205127915 gsm-vs-femtocell

1GsmvsFemtocell

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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 Frequency Division 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 Missed Calls

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.

23GsmvsFemtocell

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

data connectivity,and usually a list of other standard features too. The femtocell module is

24GsmvsFemtocell

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,

which is a Long Term Evolution (LTE) Femtocell and 3GPP2’s program for femtocells for

25GsmvsFemtocell

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

26GsmvsFemtocell

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

27GsmvsFemtocell

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

28GsmvsFemtocell

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

29GsmvsFemtocell

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

30GsmvsFemtocell

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

31GsmvsFemtocell

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.

32GsmvsFemtocell

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

33GsmvsFemtocell

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).

34GsmvsFemtocell

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 (mobileto 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

35GsmvsFemtocell

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) andTime-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

Common Elements of the Femtocell Network Architecture include:

Femtocell Access Point (FAP),

Security Gateway (SeGW)

36GsmvsFemtocell

Subsystem (OSS) Femtocell Device Management System (FMS).

References

Retrieved from:  http://www.ehow.com/list_7466480_disadvantages-gsm-

technology.html#ixzz2kOn3OusU Access on [10/11/2013]

Retrieved from: http://www.radio-electronics.com/info/cellulartelecomms/gsm_technical/

gsm_architecture.php Access on [10/11/2013]

Retrieved from: http://www.gsma.com/aboutus/gsm-technology/gsmAccess on [10/11/2013]

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

%20ISSUE%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]

37GsmvsFemtocell

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]