Transmitter and receiver for use in TDMA/TDD mobile radio communications systems having loopback test facilities

Abstract: A radio apparatus according to a TDMA/TDD system uses its own transmitter (2) and receiver (3) so as to perform a loopback test for checking normality of the apparatus (1A) during a period of an unassigned slot. A loopback test signal is output from its own transmitter (2) during an unassigned transmitting slot and is received by its own receiver (3). The signal is temporarily stored in a memory (14) and is read during an unassigned receiving slot. The apparatus (1A) thus performs a loopback test. Since a loopback test can be performed by use of its own transmitter (2) and receiver (3) during an unassigned slot, a transmitting and receiving device (tester) specifically used for a loopback test is not required. Also, a loopback test can be carried out even while normal communications are being made.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a radio apparatus, for example, a car phone base station, which performs radio communications with a plurality of mobile stations (car phones, transportable phones and the like) according to a TDMA (Time Division Multiple Access)/TDD (Time Division Duplex) system. This TDMA/TDD system is employed whereby transmitting information and receiving information can be alternately transmitted and received to effect multiplex transmission by use of respective channels of a plurality of radio carriers allocated to digital cordless phones. DESCRIPTION OF THE RELATED ART The construction of a typical conventional radio apparatus will now be explained with reference to Fig. 7. Fig. 7 is a block diagram illustrative of the construction of a radio apparatus, such as a car phone base station. Referring to Fig. 7, a radio apparatus (base station) 1, such as a car phone base station, comprises a transmitter 2, a receiver 3, an antenna change-over switch 4 for switching between transmitting and receiving modes, a transmitting/receiving antenna 5 used for normal communications, a transmitting/receiving device 6 used for loopback tests (tester), an antenna change-over switch 9 for switching between transmitting and receiving modes, and a transmitting/receiving antenna 10 used for loopback tests. The loopback test transmitting/receiving device further includes a loopback test transmitter 7 and a loopback test receiver 8. The base station 1 also comprises a controller formed of CPU, RAM, ROM, interfaces and the like, though not shown. A description will now be given of the operation of the conventional radio apparatus constructed as described above. As shown in Fig. 7, radio waves transmitted from the transmitter 2 of the radio apparatus 1 are received by the loopback test receiver 8, or radio waves transmitted from the loopback test transmitter 7 are received by the receiver 3 of the radio apparatus 1, whereby it can be conventionally checked that the radio apparatus 1 properly operates. That is, the radio apparatus 1 comprises the transmitter 2, the receiver 3, and the loopback test transmitting/receiving device 6 which is formed of the loopback test transmitter 7 and receiver 8. For performing a loopback test, a signal from the transmitter 2 is transmitted through the transmitting/receiving antenna 5 used for normal communications and is received by the loopback test receiver 8 through the loopback test transmitting/receiving antenna 10. If this receiving operation is correctly accomplished, it can be checked that the transmitter 2 and the antenna 5 properly operate. On the other hand, a signal from the loopback test transmitter 7 is transmitted through the loopback test transmitting/receiving antenna 10 and is received by the receiver 3 through the antenna 5 used for normal communications. If this receiving operation is correctly accomplished, it can be checked that the antenna 5 and the receiver 3 properly operate. However, the above-described conventional radio apparatus 1 has a problem in that the transmitting/receiving device (tester) 6 specifically used for loopback tests should be arranged within the apparatus 1. The apparatus 1 also presents the following problem. When the loopback test indicates poor results, it is difficult to identify which element is faulty, i.e., the transmitter 2, the receiver 3, or the loopback test transmitting/receiving device (tester) 6. SUMMARY OF THE INVENTION Accordingly, in order to solve the above problems, an object of the present invention is to provide a radio apparatus which is able to perform a loopback test without requiring a transmitting and receiving device (tester) specifically used for a loopback test. According to the invention, the problem is solved by a radio apparatus according to a TDMA/TDD system and suitable for performing a loopback test, the apparatus comprising: a transmitter for transmitting data during a transmitting slot; an attenuator for attenuating the data transmitted from the transmitter; a receiver for receiving during the transmitting slot the data attenuated by the attenuator; a memory for temporarily storing the data received by the receiver during the transmitting slot; and a controller for performing the following two operations during an unassigned receiving slot: (a) reading from the memory the aforementioned stored data; (b) comparing the data read from the memory with the data transmitted from the transmitter so as to assess proper operation of the apparatus. In a first specific embodiment.of the radio apparatus according to the invention, the transmitting slot is unassigned, and the data used for the loopback test are internally generated loopback test data. According to a further development of such a radio apparatus according to the invention, the controller comprises a transmitting signal processing section and a receiving signal processing section, the transmitting signal processing section generating the loopback test data and transmitting them to the transmitter, the receiving signal processing section comparing the loopback test data read from the memory with the loopback test data generated in the transmitting signal processing section, and upon such a comparison, issuing an alarm when a deviation from proper operation has occurred. In a second specific embodiment of the radio apparatus according to the invention, the transmitting slot is occupied for communication with a mobile station, and the data used for the loopback test are communication data used for communicating with the mobile station. According to a further development of such a radio apparatus according to the invention, the controller comprises a transmitting signal processing section and a receiving signal processing section, the transmitting signal processing section generating the communication data and transmitting them to the transmitter, the receiving signal processing section comparing the communication data read from the memory with the communication data generated in the transmitting signal processing section, and upon such a comparison, issuing an alarm when a deviation from proper operation has occurred. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a radio apparatus (base station) according to a first embodiment of the present invention; Fig. 2 illustrates a mobile communication system by use of the radio apparatus (base station) according to the first embodiment; Fig. 3 illustrates a time slot of the mobile communication system according to the first embodiment; Fig. 4 is a flow chart illustrative of the operation of the base station shown in Fig. 1 during a test mode; Fig. 5 illustrates a time slot of a mobile communication system according to a second embodiment of the present invention; Fig. 6 is a flow chart illustrative of the base station of the second embodiment during the test mode; and Fig. 7 is a block diagram illustrative of the construction of a conventional radio apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A description will now be given of the construction of a first embodiment of the present invention with reference to Fig. 1. Fig. 1 illustrates the construction of the first embodiment of the present invention. The same reference numerals in the respective figures designate the same or corresponding components. Referring to Fig. 1, a radio apparatus 1A having a loopback test function comprises a transmitter 2, a receiver 3, an antenna change-over switch 4, a transmitting/receiving antenna 5, a change-over switch 12, an attenuator 13, a memory 14 for temporarily storing output signal data from the receiver 3, a change-over switch 15 for selecting between a signal output from the receiver 3 and a signal read from the memory 14, and a controller 40. The controller 40 includes CPU, ROM, RAM, interfaces and the like functioning as hardware. The controller 40 also has a transmitting signal processing section 11 primarily for generating transmitting signals and a receiving signal processing section 16 largely for producing receiving signals. The operation of the first embodiment will now be explained with reference to Figs. 2, 3 and 4. Fig. 2 illustrates a mobile communication system using the first embodiment of the present invention. Fig. 3 is a time slot according to a TDMA/TDD method of the mobile communication system shown in Fig. 2. Fig. 4 is a flow chart illustrative of the operation of the controller 40 according to the first embodiment. Fig. 2 shows a radio apparatus (a car phone base station) 1A having a loopback test function and also illustrates one mobile station 20, such as a car phone or the like, having communications with the radio apparatus 1A. Reference numeral 21 indicates a radio communication path between the base station 1A and the mobile station 20. Fig. 3 illustrates the communication between the base station 1A and the mobile station 20 and also shows a loopback test performed therebetween, the horizonal axis designating a time axis. Fig. 3 indicates a time slot of a mobile communication system according to a qaudruplex TDMA/TDD method by way of example. This system enables one base station to communicate with a maximum of four mobile stations. 23 designates a time slot of the base station 1A, while 24 represents a time slot of the mobile station 20. Since the quadruplex TDMA/TDD system is employed, the time slot 23 for one frame of the base station 1A is constructed of transmitting slot segments T1, T2, T3, T4 and receiving slot segments R1, R2, R3, R4. For example, it will now be assumed that a duration of 5ms is allocated to one frame of the TDMA/TDD system, and a duration of 625µs is allocated to each slot segment. Information for a data length of 5ms is transmitted as burst signals to the respective four mobile stations from the base station 1A at 625µs, at the timing shown in Fig. 3. Each mobile station compresses its own transmitting information into a data length of 625µs after 2.5ms since it receives a signal from the base station 1A so as to perform burst transmission. Fig. 3 illustrates a communication performed between the base station 1A and the mobile station 20 shown in Fig.2 by use of a first slot (slot segments T1 and R1). When the base station 1A transmits information using the transmitting slot segment T1 of the time slot 23, the mobile station 20 receives such information using the receiving slot segment R1 of the time slot 24. On the other hand, when the mobile station 20 transmits information in the transmitting slot T1 of the time slot 24, the base station 1A receives such information in the receiving slot R1 of the time slot 23. An explanation will now be given of the operation of a loopback test performed within the base station 1A by use of a second slot (slot segments T2 and R2). While the base station 1A is communicating with the mobile station 20 using the first slot, the transmitter 2 and the receiver 3 within the base station 1A are not used to communicate with the mobile station 20 during periods of second, third and fourth slots. Based on this fact, the transmitter 2 and the receiver 3 are actuated to perform a loopback test during a period of the second slot. However, since normal communications are performed between the base station 1A and the mobile station 20 in the first slot, the construction of the time slot 23 cannot be altered. Thus, a signal transmitted from the transmitter 2 in the second slot is received by the receiver 3 so as to be temporarily stored in the memory 14. The signal which has been stored during the receiving slot segment R2 is read from the memory 14 so as to be output to the receiving signal processing section 16, thus realizing a loopback test. The attenuator 13, and the change-over switch 12 connected to a path to the attenuator 13 are disposed to prevent radio waves used for a loopback test from radiating from the transmitting/receiving antenna 5. This attenuator 13 is also disposed for decreasing power which should be increased when transmitting signals are radiated as radio waves. The operation of the controller 40 to perform a loopback test will now be explained with reference to Fig. 4. It is first determined whether an unassigned slot is available for transmitting a loopback test signal (test data), such as a press button dialing (DTMF: dual tone multi-frequency) signal or the like, generated in the transmitting signal processing section 11 within the controller 40 (step 50). For example, T2 is determined to be an unassigned slot, in this case. With this preparation, the controller 40 first changes the antenna change-over switch 4 to the side of the receiver 3 and connects (ON) the change-over switch 12 (step 51) through the receiving signal processing section 16. Then, the controller 40 transmits through the transmitter 2 a loopback test signal (step 52), which then passes through the change-over switch 12 and the attenuator 13 so as to be input into the receiver 3. The received data (loopback test signal) is then stored in the memory 14 (step 53). While normal communications other than the loopback test are performed, the antenna change-over switch 4 is connected to the side of the transmitter 2 in the transmitting slot segment T1, while it is connected to the side of the receiver 3 in the receiving slot segment R1. Also, the change-over switch 12 is disconnected (OFF), and the change-over switch 15 is connected to the side of the receiver 3. It is again determined whether an unassigned slot is available, in this case, the receiving slot segment R2 (step 54). Then, the change-over switch 15 is changed to the side of the memory 14 (step 55), and the stored received test data is read from the memory 14 (step 56). The receiving signal processing section 16 compares the received test data with the test data generated in the transmitting signal processing section 11 (step 57). The loopback test has thus been performed according to the above-described process. If the above-mentioned two items of data do not coincide with each other, the controller 40 therefore determines that an abnormality has occurred and issues an alarm to an host exchanger (step 58). This embodiment takes advantages of the characteristics of the TDMA/TDD system so that a signal transmitted from its own transmitter 2 is received by its own receiver 3 within the base station 1A during an unassigned slot period, thereby realizing a loopback test. Since the base station 1A performs a loopback test by use of its own transmitter 2 and receiver 3, a tester (transmitter and receiver) specifically used for a loopback test is not required, which further eliminates the necessity of considering a possible breakdown of the loopback test transmitter and receiver. The first embodiment also offers the advantage of performing a loopback test while normal communications are being made. Further, since the base station utilizes its own transmitter and receiver, there can be an improvement in the reliability of the loopback test. The first embodiment has been explained in which a loopback test is performed during the second slot (T2, R2). However, since only one mobile station in the first slot is communicating with the base station 1A, a loopback test may also be performed in the third slot (T3, R3) or the fourth slot (T4, R4). When all the four mobile stations are having normal communications with the base station 1A, no unassigned slot is available, and accordingly, it is impossible to perform a loopback test. Advantages similar to those obtained in the first embodiment are not limited to a quadruplex system, but may be obtained in duplex, triplex, fivefold, sixfold, sevenfold, eightfold, ninefold, tenfold and twentyfold systems. In short, any multiplex system may be employed as long as at least one unassigned (not in use) slot is available. Second Embodiment In the above-described first embodiment, an unassigned slot is employed to transmit a loopback test signal and to receive it, thereby realizing a loopback test. In a second embodiment, a signal used in a transmitting slot segment which is occupied for communicating with the mobile station is simultaneously received by its own receiver, thus performing a loopback test. A base station of the second embodiment is constructed in a manner similar to the first embodiment shown in Fig. 1, except for the operation timing illustrated in Figs. 5 and 6. Fig. 5 illustrates a time slot of a mobile communication system according to the second embodiment of the present invention. Fig. 6 is a flow chart illustrative of the operation of the controller 40 according to the second embodiment. An explanation will now be given of the operation of the controller 40 to perform a loopback test according to this embodiment with reference to Fig. 6. In the first slot during which normal communications are being made, that is, during the transmitting slot segment T1 of the time slot 23 of the base station 1A (step 60), the controller 40 changes the antenna change-over switch 4 to the side of the transmitter 2 and connects (ON) the change-over switch 12 through the receiving signal processing section 16 (step 61). Subsequently, the controller 40 actuates the transmitter 2 and simultaneously operates the receiver 3 and then writes a signal which is usually employed for normal communications (communication data) into the memory 14 (steps 62 and 63). During the period of the receiving slot segment R2, which is unassigned, of the time slot 23 (step 64), the controller 40 changes the change-over switch 15 to the side of the memory 14 (step 65) so as to read the received communication data from the memory 14 (step 66). The controller 40 then compares the received communication data with communication data stored in the transmitting signal processing section 11 (step 67). The loopback test has thus been performed according to the above-described process. If the above-mentioned two items of data do not coincide with each other, the controller 40 determines that an abnormality has occurred and issues an alarm to a host exchanger (step 68). Hence, it is not necessary to generate loopback test transmitting data (test data) by the transmitting signal processing section 11. The other advantages are similar to those obtained in the first embodiment.

Claims: A radio apparatus according to a TDMA/TDD system and suitable for performing a loopback test, the apparatus comprising: a transmitter (2) for transmitting data during a transmitting slot; an attenuator (13) for attenuating the data transmitted from the transmitter (2); a receiver (3) for receiving during the transmitting slot the data attenuated by the attenuator (13); a memory (14) for temporarily storing the data received by the receiver (3) during the transmitting slot; and a controller (11, 16, 40) for performing the following two operations during an unassigned receiving slot: (a) reading from the memory (14) the aforementioned stored data; (b) comparing the data read from the memory (14) with the data transmitted from the transmitter (2) so as to assess proper operation of the apparatus. The radio apparatus according to claim 1, wherein the transmitting slot is unassigned, and the data used for the loopback test are internally generated loopback test data. The radio apparatus according to claim 2, wherein the controller (40) comprises a transmitting signal processing section (11) and a receiving signal processing section (16), the transmitting signal processing section (11) generating the loopback test data and transmitting them to the transmitter (2), the receiving signal processing section (16) comparing the loopback test data read from the memory (14) with the loopback test data generated in the transmitting signal processing section (11), and upon such a comparison, issuing an alarm when a deviation from proper operation has occurred. The radio apparatus according to claim 1, wherein the transmitting slot is occupied for communicating with a mobile station (20), and wherein the data used for the loopback test are communication data used for communicating with the mobile station (20). The radio apparatus according to claim 4, wherein the controller (40) comprises a transmitting signal processing section (11) and a receiving signal processing section (16), the transmitting signal processing section (11) generating the communication data and transmitting them to the transmitter (2), the receiving signal processing section (16) comparing the communication data read from the memory (14) with the communication data generated in the transmitting signal processing section (11), and upon such a comparison, issuing an alarm when a deviation from proper operation has occurred.

Inventors: MURATA TAKASHI, MURATA, TAKASHI, Murata, Takashi, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1995
Main classification: H04B17
IPC codes: H04L1, H04J3, H04B17, H04B7, H04W24