Product Features
Modulation Technique
Media Access Control (MAC)
13
www.javad.com
In 868-870 MHz band the design is based on high-level modulation techniques which include
The following are its key benefits:
• FEC coding scheme used with GMSK and 4FSK modulations is based on Convolutional code and
the Viterbi decoding algorithm.
• Powerful FEC scheme used with JAVAD GNSS proprietary frame format improves the tolerance
to interference and ensures the highest link quality at distances range higher than 8 miles (13 km)
and roaming speeds of up to 60 mph (96 km/h).
2.3.1. Media Access Control (MAC)
The following Media Access protocols are available for FH915 modem:
1. Simplex protocols (Simplex Base, Simplex Remote, and Repeater) are developed primarily for
GNSS applications.
2. Half Duplex protocols (Half Duplex Base, Half Duplex Remote and Repeater) are the alternative
to Simplex protocols that provide bidirectional link with the dynamic bandwidth allocation.
Note:
Repeater decreases the user data rate. The user data rate in the link with the repeaters is equal to C /
[(n+1]), where C is a link throughput determined by the modulation technique and n is a number of
repeaters in the chain. Half duplex Base, Half duplex Remote and repeater are not supported in current
release.
3. Sleep mode is an investment provided by MAC sub-layer that provides additional power saving.
The wakeup from Sleep mode is user selectable either by an internal real-time clock, or by an
external controller through the data interface control lines (RTS or DTR), or by SLEEP input line
(CMOS/TTL compatible input lines).
2.3.2. Operating Modes
The operating modes for FH915 can be set through the CLI, and/or through AWLaunch. The following
operating modes are available for FH915:
1. The sleep mode has automatic transmitter activation by an internal real-time clock, or by an
external controller through the data interface control lines (RTS and DTR), or by the triggering of
the external Sense Inputs.
2. Adaptive RF Power control used by Remotes minimizes the transmit power levels and
interference to co-channel and adjacent channel users. It also reduces the Remote’s power
consumption.
Modulation/ Channel Spacing
12.5 kHz
20 kHz
25 kHz
GMSK – Minimal Shift Keying with Gaussian Filtering 4.8 kbps
7.5 kbps
9.6 kbps
4FSK- Four Level Frequency Shift Keying (planned)
9.6 kbps
15 kbps
19.2 kbps
