Rf Scale Communications; Fcc Statement; Rf Network Description - MSI CellScale 3750CS User Manual

MEASUREMENT
SECTION 2 – RF SCALE COMMUNICATIONS – THE CELLSCALE SYSTEM
INTRODUCTION
The 3750CS is an element of the MSI CellScale System. The CellScale system uses frequency hopping
spread-spectrum RF Modem technology transmitting in the 2.4 GHz ISM band.
RF Modems have been problematic as the RF bands are very hostile, corrupted by noise, path loss and
interfering transmission from other radios. Even in a pure interference-free environment, radio performance
faces serious degradation through a phenomenon known as multipath fading, a problem particularly prevalent
for indoor installations. Multipath fading results when two or more reflected rays of the transmitted signal
arrive at the receiving antenna with opposing phase, thereby partially or completely cancelling the desired
signal. Spread spectrum reduces the vulnerability of a radio system to both interference from jammers and
multipath fading by distributing the transmitted signal over a larger region of the frequency band than would
otherwise be necessary to send the information. This allows the signal to be reconstructed even though
part of it may be lost or corrupted in transit.
Spectrum has been set aside at 2.4 GHz in most countries for the purpose of allowing compliant spread
spectrum systems to operate freely without the requirement of a site license. In the USA, there are absolutely
no site licensing requirements. The CellScale system is also programmable for use in most European countries.
Please contact MSI for worldwide compliance information.

FCC STATEMENT

Note: This unit has been tested and found to comply with the limits for a class A digital device, pursuant to part
15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference
when the equipment is operated in a commercial environment. This equipment generates, uses, and can
radiate radio frequency energy and, if not installed and used in accordance with the instruction manual,
may cause harmful interference to radio communications. Operation of this equipment in a residential area
is likely to cause harmful interference in which case the user will be required to correct the interference
at his own expense. Commensurate with EIRP limits specified in FCC Rules 15.247b, this device may
not be used with antennas that exceed 36dB of gain in point-to-point applications or 16dB of gain in
multi-point applications.
The Transmitter Module is licensed as FCCID: HSW-2410M.
NETWORK DESCRIPTION
The CellScale system uses frequency hopping which is produced by transmitting the data signal as usual, but
varying the carrier frequency rapidly according to a pseudorandom pattern over a broad range of channels,
in this case 80 discreet frequencies. These 80 frequencies are combined in different "hopping patterns" to
provide 16 separate networks. With minor degradation in channel throughput, this can be doubled to 32
separate networks. The original 16 networks are numbered 00-15, the secondary networks are numbered
16-31. While it is possible to have all 32 networks commingled, some data rate degradation may occur
between networks 16 channels apart (e.g. Network 00 and 16, 01 and 17, 02 and 18, etc.), although in most
situations this degradation will be unnoticable.
The CellScale network uses a 'Star' network topology. One unit, usually the scale, is designated a 'Master'.
The Master transmits a sync pulse on a regular basis, providing synchronization of all remotes in the designated
Network. Thus it forms the center of a cell. MSI provides three products capable of being the master unit:
the CellScale, the CellModem, or the Trans-Weigh CS Crane Scale. Up to 254 slaves can access the master
unit. The 3750CS is always a 'Slave'. Multiple 3750CS units can coexist on one network, or can be easily
switched to other networks as required.
The CellScale system uses CSMA (Carrier sense multiple access) to arbitrate between multiple remotes. CSMA
is contention-based. Each remote listens to see if the channel is clear and then transmits. If the channel is not
clear, the remote waits a randomly chosen period of time and then tries again.
For more on setting up CellScale networks, please refer to the CellScale manual,
Software V1-15 to 1-20
SYSTEMS INTERNATIONAL
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MSI-9000 CellScale System • 3750CS User Guide Page 7