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MIMO Terminology

MIMO terminology in toolboxes from MathWorks® typically aligns with the terms used in the associated wireless communications standards. Sometimes the terminology might seem inconsistent across toolboxes. This page defines terms as used in Communications Toolbox™ software.

Notations

NotationDescription
NStreams

Number of data streams

Note

The 5G and LTE standards refer to this notation as NLayers, number of layers.

The WLAN standard refers to this notation as NSTS, number of space-time streams.

NTNumber of transmit antennas
NR

Number of receive antennas

NTxchainsNumber of transmit chains
NSymNumber of symbols
NFFTNumber of FFT bins
NCPNumber of cyclic prefix samples
NRENumber of resource elements
NUsersNumber of users
NSCNumber of subcarriers

SU-MIMO Terminology

Communications Toolbox uses these term to describe the data path for a single-user (SU) MIMO transmission.

  • Stream mapping maps a vector of input data symbols for a single user to an NSym-by- NStreams matrix.

  • Precoding codes data symbols per stream and maps them to the number of transmit chains (NTxchains).

  • Beamforming transforms the precoded data symbols (NSym) per transmit chain (NTxchains) to the transmit antennas (NT) for transmission as samples through the channel.

OFDM-MIMO Terminology

For OFDM-MIMO transmission, Communications Toolbox uses the same terminology as for SU-MIMO transmission, except the OFDM modulation converts NTxchains of NSym data symbols into NTxchains of NSamp baseband samples.

  • Stream mapping maps input data symbols to an NSym-by- NStreams matrix. For a single user, stream mapping maps a vector of input data symbols For multiple users, stream mapping maps a matrix of input data symbols.

  • Precoding codes data symbols per stream and maps them to a number of transmit chains (NTxchains).

  • The data symbols get OFDM-modulated to a number of samples (NSamp) on the transmit chains (NTxchains).

  • Beamforming transforms the precoded OFDM-modulated data samples (NSamp) per transmit chain (NTxchains) to the transmit antennas (NT) for transmission as samples through the channel.

This terminology applies for a base station (BS) or user equipment (UE). The use (by either BS or UE) dictates whether the above is for a single device or multiple devices.

Streams

Input to a MIMO system comprises NStreams parallel streams of data. These streams can be all for a single user (SU-MIMO) or for multiple users (MU-MIMO).

For SU-MIMO, a single data stream is parsed into NStreams of data for transmission over the MIMO channel to a single user.

For MU-MIMO, multiple data streams are parsed into NStreams of data for transmission over the MIMO channel to multiple users. This MU-MIMO system has a base station transmitting streams intended for different users over the same antennas at the same time:

The term streams in Communications Toolbox is synonymous with the term layers in the 5G and LTE standards.

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