How does it work?

IEEE 802.11n will incorporate several new technology approaches to improve performance and reliability of Wi-Fi networks. Some of the technologies that will be part of the final standard include:

• . Multiple Input, Multiple Output technology (MIMO)
• . Increased number of spatial streams (up to 4)
• . MIMO Power-Save mode
• . Beam-forming
• . Frame Aggregation and Packet Bursting
• . Reduced Interframe Spacing
• . Channel width 20MHz or 40MHz

One of the important components of the IEEE 802.11n draft standard is MIMO (Multiple Input Multiple Output) technology.

MIMO exploits a radio-wave phenomenon called "multipath". Transmitted signals are reflected by walls, doors, and other objects, reaching the receiving antenna multiple times via different routes and at slightly different times. Uncontrolled multipath negatively affects the original signal resulting in degraded Wi-Fi performance.
MIMO combines multipath with a technique known as space-division multiplexing. As a result the transmitting device splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end. The current IEEE 802.11n draft allows up to four spatial streams.
In order to further enhance MIMO and to overcome some trade-offs to be made because of this technology (higher power consumption, etc.) additional techniques will be implemented.
The draft-n specification includes a MIMO power-save mode, which reduces power consumption by using multiple paths only when it would result in additional performance. Transmit beam-forming and receive forming are techniques that focus radio signals directly on the target antenna, thereby improving range and performance by reducing interference.
Frame aggregation, packet bursting and reduced inter-frame spacing improve performance efficiency by allowing transmission bursts of multiple data packets and by providing a shorter delay between OFDM transmissions. Another optional mode in the IEEE 802.11n draft effectively doubles data rates by doubling the width of a WLAN communications channel from 20MHz to 40MHz.

MIMO Technology Overview

MIMO technology uses 2D transmission to greatly improve the speed per channel. Two data pipes result in twice the data rate and increased signal reliability.
Instead of sending out a single stream of data like most base stations, MIMO sends out multiple data streams simultaneously and uses multiple antennas to sort out the signals.
MIMO is compatible with existing IEEE 802.11a/b/g networks as only a single radio stream is used. Multi-mode, smart antenna chipsets improve the performance of IEEE 802.11a/b, and g Wi-Fi systems. Backward-compatible MIMO products simultaneously interoperate with existing Wi-Fi systems in the same channel, improving the power and intensity of the beam with techniques such as beam-forming and receive-forming.
When operating with conventional IEEE 802.11a/b/g equipment, MIMO still improves performance and coverage by having the effect of focusing the radio beam and amplifying the wireless power reception. This is a process (known as beam-forming) that can effectively quadruple the transmit performance when using double antennae.
When receiving the signals, the multiple antennas of a MIMO device can combine the various signals it is receiving to improve the quality and gain of the overall received signal. This is known as receive- forming and can significantly improve the reception of signals in an existing IEEE 802.11a/b/g network.

MIMO Technology Overview

MIMO technology provides several great advantages over traditional IEEE 802.11a/b/g technology, offering backward compatibility and interoperability with IEEE 802.11a/b/g solutions:

• . Improved Performance / Throughput
• . Increased Range
• . Improved Signal Reliability

The initial deployment of MIMO products is likely to happen with the upgrading of wireless access points to achieve more efficient transmission rates and better coverage.
The new MIMO wireless devices will now support new applications which though feasible, were suspectible of disruption and disturbance with conventional wireless technologies.
With the popularity of music streaming and other multimedia applications, home computers are turned into true media entertainment centers. High speed wireless means that music and films can be enjoyed anywhere in the house.
The increased range of MIMO based high speed wireless products means that more parts of a building can be reached without the need for additional access points or wireless repeaters.
Improved performance and reliability also means that new applications like VoIP (Voice over IP) can be deployed more easily without the limitations of a cable based infrastructure or the costs to extend this infrastructure accordingly.