CHAPTER 12

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1. Digital TV transmission has many advantages: improved signal quality, bandwidth efficiency through use of compression techniques, and effective control and management. Two standards HDTV (High Definition TV) and SDTV (Standard Definition TV) have been developed for digital video broadcasting. In HDTV, the aspect ratio is 16:9. Twenty-four or 30 frames are sent per second. Each frame is divided into 1080 × 1920 pixels or 720 × 1280 pixels. In SDTV, the aspect ratio is 4:3, with 24 or 30 frames per second, and each frame with 480 × 640 pixels.

2. To provide wireless local loops, small base stations are installed at various locations. The subscriber terminal (telephone instrument) communicates with the base station using CDMA access mechanism. You can get the details of wireless local loop using CDMA from the Web site http://www.qualcomm.com.

3. Though most of the trunked radio systems are analog, the latest standard developed by European Standards Telecommunications Institute (ETSI) is based on digital technology—it is called TETRA (Terrestrial Trunked Radio). You can get the details from http://www.etsi.org. Motorola is a leading supplier of trunked radio systems. You can get product details from http://www.motorola.com.

4. Path loss calculation involves finding out the loss/gain of different network elements. The network elements are filters, amplifiers, antennas, and the cable connecting the RF equipment with the antenna. A major contributor to path loss is the propagation loss in the medium.

5. Underwater communication systems are used in sports, search and rescue operations, and military applications. As the attenuation of the electrical signal is very high in water, high-power transmitters are required. VLF band is used in underwater communication. For instance, the phones used by divers operate in the frequency band 30 to 35 kHz. If the transmit power is 1/2 watt, the range is about 400 yards, and if the transmit power is 30 watts, the range is about 5 miles. You can get the details of some commercial underwater communication systems from the site http://www.oceantechnologysystems.com.

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