MIL-STD-187-721D
a. The purpose of this document is to provide the technical parameters for the functions and features of advanced adaptive HF radio and to provide logical and cohesive guidelines for both industry and the Government.
b. The user may not have a requirement for some of the features and functions included in this document. The user should establish the requirement for each function or feature called out in an acquisition based on minimum essential requirements.
6.1.2 Functions carrying high overhead costs.
Several of the functions specified in this standard are intended for use only in specific circumstances and could cause severe congestion if used in most network. Procuring activities should identify clear requirements for the following functions before acquisition.
6.1.2.1 Polling and connectivity exchange.
Polling should be used sparingly, because its overhead burden grows as the square of the number of stations in the network. Simulations have shown that polling and CONEX will seriously degrade network availability for networks of more than about 1O stations. This is because (1) channel usage for polling and CONEX functions and (2) through the suspension of station scanning while using these protocols.
6.1.2.2 LQA reporting.
LQA reports can provide valuable link quality information cases of non-reciprocal propagation. These reports are useful only if they carry recently measured data. Except for very small networks with very small volumes of user traffic, the overhead transmission required to supply
this data may be excessive. LQA reporting should be used primarily for optimizing point-to-point links that must support traffic in both directions, and for cases of a single station that has a much higher noise floor than other network members.
6.1.2.3 ALQA.
Full benefit of the ALQA techniques can be obtained only by more extensive data collection than is required for the standard LQA technique. For example, a station receiving a sound could continue to measure the sound until it ends, rather than departing after two good words are received. This action lowers the effective scanning rate, requiring longer call times. A 1O-station,
1O-channel network would need to double the call duration to maintain its linking probabilities.
Because ALQA data is measured using the ALE modem, ALQA channel evaluations may not correlate will with the performance of other modems on the channels. Thus, ALQA should only be used when all of the following conditions are met:
a. Channel quality must be determined with greater precision than is available with standard
LQA.
b. Traffic volume is sufficiently light that the overhead required for data measurement is tolerable.
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