Cambium Networks cnReach N500 handleiding

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cnReach N500 User Guide

Technical Reference

phn-4673_002v000 (March 2018)

3-7

As a general rule, when the data rate increases, the sensitivity of the radio decreases and therefore the

required signal strength at the receiving radio must increase to maintain the appropriate margin.

Adaptive Modulation

• The user may enable multiple bit rate/modulation modes, via the web GUI or the radio menu.

• The same set of modes must be enabled on all radios in the network.

• The master radio always transmits in one fixed mode (the master transmit mode), which can also be

indicated via the GUI or radio menu. The master transmit mode is one of the enabled modes.

• Radios determine the slot period based on the maximum payload length for master and slave, at the

highest-speed enabled mode.

• At lower speeds, maximum payload lengths are reduced from the maximum, to keep the slot time constant

regardless of the mode.

• A slave transmits its request for master attention in the lowest-speed mode. Each packet’s header contains

a field indicating the mode in which the slave will transmit the next packet, after the current packet is

acknowledged.

• Each slave independently determines the mode it transmits in, based on the acknowledge rate it observes

over multiple master attention sessions.

• A slave transmits its request for master attention in the lowest-speed mode.

• If no slave has master attention, an acknowledging slave transmits the acknowledge packet in the lowest-

speed mode.

• If one slave has master attention and wishes to acknowledge a master packet, it transmits the acknowledge

packet in the mode established for the current attention session.

When configured as part of a cnReach N500 PMP network, End Point radios are not required to

communicate at the same data transmit rate. This enables remote End Point radios that are closer to

the Access Point or in a better RF environment to communicate at faster data-rates than remotes that

are further away or in high-noise areas.

Since transmissions from the Access Point radio in a PTMP network must be received by all remotes

irrespective of distance or RF conditions, the Access Point radio is limited to a single AP data transmit

rate. Remote End Point radios must also be configured with the data transmit rate the Access Point will

use to communicate.

Remote End Point radios in a PTMP network independently and dynamically select the optimal data

rate. The list of data rates is selected by checking the corresponding check-boxes on the remote radio.

Data rates which remote End Point radios may use to communicate must also be defined on the Access

Point radio, therefore the configuration should match between the Access Point radio and each of the

remote End Point radios.

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