Afar AR-24010E, Руководство оператора

Страница: 23 / 108

pulsAR radio Operator's Manual
For small networks a cycle period of 20 ms is usually preferred. If you have a network with many
nodes that are simultaneously active the 40 ms cycle will give you better performance.
The cycle split controls the percentage of time allocated for outbound traffic (from parent to children)
versus inbound traffic (from children to parent). The default is an automatic mode where the parent
radio allocates the split of each cycle dynamically based on the amount of traffic queued up in each
direction. In a tree network each parent decides this split independent of the other parents, based on
the local traffic conditions. In most deployment this setting gives you the best performance.
You can also specify a fixed cycle split . You have the choice of 9 different values in 10% nominal
increments from 10/90 (outbound/inbound) all the way to 90/10. You need to use the fixed TDD split
when you co-locate multiple radios and want to avoid self-generated interference. Refer to section
2.4 for details about synchronizing co-located radios. The fixed split may also be appropriate in
applications where the data traffic is constant and with pre-determined throughput.
2.3.2 On demand bandwidth allocation
The complete TDD cycle is divided into slots of approximately 1 ms each. In automatic cycle split
mode, the parent radio examines the total traffic queued up for outbound and inbound, and selects an
appropriate cycle split. With fixed cycle split this step is omitted.
For the outbound traffic, the parent radio allocates the bandwidth on demand to each remote. If there
is no traffic to a specific remote, the parent does not transmit any packets to that remote. When the
parent has packets to multiple children, it distributes the available bandwidth evenly so that all
children get equal throughput.
The parent starts every outbound transmission with a broadcast packet that includes the current cycle
split as well as the slot allocation for the inbound phase. All children decode this packet and only
transmit if they have been assigned one or more slots during the inbound phase.
When the children radios transmit they include a bandwidth request parameter informing the parent of
how much inbound traffic they have queued up. The parent allocates slots to the children based on
this information. On a given cycle, each child may be allocated zero, one, or several contiguous slots
to transmit. If the aggregate requested bandwidth exceeds the network throughput the parent divides
the available bandwidth fairly among the active children.
Once in a while the parent allocates a single slot to children that have remained idle to check if they
now have inbound traffic. This check only takes a single inbound slot and this slot is allocated
dynamically depending on current traffic load, available slots, and traffic history.
2.4 Radio co-location and interference
2.4.1 Radio co-location
As a network grows it often becomes necessary to deploy multiple radios at the same site. The
reasons to co-locate radios include the following:
1. In a Point-to-Multipoint or Tree network you want to achieve 360-degree coverage around a
central site, but would like to use sector antennas rather than one omni. Sector antennas have
2-8