In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience fades and interference at different, random times, i.e., they are at least partly independent. 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. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels.
Terrestrial microwave radio system with two antenna arrays configured for space-diversity
The following classes of diversity schemes can be identified:
Time diversity: Multiple versions of the same signal are transmitted at different time instants. 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. Thus, error bursts are avoided, which simplifies the error correction.
Frequency diversity: The signal is transmitted using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading. Later examples include:
Space diversity: The signal is transmitted over several different propagation paths. 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). In the latter case, a diversity combining technique is applied before further signal processing takes place. If the antennas are far apart, for example at different cellular base station sites or WLAN access points, this is called macrodiversity or site diversity. If the antennas are at a distance in the order of one wavelength, this is called microdiversity. A special case is phased antenna arrays, which also can be used for beamforming, MIMO channels and space–time coding (STC).
Polarization 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.[1]
Multiuser diversity: Multiuser diversity is obtained by opportunistic user scheduling at either the transmitter or the receiver.[2] Opportunistic user scheduling is as follows: at any given time, the transmitter selects the best user among candidate receivers according to the qualities of each channel between the transmitter and each receiver. A receiver must feed back the channel quality information to the transmitter using limited levels of resolution, in order for the transmitter to implement Multiuser diversity.
Cooperative diversity: Achieves antenna diversity gain by using the cooperation of distributed antennas belonging to each node.
An important element in communication systems applying diversity schemes is the "Combiner", which processes the redundantly received signals. Combiner technologies are traditionally classified according to Brennan:[3]
Maximal-Ratio Combiner
Equal-Gain Combiner
Scanning/Switching Combiner
Selection Combiner
To combine parallel redundant transmitted longer signal sequences, for example network packets, the principle of a Timing Combiner was defined in 2012.[4] Similarly working like a Selection Combiner, the first fully received and valid data packet will be immediately further processed, whereas the later arriving redundant packets will be immediately discarded after reception. With this approach, always the faster of the redundant channels "wins", yielding significant performance improvements especially in wireless applications.[4]
^Siamack Ghadimi (2019-04-02), Differential Cross-Polarized Wireless Communications, Scientific Research
^F. Foukalas and T. Khattab, "Multi-User Diversity with Optimal Power Allocation in Spectrum Sharing under Average Interference Power Constraint." 2014 IEEE 79th Vehicular Technology Conference (VTC Spring), May 2014
^Brennan, D. G. (June 1959). "Linear Diversity Combining Techniques". Proceedings of the IRE. 47 (6): 1075–1102. doi:10.1109/JRPROC.1959.287136. ISSN 0096-8390. S2CID 51655891.
^ abRentschler, M.; Laukemann, P. (September 2012). "Performance analysis of parallel redundant WLAN". Proceedings of 2012 IEEE 17th International Conference on Emerging Technologies & Factory Automation (ETFA 2012). pp. 1–8. doi:10.1109/ETFA.2012.6489647. ISBN978-1-4673-4737-2. S2CID 10130152.
External linksedit
Diversity reception - Background information of the development of Diversity reception devices.
January 06, 2024
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In telecommunications a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics Diversity is mainly used in radio communication and is a common technique for combatting fading and co channel interference and avoiding error bursts It is based on the fact that individual channels experience fades and interference at different random times i e they are at least partly independent 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 Diversity techniques may exploit the multipath propagation resulting in a diversity gain often measured in decibels Terrestrial microwave radio system with two antenna arrays configured for space diversity Contents 1 Diversity techniques 2 Combiner techniques 3 See also 4 References 5 External linksDiversity techniques editThe following classes of diversity schemes can be identified Time diversity Multiple versions of the same signal are transmitted at different time instants 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 Thus error bursts are avoided which simplifies the error correction Frequency diversity The signal is transmitted using several frequency channels or spread over a wide spectrum that is affected by frequency selective fading Later examples include OFDM modulation in combination with subcarrier interleaving and forward error correction Spread spectrum for example frequency hopping or DS CDMA Space diversity The signal is transmitted over several different propagation paths 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 In the latter case a diversity combining technique is applied before further signal processing takes place If the antennas are far apart for example at different cellular base station sites or WLAN access points this is called macrodiversity or site diversity If the antennas are at a distance in the order of one wavelength this is called microdiversity A special case is phased antenna arrays which also can be used for beamforming MIMO channels and space time coding STC Polarization 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 1 Multiuser diversity Multiuser diversity is obtained by opportunistic user scheduling at either the transmitter or the receiver 2 Opportunistic user scheduling is as follows at any given time the transmitter selects the best user among candidate receivers according to the qualities of each channel between the transmitter and each receiver A receiver must feed back the channel quality information to the transmitter using limited levels of resolution in order for the transmitter to implement Multiuser diversity Cooperative diversity Achieves antenna diversity gain by using the cooperation of distributed antennas belonging to each node Combiner techniques editMain article Diversity combining An important element in communication systems applying diversity schemes is the Combiner which processes the redundantly received signals Combiner technologies are traditionally classified according to Brennan 3 Maximal Ratio Combiner Equal Gain Combiner Scanning Switching Combiner Selection CombinerTo combine parallel redundant transmitted longer signal sequences for example network packets the principle of a Timing Combiner was defined in 2012 4 Similarly working like a Selection Combiner the first fully received and valid data packet will be immediately further processed whereas the later arriving redundant packets will be immediately discarded after reception With this approach always the faster of the redundant channels wins yielding significant performance improvements especially in wireless applications 4 See also editSpace time coding STC Aperture synthesis Cooperative diversity Channel access method Fresnel zone Tropospheric scatter Cyclic delay diversityReferences edit Siamack Ghadimi 2019 04 02 Differential Cross Polarized Wireless Communications Scientific Research F Foukalas and T Khattab Multi User Diversity with Optimal Power Allocation in Spectrum Sharing under Average Interference Power Constraint 2014 IEEE 79th Vehicular Technology Conference VTC Spring May 2014 Brennan D G June 1959 Linear Diversity Combining Techniques Proceedings of the IRE 47 6 1075 1102 doi 10 1109 JRPROC 1959 287136 ISSN 0096 8390 S2CID 51655891 a b Rentschler M Laukemann P September 2012 Performance analysis of parallel redundant WLAN Proceedings of 2012 IEEE 17th International Conference on Emerging Technologies amp Factory Automation ETFA 2012 pp 1 8 doi 10 1109 ETFA 2012 6489647 ISBN 978 1 4673 4737 2 S2CID 10130152 External links editDiversity reception Background information of the development of Diversity reception devices Retrieved from https en wikipedia org w index php title Diversity scheme amp oldid 1191831301, wikipedia, wiki, book, books, library,
