3g ale application note - codan · pdf fileas well as being quicker acro ss all call types,...

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17-60148 Issue 2, June 2016 Page 1 of 22
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3G ALE
What is 3G ALE?
3G ALE is a call system that conforms to STANAG 4538. It provides rapid on-air linking with a high degree of link security and optional secure data transfer. It uses fast link setup and a voice or data traffic type.
Stations that communicate with the 3G ALE call system may be set to scan a set of channels, listening on each channel at precisely the same time. This is known as synchronous mode. The sending station uses its LQA data to ensure that the preamble burst is sent on the best quality channel for the receiving station. This minimises the length of preamble transmissions and maximises network availability. 3G ALE stations may also communicate asynchronously, however, preamble times will be longer.
A link may be point-to-point, point-to-multipoint (voice only), or broadcast. The link may be 1-way or 2-way. Multiple stations may be grouped under a common address, so a call to this one address attempts to create a link with all member stations.
STANAG 4538 refers to the initial part of the link establishment as a Protocol Data Unit (PDU). It contains the type of traffic to be carried on the link, the addresses of entities that are invited to join the link, and whether or not the station is required to send an acknowledgement to the invitation. This portion of a call is notionally similar to Codans Selcall or ALE/CALM preamble, except the content is different. In this document, the term preamble is used instead of the STANAG 4538 term of PDU.
When the 3G ALE call system operates in synchronous mode, the transceiver actively selects the best channel for the receiving station and confirms that a link is established before any voice or data (for example, message text or GPS information) is transferred. Figure 1 on page 2 shows a simplified diagram of the process to send a Message call in a 3G ALE network (as described in Appendix C, STANAG 4538). The initial link request and acknowledgement may utilise link protection. The data part of the call is not transmitted until the link is established. It may be transmitted in clear or with AES-256 encryption.

3G ALE
Page 2 of 22 17-60148 Issue 2, June 2016
When data is transferred, it is sent using one of three data traffic types: Codan Adaptive Signalling Technology (CAST), high-throughput data link (HDL), or low-latency data link (LDL). CAST provides the fastest method for transferring large amounts of data, and is adaptive to changing channel conditions. The LDL traffic type is the slowest method for transferring data, however, it is the most robust and provides communications in extremely poor channel conditions.
Figure 1: Sending a Message call in a 3G ALE network
1 1
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All stations aresynchronouslyscanning the
channels with adwell time of
1.35 sec/channel
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Call initiatedon Ch 2
dwell slot
Tune
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Req Ack
Calling stationrequests link
Calledstation(s)tune and
acknowledgelink request
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andtermination
Called station(s)return to
synchronousscanning
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Channeldwellslots
Link establishmentand protection
Data sent inclear or with AES-256 encryption
Scanning for incoming calls,no link activity Source: Annex C to STANAG 4538
Tune

3G ALE
Comparison between 3G ALE and 2G ALE (ALE/CALM)
Linking probability
Codan has performed link comparison tests using 3G ALE and 2G ALE calling systems.
Figure 2: Probability of linking
Figure 2 shows the probability of successfully establishing a link between two stations under varying channel conditions using 3G ALE and 2G ALE.
A disturbed channel is a simulation of a fading, multipath HF channel. These are the typical conditions encountered during propagation of HF sky waves. An AWGN channel is a simulation of a non-fading, single-path channel with added noise. Similar conditions may be encountered during propagation of short-distance ground waves. For more information on HF channel simulations refer to ITU Recommendation F.1487.
The curves show that 3G ALE linking (blue curves) is approximately 6 dB better than 2G ALE linking (brown curves) using sky wave propagation on a typical HF channel. This translates to a 3G ALE station requiring only one quarter of the power required by a 2G ALE station to propagate a sky wave with the same channel conditions.

3G ALE
Calling times
Figure 3 shows the average calling times for different call types using 3G ALE and 2G ALE protocols.
Figure 3: Calling times between 3G ALE and 2G ALE
The call times are an average of 100 calls of each call type using a typical 3G ALE network with synchronous scanning of 5 channels.
Apart from the Failed Call category, the times shown are for a successful link establishment on the first channel attempt without any repeats. In quickly changing sky wave conditions, typically experienced by a manpack or mobile station on-the-move, the LQA database loses accuracy quickly and linking on the first channel attempt is rare.
The time required to send a 3G ALE Channel Test call followed by a 3G ALE voice link is similar to the time required for a 2G ALE voice link to be established on the third channel attempt. The 3G ALE link is established on the best available channel at the time, as determined by the preceding Channel Test call, whereas the 2G ALE link made on the third channel attempt is not guaranteed to be the best channel.
As well as being quicker across all call types, the 3G ALE protocol can send much larger Message calls than the Codan Selcall or 2G ALE protocols. Text messages of up to 250 characters can be sent and received via the front panel of the transceiver. By default, the data traffic type used is LDL. If you are sending larger messages of up to 5900 characters via Codans Computer Interface Command Set (CICS), you should consider changing the data traffic type to a higher throughput or CAST. For more information refer to Application Note: Operating a transceiver via a computer and CICS (Codan part number 17-60149).

3G ALE
Figure 4: Calling times for a 90 character 3G ALE message sent using LDL traffic type over varying channel conditions
Figure 4 shows how the transmission time of a Message call in a 3G ALE network decreases with improving channel conditions. The 3G ALE protocol incorporates Automatic Repeat Request (ARQ) to resend errors. The 2G ALE protocol uses Forward Error Correction (FEC) and does not resend errors.
The 3G ALE protocol provides a more robust system than the 2G ALE protocol in deteriorating channel conditions. As channel conditions deteriorate, the 2G ALE system will fail to send messages, whereas the 3G ALE continues to successfully transfer messages, with longer transmission times.

3G ALE
Figure 5: 3G ALE data traffic types and RC50-C performance
Figure 5 compares the time taken to transmit a 5 kB text message using the different 3G ALE data traffic types with the time taken to send an email with a 5 kB attachment using RC50-C, over varying channel conditions.
The RC50-C email system reached a data transmission rate of 4800 bit/s. Although it is possible for the 2G ALE data system to transmit at higher data rates, the amount of data being sent was not enough to allow the system to reach the higher rates. The curves in Figure 5 show that for data amounts of 5 kB, the 3G ALE data traffic types outperform the 2G ALE data system.

3G ALE
3G ALE communication
Each station in the 3G ALE network may be pre-programmed with a list of member stations, and/or a station may be set up to send calls to and receive calls from unknown stations. Each station has its own individual self address. This self address must be allocated to the specific 3G ALE network in the Address entry in the Control List, for example 110/3G ALE or 110/All. Once added as a member of the network, each station may be called simultaneously via the 3G ALE broadcast address 1023. The network may be broken down into smaller groups, each with selected members, and each group has a group address that may be used to call the member stations of the group.
Figure 6: Simple 3G ALE communication network
NOTE For information on calling across the network, and between and within groups, see page 16, Station address settings.
Group
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3G ALE station
3G ALE groups
3G ALE communication network
TOD master station
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3g ale application note - codan · pdf fileas well as being quicker acro ss all call types,...

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