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| | The author is recognized by the name of Figures Wunder. My day job is a meter reader. North Dakota is our birth place. He is really fond of performing ceramics but he is struggling to find time for it.<br><br>Here is my web site; std testing at home ([http://www.animecontent.com/blog/124234 sneak a peek at this website]) |
| {{Refimprove|date=November 2006}}
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| {{Multiplex techniques}}
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| [[Image:spatial multiplexing.jpg|thumb|right|Spatial Multiplexing]]
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| [[Image:spatial multiplexing2.jpg|thumb|right|2xSMX or STC+2xMRC]]
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| '''Spatial multiplexing''' (seen abbreviated '''SM''' or '''SMX'''<!--cf. [[WiMAX MIMO#Spatial Multiplexing]]-->) is a transmission technique in [[Multiple-input multiple-output communications|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 [[Multiplexing|multiplex]]ed, more than one time.
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| If the transmitter is equipped with <math>N_t</math> antennas and the receiver has <math>N_r</math> antennas, the maximum spatial multiplexing order (the number of streams) is,
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| :<math>N_s=\min(N_t, N_r)\!</math>
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| if a linear receiver is used. This means that <math>N_s</math> streams can be transmitted in parallel, ideally leading to an <math>N_s</math> increase of the [[spectral efficiency]] (the number of bits per second and per Hz that can be transmitted over the wireless channel). The practical multiplexing gain can be limited by [[Spatial Correlation|spatial correlation]], which means that some of the parallel streams may have very weak channel gains.
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| ==Encoding==
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| === Open-loop approach ===
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| In an [[open loop (wireless)|open-loop]] [[MIMO]] system with <math>N_t</math> transmitter antennas and <math>N_r</math> receiver antennas, the input-output relationship can be described as
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| :<math>\mathbf{y}=\mathbf{Hx}+\mathbf{n}</math>
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| where <math>\mathbf{x} = [x_1, x_2, \ldots, x_{N_t}]^T</math> is the <math>N_t\times 1</math> vector of transmitted symbols, <math>\mathbf{y,n}</math> are the <math>N_r \times 1</math> vectors of received symbols and noise respectively and <math>\mathbf{H}</math> is the <math>N_r \times N_t</math> matrix of channel coefficients. An often encountered problem in open loop spatial multiplexing is to guard against instance of high channel correlation and strong power imbalances between the multiple streams. One such extension which is being considered for [[DVB-H#DVB-NGH|DVB-NGH]] systems is the so-called ''enhanced Spatial Multiplexing (eSM)'' scheme. <ref> Sangchul Moon, Woo-Suk Ko, David Vargas, David Gozalvez Serrano, M. Danish Nisar, and Volker Pauli. [http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6221323 "Enhanced Spatial Multiplexing for Rate-2 MIMO of DVB-NGH System"], ''Invited paper'' in the 19th International Conference on Telecommunications, April 2012. </ref>
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| ===Closed-loop approach===
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| A closed-loop MIMO system utilizes Channel State Information (CSI) at the transmitter. In most cases, only partial CSI is available at the transmitter because of the limitations of the feedback channel. In a closed-loop MIMO system the input-output relationship with a closed-loop approach can be described as
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| :<math>\mathbf{y}=\mathbf{HWs}+\mathbf{n}</math>
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| where <math>\mathbf{s} = [s_1, s_2, \ldots, s_{N_s}]^T</math> is the <math>N_s\times 1</math> vector of transmitted symbols, <math>\mathbf{y,n}</math> are the <math>N_r\times 1</math> vectors of received symbols and noise respectively, <math>\mathbf{H}</math> is the <math>N_r\times N_t</math> matrix of channel coefficients and <math>\mathbf{W}</math> is the <math>N_t\times N_s</math> linear [[precoding]] matrix.
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| A precoding matrix <math>\mathbf{W}</math> is used to precode the symbols in the vector to enhance the performance. The column dimension <math>N_s</math> of <math>\mathbf{W}</math> can be selected smaller than <math>N_t</math> which is useful if the system requires <math>N_s (\neq N_t)</math> 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.
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| ==History==
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| * Single-user MIMO
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| ** [[Bell Laboratories Layered Space-Time|Bell Laboratories Layered Space-Time (BLAST)]], Gerard. J. Foschini (1996)
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| ** Per Antenna Rate Control (PARC), Varanasi, Guess (1998), Chung, Huang, Lozano (2001)
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| ** Selective Per Antenna Rate Control (SPARC), Ericsson (2004)
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| *[[Advanced MIMO communication#Multi-user MIMO|Multi-user MIMO]]: Samsung, Qualcomm, Quantenna, Ericsson, TI, Huawei, Philipse, Alcatel-Lucent, Freescale, et al.
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| ** PU<sup>2</sup>RC 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.
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| * '''Enhanced multiuser MIMO'''
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| ** Employ advanced decoding techniques
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| ** Employ advanced precoding techniques
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| ==See also==
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| *[[MIMO]], [[3G MIMO]], [[WIMAX MIMO]] and [[Mimax]]
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| *[[Space–time code]]
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| *[[Space–time trellis code]]
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| *[[Precoding]]
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| ==References==
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| {{Reflist}}
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| ==External links==
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| [1] Louay M.A. Jalloul and Sam. P. Alex, "Evaluation Methodology and Performance of an IEEE 802.16e System", Presented to the IEEE Communications and Signal Processing Society, Orange County Joint Chapter (ComSig), December 7, 2006. Available at: http://chapters.comsoc.org/comsig/meet.html
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| [2] Sam P. Alex and Louay M.A. Jalloul, "Performance Evaluation of MIMO in IEEE802.16e/WiMAX", IEEE J. of Selected Topics in Signal Processing, VOL. 2, NO> 2, April, 2008.
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| {{DEFAULTSORT:Spatial Multiplexing}}
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| [[Category:IEEE 802]]
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| [[Category:Information theory]]
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| [[Category:Radio resource management]]
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The author is recognized by the name of Figures Wunder. My day job is a meter reader. North Dakota is our birth place. He is really fond of performing ceramics but he is struggling to find time for it.
Here is my web site; std testing at home (sneak a peek at this website)