|
|
|
|
|
|
Article
Heterogeneous Networks, Small Cells in 3GPP
by
Samir Amberkar
(published on 9-Jan-2020)
Abstract:
Over time, importance of Small cells and the focus on its support have increased.
This article looks at enhancements made in 3GPP from the perspective of Small cells.
Almost all of the Small cell enhancements for LTE were done till Release 12,
so we shall look at releases from Release 8 till Release 12, with a small mention of Release 13.
Heterogeneous means "different kinds (put together)".
In 3GPP context (4G and later), Heterogenous Network would imply a "radio" network
consisting of "cells" of different "sizes". Practically, the cells shall have
different "radio characteristics" (say line of sight, mobility) and "traffic
characteristics" (say number of users, data speeds).
Putting up fewer cells, each cell covering large area, with optimal overlap between
cells, and appropriate carrier frequencies (well enough in both LOS and NLOS fields)
may be the right planning in rural areas. Same planning may not work in urban areas
which present additional challenges.
Urban areas are likely to have smaller sized open spaces, more and closer buildings,
more users, higher requirement on data speeds, and so on. Operators need to study
these "fields" and then plan their radio networks accordingly. This is a practical
side of it. On 3GPP (Standards) side, features are to be introduced to make Heterogenous
networks possible (say a handover between outdoor cell to indoor cell, interference
between cells, security/access to cells, exploiting field characteristics, overcoming field challenges and so on).
We shall take a look at these features, introduced in LTE and LTE-Advanced (i.e.
Release 8 and onwards).
As cell sizes became smaller (due to increasing user density), there was pressure on
operators to make cell installation cost effective (and preferably scalable and dynamic).
The result is split of eNB into Radio unit and Base band unit. Radio unit usually
contained L1 algorithms (RF/DSP) and Base band unit contained L2 protocols (RRC/MAC).
Small Cell Forum (SCF) introduced standard interface known as FAPI (Functional Application
Platform Interface) between Radio unit and Base band unit. Radio unit could further be
split in Radio Equipment Control (DSP+Control) and Radio Equipment (RF+Antenna), the
industry interface between REC and RE is known as CPRI (Common Public Radio Interface).
Both FAPI and CPRI are industry interfaces and are not part of 3GPP.
We shall look at FAPI and CPRI later in the article.
|
|
|
|
|
|
|
|
|
|
