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G3 FACSIMILE COMMUNICATIONS

Fig. 5-48 Target of QAM Method and Spatial Pattern

5.4

High-speed MODEMs above 14400 bps

Since 9600 bps MODEMs recommended as V.29 in 1976 were adopted in

facsimiles, MODEM technology has advanced all the more to the point

that facsimiles capable of transmitting and receiving at transmission

speeds exceeding 9600 bps are in the process of becoming mainstream.

The standards for these MODEMs have already been recommended by

, and have gradually come to be installed even in low-price range

products.

Of these MODEMs, let’s describe an outline of the 14400 bps MODEM

recommended in V.17 (V.33) and the 33600 bps MODEM recommended

in V.34.

5.5

V.17 (V.33) MODEM Technology

V.17 (V.33) MODEMs recommended by ITU-T are capable of transmitting

data at a high speed of 14400 bps. Until this recommendation was reached,

several 14400 bps MODEMs using existing technology were put onto the

market. PARADYNE Inc. first put a MODEM onto the market in 1980 and

was followed by CODEX Inc. the following year in 1981, who announced

a 14400 bps MODEM using multi-value QAM technology that had a 64-

point signal constellation. These products improved transmission speeds

by using spatial diagram patterns that were resistant to factors for impaired

quality such as noise during communications. Then, in 1984, MODEMs

using a modulation system called the “error correction coding QAM

mehod” started to be developed, and a series of high-function MODEMs

Boundary