The Key PHY Features of Mobile WiMAX Technology and Provide Short OFDMA

Scalable OFDMA

OFDMA is the multiple access technique for mobile WiMAX. OFDMA is the Orthogonal Frequency Division Multiplexing (OFDM) based multiple access scheme and has become the de-facto single choice for modern broadband wireless technologies adopted in other competing technologies such as 3GPP’s Long Term Evolution (LTE) and 3GPP2’s Ultra Mobile Broadband (UMB). OFDMA demonstrates superior performance in non-line-of-sight (N-LOS) multi-path channels with its relatively simple transceiver structures and allows efficient use of the available spectrum resources by time and frequency subchannelization.

The simple transceiver structure of OFDMA also enables feasible implementation of advanced antenna techniques such as MIMO with reasonable complexity. Lastly, OFDMA employed in mobileWiMAX is scalable in the sense that by flexibly adjusting FFT sizes and channel bandwidthswith fixed symbol duration and subcarrier spacing, it can address various spectrum needs in different regional regulations in a cost-competitive manner.

TDD
The mobileWiMAX Release 1 Profile has only TDD as the duplexing mode even though the baseline IEEE Standards contain both TDD and Frequency Division Duplex (FDD). Even though future WiMAX Releases will have FDD mode as well, TDD is in many ways better positioned for mobile Internet services than FDD.

First of all, Internet traffic is asymmetric typically with the amount of downlink traffic exceeding the amount of uplink traffic; thus, conventional FDD with the same downlink and uplink channel bandwidth does not provide the optimum use of resources. With TDD products, operators are capable of adjusting downlink and uplink ratios based on their service needs in the networks.

In addition, TDD is inherently better suited to more advanced antenna techniques such as Adaptive Antenna System (AAS) or Beamforming (BF) than FDD due to the channel reciprocity between the uplink and downlink. Mobile Internet with increased multimedia services naturally requires the use of advanced antenna techniques to improve capacity and coverage.

Advanced Antenna Techniques (MIMO and BF)
Various advanced antenna techniques have been implemented in the mobile WiMAX Release 1 profile to enable higher cell and user throughputs and improved coverage. As a matter of fact, mobile WiMAX was the first commercially available cellular technology that actually realized the benefits of MIMO techniques promised by academia for years. With its downlink and uplinkMIMO features, both operators and end-users enjoy up to twice the data rates of Single-Input Single-Output (SISO) rate, resulting in up to 37 Mbps for downlink and 10 Mbps for uplink sector throughput using just 10 MHz TDD channel bandwidth.

MobileWiMAX also enhances the cell coverage with its inherent BF techniques. Coupled with TDD operation, its powerful BF mechanism allows base stations to accurately form a channel matching beam to a terminal station so that uplink and downlink signals can reach reliably from and to terminals at the cell edge, thus effectively extending the cell range.

Full Mobility Support
Full mobility support is yet another strength of the mobile WiMAX products. The baseline standard of mobile WiMAX was designed to support vehicles at highway speed with appropriate pilot design and Hybrid Automatic Repeat Request (HARQ), which helps to mitigate the effect of fast channel and interference fluctuation. The systems can detect the mobile speed and automatically switch between different types of resource blocks, called subchannels, to optimally support the mobile user. Furthermore, HARQ helps to overcome the error of link adaptation in fast fading channels and to improve overall performance with its combined gain and time diversity.

Frequency Reuse One and Flexible Frequency Reuse
From the operators’ perspective, securing greater frequency spectrum for their services is always costly. Naturally it is in their best interest if a technology allows decent performance in the highly interference-limited conditions with frequency reuse one. Mobile WiMAX technology was designed to meet this goal in a respectable way with its cell-specific subchannelization, low rate coding and power boosting and deboosting features. It also enables real-time application of flexible frequency reuse where frequency reuse one applied
to terminals close to the cell center whereas a fraction of frequency is used for terminals at the cell edge, thereby reducing heavy co-channel interference.