FINAL REPORT - Stakeholders - Ofcom

• 4V. Provides 4 voice channels (no data) in one 25 kilohertz (kHz) channel. This
mode may, as an option, include data downlink using the management (or “M”)
channel transmissions and features such as urgent/priority access,
semiautomatic frequency change, and caller ID.
• 2V2D. Provides 2 voice and 2 data channels in one 25 kHz channel. These are
paired so that one user group uses one voice and data time slot pair and a
second, independent, group uses the other voice and data pair.
• 3V1D. Provides 3 voice channels and 1 data channel in one 25 kHz channel.
The three voice channels are completely independent; however, the single data
channel is shared by the three user groups.
• 3T. Provides a trunked capability shared by all users in one 25 kHz channel in
which 1 out of 4 time slots is available for voice or data and 2 out of 4 time slots
are available exclusively for data. The fourth time slot is used exclusively for
channel management functions.
The 3-slot configurations include the following:
• 3V. Provides 3 voice channels (no data) in one 25 kHz channel. This mode is
analogous to 4V, but provides more propagation guard time.
• 2V1D. Provides 2 voice and 1 data channel in one 25 kHz channel. This mode is
analogous to 3V1D, but provides more propagation guard time.
• 3S. Provides a single voice channel in one 25 kHz channel. The same digital
voice bit-stream can be transported on each of 3 time slots used by 3 separate
ground sites to provide coverage over an area larger than that which could be
provided by a single ground site.
• 2V1X. Provides 1 wide area voice channel for 2 separate ground stations and
reserves another independent channel in one 25 kHz channel. The independent
channel is defined separately in its own beacon.
The ICAO standards for VDL3 are complete. RTCA has developed MASPS and MOPS
for the system. No activity is underway in EUROCAE, ETSI, or AEEC.
The characteristics of VDL Mode 3 are summarised in the table below.
Parameter Value Notes
Service topology Point-to-Point Broadcast uplinks can also be supported
Uplink and Downlink broadcast are the primary
mode of operation for voice communications.
ATN compliance Yes Additional voice services also included.
Frequency band 118 – 136.975 MHz Provides up to four voice/data circuits on a
single 25 KHz channel assignment.
RF Channels Single 25 KHz channel
Transmitter power Typically 15W
Modulation scheme D8PSK
Bit rate 31.5 kbps A EUROCONTROL study has estimated the
effective data rate as 5040 bps.
Page 162