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GsmvsFemtocell
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Data Communications Research Project
Gsm versus Femtocell
University of Technology, Jamaica
Tutor: Mr Udeuga
Date: November 12, 2013
Group Members

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Tasharie Williams 1004248
Quacey Harris 1104091
Anthony Brown1007532
Noel Brown 1101892
Table of Content
Overview ofGsm………………………………………………………………………………4
Transmission frequency of GSM……………………………………………………………….5
GSM Operating Spectrum………………………………………………………………………7
Bandwidth of GSM……………………………………………………………………………...8

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Transmission Impairments of GSM……………………………………………………………..9
GSM Modulation Scheme……………………………………………………………………….10
GSM Encoding Scheme………………………………………………………………………….11
Multiplexing Techniques used in GSM………………………………………………………….12
Spread Spectrum Techniques…………………………………………………………………….13
Achievable Channel Capacity……………………………………………………………………14
Uses/Application of the Technology…………………………………………………………….16
Architecture………………………………………………………………………………………17
Limitations of GSM……………………………………………………………………………...20
Suggested improvements………………………………………………………………………...21
Femtocell Frequency……………………………………………………………………………22
Application of FemtocellTechnology…………………………………………………………23
Femtocell Operating Spectrum………………………………………………………………….24
Limitation ofFemtocell Technology……………………………………………………………25
Femtocell Bandwidth……………………………………………………………………………26
Femtocell Modulation Scheme………………………………………………………………….27

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Femtocell Multiplexing Technique……………………………………………………………...28
Transmission Impairments Experienced by the Technology……………………………………29
Femtocell Architecture…………………………………………………………………………...30
Achievable Channel Capacity……………………………………………………………………31
Suggested Improvements………………………………………………………………………...32
Comparative Analysis of Gsm Technology and Femtocell Technology………………………...33
References………………………………………………………………………………………..35
Overview of GSM
GSM (Global System for Mobile Communications) is a standard set developed by the European
Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G)
digital cellular networks used by mobile phones. Today the GSM cell or mobile phone system is
the most popular in the world. GSM handsets are widely available at good prices and the
networks are robust and reliable. The GSM system is also feature-rich with applications such as
SMS text messaging, international roaming, SIM cards and the like. It is also being enhanced

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with technologies including GPRS and EDGE. To achieve this level of success has taken many
years and is the result of both technical development and international cooperation. The GSM
history can be seen to be a story of cooperation across Europe, and one that nobody thought
would lead to the success that GSM is today.
The first cell phone systems that were developed were analogue systems. Typically they used
frequency-modulated carriers for the voice channels and data was carried on a separate shared
control channel. When compared to the systems employed today these systems were
comparatively straightforward and as a result a vast number of systems appeared. Two of the
major systems that were in existence were the AMPS (Advanced Mobile Phone System) that was
used in the USA and many other countries and TACS (Total Access Communications System)
that was used in the UK as well as many other countries around the world.
Transmission frequency of GSM
Although it is possible for the GSM cellular system to work on a variety of frequencies, the GSM
standard defines GSM frequency bands and frequencies for the different spectrum allocations
that are in use around the globe. For most applications the GSM frequency allocations fall into
three or four bands, and therefore it is possible for phones to be used for global roaming.While
the majority of GSM activity falls into just a few bands, for some specialist applications, or in
countries where spectrum allocation requirements mean that the standard bands cannot be used,

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different allocations may be required. Accordingly for most global roaming dual band, tri-band
or quad-band phones will operate in most countries, although in some instances phones using
other frequencies may be required.
GSM frequency band usage
The usage of the different frequency bands varies around the globe although there is a large
degree of standardisation. The GSM frequencies available depend upon the regulatory
requirements for the particular country and the ITU (International Telecommunications Union)
region in which the country is located.As a rough guide Europe tends to use the GSM 900 and
1800 bands as standard. These bands are also generally used in the Middle East, Africa, Asia and
Oceania.For North America the USA uses both 850 and 1900 MHz bands, the actual band used
is determined by the regulatory authorities and is dependent upon the area. For Canada the 1900
MHz band is the primary one used, particularly for urban areas with 850 MHz used as a backup
in rural areas.For Central and South America, the GSM 850 and 1900 MHz frequency bands are
the most widely used although there are some areas where other frequencies are used.
Today most phones support operation on multiple bands and are known as multi-band phones.
Typically most standard phones are dual-band phones. For Europe, Middle east, Asia and
Oceania these would operate on GSM 900 and 1800 bands and for North America, etc dual band
phones would operate on GSM 850 and 1900 frequency bands.To provide better roaming
coverage, tri-band and quad-band phones are also available. European triband phones typically
cover the GSM 900, 1800 and 1900 bands giving good coverage in Europe as well as moderate
coverage in North America. Similarly North America tri-band phones use the 900, 1800 and

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1900 GSM frequencies. Quad band phones are also available covering the 850, 900, 1800 and
1900 MHz GSM frequency bands, i.e. the four major bands and thereby allowing global use.
GSM Operating Spectrum
In the frequency range specified for GSM-900 System mobile radio networks, 124 frequency
channels with a bandwidth of 200 KHz are available for both the uplink and downlink direction.
The uplink (mobile station to BTS) uses the frequencies between 890 MHz and 915 MHz and the
downlink (BTS to mobile station) uses the frequencies between 935 MHz and 960 MHz. The
duplex spacing, the spacing between the uplink and downlink channel, is 45 MHz. The E-GSM
band adds 50 frequency channels and the R-GSM another 20 frequency channels to the
spectrum.

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The ITU, which manages the international allocation of radio spectrum, allocated the 890-915
MHz bands for the uplink (mobile station to base station) and 935-960 MHz bands for the
downlink (base station to mobile station) for mobile networks in Europe. Since this range was
already being used in the early 1980s by the analog systems of the day, the CEPT had the
foresight to reserve the top 10 MHz of each band for the GSM network that was still being
developed.”It should be noted that the World Radio-Communications Conference (WRC) in
1992 identified frequency bands for FPLMTS (Future Public Land Mobile Telecommunications
Systems), which is in fact the original name of IMT-2000 (UMTS).The existing second-
generation bands for second-generation GSM services consist of spectrum between 862 and
960 MHz and the totality of the GSM1800 band 1710 - 1880 MHz
Bandwidth of GSM
The bandwidth in the GSM is 25 MHzthe Frequency band used for uplink (mobile
to base) is 890 - 915 MHz and for the downlink (base to mobile) 935 - 960 MHz The
GSM has 124 channels with 200 kHz carrier spacing.When the mobile is assigned to an
information channel, a radio channel and a time slotare also assigned. Radio channels are
assigned in frequency pairs - one for the uplinkpath and one for the downlink path (also called
reverse and forward channelsrespectively). Each pair of radio channels supports upto 8
simultaneous calls. So theGSM can support upto 992 simultaneous users with the full-rate speech

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coder, thisnumber will of course be doubled with the use of the half-rate speech coder.In the
frequency range specified for GSM-1800 System mobile radio networks, 374 frequency channels
with a bandwidth of 200 KHz are available for both the uplink and downlink direction. The
uplink uses the frequencies between 1710 MHz and 1785 MHz and the downlink uses the
frequencies between1805 MHz and 1880 MHz. The duplex spacing is 95 MHz.
Transmission Impairments of GSM
Bandwidth Lag
 Perhaps the greatest disadvantage of GSM is that multiple users share the same
bandwidth. With enough users, the transmission can encounter interference. Therefore,
faster technologies, such as 3G, have been developed on different types of networks than
GSM, such as CDMA, in order to avoid such bandwidth limitations.

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Causes Electronic Interference
 Another disadvantage of GSM is that is can interfere with certain electronics, such as
pace makers and hearing aids, according to Inc. Technology. Com. Such interference is
due to the fact that GSM uses a pulse-transmission technology. As a result, many
locations such as hospitals and airplanes require cell phones to be turned off.
GSM Modulation Scheme
GSM uses Gaussian-Fitered Minimum Shift Keying (GMSK) as it's modulation schemeGMSK is
a special type of digital FM modulation. Ones and zeroes are represented by shifting the RF
carrier by plus or minus 67.708 kHz. Modulation techniques that use two frequencies to
represent ones and zeroes are called frequency shift keying (FSK). In the case of GSM, the data
rate of 270.833 kbps is chosen to be exactly four times the RF frequency shift. This has the effect
of minimizing the modulation spectrum and improving channel efficiency. FSK modulation
where the bit rate is exactly four times the frequency shift is called minimum shift keying

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(MSK). In GSM, the modulation spectrum is further reduced by applying a gaussian pre-
modulation filter. This slows down the rapid frequency transitions, which would otherwise
spread energy into adjacent channels.GMSK is used in GSM because it provides good spectral
efficiency.
Reasons GMSK is used for GSM.
1. High spectral Efficiency
2. Since Basic MSK uses Phase variations for modulation so better immune to noise.
3.Use of non-linear amplifiers at receivers can be utilized since the information is stored
in phase variations rather than amplitude, Non-linear amplifiers give better response and
consume less power so low battery usage which is a important parameter in Cellular
technology.
GSM Encoding Scheme
According to GSM specification, a standard SMS message can contain up to 140 bytes of data.
Standard latin(ISO-8859-1) character encoding represents a single character using 1 byte, which
is 8 bits. Therefore, the maximum number of latin 1 characters that could be included in an sms
is 140. GSM encoding represents characters using 7 bits instead of 8. This therefore provides a
maximum of 160 characters per SMS.
(140 * 8 bits) / 7 bits = 160

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This effectively halves the number of characters that the GSM character set can support,
compared to ISO-8859-1. In order to include common characters that are usually represented
using the 8th bit, these characters as well as other symbol characters must be re-mapped to a
combination of lower bits. These re-mapped characters are often referred to as special characters.
This re-mapping, in combination with packing 7-bit characters into 8-bit bytes is called GSM
Encoding.
Multiplexing Techniques used in GSM
In the GSM system, TDMA in combination with FDMA is used; the usage of each radio channel
is partitioned into multiple (eight) timeslots, and each user is assigned a specific frequency/
timeslot combination. Thus, only a single mobile is using a given frequency/timeslot
combination at any particular time. Also the FDD technique is in use, that is two symmetric
frequency band, one band containing the uplink channels and the other the downlink channels.
TDMA Time Division Multiplex Access
TDMA is a technology used in digital cellular telephone communication that divides each

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cellular channel into time slots in order to increase the amount of data that can be carried.
TDMA is used by Digital-American Mobile Phone Service (D-AMPS), Global System for
Mobile communications (GSM), and Personal Digital Cellular (PDC). However, each of these
systems implements TDMA in a somewhat different and incompatible way. An alternative
multiplexing scheme to FDMA with TDMA is CDMA, which takes the entire allocated
frequency range for a given service and multiplexes information for all users across the spectrum
range at the same time.
FDMA FrequencyDivision Multiplex Access
FDMA is the division of the frequency band allocated for wireless cellular telephone
communication into 30 channels, each of which can carry a voice conversation or, carry data of a
digital service. FDMA is a basic technology in the analog Advanced Mobile Phone Service
(AMPS), the most widely-installed cellular phone system installed in North America. With
FDMA, each channel can be assigned to only one user at a time.
Spread Spectrum Techniques
Frequency hopping
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly
switching a carrier among many frequency channels, using a pseudorandom sequence known to
both transmitter and receiver. It is used as a multiple access method in the frequency-hopping
code division multiple access (FH-CDMA) scheme.
The mobile station already has to be frequency agile, meaning it can move between a transmit,
receive, and monitor time slot within one TDMA frame, which normally are on different

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frequencies. GSM makes use of this inherent frequency agility to implement slow frequency
hopping, where the mobile and BTS transmit each TDMA frame on a different carrier frequency.
The frequency hopping algorithm is broadcast on the Broadcast Control Channel. Since
multipath fading is dependent on carrier frequency, slow frequency hopping helps alleviate the
problem. In addition, co-channel interference is in effect randomized.
Achievable Channel Capacity
Channel capacity is the maximum rate at which information can be transmitted over a
communications channel of a specified bandwidth in the presence of noise. Classic Shannon
theory suggests that the achievable channel capacity increases logarithmically with the transmit
power. By contrast, the MIMO capacity increases linearly with the number of transmit antennas,
provided that the number of receive antennas is equal to the number of transmit antennas. With
the further proviso that the total transmit power is increased proportionately to the number of
transmit antennas, a linear capacity increase is achieved upon increasing the transmit power,
which justifies the spectacular success of MIMOs. Hence we may argue that MIMO-aided
transceivers and their cooperation-assisted distributed or virtual MIMO counterparts constitute
power-efficient solutions. In a nutshell, since the conception of GSM in excess of three orders of
magnitude bit-rate improvements were achieved in three decades, which corresponds to about a
factor ten for each decade, because GSM had a data rate of 9.6 Kb/s, while HSDPA is capable of

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communicating at 13.7 Mb/s. However, the possible transmit power reductions remained more
limited, even when using the most advanced multistage iterative detectors, since the required
received signal power has not been reduced by as much as 30 dB. This plausible observation
motivates the further research of advanced cooperation-aided wireless MIMO transceivers, as
detailed in this treatiseGSM bit rates can vary from a few kbps to a theoretical maximum of
171.2kbps (GPRS). But what is the actual capacity of a 200kHz GSM channel. We can use the
Shannon Capacity Theorem to find this capacity.
C=B*log2(1+SNR) or C=B*log2(1+P/N)
The noise power can be found by using the following formula:
N=B*No=k*T*B=(1.38e-23)*(293)*(200e3)=8.08e-16W=-121dBm
Let us now assume a signal power 0f -90dBm. This gives us an SNR of 31dB or 1258.9 on linear
scale. The capacity can thus be calculated as:
C=200e3*log2(1+1258.9)=2.06Mbps
This is the capacity if all time slots are allocated to a single user. If only one time slot is allocated
to a user the capacity would be reduced to 257.48kbps.
Most GSM networks work on 900 MHz or 1800 MHz bands. Western countries like USA and
Canada function on the 850 MHz and 1900 MHz bands. Few countries like Scandinavia use the
rarer frequency like 400 MHz and 450 MHz which were earlier used for the first generation
phones. The transmission power used in GSM850/900 is 1 watt and the one used in
GSM1800/1900 is maximum 2 watt.

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Uses/Application of the Technology
The term GSM is an abbreviation for Global System for Mobile communications. It was
originally used as an abbreviation for Group Special Mobile. GSM is a standard for mobile
telephones all over the world. While there are other such standards as CDMA (code Division
Multiple Access), GSM is the most popular form of telephone communication, and is nowadays
available at almost all locations in the world. GSM enables users to make use of their phones for
mobile communications. The popularity of GSM is evident from the number of users – over 2
billion people all across the world use GSM technology nowadays. GSM enables users to make
use of their cell phones in places other than their country of origin. For example if you
subscribed to a GSM connection in New York City, you could still use the same connection if
you are in London. GSM technology provides users with high quality signal and speech
channels, giving them access to high quality digital communication at very affordable rates.
GSM network operators can provide their customers with cheap calling and text messaging

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options. GSM technology is being mostly used for talking to family, friends and business
colleagues. We use communication feature of Telephone landlines for internet, e-mail, data
connectivity, remote monitoring, computer to computer communication, security systems.
The GSM-AUTO's versatility lends itself to a wide range of GSM remote control applications
including:Remote control switching of remote irrigation systems, water well pumps and pumping
stationsControl irrigation systems, water well pumps and pumping stations, switch on for a pre-
set length of time or on and off as required by sending an SMS text message from anywhere in
the world.Central heating remote controlIf you have a holiday home switch on the heating and
hot water before you arrive, periodically switch on the central heating to prevent damp, if
freezing weather conditions are forecast at your holiday home location switch on the heating to
prevent water freezing and pipes bursting.Automated gate remote control
open automatic gates using a cell phone, control user access by programming authorized users
telephone numbers into the GSM-AUTO, open the gates from anywhere in the world to allow
access for deliveries.
Architecture
GSM network architecture elements
The GSM network architecture as defined in the GSM specifications can be grouped into four
main areas:
 Mobile station (MS)
 Base-station subsystem (BSS)
 Network and Switching Subsystem (NSS)
 Operation and Support Subsystem (OSS)

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Simplified GSM Network Architecture
Mobile station
Mobile stations (MS), mobile equipment (ME) or as they are most widely known, cell or mobile
phones are the section of a GSM cellular network that the user sees and operates. In recent years
their size has fallen dramatically while the level of functionality has greatly increased. A further
advantage is that the time between charges has significantly increased.
There are a number of elements to the cell phone, although the two main elements are the main
hardware and the SIM.The hardware itself contains the main elements of the mobile phone
including the display, case, battery, and the electronics used to generate the signal, and process
the data receiver and to be transmitted. It also contains a number known as the International
Mobile Equipment Identity (IMEI). This is installed in the phone at manufacture and "cannot" be

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changed. It is accessed by the network during registration to check whether the equipment has
been reported as stolen.The SIM or Subscriber Identity Module contains the information that
provides the identity of the user to the network. It contains are variety of information including a
number known as the International Mobile Subscriber Identity (IMSI).
Base Station Subsystem (BSS)
The Base Station Subsystem (BSS) section of the GSM network architecture that is
fundamentally associated with communicating with the mobiles on the network. It consists of
two elements:Base Transceiver Station (BTS): The BTS used in a GSM network comprises the
radio transmitter receivers, and their associated antennas that transmit and receive to directly
communicate with the mobiles. The BTS is the defining element for each cell. The BTS
communicates with the mobiles and the interface between the two is known as the Um interface
with its associated protocols.Base Station Controller (BSC): The BSC forms the next stage back
into the GSM network. It controls a group of BTSs, and is often co-located with one of the BTSs
in its group. It manages the radio resources and controls items such as handover within the group
of BTSs, allocates channels and the like. It communicates with the BTSs over what is termed the
Abis interface.
Network Switching Subsystem (NSS)
The GSM network subsystem contains a variety of different elements, and is often termed the
core network. It provides the main control and interfacing for the whole mobile network. The
major elements within the core network include:Mobile Switching services Centre (MSC): The
main element within the core network area of the overall GSM network architecture is the
Mobile switching Services Centre (MSC). The MSC acts like a normal switching node within a
PSTN or ISDN, but also provides additional functionality to enable the requirements of a mobile
user to be supported. These include registration, authentication, call location, inter-MSC
handovers and call routing to a mobile subscriber. It also provides an interface to the PSTN so
that calls can be routed from the mobile network to a phone connected to a landline. Interfaces to

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other MSCs are provided to enable calls to be made to mobiles on different networks.Home
Location Register (HLR): This database contains all the administrative information about each
subscriber along with their last known location. In this way, the GSM network is able to route
calls to the relevant base station for the MS. When a user switches on their phone, the phone
registers with the network and from this it is possible to determine which BTS it communicates
with so that incoming calls can be routed appropriately. Even when the phone is not active (but
switched on) it re-registers periodically to ensure that the network (HLR) is aware of its latest
position. There is one HLR per network, although it may be distributed across various sub-
centres to for operational reasons.Authentication Centre (AuC): The AuC is a protected
database that contains the secret key also contained in the user's SIM card. It is used for
authentication and for ciphering on the radio channel.
Operation and Support Subsystem (OSS)
The OSS or operation support subsystem is an element within the overall GSM network
architecture that is connected to components of the NSS and the BSC. It is used to control and
monitor the overall GSM network and it is also used to control the traffic load of the BSS. It
must be noted that as the number of BS increases with the scaling of the subscriber population
some of the maintenance tasks are transferred to the BTS, allowing savings in the cost of
ownership of the system.
Limitations of GSM
Dropped and MissedCalls
 According to Cellular News, call quality problems, including dropped calls and missed calls are
common problems with GSM technology. These problems result directly from the technology in
use. GSM technology cannot accommodate as many callers on a single cell tower as the more
modern CDMA technology. This means that callers in areas where there are not a preponderance
of cell towers may find that the call problems on GSM will be more common.
Security Issues

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 ZDNet UK reports that GSM has a serious security flaw, demonstrated by a hacker who was able
to intercept phone calls from a number of GSM-based cellular phones. The problem is based
directly on the technology according to this hacker and his solution was to "turn off" the GSM
technology (only the older 2G technology though) that is commonly used by people all over the
world. The problem is largely mitigated however by the use of the more modern 3G technology
that is commonly used (as of November, 2010) on many GSM phones.
Efficiency
 Another problem with GSM is a network problem rather than a consumer problem, though it is a
consumer problem for those who don't want to see a proliferation of cellular towers. As
previously noted, GSM technology can handle fewer callers on a single cellular tower.
Therefore, networks who work with GSM must find ever more areas to built GSM cellular
towers, causing them to have problems with costs and locations. By the same token, some
consumers who prefer not to see a proliferation of cellular towers consider this a problem
because the cellular towers must be placed in more and more urban areas, potentially spreading
more radiation and causing what some consider blight on the landscape.
Perhaps the greatest disadvantage of GSM is that multiple users share the same bandwidth. With
enough users, the transmission can encounter interference. Therefore, faster technologies, such
as 3G, have been developed on different types of networks than GSM, such as CDMA, in order
to avoid such bandwidth limitations.
Suggested improvements
We suggest GSM to improve the coverage of the network. Not all locations will have the
coverage we would like them to.Multiple users share the same bandwidth. With enough users,
the transmission can encounter interference. GSM should improve their bandwidth to minimize
interference.
Increase network capacity and quality

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GSM operators worldwide can be able to get more from limited spectrum and improve their
overall Quality of Service (QoS). A Dynamic Frequency and Channel Allocation (DFCA)
feature that can double GSM network capacity within existing spectrum should be implemented
by GSM. The feature supports growth, while maintaining service quality and controlling costs
Signal Strength
Mobile phone conversations in buildings are often difficult, if not impossible. This is due to the
signal attenuation through walls, window panes, ceilings (underground). The problems occur in
markets, tunnels, underground car parks, petrol stations, airport halls, hotels. A similar situation
can be found in buildings located on the border range of base stations (recreational areas,
mountains).
The solution to this problem is application of a GSM repeater, being a two-way amplifier of
wireless GSM signal, which significantly improves the quality of data transmission in such
places, reducing noise and the number of lost connections.
DEFINITION
Femtocell is a small cellular base station or a wireless access point ,that is typically used to
improve indoor cellular reception inside a home or small business. A femtocell connects to the
carrier's network via broadband and can support up to five mobile phones.

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Application of FemtocellTechnology
DSL Modem
The step is to integrate the femtocell into an existing DSL broadband modem design. No
additional external connections are needed being that the modem will already have power and

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data connectivity,and usually a list of other standard features too. The femtocell module is
hardwired into the modem and can be given priority of voice calls to ensure improved
performance.
Cable Modem
More households are now receiving their broadband internet service from their cable TV
supplier than from the phone company. The modem can be separate from the TV Set-top box or
a combined unit. The large Cable TV companies in the US, such as Comcast,previously had
agreements to resell mobile services on the Sprint network.
Cellphones
Femtocells address the problem of poor cell-phone reception indoors by taking advantage of the
proliferation of home- and small-office broadband connections. A femtocell device grabs your
carrier's cellular signal and boosts it for indoor use, routing your calls through the broadband
connection rather than directly through the larger cellular network.
Femtocell Operating Spectrum
Femtocell operates on licensed spectrum which allows the mobile network operator (MNO) to
provide assured Quality of service (QoS). Most air interfaces included in the global ITU-R IMT
family have recognized standards for Femtocells including 3GPP standards for Home eNode-B,

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which is a Long Term Evolution (LTE) Femtocell and 3GPP2’s program for femtocells for
cdma2000 among others. Once activated, the femtocell connects to the MNO’s mobile network,
and provides extra coverage. The user is required to specify which mobile phone numbers are
allowed to connect to the femtocell, usually via a web interface provided by the MNO.When in
the range of the femtocell coverage, the mobile device automatically switch over from the
macrocell (which is outdoor) to the femtocell. There are different interferences like the Macro-
Femto Interference and the Femto-Femto Interference. In any situation, twenty (20)femtocells
required to share 10 MHz bandwidth as universal frequency reuse interference from all
otherfemtocells.
Limitation of Femtocell Technology
 Femtocell interference
One key issue associated with femtocells is that of interference. There is only limited
spectrum on which the cellular systems can run. Some 3G operators for example may

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only have one channel in some places. Therefore it is necessary that femtocells are able to
operate within the normal spectrum shared with many other cellular base stations.
 Femtocell spectrum
Radio spectrum is a particularly scarce resource, especially when large amounts of data
are required. Planning the available spectrum so that it can be used with the possible huge
numbers of femtocells can require careful attention, although in some instances single
channel operation with main base stations may be required.
 Femtocell regulatory
Femtocells need regulatory approval. The spectrum and radio regulations vary from one
country to the next and therefore regulations may need to be changed in each country.
International agreement may also be required, because private individuals may take
femtocells from one country to the next.
 High price ($300 US)- The total cost of purchasing a femtocell device maybe at the
lowest cost $300.
 Difficult to install (Cabling, roof access etc)-More complex to set up, requires a
new/different phone number, more potential for errors.
 It does not provide good coverage in outdoors.
Femtocell Bandwidth
A requirement for femtocells to support 4 simultaneous voice calls must be available with uplink
bandwidth on a standard broadband connection. This means significantly less than 200 kbps (not

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only because some homes will have a slower uplink, but also because the femtocell must share
the broadband connection with PCs accessing the internet in the home). One of the common
concerns about femtocells is that they may use up a lot of broadband internet service, either
exceeding a basic allowance or causing additional charges. The bandwidth required for a
femtocell depends on the type of traffics. In downlink side it requires about 602 kbps to
perfectly handle mix traffic from 4 smartphones while in uplink is about 175 kbps. The uplink
traffic in smartphone contains voice AMR (12.2kbps) so ideally the bandwidth should be
preserved above 84.8 kbps.
Femtocell Modulation Scheme
4G Femtocell
QAM also known as quadrature amplitude modulation is a method of merging 2 amplitude-
modulated signals into one channel with the intention of doubling the effective bandwidth. The

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method works by modulating the amplitude of two separate carrier waves, mostly sine and
cosine waves.
A variation on the quadrature amplitude modulation (QAM) signal modulation scheme. 64-QAM
yields 64 possible signal combinations, with each symbol representing six bits (2 6 = 64). The
yield of this complex modulation scheme is that the transmission rate is six times the signaling
rate.
2G Femtocell
The modulation used is Gaussian minimum-shift keying (GMSK), a kind of continuous-phase
frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothed
with a Gaussian low-pass filter prior to being fed to a frequency modulator, which greatly
reduces the interference to neighboring channels (adjacent channel interference).
Femtocell Multiplexing Technique
4G Femtocell

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GsmvsFemtocell
OFDM is a multicarrier system uses discrete Fourier Transform/Fast Fourier Transform
(DFT/FFT) .Available bandwidth is divided into very many narrow bands. Data is transmitted in
parallel on these bands. An OFDM signal consists of a number of closely spaced modulated
carriers. When modulation of any form - voice, data, etc. is applied to a carrier, then sidebands
spread out either side.
2G Femtocell
FDM
Frequency Division Multiplexing (FDM) is a networking technique in which multiple data
signals are combined for simultaneous transmission via a shared communication medium. FDM
uses a carrier signal at a discrete frequency for each data stream and then combines many
modulated signals.
TDM
Time-division multiplexing is carried out by which two or more signals or bit streams are
transferred appearing simultaneously as sub-channels in one communication channel, but are
physically taking turns on the channel. It involves means of synchronized switches at each end
of the transmission line so that each signal appears on the line only a fraction of time in an
alternating pattern.
Transmission Impairments Experienced by the Technology
Femtocells utilize the broadband connection, which may also be used for other applications such
as video streaming and this can help to decrease its transmission speed. Interferences can cause

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GsmvsFemtocell
problems as well even though it is said that interference with other femtocells is not a big issue.
When a femtocell is transmitting at a power level that is too high it creates interference to a
nearby mobile device that is being served on the same radio channel by a far awaymacrocell.
This results in the creation of what is known as a “dead zone” where even basic voice
communication with the macrocell base station may become impossible. According to
Interference Management in Femtocells byTalhaZahir, Kamran Arshad, Atsushi Nakata, and
Klaus Moessner, “The deployment of femtocell is random and they can be deployed very close
to each other in apartments, where the wall separation might not be enough to avoid causing
interference to each other. Inthe case of dense deployment, where there might be a number of
neighboring interferers, the overall interference observed at a femtocell can be higher than any of
the individualinterfering femtocells.”
Femtocell Architecture

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GsmvsFemtocell
The femtocell network architecture supportsService Parity, Call Continuity, Self-Installation and
Simple Operational Management, Security and Scalability. Common Elements of the Femtocell
Network Architecture include:
 Femtocell Access Point (FAP),
 Security Gateway (SeGW)
 Femtocell Device Management System (FMS).
There can either be a Femtocell Convergence Server (FCS) or a Femtocell Network Gateway
(FNG) depending on the architecture used on the circuit switch call. The femtocell Access Point
creates the functions of the base station and base station controller and connects to the operator
network over a secure tunnel via the Internet. It is the primary node in a femtocell network. The
security gateway uses standard Internet security protocols such as IPSec and IKEv2 to authorize
femtocells and is a network node that secures the Internet connection between femtocell users
and the mobile operator core network. The femtocell management system,activates and control
operational management of femtocells using industry standards such as TR-069.

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GsmvsFemtocell
Achievable Channel Capacity
For both for both the 850 MHz (3GPP Band 17) and 2100 MHz (3GPP Band 1), simulations
show that femtocell deployments with interference mitigation technique implemented, it can
enable very high capacity networks by providing between a 10 and 100 times increase in
capacity with minimal deadzone impact and acceptable noise rise.Femtocells can also create a
much better user experience by enabling substantially higher data rates than can be obtained with
a macro network and net throughputs that will be ultimately limited by backhaul in most cases
(over 20 Mbps in 5 MHz).
Suggested Improvements

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GsmvsFemtocell
Improvements can be made in the area of interruptions. By putting in place proper interruption
control strategies and thus lead to better transition and prevent “dead zones”. Femtocells should
be able to get higher bandwidth thus enabling it to utilize the bandwidth it needs without
interrupting the speed of other applications such as streaming video. A femtocell exclusion
region and a tier selection based handoff policy offers modest improvements in the operating
contour (OC).

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GsmvsFemtocell
Comparative Analysis of Gsm Technology and Femtocell
Technology
Technologies GSM Femtocell
Transmission
frequency
Gsm operates on the four
major frequency
bandscovering the 850, 900,
1800 and 1900.
Frequency 1.9 and 2.6Ghz
Bandwidth The bandwidth in the GSM is
25 MHz the Frequency band
used for uplink (mobile
to base) is 890 - 915 MHz and
for the downlink (base to
mobile) 935 - 960 MHz The
GSM has 124 channels with
200 kHz carrier spacing.
The bandwidth required for a
femtocell depends on the type
of traffics. In downlink side it
requires about 602 kbps to
perfectly handle mix traffic
from 4 smartphones while in
uplink is about 175 kbps. The
uplink traffic in smartphone
contains voice AMR
(12.2kbps) so ideally the
bandwidth should be
preserved above 84.8 kbps.
Spectrum In the frequency range
specified for GSM-900
System mobile radio
networks, 124 frequency
channels with a bandwidth of
200 KHz are available for both
the uplink and downlink
direction.
Radio spectrum is a
particularly scarce resource,
especially when large amounts
of data are required and The
spectrum and radio regulations
vary from one country to the
next and therefore regulations
may need to be changed in
each country

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GsmvsFemtocell
Transmittion
impairments
GSM is can interfere with
certain electronics, such as
pace makers and hearing aids,
according to Inc. Technology.
Com. Such interference is due
to the fact that GSM uses a
pulse-transmission
technology.
When a femtocell is
transmitting at a power level
that is too high it creates
interference to a nearby
mobile device that is being
served on the same radio
channel by a far
awaymacrocell. This results
in the creation of what is
known as a “dead zone” where
even basic voice
communication with the
macrocell base station may
become impossible
Modulation
Scheme GSM uses Gaussian-Fitered
Minimum Shift Keying
(GMSK) as it's modulation
schemeGMSK is a special
type of digital FM modulation.
The modulation used is
Gaussian minimum-shift
keying (GMSK), a kind of
continuous-phase frequency
shift keying
Multiplexing
Techniques
In the GSM system, TDMA in
combination with FDMA is
used.
Uses Frequency Division
Multiplexing (FDM) and
Time-division multiplexing
(TDM)
Architecture The GSM network
architecture can be grouped
into four main areas:Mobile
station (MS)Base-station
subsystem (BSS)Network and
Switching Subsystem
(NSS)Operation and Support
Subsystem (OSS)
Common Elements of the
Femtocell Network
Architecture include:
 Femtocell Access
Point (FAP),
 Security Gateway
(SeGW)
 Femtocell Device
Management System
(FMS).

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GsmvsFemtocell
References
Retrieved from: http://www.ehow.com/list_7466480_disadvantages-gsm-
technology.html#ixzz2kOn3OusU Access on [10/11/2013]
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electronics.com/info/cellulartelecomms/gsm_technical/gsm_architecture.php Access on
[10/11/2013]
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Retrieved from: http://technology.blurtit.com/67863/what-are-the-uses-of-gsm Access on
[10/11/2013]
International Journal of Advanced Engineering Research and Studies Retrieved from:
http://www.technicaljournalsonline.com/ijaers/VOL%20I/IJAERS%20VOL%20I%20ISS
UE%20III%20APRIL%20JUNE%202012/181.pdf Accessed on [07/11/2013]
Retrieved from: http://www.airvana.com/products/cdma-femtocell/ Accessed on [07/11/2013]
Retrieved from: http://www.techrepublic.com/blog/data-center/pros-and-cons-of-using-
femtocells/ Accessed on [07/11/2013]

37. 37
GsmvsFemtocell
Retrieved from: http://transition.fcc.gov/pshs/techtopics/techtopics23.html
http://www.ece.umn.edu/users/meha0006/Files/Work%20Summary%20SPINCOM.pdf
Accessed on [07/11/2013]
TalhaZahir, Kamran Arshad, Atsushi Nakata, and Klaus Moessner, (Interference Management in
Femtocells, Retrieved from: http://epubs.surrey.ac.uk/738896/1/talha_surv.pdfAccessed
on [02/11/2013]
Retrieved from: http://www.airvana.com/technology/femtocell-network-
architecture/[02/11/2013]