Answers to the Introduction Review Questions

1. Frequency reuse is the ultimate in "Spectrum Conservation." Pre-cellular systems (e.g., IMTS) operated on the philosophy of "Maximum power, Maximum coverage." By that approach, a single 80-watt mobile could transmit to a base station 50 miles away, and as long as that mobile was transmitting, no other mobile within that 50 mile radius could use that same RF channel. With only ~15 to 25 RF channels available in a city, only ~15 to 25 calls could be serviced at any given moment. Such an approach may be viable in Casper, Wyoming or Fargo, North Dakota, but it is clearly not viable in Manhattan or Washington DC. As a result, when cellular systems were developed and deployed, they reduced mobile power to 0.5 to 3 watts, and shrunk the serving area of each base station to a ~1 to 3 mile radius, allowing the same RF channels to be re-used in several locations around the city. As more base stations were deployed, each of their coverage areas were further constricted, allowing the same RF channels to be re-used many more times. As CDMA enters the scene, we will find this same re-use approach being applied there as well, not only to physical RF channels, but to other traffic handling resources (e.g., channel codes such as Short Codes and Walsh Codes, etc.).

2. When Rogoff shot his modulated light beam through his noise wheel, his low frequency voice signal was "chopped" by...