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Depolyment concepts of fronthaul/backhaul/moving cells/small cells/split user plane need centralised RRM and/or more flexible radio access.
In [11] , it is called "Cloud-RAN".
Basic idea behind Cloud-RAN is having virtual RAN on top of actual physical RAN (consisting of distributed and connected BB units and RF units).
As the name indicate, Massive MIMO is using large number of antenna elements (placed in matrix pattern).
Basic idea behind Massive MIMO is spatial multiplexing i.e. multiplexing signals received from multiple antenna elements separated in calculated space.
In reverse direction, by configuring (phase shift change) each antenna element,
transmitted signals may be made to converge or overlap happily on receiver's location.
The result is low inter-frequency interference and so high spectral efficiency.
This type of signal convergence or beamforming may be done in both vertical and horizontal dimensions.
As higher band (say > 30 GHz) have lesser penetration (more reflection), higher bands may be used.
Thus Massive MIMO with higher carrier frequencies seem well suited in (outdoor) urban areas
(characterised by relatively dense number of constructions).
Outdoor wireless backhaul link is likely to use beamforming for its operation.
Another MIMO variant is Network MIMO or CoMP (Coordinated Multi-Point), part of LTE-Advanced in Rel 11.
Idea is: multiple cells coordinate to provide better reception at user location.
Refer [12] for more information.
Amount of data flowing in downlink and uplink keep changing over a period of time.
Amount of data in downlink is almost always much higher compared to that in uplink.
Dynamic DL:UL ratio adjustment help in achieving efficient use of radio resources.
TDD (Time Division Duplexing), by its concept, offer unequal or equal allocation of resources in downlink and uplink.
FDD, on the other hand, require protocol support to adjust DL:UL ratio dynamically (which carriers are downlink and which ones are uplink).
As pointed out on page 5 , user and machine communications have different requirements.
Also, the requirements for some of the new services may be take care of existing technology and/or networks.
We shall need networks to handle 5G intended services and any future services that may come.
Say we have network with individual/split components,
each component mapped to one (or more) network functions, and
these (virtual) components may be connected to provide particular broad service.
Components may be mapped to existing network elements from existing RATs.
The concept is being implemented in 3GPP under the title of "network slicing".
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