Method for frequency sharing in frequency hopping communications network

• US 5,079,768 A
• Filed: 09/11/1990
• Issued: 01/07/1992
• Est. Priority Date: 03/23/1990
• Status: Expired due to Term

• Current Assignee: Proxim Wireless Corporation
• Original Assignee: Metricom, Inc.
• Inventors: Flammer, George H.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): KIZOU, HASSAN
• Application Number:
  US07/581,497
• Time in Patent Office: 483 Days
• Field of Search: 370/103, 370/100.1, 370/94.1, 370/94.2, 370/50, 370/77, 375/1, 375/107, 455/51, 455/71, 455/166, 455/179, 455/62, 455/63, 340/825.03
• US Class Current: 370/349
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0676 Mutual
• CPC Class Codes: Y10S 370/913 Wireless or radio

Abstract

A frequency-hopping packet communication system without a master clock or master control unit is based on use of a receiver'"'"'s frequency hopping timing and identification to control communication. A frequency-hopping band plan, involving the number of channels and the pseudo-random pattern of frequency change and nominal timing of changes, is universally known to each node in the network. Frequency-hopping is implemented by the division of communication slots and the accumulation of slots into epochs, wherein each epoch equals the total number of available slots (number of channels times the number of time frames per channel). A transmitting node tracks the preestablished frequency-hopping pattern for its target receiver based on previously-acquired information. The transmission node identifies a receiver node and a current frequency channel of such receiver node. The transmission node then checks the frequency channel to determine if available (e.g., not in use and within an acceptable noise margin). If unavailable, the transmission node delays transmission to the identified node to a later slot. During the delay, the transmission node identifies another receiver node and a corresponding current frequency channel. The steps of identifying a receiver node and checking the corresponding current frequency channel are repeated until a node having an available frequency channel is identified. The transmission node then sends a packet to the selected receiver node at a frequency and for a duration defined according to the current slot. Such transmission node tracks the changing frequency of the selected receiver node to maintain frequency synchronization.

Claims

1. In a packet communication network having a plurality of communication nodes, each node having a terminal node controller which includes processing means and memory means, a method for frequency sharing within said network comprising the steps of:

at each node, changing, according to a known pattern, a slot for transmission and reception of signals to a current slot, a slot being a frequency channel during a preselected time period, a current slot being the frequency channel for a current time period, said known pattern being known to each other node in said network, said step of changing at one node being independent of the changing for each other node;

at a source node, identifying a first receiver node and the frequency channel of the current slot of said first receiver node;

checking the frequency channel of said first receiver node to determine if available for a transmission;

when said frequency channel of said first receiver node is unavailable, repeating the steps of identifying and checking until an available frequency channel is found, the receiver node which has an available frequency channel being a selected receiver node; and

transmitting an information packet from said source node to the selected receiver node during the current slot of said selected receiver node, the source node tracking the changing frequency of the selected receiver node.

2. The method of claim 1 in which transmission to an identified receiver node is delayed to a later slot when the frequency channel of the current slot of said identified receiver node is unavailable.

3. In a packet communication network having a plurality of communication nodes, each node having a terminal node controller which includes processing means and memory means and employing a clock, a method for maintaining frequency and time synchronization within said network comprising the steps of:

generating at each node an age value by means of the clock of said node, said age value being representative of the age of said node;

at each node, supplying a representation of the age value to any other node as part of transmission of a packet;

at each node, collecting said representation of the age value for other nodes within said network;

at each node, changing, according to a known pattern, a slot for transmission and reception of signals to a current slot, a slot being a frequency channel during a preselected time period, a current slot being the frequency channel for a current time period, said known pattern being known to each other node in said network, said step of changing at one node being independent of the changing for each other node;

at a source node, identifying a receiver node and frequency channel of the current slot of said receiver node which is available to receive a packet of information; and

transmitting said information packet from said source node to said identified receiver node on the frequency channel defined by the current slot of said identified receiver node during said current slot of said identified receiver node, the source node tracking the changing frequency of the identified receiver node.

4. The method of claim 3, in which said step of identifying comprises the steps of testing said frequency channel of said current slot to determine whether said channel is currently available;

and, when said frequency channel of said current slot is unavailable, delaying said step of transmitting until a later slot.

5. The method of claim 3, in which said step of identifying comprises the steps of testing said frequency channel of said current slot to determine whether said channel is currently available, said tested frequency channel being a first frequency channel, and of testing a frequency channel of the current slot of another receiver node when said first current frequency channel is unavailable, said another receiver node being said identified receiver node when said first frequency channel is unavailable and the frequency channel of said another receiver node is available.