4RF Aprisa SR+, Описание продукта

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Architecture | 41
Aprisa SR+ Product Description
6. Architecture
Product Description
There are three components to the wireless interface: the Physical Layer (PHY), the Data Link Layer (DLL)
and the Network Layer. These three layers are required to transport data across the wireless channel in
the Point-to-Multipoint (PMP) configuration. The Aprisa SR+ DLL is largely based on the 802.15.4 MAC layer
using a proprietary implementation.
Physical Layer
The Aprisa SR+ supports one or two frequency ½ duplex RF operation or full duplex two frequency RF
operation.
The ½ duplex RF operation eliminates the need for an external duplexer.
The full duplex RF operation requires the use of an external duplexer connected to the radio’s dual
antenna ports (TX and RX).
The Aprisa SR+ is a packet based radio. Data is sent over the wireless channel in discrete packets /
frames, separated in time. The PHY demodulates data within these packets with coherent detection.
The Aprisa SR+ PHY provides carrier, symbol and frame synchronisation predominantly through the use of
preambles. This preamble prefixes all packets sent over the wireless channel which enables fast
synchronisation.
Remote nodes are predominantly in receive mode with only sporadic bursts of transmit data. This reduces
power consumption.
Data Link Layer / MAC layer
The Aprisa SR+ PHY enables multiple users to be able to share a single wireless channel; however a DLL is
required to manage data transport. The two key components to the DLL are channel access and hop by
hop transmission.
Channel Access
The Aprisa SR+ radio has two modes of channel access, Access Request and Listen Before Send.
Access Mode Function
Access Request Channel access scheme where the base stations controls the
communication on the channel. Remotes ask for access to the
channel, and the base station grants access if the channel is not
occupied.
Listen Before Send Channel access scheme where network elements listen to ensure
the channel is clear, before trying to access the channel.