As a consequence of the proliferation of smart phones and tablets, data traffic is growing significantly, both on the radio access links and the backhaul infrastructure of mobile operators’ networks. And although LTE and LTE Advanced offer higher data traffic throughput than that of 3G, given to their wider allocated bandwidths, the combined capacities of even these networks is not sufficient to meet projected future capacity demands. The conventional solution to increasing the capacity of LTE mobile networks includes splitting macro-cells and/or adding more sites. Both of these solutions require high CAPEX and OPEX, so mobile operators are seeking new and cost effective ways of increasing their network capacity. One solution is to deploy small-cell base stations (BSs) within their existing macro-cellular networks, an approach referred to as Heterogeneous Networks. It is well known that a HetNet not only increases the network capacity, but also provides better coverage and enhances the user’s experience. These benefits are achieved by offloading data traffic dynamically from MCBSs to SCBSs using an algorithm based on several parameters such as the characteristics of the traffic, the required QoS and network

1. 1. Introduction
2.
Contents of Paper:
1. Introduction
2. Composition of
Heterogeneous Network
3. Base Station Classification
Based on the Rated Power
4. LTE Base Station
Composition
5. Macro Cell Base Station
6. Micro Cell Base Station
7. Pico Cell Base Station
8. Femto Cell Base Station
9. Repeater Cell Base Station
10. Relay Cell
Sukhvinder Malik, Mohit Luthra, Rahul Atri, Mehdi Sadeghian January 10, 2016
Heterogeneous Network (HetNet)
A Short Description on HetNet Elements
As a consequence of the proliferation of smart phones and tablets, data
traffic is growing significantly, both on the radio access links and the
backhaul infrastructure of mobile operators’ networks. And although
LTE and LTE Advanced offer higher data traffic throughput than that of
3G, given to their wider allocated bandwidths, the combined capacities
of even these networks is not sufficient to meet projected future capacity
demands.
The conventional solution to increasing the capacity of LTE mobile
networks includes splitting macro-cells and/or adding more sites. Both
of these solutions require high CAPEX and OPEX, so mobile operators
are seeking new and cost effective ways of increasing their network
capacity. One solution is to deploy small-cell base stations (BSs) within
their existing macro-cellular networks, an approach referred to as
Heterogeneous Networks.
It is well known that a HetNet not only increases the network capacity,
but also provides better coverage and enhances the user’s experience.
These benefits are achieved by offloading data traffic dynamically from
MCBSs to SCBSs using an algorithm based on several parameters such
as the characteristics of the traffic, the required QoS and network
congestion.

2. 2. Composition of Heterogeneous Network
There are two types of Networks:
 Homogenous Network
 Heterogeneous Network
HetNet Network Has Two Layers:
 Macro Cell Base Station
Layer
 Small Cell Base Station
Layer
Different types of Cell in HetNet:
 Macro Cells
 Micro Cells
 Pico Cells
 Femto Cells
 Repeater Cells
 Relay Cells
A network which consists of only one type of cell(i.e. macro or small
cell) is known as a homogenous network where as network composed of
multiple types of cells(Macro, Micro, Pico and Femto) from same or
different technology is known as a heterogeneous network.
The figure below shows the composition of HetNet components:
At high level this can be divided in two major Layers.
 Marco Cell Base Station Layer (MCBS)
 Small Cell Base Station Layer (SCBS)
Macro Cell Base Station layer provide the overlay coverage to the
morphology and mainly used to cover maximum area by installing the
antennas at some height either on Tower, mast or may be on the wall of
high rise building.
Here the UE are quite away from the base station and the minimum
coupling loss 70 dB between the UE and Base station so based on this
the best signal at can see is 55-65 dBm of RSRP. This layer of base
station covers most of the outdoor area and limited indoor area. In
MCBS layer the Macro cell have multi sector deployments.
Small Cell Base Station layer provide the underlay coverage and covers
the outdoor and indoor area. This layer composed of Micro, Pico and
Femto, Repeater types of cell. While comparing with the Macro Cell
Base Station layer here UE is much closer to the base station and
minimum coupling loss can be seen about 50 dB, but due to reduction in
transmit power at the cell the best signal seen at the UE remains same.

3. 3. Base Station Classification Based on the Rated
Power
4. LTE Base Station Compositions
As Per 3GPP, there are Four Types
of Base Station Classes.
 Wide Area Base Station
 Medium Area Base Station
 Local Area Base Station
 Home Base Station
 Specification gave Rated Power
for one antenna Configuration.
 Designer needs to main this
Maximum power per port while
designing multi port Remote
Radio Head.
As per 3GPP reference 36.104 release 12, there are four classes for the
base stations based on the rated power is listed below
S. No. Base station
Class
Rated Output Transmission Power
1 Wide Area Base
Station
No Upper limited defined by 3GPP, Max
power is restricted by local Regulatory
2 Medium Area
Base Station
<=38 dBm for single antenna Port
3 Local Area Base
Station
<= 24 dBm for single antenna Port
4 Home Base
station
<=20 dBm for single antenna Port
The rated power defined here is for single antenna configuration and it
will be divided across antenna ports when more than one antenna is
used. For example a Home Base station the max rated power is 20 dBm
for one antenna, if we change the antenna configuration to 2 antenna
configuration then per antenna port power will reduced to 17dBm.
Here it can be clearly seen whenever doubling the antenna port the
power is reduced by 3dB (Half of the power), so for 4 antenna
configuration it will be further reduced by 3dB providing 14 dBm power
per antenna port and so on. Form here it can be concluded that the
specification provides the max rated power and a designer need to take
this in consideration while designing the power amplifier and other
active elements of base station Radio.
In traditional 2G and 3G base-station the base band unit and Radio Unit
are enclosed in a single chassis, then the RF feeder cables are connected
to the antenna. This type of topology passes high losses due to lengthy
RF cables.
The 4G LTE bases stations are next generation base stations and having
advance split architecture where base unit and Radio unit are kept in
two different enclosures named as Base Band Unit/Digital Unit
(BBU/DU) and Remote Radio Head (RRH).

4. Base Band Function:
 Call processing, resource
allocation and OAM.
 GTP, PDCP, OAM, RRC, RRM
processing, Subscriber data
traffic processing.
 Reception of the GPS signal
and creation and supply of the
clock.
 Fault diagnosis and alarm
collection and control.
 Fast Ethernet/Gigabit Ethernet
interface to backhaul.
 RLC, MAC/PHY processing.
Base band unit and Remote Radio Head can be connected using very
famous optical interface known as CPRI or OBSAI.
The advance of this spilt architecture is that, the RRH can be kept as
close as possible to antenna and loss due to RF cables can be
minimized. This new topology enables the centralized baseband
concept, where multiples sector baseband processing can be kept in one
centralized location and dark fiber can be run to remote location where
RRH and antennas are placed. This helps MNOs to save lots of money
as OPEX and CAPEX.
LTE eNodeB Building Blocks:
As it is know that LTE eNodeB is consist of BBU and RRH. Below
diagram show the block/subsystems of a LTE Base Band unit.
Base Band Unit: It performs all L1, L2 and L3 process of eNodeB.
Transport Unit: This block communicates with the outer world over IP
link like communication to MME, Gateway and other eNodeB.
Power Sub-system: It provides the power to the each subsystem.
OAM & Evn. Monitoring Subsystem: This subsystem is used for
configuration purpose and it also monitor the environment like Temp,
humidity etc. and based on that it can optimized other operations, for
example when temp is increased eNodeB can automatically turn on the
fans.

5. Remote Radio Head Functions:
 Up conversion/down
conversion of frequency.
 High-power amplification of RF
transmission signal.
 Suppression of out-of-band
spurious wave emitted from RF
Rx/Tx signal.
 Gain control of RF Rx/Tx
signal.
 Rx/Tx RF signal from/to an
antenna.
 Low noise amplification of
band-pass filtered RF Rx signal.
 Network Sniffer mode for SON
purpose.
Control Unit: This is the master block of an eNodeB which controls all
other block functionality. It controls all the functions reside in eNodeB
Remote Radio Head is the radio part of LTE eNodeB. It receives IQ
sample from the Base Band over the CPRI and converts them to Radio
frequency. A RRH have following blocks to perform this function.
Transmit chain takes the digital data from base band unit and convert
that digital signal to analog signal and up convert the analog signal to
RF frequency. Transmit chain includes RF filter, mixer, driver
amplifier, power amplifier, circulator etc. Most of the power of RRH is
consumed by power amplifier.
Receive chain converts the incoming RF signal back to digital signal.
Receive chain includes Low Noise amplifier, RF filter, mixer etc.
In FDD technology, duplexer is used at the end of transmit chain and in
TDD technology, TDD switch is used which switches between transmit
and receive chain.
There may be multiple transmit and receive chains as per design
requirements. For example for implementing 2x2 MIMO, there are two
transmit chains on the eNodeB side and two receive chains on the
receiver side.
For implementing SON feature in LTE network, there is one separate
receiver chain that includes wide band components like wide band low
noise amplifier, wide band filters etc. Mode of having this chain in RRH
is called Network Listen Mode or Network Sniffer mode. This chain
helps detecting neighbor Cells of GSM, WCDMA, LTE and thus
accordingly self-configuration of RRH, interference mitigation with
other eNodeBs etc.
Receive Chain
Duplexer or
TDD Switch
Transmit Chain
CPRI

6. Macro Cell Base Stations:
 Known as “Wide Area
Network” BS as per 3 GPP.
 Max Transmit Power for Macro
is limited by local Regulators.
 Macro cell use antenna above
the rooftop level and cover
large area.
 It uses directional antenna to
cover large area.
5. Macro Cell Base Station
Macro Cell base station fall under the category of “Wide Area Network”
specified by the 3GPP. The macro cells are characterized by having the
antenna above the rooftop level so that it can cover the large area. The
Max rated power this types of cell is not defined by the 3GPP but they
have given that per antenna port power should not be less than 10 Watts
or 40 dBm.
The upper transmit power for macro cell is restricted by the local
Regulatory for each region of Globe. The telecom regulatory provides
the Max EIRP (Effective Isotropic Radiated Power) limits and it is
responsibility of MNOs (Mobile Network Operators) to meet these
requirements to limit the health hazards due to excessive RF
transmission.
Here is the example to understand it more clearly, let’s say one country
has the upper limits of EIRP of 60 dBi. This power limits includes
antenna gain also, so operator need to ensure that transmit power should
not exceed the upper limit. If it is a 4x4 MIMO base station and each
transmit port’s power is 40 dBm then composite four port power is 46
dBm (Four times in dB scale is 6 dB). And gain of antenna being used
is 17dBi (dBi is gain compare to Isotropic antenna) then total
transmission power is EIRP = 46+17=63 dBi which exceeds the upper
limits of Regulatory.
Then it has only two option ether it need to reduce the power at the
base station or use an antenna with less gain. With same 17 dBi antenna
it need to reduce the per port power to 37 dBm to achieve total EIRP of
60dBi (43+17=60dBi) or with 40 dBm it can use an antenna with gain
of 14 dBi to transmit within limits. A Macro base station is consist of a
baseband unit which does all digital signal processing and a Remote
Radio Unit (RRU) (RF part) which are connected via an interface called
CPRI, (Common Personal Radio Interface) a fiber connection.

7. Macro Cell Base Stations:
 Macro cell should have
sensitivity atleast of -101.5
dBm.
 It support MIMO and uses cross
polarized antenna in
deployments to get good MIMO
benefits.
 Use CPRI while connecting
Remote Read Head and Base
Band.
 Provide Outdoor Coverage.
Properties of Macro Cell Base Station:
 Macro cell should have better sensitivity compare to other base
station which is of atleast -101.5 dBm when operating at 20
MHz channel bandwidth to achieve high uplink throughput with
lower received signals.
 It can be deployed with active antenna system where the remote
radio unit can be deployed just behind the antenna elements
inside the antenna enclosure. This avoids the losses due to feeder
cable between antenna and remote radio head.
 Macro cell generally uses cross polarized directional antenna
where antenna elements are kept at +/- 45 degrees.
 It support MIMO configuration both in uplink and downlink
with 2x2 or 4x4 MIMO or more
 Macro cell covers large area having a radius of few hundreds of
meters (Radius depends on the Morphology, operating
Frequency and Height of Transmitter)
 Macro cell support large number of user more than 200
connected user per sector
 Macro cell support Multi sector deployments, theoretical a
macro cell can support up to 256 cell or sectors as per 3 GPP
specifications.
 Major contribution in providing the outdoor coverage.

8. Micro Cell Base Stations:
 Known as “Medium Range
Base Station” BS as per 3 GPP.
 It’s power is more than 20 dBm
but less than 38 dBm for single
antenna.
 In deployments, the antenna
installed for Micro base station
is below the rooftop level.
 They can use both direction
antenna and Omni antenna
based on the deployment
scenarios.
 They have high average sector
throughput compare to Macro
base stations.
6. Micro Cell Base Station
Macro Base station fall under “Medium Range Base station” category
defined by the 3GPP where power should not be more than the 38 dBm
and should not be less than 20 dBm. These base stations are very similar
to macro base station in terms of deployment, main difference is output
transmit power. Here due low transmission power, the size of remote
radio unit is reduced significantly because low power requirement need
small size power amplifier and less number for components.
Properties of Micro Cell Base Station:
 Micro cells are basically deployed by having their antenna below
rooftop so that its coverage tends to the interested area only to
avoid the overshooting coverage.
 It has cell coverage of few hundred meters and is deployed at a
location where signal strength from macro cell is very week.
 A Micro cell can be deployed with directional antenna or with
Omni antenna based on the area to be covered.
 Macro cell is generally deployed co-channel to macro cell base
station
 Macro cell base stations can be used for both outdoor as well as
indoor coverage
 The main objective to deploy the micro cell to fill the large
coverage hole not covered by macro cells and to meet the
capacity requirements.
 A micro cell can support the same number of users as of Marco
cell while assuming same macro base station’s baseband is used
with low power radio unit.
 The UE is much closer to the micro cell and the minimum
coupling loss is considered about 50-55dB between UE and
micro base station.
 Micro cell provide high average sector throughput compare to
Macro cell because UE are more closer to base station result is
good signal to noise ration providing higher modulation and
spectral efficiency.
 The UE is much closer to the micro cell and the minimum
coupling loss is considered about 50-55dB between UE and
micro base station.

9. Pico Cell Base Stations:
 Known as “Local Area Base
Station” BS as per 3 GPP.
 Its power is more than 20 dBm
but less than 24 dBm for single
antenna.
 While deploying it uses Omni
and panel Antenna.
 Small size and light weight base
stations
 Micro cell provide high average sector throughput compare to
Macro cell because UE are more closer to base station result is
good signal to noise ration providing higher modulation and
spectral efficiency.
 In micro cell deployment the user gets best MIMO performance
benefits due to scattering from the neighboring building. MIMO
requires to un-correlated channel to provide the best effort and
scatter may help to reduce the correlation between the propagation
paths results in improvement in performance of MIMO.
7. PICO Cell Base Station
The Pico cell Base station comes under the “Local Area Base stations”
category defined by 3GPP. The transmission power for the PICO cell
base station should be not be more than 24 dBm and should not less
than 20 dB for single antenna configuration.
Properties of PICO Cell Base Station:
 Pico cell base station has low power and relatively small coverage
areas due to less max output power
 It is mainly used for dedicated indoor coverage and deployed close
to Users
 A PICO cell can support 2 antenna,4 antenna and 8 antenna
configuration and based on this per antenna power will change. For
2 antennas Pico Base station Max rated output power is 21dBm per
port, 4 antennas it will be 18dBm per port and for 8 antennas it will
be 15dBm.
 It can be deployed co-channel with macro cell and micro cell base
station
 A PICO cell have baseband and radio head in the same box results
in less footprint , compact in size and light weight. This make site
acquisition easy for deployment
 It uses small antenna and provide indoor coverage with Omni
directional, ceiling mounted, wall mounted panel antenna.
 PICO cell base stations are single sector base station with less
number of connected users compare to macro and micro base
stations

10. Pico Cell Base Stations:
 Known as “Home Base Station”
BS as per 3 GPP.
 Femto cell can transmit Max
upto 20 dBm
 Femto Cell have base band unit
and Radio Head unit in same
enclosure.
 These are plug and play device
and can be as hot-spot or
personal base station
 It supports all three access
mode open Access, Close
Access and Hybrid Access
 Mostly Deployed with Omni
antennas
8. Femto Cell Base Station
A Femto cell base station is known a “Home Base Station” as per
3GPP specifications. The max rated transmit power Femto cell is
limited to 20 dBm per antenna port and it can be designed to support
up to 8x8 antenna configuration.
Properties of FEMTO Cell Base Station:
 The Femto Cell base stations are mainly used at home or in small
offices. Their transmit power is very less so they are intended to
provide the coverage in indoor location closer to user.
 Femto cell base station is very small in size and portable. The
location of Femto cell base station is not controlled by the MNOs,
the personal can carry and use where one wants e.g. during
weekend a user want to use it at home and during weekdays he
want to use at office.
 These are plug and play devices and having slightly different
deployment architecture compare to other types of base stations.
It supports two types of architecture with Femto Gateways and
without Femto gateways. The connection between Femto cell and
Femto gateway is similar to home broadband connection e.g.
ADSL line to communicate to EPC elements.

11. Repeater Cell Base Stations:
 A repeater cell is used for
coverage extension.
 It act as an mediator between
Macro Cell and User
Equipments
 A repeater cell uses two antenna
one as donor antenna and other
is coverage antenna
 Donor antenna should be more
directive antenna to get more
signal from the Macro donor
cell
 The coverage antenna generally
used is a Omni antenna or a
Panel Antenna to limit the
coverage to only indented area
 It does not have any intelligence
just amplify the signal in uplink
and Downlink directions.
 It transmits the same PCI of
Macro Cell , so UE does not
aware about the presence of
repeater cell.
 It can operate on the same frequency channels where Macro,
Micro, Pico base station are transmitting.
 As Femto cell location is not fixed so during the network design
operator reserves a pool of the PCIs for Femto cell and Femto
cell select PCI from the pool after network scan
 A Femto cell can support three types of access mode , open cell,
Hybrid cell and CSG cell configuration. With Open cell
configuration a user can connect to it, while it is configured with
the CSG configuration only CSG user can connect to it(kind of
private cell) where as the Hybrid cell configuration provide all
access to both CSG users as well as the normal users.
 Femto cell are mostly deployed with the Omni directional
antennas and multiple Omni antenna with sufficient distance
(2 lambda distance required to get the best MIMO performance)
can be installed to get the MIMO capabilities.
9. Repeaters/Booster Cell Base Stations
A repeater is used to provide the extended coverage of already
deployed macro base station. It re-transmits the uplink and
downlink signals without decoding the content. Repeaters have two
antennas installed, one toward the donor macro cell while second
antenna toward the intended area where coverage is to be provided.
Repeaters are transparent to the functionality of the donor cell
means the macro cell which is acting as the donor cell does not
have any knowledge of repeater.
Properties of Repeater Cell Base Station:
 Repeaters amplify the signal in both uplink and downlink
directions to provide the extended coverage.
 Based on the implementation a repeater may automatically
configure their gains based upon the signal measurement from
the donor cell.
 A repeater should provide equal gain in both directions to
maintain the both uplink and downlink link symmetric.

12. Relay Cell:
 Relay Cells are similar to
repeater but they are intelligent
and defined in release 10 of
3GPP
 It uses LTE macro coverage as
backhaul over Un interface and
provides its own coverage.
 Relay cell also use two antenna
concept same as repeater cell
know as donor and coverage
antenna
 Relay also use a Physical cell
ID and UE treats its as a
separate cell.
 Based on the signal
measurements a UE can
perform handover between a
relay cell and Macro cell.
 While designing a repeater, it is to be ensure that both donor
antenna and coverage antenna have proper isolation to avoid the
own transmission loop. If both the antennas are not properly
isolated then donor antenna may receive the signal from the
coverage antenna along with the signal from the macro cell base
station.
 Repeater introduces some delay to the signal received from UE
as first it receive and then transmit toward the macro cell over the
air. Macro cell timing advance accounts this delay so that UE
uplink synchronization is maintained.
 A repeater cell can use directional antenna (Narrow beam)
pointing toward donor cell to get point to point link while the
coverage antenna at repeater can be less directive with wider
beam to provide the coverage to large area.
10. Relay Cell
Relay Nodes are introduced from 3GPP release 10 as a part of LTE
advance. A relay node looks similar to repeater cell base station as
it also have same concept of donor cell antenna and coverage
antenna and used for coverage extension of the LTE network.
Properties of Relay Cell:
 Relay does not use wired backhaul, it uses LTE network as
backhaul and that interface is known as “Un” interface. This
interface support both user and data plane of normal LTE.
 Relay node transmits its own Physical cell ID and for UE it
appears a separate cell, while repeater transmits the same PCI as
of donor cell.
 Relay cell introduces additional delay in data transfer as first
donor eNodeB schedule data for relay node and then relay node
schedule it for the UE.
 Relay does not have same processing layer as an eNodeB has
like Physical layer, MAC, RLC and PDCP in user plane and
RRC, NAS along with Physical, MAC, RLC and PDCP in
control plane.

13. Authors
Disclaimer:
Authors state that this whitepaper has been compiled meticulously and to the best of their
knowledge as of the date of publication. The information contained herein the white paper is
for information purposes only and is intended only to transfer knowledge about the
respective topic and not to earn any kind of profit.
Every effort has been made to ensure the information in this paper is accurate. Authors does
not accept any responsibility or liability whatsoever for any error of fact, omission,
Mehdi Sadeghian
He holds M.Sc. degree from
the department of Comp.
Network in Islamic Azad
University, 2014 .
His research areas include
Wireless Network, telecomm.
and etc.
Sukhvinder Malik
He holds Bachelor Degree in
engineering from MDU
University, 2010.His area of
interest including testing and
designing the next
generations’ network
including 4G, 5G.
Rahul Atri
He holds Bachelor Degree in
engineering from PTU
University, 2010.His area of
interest including testing and
designing the next
generations’ network
including 4G, 5G, Wifi etc
Mohit Luthra
He holds Bachelor Degree in
engineering from MDU
University, 2010. His area of
interest includes RF
Hardware design &
development, testing etc.
11. Conclusion
In this paper authors have discussed about different types of LTE
base station which are part of HetNet. Authors have provided the
short descriptions about the properties and deployment architecture
of each types of base station. A HetNet network is consist of Macros,
Micros, small cells (Pico and Femto), repeaters and replays.
They provided the information about the Power limits of each types
of base station and mapped them with 3GPP specifications. They
also provided the information about composition of a base station
providing functionality of base band and radio head. The deployment
scenarios for each types of base station also discussed.