• Overview
• About The Automatic Link Establishment Datalink Layer
• Configuration for Optimized ALE Performance

The IC-F8101-3X does not provide sufficient parameter descriptions to arrive at a radio configuration that provides optimized Automatic Link Establishment (ALE) performance. Further, many of the recommended or default parameter values do not provide the level of performance that the IC-F8101 is capable of achieving.

This article was constructed with input from Icom, and United States Army NETCOM, in order to provide additional guidance in configuring the IC-F8101 for ALE operations. Application of the recommendations in this document will result in maximizing performance of the ALE capabilities of the IC-F8101.

ALE achieves a high level of reliability by implementing Forward Error Correction (FEC) in conjunction with the transmission of triple redundant data, and majority voting on received triple redundant data. The adjustments that are available in the IC-F8101 reside within Word Sync, Pattern Sync and the FEC sublayers within the Datalink Layer.

During transmit, the FEC sublayer of the Datalink layer is provided a 24-bit ALE data word, which is formatted by the ALE Protocol, and performs the following actions upon the ALE data word:

• Divide the 24-bit ALE data word into two 12-bit words.
• Translate each 12-bit data word into a 12-bit Golay Forward Error Correction word.
• Concatenate the 12-bit Golay Forward Error Correction word to the 12-bit data word, constructing a 24-bit FEC word.
• Interleaves the two 24-bit FEC words, creating a 48-bit data word.
• Concatenate a zero value bit to the 48-bit data word
• Concatenate a zero value bit to the 48-bit data word, resulting in a 49-bit transmission word.
• The 49-bit data word is transmitted in triplicate.

These transmit operations are illustrated in the figure below.

During reception, the FEC sublayer of the Datalink layer is provided a 48-bit data word, which has to be processed to produce the original 24-bit ALE protocol word. The following actions are performed by the FEC sublayer of the Datalink layer to reproduce the original 24-bit ALE protocol word:

• Remove the zero stuffed 49th data bit.
• De-interleave the 48-bit data word into two 24-bit Golay Forward Error Correction data words.
• Apply Golay Forward Error Correction to each of the 24-bit FEC data words to produce two corrected 12-bit data words.
• Recompose the two 12-bit data words into a 24-bit ALE data word.
• Save the data into a buffer of three data-lanes, one for each of the individual transmissions that comprises the triple data redundancy.
• After the reception of the last of the three transissions that make up the triple redundancy, perform a majority vote on each the the three data lanes to produce the final result for the 12-bit ALE data word.

These receive operations are illustrated in the following figure.

The Icom IC-F8101-3X customer programming software provides adjustments to the handling of errors within the Datalink layer. Errors are detected in the recovery of the 48-bit data word (i.e. in the synchronization / demodulator stages), and within the Golay FEC stages. The locations where error detection occurs are illustrated by the dashed red-line shapes in the following image.

The following image shows the ALE configuration subsection of the Setmode section of the customer programming software.

Select parameters within the ALE settings should be configured as follows:

• The Bit Error Rate Threshold, labeled BER Threshold, controls a threshold for the maximum number of error bits that will be accepted at the Synchronization / Demodulator stages in the Datalink layer. The BER Threshold should be set to a value of 34 or 35.
• The Golay Threshold controls a threshold for the maximum number of erroneous bits that will be accepted as a result of Golay error bit detection. This parameter should be set to a value of 2. A value of 2 is the maximum number of bits that can be corrected by the Golay Forward Error Correction within the Data Link Layer. The Golay Forward Error Correction is capable of correcting up to 2-bits of a 12-bit data word, and is capable of detecting up to erroneous 4-bits. The Bit Error Ratio (BER) Threshold in the Icom IC-F8101-3X should not be set to the maximum number of correctable bits.
• The Error Threshold controls a threshold of the maximum number of erroneous bits, which is the sum of error bits from the Synchronization / Demodulation stage plus the error bits detected at the GOLAY FEC stage, that should be accepted. A higher total error count than this threshold will result in cancelling communications. The value of this parameter should be set to a value of 0 or 2.
• The AMD Position should be set to Acknowledgement, which places the AMD message transmission into the acknowledgement phase of the transmission, where the handshake between the stations has been completed, and where message delivery is more likely to be guaranteed.

Select parameters within the Call settings should be configured as follows:

• The Auto Start Type should be set to a value of Scan.
• The Auto Start Wait Time should be set to a value that allows for unattended station operation to receive a call, and possibly transact a digital transmission while using a mode other than ALE AMD, and then return to scan so that other subsequent calls can be received. This is necessary as the IC-F8101 has been observed to sometimes not return to scan mode when the ALE LINK is terminated by another station, and when this occurs, other stations will not be able to complete an ALE call to your station until your radio is placed back into scan mode (e.g. either manual or timer entry into scan mode).

For all other Setmode parameters, Icom's recommended or default parameter values should be acceptable.