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Claims  |
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I claim:
1. A remote radio locating and two-way message delivery system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder including means for
generating and transmitting a radio frequency data signal representing the
current status of the vehicle,
an array of at least three fixed base stations for communicating with each
transponder via radio frequency signals, each base station including means
for periodically polling each transponder to initiate the generation and
transmission of a data signal from the polled transponder, and
a control center containing means for determining the location of the
polled transponder using the time shift of the data signal received from
the polled transponder with respect to the polling signal.
2. The system of claim 1 wherein said data signal comprises data indicating
the current status of said transponder.
3. The system of claim 1 wherein said means for periodically polling each
transponder includes
means for producing a response message from the polled transponder on said
vehicle which includes the current status of said vehicle,
an applications center containing means for receiving and analyzing said
response message from the polled transponder and means for sending a
request to change current status of said vehicle to a control center,
wherein said control center, is communicatively coupled to said base
stations and said applications center, and contains means for scheduling
communications between said transponders and said base stations, and means
for communicating response messages from said control center to said
applications center,
means in said control center for determining the location of said
transponder, means for determining if said location is unknown, and means,
if said location is unknown, for scheduling a polling request, which
comprises data indicating the sequence of base stations used for polling
the transponder,
means in said control center for transmitting said polling request to said
base stations,
means in each base station for interpreting said polling request,
constructing a polling message, and transmitting said polling message to
one or a group of transponders, said polling message including a portion
for data sent to the vehicle and a response portion for data sent from the
transponder,
means in each transponder responsive to the detection of said polling
request for decoding said polling request and for transmitting a
transponder response containing the current status or service request
information to base station, and
means in each base station responsive to the detection of the absence of a
transponder response for causing other base stations to poll the
transponder.
4. The system of claim 1 wherein said means for determining the location of
the polled transponder includes
means for assigning a base station to one of a plurality of groups, each
base station in each group having coverage areas which do not overlap,
means in each base station for transmitting a polling signal,
means for producing a response message from the polled transponder which
includes the current status of said vehicle,
means in each base station for detecting said response message,
means in each base station for detecting the absence of said response
message, and
means in each base station in each group for transmitting another polling
signal upon detecting the absence of said response message.
5. The system of claim 1 wherein the current status includes data
indicating whether said vehicle is being used for some user-defined
operation, and whether said vehicle is free to be used for some operation
or any other user-defined status indicating vehicle availability.
6. The system of claim 3 which includes
means for assembling transponders into groups, the transponders in each
group having a common secondary address and responding identically to said
secondary address,
means for modifying the membership of each group and communicating such
modifications to the appropriate transponders, and
means, in each transponder, responsive to the detection of said secondary
address for receiving a message containing the detected secondary address,
interpreting data in the message, and performing the action signified by
the secondary address.
7. The system of claim 6 wherein said means for assembling transponders
into groups which means for programming said transponders with said
secondary addresses which represent said groups, and means in each
transponder for receiving and storing the programmed secondary address.
8. The system of claim 6 wherein the transponder is either a modem in which
said transponder is attached to a terminal with comprehensive data
functions or is a communications terminal in which said transponder itself
acts as a data terminal or similar device.
9. The system of claim 6 wherein said means for performing the action
signified by the secondary address includes
means for associating with said transponder's secondary address a unique
time slot number which represents the time in the next system cycle during
which the transponder will respond to a message from the control center,
means for producing a message from the control center including the
message's secondary address,
means, in each transponder, for comparing said transponder's secondary
address with said message's secondary address, and
means for causing all transponders with the same transponder secondary
address as message secondary address to respond substantially
simultaneously and to respond identically to said message from the control
center by placing requested information into their unique time slots.
10. The system of claim 6 which includes means for computing the ratio of
polled messages to transponder service requests with respect to any
transponder or group of transponders, and means for constructing a message
to said transponder or group of transponders, said message having a format
of variable length segments, said lengths determined by said computed
ratio.
11. The system of claim 10 which includes means for producing transponder
service requests including information indicating whether a transponder
needs to send information to the control center.
12. The system of claim 1 which includes
a master controller base station which includes means for communicating
with other base stations, means for sending a message to all base stations
within its communication range, and a master base station clock containing
means for measuring time in predetermined intervals,
means for choosing one base station to function as a master controller base
station relative to all other base stations and for choosing the
predetermined time interval,
means in each base station for calculating the arrival time of said
messages,
a base station clock in each base station containing means for measuring
time in predetermined intervals identical to the predetermined intervals
in said master base station clock, and
means in each base station for calculating the time difference between one
message received and the next message received, comparing said difference
with the same interval as measured by the said master base station clock,
and adjusting said base station clock so as to be in synchronization with
said master base station clock.
13. The system of claim 12 which includes means for self-calibrating the
system comprising
means for transmitting calibration messages from a control center to base
stations at accurately known times,
means in said base stations for measuring the arrival of said calibration
messages and sending to a control center the instances of transmissions of
said calibration messages,
means in said base stations for transmitting said arrival time to said
control center, and
means in said control center for computing the positions of the base
stations based upon said arrival time but adjusting said positions because
of variations in air temperature, humidity, and barometric pressure.
14. A system of claim 13 which includes
means for assembling a group of identical messages received at different
base stations into an event ensemble,
means for performing CRC polynomial error checking on said messages in said
event ensemble,
means for performing multiple-message redundancy cross-checking as between
the same message received at different base stations as contained in said
event ensemble, and
means for using the results of said multiple file redundancy cross-checking
to perform error correction on said message.
15. A remote radio locating and two-way message delivery system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder including means for
generating and transmitting a radio frequency data signal representing the
current status of the vehicle,
an array of at least three fixed base stations for communicating with each
transponder via radio frequency signals, each base station including means
for periodically polling each transponder to initiate the generation and
transmission of a data signal from the polled transponder, and means for
determining the location of the polled transponder using the time shift of
the data signal received from the polled transponder with respect to the
polling signal,
means for producing a response message from the polled transponder which
includes the current status of said vehicle,
an applications center containing means for receiving and analyzing said
response message from the polled transponder and means for sending a
request to change current status of said vehicle to a control center,
a control center, communicatively coupled to said base stations and said
applications center, containing means for scheduling communications
between said transponders and said base stations, and means for
communicating response messages from said control center to said
applications center,
means for assembling transponders into groups, the transponders in each
group having a common secondary address and responding identically to said
secondary address,
means for modifying the membership of each group and communicating such
modifications to the appropriate transponders,
means in each transponder responsive to the detection of said secondary
address for receiving a message containing the detected secondary address,
interpreting data in the message, and performing the action signified by
the secondary address,
means for assembling transponders into groups, including means for
programming said transponders with said secondary addresses which
represent said groups, and means in each transponder for receiving and
storing the programmed secondary address,
means for associating with each transponder's secondary address a unique
time slot number which represents the time in the next system cycle during
which the transponder will respond to a message from the control center,
means for producing a message from the control center, said message
including the message's secondary address,
means in each transponder for comparing said transponder's secondary
address with said message's secondary address,
means for causing all transponders with the same transponder secondary
address as the message secondary address to respond substantially
simultaneously and to respond identically to said message from the control
center by placing requested information into their unique time slots,
a master controller base station which includes means for communicating
with other base stations, means for sending a message to all base stations
within its communication range, and a master base station clock containing
means for measuring time in predetermined intervals,
means for choosing one base station to function as a master controller base
station relative to all other base stations and for choosing the
predetermined time interval,
means in each base station for calculating the arrival time of said
messages,
a base station clock in each base station containing means for measuring
time in predetermined intervals identical to the predetermined intervals
in said master base station clock,
means in each base station for calculating the time difference between one
message received and the next message received, comparing said difference
with the same interval as measured by the said master base station clock,
and adjusting said base station clock so as to be in synchronization with
said master base station clock,
means for transmitting calibration messages from a control center to base
stations at accurately known times,
means in said base stations for measuring the arrival of said calibration
messages and sending to a control center the instances of transmissions of
said calibration messages,
means in said base stations for transmitting said arrival time to said
control center, and
means in said control center for computing the positions of the base
stations based upon said arrival time but adjusting said positions because
of variations in air temperature, humidity, and barometric pressure.
16. A remote radio locating and two-way message delivery system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder including means for
generating and transmitting a radio frequency data signal representing the
current status of the vehicle,
an array of at least three fixed base stations for communicating with each
transponder via radio frequency signals, each base station including means
for periodically polling each transponder to initiate the generation and
transmission of a data signal from the polled transponder, and means for
determining the location of the polled transponder using the time shift of
the data signal received from the polled transponder with respect to the
polling signal,
means for producing a response message from the polled transponder which
includes the current status of said vehicle,
an applications center containing means for receiving and analyzing said
response message from the polled transponder and means for sending a
request to change current status of said vehicle to a control center,
a control center, communicatively coupled to said base stations and said
applications center, containing means for scheduling communications
between said transponders and said base stations, and means for
communicating response messages from said control center to said
applications center,
means for assembling transponders into groups, the transponders in each
group having a common secondary address and responding identically to said
secondary address,
means for modifying the membership of each group and communicating such
modifications to the appropriate transponders,
means in each transponder responsive to the detection of said secondary
address for receiving a message containing the detected secondary address,
interpreting data in the message, and performing the action signified by
the secondary address,
means for assembling transponders into groups includes means for
programming said transponders with said secondary addresses which
represent said groups, and means in each transponder for receiving and
storing the programmed secondary address,
means for associating with said transponder's secondary address a unique
time slot number which represents the time in the next system cycle during
which the transponder will respond to a message from the control center,
means for producing a message from the control center including the
message's secondary address,
means in each transponder for comparing said transponder's secondary
address with said message's secondary address,
means for causing all transponders with the same transponder secondary
address as the message secondary address to respond substantially
simultaneously and to respond identically to said message from the control
center by placing requested information into their unique time slots,
means for computing the ratio of polled messages to transponder service
requests with respect to any transponder or group of transponders, and
means for constructing a message to said transponder or group of
transponders, said message having a format of variable length segments,
said lengths determined by said computed ratio,
means for assigning a base station to one of a plurality of groups, each
base station in each group having coverage areas which do not overlap,
means in each base station for transmitting a polling signal,
means for producing a response message from the polled transponder which
includes the current status of said vehicle,
means in each base station for detecting said response message,
means in each base station for detecting the absence of said response
message, and
means in each base station in each group for transmitting another polling
signal upon detecting the absence of said response message.
17. A remote radio locating and two-way message delivery system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder including means for
generating and transmitting a radio frequency data signal representing the
current status of the vehicle,
an array of at least three fixed base stations for communicating with each
transponder via radio frequency signals, each base station including means
for periodically polling each transponder to initiate the generation and
transmission of a data signal from the polled transponder, and means for
determining the location of the polled transponder using the time shift of
the data signal received from the polled transponder with respect to the
polling signal,
means for producing a response message from the polled transponder which
includes the current status of said vehicle,
an applications center containing means for receiving and analyzing said
response message from the polled transponder and means for sending a
request to change current status of said vehicle to a control center,
a control center, communicatively coupled to said base stations and said
applications center, containing means for scheduling communications
between said transponders and said base stations, and means for
communicating response messages from said control center to said
applications center,
means for assembling transponders into groups, the transponders in each
group having a common secondary address and responding identically to said
secondary address,
means for modifying the membership of each group and communicating such
modifications to the appropriate transponders,
means in each transponder responsive to the detection of said secondary
address for receiving a message containing the detected secondary address,
interpreting data in the message, and performing the action signified by
the secondary address,
means for assembling transponders into groups, including means for
programming said transponders with said secondary addresses which
represent said groups, and means in each transponder for receiving and
storing the programmed secondary address,
means for associating with said transponder's secondary address a unique
time slot number which represents the time in the next system cycle during
which the transponder will respond to a message from the control center,
means for producing a message from the control center including the
message's secondary address,
means in each transponder for comparing said transponder's secondary
address with said message's secondary address,
means for causing all transponders with the same transponder secondary
address as the message secondary address to respond substantially
simultaneously and to respond identically to said message from the control
center by placing requested information into their unique time slots,
means for assembling a group of identical messages received at different
base stations into an event ensemble,
means for performing CRC polynomial error checking on said messages in said
event ensemble,
means for performing multiple-message redundancy cross-checking as between
the same message received at different base stations as contained in said
event ensemble, and
means for using the results of said multiple file redundancy cross-checking
to perform error correction on said message.
18. A time-slotted polling and location determination system for mobile
vehicles, said system comprising
means for scheduling radio communications during a series of system cycles,
each system cycle including polling messages and response messages each
comprising a plurality of contiguous time slots of a fixed time slot
duration,
at least three fixed base stations, each containing means for transmitting
a polling message from said base stations during a system cycle in time
slots, said polling message containing data including a transponder
identification number,
a transponder on each vehicle, said transponder containing means for
receiving a polling message during the system cycle and means for
generating and transmitting a response message to said base stations
during the system cycle, said response message containing data indicating
the current status of the vehicle, and
a control center communicatively coupled to said base stations and
containing means for selecting said time slot duration, means for
analyzing the data contained in the polling messages and response
messages, and means, responsive to the detection of a response message,
for determining the location of a transponder.
19. A time-slotted polling and location determination system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder including means for
generating and transmitting radio frequency signals,
at least three fixed base stations, each containing
means for communicating with each transponder via radio frequency signals,
means for scheduling all radio frequency signals for transmission during a
series of system cycles and means for dividing each system cycle into a
plurality of contiguous time periods including a polling time period, said
polling time period comprising a plurality of contiguous time slots
including message packets, or a header packet and a response packet,
means in each base station for constructing a message packet containing
data representing a plurality of coded characters,
means for constructing and transmitting a header packet during the polling
time period, said header packet containing data indicating a unique
transponder number, a control status word comprising a request to change
the operational status of a vehicle, check bit data, and a unique
transaction number for identifying each communication between a base
station and a transponder,
means in each transponder responsive to the receipt of a header packet for
constructing a response packet containing data representing the
operational status of the vehicle, said operational status comprising data
indicating the availability of the vehicle for use or the physical
condition of the vehicle, and means for transmitting said response packet
to a base station during the system cycle, and
a control center communicatively coupled to said base stations and
containing means for scheduling all communications among the base
stations, the control center, and the transponders, means responsive to
the detection of a response packet or a message packet for determining the
location of each transponder using either radius-radius multilateration or
hyperbolic multilateration techniques, means for assigning a transaction
number to each communication, and means for assigning a unique transponder
number to each transponder.
20. A periodic status monitoring, location monitoring, and event detection
system for transponders on mobile vehicles comprising
at least three fixed base stations, each containing means for communicating
with each transponder within the base station's coverage area via radio
frequency signals, means for receiving a response message from a
transponder containing the current status of a vehicle, and means for
communicating said response message to a control center,
a transponder on each vehicle, said transponder containing means for
receiving radio frequency signals and means for generating and
transmitting a response message containing the current status of the
vehicle to said base stations,
a control center communicatively coupled to said base stations, said
control center containing means responsive to the detection of a response
message of a transponder for computing the location of the vehicle
carrying that transponder,
means for periodically monitoring said current status and said computed
location of each vehicle, means for detecting changes in the current
status of a vehicle or the location of a vehicle, and
a plurality of user output devices for receiving from said control center
said detected changes in said current status or location.
21. A periodic status monitoring, location monitoring, and event detection
system for transponders on mobile vehicles comprising
at least three fixed base stations, each containing means for communicating
with each transponder within the base station's coverage area via radio
frequency signals, and means for receiving a response message from a
transponder,
a transponder on each vehicle, said transponder containing means for
receiving radio frequency signals and means for generating and
transmitting a response message at regular intervals to said base
stations, said response message containing the current status of the
vehicle,
means for determining the current status of a vehicle, said current status
comprising data indicating vehicle availability or a physical condition of
the vehicle,
a control center communicatively coupled to said base stations and
containing means responsive to the detection of a response message for
computing the location of the vehicle carrying the transponder that
transmitted said response message, said computation using radius-radius
multilateration or hyperbolic multilateration techniques, means for
extracting the current status of the vehicle from said response message,
and means for transmitting the location and current status, and
an applications center communicatively coupled to said base stations and
containing means for periodically monitoring the status and location of
each vehicle, said monitoring means including means for recording the
status and location of each transponder at regular intervals, means for
comparing the recorded status and location with the current status and
location at regular intervals, means for detecting changes in the status
or location of a vehicle at regular intervals, and means for communicating
said changes to the system's users via an application-specific computer
terminal at regular intervals.
22. A periodic status monitoring and location monitoring system for
transponders on mobile vehicles using time-slotted communications said
system including
means for scheduling all radio frequency signals for transmission during a
series of system cycles said system cycles comprising a plurality of
contiguous time slots,
at least four fixed base stations each containing means for receiving a
radio signal from transponders said radio signal containing the
transponder's current status,
a transponder on each vehicle, each transponder containing means for
sending the transponder's current status to a base station said current
status containing data indicating the availability of the vehicle for use
or the physical condition of the vehicle,
an application-specific computer terminal containing means for receiving a
particular geographic location to send a vehicle from a user, means for
selecting a particular vehicle to go to said particular geographic
location, means instructing the control center to construct a message to
said particular vehicle, said message containing data indicating said
particular geographic location, and means for monitoring the current
status and location of any vehicle, and
a control center communicatively coupled to said base stations and
application-specific computer terminal containing means for determining
the location of a transponder using radius-radius multilateration
techniques or hyperbolic multilateration techniques, and means for
reporting the location of said transponders to said application-specific
computer terminal.
23. A periodic status monitoring, location monitoring, and event detection
system for transponders on mobile vehicles using time-slotted
communications said system including
means for scheduling all radio frequency signals for transmission during a
series of system cycles, said system cycles comprising a plurality of
contiguous time slots,
at least four fixed base stations each containing means for receiving a
radio signal from transponders said radio signal containing the
transponder's current status, and means for sending a polling signal to
transponders,
a transponder on each vehicle, each transponder containing means responsive
to the detection of a polling signal for sending the transponder's current
status to a base station said current status containing data indicating
the availability of the vehicle for use or the physical condition of the
vehicle,
an application-specific computer terminal containing means for compiling
lists of vehicles to be polled, means for providing said lists to a
control center, means for monitoring the current status and location of a
vehicle, and
a control center communicatively coupled to said base stations and
application-specific computer terminal containing means for determining
the location of a transponder using radius-radius multilateration
techniques or hyperbolic multilateration techniques, means for reporting
the location of said transponders to said application-specific computer
terminal, and means for polling transponders on said lists.
24. A simulcast avoidance and message scheduling system for mobile
vehicles, said system comprising
a transponder on each vehicle, said transponder containing means for
receiving radio frequency signals and means for generating and
transmitting a response message containing the current availability or
physical condition of a vehicle,
at least three fixed base stations, each containing means for communicating
with each transponder within the base station's coverage area via radio
frequency signals, and means for receiving a response message from a
transponder, and
a control center communicatively coupled to said base stations and
containing means for determining the coverage areas of each base station,
means for detecting overlapping coverage areas among base stations, means
for scheduling and transmitting radio frequency communications
simultaneously or substantially simultaneously using base stations with
non-overlapping coverage areas.
25. A wide-area location determination system for mobile vehicles, said
system comprising
a transponder on each vehicle, said transponder containing means for
receiving a polling signal from a base station and means for generating
and transmitting a response message containing data indicating the current
availability or physical condition of a vehicle,
at least three fixed base stations, each containing means for transmitting
a polling signal to each transponder within the base station's coverage
area, and means for receiving a response message from each transponder
within said coverage area,
a control center communicatively coupled to said base stations and
containing means for determining the coverage area of each base station,
means for detecting overlapping coverage areas among base stations, means
for grouping base stations into a plurality of groups, means for selecting
non-adjacent base stations with non-overlapping coverage areas for
membership in a group, and means for sequencing a polling signal through
groups of base stations,
means in each base station for transmitting polling signals substantially
simultaneously from all the base stations in a group, and
means in said control center responsive to the detection of a response
message for terminating said sequencing of the polling signal through
groups of base stations.
26. A wide-area location determination system for mobile vehicles, said
system comprising
a transponder on each vehicle, said transponder containing means for
receiving a polling signal from a base station and means for generating
and transmitting a response message containing data indicating the current
availability or physical condition of the vehicle,
at least three fixed base stations, each containing means for transmitting
a polling signal to each transponder within the base station's coverage
area, and means for receiving a response message from each transponder
within said coverage area,
a control center communicatively coupled to said base stations and
containing means for determining the coverage area of each base station,
said control center including means for determining if two or more base
stations have coverage areas which overlap, means for grouping base
stations into a plurality of base station groups, means for selecting
non-adjacent base stations with non-overlapping coverage areas for any
base station group, means for constructing an ordered ranking of said base
station groups, means for sequencing a polling signal through base station
groups in the order indicated by the ordered ranking of the base station
groups, means responsive to the absence of detection of a response message
for sequencing the polling signal to the next base station group indicated
by the ordered ranking of the base station groups, and means responsive to
the detection of a response message for terminating the sequencing of the
polling signal, and
means in each base station for transmitting polling signals substantially
simultaneously with the transmission of polling signals from all the other
members of a selected base station group.
27. A dynamic group assignment system for mobile vehicles, said system
comprising
a transponder on each vehicle, said transponder containing means for
receiving a polling message from a base station and means for transmitting
a response message,
at least three fixed base stations, each containing means for transmitting
polling messages to each transponder within the base station's coverage
area, and means for receiving response messages from each transponder
within said coverage area, and
a control center communicatively coupled to said base stations and
containing means for assigning transponders to transponder groups, means
for periodically determining the status and location of transponders
within transponder groups, and means responsive to the detection of a
change in a transponder's location or status for changing the memberships
of said transponder groups.
28. A dynamic group assignment system for mobile vehicles, said system
comprising
a transponder on each vehicle, said transponder containing means for
receiving a polling message from a base station and means for generating
and transmitting a response message comprising data indicating the current
availability or physical condition of a vehicle,
at least three fixed base stations, each containing means for transmitting
polling signals to each transponder within the base station's coverage
area, and means for receiving response messages from a transponder, and
a control center communicatively coupled to said base stations and
containing means for periodically determining the status of a transponder,
means for periodically determining the location of a transponder, means
for determining which transponders have the same status and similar
location, means for assigning transponders to groups each group having
transponders with the same status or a similar location, and means
responsive to a change in status or location of a transponder for changing
the membership of said groups.
29. A dynamic group assignment system for mobile vehicles, said system
comprising
a transponder on each vehicle, said transponder containing means for
receiving a polling message from a base station and means for generating
and transmitting a response message comprising the current status of a
vehicle, said current status including data indicating the current
availability or physical condition of a vehicle,
at least three fixed base stations, each containing means for transmitting
polling messages to each transponder within the base station's coverage
area, and means for receiving response messages from each transponder
within said coverage area,
a control center communicatively coupled to said base stations and
containing means for extracting the current status from the response
message,
means in said control center responsive to the detection of the
transmission of a response message for determining the location of a
transponder using radius-radius multilateration or hyperbolic
multilateration techniques,
means in said control center for periodically identifying transponders with
the same current status, and means for assigning transponders with the
same current status to the same transponder group,
means for defining particular geographic areas, means for periodically
determining which of the transponder locations are within a particular
geographic area, and means for assigning transponders within a particular
geographic area to another transponder group, and
means responsive to a change in the current status or geographic location
of a transponder for changing the membership of said transponder groups.
30. An on-demand service request system for transponders on mobile
vehicles, said system comprising
a transponder in each vehicle, said transponder containing means for
initiating, constructing, and transmitting a service request message
including data indicating the type of service required by said
transponder,
a control center communicatively coupled to said base stations and
containing means for determining and allocating the amount of time
available for service request messages, means for determining the time
period for a transponder to transmit data, and means responsive to the
detection of a service request message for scheduling a polling message
containing data indicating the time period for the transponder to transmit
data, and
at least three base stations, each containing means for receiving said
service request messages from the transponders and transmitting said
service request messages to the control center, means for transmitting a
polling message to a transponder, and means for receiving data from the
transponders.
31. An on-demand service request system for transponders on mobile vehicles
said system comprising
means for scheduling radio communications during a series of system cycles,
each system cycle including a polling time period for transmitting polling
messages and response messages, and a service request time period for
transmitting service request messages, and means for adjusting the
proportion of the system cycle allocated to said polling time period and
said service request time period,
at least three fixed base stations, each containing means for transmitting
a polling message to all transponders within the base station's coverage
area during said polling time period determined by said scheduling means,
a control center containing means responsive to the detection of a service
request message for constructing a polling message within two system
cycles of receipt of said service request message, and
a transponder on each vehicle, said transponder containing means for
receiving said polling messages from said base stations, means for
generating and transmitting a service request message, means for randomly
selecting a time slot within said service request time period determined
by said scheduling means for transmitting said service request message,
means for determining the validity of the service request message received
by the base station, and means responsive to the detection of an invalid
service request message at said base station for re-transmitting the
service request message to said base station.
32. An on-demand service request system for transponders on mobile
vehicles, said system comprising
means for scheduling radio communications during a series of system cycles,
each system cycle containing a variable length service request time period
and a variable length polling time period,
means for constructing a service request time period comprising a plurality
of time slots each of which contains a single service request message,
means for constructing a | | |
