Methods and apparatus for detecting the presence of a prescribed signal in a channel of a communications system

A method for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the method comprising the steps of:

• (a) sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;
• (b) computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;
• (c) determining a minimum error value;
• (d) comparing a function of the minimum error value to a reference value;
• and
• (e) making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal.

A method for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the method comprising the steps of:

• (a) sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;
• (b) computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;
• (c) determining a minimum error value;
• (d) comparing a function of the minimum error value to a reference value;
• and
• (e) making a decision as to whether the received signal is said prescribed signal on the basis of the comparison,
• wherein said prescribed signal is a DQPSK signal;
• wherein said error values are mean-squared error (MSE) values;
• and wherein a first of said MSE values (MSE.sub.1) is computed over a plurality of symbols with respect to a first sample of each of said symbols, a second of said MSE values (MSE.sub.2) is computed over said plurality of symbols with respect to a second sample of each of said symbols, a third of said MSE values (MSE.sub.3) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE.sub.4) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.

A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

• (a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;
• (b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;
• (c) means for determining a minimum error value;
• (d) means for comparing a function of the minimum error value to a reference value;
• and
• (e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison.

A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

• (a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;
• (b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;
• (c) means for determining a minimum error value;
• (d) means for comparing a function of the minimum error value to a reference value;
• and
• (e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal.

A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

• (a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;
• (b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;
• (c) means for determining a minimum error value;
• (d) means for comparing a function of the minimum error value to a reference value;
• and
• (e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal;
• wherein said error values are mean-squared error (MSE) values;
• and wherein a first of said MSE values (MSE.sub.1) is computed over a plurality of symbols with respect to a first sample of each of said symbols, a second of said MSE values (MSE.sub.2) is computed over said plurality of symbols with respect to a second sample of each of said symbols, a third of said MSE values (MSE.sub.3) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE.sub.4) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.