Terrestrial microwave radio system with two antenna arrays configured for space-diversity

In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by utilizing two or more communication channels with different characteristics. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a Diversity plays an important role in combating fading and co-channel interference and avoiding error bursts. This is about the phenomenon of loss of signal in telecommunications Co-channel interference or CCI is Crosstalk from two different Radio transmitters using the same Frequency. In Telecommunication, an error burst is a contiguous Sequence of symbols received over a Data transmission channel, such that the first and It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. In Telecommunication and Information theory, forward error correction (FEC is a System of Error control for Data transmission, whereby Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels. In Wireless Telecommunications multipath is the propagation phenomenon that results in Radio signals reaching the receiving In Wireless communications diversity gain is the increase in signal-to-interference ratio due to some Diversity scheme, or how much the transmission power can be The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to

The following classes of diversity schemes can be identified:

• Time diversity: Multiple versions of the same signal are transmitted at different time instants. Time Diversity is used in digital communication systems to combat that the transmissions channel may suffer from Error bursts due to time-varying channel conditions Alternatively, a redundant forward error correction code is added and the message is spread in time by means of bit-interleaving before it is transmitted. In Telecommunication and Information theory, forward error correction (FEC is a System of Error control for Data transmission, whereby Interleaving in Computer science is a way to arrange Data in a non- Contiguous way in order to increase performance Thus, error bursts are avoided, which simplifies the error correction. In Telecommunication, an error burst is a contiguous Sequence of symbols received over a Data transmission channel, such that the first and

• Frequency diversity: The signal is transferred using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading. This is about the phenomenon of loss of signal in telecommunications Middle-late 20th century microwave radio relay lines often used several regular wideband radio channels, and one protection channel for automatic use by any faded channel. Microwave radio relay is a technology for transmitting digital and analog signals, such as long-distance Telephone calls and the relay of In communications, wideband is a relative term used to describe a wide range of frequencies in a Spectrum. Later examples include:
  • OFDM modulation in combination with subcarrier interleaving and forward error correction
  • Spread spectrum, for example frequency hopping or DS-CDMA. Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( Interleaving in Computer science is a way to arrange Data in a non- Contiguous way in order to increase performance In Telecommunication and Information theory, forward error correction (FEC is a System of Error control for Data transmission, whereby Spread-spectrum techniques are methods by which Energy generated in a particular bandwidth is deliberately spread in the Frequency domain, resulting Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using Direct-Sequence Code Division Multiple Access ( DS-CDMA) is a Multiple access scheme based on Direct-sequence spread spectrum, by spreading the signals from/to

• Space diversity: The signal is transferred over several different propagation paths. Antenna diversity, also known as space diversity, is one in a superset of wireless Diversity schemes that utilizes two or more antennas to improve the quality and reliability In the case of wired transmission, this can be achieved by transmitting via multiple wires. In the case of wireless transmission, it can be achieved by antenna diversity using multiple transmitter antennas (transmit diversity) and/or multiple receiving antennas (reception diversity). Antenna diversity, also known as space diversity, is one in a superset of wireless Diversity schemes that utilizes two or more antennas to improve the quality and reliability Transmit diversity is Radio communication using signals that originate from two or more independent sources that have been modulated with identical Information Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal In the latter case, a diversity combining technique is applied before further signal processing takes place. Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal If the antennas are far apart, for example at different cellular base station sites or WLAN access points, this is called macrodiversity. In wireless communication Macrodiversity means a situation where several receiver antennas and/or transmitter antennas are used for transferring the same signal If the antennas are at a distance in the order of one wavelength, this is called microdiversity. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. A special case is phased antenna arrays, which also can be utilized for beamforming, MIMO channels and Space–time coding (STC). Beamforming is a Signal processing technique used in sensor arrays for directional signal transmission or reception In Radio, multiple-input and multiple-output, or MIMO (pronounced mee-moh or my-moh) is the use of multiple antennas at both the transmitter A space&ndashtime code (STC is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas

• Polarisation diversity: Multiple versions of a signal are transmitted and received via antennas with different polarization. A diversity combining technique is applied on the receiver side. Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal

• Multiuser diversity: Multiuser diversity is obtained by opportunistic user scheduling at either the transmitter or the receiver. Opportunistic user scheduling is as follows: the transmit selects the best user among candidate receivers according to the qualities of each channel between the transmitter and each receiver. In FDD systems, a receiver must feed back the channel quality information to the transmitter with the limited level of resolution. A duplex Communication system is a system composed of two connected parties or devices which can communicate with one another in both directions

• Cooperative diversity: Achieves antenna diversity gain by utilizing the cooperation of distributed antennas belonging to each node. Cooperative diversity is a cooperative multiple antenna techniques which exploits user diversity by decoding the combined signal of the relayed signal and the direct signal in

See also

• Space–time coding (STC)
• Antenna diversity
• Macrodiversity
• Diversity combining
• Aperture synthesis
• Cooperative diversity
• Channel access method
• Fresnel zone
• Tropospheric scatter

External links

• Diversity reception - Background information of the development of Diversity reception devices. A space&ndashtime code (STC is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas Antenna diversity, also known as space diversity, is one in a superset of wireless Diversity schemes that utilizes two or more antennas to improve the quality and reliability In wireless communication Macrodiversity means a situation where several receiver antennas and/or transmitter antennas are used for transferring the same signal Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal Cooperative diversity is a cooperative multiple antenna techniques which exploits user diversity by decoding the combined signal of the relayed signal and the direct signal in In Telecommunications and Computer networks, a channel access method or multiple access method allows several terminals connected to the same In Optics and Radio communications, a Fresnel zone (pronounced FRA-nel Zone) named for physicist Augustin-Jean Fresnel, is one of Tropospheric scatter (or troposcatter) is the scattering of distant TV and FM radio stations by the Troposphere so that they travel farther than