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Error Correction Techniques, Provide Better Overall Performance
Error correction techniques have been incorporated into WiMAX to reduce the system signal-to-noise ratio requirements. Forward error
correction, convolutional encoding and interleaving algorithms are used to detect and correct errors to improve throughput. These robust error correction techniques help to recover erroneous frames that may have been lost due to frequency selective fading or burst errors. Automatic repeat request (ARQ) is used to correct errors that cannot be corrected by the FEC, by having the erroneous information resent. This significantly improves the bit error rate (BER) performance for a similar threshold level.
Power Control, Provides Better Power Efficiency and Coexistence
Power control algorithms are used to improve the overall performance of the system; it is implemented by the base station sending power control information to each of the CPEs to regulate the transmit power level so that the level received at the base station is at a predetermined level. In a dynamical changing fading environment, this predetermined performance level means that the CPE only transmits enough power to meet this requirement. The converse would be for the CPE transmit level to be based on worst-case conditions. The power control reduces the overall power consumption of the CPE and the potential interference with other colocated base stations. For LOS the transmit power of the CPE is approximately proportional to its distance from the base station; for NLOS it is also heavily dependent on the clearance and obstructions.
Data Security, Provides Secure Communication
WiMAX proposes a full range of security features to ensure secured data exchange: terminal authentication by exchanging certificates to prevent rogue devices, user authentication using the EAP, data encryption using the data encryption standard (DES) or advanced encryption standard (AES), both much more robust than the WEP initially used by WLAN. Furthermore, each service is encrypted with its own security association and private keys.
Since its early days, IEEE 802.16 standards have seen many changes. Even today they continue to innovate and evolve with time and technology advancements. Security concern for wide-range connectivity
is always there. The security features of the standard are being worked on so that, when its time for the product release to market, the technology will be more secure.
Backing from Giants Industry, Provides Better Value for Money
Intel is actively participating in WiMAX industry efforts to help reduce investment risks for operators and service providers while enabling them to more cost effectively take advantage of the tremendous market potential of wireless broadband access. The 802.16 wireless standard will provide a flexible, cost-effective means of filling existing gaps in broadband coverage, and creating new forms of broadband services, not thought of in a wired world. With Intel, Fujitsu and Nokia backing this wireless technology and standards, 802.16 and its variants will find many takers in the product arena.
3.4 THE ‘OOP(S)’
Some of the challenges faced by WiMAX are as follows.
An interfering RF source disrupts a transmission and decreases performance by making it difficult for a receiving station to interpret a signal. Forms of RF interference frequently encountered are multipath interference and attenuation. Multipath interference is caused by signals reflected from objects, resulting in reception distortion. Attenuation occurs when an RF signal passes through a solid object, such as a tree, reducing the strength of the signal and subsequently its range. Overlapping interference from an adjacent base station can generate random noise.
Licence-exempt solutions have to contend with more interference than licensed solutions, including intranetwork interference caused by the service provider’s own equipment operating in close proximity and external network interference. Licensed solutions must only contend with internetwork interference. For licence-exempt solutions, RF interference is a more serious issue in networks with centralized control than
in a shared network because the base station coordinates all traffic and bandwidth allocation.
Addressing issues with interference
Interference is the disruption or degradation of a transmitted signal by extraneous RF energy. Interference impedes the ability of an RF receiver to distinguish between the transmitted signal and the background RF energy that exists at that specific point in time. Causes of extraneous RF energy include noise, and direct spectrum overlap by identified and unidentified sources.
Extraneous RF energy can be addressed by subchannelization and adaptive modulation, proper network design, filtering, shielding, synchronization of signals and the use of power amplifiers and antenna technologies.