System for detecting non-coincidence of codes

Abstract: An input coded signal is compared with a predetermined coded signal to generate a non-coincidence signal. Error bits of the non-coincidence signal are changed to correct bit by a predetermined number of bits. When the non-coincidence signal has no longer any error bit as a result of changing the error bits to the correct bits, the input coded signal is determined to be correct.

Description: This invention relates to a system for detecting non-coincidence of codes, and more particularly to, a system in which the number of error bits of a coded signal is detected as to whether it is less than or equal to a tolerable number. One type of a conventional system for detecting non-coincidence of codes, which is used in, for instance, a cordless telephone system, includes a circuit for detecting non-coincidence of each two bits between an input coded signal and a predetermined coded signal, a shift register for storing the detected results of the non-coincidence in each bit of the input coded signal, and a counter for counting the number of bits which are determined to be non-coincided. In operation, the input coded signal is compared in the non-coincidence detecting circuit with the predetermined coded signal bit by bit, so that the detected results of high and low level signals are generated in accordance with the non-coincidence and the coincidence of each two bits between the input and predetermined coded signals. The high and low level signals are stored in the shift register, and supplied in series to an AND gate for permitting clock signals to be supplied to the counter, in which the number of the high level signal is counted. When the counted number is less than or equal to a predetermined tolerable number in the counter, the input coded signal is determined to be correct, even if the input coded signal includes errors in some bits. Another type of a conventional system for detecting non-coincidence of codes includes a predetermined number of circuits each detecting coincidence between an input coded signal and one of predetermined coded signals, wherein the predetermined number is set to be a bit error tolerable number, and all error coded signals which may occur in the bit error tolerable number for an input coded signal are supplied to the coincidence detecting circuits, correspondingly. In operation, the input coded signal is supplied to the coincidence detecting circuits, and compared therein with the supplied one of the error coded signals to be detected in regard to the coincidence therewith. Unless any one of the coincidence detecting circuits generates a high level signal representing the coincidence between the input coded signal and one of the error coded signals, the input coded signal is determined to be correct. However, there are disadvantages in the conventional systems for detecting non-coincidence of codes in that: (1) the detection takes a long time in the former system, because the detected results are supplied in series from the shift register to the AND gate, although an advantage is found in that the scale of the system is relatively small, and (2) the scale of the system becomes large, because the bit error tolerable number of the coincidence detecting circuit must be provided, although an advantage is found in that the detection is carried out in a short time. JP-A-56-093452 discloses a digital synchronization detector which stores the number of errors for each bit pattern in a ROM. This number is compared with the number of allowable error bits resulting in a synchronisation detection signal. Accordingly, it is an object of the invention to provide a system for detecting non-coincidence of codes in which a time for detecting the non-coincidence between an input coded signal and a predetermined coded signal is short and in which the scale of system is suppressed not to be large in realizing a detecting time to be short. This object is solved with the features of the claims. The invention will be described in more detail in conjunction with appended drawings, wherein: Figs. 1 and 2 are block diagrams showing two type of conventional systems for detecting non-coincidence of codes; Fig.3 is a block diagram showing a system for detecting non-coincidence of codes in a preferred embodiment according to the invention; Fig. 4 is a block diagram showing a non-coincidence detecting circuit in the preferred embodiment; Fig. 5 is a block diagram showing a circuit for detecting residual error bits in the preferred embodiment; Fig. 6 is a block diagram showing a circuit for detecting coincidence between an input coded signal and a predetermined coded signal in the preferred embodiment; Fig. 7 is a block diagram showing a cordless telephone system in which the invention is included; and Fig. 8 is an explanatory diagram showing a coded signal used in the cordless telephone system. Before describing a system for detecting non-coincidence of codes in a preferred embodiment according to the invention, the aforementioned conventional systems will be explained in Figs. 1 and 2. Fig. 1 shows the former one of the conventional systems which includes a non-coincidence detecting circuit 51, a shift register 52, an inverter 53, a differentiation circuit 54, an AND gate 55, and a counter 56. In operation, a predetermined (correct or reference) coded signal 500 and an input coded signal 501 are supplied to the non-coincidence detecting circuit 51, in which exclusive OR process is carried out between each two corresponding bits of the input and predetermined coded signals, so that a high level signal is generated, when the two bits are coincided, and a low level signal is generated, when the two bits are not coincided. The high and low level signals are transferred via a signal line 502 to the shift register 52 by a load signal supplied to a control line 503. The shift register 52 supplies the AND gate 55 via a signal line 505 with the high and low level signals in series in accordance with a clock signal supplied to a clock line 504. The clock signal is inverted in the invertor 53, and the inverted signal is differentiated in the differentiation circuit 54 to be a pulse signal which is then supplied to the AND gate 55 via the signal line 506. Thus, the pulse signal is supplied via the AND gate 55 and a signal line 507 to be counted in the counter 56, when the high level signal is supplied from the shift register 52 to the AND gate 55. When the counted number becomes more than a predetermined tolerable bit error number, a signal representing the non-coincidence between the input and predetermined coded signals is obtained at a signal line 508 connected to the counter 56. Fig. 2 shows the latter one of the conventional systems which includes a predetermined number of coincidence circuits 61, 62,----- 6n, and an OR circuit 70, wherein the predetermined number is a number of signals possible to be coded by a tolerable number of bit errors. In operation, an input coded signal is supplied via a signal line 600 to the coincidence circuits 61, 62, ----- 6n, and error coded signals which are possible to be coded by the predetermined number of error bits and a correct coded signal are supplied via signal lines 601, 602, ----- 60n to the coincidence circuits 61, 62, ----- 6n. In one of the coincidence circuits 61, 62, -- --- 6n, a coincidence signal is generated, when the input coded signal is coincided with one of the coded signals supplied via the signal lines 601, 602, ----- 60n. The coincidence signal is supplied via one of signal lines 611, 612, ----- 61n to the OR gate 70, and obtained at an output signal line 620 connected to the OR gate 70. Next, a system for detecting non-coincidence of codes in a preferred embodiment according to the invention will be explained in Figs. 3 to 6. Fig. 3 shows the system for detecting non-coincidence of codes which comprises a non-coincidence detecting circuit 11 for comparing corresponding bits between an input coded signal on a signal line 100 and a predetermined coded signal on a signal line 101 and providing compared results on a signal line 102, first to third residual error bit detecting circuits 14 to 16 connected in series by signal lines 105 and 106 each detecting residual error bits in the compared results on the signal line 102 and decreasing the residual error bits by one bit, and a coincidence detecting circuit 17 for detecting the coincidence between the input coded signal and the predetermined coded signal to provide a coincidence signal on a signal line 108 by detecting the non-existence of an error bit supplied on a signal line 107 from the third residual error bit detecting circuit 16. Fig. 4 shows the non-coincidence detecting circuit 11 which includes exclusive OR circuits 21, 22, ----- 2i having first inputs connected to the signal line 100 for the input coded signal a1, a2, ----- ai, second inputs connected to the signal line 101 for the predetermined coded signal b1, b2, ----- bi, and outputs connected to the signal line 102 for a non-coincidence coincidence signal composed of the coincidence results c1, c2, ----- ci. Fig. 5 shows the first residual error bit detecting circuit 14 which includes an adding circuit (full adder) 12 for adding the non-coincidence signal d1, d2, ----- di(equal to c1, c2, ----- ci) and a signal of "1" in all i bits supplied on a signal line 103, and AND gates 131, 132, ----- 13i having first inputs connected to the signal line 102, second inputs connected to outputs of the adding circuit 12, and outputs connected to the signal line 105. In the adding circuit 12, a carry signal is added to a bit higher by on bit in the ordinary manner, and a carry signal obtained at the MSB is abandoned. The second and third residual error bit detecting circuits 15 and 16 are the same in construction as the first residual error bit detecting circuit 14. Fig. 6 shows the coincidence detecting circuit 17 which includes an OR circuit 170 having inputs connected to the signal line 107 for a residual error bit-decreased signal g1, g2, ----- gi and an output connected to the signal line 108. In operation, it is assumed that a tolerable number for error bits is three, and that the input coded signal is "10010000", and the predetermined coded signal is "10100001" (i=8). First, "10010000" (a1, a2, ----- ai) is supplied via the signal line 100 to the first inputs of the exclusive OR circuits 21, 22, ----- 2i in the non-coincidence detecting circuit 11, and "10100001" (b1, b2, ----- bi) is supplied via the signal line 101 to the second inputs of the exclusive OR circuits 21, 22, ----- 2i, so that the non-coincidence signal "00110001" (c1, c2, ----- ci) representing the existence of three bit errors is obtained on the signal line 102 from outputs of the exclusive OR circuits 21, 22, ----- 2i. Second, the non-coincidence signal "00110001" (d1, d2, ----- di) and the adding signal "11111111" are added in the adding circuit 12 in the first residual error bit detecting circuit 14, so that an added signal "00110000" is obtained on the signal line 104 from the outputs of the adding circuit 12. The added signal "00110000" thus obtained and the non-coincidence signal "00110001" (d1, d2, ----- di) are supplied to the AND gates 131, 132, ----- 13i in the first residual error bit detecting circuit 14, so that one error bit decreased signal "00110000" (f1, f2, ----- fi) is obtained on the signal line 105 from the outputs of the AND gates 131, 132, ----- 13i. The process in the first residual error bit detecting circuit 14 in which an error bit is decreased by one bit is subsequently carried out in the second and third residual error bit detecting circuits 15 and 16. Consequently, a non-coincidence signal "00100000" is obtained on the signal line 106 from outputs of AND gates (not shown) in the second residual error bit detecting circuit 15, and a non-coincidence signal "00000000" is obtained on the signal line 107 from outputs of AND gates (not shown) in the third residual error bit detecting circuit 16. Finally, the non-coincidence signal "00000000" is supplied from the third residual error bit detecting circuit 16 to the OR circuit 170 in the coincidence detecting circuit 17, so that a high level signal representing the coincidence between the input coded signal "10010000" and the predetermined coded signal "10100001" is obtained on the signal line 108 from an output of the coincidence detecting circuit 17. On the other hand, if an input coded signal (a1, a2, ----- ai) includes error bits more in number than the tolerable number, for instance, three in the preferred embodiment, the coincidence detecting circuit 17 generates a low level signal. In practical, the tolerable number is two or three in case where an input coded signal is of 32 bits, and it is zero or one in case of 16 bits. Fig. 7 shows a cordless telephone set system in which a system for detecting non-coincidence of codes is included in accordance with the invention. The cordless telephone set system includes an antenna 71 for receiving and transmitting radio signals, a radio receiving circuit 72 for amplifying and demodulating the received radio signal, a radio transmitting circuit 73 for amplifying and modulating the transmitting radio signal, a TDMA/TDD (time division multiplexing access/time division duplex) unit 74, a codec 80 for decoding the received radio signal and encoding the transmitting radio signal, a control unit 81 for controlling the TDMA/TDD unit 74 and the codec 80, and a handset 82 having a microphone and a phone-receiver for an operator. The TDMA/TDD unit 74 includes a code coincidence circuit 75 for generating a code coincidence signal by using the system for detecting non-coincidence of codes in the aforementioned preferred embodiment, a timing control circuit 76 for generating a timing signal by receiving the coincidence signal, a gate 77 which is turned on by receiving the timing signal, a buffer circuit 78 for storing the received signal, and a transmitting system 79 for supplying coded signals to the transmitting circuit 73 at predetermined timings. Fig. 8 shows one example of a received or transmitting signal including PRE(preamble), UW(unique word), CI(channel identifier), DATA, and CRC(cyclic redundancy code), wherein the UW is a code for timing which is checked in regard to the coincidence and non-coincidence with a predetermined coded signal. In operation, the received radio signal is demodulated in the receiving circuit 72, and the demodulated signal is checked as to whether the UW is coincided with a predetermined coded signal, as explained in the aforementioned preferred embodiment. When the coincidence signal is generated from the code coincidence circuit 75, the timing control circuit 76 controls the gate 77 to be turned on at a predetermined timing, so that the demodulated signal is passed through the gate 77 to be stored in the buffer circuit 78. Then, the buffer circuit 78 is controlled by the control unit 81, so that a signal read from the buffer circuit 78 is supplied to the codec 80, in which the supplied signal is decoded in the codec 80. Thus an operator can receive voice information based on the decoded signal by using the handset 82.

Claims: A system for detecting non-coincidence between an input code signal of a number of plural bits and a reference code signal of the same number of plural bits, in which each corresponding bits are compared to generate a first logical signal when said each corresponding bits are coincident, and a second logical signal opposite to said first logical signal when said each corresponding bits are non-coincident, and said non-coincidence is detected between said input code signal and said reference code signal when the number of the second logical signals is more than a predetermined tolerable number, characterized by: said predetermined tolerable number of residual error bit detecting circuits (14 to 16) connected in series and each changing only one of said second logical signals to said first logical signal; and a coincidence detecting circuit (17) for detecting a coincidence between said input code signal and said reference code signal, when said second logical signal is not detected after said predetermined tolerable number of said second logical signals are changed to said first logical signals by said predetermined tolerable number of said residual error bit detecting circuits (14 to 16). A system according to claim 1, wherein each of said residual error bit detecting circuits (14 to 16) comprises: a full adder (12) for adding said non-coincidence signal (line 102) and a signal of "1" (line 103) in all bits; and AND gates (13) for carrying out AND process between two corresponding bits of said non-coincidence signal (line 102) and an added signal (line 104) supplied from said full adder (12).

Inventors: NAGASHIMA NORIAKI, NAGASHIMA, NORIAKI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1993
Main classification: G06F7
IPC codes: H04M1, H03M13, G06F7, H04J3, G06F11