CECS 5400
The Difference between Analog and Digital Telephones
Fall 1999
Introduction:
The boom in technology in many fields has taken a fast track in the latest years and telecommunications is on the frontier of such rapid change. Telephones are the devices we use everyday to communicate information and the latest improvement on such devices is the entry of mobile digital technology in an attempt to solve the shortcomings of the regular analogue telephones. Home mobile telephones are of 3 main types:
Figure 1
As we speak in the telephone the variation in sound level is converted to electrical analog signal and the amplitude reflects the volume and the frequency reflects the pitch. In the digital mobile telephone the sound which is an analog signal is converted to a digital signal using a coder/decoder device which in turn translates it to zero’s and one’s.
Figure 2
The sequences formed by the 0 and 1 combination forms the NRZ coding see Fig. (3).
Figure 3
Analogue Telephones:
These come in different frequencies such as 43-49 MHz. Today this has been subsided by the 900 MHz analogue phones, which provide better clarity and range.
Advantages:
Digital Telephones:
The direction of the telephone market is heading in the digital direction. In 1998 Americans took home 31 million cordless phones most of which are digital. The digital telephones currently presents in the 900MHz or the 2.4 Gig Hz. The popularity of these systems has been increasing lately due to the advantages over the analogue telephones.
Advantages:
The way the digital telephones work is that the radio wave is digitized in the handset before its transmitted to the base and the base reassembles the signals. Basically the signal is scrambled and scanners or other devices can not pick up the signal.
Most of the cordless phone activity is taking place at the 900-MHz level, but Panasonic has expanded the market into the 2.4-GHz band of the radio frequency spectrum. The company claims better operating range than what's possible with 900-MHz digital spread-spectrum phones. The Panasonic KX-TG-2550 Giga Range ($199.95), for example, boasts a range that's 20 times greater than that of conventional cordless, eight times farther than for 900-MHz and twice that of digital spread-spectrum.
Of course,
the operation of any cordless phone is affected by real-world conditions.
The company warns that influences such as building construction and electrical
interference can affect range performance indoors.
Panasonic uses both the 2.4-GHz band and the 900-MHz band in its Giga Range phones, unlike typical cordless phones that transmit and receive signals over the same band. When both talk and listen signals are operating on one band, they can interfere with each other. Using a 2.4-GHz signal for transmission from the base to the handset and a 900-MHz signal for conversation back to the base eliminates the potential for interference. The result, the company says, is improved distance performance, true duplex, or two-way, conversation and no echo.
Future directives:
Although communication technology has changed rapidly
and it is difficult to speculate on which direction it’s going to take.
Its expected that in future the improvement will be on the digital technology
and the coding of such signals and analog technology will diminish or will
be very limited.
References:
1.Shay William A. Understanding Data Communication & Networks. 1998 2nd Ed. PWR publishing. California.
2. Rebecca Day. Long on the Rang. Popular Mechanics Sept.1999.
3. Rebecca Day. Phones of the Future that Do it All.
http://38.202.43.5/popmech/elect/9805EFTCP.html
4. http://www.millennianet.com/celfones/newswire.html
5. http://www.biznetonline.com/12-97/hello12-97.htm
6. http://38.202.43.5/popmech/elect/9909EFTCP.html
Other references:
http://www.in-asiatoday.com/hk/udc/wire/wirehome.htm
http://millennianet.com/celfones/
http://www.analog.com/publications/press/misc/adamf.html