Performance Advantages of Mobile WiMAX

Mobile WiMAX is expected to deliver significant improvements over Fixed WiMAX which makes it even more attractive for fixed deployments. In wireless environments, link budget (measured in dB) and spectral efficiency are the two primary parameters used for evaluating system performance. Listed below are some of the improvements in link budget and/or spectral efficiency achievable by Mobile WiMAX which are equally applicable to fixed deployments:

• Convolutional Turbo Coding, Hybrid-Automatic Repeat Request (HARQ) and Frequency- as well as Time-Selective Scheduling adds up to 10 dB to the link margin, significantly increasing cell radius and spectral efficiency (bits per second per Hertz).

• Antenna techniques such as MIMO and AAS2 can deliver almost a 50% improvement3 in spectral efficiency over SISO/SIMO implementations as well as link budget improvements.

• Additional improvements to spectral efficiency and the support of users with different QoS come from the use of a two-dimensional (frequency and time) channel aware resource scheduling as well as interference cancellation at the devices.

• Additional reduction of the control overhead is enabled by the use of compressed MAP info.

• Use of sub-MAPs enables the base station to optimize the link to subscribers based upon their location, e.g., whether they’re at the cell edge or close-in.

• Mobile WiMAX uses TDD (Time Division Duplex) as its duplexing mechanism which provides significant benefits for asymmetric data flows:

i. By their nature, FDD systems have symmetric DL and UL channel allocations. TDD allows the operator to vary DL vs. UL allocations. For example, by using a 3:1 DL to UL ratio instead of a symmetric, 1:1 ratio, the DL data rate can be increased by more than 50%.

ii. Because the same channel is used for UL and DL for TDD, it allows for more efficient channel estimation which aids MIMO & AAS techniques.

• Efficient utilization of bandwidth for multicast/broadcast services, and power savings by implementing sleep/idle modes.

• The OFDMA-based air interface is designed to combat inter-cell interference by appropriate resource allocation in different cells.
Note that typical multi-cell deployments can use a frequency re-use scheme of one: 1 (cluster) x 3 (number of sectors) x 1 (number of frequencies in the cell). This scheme results in the most efficient use of spectrum.