be made by the MT. Thus, each TA
command signal includes TA data and a Connect Frame Number (CFN)
which specifies a particular radio frame in which the MT will
effectuate a TA command.
[0058] Upon determining TA adjustment is necessary, the BS
controller generates a TA command signal without incurring the
delay required for the prior art periodic TA frame number based
adjustment method such as discussed in connection with prior art
FIG. 4. Each TA command sent to the MT indicates a specific frame
identified by the CFN when the MT will perform the TA adjustment.
As illustrated in the signaling flow diagram shown in FIG. 7, when
the BS controller determines TA adjustment is necessary, based on
received TD measurements at time T1, a TA command is immediately
generated. Only an extremely short BS controller processing delay
is incurred so time T1 is approximately equal to time T2. The TA
command includes a CFN specifying the particular radio frame at a
time T3, when the MT performs the TA as illustrated in FIG. 7. The
CFN is selected so that TA adjustment is applied at a time
accounting for the expected BS controller to MT propagation and MT
processing delay and that the CFN identified frame as transmitted
by the MT will arrive at the BS with a corrected TD.
[0059] Since the BS controller specified the frame number in which
the TA adjustment was to occur, a TD measurement at T4 conducted by
the BS for the CFN specified time slot as received at the BS
indicates to the BS controller if the TA was successfully performed
by the MT. If TD of the CFN frame received at the BS is changed by
substantially the adjustment to the timing which was to be effected
by the TA command signal, the TA command was successful. If not,
the BS controller can very quickly react to failed TA command
transmissions and, also, can act to readjust MTs that have
considerably changed distance from the BS since time T1 by issuing
a new TA command signal.
[0060] The case of a failed TA adjustment command is shown in FIG.
8. The TA command has not been processed by the MT, so that a TA
adjusted signal is not transmitted in the CFN frame at T0 by the
MT. The TD measurement at the BS at time T1 on the CFN frame
specified in the TA command, accordingly, does not indicate the TA
adjustment has taken place. The base station controller then
generates a new TA command at time T2. Since a deterministic method
has been used to synchronize TA adjustment to a known frame number
by the MT and BS controller, very little time is needed to generate
the new TA command signal. Thus, time T2 is approximately equal to
time T1.
[0061] The ability for the BS controller to react immediately upon
reception of the TD measurement on the frame number specified in
the previous TA command allows more time to generate TA commands
without exceeding the physical channel reception window or
overwriting the neighboring time slot guard period. This results in
lowering the required frequency of TA commands and correspondingly
reduces the physical resources required to support the TA signaling
function.
[0062] The invention additionally allows for the case of a MT that
has changed distance with respect to the BS to be quickly
distinguished from the failed TA command case. Since the BS
controller specifies via the CFN the particular radio frame a TA is
to take effect, the TD measurement received for that particular
radio frame will indicate if the TA command was correctly received
and performed by the MT. Accordingly, TD measurements outside the
specified threshold occurring in the CFN specified time frames will
normally indicate failed TA commands, while such TD measurements in
other time frames will normally indicate a change in MT location.
Even where the TD measurement of a received CFN specified time
frame is attributable to MT relocation, the new TA signal is
generated based on that TD measurement to produce an accurate TA
for the MT. This is an important capability since the BS controller
is aware of is a previously failed TA command adjustment so that a
complete adjustment can be made avoiding the need to repeat the
failed TA command.
[0063] For geolocation, the geolocator can employ triangulation of
received signals from a selected MT by several BSs with a higher
degree of reliability. Where a selected MT is in communication with
a BS for conducting normal telecommunications, that BS normally
transmits the TA command signals generated by the BS controller to
the selected MT. Since in accordance with the invention, the TA of
MT transmissions is known for all radio frames, the geographic
location can be easily calculated by conventional triangulation
methods utilizing the known location of the BS, the TA data of most
recent successful TA command signal (or 0 where no TA commands have
been successful), and TD measurements from one or more BSs. While
it is possible to provide geographic location based using
triangulation upon the TA, the TD measurements from two BSs,
unambiguous geographic location information via conventional
triangulation is provided where TD measurements are obtained from
at least three BSs.
[0064] In TDD systems where there is only communication with one
BS, the MT also measures relative frame reception difference
between cells. The cell reception difference measurements combined
with distance from the current cell as reflected by the TD measured
at the BS allows for geographic location determination in such
systems based on the TA of the MT and the single BS TD measurement.
It is also known to use pathloss measurements in such
calculations.
[0065] Preferably, when a geographic location request is received,
the geographic locator specifies a system time frame in which BS TD
measurement of received transmissions from the selected MT is
collected from the BS in primary communication with the selected
MT, in a TDD system, and, in a conventional BS triangulation
system, also from one or more other BSs. The geolocation is
calculated based upon the TD measurements gathered for the
specified time frame and the TA reflected by the most recent
successful TA command effected by the selected MT. Accordingly,
accurate geographic location of MTs can be performed virtually at
all times since the TA of the selected MT is known from the TA
command signals which have been successful as determined in
accordance with this invention.
[0066] While the present invention has been described in terms of
the preferred embodiments, other variations which are within the
scope of the invention as outlined in the claims below will be
apparent to those skilled in the art.
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