Anaren A8520E24A91, Руководство пользователя

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A8520E24A91 – Users Manual Page 11 of 28
Release Date: Dec 27
th
2010
minimum data throughput is to be guaranteed (as audio streaming requires). Frequency
hopping systems can either implement a fixed sequence of channel hops or adapt its hopping
sequence dynamically to the changing environment it operates in. In order to maximize its own
chances of delivering audio data in time and to co-exist amicably with other fixed-frequency or
adaptive frequency hopping systems, PurePath Wireless uses an adaptive frequency hopping
(AFH) scheme that adapts to changing conditions within tens of milliseconds. PurePath
Wireless divides the 2.4 GHz band into 18 RF channels with 4 MHz bandwidth. A protocol
master, which controls the adaptive frequency hopping scheme for the audio network, maintains
a table with an entry for each RF channel and an associated quality-of-service (QoS) estimate
for each. Each time an RF channel is used the QoS estimate is updated based on what
happens during the timeslot. The frequency hopping algorithm separates the 18 RF channels
into two sets:

A set of 4 active channels

A set of 14 trial channels
The active channel set contains the preferred RF channels that have proven that they provide
sufficiently good quality-of-service. The trial channel set contains the remaining RF channels
that are only evaluated occasionally in order to be able to maintain an accurate picture of their
quality-of-service. If the QoS estimate of an RF channel in the active set goes beyond a
minimum threshold this channel is swapped out with the RF channel in the trial channel set that
has the best QoS estimate. Other factors play in when selecting a new RF channel to the active
channel set, such as trying to maintain a certain minimum distance in frequency between the
different active channels.