Autospeed

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4. Autospeed

Normally all radio modems in a network have to transmit with the same data rate on the same radio channel. The Autospeed feature of RipEX enables different speeds to be used simultaneously in a radio modem network.

The following picture gives an example of a network layout. Let us assume, that all signals are strong enough to ensure almost perfect operation:

Autospeed - initial situation

Fig. 4.1: Autospeed – initial situation

After some time situation changes and path loss on one of these links significantly increases, rendering the communication unreliable:

Autospeed - problem

Fig. 4.2: Autospeed – problem

What can we do:

  • Change antennas on one or both sides of the link

  • Use higher masts on one or both sides of the link

  • Build additional repeater(s)

  • Lower the data rate significantly to increase the system gain

The first three possibilities require time and money, i.e. additional investment. The fourth possibility (when applied to whole network, as it normally is the case) would slow down the response time (two to four times) of the whole network, quite probably making it unusable for the application. RipEX Auto-speed feature allows to change the transmission data rate at the affected radios only, the rest of the network may continue in full speed. Consequently the overall performance of network is maintained practically at the same level while no additional investment is required. More over, the whole fix can be done in minutes from behind a web-browser screen while sitting in your office.

Of course a similar scenario can be used right from the moment of planning a new network. The investment cost can be reduced by purposefully configuring the few „difficult“ radio links to a lower data rate.

The above scenarios are made possible by the unique capability of RipEX to automatically adjust its receiver to the data rate of the incoming frame. Note that when an ACK frame is sent by the receiving RipEX, it always uses the same data rate as the frame it acknowledges. The only limitation of this feature is that all the frames have to have the same symbol rate and the same principle of modulation (i.e. CPFSK or linear).

Modulation types which can be combined within one approval type (FCC or CE):

2CPFSK & 4CPFSK with or without FEC
  or
D2PSK & Pi/4DQPSK & D8PSK &16DEQAM with or without FEC

The improvement in system gain value using this technique may be more than 15 dB. Increasing gain of antenna system by that value would be impractical, often impossible – the „difficult“ hops are designed to use high-gain directional antennas from the beginning. Hence the Autospeed may make a radio modem network the optimum choice in situations where it could not be economically feasible before.

Autospeed - solution

Fig. 4.3: Autospeed – solution