Macrodiversity
In the field of wireless communication, macrodiversity is a kind of space diversity scheme using several receiver 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. In a cellular network or a wireless LAN, macro-diversity implies that the antennas are typically situated in different base station sites or 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 the spreading sequence), the transmitters are said to form a single-frequency network—a term used especially in the broadcasting world. 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 multicast 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. Forms. 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. 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. Mathematical description. The macrodiversity multi-user MIMO uplink communication system considered here consists of formula_1 distributed single antenna users and formula_2 distributed single antenna base stations (BS). Following the well established narrow band flat fading MIMO system model, input-output relationship can be given as where formula_4 and formula_5 are the receive and transmit vectors, respectively, and formula_6 and formula_7 are the macrodiversity channel matrix and the  spatially uncorrelated AWGN noise vector, respectively. The power spectral density of AWGN noise is assumed to be formula_8. The formula_9th element of formula_6, formula_11 represents the fading coefficient (see Fading) of the formula_12th constituent link which in this particular case, is the link between formula_13th user and the formula_14th base station. In macrodiversity scenario, where formula_16 is called the average link gain giving average link SNR of formula_17. The macrodiversity power profile matrix can thus be defined as The original input-output relationship may be rewritten in terms of the macrodiversity power profile and so-called normalized channel matrix, formula_19 , as where formula_21 is the element-wise square root of formula_22, and the operator, formula_23, represents Hadamard multiplication (see Hadamard product). The formula_9th element of formula_19, formula_26, satisfies the condition given by It has been shown that there exists a functional link between the permanent of macrodiversity power profile matrix, formula_22 and the performance of multi-user macrodiversity systems in fading. 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 formula_29 has a limited average power) and  different sets of coordinating transmitters/receivers when communicating with different users. Note that the input-output relationship above can be easily extended to the case when each transmitter and/or receiver have multiple antennas.