1. In case of an accident， there is a high chance of getting lost. The transportation cost is very high each time. However， if the infrastructure is set once， it will be very easy to use it repeatedly. Time for wireless transmission is negligible as signals travel at the speed of light. 2. Advantages of bursty data communication （a） Pulses are made very narrow， so multipaths are resolvable （b） The transmission device needs to be switched on for less time. Disadvantages （a） Bandwidth required is very high （b） Peak transmit power can be very high. 3. Pb = 10?12 1 2γ = 10?12 γ = 1012 2 = 5 × 1011 （very high） 4. Geo： 35，786 Km above earth ? RT T = 2×35786×103 c = 0.2386s Meo： 8，000- 20，000 Km above earth ? RT T = 2×8000×103 c = 0.0533s Leo： 500- 2，000 Km above earth ? RT T = 2×500×103 c = 0.0033s Only Leo satellites as delay = 3.3ms 《 30ms