Wireless communication is the transfer of information or power between two or more points that are not connected by an electrical conductor. The most common wireless technologies use radio waves. With radio waves distances can be short, such as a few meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking.
The above properties led to a great many simplifications in the design of broadcast radio networks.The transmitter does not need to have any knowledge or consideration about the receivers. There is no requirement to provide for duplex channels (i.e., for bringing information from the receiver to the transmitter). The number of possible users of the service does not influence the transmitter structure either – irrespective of whether there are millions of users, or just a single one, the transmitter sends out the same information.
The above description has been mainly true for traditional broadcast TV and radio. Satellite TV and radio differ in the fact that often the transmissions are intended only for a subset of all possible users (pay-TV or pay-per-view customers), and therefore, encryption of the content is required in order to prevent unauthorized viewing. Note, however, that this “privacy” problem is different from regular cellphones: for pay-TV, the content should be accessible to all members of the authorized user group, (“multicast”) while for cellphones, each call should be accessible only for the single person it is intended for (“unicast”) and not to all customers of a network provider.
Do you know what is the first wireless service?
The first wireless service was broadcast radio. In this application, information is transmitted to different, possibly mobile, users. Four properties differentiate broadcast radio from, e.g., cellular telephony:- The information is only sent in one direction. It is only the broadcast station that sends information to the radio or TV receivers; the listeners (or viewers) do not transmit any information back to the broadcast station.
- The transmitted information is the same for all users.
- The information is transmitted continuously.
- In many cases, multiple transmitters send the same information. This is especially true in Europe,where national broadcast networks cover a whole country and broadcast the same program in every part of that country.
The above properties led to a great many simplifications in the design of broadcast radio networks.The transmitter does not need to have any knowledge or consideration about the receivers. There is no requirement to provide for duplex channels (i.e., for bringing information from the receiver to the transmitter). The number of possible users of the service does not influence the transmitter structure either – irrespective of whether there are millions of users, or just a single one, the transmitter sends out the same information.
The above description has been mainly true for traditional broadcast TV and radio. Satellite TV and radio differ in the fact that often the transmissions are intended only for a subset of all possible users (pay-TV or pay-per-view customers), and therefore, encryption of the content is required in order to prevent unauthorized viewing. Note, however, that this “privacy” problem is different from regular cellphones: for pay-TV, the content should be accessible to all members of the authorized user group, (“multicast”) while for cellphones, each call should be accessible only for the single person it is intended for (“unicast”) and not to all customers of a network provider.
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