Bandwidth Constraints

Increased use of higher frequencies and digital "messaging" techniques that permit greater throughput on the same bandwidth mean that there's no reason for wireless transmissions to be slower than wired ones, but current cost and policy issues combined with the fragility of the signal at higher frequencies mean that for all practical purposes they are slower. Although you can get equivalent bandwidths from wired and wireless networks, it costs you far more to get the wireless speed because of the following:

- The more sensitive equipment required to receive higher frequency

transmissions

- In some cases, the cost of purchasing rights to a particular frequency

- The cost of installing sufficient transmitters to get the signal to its destination (because the unprotected signals of wireless transmissions suffer more from attenuation than do the protected signals of wired networks)

Anyone who's ever accidentally overheard a neighbor's conversation on their cordless telephone is aware that data traveling through the ether is pretty open to tapping. Anyone who is equipped with the proper equipment can intercept the signal. However, this is not a problem unique to wireless networks it's just easier to intercept a wireless signal accidentally.

Before you decide that wireless communications (especially data) are more vulnerable to tapping than wired ones, consider the following points:

- To tap any transmission, you need to have the receiving device in the area where the signal is this means that cables, which show the signal's path precisely, are in some ways easier to tap.

- No cable, even fiber-optic cable, is completely safe from illicit access.

- Digital encoding can scramble the information transmitted from the sender to the receiver, making any tapped information useless without the decoder.

Although older RF transmissions used a transmission method called direct sequencing, which was vulnerable to tapping because it sent the data all on the same frequency, newer transmission methods call for frequency hopping, in which the transmission uses more than one frequency during a transmittal, making the signal more difficult to intercept. Combined with encoding, frequency-hopped transmissions are relatively secure.

The narrow beam of some wireless transmissions (such as infrared signals) makes them almost impossible to tap unless you are at one end of the transmission and can determine the exact path.

Text 8

I. Memorize the following word combinations:

1. the number of oscillations per time unit - число колебаний за единицу

времени

2. bandwidth - полоса пропускания

3. High Frequency = (HF) - высокая частота

4. Very High Frequency = (VHF) - очень высокая частота, ОВЧ

5. Ultra High Frequency = (UHF) - ультра высокая частота

6. saturated - насыщенный

II. Look through the text and answer the questions below in writing:

1. What have you learn about wireless signal from the text?

2. What is the number of cycles per second measured in?

3. What are important RF wireless bands?

4. Why do IR transmissions have greater carrying capacity than RF

transmissions?

III. Translate the 4^th paragraph in writing.

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