Circuit for reliable switching over of signal processing circuits

Abstract: Switching circuitry incorporated in a system including a plurality of signal processing circuits (21 - 2n) having an identical function. The circuitry has a selector (8) and a controller (9) which replace, in response to alarm signals (71 to 7n) from individual signal processing circuits, the processing timing of a failed signal processing circuit handling important information with that of another signal processing circuit which has not failed.

Description: The present invention relates to circuitry incorporated in a system including a plurality of signal processing circuits having an identical function for switching them over. A system including a plurality of signal processing circuits having an identical function additionally includes a standby signal processing circuit. When any one of the active signal processing circuits fails, it is replaced with the standby signal processing circuit to insure the reliability of the system. However, this kind of system is totally shut down when the standby signal processing circuit substituting the failed circuit fails itself. While a number of standby circuits may be incorporated in the system to cope with the above occurrence, such an approach is not desirable from the cost standpoint since standby circuits are simply useless so long as the other circuits are normal. NEC Research and Development N° 94, July 1989, Tokyo, Japan pages 129-135 discloses a multiprocessing system including a plurality of processing devices for processing a plurality of software. When any one of the processing devices fails, the other or normal processing devices deal with the signal having been processed by the failed processing device; the software that is not important is not processed. United States Patent N° US-A-4,857,760 (REID et al) discloses circuitry having a plurality of processing circuits for processing a plurality of time slots constituting a TDMA signal, and a standby or spare processing circuit. When an error occurs in any one of the former circuits, the latter circuit or standby circuit processes the signal having been handled by the defective circuit. In accordance with the present invention, circuitry for switching signal processing circuits comprises n signal processing circuits each receiving an input signal having n time division multiplexed signals to thereby output a result of processing as a data signal, a selector for generating a switching signal in response to n alarm signals each being generated by respective one of the n signal processing circuits when associated one of the signal processing circuits fails, and a controller receiving a timing signal representative of a relation between the switching signal and the input signal for switching over timings at which the n signal processing circuits should process the input signal, characterised in that when a processing circuit dealing with an important time slot fails, the selector is adapted to deliver the switching signal to the controller, causing the controller to hand over the processing of the important time slot to any one of the other, normal signal processing circuits, in place of the failed circuit, in accordance with the switching signal. Also, in accordance with the present invention, a method of switching n signal processing circuits each receiving an input signal made up of n signal processing circuits each receiving an input signal made u of n time division multiplexed signals to thereby produce a result of processing as a data signal comprises the steps of causing each of the n signal processing circuits to generate an alarm signal when failed, generating a switching signal by means of a selector in response to the alarm signal, feeding a timing signal representative of a relation between the switching signal and the input signal, and switching timings for particular ones of the n signal processing circuits to process the input signal, characterised in that when a processing circuit dealing with an important time slot fails, the selector delivers the switching signal to the controller causing the controller to hand over the processing of the important time slot to any one of the other, normal signal processing circuits, in place of the failed circuit, in accordance with the switching signal. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: Figure 1 is a block diagram schematically showing conventional circuitry for switching signal processing circuits; Figures 2A-2D are timing charts demonstrating a specific operation of the conventional switching circuitry; Figure 3 is a schematic block diagram showing circuitry for switching signal processing circuits embodying the present invention; and Figures 4A-4D are timing charts representative of a specific operation of the embodiment. To better understand the present invention, a brief reference will be made to conventional switching circuitry incorporated in a TDMA (Time Division Multiple Access) receiver by way of example, shown in Figure 1. As shown, the switching circuitry has n signal processing circuits 21-2n, a standby circuit 10, and a switching circuit 11. The n signal processing circuits 21-2n receive an input signal 1 made up of n time division multiplexed signals and produce data signals 31 - 3n, respectively. The standby circuit 10 is connected in parallel with the signal processing circuit 21 for producing a data signal 31 in response to the input signal 1. The switching circuit 11 selectively switches over the signal processing circuit 21 and standby circuit 10 with control signals 121 and 122. The input signal 1 is made up of n time slots, i. e., a time slot including system information and similar signals of primary importance for the system (referred to as an important time slot hereinafter) and time slots for handling general signals (referred to as general time slots hereinafter). The important time slot is assigned to the signal processing circuit 21 while the general time slots are each assigned to particular one of the signal processing circuits 22-2n. In response to a timing signal shown in FIG. 2B and included in the input signal 1, the signal processing circuits 21-2n each processes the associated time slot, as shown in FIG. 2C. When the signal processing circuit 21 assigned to the important time slot fails, the switching circuit 11 delivers the control signals 121 and 122 to replace the signal processing circuit 21 with the standby circuit 10. As a result, as shown in FIG. 2D, the standby circuit 10 handles the important time slot afterwards to thereby insure the reliability of the system. However, the problem with the conventional switching circuitry is that once the standby circuit 10 fails itself, the circuitry cannot deal with the important time slot at all, resulting in total system down. While this problem may be eliminated if a number of standby circuits are used, such an implementation is not desirable from the economy standpoint since the standby circuits are simply useless so long as the signal processing circuit are free from errors. Referring to FIG. 3, circuitry for switching signal processing circuits embodying the present invention is shown. As shown, n signal processing circuits 21-2n output respectively data signals 31-3n in response to an input signal 1 having n signals including an important time slot and general time slots multiplexed on a time division basis. A controller 5 is connected to the signal processing circuits 21-2n and receives a timing signal 4 representative of a relation of the multiplexed input signal 1 with respect to time. The controller 5 delivers control signals 61-6n to the signal processing circuits 21-2n, respectively. The signal processing circuits 21-2n deliver respectively alarm signals 71 -7n to a selector 8. The selector 8 feeds a switching signal 9 matching the alarm signals 71-7n to the controller 5. The selector 8 constantly determines which of the signal processing circuits 21-2n is handling the important time slot, and it assigns the important time slot to normal one of the signal processing circuits 21-2n prior to the general time slots. A reference will be made to FIGS. 4A-4D for describing a specific operation of the embodiment. As shown in FIG. 4A, the input signal 1 has an important time slot and general time slots multiplexed on a time division basis. The controller 5 sequentially switches the signal processing circuits 21-2n in response to the timing signal 4 shown in FIG. 4B and corresponding to the input signal 1. Assume that the time slot No. 0 is the important time slot and is handled by the signal processing circuit 21, as shown in FIG. 4C. Then, as the signal processing circuit 21 fails, the circuit 21 sends an alarm signal 71 to the selector 8. In response, the selector 8 determines that the signal processing circuit 21 is handling the important time slot, while determining whether or not the other signal processing circuits are normal. Then, the selector 8 delivers a switching signal 9 to the controller 5 for causing the controller 5 to replace the processing timing of the failed signal processing circuit 21 with that of any one of the normal signal processing circuits. On receiving the switching signal 9, the controller 5 shuts down the signal processing circuit 21 represented by the alarm signal 71. At the same time, the controller 5 replaces the signal processing circuit 21 with one of the other signal processing circuits dealing with the general time slots, e. g. , the signal processing circuit 22 by changing the timings for generating the control signals 61 and 62. As a result, the important time slot No. 0 is handed over to the signal processing circuit 22 afterwards. If the signal processing circuit to handle the important time slot is sequentially replaced in the above-described manner, an occurrence that the processing of the important time slot is practicaily interrupted due to a failure of a signal processing circuit is almost eliminated. This is successful in preventing the whole system from being disabled. In summary, it will be seen that the present invention provides switching circuitry including a selector and a controller which replaces, in response to alarm signals from individual signal processing circuits, the processing timing of a failed signal processing circuit with that of another signal processing circuit. Hence, the circuitry guarantees the processing of an important time slot until all the signal processing circuits fail, reducing the system down rate and thereby enhancing the reliability of the system. The circuitry of the invention will be especially desirable when the system is situated at a location too remote to effect immediate maintenance in the event of failure Various modifications will become possible for those skilled in the art after receiving the teachings of the present disciosure without departing from the scope thereof.

Claims: Circuitry for switching signal processing circuits, comprising: n signal processing circuits (21-2n) each receiving an input signal (1) having n time division multiplexed signals to thereby output a result of processing as a data signal; a selector (8) for generating a switching signal (9) in response to n alarm signals each being generated by respective one of said n signal processing circuits when associated one of said signal processing circuits fails; and a controller (5) receiving a timing signal (4) representative of a relation between the switching signal and the input signal for switching over timings at which said n signal processing circuits should process the input signal, characterised in that when a processing circuit dealing with an important time slot fails, the selector is adapted to deliver the switching signal to the controller, causing the controller to hand over the processing of the important time slot to any one of the other, normal signal processing circuits, in place of the failed circuit, in accordance with the switching signal. Circuit as claimed in Claim 1, wherein said selector is adapted to constantly determine which one of said n signal processing circuits is handling a particular time slot of the input signal which includes important information and replacing on receiving the alarm signal from the one signal processing circuit,processing timing of said one signal processing circuit with processing timing of one of the other signal processing circuits which are normal. A method of switching n signal processing circuits (21-2n) each receiving an input signal (1) made up of n time division multiplexed signals to thereby produce a result of processing as a data signal, said method comprising the steps of: (a) causing each of said n signal processing circuits to generate an alarm signal (71-7n) when failed; (b) generating a switching signal (9) by means of a selector (8) in response to the alarm signal; (c) feeding to a controller (5) a timing signal (4) representative of a relation between the switching signal and the input signal; and (d) switching timings for particular ones of said n signal processing circuits to process the input signal characterised in that when a processing circuit dealing with an important time slot fails, the selector delivers the switching signal to the controller, causing the controller to hand over the processing of the important time slot to any one of the other, normal signal processing circuits, in place of the failed circuit, in accordance with the switching signal. A method as claimed in Claim 3, wherein step (b) comprises determining which of said n signal processing circuits is handling a particular time slot of the input signal which includes important information, and generating, on receiving the alarm signal from the signal processing circuit handling the particular time slot, the switching signal for replacing a processing timing of said signal processing circuit with processing timing of another signal processing circuit which is normal.

Inventors: AKAHORI HIROSH, HORI TSUGUO, AKAHORI, HIROSHI, HORI, TSUGUO, Akahori, Hiroshi, c/o Ando Electric Co.,Ltd., HORI, TSUGUO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H04J3
IPC codes: H04B7, H04B1, H04L1, H04J3