MIL-STD-187-721 Interoperability And Performance Standard For Advanced Adaptive Hf RadioThe purpose of this document is to describe the technical parameters for adaptive high frequency HF radio that are more advanced than those described in MIL-STD-188-141. The advanced technology contained in this standard will guide the planning of military adaptive HF radio network technology into the 21st century. To fully understand and utilize this document, it is necessary to refer to portions of MIL-STD-188-141.

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MIL-STD-187-721D

5.5.1 Channel quality measures.

Channel quality measurements for ALQA shall be in accordance with the applicable paragraph below.

5.5.1.1 SINAD and PBER.

SINAD and PBER shall be measured as described in MIL-STD-188-141 for each ALE word received beginning when word synchronization is achieved. For ALQA use, the word-by-word samples shall not be averaged (as in MIL-STD-188-141), but shall be histogrammed as described in 4.5.3.

5.5.1.2 Articulation index.

a. Articulation index shall be computed using a weighted sum of the signal-to-noise ratios within the frequency bands centered on the 8 ALE modem tones in accordance with table VII. (The weights Fi shown in table VII reflect the varying sensitivity of human hearing to different frequencies.) The effective sensation levels Ei in each sub-band (1 < i < 8) shall be accumulated during each ALE triple-redundant word reception (49 symbol periods). For each sub-band i, Si is the mean spectral density of the ALE modem input signal in the i-th

frequency band (in decibel referenced to one milliwatt (dBm)/hertz (Hz)) averaged over those

symbol periods for which the demodulator chose symbol i, while NOi is the mean spectral density in the i-th frequency band (in dBm/Hz) averaged over those symbol periods for which symbol i was not chosen (an estimate of the noise and interference in sub-band i). The Ei (in dB) shall be determined from these measurements using the formula Ei = Si - NOi.

TABLE VII. ALE tone weighting factors.

b. Scaled measurements Wi (ranging from 0 to 1) shall be determined from the effective sensation level Ei of each speech sub-band as follows: