Bidirectional

Unidirectional

...

Shared

M0213-01

CC2570

CC2571

SWRS095A

– FEBRUARY 2011 – REVISED MARCH 2011

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ANT Channel Types

There are different types of ANT channels, including bidirectional channels, unidirectional channels, shared

channels, and scanning channels. The type of channel chosen for a particular application is dependent on the

application requirements for use case, power consumption, topology, and battery life expectancy.

Bidirectional channels support two-way communication between the master and the slave. The master transmits

a message on every channel period, whereas the slave only transmits a message to the master if required to do

so by the application. For every message that the slave receives from the master, the slave can transmit a

message back. Hence, the effective data through put is the same in both directions. Bidirectional channels are

also necessary to take advantage of ANT

’s unique channel co-existence mechanisms.

Unidirectional, or transmit-only, channels allow for communication from the master to the slave only. These types

of channels support the broadcast message type only and do not offer the co-existence mechanisms built into

bidirectional channels. Although unidirectional channels provide the lowest power solution, they are generally not

recommended for systems that require co-existence of several ANT channels in a common RF space.

Shared channels are a special type of bidirectional channel that allow a single master endpoint to address up to

64K slaves. Each slave synchronizes to the channel period of the master. The master can address a different

slave on each channel timeslot by specifying the address of the slave in the first 2 bytes of the data payload. The

master may also send a broadcast message to all of the slaves simultaneously by specifying an address of 0.

Shared channels are an excellent solution for networks that require many of nodes and are sensitive to power

requirements but not to latency requirements.

Figure 5. Synchronous ANT Channel Types

Unlike the channel types listed previously, scanning channels are different in that they are asynchronous. That is,

the slave does not synchronize to a master channel. Instead, any message received from a master is passed

onto the application MCU, along with the channel ID of the device received from. This allows a slave to receive

from multiple masters without actually forming a connection to any particular master. Scanning channels come in

two flavors

– continuous-scanning and background-scanning. The difference between the two amounts to a

tradeoff between power consumption and latency. A continuous-scanning channel keeps its receiver on all the

time. This means that any transmissions are received immediately, eliminating latency at the cost of power

consumption to keep the radio on all the time. Continuous-scanning channels are an ideal solution for systems

that must be very low power on one side of the link but not the other, for example, a remote control. A

background scanning channel does not keep its receiver on all of the time. Instead, it continually searches for

transmissions, without ever actually synchronizing to a channel. The power consumption is drastically reduced at

the expense of data latency. Background scanning channels are ideal for battery-operated systems where the

hub must be able to communicate with multiple nodes with reasonable latency, for example, a proximity

awareness application.

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