Abstract: An apparatus for automatically exchanging a number of record medium cassettes. The apparatus includes a plurality of cassette exchange units 21-24. Each cassette exchange unit has a cassette storing device 32 in which a plurality of record medium cassettes are installed, one or more recording and reproducing devices 33, a cassette transporting device 34 including a cassette hand over mechanism 35 for transporting desired record medium cassettes between the cassette storing devices and the recording and reproducing devices, and a controller 39. The controllers 39 of the cassette exchange units are controlled by a system controller 40 which is connected to a host computer 70 by means of SCSI cables or interface cables 61-69. The recording and reproducing devices 33 are connected in series with the host computer 70. The cassettes can be transported between the cassette exchange units by means of bridging mechanisms 25-27.

Abstract: A transmission power control method in a mobile satellite communication system implementing accurate control of transmission power of a base station by obtaining an average received signal level at a mobile station at high accuracy. The mobile station measures an average received signal level Q.sub.k in a predetermined period (step SP2), and informs the base station of the average received signal level Q.sub.k and an actual measuring time T.sub.k (step SP3). The base station calculates a total measuring time t.sub.k which is the sum total of the actual measuring time T.sub.k (step SP16), a corrected average received signal level R.sub.k associated with the average received signal level during the total measuring time t.sub.k (step SP18), and a measuring error .DELTA.D.sub.k (step SP17), and controls the transmission power on the basis of these values (step SP21). Estimating the measuring error .DELTA.D.sub.k in the total measuring time t.sub.k longer than the individual actual measuring time T.sub.