Adaptive TDMA (time division multiple access) communication systems have been previously designed which dynamically maintain potentially different frequencies between nodes of the communication system using a process of communicating the quality of received signals between the nodes and storing this information so that an optimum frequency band can be selected whereby whenever signal quality deteriorates, an alternate frequency can be selected to provide continued communications. An example of such a system is shown in an already issued U.S. Pat. No. 4,937,822, dated Jun. 26, 1990, and assigned to the same assignee as the present invention. The system outlined in the referenced patent utilized a connectivity phase which could only start a connectivity process on twelve minute intervals distributed at predetermined times throughout the day, and the process used required checking each of a number of prospective frequencies before deciding which signal would be appropriate to use in initial communications. Thus, even under the best propagation conditions, there would be times when a start-up would be attempted immediately after the occurrence of a twelve minute start time interval thereby preventing start-up for as much as almost 24 minutes even when propagation characteristics were favorable. If, in fact, propagation characteristics were unfavorable and other sets of potential frequencies needed to be tried, the connection process could take much longer than could be tolerated in a practical operating environment where nodes of the network need, for some reason or another, to be off-line from time to time and then need to suddenly access the system.
This long start-up problem is addressed by the present invention in accordance with the following parameters. Each of the nodes operates from a precise clock as was the case in the referenced patent. Further, each of the nodes use a common algorithm such that each node knows exactly what frequency would be attempted by a given neighbor node if that neighbor node were to be transmitting at that time. Thus, each operating node continuously checks a set of frequencies for receipt of signal from other nodes, whether or not the other nodes are operating at that time, to see if start-up is commencing. Since each of the nodes transmits unique preamble signals that identify the source of the transmission, when a given nodes receives such a transmission identifiable as belonging to a previously assigned neighbor, that node henceforth in transmissions to the node coming on line provides information as to the frequency of the first signal heard as long as the quality of the signal meets minimum standards of quality. As soon as both of the communicants have heard a signal from the other of the stated minimum quality, a connection is declared, and traffic data is transmitted as appropriate. The system continues to search for better frequencies (higher quality) to use in future traffic situations but in the meantime, traffic data can be delivered. The protocol of the present invention is such that half of each transmission and reception time is used for maintenance purposes in trying out new frequencies, and the other half is available for traffic data. Normally, the traffic data portion and the maintenance portion are at different frequencies, and both of the traffic data portion and the maintenance portion are used to provide information to the receiving node as to the frequency to be used for future traffic data as well as the quality of signals received recently on the traffic frequencies. The present concept in typical situations has reduced the connectivity phase from as much as 12 to 24 minutes down to less than two minutes. Typical situations show a drastic improvement since the present invention can declare connectivity and start transmitting traffic data as soon as the new entry into the system (or a node which has lost sychronization for whatever reason) hears from an assigned neighbor and successfully transmits to that neighbor.
It is thus an object of the present invention to provide an improved connectivity algorithm for establishing and maintaining traffic data transfer situations between two transceiver nodes which may or may not comprise a part of an overall network.
It is a further object of the present invention to improve link-up time of the present invention by using a predictive frequency in the traffic slot, which predictive frequency is known to both nodes to reduce the link-up time in instances where the environment conforms with typical conditions for location of transmitter and receiver, time of day, etc.
USPTO Backgrounds
USPTO Backgrounds