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Adaptive Equalization

Adaptive equalization can be applied to transmissions that carry analog information (e.g., analog voice or video) or digital information (e.g., digital data, digitized voice or video) and is used to combat intersymbol interference.

Forward Error Correction

in satellite communications, the amount of delay involved makes retransmission undesirable.

those in which the transmitted signal carries digital data or digitized voice or video data.

The Fading Channel

The other small-scale effect, multipath fading, can cause distortion and inter- symbol interference.

Types of Fading

This change is mainly caused by shadowing and differences in distance from the transmitter.

Fading effects in a mobile environment can be classified as either small-scale or large-scale.

The Effects of Multipath Propagation

As multipath signals add together, the resulting signal power can be stronger, but can also be lower by a factor of 100 or 1000 (20 or 30 dB). The signal level relative to noise declines, making signal detec- tion at the receiver more difficult.

Multipath Propagation

This is generally the case for many satellite facilities and for point-to-point microwave.

One of the key effects causing fading is multipath propagation.

Bandwidth Expansion

Carrier aggregation combines multiple channels. For example, 802.11n and 802.11ac combine the 20 MHz channels from earlier 802.11 standards into 40, 80, or 160 MHz channels.

OFDM and Spread Spectrum

MIMO and OFDM technol- ogies are the cornerstone of emerging broadband wireless networks.

Multi-User MIMO

The MIMO antenna architecture has become a key technology in evolving high-speed wireless networks,

MIMO Principles

Multilayer transmission: Multiple, parallel data streams can flow between a pair of transmit and receive antennas.

Multi-user MIMO (MU-MIMO): With enough MIMO antennas, directional antenna beams can be established to multiple users simultaneously.

(MIMO) Antennas

Beam-forming: Multiple antennas can be configured to create directional antenna patterns to focus and increase energy to intended recipients.

Diversity: Diversity can be accomplished to have multiple received signals through multiple transmit and/or receive antennas.

Diversity Techniques and MIMO

Diversity is based on the fact that individual channels experience independent fading events.

Adaptive Modulation and Coding

The process of equaliza- tion involves some method of gathering the dispersed symbol energy