User's Manual Part 1
Release8OverviewofCycloneNetworks
Issue2,November2007 Draft5forRegulatoryReview 93
7.1.14 3XOperation(CycloneOFDMmodulesonly)
Cyclone OFDM modules offer an additional modulation scheme that provides 3X
operation in addition to 1X and 2X operation. In clear space, 3X operation is possible
over half the range of 2X (which means it is possible over ¼ the range of 1X). However,
in NLOS installations (typical for Cyclone OFDM), multipathing may be the predominant
RF issue, not free-space attenuation, so the relationship between 1X, 2X, and 3X range
may differ from clear space situations.
3X operation is configured on a Cyclone OFDM module’s Configuration => General page
using the Dynamic Rate Adapt pop-up under Mac Control Parameters.
7.2 UNDERSTANDINGSYNCHRONIZATION
The system usesTime Division Duplexing (TDD) - one channel alternately transmits and
receives - rather than using one channel for transmitting and a second channel for
receiving. To accomplish TDD, the AP must provide sync to its SMs – it must keep them
in sync. Furthermore, collocated APs must be synced together - an unsynchronized AP
that transmits during the receive cycle of a collocated AP can prevent that second AP
from being able to decode the signals from its SMs. In addition, across a geographical
area, APs that can “hear” each other benefit from using a common sync to further reduce
self-interference within the network.
7.2.1 GPSSynchronization
The Navigation Satellite Timing and Ranging (NAVSTAR) Global Positioning System
(GPS) uses 24 satellites to relay information for precise derivation of position and time.
The Cyclone Cluster Management Module (CMM) contains a Last Mile Gear Oncore
GPS Receiver. The CMM is a critical element in the operation of the Cyclone system. At
one AP cluster site or throughout an entire wireless system, the CMM provides a GPS
timing pulse to each module, synchronizing the network transmission cycles.
The Oncore GPS Receiver tracks eight or more satellites. The CMM uses the signal from
at least four of these satellites to generate a one-second interval clock that has a rise
time of 100 nsec. This clock directly synchronizes APs and BHMs which, in turn,
synchronize the SMs and BHSs in the Cyclone network.
The Oncore GPS Receiver also provides
• the latitude and longitude of the GPS antenna (collocated with the CMM)
• the number of satellites that are being tracked
• the number of satellites that are available
• the date
• the time in Universal Coordinated Time (UCT)
• the altitude of the GPS antenna
• other information that can be used to diagnose network problems.
Alternative to GPS Sync
A Cyclone link can operate without GPS sync, but cannot operate without sync. The
alternative to GPS sync is to configure the AP or BHM in the link to generate a sync pulse
to pass to the SM or BHS, respectively. Depending on the RF environment in which the
link operates, this latter alternative may or may not be plausible.