Definition of Echo and Singing

As the name implies, echo in telephone systems is the return of a talker's voice. It is most apparent to the talker himself or herself. Secondarily, it can also be an annoyance to the listener. To be an impairment, the returned voice must suffer some noticeable delay. Thus we can say that echo is a reflection of the voice. The cause of echo is impedance mismatches that might be present any place in the electrical telephone connection. Echo is a major annoyance to the telephone user....

Advantages and Disadvantages of a Low Earth Orbit

The low earth orbit (LEO) offers a number of advantages over the geostationary orbit, and at least one serious disadvantage. Delay. One-way delay to a GEO satellite is budgeted at 125 ms one-way up and down is double this value of 250 ms. Round-trip delay is about 0.5 s. Delay to a typical LEO is 2.67 ms and round-trip delay is 4 x 2.67 ms or about 10.66 ms. Calls to from mobile users of such systems may be relayed still again by conventional satellite services. Data services do not have to be...