Fast terminal entry in link 16 tactical networks

Abstract

A process for allowing a Concurrent Multi-Netting (CMN-4) equipped Link 16 terminal to enter an active network. After an initial entry command is entered at the terminal at a given current time at the terminal, a number of time slots are identified in which multiple receivers at the terminal have an opportunity to detect an initial entry message (IEM) after the given current time. Each of the receivers is set to detect an IEM during a different one of the identified time slots. When an IEM is first detected by one of the receivers, the current time at the terminal is reset based on the time slot in which the IEM was detected.

Claims

1. A process for allowing a terminal equipped for operation in a time division multiple access (TDMA) network to enter the network, wherein an initial entry message (IEM) is transmitted periodically in certain identified time slots by one or more members of the network for reception by the terminal, comprising: providing a time base at the terminal for indicating a terminal current time: providing a receiver system at the terminal including multiple receivers; entering an initial entry command at the terminal at the terminal current time; identifying a number of time slots in which the receivers at the terminal have an opportunity to detect an IEM after the terminal current time; adding a determined time error window to the terminal current time, a first one of the identified time slots is the first slot in which one of the receivers has the opportunity to detect the IEM after the initial entry command is entered, a second one, of the identified time slots is the second slot in which one of the receivers has the opportunity to detect the IEM after the time error window is added to the terminal current time, and identifying one or more additional time slots in which one of the receivers has the opportunity to detect the IEM after the time error window is added to the terminal current time, identifying at least a third time slot in which one of the receivers has the opportunity to detect the IEM between the first and the second time slots; setting each of the receivers to detect the IEM during a different one of the identified time slots; detecting the IEM in each of the identified time slots; and resetting the terminal current time at the terminal based on the time slot in which the IEM is first detected.

2. A process according to claim 1, wherein the setting step includes setting each receiver according to an assigned frequency and code for the time slot during which the receiver is set to detect the IEM.

3. A process according to claim 1, including identifying a fourth time slot in which one of the receivers has an opportunity to detect the IEM between the first and the second time slots, and the third and the fourth time slots occur approximately at one-third and two-thirds the time error window, respectively.

4. A process according to claim 1, including providing the terminal in the form of a Concurrent Multi-Netting (CMN-4) enhanced Link 16 tactical network terminal.

5. A process according to claim 4, including performing at least some of the steps by configuring and programming an application processor provided in the terminal.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) In the drawing:

(2) FIG. 1 is a representation of time slot structure in multiple stacked nets of a Link 16 tactical network;

(3) FIG. 2 is a schematic block diagram of a receiver system in prior Link 16 network terminals;

(4) FIG. 3 is a detailed representation of time slot structure in a Link 16 network;

(5) FIG. 4 is another detailed representation of the time slot structure in a Link 16 network, showing identification of time slots by set and number;

(6) FIGS. 5 to 7 are diagrams showing timing for an outside terminal having the receiver system of FIG. 2, to detect an initial entry message (IEM) and enter an active Link 16 network;

(7) FIG. 8 is a schematic block diagram of a receiver system in an enhanced Link 16 network terminal;

(8) FIG. 9 is a flow diagram of steps taken during operation of the receiver system of FIG. 8;

(9) FIGS. 10A and 10B are flow diagrams of steps taken during operation of the receiver system of FIG. 8 when modified according to the invention; and

(10) FIGS. 11 and 12 are diagrams showing timing for an outside terminal to detect an IEM and enter an active Link 16 network, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) The present invention enables Link 16 network terminals that have the capability for concurrent multi-net operation, i.e., CMN-4 enhanced terminals, to detect an initial entry message (IEM) from an active Link 16 network and to enter the network in significantly less time than now required.

(12) During normal operation of a CMN-4 terminal and as shown in the flow diagram of FIG. 9, each of the four receivers 118 in the receive system 100 (FIG. 8) of the terminal is adjusted to receive message data associated with a corresponding net during a given time slot number N, by setting each receiver to listen on the frequency and to use a PN code assigned to the associated net for a given time slot number N. Software for implementing the operation may reside, for example, in the Link 16 application processor 124 of the terminal. Known as Link 16 Waveform Protocol Resource software, the software configures the processor 124 to calculate the required settings for each of the receivers 118 as shown in FIG. 9. The application processor 124 then outputs the calculated settings to each of the Link 16 signal processors 120 associated with the four receivers 118 in FIG. 8.

(13) FIGS. 10A and 10B are flow diagrams illustrating steps of an entry process 200 according to the invention. The process 200 can performed, for example, by modifying existing software and/or containing additional software in the application processor 124 in FIG. 8. The entry process 200 can allow a CMN-4 equipped Link 16 terminal to obtain net entry in significantly less time than ordinarily required.

(14) In response to a network entry command at the terminal and as shown in FIG. 10A, the application processor 124 calculates when the next opportunity to receive an IEM will occur based on the current time at the terminal. Each of the four receivers 118 in the terminal is then set to detect an IEM that is transmitted in a different one of four time slot numbers after the current time, and on the same net number (e.g., default net) on which the IEMs are periodically transmitted. That is, instead of assigning a different net number to each of the four receivers 118 to perform concurrent multi-netting as in FIG. 9, the receivers 118 are set to detect an IEM at four different times and on the same net number in response to a network entry command.

(15) In the illustrated embodiment, a first one of the four time slots is calculated without adding a time error window to the current time at the terminal. A fourth or last one of the slots is calculated after adding the total time error window to the current time as is done by the current terminals. Second and third slots are calculated after adding, for example, one-third and two-thirds of the time error to the current time at the terminal, respectively. That is, the second and the third time slots are each calculated after adding only a fraction of the total time error window to the current time at the terminal. Persons skilled in the art will appreciate that fractions other than one-third and two-thirds of the time error window may be used when calculating the time slot numbers of the next IEMs expected to be received at the terminal.

(16) Accordingly, by using the entry process 200, the terminal is set to detect an IEM at four different times only the last of which occurs after the entire time error window is added to the current time at the terminal. The terminal therefore does not miss an opportunity to detect an IEM in earlier time slots if the true error in the current time at the terminal is less than the error window.

(17) As shown in Table 1 and the timing diagrams of FIGS. 11 and 12, the time for a CMN-4 Link 16 terminal to receive an IEM by use of the inventive entry process 200, is substantially less than that needed by a conventional terminal under any of the listed entry conditions.

(18) TABLE-US-00001 TABLE 1 Initial Entry Timing First set time First set time to receive to receive IEM with IEM with modified conventional CMN-4 terminal Initial Entry Condition terminal (seconds) (seconds) Terminal behind network by 36 24 30 seconds (initialization time error 1 minute) Terminal ahead network by 96 30 30 seconds (initialization time error 1 minute) Terminal behind network by 156 36 30 seconds (initialization time error 1 minute) and fails to receive first IEM Terminal ahead network by 216 54 30 seconds (initialization time error 1 minute) and fails to receive first IEM

(19) FIG. 11 shows the timing for an outside CMN-4 Link 16 terminal from a network entry command to the reception of an IEM when the application processor 124 in the terminal is programmed to carry out the inventive entry process 200. In FIG. 11, the current time at the terminal is approximately 30 seconds ahead of network time, and the terminal is initialized with a time error of one minute. The terminal receiver system 100 operates to configure each of the four receivers 118 to detect an IEM at four different times, all on the same (e.g., default) net number. The latest time is calculated per the current scheme (the first expected IEM time after the time base error entered at the terminal by the user), the earliest time is determined assuming a time error of zero in the current time at the terminal. The second and the third times can be the first IEM detection opportunities that occur after, for example, one-third and two-thirds the error entered by the user. Under the timing conditions in FIG. 11, the terminal detects an IEM in about only 30 seconds, i.e., the earliest set listening time. If for some reason the first IEM is missed, another IEM can be detected only 24 seconds later. See Table 1, second row, and FIG. 11.

(20) In FIG. 12, the current time at an outside CMN-4 terminal is approximately 30 seconds behind network time, and the terminal is initialized with a time error of one minute. As in the case of FIG. 11, the terminal receiver system 100 configures each of the receivers 118 to detect an IEM at a different one of four different times, all on the same (e.g., default) net number. The latest time is calculated per the current scheme (the first expected IEM after the time base error entered at the terminal by the user), the earliest time is determined assuming an initialized time error of zero for the terminal's current time, and the second and the third times can be the first IEM detection opportunities that occur after, for example, one-third and two-thirds the error entered by the user.

(21) Under the timing conditions in FIG. 12, the terminal detects an IEM in about only 24 seconds, i.e., the earliest calculated listening time. If for some reason the first IEM is missed, another IEM can be detected only 12 seconds later. See Table 1, first row.

(22) As disclosed herein, the present invention uses to advantage the ability of a CMN-4 Link 16 terminal to receive multiple messages simultaneously, but in a way that enables the terminal to detect an IEM at four different times after a network entry command. The invention substantially reduces the time needed for the terminal to complete the initial entry process and proceed to synchronize with an active Link 16 network.

(23) While certain embodiments of the present invention are described and illustrated herein, it will be understood by persons skilled in the art that various modifications, additions, and changes can be made without departing from the spirit and scope of the invention. Accordingly, the invention encompasses all such modifications, additions, and changes that lie within the bounds of the following claims.