WiMAX MIMO

This helps to maximize the sector throughput by leveraging the different capabilities of a diverse set of vendor mobile stations.

The 802.16 specification supports the Multiple-input and single-output (MISO) technique of Transmit Diversity, which is commonly referred to Space Time Code (STC).

The 802.16 specification also supports the MIMO technique of Spatial Multiplexing (SMX), also known as Transmit Diversity rate = 2 (a.k.a.

One specific use of Spatial Multiplexing is to apply it to users who have the best signal quality, so that less time is spent transmitting to them.

Note: MRC (Maximum Ratio Combining) is vendor discretionary and improves rate and range.

This type of spatial multiplexing improves the sector throughput without requiring multiple transmit antennas at the mobile device.

In the case of WiMAX, Uplink Collaborative MIMO is spatial multiplexing with two different devices, each with one antenna.

As long as the signal quality is sufficiently good and the receiver at the base station has at least two antennas, the two data streams can be separated again.

Another MIMO-related technique that can be used in WiMAX systems, but which is outside of the scope of the 802.16 specification, is known as Cyclic Delay Diversity.

The closer the signal can get towards a flat channel at a certain power level, the higher the throughput that can be obtained.

Generally, any aspect of the IEEE 802.16 standard that does not have a test procedure in the RCT may be assumed to not yet be widely implemented.

Companies that make RFICs that support WiMAX MIMO include Intel, Beceem [1], NXP Semiconductors and PMC-Sierra.