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Electromagnetic Radiation or Wave travels through vacuum and matter. The properties of electromagnetic waves such as amplitude, frequency, and wavelength are explained below.
Wavelength is the length of a cycle in a wave. Frequency is the number of cycles per second and it is measured in Hertz. Amplitude is the height of the wave from its axis.
The entire range of frequencies of electromagnetic radiations is called Electromagnetic Spectrum. The spectrum is divided into segments called bands such as ELF, VLF, LF, MF, HF, VHF, UHF, SHF, and EHF and so on. Based on the properties of the band, they are used for different purposes. UHF (Ultra High Frequency) is used for TV and cell phones. SHF (Super High Frequency) is used for Fixed Wireless and Satellites communication. EHF (Extra High Frequency) is used for Satellites and Radar communication. These bands fall under the Radio wave and Micro wave part of the spectrum. The electro magnetic spectrum extends beyond these frequency ranges. WiMAX generally uses SHF and EHF bands.
[Reference - WiMAX: A Wireless Technology Revolution by G. S. V. Radha Krishna Rao and G. Radhamani ]
The disadvantage of high frequency waves is that they have shorter wavelength and greater attenuation. So high frequency waves have shorter range. Waves with higher frequency can be blocked by many things and that is the reason why they can't pass through walls. The advantage of having shorter range is that the frequencies can be reused in areas which are far enough to cause less interference.
The transmitted signal should reach the destination in an understandable format. This is achieved by a process called modulation in which the information signal is superimposed on the carrier wave. The superimposition is done in terms of Amplitude, Phase or Frequency. The transmitter modulates and transmits the signal. The receiver receives the signal and recreates it. The signal will suffer form distortion, noise and interference during its travel through the transmission medium. The receiver may not be able to recreate the original signal. The amount of distortion of the received signal is depended on the type of modulation technique used. Some of the modulation techniques are Frequency Modulation, Phase Modulation, and Amplitude Modulation and so on. Multiplexing is a process that also uses modulation. In multiplexing, several signals are combined and transmitted simultaneously over the same medium. Commonly used multiplexing techniques are Frequency Division Multiplexing, Code Division Multiplexing and Time Division Multiplexing. WiMAX primarily uses Orthogonal Frequency Division Multiplexing.
WiMAX stands for Worldwide Interoperability for Microwave Access. WIMAX provides wireless data communication over a wider metropolitan area. It is a fixed wireless technology with range up to 30 miles from one Base Station and data transmission rate up to 70 Mbps.
Like an ISP, the Wireless Internet Service provider (WISP) gives the WiMAX Internet service. The WISP is connected to the tower. The tower provides internet connection and not cell phone service. The tower provides the connection to consumers via Line Of Sight mode and Non Line Of Sight mode. The connection via Line Of Sight mode is faster than the other. The figure below describes what Line of Sight is.
[Reference - Wireless Communication and Network by William Stallings]
The Institute of Electrical and Electronics Engineers (IEEE) gave the standards for WiMAX. The standards are given in the specification 802.16 and its variations such as 802.16a, 802.16b, 802.16c, 802.16e etc.
The 802.16 radio interface specification is the original standard. 802.16 covers the physical layer, MAC and the Quality of Service that can be provided. Later other variations were developed because of growing needs of different industries. 802.16-2004 revised and replaced 802.16 and 802.16a . 802.16e defined mobile operation for 802.16 systems. 802.16e worked in the 2 to 6 GHz range. It defined mobility management, call transfer ability, and sleep modes for power saving and so on. 802.16f defined the network management for 802.16 systems. 802.16g defined management process for 802.16 systems.
The frequency range of 802.16 standards is between 10 and 66GHz. The frequency range of 802.16A standard is between 2 and 11GHz. The vendors can use licensed or unlicensed spectrum of the frequency range. The advantage of using licensed spectrum is less interference but the disadvantage is managing the licensing process. Unlicensed spectrum poses the risk of interference from other transmitters.
The figure below shows the evolution of the standards.
[Reference - - WIMAX Explained by Kalai Kalaichelvan and Lawrence Harte ]
'WiMAX Forum' was created to implement the standards. It is a non profit organization that ensures that the developed WiMAX products are compliant with IEEE 802.16 standards and are interoperable. It enforces member companies to comply with the standards. The WiMAX Forum is divided into several working groups with each group working towards a specific goal.
Some of the technologies used are Modulation, Multiplexing, Orthogonal Frequency Division Multiplexing, Frequency reuse, Adaptive Modulation and so on.
The transmitted signal should reach the destination in an understandable format. This is achieved by a process called modulation in which the information signal is superimposed on the carrier wave. The superimposition is done in terms of Amplitude, Phase or Frequency. The transmitter modulates and transmits the signal. The receiver receives the signal and recreates it. The signal will suffer form distortion, noise and interference during its travel through the transmission medium. The receiver may not be able to recreate the original signal. The amount of distortion of the received signal is depended on the type of modulation technique used. Standard 802.16 supports BPSK, QPSK, 16 QAM and 64 QAM.
Adaptive modulation is a process in which the modulation technique used is changed automatically based on criteria.
Multiple signals can be sent over a single link to a demultiplexer simultaneously. The most commonly used multiplexing techniques are Frequency Division Multiplexing, Time Division Multiplexing and Code Division Multiplexing.
Orthogonal Frequency Division Multiplexing:
OFDM is modulation and multiplexing technique. A single data stream is divided, modulated and transmitted over multiple sub-carriers (frequencies) of lower rate. In traditional FDM, the sub -carriers are spaced apart so that their bandwidths don't interfere and there is a guard band. This causes the available bandwidth to be utilized soon. OFDM sub-carriers will overlap each other. To prevent interference the sub-carriers (frequencies) will be orthogonal to each other. Spectral efficiency can be achieved in this manner. The figure below explains the difference between FDM and OFDM.
[Reference - http://www.create.ucsb.edu/ATON/01.01/OFDM.pdf ]
Any of the conventional modulation techniques will be used for modulating the signal.
OFDM reduces delay spread and multi-path problems in wireless communication. Multipath is the process by which wireless signals travel through multiple paths before reaching destination. This may cause constructive or destructive interference. Delay path is the distortion caused by the signals arriving from multiple paths. Identical signals may arrive with a delay and cause distortion.
If the geographic area is sufficiently apart, there will be less interference if the same frequency is used.
WiMAX systems have Subscriber Stations (SS), Base Stations (BS), Packet Switches, Gateways, and Antennas etc.
A Subscriber Station is a transceiver. A transceiver is made up of transmitter and receiver. As the name suggests, it transmits and receives radio and digital signals. A Subscriber Station uses Frequency Division Duplex, Time Division Duplex or a combination of both. There are indoor and outdoor SS.
A Base Station is another transceiver which connects wireless systems and network backbones. A Base Station should support several SS. There are indoor and outdoor BS.
A packet switch is a device which transmits information as bytes of data. Packet Switches have internal table. When they receive packets, they read the destination addresses in the packets, look up the addresses in their table and forwards the packets to next destination.
Gateway is a connection between networks. It transmits data between network in a format that each understands.
Antenna transmits, receives and converts signals between electrical and electromagnetic form.
Quality of Service:
Other Technologies: Wi-Fi:
The word Wi-Fi stands for Wireless Fidelity. Wi-Fi provides wireless communication over isolated smaller areas like how a LAN does. It works like any other LAN network but without wires. Computers, printers, laptops etc can connect and communicate using Wi-Fi. The major difference between Wi-Fi and WiMAX is that Wi-Fi works for smaller areas. Another difference is that the Wi-Fi has lower signal range compared to WiMAX. IEEE developed standards 802.11b, 802.11a, 802.11a/g, 802.11n etc for Wi-Fi.
Spectral range of Wi-Fi is between 2.4 GHz and 5.8 GHz. Wi-Fi uses unlicensed spectrum so there is disadvantage of interference. Data transmission rate of Wi-Fi is between 1 Mbps to 54 Mbps based on different standards.
As per Wi-Fi standards, computers are called stations. 802.11 standards and its revisions talk about two modes: Infrastructure mode and Ad hoc mode. In infrastructure mode, a Wi-Fi Access Point (AP) is connected to a wired network and also to a wireless end stations. Such a connected network is called Basic Service Set (BSS). Several connected BSSs make an Extended Service Set (ESS). Several ESSs can be connected using Data System (DS). A DS is a medium to transfer packets between different ESSs. In Ad Hoc mode, different stations connect to others directly. An Ad Hoc system can be set up fast but it has several limitations.
Advantages of WiMAX:
Standardized technology - WiMAX Forum ensures that the member companies comply with IEEE 802.16 standards and its revisions. It certifies the compliance and interoperability of the WiMAX products. Standardized technology means easier and faster deployment. This also decreases the cost of the equipments
WiMAX has signal range of about 30 miles. Other technologies such as Wi-Fi have signal range in meters.
WiMAX has data transmission rate of 70 Mbps.
WiMAX vendors can use licensed or unlicensed spectrum. Using licensed spectrum will decrease interference from other wireless operators. Wi-Fi vendors use unlicensed spectrum.