Frequency control for point to multipoint radio

• US 4,670,889 A
• Filed: 09/05/1984
• Issued: 06/02/1987
• Est. Priority Date: 09/07/1983
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Hewitt, Michael T. H.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Huseman, M.
• Application Number:
  US06/647,487
• Time in Patent Office: 1,000 Days
• Field of Search: 455/3, 455/4, 455/5, 455/71, 455/69, 455/68, 455/70, 455/53, 455/54, 455/62, 455/75, 455/51, 375/109, 375/107.97, 370/69.1, 370/71, 370/121, 370/124
• US Class Current: 375/356
• CPC Class Codes: H04B 1/50 using different frequencies for the two directions of communication
• CPC Class Codes: H04B 7/2643 using time-division multiple access [TDMA] H04B7/2615, H04B7/2618 take precedence

Abstract

A multipoint radio system has a single node which communicates with a plurality of outstations on one frequency. The outstations using a different single frequency to communicate with the node. The node controls the transmission frequency at the outstations, e.g. by transmitting error signals which adjust the set points of frequency control loops in the outstations. In a preferred embodiment the node allows for residual errors by adjusting the decision threshold of its regenerator to the outstation on transmission.

Claims

1. A method of communicating between a plurality of outstations and a single node wherein said communication is carried out in a first radio channel having a first carrier frequency signal used by all the outstations to communicate with the node and a second radio channel having a second carrier frequency signal used by the node to communicate with all the outstations, characterized in that the node controls the stability of the carrier frequency used by the outstations, wherein the node assesses carrier frequency errors for each outstation and returns to each outstation a signal indicating the error, and also wherein each outstation on receipt of error signals addressed to itself adjusts the carrier frequency of its transmission so as to reduce the error.

2. A method according to claim 1, utilizing a feedback loop having an adjustable control set point for controlling the frequency of the outstation transmitter and wherein the error signals are employed to adjust the set point of said feed-back loop.

3. A method according to claim 1 wherein the radio channels are frequency modulated and wherein frequency modulated signals therefrom are demodulated and error assessments are made on the demodulated signals at the node.

4. A method according to any one of claims 1, 2 or 3, wherein the error assessments are made at predetermined intervals, as assessment on only one outstation being made during any one interval.

5. A node for participating with plural outstations in a communication mode wherein a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations according to any one of claims 1, 2 or 3, which node comprises

(a) a radio receiver adapted to receive signals from a plurality of outstations on a second carrier frequency,

(b) a radio transmitter for sending radio signals to said outstations on a first carrier frequency,

(c) means for generating error signals indicative of the divergence of the received second carrier frequency from a specified frequency, and

(d) means for providing said error signals to the transmitter

whereby an error signal is sent to the outstation which transmitted the signal to which an error signal relates.

9. An outstation for participating with plural outstations in a communication mode wherein a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations according to any one of claims 1, 2 or 3, which outstation comprises:

(a) a radio receiver for receiving signals from a node,

(b) a radio transmitter for sending signals to the node,

(c) means for recognizing error signals sent from the node to the outstation,

(d) means for adjusting the frequencies of the radio transmitter, said means for adjusting being responsive to error signal recognized by item (c).

6. A node for participating with plural outstations in a communications mode wherein a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, which node comprises:

(a) a radio receiver adapted to receive signals from a plurality of outstations,

(b) a radio transmitter for sending radio signals to said outstations,

(c) means for generating error signals indicative of the divergence of the received frequency from a specified frequency,

(d) means for providing said error signals to the transmitter

whereby an error signal is sent to the outstation which transmitted the signal to which an error signal relates;

(e) means for detecting a resumption of signal reception after a break therein,

(f) averaging means operatively connected to detecting means (e), said averaging means being adapted to produce a signal indicative of the average frequency received, and

(g) sample-and-hold means operatively connected to retain the signal produced by averaging means (f) when detector (e) indicates a resumption of reception,

wherein the error generator specified in (c) is operatively connected to receive a signal retained in a sample-and-hold means (g) and to generate error signals in accordance, therewith.

7. A node for participating with plural outstations in a communication mode wherein a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations and wherein the radio channels are frequency modulated and wherein frequency modulated signals therefrom are demodulated and error assessments are made on the demodulated signals at the node, which node comprises:

(a) a radio receiver for receiving frequency modulated signals from a plurality of outstations,

(b) a radio transmitter for sending frequency modulated signals to said plurality of outstations,

(c) a frequency discriminator for producing a demodulated signal from an output of the receiver,

(d) a regenerator for producing regenerated data from the demodulated signal produced by the frequency discriminator, and

(e) a smoothing circuit for producing an average signal from the demodulated signal produced by the frequency discriminator,

wherein the smoothing circuit is connected to the regnerator so as to provide a decision threshold for the regeneration.

8. A node according to claim 7, which also comprises

(f) means for detecting the resumption of radio reception after a break therein,

(g) a sample-and-hold means connected to said smoothing circuit as input, to detecting means (f) as trigger, and to said regenerator to provide the decision threshold.

10. A method of communicating between a plurality of outstations and a single node wherein said communication is carried out in a first radio channel used by all the outstations to communicate with the node and a second radio channel used by the node to communicate with all the outstations, characterized in that

the node controls the frequency used by the outstations;

wherein the node assesses frequency errors for each outstation and returns to each outstation a signal indicating the error, and also wherein each outstation on receipt of error signals addressed to itself adjusts the frequency of its transmission so as to reduce the error; and

wherein the node utilizes a data regeneration circuit having an adjustable decision threshold for determining regenerated data values and wherein the node uses the assessments of frequency errors to adjust the decision threshold used for data regeneration.

13. A method according to claim 10 or 12 wherein the error assesments are made at predetermined intervals, an assessment on only one outstation being made during any one interval.

11. An outstation for participation with a node station and plural other outstations in a communication mode wherein (1) a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, with the node controlling the frequency of transmitters at the outstations which outstation comprises:

(a) a radio receiver for receiving signals from a node,

(b) a radio transmitter for sending signals to the node,

(c) means for recognizing error signals sent from the node to the outstation,

(d) means for adjusting the frequencies of the radio transmitter, said means for adjusting being responsive to error signal recognized by item (c); and

a feed-back loop for controlling the frequency of the radio transmitter,

wherein said feed-back loop includes a frequency discriminator for producing a signal related to the output of the transmitter, a voltage controlled oscillator, said oscillator being included in the signal generator of the transmitter, and an analogue adder for combining a bias signal with the output of the frequency discriminator, wherein said outstation also comprises a bias signal generator adapted for control by error signals received by the outstation and connected to said analogue adder to provide the bias signal.

12. A method of communicating between a plurality of outstations and a single node wherein said communication is carried out in a first radio channel used by all the outstations to communicate with the node and a second radio channel used by the node to communicate with all the outstations, characterized in that

the node controls the frequency used by the outstations;

wherein the radio channels are frequency modulated and wherein frequency modulated signals therefrom are demodulated and the error assessments are made on the demodulated signals at the node; and

wherein each transmission from an outstation starts with a preamble being an alteration of two keying frequencies, the demodulated signals at the node are averaged during said preamble and error signals generated when said average falls outside a pre-set window.

14. A node for participating with plural outstations in a communication mode wherein (1) a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, (2) the node assesses frequency errors for each outstation and returns to each outstation a signal indicating the error, (3) each outstation on receipt of error signals addressed to itself adjusts the frequency of its transmission so as to reduce the error, (4) the node utilizes a data regenration circit having an adjustable decision threshold for determining regenerated data values and (5) the node uses the assesments of frequency errors to adjust the decision threshold used for data regeneration;

which node comprises;

(a) a radio receiver adapted to receive signals from a plurality of outstations,

(b) a radio transmitter for sending radio signals to said outstations,

(c) means for generating error signals indicative of the divergence of the received frequency from a specifided frequency, and

(d) means for providing said error signals to the transmitter

whereby an error signal is sent to the outstation which transmitted the signal to which an error signal relates.

15. A node for participating with plural outstations in a communication mode wherein (1) a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, (2) the radio channels are frequency modulated and frequency modulated signals therefrom are demodulated and error assessments are made on the demodulate signals at the node, and (3) each transmission from an outstation starts with a preamble being an alternation of two keying frequencies, the demodulated signals at the node are averaged during said preamble and error signals are generated when said average falls outside a pre-set window;

which node comprises;

(a) a radio receiver adapted to receive signals from a plurality of outstations,

(b) a radio transmitter for sending radio signals to said outstations,

(c) means for generating error signals indicative of the divergence of the received frequency from a specified frequency, and

(d) means for providing said error signals to the transmitter

whereby an error signal is sent to the outstation which transmitted the signal to which an error signal relates.

16. An outstation for participation with a node station and plural other outstations in a communication mode wherein (1) a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, with the node controlling the frequency of transmitters at the outstations, (2) the node assesses frequency errors from each outstation and returns to each outstation a signal indicating the error, (3) each outstation on receipt of error signals addressed to itself adjusts the frequency of its transmission so as to reduce the error, and (4) each node utilizes a data regeneration circuit having an adjustable decision threshold for determining regenerated data values and the node uses the assessments of frequency errors to adjust the decision threshold used for data regeneration, which outstation comprises:

(a) a radio receiver for receiving signals from a node,

(b) a radio transmitter for sending signals to the node,

(c) means for recognizing error signals sent from the node to the outstation,

(d) means for adjusting the frequencies of the radio transmitter, said means for adjusting being responsive to error signal recongized by item (c).

17. An outstation for participation with a node station and plural other outstations in a communication mode wherein (1) a first radio channel is used by the outstations to communicate with the node and a second radio channel is used by the node to communicate with the outstations, with the node controlling the frequency of transmitters at the outstations, (2) the radio channels are frequency modulated and frequency modulated signals therefrom are demodulated and error assessments are made on the demodulated signals at the node, and (3) each transmission from an outstation starts with a preamble being an alteration of two keying frequencies, the demodulated signals at the node are averaged during said preamble and error signals generated when said average falls outside a pre-set window, said outstation comprising:

(a) a radio receiver for receiving signals from a node,

(b) a radio transmitter for sending signals to the node,

(c) means for recognizing error signals sent from the node to the outstation,

(d) means for adjusting the frequencies of the radio transmitter, said means for adjusting being responsive to error signal recognized by item (c).