Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

System to Synchronize Multipe Frequency Hopping Networks

IP.com Disclosure Number: IPCOM000112198D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 221K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR

Abstract

Described is a way to synchronize many independent frequency hopping systems so they hop together using the same hop pattern. Individual systems use different phases of the same pattern, so that as one system hops off a channel, another hops onto it. This minimizes the collisions and maximizes the utilization of the radio media.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 25% of the total text.

System to Synchronize Multipe Frequency Hopping Networks

      Described is a way to synchronize many independent frequency
hopping systems so they hop together using the same hop pattern.
Individual systems use different phases of the same pattern, so that
as one system hops off a channel, another hops onto it.  This
minimizes the collisions and maximizes the utilization of the radio
media.

      Since the systems that are trying to cooperate are all
independent, a method is necessary to establish one of the systems as
the reference for synchronization.  All the systems are considered
"peers" or equals, but only one system will be the synchronization
reference.  There are numerous methods around to do such a job, such
as the technique of determining which station controls the token in
the Token Bus LAN protocol.

      A straightforward technique would be to allow the system that
had the highest system ID number to be the reference.  Alternatively,
or as a tie breaker, the system that had been powered on the longest
would be the reference.  This information could be conveyed by
comparing the exact times and dates the systems had been powered up.
Or else by using a count that represents how long the systems had
been powered up.  (This would not require a battery powered clock.)
Any remaining ties between systems could be resolved by choosing the
system with the largest number of nodes or using a random number
generating process similar to the way terminals contend for the media
when using a CSMA type protocol.

      For this discussion, the system with most "seniority" will be
the synchronization reference system.  When two systems interact, the
system with the least seniority will modify its synchronization.  A
node will remember the system ID of its sync reference system, for
use later.

      Obviously the independent systems must be able to communicate
with each other in order to establish this reference.  Spread
spectrum frequency hoppers are merely traditional narrow band
transceivers which hop around.  Consequently a hopper can receive any
other hopper's transmission if the receiving hopper is listening on
the same hop frequency that the transmitter is transmitting on.
There is only a finite number of possible hop frequencies and the FCC
requires that a very high percentage be used.  If the receiver merely
waits on a hop channel long enough, it will probably pick up another
system's transmission.  At worst, the sync seeking station would have
to try another hop frequency or two to wait on.  This is a common
frequency hopper synchronization acquisition technique.

      Wireless communication nodes, masters or slaves, always have a
microprocessor and a crystal oscillator.  The oscillators are
extremely accurate sources of timing, often with a tolerance of
0.01% or better.  This means that time difference measurements from
node to node will be very small.  However, the small differences in
frequ...