Small cells are Low-powered radio access nodes, Operate in licensed and unlicensed spectrum, Short range mobile phone base stations, Range from very compact residential femto-cells of area 10 meters to larger equipment used inside commercial offices or outdoor public spaces of area 1 or 2 kilometers, "small" compared to a mobile macro cell, with range of a few tens of kilometers, Complements mobile phone service from larger macro cell towers, Offer excellent mobile phone coverage and data speeds at home, in the office and public areas for both voice and data, Developed for both 3G and the newer 4G/LTE radio technologies.
Femto cells are Initially designed for residential and small business use with a short range and a limited number of channels. Femtocell devices use licenced radio spectrum. Femto cells must be operated and controlled by a mobile phone company, One cell with one mobile phone operator. When in range, the mobile phone will detect cell and use it in preference to the larger macrocell sites. Calls are made and received in exactly the same way as macrocell. Except, the signals are sent encrypted from the small cell via the public or private broadband IP network to one of the mobile operators main switching centres.
Small Cell Types
Femto cell :
Power and Quality
Security and Management
Components and building
Timing and synchronization
Low-powered radio access nodes.
Operate in licensed and unlicensed spectrum.
Short range mobile phone base stations.
Range from very compact residential femto-cells of
area 10 meters to larger equipment used inside
commercial offices or outdoor public spaces of
area 1 or 2 kilometers.
"small" compared to a mobile macro cell, with
range of a few tens of kilometers.
Complements mobile phone service from larger
macro cell towers.
Offer excellent mobile phone coverage and data
speeds at home, in the office and public areas for
both voice and data.
Developed for both 3G and the newer 4G/LTE radio
Small cells may encompass femtocell, picocell and
Small cells provide a small radio footprint, ranging
from 10 meters within urban and in-building
locations to 2 km for a rural location.
Picocells and microcells can also have a range of a
few hundred meters to a few kilometers,
But they differ from femtocells in that they do not
always have self-organising and self-management
networks can also
be realized by
The most common form of small cells.
Initially designed for residential and small business
use with a short range and a limited number of
Femtocells with increased range and capacity is
frequently known by names like:
Class 3 femtos,
Femtocell devices use licenced radio spectrum.
Must be operated and controlled by a mobile
One cell with one mobile phone operator.
When in range, the mobile phone will detect cell
and use it in preference to the larger macrocell
Calls are made and received in exactly the same
way as macrocell.
Except, the signals are sent encrypted from the
small cell via the public or private broadband IP
network to one of the mobile operators main
Making and receiving calls uses the same
procedures and telephone numbers as macro-cell.
All standard features- call divert, text messaging,
web browsing are available in the same way.
Data services should operate more quickly and
efficiently due to the short range involved.
Power & Quality
Small cells operate at very low radio power levels.
Less than cordless phones, Wi-Fi or some other
This substantially increases the battery life, both on
standby and talk time.
In close vicinity to the handset or mobile device,
call quality is excellent.
data devices can operate at full speed.
Most indoor products have standard capacity of 8.
The smallest femtocells can handle up to 4
simultaneous active calls from different users.
Larger small cell designs for business (enterprise) or
public areas use can handle 16, 32 or more
concurrent calls or data sessions.
A few of the latest multi-mode 3G and LTE small
cells can cope with up to 64 3G and 128 LTE
concurrent active sessions.
Restrictions can be applied on who can access a
Security & Management
Small cells encrypt all voice and data sent and
Ensures a high level of protection from sniffing or
In order to reduce operational and installation costs,
these units are self –installing
sense which frequency to transmit on and power level to
Unlike large outdoor mobile phone base stations they –
don't require specialists to design, calibrate or configure
minimise the on-going cost of maintaining them.
They have remote management from the network
operator to upgrade the configuration and software as
Compatible with 3G and 4G mobile phones.
No additional software required.
Same interface for radio to mobile phone and to
Compatible with existing mobile phone networks,
phones and services.
3G UMTS- Small cell subsystem connects into
operator's core network using IU interface same as
traditional outdoor cell sites.
LTE- Standard S1 interface to the core is used,
conforming to standard radio transmission
frequencies and protocols of today.
MSC and data switch (SGSN) communicate with
the small cell controller same way as other mobile
Services like phone numbers, call diversion,
voicemail operate in exactly the same way and
appear the same to the end user.
The small cell appears to the standard 3G or LTE
phone as just another cell-site from the host mobile
Can be used by any phone including roamers from
The connection between the small cell and
controller/gateway is the Iu-h interface.
It uses a secure IP encryption (IPsec) to avoid
LTE uses the standard S1 interface protected by
Authentication of the small cell ensures valid access
Each small cell connects with a small cell gateway
over broadband IP.
Gateway consolidates hundreds of thousands of
small cells into a single IU or S1 interface.
Carries thousands of concurrent calls and data
Complete working of a mobile phone base station
is inside femtocell .
Additional functions like RNC (Radio Network
Controller) processing also included.
May have Core network element to manage data
The extra capabilities demand it to be self-installing
Requires S/W to scan environment continuously for
frequencies, power level , scrambling codes.
Femtocell gateways aggregate large numbers of
femtocell connections (typically 100,000 to 300,000).
These are first securely connected through high
capacity IP security firewalls.
Industry has standardised on common solutions
published by the 3GPP standards committees.
There are three architectures, one for each of the
three main different radio technologies-
UMTS - the most common and used for today's 3G UMTS
CDMA- applies to 3G CDMA femtocells compatible with 3G
LTE- the 4G standard uses a different approach, having
incorporated small cells into the system from the outset.
3GPP (3rd generation partnership project)
UMTS(Universal Mobile Telecommunication System)
CDMA(Code Division Multiple Access)
LTE(Long Term Evolution)
3GPP HNB femtocell network architecture:
Home NodeB (HNB): 3G UMTS terminology for
femtocell access point within the home, or other
Incorporates the capabilities of a standard Node B as
well as the radio resource management functions
found within a Radio Network Controller, RNC.
HNB Gateway (HNB-GW): Entry point to the core
The link into the core network is provided over Iu-cs
and Iu-ps interface.
Already used for links from Radio Network Controllers
to the remaining core network.
Provides authentication and certification to allow only
data to and from authorised HNBs.
Aggregates traffic from a large number of HNBs and
provides an entry point into the operator core network.
Provides a mechanism to support enhanced features
such as clock sync distribution, other IP based
Iu-h Interface: Used to provide the link or interface
that connects the HNB with the HNB-GW.
Includes a new HNB Application Protocol, HNBAP that
provides the high level of scalability required for the
HNB deployment in ad-hoc fashion.
E-UTRA: Evolved UMTS Terrestrial Radio Access
UE: User Equipment
Uu: Unique user
HeNB: Home e-node B
MME: Mobility Management Entity
CSG: Closed Subscriber Group
HSS: Home Subscriber Server
SGW: Serving Gateway
PGW: Packet data n/w Gateway
PCRF: Policy and Charging Rule Function
IMS: IP Multimedia Subsystem
LTE femtocell architecture:
Required to take account of the LTE SAE, System
Architecture Evolution requirements.
Provides a much flatter overall network architecture.
This has many advantages in terms of network
Key element in enabling much lower levels of latency -
a key requirement for LTE.
Allows maximum flexibility and scalability to ensure
that the deployment can be easily incorporated into
the existing structures.
Deployment of femtocells is achieved on an ad-hoc
basis, this forms a large requirement for the system.
Enterprise Small Cells
The same technology and architecture used.
Small cells have higher capacity and slightly higher
RF power to give a larger range.
Small cells may co-operate in clusters to provide
For larger enterprises, a small cell controller may be
used to provide additional local services including
direct connection to the enterprise network.
Urban and Rural Small Cells
Public areas use specially designed urban small
cells (metro-cells) which are also based on the
Take advantage of Femto-cell gateway, sharing its
use between residential, enterprise and urban
weather proof and vandal proof.
Operating in harsh unsupervised environments with wide
Urban small cells are installed by the network
Broadband IP connection back to the regional
switching centre (backhaul) is also required.
Components and Building Blocks
RF Front-End connects to the antenna-
converts the digital signals to and from radio
Baseband processing –
analyse and decode the complex transmissions into
Control processing runs the software –
to communicate with handsets and the femtocell
Memory chips, read/write chip for transient data
Read only chip which holds the program (ROM)
Crystal frequency oscillator , provides a very
important for synchronising the timing of signals to
Software controls overall operation of femtocell:-
what the femtocell does on startup and how quickly it
is ready to make/receive a call
how it searches out and determines the correct
frequency/scrambling codes to transmit on
how quickly it responds to a changing environment
(e.g. someone opening a window)
What handover options are available when
entering/leaving the home
what features are provided specifically for
what self-service management features are included,
such as setting up a list of barred/enabled phones
what diagnostic features are incorporated to reduce
the cost of remote diagnostic/maintenance and
Femtocells require no radio planning.
Reduced impact on the outdoor macrocellular
network, ( low power, no wall penetration.
No negotiation for site acquisition.
No ongoing running costs per site for site rental,
power or backhaul transmission .
Femtocells are “self configuring”. (directly
connected to RNC for configuration).
Can be managed on rental basis, like TV or Set Top
Standards needed for enforcing interoperability.
Device can be used around the world.
Drastically reduced cost from mass production.
Indicators are required to show:
Broadband signal connection active and online.
Connection into the operator’s network active and online.
If a mobile phone is “camped” on the femtocell.
When a voice or data call is active.
“camped” – only determined by mobile when an
active call is made / received.
Mobile network only aware of “location area” of
Phone sends location update message, when
changes cell, to network for broadcast to all
cellsites in the paging area.
Each femtocell may be configured as an individual
ensures femtocell knows when the mobile phone enters the
impacts on the sizing capacity of the MSC and SGSN which
initiate the paging messages
potential for increased numbers of location update
messages to the network.
A straightforward installation is connecting the box
to the broadband DSL line and power.
If GPS equipped, it needs to be located near to a
Femtocells including WiFi and/or PC connections,
onboard configuration website required.
DHCP should be enabled for all wired and wifi
WPA should be enabled for wifi requiring
reconfiguring the WPA clients on each laptop.
Benefits of using mobile broadband than WiFi -more
automatic security setup.
Two stage registration process:
The femtocell has standard, common software
installed in the factory
On first powerup, it connects to the vendor’s
website, sending its serial number.
The vendor’s website downloads any firmware and
security updates to the device
Vendor’s website uses serial number to identify the
mobile, redirects femtocell to contact mobile
Femtocell registers with the mobile operator’s
network and receives operator specific
configuration (operating frequency, max power
level, cell id, paging area)
Two stage registration process:
The mobile operator network also downloads the list
of phones allowed to use the femtocell
indication can be given to the customer before a call to
show applied billing rates.
To restrict use of femtocell to authorised phones where the
customer requests it.
The femtocell is authorised to transmit by the mobile
operator’s network and becomes part of the live
The customer can make or receive calls using the
Outdoor cellsite installation
Complex radio planning tools are used to analyse
the area to be covered.
Using topology of the area , simulation run to identify
best locations for cellsites.
Operators’ targets for their plans:
coverage (able to use phone in any part of the
country, inside buildings, cars, moving trains etc)
capacity ( ensuring enough traffic channels for
everyone in an area to make and receive calls).
Radio parameters are computed - maximum
transmission power, frequency hopping (for 2G),
coding sequence (for 3G), angle of the transmission
antenna , list of neighbour cellsites to handover
Outdoor cellsite installation
Transmission network connects cellsite to core network of
the operator via leased lines, microwave links or high
capacity SDH fibre owned by the operator
These are concentrated into an RNC (Radio Network
Controller for 3G) or BSC (Base Station Controller for 2G).
The transmission planners will allocate capacity from the
cellsite to the central switching centre.
Includs port mappings for each input and output across
every transmission hub.
Actively configured at the appropriate point in the
All basestations and RNCs are managed by a central
Network Management System.
Radio configuration parameters periodically
downloaded into basestations via NMS for
Outdoor cellsite installation
Fault management systems used-
to capture, collate and analyse alarms and fault
indications from the network equipment.
Performance management systems used –
to monitor the capacity and overall throughput of the
to ensure maximum utilisation of the network.
to identify additional capacity or coverage required
Handover/handoff - process by which:-
a mobile phone switches between different cellsites
during a phone call
continues with seamless audio in both directions.
Femtocell users need this capability when entering
or leaving their home .
Handover in Mobile phone Mobile phone
As we move around when on a call, mobile phone
continuously measures the signal level and quality
from nearby cellsites.
Current active basestation determines when and
where to initiate a handover sequence.
Complex algorithms uses all available capacity
whilst reducing call dropping during a handover.
3G systems and CDMA are complex as mobile may
be actively connected to more than one cellsite at
the same time.
Called soft handover- same signal transmitted by a
mobile phone to be picked up by multiple cellsites
In Femto cell
Do not implement soft handover.
All calls switched instantly to or from femtocell and
the external outdoor cellular network.
This is known as “hard handover” .
Not audible or noticeable to the caller.
Handover between 2G and 3G can occur-GSM and
3G systems more common because of higher traffic
capacity and lower costs.
User unaware whether using 2G or 3G mode.
Calls originating using 2G continues until
completion, even entering the femtocell.
No automatic handover into the femtocell zone.
Charges based on where the call originated.
i.e. inside or outside the femtocell coverage.
Irrespective of discounts offered inside/outside
Clarity of the billing mechanism.
No large loophole for revenue loss to exploit.
Forced handovers are possible.
Adding femtocells to the neighbour lists of the
Adding some smarts into the mobile phone.
Making the femtocell as clever as possible.
Location lock prevents a femtocell from changing its
location without network operator’s awareness and
Emergency Call Location: Operators report the
location of emergency calls.
Femtocell only operates at the specified location.
Any moves to a new address are properly registered
Spectrum Use: Femtocells must be used at the
correct frequencies for the area they are located.
Disabled when away from licenced territories. (e.g.
abroad on trip).
Commercial: Operators can charge additional fee
to process a femtocell relocation.
Includs updating the registered operating address.
Location Lock implementation
Femtocells are connected via broadband IP and are
associated with an IP address.
If wired broadband and femtocell have same provider,
IP address may associate with registered physical
But domestic customers allocated dynamic IPv4
restrict identification to area served by pool of IP addresses.
Sniffing external 2G and 3G cellsites: Femtocells can
detect and remember the cellsite IDs, which shouldn’t
GPS: Although indoors, femtocells can have low power
and sensitive GPS receiver for:
Location and look-up for licenced frequencies.
long term frequency clock accuracy.
Network management operation- cellsite is switched
across to a different controller (BSC or RNC).
Managed task under the planning and direction of
the network planning and operations department.
Organic Network Growth: As networks grow, new
controller is installed and some cellsites swapped
across to balance the load.
Swanky New Products: Several controllers can be
replaced by single, larger product with increased
capacity /more cost effective technology.
Grooming: Existing transmission and location of
controllers may be organised to be more efficient.
Commercial changes: For changing commercial
Identity Theft - No security loophole to exploit.
Authentication take place in the operator’s network
before allowing voice or data calls through the system.
Phone-Tapping – Femtocells encrypt their voice and
data traffic using secure tunnels (IPsec) between the
femtocell and operators network.
More secure than mobile phone outdoors with no
encryption is used.
Bill Avoidance – It is proposed to include a SIM card
in the femtocell to validate the owner of the device.
Stolen or compromised units can be disconnected
from the network.
Use of IPsec: In order to ensure femtocell security
IPsec or IP security is used.
Defined by the Internet Engineering Task Force (IETF).
Femtocell Secure Authentication: Femtocell
security procedures using SIM cards authentication
or X.509 are used.
Wireless link security: To ensure that unauthorised
users do not connect or take over the femtocell
Techniques include femtocll coverage area not
exceeding the physical area where the femtocell is
to be used.
EAP, Extensible Authentication Protocol: for
providing femtocell security.
Timing and synchronisation
GPS: Provides very accurate frequency and phase
alignment but little extra hardware.
Can also determine the location of the device.
NTP (Network Timing Protocol): Operates across
domestic quality broadband Internet, low cost but
potentially long time to acquire and lock-on to
Network sniffing: Nearby macrocells used as an
alternative clock source.
Synchronization needed for
Supply frequency information to handsets to
synchronize to base stations.
Ensure reliable handover
Ensures femtocell to be aware of adjacent cell sites
Integrated with existing DSL broadband modem
TV Set-Top Box
Interference issues : Femtocells operate within spectrum
shared with other cellular base stations.
3G and 4G are able to tolerate interference and single
Spectrum issues: Spectrum is scare resource, especially
when large amounts of data are required.
Careful planning required.
Regulatory issues: Femtocells need regulatory approval
to operate in licensed or regulated spectrum in each
International agreement may also be required,as private
individuals take femtocells from one country to the next.
Health issues: RF radiation issue with health and safety.
Power levels emitted by femtocells are small - no greater
than most Wi-Fi access points ,common in very many homes.
As per industry, no health issues of any concern.