Method and system for detecting transmitted data signal quality and integrity
View Patent ↗The invention relates to a method and system for use in assessing the quality and integrity of a data transmission path or link between a data transmitting location and at least one receiving location at which a broadcast data receiver is located with means to allow an error rate calculation to be made with respect to a known data signal sequence which is inserted into the transmitted signal. On the basis of the calculations made and sent to the transmitting location a particular data modulation scheme is adopted to provide the most efficient data transmission method for each receiving location. The invention is of particular use in cable data transmission networks of the type which for example allow television channels and other services to be provided to a plurality of receiving locations.
1. A method of assessing the quality of data signals which are transmitted from a transmitter location to at least one data receiving location, said method including the steps of:
identifying a known signal data sequence;
inserting said known signal data sequence into the transmitted signal: and
wherein a broadcast data receiver at said at least one receiving location includes detection means to detect whether the known signal data sequence is present or not in the signal received at the receiving location, the method further including the steps of;
using a sequence detector which operates on the received samples to generate approximations of the known data signal sequence at a default symbol rate;
using a correlator to generate a correlation between the known marker symbol values and the symbol approximations; and
setting a threshold above which a correlation is determined to represent a match of correlated signals and provides symbol retiming information, where the modulation error ratio is calculated using the received retimed sample marker data sequence and the ideal representation of the mark or symbol sequence when the threshold is attained, to provide an indication of signal quality and integrity for the data transmission path between the transmitting and receiving locations;
such that when the broadcast data receiver is unable to lock to a data signal, the modulation scheme required to allow said lock may be determined without changing the applied modulation scheme, by characterizing the quality of the known signal data sequence detected.
2. A method according to claim 1 wherein the broadcast data network is a cable network and the data signals are transmitted between locations over along cable connections.
3. A method according to claim 1 wherein said method includes the step of generating the known signal data sequence and inserting the same at the data transmitter into a specific part of the transmission data stream.
4. A method according to claim 3 wherein the known signal data sequence is provided to generate a specific sequence of marks or symbols transmitted at a known frequency.
5. A method according to claim 4 wherein at the receiving location the broadcast data receiver includes a tuner which is tuned to the known frequency to receive the said known signal data sequence.
6. A method according to claim 1 wherein the method includes the means to discriminate between false and/or random correlations.
7. A method according to claim 1 wherein the method includes the step of inserting the known data signal sequence at fixed regular intervals and checking the interval between sequence correlations to see if they are coincident and rejecting matches outside this interval.
8. A method according to claim 7 wherein the method allows discrimination between false and/or random correlations by collecting a set of modulation error ratios from the matches such that they can be averaged or otherwise processed to remove the effect of false matches by the correlator.
9. A method according to claim 1 wherein results of the analysis of the received data at the broadcast data receiver include the calculation of the modulation error ratio.
10. A method according to claim 9 wherein the modulation error ratio results arc transmitted to the transmitting location from each of the receiving locations connected thereto.
11. A method according to claim 10 wherein for each receiving location a modulation scheme is selected based on the modulation error ratio results received and with reference to a look up table or predetermined parameters.
12. A method according to claim 11 wherein different modulation schemes are selected for different receiving locations.
13. A method according to claim 12 wherein calculation of the modulation error ratio occurs at regular intervals and if at any time the same changes to a sufficient degree the modulation scheme for the particular receiving location can be changed.
14. A system for the transmission of data between a transmitting location and at least one receiving location, said system comprising:
a transmitter at said transmitting location which is capable of inserting a known signal data sequence into the transmitted signal;
a broadcast data receiver at said receiving location with:
a sequence detector which operates on the received samples to generate approximations of the known data signal sequence at a default symbol rate;
a correlator for generating a correlation between the known marker symbol values and the symbol approximations, wherein a threshold is set above which a correlation is determined to represent a match of correlated signals to provide symbol retiming information; and
calculating means to calculate a modulation error ratio value when the broadcast data receiver is unable to lock to said transmitted data signal, using the received retimed sample marker data sequence and the ideal representation of the mark or symbol sequence when the threshold is attained; and
wherein the modulation error ratio values provide an indication of signal quality and integrity for the data transmission path between the transmitting and receiving locations, and are returned from the broadcast data receiver to the transmitting location via a return path channel so that the modulation scheme to allow lock to be achieved may be determined.
15. A system according to claim 14 wherein at the transmitting location the modulation error ratio values are used to select from a look up table of predetermined parameters one of a range of modulation schemes.
16. A system according to claim 15 wherein the selection is based with respect to the quality of the data transmission between the locations in order to maximise spectral efficiency while maintaining a reliable symbol lock at all broadcast data receiver locations on one or more channels.
17. A system according to claim 15 wherein the selected modulation scheme is communicated to the transmitter and the selected modulation scheme is used for subsequent data transmission to the said at least one receiving location unless the quality of the data transmission is subsequently detected to have changed.
18. A system according to claim 15 wherein the selection is based with respect to the quality of the data transmission between the locations in order to maximize number of receivers able to receive data on the network while maintaining a reliable symbol lock at all broadcast data receiver locations on one or more channels.
19. A system according to claim 14 wherein the data transmission link is monitored to ascertain whether further changes in the modulation scheme are beneficial.