Further information T.S. Rappaport, The wireless revolution, "IEEE Commun. Magazine, Pp 52-71, Nov. 1991 Gilhousan et al., " On the capacity of cellular CDMA systems, " IEEE Trans. Vehicular Technol., vol. 40, no. 2, Pp.303-311,May1991 D J. Goodman, Trends in cellular and cordless communications, IEEE Commun. Magazine, Pp 31-39, June 1991 Raith, K and Uddenfeldt, J,Capacity of digital cellular TDMA systems, IEEE Trans. Vehicular Technol., voL. 40, no.2,PP.323-331,May1991 75.2 Facsimile Rodger e. Ziemer Facsimile combines copying with data transmission to produce an image of a subject copy at another location, either nearby or distant. Although the Latin phrase fac simile means to"make similar, "the compressed phrase facsimile has been taken to mean"exact copy of a transmission"since 1815 [Quinn, 1989]. The image of the bject copy is referred to as a facsimile copy or record copy. Often the abbreviated reference"fax"is used in place of the longer term facsimile. Facsimile was invented by Alexander Bain in 1842; Bain,s system used a synchronized pendulum arrangement to send a facsimile of dot patterns and record them on electrosensitive paper. Over the years, much technological development has taken place to make facsimile a practical and affordable document transmission process. An tant role in the wide acceptance of facsimile for image transmission has been the adoption of tandards by the Consultative Committee on International Telephone and Telegraph(CCITT). The advent of a nationwide dial telephone network in the 1960s provided impetus for the rebirth of facsimile after television up 2 fax machines wh red in the mid-1970s were cap of transmitting a page within a couple of minutes. These machines, based on analog transmission methods, were developed by Graphic Sciences and 3M. The Group 3 fax machines, developed in the mid-1970s by the Japanese, are based on digital transmission technology and are capable of transmitting a page in 20 seconds or less. They can automatically switch to an analog mode to communicate with the older group 1 and 2 fax machines Group 4 fax units offer the highest resolution at the fastest rates but rely on digital telephone lines which are just now becoming widely available[Quinn, 1989]. Group 3 facsimile will be featured in the remainder of this article. Group 3 facsimile refers to apparatus which is capable of transmitting an 8.5 X 11-inch page over telephone-type circuits in one minute or less. Detailed standards for Group 3 equipment may be found in Recommendation t4 of ccitt, Vol vil Facsimile transmission involves the separate processes of scanning, encoding, modulation, tran demodulation, decoding, and recording. Each of these will be ibed in greater detail below. Scanning Before transmission of the facsimile signal, the subject copy must be scanned. This involves the sensing of the diffuse reflectances of light from the elemental areas making up the subject copy. For CCITT Group 3 high resolution facsimile, these elemental areas are rectangles 1/208 inch wide by 1/196 inch high. The signa corresponding to an elemental area is called a pixel which stands for picture element For pixels that can assume only one of two possible states(i. e, white on black or vice versa), the term used is a pel. Various arrangements of illuminating sources, light-sensing transducers, and mechanical scanning methods can be employed. For more than six sweeps per second across the subject copy, electronic scanning utilizing a cathode-ray tube or photosensitive arrays or laser sources with polygon mirrors are utilized. a photosensitive array arrangement for scanning a flood-illuminated subject copy is illustrated in Fig. 75. 2. This is the most often encountered anning mechanism for modern facsimile scanners, and the sensors are typically silicon photosensitive devices Two photosensor arrays in common use are photodiode arrays and charge-coupled device linear image sensors For digital facsimile, the array is composed of 1728 sensors in a row 1.02 inches long with the optics designed so that an 8.5 inch subject copy can be scanned c 2000 by CRC Press LLC© 2000 by CRC Press LLC Further Information T. S. Rappaport, “The wireless revolution,” IEEE Commun. Magazine, pp. 52–71, Nov. 1991. Gilhousan et al., “On the capacity of cellular CDMA systems,” IEEE Trans. Vehicular Technol., vol. 40, no. 2, pp. 303–311, May 1991. D. J. Goodman, “Trends in cellular and cordless communications, IEEE Commun. Magazine, pp. 31–39, June 1991. Raith, K. and Uddenfeldt, J., “Capacity of digital cellular TDMA systems,” IEEE Trans. Vehicular Technol., vol. 40, no. 2, pp. 323–331, May 1991. 75.2 Facsimile Rodger E. Ziemer Facsimile combines copying with data transmission to produce an image of a subject copy at another location, either nearby or distant. Although the Latin phrase fac simile means to “make similar,” the compressed phrase facsimile has been taken to mean “exact copy of a transmission” since 1815 [Quinn, 1989]. The image of the subject copy is referred to as a facsimile copy, or record copy. Often the abbreviated reference “fax” is used in place of the longer term facsimile. Facsimile was invented by Alexander Bain in 1842; Bain’s system used a synchronized pendulum arrangement to send a facsimile of dot patterns and record them on electrosensitive paper. Over the years, much technological development has taken place to make facsimile a practical and affordable document transmission process. An equally important role in the wide acceptance of facsimile for image transmission has been the adoption of standards by the Consultative Committee on International Telephone and Telegraph (CCITT). The advent of a nationwide dial telephone network in the 1960s provided impetus for the rebirth of facsimile after television put the damper on early facsimile use. Group 2 fax machines which appeared in the mid-1970s were capable of transmitting a page within a couple of minutes. These machines, based on analog transmission methods, were developed by Graphic Sciences and 3M. The Group 3 fax machines, developed in the mid-1970s by the Japanese, are based on digital transmission technology and are capable of transmitting a page in 20 seconds or less. They can automatically switch to an analog mode to communicate with the older Group 1 and 2 fax machines. Group 4 fax units offer the highest resolution at the fastest rates but rely on digital telephone lines which are just now becoming widely available [Quinn, 1989]. Group 3 facsimile will be featured in the remainder of this article. Group 3 facsimile refers to apparatus which is capable of transmitting an 8.5 ¥ 11-inch page over telephone-type circuits in one minute or less. Detailed standards for Group 3 equipment may be found in Recommendation T.4 of CCITT, Vol. VII. Facsimile transmission involves the separate processes of scanning, encoding, modulation, transmission, demodulation, decoding, and recording. Each of these will be described in greater detail below. Scanning Before transmission of the facsimile signal, the subject copy must be scanned. This involves the sensing of the diffuse reflectances of light from the elemental areas making up the subject copy. For CCITT Group 3 high￾resolution facsimile, these elemental areas are rectangles 1/208 inch wide by 1/196 inch high. The signal corresponding to an elemental area is called a pixel which stands for picture element. For pixels that can assume only one of two possible states (i.e., white on black or vice versa), the term used is a pel. Various arrangements of illuminating sources, light-sensing transducers, and mechanical scanning methods can be employed. For more than six sweeps per second across the subject copy, electronic scanning utilizing a cathode-ray tube or photosensitive arrays or laser sources with polygon mirrors are utilized. A photosensitive array arrangement for scanning a flood-illuminated subject copy is illustrated in Fig. 75.2. This is the most often encountered scanning mechanism for modern facsimile scanners, and the sensors are typically silicon photosensitive devices. Two photosensor arrays in common use are photodiode arrays and charge-coupled device linear image sensors. For digital facsimile, the array is composed of 1728 sensors in a row 1.02 inches long with the optics designed so that an 8.5 inch subject copy can be scanned