BIM-418-10 Radiometrix, BIM-418-10 Datasheet - Page 14

• Manufacturer Part Number: BIM-418-10
• Description: Low Power UHF Data Transceiver Module
• Manufacturer: Radiometrix

Where: Preamble:
The exact makeup of the packet depends upon the system requirements and may involve some complex
air-traffic density statistics to optimise through-put in large networked systems.
Networks
BiM's may be used in many different configurations from simple pair's to multi-node random access
networks. The BiM is a single frequency device thus in a multi node system the signalling protocol must
use Time Division Multiple Access. In a TDMA network only one transmitter may be on at a time,
"clash" occurs when two or more transmitters are on at the same time and will often cause data loss at
the receivers. TDMA networks may be configured in several ways - Synchronous (time slots), Polling
(master-slave) or Random access (async packet switching e.g. X25). Networked BiM's allow several
techniques for range / reliability enhancement:
Radiometrix Ltd, BiM Data Sheet
Control:
Address:
Data:
CRC:
Store and forward Repeaters: If the operating protocol of the network is designed to
Spacial Diversity:
Preamble - Control - Address - Data - CRC
This is mandatory for the receiver in the BiM to stabilise. The BiM will
be stable after 3ms. Additional preamble time may be desired for
decoder bit sync., software carrier detection or receiver wake up.
The minimum requirement is a single bit or unique bit pattern to
indicate the start of message (frame sync.). Additionally, decoder
information is often placed here such as: packet count, byte count, flow
control bits (e.g. ACK, repeat count), repeater control, scrambler
information etc.
This information is used for identification purposes and would at least
contain a 16/24 bit source address, additionally - destination address,
site / system code , unit number and repeater address's may be placed
here.
User data , generally limited to 256 bytes of less (very long packets
should be avoided to minimise repeat overheads on CRC failure and
channel hogging).
16/24 Bit CRC or Checksum of control-address-data fields used by the
decoder to verify the integrity of the packet.
allow data path control then data may be routed "via"
intermediate nodes. The inclusion of a repeating
function in the network protocol either via dedicated
repeater/router nodes or simply utilising existing
nodes allows limitless network expansion.
In buildings multi-path signals create null spots in the
coverage pattern as a result of signal cancellation. In
master-slave networks it is cost effective to provide 2
BiM's with separate antenna at the master station.
The null spot patterns will be different for the two
BiM's . This technique 'fills in' the null spots, i.e. a
handshake failure on the first BiM due to a signal null
is likely to succeed on the 2nd BiM.
page 14