Wireless communication

Wireless communication
1. Infra Red Transmission
2. Radio Transmission
a. Narrow Band
b. Spread Spectrum

1.Infra Red Transmission
This type of transmission is cheapest and easy to use for short distance, that is why it comes built-in in laptops and mobile phones, its has number of disadvantages, e.g low bandwidth, cannot be used for long distance communication, as it reflect back when strike with any obstacle like wall, furniture etc. [1]

2. Radio Transmission
This is a commonly used technology used in wireless LANs, it can be either directional or can operate at 360 degree, but depends on type of antenna being used, unlike Infra red it can pass through building and hence used for long distance transmission. Using RF Transmission the same device can communicate with more than one device at a time, by using different frequencies. The RF Transmission uses Electro magnetic waves, and used as a carrier i.e. either digital or analog data can be super imposed on it, it has three characteristics i.e. frequency, amplitude, and phase, any one of these characteristics can be used to encode/super-imposed analog or digital data for transmission.

The RF transmission is used widely in mobile, TV, Radio station etc. That is why Government tightly enforce license, because two or more stations can operate at same frequencies.

1. Narrow Band: uses minimum Radio Frequency band for transmitting data, for the purpose of avoiding cross talk with other stations.
2. Spread Spectrum: uses more bandwidth for transmission, it is commonly used by military, because Spread spectrum signal are easy to detect as uses high bandwidth.

Microwave is an extension of RF, it gives higher data rates, but it is considered as line-of sight medium and suffered for atmospheric conditions e.g. fog, rain etc.[2]

IEEE 802.11
Wireless LANs are based on IEEE 802.11; there are many versions of IEEE 802.11 i.e. IEEE 802.11(legacy), IEEE 802.11a, IEEE 802.11b, and 802.11g. These standards permit 1-2 Mbits/second and 5 to 10 Mbits/second.

It is standardized for both Infra Red and RF transmission. It uses CSMA/CD MAC protocol, which ensures that collision will not takes place; Wireless LANs, operates at less speed as compared to wired LANs, wireless LANs are more susceptible to interference, as air is the medium. [2]

Reference:
[1] http://en.wikipedia.org/wiki/IEEE_802.11
[2] http://www.smarthomeforum.com/start/wlan.asp?ID=24