WiMAX Salient Features - WiMAX

What are the salient features of WiMAX?

WiMAX is a wireless broadband solution which provides a rich set of features with lot of flexibility in terms of deployment options and potential service offerings. Below are few most important salient.

Two Type of Services

WiMAX provides two forms of wireless service

  • Non-line-of-sight – this is similar to WiFi service. Here a small antenna on your computer will connect to the WiMAX tower. In this mode, WiMAX makes use of a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi).
  • Line-of-sight – this is a service where a fixed dish antenna points straight to the WiMAX tower from a rooftop or pole. Line-of-sight connection is tougher and steadier, therefore it can send huge data with less errors. Line-of-sight transmissions make use of higher frequencies with ranges reaching a possible 66 GHz.

OFDM-based Physical Layer

WiMAX physical layer (PHY) depends on orthogonal frequency division multiplexing, a scheme which provides good resistance to multipath and allows WiMAX to operate in NLOS conditions.

Very High Peak Data Rates

WiMAX supports very high peak data rates. In reality, peak PHY data rate will be as high as 74Mbps while operating using a 20MHz wide spectrum.

Usually, by using a 10MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio, peak PHY data rate is about 25Mbps and 6.7Mbps for the downlink and the uplink, respectively.

Scalable Bandwidth and Data Rate Support

WiMAX has a scalable physical-layer architecture which will allow the data rate to scale easily with available channel bandwidth.

For example, a WiMAX system can use 128, 512, or 1,048-bit FFTs (fast Fourier transforms) depending on if the channel bandwidth is 1.25MHz, 5MHz, or 10MHz, respectively. This scaling is done dynamically for supporting user roaming through various networks which have different bandwidth allocations.

Adaptive Modulation and Coding (AMC)

WiMAX provides support to many modulation and forward error correction (FEC) coding schemes and allows the scheme to change based on the user and per frame basis, based on channel conditions.

AMC is an efficient device for maximising throughput in a time-varying channel.

Link-layer Retransmissions

WiMAX provides support to automatic retransmission requests (ARQ) at the link layer for connections which need improved reliability. ARQ-enabled connections need each transmitted packet to be acknowledged by the receiver; unacknowledged packets will be lost and will be retransmitted.

Support for TDD and FDD

IEEE 802.16-2004 and IEEE 802.16e-2005 provides support for both time division duplexing and frequency division duplexing, and also a half-duplex FDD, which allows for a low-cost system implementation.

WiMAX Uses OFDM

Mobile WiMAX makes use of orthogonal frequency division multiple access (OFDM) as a multiple-access technique so that different users are allocated different subsets of the OFDM tones.

Flexible and Dynamic per User Resource Allocation

Both uplink and downlink resource allocation will be controlled by a scheduler in the base station. Capacity will be shared between multiple users by using a burst TDM scheme based on the demand.

Support for Advanced Antenna Techniques

WiMAX solution provides a number of hooks built into the physical-layer design, which will allow the usage of multiple-antenna techniques, such as beamforming, space-time coding, and spatial multiplexing.

Quality-of-service Support

WiMAX MAC layer has a connection-oriented architecture which is designed for supporting a variety of applications, including voice and multimedia services.

WiMAX system provides support for continuous bit rate, variable bit rate, real-time, and non-real-time traffic flows, additionally to the best-effort data traffic.

WiMAX MAC is designed for supporting huge number of users, with multiple connections per terminal, each with its own QoS requirement.

Robust Security

WiMAX supports strong encryption by using Advanced Encryption Standard (AES) and it has a strong privacy and key-management protocol.

System also provides a very flexible authentication architecture based on Extensible Authentication Protocol (EAP), which allows range of user credentials including username/password, digital certificates, and smart cards.

Support for Mobility

Mobile WiMAX variant of the system will have mechanisms for supporting secure seamless handovers for delay-tolerant full-mobility applications, like VoIP.

IP-based Architecture

WiMAX Forum has defined a reference network architecture based on an all-IP platform. All end-to-end services will be delivered over an IP architecture depending on IP-based protocols for end-to-end transport, QoS, session management, security, and mobility.

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