# Spatial multiplexing

Spatial multiplexing

Spatial multiplexing is a transmission technique in MIMO wireless communication to transmit independent and separately encoded data signals, so called "streams", from each of the multiple transmit antennas. Therefore, the space dimension is reused, or multiplexed, more than one time.

If the transmitter is equipped with $N_t$ antennas and the receiver has $N_r$ antennas, the maximum spatial multiplexing order (the number of streams) is

:$mathbf\left\{N_s\right\}=min\left(N_t,N_r\right)$

if a linear receiver is used. This means that $N_s$ streams can be transmitted in parallel, leading to a $N_s$ increase of the spectral efficiency (the number of bits per second and per Hz that can be transmitted over the wireless channel).

Encoding

Open-loop approach

In an open-loop MIMO system with $N_t$ transmitter antennas and $N_r$ receiver antennas, the input-output relationship can be described as:$mathbf\left\{y\right\}=mathbf\left\{Hx\right\}+mathbf\left\{n\right\}$ where $mathbf\left\{x\right\} = \left[x_1, x_2, ldots, x_\left\{N_t\right\}\right] ^T$ is the $N_t imes 1$ vector of transmitted symbols, $mathbf\left\{y,n\right\}$ are the $N_r imes 1$ vectors of received symbols and noise respectively and $mathbf\left\{H\right\}$ is the $N_r imes N_t$ matrix of channel coefficients.

Closed-loop approach

In a closed-loop MIMO system the input-output relationship with a closed-loop approach can be described as:$mathbf\left\{y\right\}=mathbf\left\{HWs\right\}+mathbf\left\{n\right\}$ where $mathbf\left\{s\right\} = \left[s_1, s_2, ldots, s_\left\{N_s\right\}\right] ^T$ is the $N_s imes 1$ vector of transmitted symbols, $mathbf\left\{y,n\right\}$ are the $N_r imes 1$ vectors of received symbols and noise respectively, $mathbf\left\{H\right\}$ is the $N_r imes N_t$ matrix of channel coefficients and $mathbf\left\{W\right\}$ is the $N_t imes N_s$ linear precoding matrix.

A precoding matrix $mathbf\left\{W\right\}$ is used to precode the symbols in the vector to enhance the performance. The column dimension $N_s$ of $mathbf\left\{W\right\}$ can be selected smaller than $N_t$ which is useful if the system requires $N_s \left( eq N_t\right)$ streams because of several reasons. Examples of the reasons are as follows: either the rank of the MIMO channel or the number of receiver antennas is smaller than the number of transmit antennas.

History

* Single-user MIMO
** Bell Laboratories Layered Space-Time (BLAST), Gerard. J. Foschini (1996)
** Per Antenna Rate Control (PARC), Varanasi, Guess (1998), Chung, Huang, Lozano (2001)
** Selective Per Antenna Rate Control (SPARC), Ericsson (2004)
*Multi-user MIMO: Samsung, Qualcomm, Ericsson, TI, Huawei, Philipse, Alcatel-Lucent, Freescale, et al.
** PU2RC allows the network to allocate each antenna to the different user which is not considered in single-user MIMO scheduling. Instead of a physical antenna, the network can transmit a user date through a codebook based spatial beam, i.e., a virtual antenna. The efficient user scheduling such as pairing spatially distinguishable users with codebook based spatial beams are additionally used for the simplification of wireless networks in terms of additionally required wireless resource and complex protocol modification.
* Enhanced multiuser MIMO

ee also

*MIMO, 3G MIMO and WIMAX MIMO
*Space–time code
*Space–time trellis code
*Precoding

Wikimedia Foundation. 2010.

Нужен реферат?

### Look at other dictionaries:

• Multiplexing — General multiplex scheme: the ν input lines channels are multiplexed into a single fast line. The demultiplexer receives the multiplexed data stream and extracts the original channels to be transferred …   Wikipedia

• Wavelength-division multiplexing — For the radio station, see DWDM FM. Multiplex techniques Circuit mode (constant bandwidth) TDM · FDM · SDM Polarization multiplexing Spatial m …   Wikipedia

• MIMO — This article is about MIMO in wireless communication. For other uses, see MIMO (disambiguation). Understanding of SISO, SIMO, MISO and MIMO (note that the terms input and output refer to the radio channel carrying the signal, not to the devices… …   Wikipedia

• WiMAX MIMO — refers to the use of Multiple input multiple output communications (MIMO) technology on WiMAX, which is the technology brand name for the implementation of the standard IEEE 802.16. BackgroundWiMAXWiMAX is the technology brand name for the… …   Wikipedia

• Multi-user MIMO — In radio, multi user MIMO (MU MIMO) is a set of advanced MIMO, multiple input and multiple output (pronounced mee moh or my moh), technologies that exploit the availability of multiple independent radio terminals in order to enhance the… …   Wikipedia

• 4G — (also known as Beyond 3G), an abbreviation for Fourth Generation, is a term used to describe the next complete evolution in wireless communications . A 4G system will be able to provide a comprehensive IP solution where voice, data and streamed… …   Wikipedia

• IEEE 802.11n — is a proposed amendment to the IEEE 802.11 2007 wireless networking standard to significantly improve network throughput over previous standards, such as 802.11b and 802.11g, with a significant increase in the maximum raw (PHY) data rate from 54… …   Wikipedia

• PU2RC — Per User Unitary Rate Control (PU2RC) is the world first codebook based multi user MIMO platform [cite conference|author=Niranjay Ravindran, Nihar Jindal, and Howard Huang|title=Beamforming with FiniteRate Feedback for LOS MIMO Downlink… …   Wikipedia

• IEEE 802.11n-2009 — is an amendment to the IEEE 802.11 2007 wireless networking standard to improve network throughput over the two previous standards 802.11a and 802.11g with a significant increase in the maximum net data rate from 54 Mbit/s to 600 Mbit/s (slightly …   Wikipedia

• Many antennas — Many antennas,[1] is a smart antenna technique, which overcomes the performance limitation of single user multiple input multiple output (MIMO) techniques. In cellular communication, the maximum number of considered antennas for downlink is 2 and …   Wikipedia