WO2002035253A1

WO2002035253A1 - Mobile radio device having adaptive position transmitting capabilities

Info

Publication number: WO2002035253A1
Application number: PCT/US2000/026265
Authority: WO
Inventors: Bradley J. Hamilton; William E. Rogers
Original assignee: Itt Manufacturing Enterprises, Inc.
Priority date: 2000-10-20
Filing date: 2000-10-20
Publication date: 2002-05-02
Also published as: AU2001230715A1

Abstract

An Adaptive Position Transmission Algorithm (APTA) for mobile radio device where position information is required, using any transmission medium such as high frequency (HF), very high frequency (VHF), ultra high frequency (UHF), Satellite Communications (SATCOM), etc. A mobile radio device employing the APTA provides accurate and automatic position reporting and thus, in a tactical environment improves situation awareness and reduces the probability of fratricide. A mobile radio device employing the APTA also reduces the number of options available to the user thereby simplifying the operation thereof while improving overall performance in most applications. The APTA accomplishes this by monitoring position, time and radio network parameters to determine when stand alone messages will be transmitted. The APTA factors radio network loading with movement and periodic thresholds. As radio network loading increases, the movement and periodic thresholds are increased to reduce the impact of position reporting on the radio network. The APTA also incorporates a time limit which prevents the radio form transmitting too often. This time limit is based on radio network loading.

Description

MOBILE RADIO DEVICE HAVING ADAPTINE POSITION TRANSMITTING CAPABILITIES

FIELD OF THE INVENTION

The present invention relates to radio communication and more particularly to a

method for enabling a mobile radio device to automatically transmit position messages based on

user position, time and network parameters.

BACKGROUND OF THE INVENTION

Global Positioning Satellite (GPS) navigation as exemplified by NAVSTAPJGPS,

is an accurate, three-dimensional navigation system which has become one of the most important

technologies of the era, impacting a myriad of users from aircraft and ships, to farmers and hikers.

The GPS comprises a constellation of twenty four satellites and three spares which orbit the earth

twice a day. The orbits of the GPS satellites are maintained in a virtually circular manner at

approximately 10,898 nautical miles above the earth, the GPS satellites orbiting the earth in six

overlapping orbital planes based on the equatorial plane of the earth. These orbits are chosen so

that the GPS system can provide information to users regardless of the time that the user requests

information and regardless of the user's position on the earth's surface. This information contains

a navigation message, which includes satellite ephemerides and satellite clock drift information.

Accordingly, the Global Positioning System (GPS) enables user position

information to be easily and automatically transmitted in voice and data messages to support

situation awareness (SA) in military tactical environments using for example, a United States (US) Army, Single Channel Ground-Airborne Radio System (SINCGARS) Combat Net Radio (CNR).

The SINCGARS is a frequency hopping radio network system that hops over the 30-88 MHZ

band, with 25 kHz frequency spacing and thus, enables GPS-based range measurements to be

made even. while transmitting. For more information, see Robert C. Dixon, Spread Spectrum

Systems (second edition, 1984). The existing US Army CNR provides GPS user position

information, attached to voice and data messages and employs user position transmitting

techniques which initiate stand-alone SA GPS position messages based on user movement or

elapsed time so that position updates are not totally dependent on voice or data transmissions.

The SA GPS position messages are initiated by the existing US Army CNR in two

different user-selectable modes of operation. The first mode of operation is based on radio

movement (referred to as the "movement" mode), where a SA message is sent when the CNR has

moved either 100 meters (manpack configuration) or 300 meters (vehicular configuration). The

second mode of operation is based on elapsed time (referred to as the "periodic" mode), where

a SA message is sent every two minutes. The radio operator can select either mode of operation

(but not both) from the front panel of the CNR. In addition, the radio operator can turn the GPS

function off or set the CNR to send position information only attached to voice and data messages

but not as a stand alone SA message (AUTO position). The GPS mode front panel indications

and corresponding functions for a prior art CNR are shown in FIG. 1.

There are several problems associated with the US Army implementation of the SA

position message reporting in the "movement" and "periodic" modes of operation. In the

"movement" mode of operation, the first problem associated therewith relates to the decreasing

number of automatic position updates which occur as the CNR moves slower. When the CNR is in the "movement" mode, there are no stand alone SA position messages generated when the CNR

is stationary. That is, if the person or vehicle carrying the CNR is not moving for any period of

time, there will be no SA position messages generated by the CNR. If voice and data messages

are not being sent on a regular basis, and the CNR is not moving, the user's position will not be

sent.

The second problem associated with the "movement" mode of operation is that the

faster the vehicle is moving, the more often the automatic position updates are generated. Since

the movement threshold is set to 300 meters, vehicles moving at a faster rate of speed will generate

SA position messages at an excessively quick rate. For example, vehicles traveling over 30 ph

will generate SA position messages faster than once every 15 seconds. This can severely impact

SINCGARS (radio net or radio network) loading; especially when multiple vehicles are moving

in formation at a fast rate.

In the "periodic" mode of operation the problem associated therewith is that the

accuracy of the position reporting becomes significantly less as the CNR moves faster. When the

CNR is in the "periodic" mode, SA position messages are sent every two minutes. When a

vehicle is moving rapidly, the distance between position updates can become large. For example,

a vehicle traveling 25 miles per hour will transmit periodic position updates over 1.3 km apart.

At 40 miles per hour, the distance between SA position messages will be greater than 2 km.

Accordingly, an object of the present invention is to provide a method for reducing

the number of operating options available to a user of mobile radio device in order to simplify the operation of the device and improve the overall performance of the device in most of its

applications. Another object of the present invention is to provide a mobile radio device which

employs the above method.

SUMMARY

A method for automatically transmitting position messages across a radio network

with a mobile radio device. One aspect of the method comprises the steps of initiating the start

of a predetermined time limit, resetting a predetermined periodic time mterval, setting a movement

starting point which is equal to the radio device's current position, determining whether a position

message in voice and data has been transmitted, and repeating the initiating, resetting, setting, and

deterπύning steps when a position message in voice and data has been transmitted.

Another aspect of the present invention comprises the steps of deteπmning whether

a stand alone position message was transmitted within the predetermined time limit When a

position message in voice and data has not been transmitted and restarting the predetermined time

limit when a stand alone position message has been transmitted.

A further aspect of the present invention comprises the steps of determining whether

the periodic time interval has expired when a stand alone position message has not been

transmitted within the predetermined time limit and transmitting a stand alone position message

from the radio device which identifies the radio device's new current position when the

predetermined periodic time interval has expired.

Still a further aspect of the present invention comprises the steps of restarting the

predetermined time limit, resetting the predetermined periodic time interval, and resetting the

movement starting point in accordance with the radio device's new current position. In still another aspect of the present invention there comprises the steps of determining

whether the radio device's distance from the movement starting point has achieved a

predetermined distance threshold when the predetermined periodic time interval has not expired

and ttansmitting a stand alone position message from the radio device which identifies the radio

device's new current position when the distance from the movement starting point achieves the

predetermined distance threshold.

A further aspect of the present invention comprises the step of restarting the

predetermined time limit when the distance from the movement starting point is less than the

predetermined distance threshold.

Another aspect of the present invention involves the step of initiating which includes

starting a predetermined time period and further comprising the step of checking whether the

predeteπnined time period has lapsed.

Still another aspect of the present invention relates to the step of determining

whether a position message in voice and data has been transmitted, which is performed when the

predeteπnined time period has not lapsed and the step of repeating includes repeating the checking

step.

In still another aspect of the present invention, there comprises the step of

measuring radio network activity over the predetermined time period when the predetermined time

period has lapsed, to determine idle time on the radio network.

A further aspect of the present invention involves when the mobile radio device has

one of at least two structural configurations and further comprising the steps of determining which

of the at least two structural configurations the radio device is in and selectively increasing the predeteπnined distance threshold, the predetermined time limit and the predetermined periodic

time interval in accordance with the determined one of the two structural configurations when the

idle time on the radio network is less than a predetermined value.

Another aspect of the present invention includes a mobile radio device which

performs the above described method.

BRIEF D----5CRIPTION OF THE DRAWINGS

For a detailed understanding of the present invention, reference should be made to

the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 depicts the GPS mode front panel indications and corresponding functions for a prior art CNR;

FIG. 2 is a block diagram of an exemplary CNR employing the Adaptive Position

Transmission -Algorithm of the present invention; and

FIG. 3 is a flowchart of the Adaptive Position Transmission Algorithm of the

present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an Adaptive Position Transmission Algorithm

(APTA) which has application in almost any mobile radio device where position information is

required, using any transmission medium such as high frequency (HF), very high frequency

(VHF), ultra high frequency (UHF), Satellite Communications (SATCOM), etc. The APTA of

the present invention is especially useful in its application to a United States (US) Army, Single Channel Ground-Airborne Radio System (SINCGARS) Combat Net Radio (CNR) since a CNR

employing the APTA of the present invention provides accurate and automatic position reporting

and thus, in a tactical environment improves situation awareness and reduces the probability of

fratricide. Accordingly the APTA of the present invention will be described in its application to

a CNR.

As will be described further on, a CNR or other similar mobile radio device

employing the APTA of the present invention is substantially simpler to operate than existing

CNRs as earlier described. This is because the APTA enables the CNR to provide only one mode

of operation for generating and transmitting stand-alone (SA) position messages. In addition,

improvements in reporting performance and more efficient use of the radio net are achieved, since

the APTA .utilizes factors other than just movement or elapsed time. Consequently, a CNR or

other mobile radio device employing the APTA of the present invention has a reduced number of

options available to the user thereby simplifying the operation thereof while improving overall

performance in most applications.

Referring to FIG. 2, a CNR employing the APTA of present invention is denoted

by numeral 10. The CNR 10 is conventionally configured in terms of hardware and thus,

comprises a receiver 12 for receiving navigation data from the GPS or like satellite navigation

system and a transmitter 16 for transmitting the position of the CNR 10. The CNR also includes

a computing device 14 such as a microprocessor, that calculates the position of the CNR 10 using

the navigation data received by the receiver 12 from the GPS and executes the APTA 18 which

monitors position, time, and net parameters to determine when SA position messages will be

transmitted by the transmitter 16 of the CNR 10 as will be further explained. The construction and operation of such hardware in a CNR are well known in the art and therefore, needn't be

described here any further. It is also well known in the art that the CNR 10 can be provided in

a manpack configuration that allows the CNR 10 to be attached to a user's back, in a vehicular

configuration that allows the CNR 10 to be mounted in a vehicle such as a Jeep or tank, in a hand-

held configuration that allows the CNR 10 to be hand-held, or in a airborne configuration that

allows the CNR 10 to be mounted in an airplane.

The APTA 18 of the present invention enables the CNR 10 to achieve the objectives

of simplified operation and improved overall performance, by factoring net loading with

movement and periodic thresholds. As net loading increases, the movement and periodic

thresholds are increased to reduce the impact of position reporting on the net. In addition, a time

limit is incorporated which prevents the CNR 10 from transmitting too often. This time limit is

also set based on net loading.

The APTA 18 provides many advantages over the "movement" and "periodic"

position transmitting algorithms of existing CNRs. For example, SA position messages are sent

periodically by the present CNR 10, even when the user (manpack configuration) or vehicle

(vehicular configuration) is stationary. In the case of vehicular configuration, as the vehicle speed

increases, the present CNR 10 employing the APTA 18, limits the number of SA position

messages transmitted. Further, as net loading increases, both movement and periodic thresholds

are increased to mi-t-im e the impact to the net.

Existing CNRs automatically transmit GPS SA messages based on radio

configuration (manpack or vehicular), movement, time since last position update (elapsed time),

and radio net loading. The APTA 18 provides timely and accurate position information, while π-in-u-αizing the impact to radio net loading. The APTA 18 is enabled when the CNR 10 is placed

in the GPS AUTO mode of operation. This allows the MOV and PER modes shown in FIG. 1

to be eliminated if desired.

Referring now to FIG. 3, a flowchart depicting an embodiment of the APTA 18

of the present invention is shown. The APTA 18 is based on a 15 second scheduler (SA

Scheduler) shown in block 28 that tests system parameters every 15 seconds to identify whether

GPS SA position messages should be sent. The SA position messages are sent when the dynamic

thresholds of these parameters are met.

There are two entry points into the APTA 18. The first entry point 20 is from

operator selection of the GPS AUTO mode of operation. When the GPS AUTO mode of the CNR

10 of the present invention is first selected, the GPS and APTA system parameters are initialized

in block 24. The APTA 18 relies on multiple users entering the GPS AUTO mode at different

times, thereby creating a "randomized'' start to prevent CNRs in a net from attempting to transmit

SA position messages at the same time. The second entry point 22 is from the SA Scheduler of

block 28 during operation of the CNR after the APTA 18 has been enabled.

The APTA 18 uses the following system parameters shown in block 34 to provide

adaptive position transmission capabilities to the CNR 10. These system parameters comprise

"idle time," "limit time," "movement starting point," "movement threshold," and "periodic

time." In order to fully understand the operation of the APTA 18, these system parameters are

defined immediately below.

The system parameter referred to herein as "idle time" is the percentage of time of

no net activity during a two minute period time. The CNR 10 measures net activity and determines the amount of idle time on the net. The idle time data obtained by the CNR 10 is

processed by the APTA 18 to determine the values for movement threshold, limit time, and

periodic time.

The system parameter referred to herein as "limit time" is the minimum time

between transmitted SA position messages or the -----j-nimum time between a user initiated voice

or data message with attached SA position message and a stand alone SA message. Limit time

data is generated by the APTA 18 and is used by the APTA 18 to set a limit on the transmission

rate of SA position messages. The APTA 18 sets the limit time to a mii-imum of 15 seconds and

is dependent on other parameters as will be explained further on.

The system parameter referred to herein as "movement starting point" is the GPS

position of the last transmitted SA position message. The movement starting point is used as the

starting position for detern-uning the movement distance. Upon initialization, this parameter is set

to the current GPS position.

The system parameter referred to herein as "movement threshold" is the distance

set for transmitting S A position messages. When the distance between a current user's position and the last SA position message (the movement starting point) is greater than the movement

threshold, the APTA 18 initiates a SA position message.

The system parameter referred to herein as "periodic time" is the time set for

transmitting SA position messages. When the periodic time is reached, a SA position message is

transmitted. The periodic time is set to a minimum of two minutes and is dependent on other

parameters.

Referring still to FIG. 3, APTA initialization of block 24 commences when the GPS AUTO mode of the CNR 10 is selected. Each time the GPS AUTO mode of the CNR 10 is

selected, the APTA 18 is enabled and the system parameters of block 34 are set to the default

values shown in Table 1 below.

Table 1 APTA System Parameter Default Values

Enabling the GPS AUTO mode of the CNR 10 and thus, the APTA 18 also

activates the SA Scheduler of block 28 and a two-minute update timer of block 26. The SA

Scheduler 28 and the two-minute timer 26 create "random" transmission timers for each CNR in

the net for the purpose of randomizing in time the generation of SA messages on the net. In

addition, initialization will set the current position as the movement starting point.

The first SA position message is transmitted by the CNR 10 when the criteria for

the APTA 18 are met. No SA position message will be transmitted prior to that time. _.

The SA Scheduler 28 ensures that the APTA 18 is performed approximately every

15 seconds. At the start of each pass through the APTA 18, the APTA 18 checks in block 38

whether the two minute Net Load Update timer 26 has expired. If the two minute Net Load

Update timer 26 has expired the Net Loading Idle Time is determined in block 40. Accordingly, the APTA checks Idle Time every two minutes. In block 42, whenever the total net "on-air"

activity time reaches 10% of the two minute measurement interval (less than 90% Idle Time), SA

position message reporting thresholds (both movement and periodic) are increased to lower SA

position message traffic on the net. The SA position message reporting thresholds in block 42 are

progressively increased at 25% and 40% activity levels. The SA position message reporting

thresholds are dependent on the CNR's configuration. The APTA 18 determines in block 44

whether the CNR configuration is manpack. If the CNR configuration is manpack, the SA

position message reporting thresholds are set in block 46 for a CNR in a manpack configuration.

The manpack configuration thresholds are shown in Table 2 below.

Table 2

Manpack Configuration Thresholds

If the APTA 18 determines in block 44 that the CNR configuration is not manpack,

the SA position message reporting thresholds are set in block 48 for a CNR in a vehicular

configuration. The vehicular configuration thresholds are shown in Table 3 below. Table 3

Vehicular Configuration Thresholds

After the APTA 18 sets the SA position message thresholds, or if it is not time to

check net loading Idle Time (two minute Net Load Update of block 38 has not expired), the APTA

18 tests for any voice or data messages transmitted with SA position information in block 50. If

a radio message has been transmitted with SA position information, the Periodic Time threshold

will be reset and the current position will be entered as the Movement Starting Point in block 34.

If no messages with SA information have been transmitted in block 50, the APTA

18 will deteπnine if the minimum Limit Time has been reached in block 52. If Limit Time has

not been reached, the APTA 18 will return to the SA Scheduler 28 in block 36. If Limit Time has

been reached in block 52, the APTA 18 checks whether the Periodic Time has expired in block

54. If Periodic Time has expired, a stand-alone SA message is transmitted in block 32 and then

the Periodic Time is reset and the Movement Starting Point is set to the current position in block

34.

If the Periodic Time has not expired in block 54, the APTA 18 checks whether the Movement Threshold has been exceeded in block 56. If the Movement Threshold has been

exceeded, a SA position message is transmitted in block 32 and then the Periodic Time is reset and

the Movement Starting Point is set to the current position in block 34. If the Movement Threshold

has not been exceeded in block 56, the APTA 18 at block 36, returns to the SA Scheduler 28.

Or in other words, at the end of each pass, the APTA 18 always returns to the SA Scheduler 28.

As should now be apparent, a CNR controlled by the APTA of the present invention

is capable of periodically transmitting SA position messages even when the CNR is stationary.

Moreover, when an APTA controlled CNR is in the vehicular or airborne configuration,

increasing vehicle or airplane speeds will not result in an excessive number of SA position

messages since the APTA enables the CNR to automatically adapt the frequency of position

reporting to the vehicle's/airplane's speed. Furthermore, an APTA controlled CNR is simpler to

operate because it provides only one mode of operation for generating and transmitting SA

position messages instead of two modes as in prior art CNRs. Additionally, as net loading

increases, an APTA controlled CNR automatically adapts both the periodic and movement

thresholds by increasing their values to rninimize the impact on the net.

It should be apparent to one of ordinary skill in the art that the embodiment

described herein is merely exemplary and that many variations and modifications to the

embodiment can be made. For example, the APTA of the present invention can also be applied

to mobile radios used in Identification of Friend or Foe (IFF), Command and Control, Personnel

Recovery (Extraction) and Paramilitary/Civilian Radios. Any and all such variations or

modifications as well as others which may become apparent to those skilled in the art, are intended

to be included within the scope of the invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. In a radio network including a mobile radio, a method of scheduling the transmission

by the mobile radio of a position message that indicates a position of the mobile radio, the

method comprising the steps of:

(a) periodically determining a network loading parameter indicating a level of transmission

activity on the radio network; and

(b) determining when to transmit the position message from the mobile radio across the

network as a function of the network loading parameter.

2. The method of claim 1 , wherein step (a) includes periodically determining an idle time

as a percentage of time of no network activity during a predetermined time period.

3. The method of claim 1, wherein step (b) includes

(bl) limiting a rate at which scheduled position messages are transmitted by setting a

minimum time between transmission of a most recently transmitted position message and

transmission of a next scheduled position message, the minimum time being set as a function of

the network loading parameter.

4. The method of claim 3, wherein step (b) further includes:

(b2) transmitting a position message if a time since transmission of the most recently

transmitted position message is greater than the minimum time and the distance traveled by the mobile radio since transmission of the most recently transmitted position message is greater than a movement threshold.

5. The method of claim 4, wherein step (b) includes:

(b3) setting the movement threshold as a function of the network loading parameter.

6. The method of claim 1, wherein step (b) includes:

(bl) setting a duration of a periodic time interval as a function of the network loading

parameter;

(b2) initializing a start time of the periodic time interval when a most recently transmitted

position message is transmitted; and

(b3) transmitting a position message if a time since transmission of the most recently

transmitted position message is greater than the periodic time interval.

7. The method of claim 1, wherein step (b) includes:

(bl) setting a movement threshold as a function of the network loading parameter; and

(b2) transmitting a position message if the distance traveled by the mobile radio since

transmission of a most recently transmitted position message is greater than the movement

threshold.

8. The method of claim 1, wherein the mobile radio is capable of automatically

transmitting position messages with voice or data messages and scheduling transmission of stand¬

alone position messages, wherein: step (b) includes scheduling transmission of a next stand-alone position message as a

function of: a minimum time elapsed since transmission of a most recently transmitted position

message; a periodic time interval; and a minimum distance traveled by the mobile radio since

transmission of the most recently transmitted position message, wherein the minimum time, the

periodic time interval and the minimum distance are parameters whose values are set as a function

of the network loading parameter.

9. The method of claim 8, wherein step (b) further includes transmitting a stand-alone

position message if a time since transmission of the most recently transmitted position message

is greater than the minimum time and, either the time since transmission of the most recently

transmitted position message is greater than the periodic time interval or the distance traveled by

the mobile radio since transmission of the most recently transmitted position message is greater

than the minimum distance.

10. The method of claim 8, wherein step (a) includes periodically determining an idle time

as a percentage of time of no network activity during a predetermined time period, and step (b)

includes increasing the minimum time, the periodic time interval and the minimum distance as

idle time decreases.

11. The method of claim 8, wherein the most recently transmitted position message is a

stand-alone position message or a position message transmitted with a voice or data message.

12. The method of claim 8, wherein the mobile radio is configurable to be in one of a

plurality of movement modes, wherein the minimum distance is set as a function of the movement

mode.

13. In a radio network including a mobile radio, a method of scheduling the transmission

by the mobile radio of a position message that indicates a position of the mobile radio, the method

comprising the steps of:

(a) initializing a start time of a periodic time interval when a most recently transmitted

position message is transmitted; and

(b) transmitting a position message if either a time since transmission of the most recently

transmitted position message is greater than the periodic time interval or the distance traveled by the mobile radio since transmission of the most recently transmitted position message is greater

than a movement threshold.

14. In a radio network including a mobile radio, a method of scheduling the transmission by the mobile radio of a position message that indicates a position of the mobile radio, the method

comprising the steps of:

(a) setting a minimum time between transmission of a most recently transmitted position

message and transmission of a next scheduled position message; and

(b) transmitting a position message if a time since transmission of the most recently

transmitted position message is greater than the minimum time and the distance traveled by the mobile radio since transmission of the most recently transmitted position message is greater than a movement threshold, thereby limiting a rate at which scheduled position messages are

transmitted when the mobile radio is moving rapidly.

15. A mobile radio capable of transmitting across a radio network position messages that

indicate the position of the mobile radio, comprising:

a receiver adapted to receive navigation data;

a processor coupled to said receiver and responsive to the navigation data to determine a

position of the mobile radio, said processor periodically determining a network loading parameter

indicating a level of transmission activity on the radio network and scheduling a time to transmit

a position message from the mobile radio across the radio network as a function of the network

loading parameter; and

a transmitter coupled to said processor and adapted to transmit across the radio network

the position message indicating the position of the mobile radio.

16. The radio of claim 15, wherein said processor periodically determines an idle time as

a percentage of time of no network activity during a predetermined time period.

17. The radio of claim 15, wherein said processor limits a rate at which scheduled position

messages are transmitted by setting a minimum time between transmission of a most recently transmitted position message and transmission of a next scheduled position message, the

minimum time being set as a function of the network loading parameter.

18. The radio of claim 17, wherein said processor schedules transmission of a position

message if a time since transmission of the most recently transmitted position message is greater than the minimum time and the distance traveled by the mobile radio since transmission of the

most recently transmitted position message is greater than a movement threshold.

19. The radio of claim 18, wherein said processor sets the movement threshold as a function of the network loading parameter.

20. The radio of claim 15, wherein said processor sets a duration of a periodic time

interval as a function of the network loading parameter, initializes a start time of the periodic time

interval when a most recently transmitted position message is transmitted, and transmits a position message if a time since transmission of the most recently transmitted position message is greater

than the periodic time interval.

21. The radio of claim 15, wherein said processor sets a movement threshold as a function

of the network loading parameter and schedules transmission of a position message if the distance traveled by the mobile radio since transmission of a most recently transmitted position message is greater than the movement threshold.

22. The radio of claim 15, wherein:

the mobile radio is capable of automatically transmitting position messages with voice or data messages and scheduling transmission of stand-alone position messages; and said processor schedules transmission of anext stand-alone position message as a function

of: a minimum time elapsed since transmission of a most recently transmitted position message;

a periodic time interval; and a minimum distance traveled by the mobile radio since transmission

of the most recently transmitted position message, wherein the minimum time, the periodic time

interval and the minimum distance are parameters whose values are set as a function of the

network loading parameter.

23. The radio of claim 22, wherein said processor schedules transmission of a stand-alone

transmitted position message is greater than the periodic time interval, or the distance traveled by

the mobile radio since transmission of the most recently transmitted position message is greater than the minimum distance.

24. The radio of claim 22, wherein said processor periodically determines an idle time as

a percentage of time of no network activity during a predetermined time period and increases the

minimum time, the periodic time interval and the minimum distance as idle time decreases.

25. The radio of claim 22, wherein the most recently transmitted position message is a

26. The radio of claim 22, wherein the mobile radio is configurable to be in one of a

plurality of movement modes, wherein the minimum distance is set as a function of the movement mode.

27. A mobile radio capable of transmitting across a radio network position messages that

indicate the position of the mobile radio, comprising: a receiver adapted to receive navigation data;

position of the mobile radio, said processor scheduling a time to transmit a position message if

either a time since transmission of a most recently transmitted position message is greater than

a periodic time interval or the distance traveled by the mobile radio since transmission of the most

recently transmitted position message is greater than a movement threshold; and

a transmitter coupled to said processor and adapted to transmit across the radio network the position message indicating the position of the mobile radio.

28. A mobile radio capable of transmitting across a radio network position messages that

position of the mobile radio, said processor setting a minimum time between transmission of a

most recently transmitted position message and transmission of a next scheduled position

message, and scheduling a time to transmit a position message if a time since transmission of the most recently transmitted position message is greater than the minimum time and the distance traveled by the mobile radio since transmission of the most recently transmitted position message

is greater than a movement threshold; and