Service manual

Guide to ASTRO™ Digital Radios
History
Development of Motorola Inc.’s ASTRO™ products began sometime around 1992. This is
evidenced through reference to the 1992 time-line in all versions of product firmware at address C03Dh.
Figure 1.1 Screen-shot of host firmware code referencing 1992 development.
It is believed Motorola Inc.’s first ASTRO™ product, the ASTRO Digital Saber™, was released in
1995. When it was introduced, it was marketed to the U.S. Military and federal government as a
replacement and upgrade over existing SecureNet™ products.
The ASTRO Digital Saber™ was capable of transmitting digital voice at 9.6Kbps using the C4FM
modulation scheme, in addition to transmitting regular analog FM signals and CVSD SecureNet™.
ASTRO™, Motorola Inc.’s first digital voice platform, utilized the Vector Sum Excited Linear
Prediction (VSELP) codec. (A variant of the Code Exciter Linear Prediction (CELP) codec family) VSELP
codec implementation in the ASTRO™ radio platform was at 4.8Kbps, with 2.1Kbps error correction
coding (6.9Kbps).
In 1995 or thereabouts, the Association of Public Safety Communications Officials (APCO)
devised a plan called APCO Project-25, which outlines the standards for digital public safety radio-
communications systems.
Digital Voice Systems Inc.’s (DVSI) Improved Multi-Band Excitation (IMBE™) codec was chosen as
the APCO-25 standard after tests were carried out to determine the most effective low-bitrate codec. It
was determined the 4.4Kbps codec with 2.8Kbps of error correction coding (7.2Kbps) was best-suited for
APCO Project-25.
Figure 1.2 Speech quality vs. channel condition. Inmarsat has formally tested the IMBE™ vocoder against a variety of CELP based codecs to
determine the speech quality under various channel conditions. The results of this evaluation illustrate that the IMBE™ Vocoder is very resilient
to high Bit Error Rates. (Source: DVSI)