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| In the field of wireless communication, '''''macrodiversity'''''<ref name=Gesbert2010>D. Gesbert, S. Hanly, H. Huang, S. Shamai, O. Simeone, W. Yu, [http://dx.doi.org/10.1109/JSAC.2010.101202 Multi-cell MIMO cooperative networks: A new look at interference] IEEE Journal on Selected Areas in Communications, vol. 28, no. 9, pp. 1380-1408, Dec. 2010.</ref><ref name=Basnayaka>D. A. Basnayaka, P. J. Smith and P. A. Martin, [http://dx.doi.org/10.1109/TWC.2013.032113.120798 Performance analysis of macrodiversity MIMO systems with MMSE and ZF receivers in flat Rayleigh fading] IEEE Transactions on Wireless Communications, vol. 12, no. 5, pp. 2240-2251, May 2013.</ref> is a kind of [[space diversity]] scheme using several receiver antennas and/or transmitter antennas for transferring the same signal. The distance between the transmitters is much longer than the [[wavelength]], as opposed to [[microdiversity]] where the distance is in the order of or shorter than the wavelength.
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| In a [[cellular network]] or a [[wireless LAN]], macro-diversity implies that the antennas are typically situated in different [[base station]] sites or [[Wireless access point|access points]]. Receiver macro-diversity is a form of [[antenna combining]], and requires an infrastructure that mediates the signals from the local antennas or receivers to a central receiver or decoder. Transmitter macro-diversity may be a form of [[simulcasting]], where the same signal is sent from several nodes. If the signals are sent over the same physical channel (e.g. the channel frequency and spreading sequence), the transmitters are said to form a [[single frequency network]] - a term used especially in the broadcasting world.
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| The aim is to combat [[fading]] and to increase the received signal strength and signal quality in exposed positions in between the base stations or access points. Macro diversity may also facilitate efficient [[broadcasting]] and [[multicasting]] services, where the same frequency channel can be used for all transmitters sending the same information. The diversity scheme may be based on transmitter (downlink) macro-diversity and/or receiver (uplink) macro-diversity.
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| ==Examples==
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| * [[CDMA]] [[soft handoff]]:
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| ** [[UMTS]] [[softer handoff|softer handover]].
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| * [[OFDM]] and [[frequency-domain equalization]] (FDE) based [[Single Frequency Network]]s ('''SFN''') are a form of ''transmitter macrodiversity'' used in broadcasting networks such as [[DVB-T]] and [[digital audio broadcasting|DAB]]
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| ** [[Dynamic Single Frequency Networks]] ([[DSFN]]), where a scheduling scheme adapts the SFN formations dynamically to traffic conditions and/or receiver conditions
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| ** [[802.16e]] [[macro diversity handover (MDHO)]]
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| ** 3GPP [[long term evolution]] (LTE) multicast-broadcast single frequency network (MBSFN), making it possible to efficiently send the same data to many mobiles in adjacent cells.
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| ** [[Cooperative diversity]], for example 3GPP long term evolution (LTE) ''coordinated multipoint transmission/reception'' (CoMP), making it possible to increase the data rate to a mobile situated in the overlap of several base station transmission ranges.
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| ==Forms of Macrodiversity==
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| The baseline form of macrodiversity is called single-user macrodiversity. In this form, single user which may have multiple antennas, communicates with several base stations. Therefore, depending on the spatial degree of freedom (DoF) of the system, user may transmit or receive multiple independent data streams to/from base stations in the same time and frequency resource.
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| *Single-user macrodiversity
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| **Uplink macrodiversity
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| **Downlink macrodiversity
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| In next more advanced form of macrodiversity, multiple distributed users communicate with multiple distributed base stations in the same time and frequency resource. This form of configuration has been shown to utilize available spatial DoF optimally and thus increasing the cellular system capacity and user capacity considerably.
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| *Multi-user macrodiversity
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| **Macrodiversity multiple access channel (MAC)
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| **Macrodiversity broadcast channel (BC)<ref name=Karakayali>M. K. Karakayali, G. J. Foschini, and R. A. Valenzuela, [http://dx.doi.org/10.1109/MWC.2006.1678166 Network coordination for spectrally efficient communications in cellular systems] IEEE Wireless Communication Magazine, vol. 13, no. 4, pp. 56-61, Aug. 2006.</ref><ref name=fnt2013>E. Björnson and E. Jorswieck, [http://kth.diva-portal.org/smash/get/diva2:608533/FULLTEXT01 Optimal Resource Allocation in Coordinated Multi-Cell Systems], Foundations and Trends in Communications and Information Theory, vol. 9, no. 2-3, pp. 113-381, 2013.</ref>
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| ==Mathematical description==
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| [[File:Macrodiversity mimo mac 2013.jpg|thumb|500px|Typical multi-user macrodiversity uplink communication scenario with three base stations (BS) and two mobile stations (MS). All BSs are connected to a back-haul processing unit (BPU).<ref name=Basnayaka />]]
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| The macrodiversity multi-user [[MIMO]] uplink communication system considered here
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| consists of <math>\scriptstyle N</math> distributed single antenna
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| users and <math>\scriptstyle n_{R}</math> distributed single antenna
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| base stations (BS). Following the well established narrow band flat
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| fading [[MIMO]] system model, input-output relationship can be given as
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| :<math>\mathbf{y} = \mathbf{H}\mathbf{x} + \mathbf{n}</math> | |
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| where <math>\scriptstyle\mathbf{y}</math> and
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| <math>\scriptstyle\mathbf{x}</math> are the receive and transmit
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| vectors, respectively, and <math>\scriptstyle\mathbf{H}</math> and
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| <math>\scriptstyle\mathbf{n}</math> are the macrodiversity channel
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| matrix and the spatially uncorrelated [[AWGN]] noise vector,
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| respectively. The power spectral density of [[AWGN]] noise is assumed to
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| be <math>\scriptstyle N_0</math>. The <math>\scriptstyle
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| i,j</math>th element of <math>\scriptstyle\mathbf{H}</math>, <math>h_{ij}</math>
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| represents the fading coefficient (see [[Fading]]) of the <math>\scriptstyle i,j</math>th constituent link
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| which in this particular case, is the link between
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| <math>\scriptstyle j</math>th user and the <math>\scriptstyle
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| i</math>th base station. In macrodiversity scenario,
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| :<math>E \left \{ \left| h_{ij} \right |^2 \right \} =
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| g_{ij} \quad \forall i,j</math>,
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| where <math>\scriptstyle g_{i,j}</math> is called the average link
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| gain giving average link [[Signal-to-noise ratio|SNR]] of <math>\scriptstyle
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| \frac{g_{ij}}{N_0}</math>. The macrodiversity power profile matrix<ref name=Basnayaka />
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| can thus be defined as
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| :<math> \mathbf{G} = \begin{pmatrix}
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| g_{11} & \dots & g_{1N} \\
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| g_{21} & \dots & g_{2N} \\
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| \dots & \dots & \dots \\
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| g_{n_R1} & \dots & g_{n_RN} \\
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| \end{pmatrix}.
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| </math>
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| The original input-output relationship may be rewritten in terms of
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| the macrodiversity power profile and so-called normalized channel
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| matrix, <math>\mathbf{H}_w</math>, as
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| :<math>\mathbf{y} = \left( \left( \mathbf{G}^{\circ\frac{1}{2}} \right) \circ \mathbf{H}_w \right)
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| \mathbf{x} + \mathbf{n}</math>.
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| where <math>\mathbf{G}^{\circ \frac{1}{2}}</math> is the element-wise
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| square root of <math>\mathbf{G}</math>, and the operator, <math>\circ</math>, represents Hadamard
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| multiplication (see [[Hadamard product (matrices)|Hadamard product]]). The <math>\scriptstyle
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| i,j</math>th element of <math>\mathbf{H}_w</math>, <math>h_{w,ij}</math>, satisfies the condition given by
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| :<math>E \left \{ \left| h_{w,ij} \right |^2 \right \} = 1 \quad \forall i,j </math>.
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| It has been shown that there exists a functional link between the [[permanent]] of marodiversity power profile matrix, <math>\mathbf{G}</math> and the performance of multi-user macrodiversity systems in fading.<ref name=Basnayaka /> Although it appears as if the macrodiversity only manifests itself in the power profile, systems that rely on macrodiversity will typically have other types of transmit power constraints (e.g., each element of <math>\mathbf{x}</math> has a limited average power) and different sets of coordinating transmitters/receivers when communicating with different users.<ref name=fnt2013 /> Note that the input-output relationship above can be easily extended to the case when each transmitter and/or receiver have multiple antennas.
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| ==See also==
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| *[[MIMO]]
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| **[[Multi-user MIMO]]
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| * [[Antenna diversity]]
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| * [[Diversity scheme]]s
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| * [[Diversity combining]]
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| ** [[Maximum ratio combining]]
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| ** Selective combining
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| * [[Diversity gain]]
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| * [[Microdiversity]]
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| * [[Many Antenna]]
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| * [[Distributed antenna system]]
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| | |
| ==References==
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| {{reflist}}
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| [[Category:Antennas]]
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| [[Category:Radio resource management]]
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