Archive for the ‘Spatial Multiplexing’ Tag

How Stuff Works – 802.11n and Spatial Multiplexing

This is the third post in my “How Stuff Works” series.  The first two posting discussed MIMO and channel bonding.  This post looks at another technical improvement that leads to greater speed in 802.11n networks – spatial multiplexing.

It is helpful to take a quick look at a classic 802.11 transmitter.

802.11 Classic Transmitter

802.11 Classic Transmitter

In this scenario, only one data stream is sent from the transmitter to the receiver (represented by the orange line).

With spatial multiplexing, multiple data streams are transmitted at the same time.  They are transmitted on the same channel, but by different antenna.  They are recombined at the receiver using MIMO signal processing.  This is represented in the diagram above with two spatial streams – an orange colored one and a navy blue colored one.

Spatial Multiplexing - Two Streams

Spatial Multiplexing - Two Streams

Spatial multiplexing doubles, triples, or quadruples the data rate depending on the number of transmit antennas.   Remember, you may hear three numbers when referring to 802.11n or MIMO networks – the first is the number of transmit antenna, the second is the number of receive antenna, and the third is the number of spatial streams.   For example, a 3×3x2 system has two spatial streams.

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802.11n Challenge – Speed

First, vote on the greatest deployment challenge for 802.11n in the Enterprise (if you haven’t done so already).

Let’s take a closer look at one of these challenges – speed.

There are many technical improvements in 802.11n that make it significantly faster than 802.11 a/g.   In no particular order, here are some of the improvements:

  • MIMO (Multiple In, Multiple Out) Antennas
  • Spatial Multiplexing
  • Channel Bonding
  • Short Guard Interval
  • Frame Aggregation
  • Block Acknowledgments

It is my intent to have a blog post “tutorial” on each of these improvements, so check back shortly!

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