g that spectrum into four sectors of 3.5 MHz. With a dedicated antenna, each sector can provide users with more throughput over longer ranges as compared to an omni-directional antenna.
3.4 SMART ANTENNA SUPPORT
Smart antennas enhance the spectral density (the number of bits communicated over a given channel in a given time) and also boost the signal-to-noise ratio for both Wi-Fi and WiMAX solutions. Because of performance and technology, several adaptive smart antenna types supported by the 802.16-2004 standard include[21]:
Receive spatial diversity antennas
Involves more than one antenna receiving the signal. To function efficiently, the antennas have to be placed no less than half a wavelength apart. Note that wavelength can be found by taking the inverse of the frequency. Maintaining this smallest distance makes sure that the antennas are incoherent, that is, additive/subtractive effects of signals arriving by means of multiple paths impact on them differently.
Simple diversity antennas
The signal strength of the multiple (two or more) antennas attached is detected and that antenna is switched into the receiver. The possibility of getting a strong signal will be higher if selection is from more incoherent antennas.
Beam-steering antennas
The antenna array pattern is shaped to produce high gains in the useful signal direction or notches that reject interference. High antenna gain enhances the signal, noise and rate. The interference is attenuated out of the main beam with directional patterns. If multi-path components arrive with a enough angular separation, selective fading can be alleviated.
Beam-forming antennas
Permit the area to be divided around a base station into sectors, allowing additional frequency reuse between sectors. The number of sectors can be as few as four to as many as 24. Base stations which cleverly manage sectors have been used for a long time in mobile-service base stations.
3.5 BNEFITS and CHALLENGES
The WiMAX basis benefits are:
Built-in QoS
High performance
Standards-based
Smart antenna support [25]
For WiMAX the most important challenge is that it's a fresh technology with emerging support.
3.6 FEATURES
The WiMAX is designed with various aims in mind. Below is the summary of potential features of WiMAX:
Flexible Architecture
Numerous system architectures are supported by WiMAX, consisting P2P, P2MP, and omnipresent coverage. The time slot for every SS are scheduled through WiMAX MAC to support Point-to-Multipoint and ubiquitous service. When there is only one SS in the network, the WiMAX BS uses Point-to-Point service to communicate with the SS. In P2P configuration to cover longer distances a BS might use a narrower beam antenna.
High Security
WiMAX encrypts the links among the base station and the subscriber station to provide privacy (reluctant to eavesdropping) and safety across the broadband wireless link to the users. With security operators can be protected reluctant to stealing of service.
WiMAX QOS
WiMAX is dynamically optimized for carrying mix of traffic. WiMaX supports four service types: UGS,rtPS,nrtPS, BE Services.
Quick Deployment
WiMAX needs little or no external plant construction as compared with the deployme
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