Wireless Communication | Set 1
Before talking about wireless medium, we need to talk about the wired medium. Wired network is a bounded medium where data travels over a path that a wire or cable takes. In modern era of advanced and enormous no of devices, wired medium of communication imposes a restriction on fluent communication. There are various problems with wired networks. Consider a situation, you want to connect to 10 or more devices around you.
You need exact same no of ports to be able to connect to devices, but large no of ports seems to be impractical but with wireless network, it can be easily done.
As the name suggests, wireless network eliminates needs to be tethered with wire or cable. Convenience and Mobility becomes its main characteristics. Many different wireless devices can connect to network easily and seamlessly. As wireless data travel through air, there must be some constraints within which wireless communication takes place.
- All wireless devices must follow a common standard i.e., IEEE 802.11
- Wireless coverage must be there where devices are expected to use.
- Wired network comes under IEEE standard 802.3
- wireless network comes under IEEE standard 802.11
IEEE stands for “Institute of Electrical and Electronics Engineers”, is an organization composed of engineers that issues and manages standards for electrical and electronic devices.
Basics of Wireless Communication:
Wireless communication takes places over free space through RF (radio frequency), one device, a Transmitter, sends signal to another device, a Receiver. Two devices (transmitter and receiver) must use same frequency (or channel) to be able to communicate with each other. If a large number of wireless devices communicate at same time, radio frequency can cause interference with each other. Interference increases as no of devices increases.
Wireless devices share airtime just like wired devices connect to shared media and share common bandwidth. For effective use of media, all wireless devices operate in half duplex mode to avoid collision or interference. Before the transmission begins, devices following IEEE 802.11 standard must check whether channel is available and clear.
Wireless communication is always half duplex as transmission uses same frequency or channel. To achieve full duplex mode, devices use different frequency or channel of transmission and receiving of signals. You can say that wireless communication is Full duplex but technically it is not.
In free space, the sender (transmitter) sends an alternating current into a section of wire (an antenna). This sets up a moving electric and magnetic fields that travel as travelling waves. The electric and magnetic field moves along each other at a right angle to each other as shown. The signal must keep changing or alternating by cycle up and down to keep electric and magnetic field cyclic and pushing forward. The no of cycles a wave taking in a second is called Frequency of the wave.
frequency = no of cycles per second
Antennas in our daily lives send out Electromagnetic waves in all directions, like the waves travelling in water when a stone is dropped in a water body.
Frequency Unit Names :
|Hertz||Hz||Cycles per second|
|Megahertz||MHz||1, 000, 000 Hz|
|Gigahertz||GHz||1, 000, 000, 000 Hz|