R&S M3SR 4100 Series, Operating Manual

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Operating Manual 6175.4760.02 – 01 4.67
M3SR Series 4100 Automatic Link Establishment 3
rd
Generation (ALE-3G)
4.4 Automatic Link Establishment 3
rd
Generation (ALE-3G)
4.4.1 Basics of ALE-3G
The third generation Automatic Link Establishment ALE-3G is a standard defined in STAN-
AG-4538. It offers advantages over ALE-2G (second generation) like faster link setup, higher
sensitivity and higher throughput for data traffic.
The enhancements were achieved by
• using the same family of waveforms for link setup and data transmissions (PSK = Phase
Shift Keying)
• including embedded data transmission protocols with ARQ (Automatic Repeat Request)
• synchronous scanning of channels by all radios in an ALE-3G network (time synchroni-
zation of all radios in a network is required).
4.4.1.1 Achieving Network Synchronization
For highest performance network synchronization may be obtained using the GPS (Global
Positioning System) or NTP (Network Time Protocol) time in all radios of a network.
If GPS or NTP time is not available, one time server station in a network is defined. For the
other stations in the network at first manual time entry (e.g. time from wristwatch) and sub-
sequent time synchronization over the air is needed.
4.4.1.2 Improved LQA Mechanism and Automatic Channel Selection
During synchronous LQA (link quality analysis) sounding, LQA exchange, link setup and
data exchange, the ALE-3G system monitors the channel quality and stores BER (Bit Rrror
Rate) and S/N (Signal-to-Noise ratio) values in a database. To have the best channel condi-
tions for the next link setup, the radio refers to the database and chooses the best quality
channel. This function is called ACS (Automatic Channel Selection).