Communication system including a digital roll-off filter

A transversal type roll-off filter having a function of an automatic equalizer, receiving a single bit line of a channel signal of I channel, orthogonal with a Q channel signal of a parallel digital signal sampled n times from an analog signal demodulated from a quadrature amplitude modulation signal carrying a pulse train having a pulse spacing T, said transversal type roll-off filter comprising:

• a first delay line (11) comprising a first even number of first delay elements (11-D) each having a delay time T/n where n is an integer greater than or equal to 1;
• first group of adders (12), each arranged between adjacent two of said first delay elements (11-D) and at an output terminal of the last one of said first delay elements (11-D);
• a first group of multipliers (4'), input terminals of said first group multipliers (4') being connected with an input terminal of the roll-off filter, an output terminal of each of said first group multipliers being respectively input to a central one and every n-th ones counted from said central one of said first group adders (12),
• a second group of multipliers (5'), input terminals of said second group multipliers being connected with said input terminal of the roll-off filter, an output terminal of each of said second group multipliers (5') being respectively input to all other first group adders (12) than those connected with said first group multipliers (4'), each of said first group adders (12) summing an input from preceding one of said first delay elements and an input from said first and second group multipliers (4', 5'), an output of each of said first group adders (12) being input to subsequent one of said delay elements (11-D), an output first one of said first or second group multipliers (4' or 5') being input to a first one of said delay elements (11-D),
• a second delay line (13) comprising a second even number of second delay elements (13-D) each having a delay time T;
• a second group of adders, each arranged between adjacent two of said second delay elements (13-D), one of inputs to each of second group adder (14) is an output of preceding one of said second delay elements (13-D), an output of each of said second group adders (14) being input to a subsequent one of said second delay elements (13-D);
• a third delay element (15) having said delay time T/n, connected to an output terminal of last one of said second group adders (14), whereby outputs of said first delay line (11) and said second delay line (13) are cophased;
• a third group of multipliers (3'), all of input terminals of said third group multipliers being connected with an input terminal of an opposite (Q) channel roll-off filter, output terminals of said third group multipliers (3') being respectively input to said second group adders (14);
• a fourth adder provided at an output of a last one (16) of said first adders (12), for summing an output of said third delay element (15) and an output of said last one (16) of said first adders (12);
• a memory device (6) for storing and outputting a first group and a second group of tap rating ratios (.alpha.1, .alpha.2) to determine a roll-off filter frequency characteristic of the roll-off filter, said second group tap rating ratios (.alpha.2) being input to said second group multipliers (5'), respectively;
• a calculation circuit (7) monitoring an output signal of the digital filter, for calculating according to a predetermined algorithm and outputting a third and a fourth group of tap rating ratios (C', C), each of said third group tap rating ratios (C') being input to each of said third group multipliers (3'), said predetermined algorithm being such that said third and fourth tap rating ratios (C', C) are optimum for the roll-off filter to output pulses in a good shape;
• a third adder (8) for summing each of said third group tap rating ratios (C) with respective one of said first group tap rating ratios (.alpha.1), outputs (.alpha.') of said third adders being input to said first group multipliers (4'), respectively;
• and
• a divider (18) connected to an output of last one (16) of said first group adders, for outputting every n-th pulse input thereto;
• wherein an output of said pulse divider (18) is an output of the roll-off filter.

A transversal type roll-off filter having a function of an automatic equalizer, receiving a serial bit line of a first channel (I channel) signal, orthogonal with a second channel (Q channel) signal, of a parallel digital signal sampled n times from an analog signal demodulated from a quadrature amplitude modulation signal carrying a pulse train having a pulse spacing T where n is an integer greater than or equal to 1, said transversal type roll-off filter comprising

• a first delay line (11) comparing a first even number of first delay elements (11-D) each having a delay time T/n;
• a first group of adders (12), each arranged between adjacent two of said first delay elements and at an output terminal of a last one of said first delay elements (11-D);
• a first group of multipliers (4'), all of input terminals of said first group multipliers being connected with an input terminal of the roll-off filter, an output terminal of each of said first group multipliers being respectively input to a central one and every n-th ones, counted from said central one, of said first group adders,
• a second group of multipliers (5'), input terminals of said second group multipliers being connected with said input terminal of the roll-off filter, an output terminal of each of said second group multipliers being respectively input to all other first group adders than those connected with said first group multipliers, each of said first group adders summing an input from preceding one of said first delay elements and an input from said first and second group multipliers, an output of each of said first group adders being input to a subsequent one of said first adders, an output of a first one of said first or second group multipliers being input to a first one of said delay elements,
• a second delay line (13) comprising a second even number of second delay elements (13-D) each having a delay time T;
• a second group of adders (14), each arranged between adjacent two of said second delay elements (13-D) and at a n output terminal of a last one of said second delay elements (13-D), one of inputs to said second group adder is an output of preceding one of said second delay elements, an output of each of said second group adders being input to a subsequent one of said second delay elements;
• a third delay element (15') having said delay time T, connected to an output terminal of last one of said second group adders;
• a third group of multipliers (3'), input terminals of said third group multipliers being connected with an input terminal of a second channel roll-off filter, output terminals of said third group multipliers being respectively input to said second group adders;
• a memory device (6) for storing and outputting a first group and a second group of tap rating ratios (.alpha.1, .alpha.2) to determine a roll-off filter frequency characteristic of the roll-off filter, said second group tap rating ratios (.alpha.2) being input to said second group multipliers (5'), respectively;
• a calculation circuit (7) monitoring an output signal of the digital filter, for calculating according to a predetermined algorithm and outputting a first and a second group of tap rating ratios (C', C), each of said first group tap rating ratios (C') being input to each of said third group multipliers (3');
• a third adder (8) for summing each of said second group tap rating ratios (C) with respective one of said first group tap rating ratios (.alpha.1), outputs (.alpha.') of said third adders being input to said first group multipliers (4'), respectively;
• a divider (18') connected to an output of last one of said first group adders (12), for outputting every n-th pulse input thereto;
• and
• a fourth adder (17') for summing an output of said last one of said first group adders and an output of said third delay element,
• wherein an output of said fourth adder (17') is an output of the roll-off filter.

A transversal type roll-off filter receiving a serial bit line of a digital signal sampled n times from an analog signal carrying a pulse train having a pulse spacing T where n is an integer greater than or equal to 1, the transversal type roll-off filter comprising:

• a transversal type delay line comprising an even number of delay elements each having a delay time T/n;
• nodes between adjacent two of said delay elements;
• a memory device for providing first tap rating ratios to control signals of said nodes, respectively;
• and
• a calculation circuit for monitoring pulse wave forms of an output signal of the roll-off filter, and calculating second tap rating ratios, an addition of each of said second tap rating ratios with corresponding one of said first tap rating ratios additionally controlling an output from a central one of said nodes and every other node counted from said central node;
• said second tap rating ratios being calculated so as to be optimum to make said output pulse forms,
• wherein said delay line operates as a roll-off filter whose frequency characteristic is determined by said first tap rating ratios and operates as an automatic equalizer whose frequency characteristic is variably controlled by said second tap rating ratios.

A transversal type roll-off filter receiving a serial bit line of a digital signal sampled n times from an analog signal carrying a pulse train having a pulse spacing T where n is an integer greater than or equal to 1, the transversal type roll-off filter comprising:

• a first transversal type delay line comprising a plurality of first delay elements each having a delay time T/n;
• first nodes, each between adjacent two of said first delay elements;
• a second transversal type delay line comprising a plurality of second delay elements each having a delay time T, said second delay line receiving an input from a first delay line of the opposite channel;
• second nodes, each between adjacent two of said second delay elements;
• a memory device for providing first group tap rating ratios to control signals of said first nodes, respectively;
• and
• a calculation circuit for monitoring pulse forms of an output signal of the roll-off filter, and calculating second tap rating ratios to control signals of said second nodes, an addition of each of said second tap rating ratios with corresponding one of said first tap rating ratios additionally controlling a central one of said nodes, and every other node counted from said central node of said first nodes;
• said second tap rating ratios being calculated so as to be optimum to make said output pulse forms;
• and
• an adder to sum outputs of said first and second delay lines, an output of said adder being an output of the roll-off filter,
• so that delay lines operate as a roll-off filter having a frequency characteristic determined by said first tap rating ratios and operate as an automatic equalizer having a frequency characteristic variably controlled by said second tap rating ratios.

A method of diagnosing electronic circuits used in a communication system, said communication system comprising:

• a first digital roll-off filter provided in a transmitting station, comprising:
• a first memory device (113-1) for storing and outputting first tap rating ratios to be used for a regular operation of the system and a second tap rating ratios to be used to diagnose the system, said first and second tap rating ratios being switchably output to said first roll-off filter;
• a second digital roll-off filter provided in a receiving station, comprising:
• a second memory device (6-1) for storing and outputting third tap rating ratios to be used for said regular operation of the system and fourth tap rating ratios to be used to diagnose the system,
• wherein second tap rating ratios are such that frequency characteristic of said first roll-off filter determined by said second tap rating ratios is the same as an overall frequency characteristic of said first and second roll-off filters,
• the method for diagnosing the system comprising steps of:
• switching said first memory device (113-1) so as to selectively output said second tap rating ratios, respectively;
• comparing a width or a height of an eye in an eye diagram with a predetermined reference level, at a check point provided at a circuit after said first roll-off filter, so as to detect a location of a cause of deteriorating pulse forms,
• wherein said second memory device (6-1) further comprises means for providing fourth tap rating ratios switchable from said third tap rating ratios, said third tap rating ratios being such as to make said second roll-off filter transparent to the signal input thereto, and
• wherein said fourth tap rating ratios are such that tap rating ratios to be input to multipliers connected with a central node are one, and tap rating ratios to be input to multipliers connected with all other nodes than said central node are zero.