WiMax Matrix A and Matrix B MIMO

Ever wondered what the difference is between WiMAX Matrix A and Matrix B MIMO? As a reader of this blog you just might have. In recent certification reports and functionality comparisons between WiMAX kit of different vendors these acronyms have sprung up but, as usual, without further explanations. Don’t fear, help is on the way! This article written by Shamik Mukherjee of Motorola and published on WiMAX.com gives a very good overview including a look at WiMAX beamforming.

So here’s a quick summary of Matrix A and B:

Matrix A: Coverage Gain

In a 2×2 antenna configuration (2 transmitter antennas, 2 receiver antennas), a single data stream is transmitted in parallel over the two paths. A mathematical algorithm known as Space Time Block Codes (STBC) is used to encode the data streams of the two antennas to make them orthogonal to each other. This improves the signal to noise ratio at the receiver side which can be used to:

  • Increase the cell radius
  • To provide better throughput for subscribers that are difficult to reach (e.g. deep indoors or moving at higher speeds).
  • For terminals which already experience good signal conditions Matrix A has the benefit that higher order modulation (e.g. 64QAM) can be used and fewer error correction bits are necessary which in turn increases transmission speeds to that subscriber.

Matrix B: Capacity Increase

This flavor of MIMO, also known as Spacial Multiplexing MIMO (SM-MIMO), sends an independent data stream over each antenna. Thus, in case signal conditions are excellent, the data rate is doubled, tripled or quadrupled depending on the number of antennas used in both the transmitter and receiver. In practice, WiMAX MIMO is defined for two antennas at each side.

Mandatory and Optional Features

For WiMAX Wave 2 certification, both 2×2 Matrix A and Matrix B capabilities are required according to the article. Beamforming capabilities, also known as Adaptive Antenna Systems (AAS), is optional.