Macrodiversity
In the field of wireless communication, macrodiversity[1][2] is a kind of space diversity scheme using several receiver or transmitter antennas for transferring the same signal.
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.
Transmitter macro-diversity may be a form of simulcasting, where the same signal is sent from several nodes.
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.
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.
The macrodiversity multi-user MIMO uplink communication system considered here consists of
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
are the macrodiversity channel matrix and the spatially uncorrelated AWGN noise vector, respectively.
The power spectral density of AWGN noise is assumed to be
The macrodiversity power profile matrix[2] 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,
, satisfies the condition given by It has been shown that there exists a functional link between the permanent of macrodiversity power profile matrix,
[2] 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
has a limited average power) and different sets of coordinating transmitters/receivers when communicating with different users.
[4] Note that the input-output relationship above can be easily extended to the case when each transmitter and/or receiver have multiple antennas.
