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Internet Access Guide : WiMAX

WiMAX performance (throughput and range) is determined by many factors, i.e. on which frequency band it operates, channel bandwidth, duplexing scheme (TDD or FDD), modulation (whether BPSK, QPSK, 16-QAM, or 64-QAM) and code rate, antenna types, whether LOS or NLOS, transmit power, receiver sensitivity, and the number of users per base station sector. It certainly varies from one case to another.

Looking from some pre-WiMAX implementations, fixed broadband wireless access subscribers at average get 512 kbps - 2 Mbps download data rate and 128 kbps - 1 Mbps upload rate in a NLOS environment and PMP configuration. Fixed WiMAX operators will likely multiply those rates up to several Mbps to compete with DSL/cable. They can adjust the number of subscribers that will be served by a Base Station sector based on the Service Level Agreement (SLA) of each  subscriber (or user) and the maximum capacity per sector. For PTP backhaul in a LOS environment, WiMAX capacity per base station sector can reach 70 Mbps in a 20 MHz channel with range over 30 miles. As for Mobile WiMAX, if WiBro - which is deployed this year in Korea - is taken as a baseline, the effective download and upload rate per user will be over 1 Mbps outpacing 3G and enhanced 3G (a.k.a. 3.5G) technologies such as EV-DO and HSDPA.

Adaptive Modulation and Coding (AMC) in WiMAX
Picture: Adaptive Modulation and Coding (AMC)
Users with better SNR (closer to the BS) get higher order modulation,
those farther from the BS get lower order modulation,
ensuring the best performance for each user within the BS coverage.

WiMAX offers a number of techniques that can improve its performance, i.e. throughput, capacity, coverage or range, indoor penetration. Some of these techniques are adaptive modulation and coding (AMC), uplink subchannelization (using OFDMA), hybrid automatic repeat request (H-ARQ), Forward Error Correction (FEC), and smart antenna technologies (via optional AAS and MIMO features). They can improve performance by improving spectral efficiency or signal strength (SNR).

Several Fixed WiMAX products (base stations and CPEs) have become WiMAX Forum Certified after passing compliance and interoperability tests last year (2005). That was the first round of certification. Another round will follow and from the second half of this year (2006) will include certification for Mobile WiMAX profiles. But despite certification process is still in early phase, in many developing countries WiMAX has gained traction with pre-WiMAX products being installed or trialed for providing fixed, nomadic, portable, or mobile broadband access. Meanwhile, WISPs or independent service providers are expected to be the first WiMAX adopters in developed countries, many of them already have Fixed WiMAX-like products installed for backhauling traffic from their access networks.

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