Skywave adaptable network transceiver apparatus

• US 5,204,855 A
• Filed: 01/09/1991
• Issued: 04/20/1993
• Est. Priority Date: 01/09/1991
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Werth, W. P., Young, C. David, Weddle, Daniel O., Miller, Bill C., Bebee, Melvin G.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Shankar, Vijay
• Application Number:
  US07/639,487
• Time in Patent Office: 832 Days
• Field of Search: 370/124, 370/76, 370/50, 370/70, 370/120, 455/52, 455/62, 455/71, 375/38
• US Class Current: 370/436
• CPC Class Codes: H04B 7/12 Frequency diversity

Abstract

In a skywave adaptable communications network, the time required to initiate communications between two transceivers can often be an important factor where the propagation characteristics of signals at various frequencies vary drastically with time. The present invention improved upon the prior art by accepting the first frequency that it hears as a communication frequency when two nodes are attempting to communicate from a known list of frequencies to be transmitted at known times. The system then adaptively changes to better quality signals as these better quality signals are received, analyzed and compared with present working frequency signals.

Claims

1. A node in a network of operationally identical nodes where each node can directly communicate with a predetermined number of neighbor nodes on a time multiplexed basis with each neighbor being assigned separate and exclusive transmitting and receiving time slots where the communication carrier frequencies used may be different for transmitting and receiving as well as different for each neighbor, where a set of transmitting and receiving time slots for each neighbor is defined as a cycle and where the time slots comprise probe and traffic portions, comprising in combination:

clock means for maintaining accurate time relative to a common reference of all nodes;

list means for storing a frequency-time related list of probe frequencies to be used for any given time between nodes with the number of cycles required to transmit each of the probe frequencies on said list being defined as an epoch;

transmission means, connected to said clock means, for transmitting a different frequency probe each cycle during a probe preamble portion of the transmitting time slot, in accordance with said frequency-time related list, with no frequency being repeated until an epoch is completed;

reception means for detecting probes transmitted from each of said predetermined neighbor nodes each cycle at a frequency as defined in said frequency-time related list;

means, connected to said list means, said transmission means and said reception means, for at any time calculating the next frequency to be used from said frequency-time related list thereby permitting the joining of the network asynchronously by any already designated neighbor at any time;

measurement means, connected to said transmission and reception means, for adding a frequency used during the successful reception of a probe to a stored set of working frequencies and storing quality measurements associated with that successful reception frequency;

control data means, associated with said transmission means, for using at least some of the transmitting time slot after a probe preamble to transmit control data; and

information transfer means, connected to said transmission means, for using the other of said first and second portions of the transmitting time slot to carry traffic information subsequent to recognizing link-up with a given neighbor node.

2. Apparatus as in claim 1 and comprising in addition:

adaptive means, associated with said transmission means, for announcing to a given neighbor node a new set of probe frequencies to be used in future probes to more efficiently cover a frequency spectrum of interest.

3. Apparatus as claimed in claim 1 comprising in addition:

priority means, connected to said transmission means, for temporarily combining the first and second portions of a given time slot into a traffic time slot.

4. Apparatus as claimed in claim 1 comprising in addition:

frequency hopping means, connected to said transmission means, for modifying the carrier frequency multiple times during the transmission of a single probe in a manner known to both sender and a given receiving neighbor node at the time of transmission, and resulting in a sequence of hop frequencies centered about the carrier frequency, said measurement means taking measurements on each of the individual hop frequencies whereby the receipt of a probe in a single time slot results in a set of measurements encompassing all the carrier hop frequencies employed during that transmission.

5. Apparatus as claimed in claim 4 comprising in addition:

probe hop modifying means, connected to said transmission means, for announcing, to a given neighbor node, that a change is to be initiated in said frequency hopping means for the purpose of causing the spectrum of frequencies used in a given time slot to be altered.

6. Apparatus as claimed in claim 1 and comprising in addition:

selection means for selecting up to N best traffic frequencies; and

report means, connected to said selection means and said control data means, for reporting the frequencies selected by said selection means to a neighbor node using said control data.

7. Apparatus as claimed in claim 6 and comprising in addition:

quality means, associated with said selection means, for continually updating the selection of said N best traffic frequencies based upon information stored by said measurement means and advising each neighbor node of any changes via control data in subsequent probe frequency transmissions.

8. Apparatus as claimed in claim 6 and comprising in addition:

working frequency means associated with said transmission means for establishing at least one working frequency to be used to transmit traffic to a given neighbor node based upon information received from the report means of said given neighbor node; and

rotational use means, connected to said working frequency means for alternating traffic transmission frequencies among said N best frequencies on a predetermined basis.

9. Apparatus as claimed in claim 8 comprising in addition:

means, associated with said rotational use means, for increasing the percentage of time that the best of any frequencies selected is used as a traffic transmission frequency when there are less than N frequencies selected.

10. A method by which nodes in a network each link up with, that is, establish traffic communication conditions with, neighbor nodes on a time multiplexed basis, with each neighbor node being assigned separate transmitting and receiving time slots, wherein the communication carrier frequencies used may be different for transmitting and receiving, as well as different for each neighbor, with a set of transmitting and receiving slots for each neighbor being defined as a cycle, and wherein each time slot includes first and second portions, with one of the portions being reserved for probe signals, comprising the steps of:

maintaining an accurate time relative to a common reference used by all the neighbor nodes;

referring to said accurate time and selecting for each cycle a probe frequency from a frequency-time related list of frequencies to be used between nodes at any given time;

transmitting a probe signal of a different one of the list frequencies for each cycle, said probe signal including a preamble and control data in the portion of the transmitting slot reserved for probe signals;

receiving probe signals from neighbor nodes on frequencies in accordance with said list and said accurate time and thereby permitting said neighbor nodes to asynchronously begin the process of linking up with other neighbor nodes;

storing the transmission frequency of successfully received probe signals in a set of working frequencies, along with a quality measure associated with the stored frequency;

announcing, in at least one of said transmission time slots, a successful reception of a signal transmitted by a neighbor node;

recognizing a link up with a particular neighbor node as signals transmitted to and from the particular node are successfully received; and

transmitting traffic signals in the other of said first and second portions of the transmitting slot, after recognizing a link up.

11. The method of claim 10, wherein

said traffic signals include preamble and data bit portions;

said method includes the additional step of storing in said set, along with the working frequencies and quality measures, the time of reception associated with each frequency, for determining from said set which frequencies should be used by each neighbor node when transmitting traffic to the present node; and

wherein said announcing includes informing a given neighbor node of a carrier frequency to be used for future traffic preamble and data portions, using at least one of the data portions following the probe and traffic preambles.

12. The method of claim 11 comprising the additional steps of:

informing a given neighbor node of the quality of received traffic signals from that neighbor node as part of the control data information; and

modifying output power levels of transmitted signals to a given neighbor node in accordance with signal quality information received from that neighbor node.

13. The method of claim 11 comprising the additional step of:

informing a given neighbor node that said given neighbor node should use a new set of probe carrier frequencies in future transmissions as a result of link quality measurements made previously on transmissions from said neighbor node.

14. The method of claim 11 comprising the additional step of:

transmitting a preamble different from said probe and traffic preambles to inform a given neighbor that the entire remaining portion of the time slot will be used for priority data rather than the normal format of first and second portions.

15. The method of claim 11 comprising the additional steps of:

assigning a unique identification number to each node in the network;

modifying the probe carrier frequency multiple times during a probe transmission by adding a predetermined series of offsets based on a given nodes identification number whereby a probe transmission comprises a sequence of hop frequencies centered about said probe carrier frequency.

16. The method of claim 15 comprising the additional steps of:

measuring the quality of each hop frequency signal;

informing a given neighbor node to change the size of the offset in future transmissions.

17. The method of claim 11 comprising the additional step of:

selecting up to M best frequencies from the set of working frequencies to be used by a given neighbor node for transmitting traffic preambles and informing said given neighbor node of the order in which the selected frequencies are to be used in future traffic transmissions using at least one of the data portions following the probe and traffic preambles.

18. The method of claim 17 comprising the additional step of:

acknowledging the sucessful receipt of selection data from a neighbor node as part of at least one of the data portions following the probe and traffic preambles in future transmission to that neighbor node.

19. The method of claim 17 comprising the additional step of:

maintaining optimal traffic frequencies by continuously reviewing the data in the set of working frequencies and modifying the selected up to M best frequencies as conditions change.

20. The method of claim 17 comprising the additional steps of:

recognizing that an initial state exists internally and clearing any stored sets of working frequencies received and to be transmitted;

informing neighbor nodes that initial state exists internally using the data portions of time slots of future probe signals; and

clearing the working frequencies of a specific neighbor node from any set of M working frequencies upon receiving a probe signal from that neighbor node with an indication that said neighbor node is in an initial state.

21. A method of maintaining efficient communication between two transceivers, each receiving signals from the other node on a time multiplexed basis, comprising the steps of:

transmitting signals at a selected data rate to the other node in signal packets comprising a receiver unique preamble, a control data portion and a traffic data portion;

periodically informing the other node of the quality of received signals;

varying the data rate of the traffic portion of a signal packet as a function of the quality of previously transmitted signal packets based upon quality information as received from the other node;

informing the other node of the data rate to follow in the control data portion of a given signal packet; and

dynamically maintaining traffic data rates at the best known value by continuously monitoring the quality of signals received and informing the other node of changes in the quality most recently received signals.

22. A method of maintaining efficient communication between two transceivers, each receiving signals from the other node on a time multiplexed basis, comprising the steps of:

transmitting signals to the other node in signal packets, at a selected power level and comprising a receiver unique preamble, a control data portion and a traffic data portion;

periodically informing the other node of the quality of received signals;

varying the power level of the signal packet as a function of the quality of previously transmitted signal packets based upon quality information as received from the other node; and

dynamically maintaining traffic signal power at the lowest value consistent with reliable signal reception by continuously monitoring the quality of signals received and informing the other node of changes in the quality most recently received signals.