tal Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The Base Station Key Radio Concepts Signal Voltage Figure 4.2 Phased array or smart antenna. A phased array can transmit narrow beams in any direction with the correct choice of phase shifting. From the reciprocity of transmitting and receiving, we can deduce that the same phase shifts can be used in the receiver to select a narrow angle. When that narrow angle is dynamically adjusted by continuously optimizing the received sig- nal, we call the configuration an adaptive phased array. Adaptive phased arrays are particularly useful for receiving a signal from a source that is moving. 4.2 The Tower and Cable The big question for any base-station deployment is how high to build the tower. High towers have wider coverage, but they are more expensive, and they receive the most re- sistance from neighbors. It is far easier to get zoning approval to put up low towers or to colocate antennas on existing towers. Any kind of radio tower can be used for colo- cation. There are also a variety of techniques for making towers less obtrusive, includ- ing locating them on the tops of buildings and disguising them as trees or parking lot Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The Base Station The Base Station lighting poles. Antennas are placed on platforms at any height from the base to the top of the tower SO that if an antenna needs to be lowered later, the tower is not cut shorter. The initial cell layout of a new system is usually a grid of large coverage cells. We call them coverage cells because their mission is to create a seamless region of wireless tele- phone service. These towers need to be high to reach as far as possible. Coverage cells