. Properly designed LEO systems will not have such drawbacks. Coverage will be available at any orientation. Tracking, a Disadvantage of LEO and MEO9 Satellites At L-band quasiomnidirectional antennas for the mobile user are fairly easy to design and produce. Although such antennas display only modest gain of several decibels, links to a LEO satellite can be easily closed with hand-held terminals. However, large feeder, fixed-earth terminals will require a good tracking capability as LEO satellites pass overhead. Handoff is also required as a LEO satellite disappears over the horizon and another satellite just appears over the opposite horizon. The handoff should be seamless. The quasi-omnidirectional user terminal antennas will not require tracking, and the handoff should not be noticeable to the mobile user. 9 MEO stands for medium earth orbit. REVIEW EXERCISES REVIEW EXERCISES 1. What is the principal drawback in cellular radio considering its explosive growth over the past decade? 2. Why is transmission loss SO much greater on a cellular path compared to a LOS microwave path on the same frequency covering the same distance? What is the function of the MTSO or MSC in a cellular network? What is the channel spacing in kHz of the AMPS system? What type of modulation does it employ? 5. Why are cell site antennas limited to just sufficient height to cover cell boundaries? Why do we do cell splitting? What is the approximate minimum practical cell diameter (this limits splitting). 7. When is handover necessary? Cellular transmission loss varies with what four factors besides distance and frequency? What are some of the fade ranges (decibels) we might expect on a cellular link? If the delay spread on a cellular link is about 10 usec, up to about what bit rate will there be little deleterious effects due to multipath fading? 11. Space diversity reception is common at cells sites. Antenna separation varies with? For effective space diversity operation, there is a law of diminishing returns when we lower the correlatio