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MIMO Glossary

Don't let all the terms and acronyms around MIMO confuse you. Here is a glossary of terms you should know.

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    Angle of Arrival - direction from which a radiated RF path (either reflected or line-of-sight) appears at receiving antenna(s); abbreviated as “AoA” Angle of Departure - direction towards which a radiated RF path is transmitted from transmitting antenna(s); abbreviated as “AoD” Angle Spread - A value describing how “widely” a radio path (reflected or line-of- site) is dispersed; a combination of azimuth spread and elevation spread AoA - see Angle of Arrival AoD - see Angle of Departure Azimuth Spread - A value describing how “widely” a radio path (reflected or line-of-site) is dispersed in the direction parallel to the direction between transmit- ting antennas Beamforming - In simple beam steering, transmitted signals are steered in specific spatial directions so as to improve the SNR of the received signal CDD - Cyclic Delay Diversity – In CDD, a delay between transmitted streams is purposely added to minimize the correla- tion between transmitted signals Channel Estimation - process used to evaluate and quantify RF channel conditions so the system can make optimal transmission systems. Channel Quality Indicator - in LTE, part of the feedback loop that tells the system (among other things) how to best use MIMO at that point in time. Channel Rank - See rank Codebook - A lookup table of different possible matrices used for precoding Correlation - A measure of similarity between transmitted signals. Low correlation between MIMO paths (little similarity between the way the RF environment affects paths) affords the best opportunity for MIMO to increase data rates CQI - see Channel Quality Indicator Diversity - Combats the effects of signal fading by providing redundancy. Can be either Receive Diversity (multiple receiv- ing antenna elements) or Transmit Diversity (multiple transmitting antenna elements). Elevation Spread - A value describing how “widely” a radio path (reflected or line-of-site) is dispersed in the direction perpendicular to the direction between transmitting antennas Equal Gain Combining - Used in SIMO diversity - A signal sent by one antenna and received by multiple receiver antennas (thus experiencing different sets of fading effects along different spatial paths) is summed together (without weighting) to achieve redundancy. H Matrix - A complex matrix used to describe path gains between each transmitting antenna element and each receiving antenna element. Input - When used in reference to a MIMO channel, the channel input is the transmitted signal as seen at the transmit- ting antenna(s) Layer - In LTE, a layer is a data stream than can be transmitted Maximal-ratio Combining - see maximum-ratio combining Maximum-ratio Combining - (aka “maximal ratio combining”) Used in diversity systems (see diversity). Multiple signals (either sent by multiple transmit- ting antennas or received by multiple receiver antennas) are prioritized (weighted) and then summed to achieve redundancy. MEA - Multi-element antenna MIMO - Multiple-Input Multiple-Output antenna system – Multiple transmitting and receiving antennas MIMO-OTA - MIMO Over-the-Air testing – chamber-based radiated-signal testing used to ensure that the effects of antenna design are taken into account MISO - Multiple-In Single-Out antenna system - Multiple transmitting antennas and a single receiving antenna MRC - see maximum-ratio combining MU-MIMO - Multi-User MIMO – used in the LTE uplink, multiple UEs act like multiple transmit antennas to create a MIMO channel OTA - See MIMO-OTA Output - When used in reference to a MIMO channel, the channel output is the transmitted signal as seen at the receiv- ing antenna(s) PARC - Per-antenna rate control - used in HSDPA, a PARC system adjusts the data rates transmitted per each transmit- ting antenna (based on feedback from the UE) Pilots - In LTE, some subcarriers are used as pilots in order to aid with channel estimation PMI - see precoding matrix indicator Precoding - In a MIMO system, precoding assigns weights to multiple transmitted data streams and mixes them before transmission to increase the probability of receiving the transmitted streams. For simplicity’s sake, the possibilities are limited to a small number of matrices stored in the codebook. Precoding Matrix Indicator - In LTE, the PMI is part of the feedback loop from the UE to the base-station (eNode B). It is an index into the codebook, telling the system which precoding matrix to use Rank - The rank or channel rank is a measure of the number of streams or layers that can be simultaneously transmitted. It is a function of correlation and can never be more than the number of transmitting antenna elements or receiving antenna elements (whichever is less). Receive Diversity - Use of redundancy through multiple receiving antenna elements to increase the probability of proper signal reception Reference Signals - Also called “pilot signals”, reference signal conditions are measured by receivers to be used in channel estimation RX Diversity - See receive diversity Scatterer - Signal-reflective object(s) located near a radio receiver SCM - spatial channel models defined by a 3GPP/3GPP2 ad hoc group for mobile device testing SCME - Based on the SCM, the SCME models provide extended bandwidth (to 100 MHz vs. 5MHz) Selection Combining - Used in diversity systems (see diversity). When multiple signals (either sent by multiple transmitting antennas or received by multiple receiver antennas) are present, the system selects the strongest for demodulation... SFBC - see space frequency block coding SIMO - Single-Input, Multiple Output antenna system - single transmitting antenna and multiple receiving antennas SINR - Signal-to-Interference-and-Noise ratio SISO - Single-Input, Single-Output antenna system - single transmitting antenna and signal receiving antenna SNR - Signal-to-Noise ratio Space Frequency Block Coding - A transmit diversity method used in MISO systems. An SFBC system uses multiple TX antennas to provide redundancy by splitting copies of each transmitted block across space (transmitting copies from dif ferent antennas than the original) or frequencies (transmitting copies of original data blocks on dif ferent frequencies [subcarriers] than the originals)Space-T ime Block Coding - A transmit diversity method used in MISO systems. An STBC system uses multiple TX antennas to provide redundancy by splitting copies of each transmitted block across space (transmitting copies from dif ferent antennas than the original) or time (transmitting copies of original data blocks after the original has been trans - mitted)Spatial Correlation - correlation between a signal’ s transfer characteristics (as seen by the receiver) and the Angle of ArrivalSpatial Multiplexing - The use of physi cal spatial information (as in a MIMO system) to dif ferentiate between data streams transmitted in the same frequency space at the same time STBC - See Space-T ime Block Coding SU-MIMO - Single-User MIMO – used in the L TE downlink Switched Combining - Used in diversity systems (see diversity). When a received signal (among multiple signals either sent by multiple transmitting antennas or received by multiple receiver antennas) becomes too weak to demodu - late, the system switches to another . T ransmission Mode - T ype of multi - antenna transmission scheme – for example, L TE defines several transmis - sion modes, including transmit diversity , MU-MIMO, etc.T ransmit Diversity - Use of redun - dancy through multiple transmitting antenna elements to increase the probability of proper signal receptionTX Diversity - see transmit diversity Is MIMO t e s tin g c omp l e x? Not an ymor e... Intr oduc in g S pir ent’s VR5 HD S p ati al Ch annel Emu l at or S pir ent’s new VR5 HD S p ati al Ch annel Emu l at or brin g s u npr ec edent ed e a se of u se t o t e s tin g high- ant enn a-c ou nt MIMO/be amf ormin g dev ic e s and b a se- s t ation s. www .spir ent.com/VR5 MIMO: T erms Y ou Should Kno w (MIMO Glossar y) Angle of Arrival - direction from which a radiated RF path (either reflected or line-of-sight) appears at receiving antenna(s); abbreviated as “AoA”Angle of Departure - direction towards which a radiated RF path is transmitted from transmitting antenna(s); abbreviated as “AoD”Angle Spread - A value describing how “widely” a radio path (reflected or line-of - site) is dispersed; a combination of azimuth spread and elevation spreadAoA - see Angle of Arrival AoD - see Angle of Departure Azimuth Spread - A value describing how “widely” a radio path (reflected or line-of-site) is dispersed in the direction parallel to the direction between transmit - ting antennasBeamforming - In simple beam steering, transmitted signals are steered in speci fic spatial directions so as to improve the SNR of the received signal CDD - Cyclic Delay Diversity – In CDD, a delay between transmitted streams is purposely added to minimize the correla - tion between transmitted signalsChannel Estimation - process used to evaluate and quantify RF channel conditions so the system can make optimal transmission systems.Channel Quality Indicator - in L TE, part of the feedback loop that tells the system (among other things) how to best use MIMO at that point in time.Channel Rank - See rank Codebook - A lookup table of dif ferent possi ble matrices used for precoding Correlation - A measure of similarity between transmitted signals. Low correlation between MIMO paths (little similarity between the way the RF environment af fects paths) af fords the best opportunity for MIMO to increase data ratesCQI - see Channel Quality Indicator Diversity - Combats the ef fects of signal fading by providing redundancy . Can be either Receive Diversity (multiple receiv - ing antenna elements) or T ransmit Diversity (multiple transmitting antenna elements). Elevation Spread - A value describing how “widely” a radio path (reflected or line-of-site) is dispersed in the direction perpendicular to the direction between transmitting antennas Equal Gain Combining - Used in SIMO diversity - A signal sent by one antenna and received by multiple receiver antennas (thus experiencing dif ferent sets of fading ef fects along dif ferent spatial paths) is summed together (without weighting) to achieve redundancy . H Matrix - A complex matrix used to describe path gains between each transmitting antenna element and each receiving antenna element.Input - When used in reference to a MIMO channel, the channel input is the transmitted signal as seen at the transmit - ting antenna(s)Layer - In L TE, a layer is a data stream than can be transmitted Maximal-ratio Combining - see maximum-ratio combiningMaximum-ratio Combining - (aka “maximal ratio combining”) Used in diversity systems (see diversity). Multiple signals (either sent by multiple transmit - ting antennas or received by multiple receiver antennas) are prioritized (weighted) and then summed to achieve redundancy . MEA - Multi-element antenna MIMO - Multiple-Input Multiple-Output antenna system – Multiple transmitting and receiving antennasMIMO-OT A - MIMO Over-the-Air testing – chamber-based radiated-signal testing used to ensure that the ef fects of antenna design are taken into account MISO - Multiple-In Single-Out antenna system - Multiple transmitting antennas and a single receiving antennaMRC - see maximum-ratio combining MU-MIMO - Multi-User MIMO – used in the L TE uplink, multiple UEs act like multiple transmit antennas to create a MIMO channelO TA - See MIMO-OT A Output - When used in reference to a MIMO channel, the channel output is the transmitted signal as seen at the receiv - ing antenna(s)P ARC - Per-antenna rate control - used in HSDP A, a P ARC system adjusts the data rates transmitted per each transmit - ting antenna (based on feedback from the UE)Pilots - In L TE, some subcarriers are used as pilots in order to aid with channel estimationPMI - see precoding matrix indicator Precoding - In a MIMO system, precoding assigns weights to multiple transmitted data streams and mixes them before transmission to increase the probability of receiving the transmitted streams. For simplicity’ s sake, the possi bilities are limited to a small number of matrices stored in the codebook.Precoding Matrix Indicator - In L TE, the PMI is part of the feedback loop from the UE to the base-station (eNode B). It is an index into the codebook, telling the system which precoding matrix to useRank - The rank or channel rank is a measure of the number of streams or layers that can be simultaneously transmitted. It is a function of correlation and can never be more than the number of transmitting antenna elements or receiving antenna elements (whichever is less).Receive Diversity - Use of redundancy through multiple receiving antenna elements to increase the probability of proper signal receptionReference Signals - Also called “pilot signals”, reference signal conditions are measured by receivers to be used in channel estimationRX Diversity - See receive diversity Scatterer - Signal-reflective object(s) located near a radio receiverSCM - spatial channel models defined by a 3GPP/3GPP2 ad hoc group for mobile device testingSCME - Based on the SCM, the SCME models provide extended bandwidth (to 100 MHz vs. 5MHz)Selection Combining - Used in diversity systems (see diversity). When multiple signals (either sent by multiple transmitting antennas or received by multiple receiver antennas) are present, the system selects the strongest for demodulation...SFBC - see space frequency block codingSIMO - Single-Input, Multiple Output antenna system - single transmitting antenna and multiple receiving antennasSINR - Signal-to-Interference-and-Noise ratioSISO - Single-Input, Single-Output antenna system - single transmitting antenna and signal receiving antennaSNR - Signal-to-Noise ratio Space Frequency Block Coding - A transmit diversity method used in MISO systems. An SFBC system uses multiple TX antennas to provide redundancy by splitting copies of each transmitted block across space (transmitting copies from different antennas than the original) or frequencies (transmitting copies of original data blocks on different frequencies [subcarriers] than the originals) Space-Time Block Coding - A transmit diversity method used in MISO systems. An STBC system uses multiple TX antennas to provide redundancy by splitting copies of each transmitted block across space (transmitting copies from different antennas than the original) or time (transmitting copies of original data blocks after the original has been trans- mitted) Spatial Correlation - correlation between a signal’s transfer characteristics (as seen by the receiver) and the Angle of Arrival Spatial Multiplexing - The use of physical spatial information (as in a MIMO system) to differentiate between data streams transmitted in the same frequency space at the same time STBC - See Space-Time Block Coding SU-MIMO - Single-User MIMO – used in the LTE downlink Switched Combining - Used in diversity systems (see diversity). When a received signal (among multiple signals either sent by multiple transmitting antennas or received by multiple receiver antennas) becomes too weak to demodu- late, the system switches to another. Transmission Mode - Type of multi- antenna transmission scheme – for example, LTE defines several transmis- sion modes, including transmit diversity, MU-MIMO, etc. Transmit Diversity - Use of redun- dancy through multiple transmitting antenna elements to increase the probability of proper signal reception TX Diversity - see transmit diversity