33Gsm vs FemtocellData Communications Research ProjectGsm versus FemtocellUniversity of Technology, JamaicaTutor: Mr UdeugaDate: November 12, 2013Group MembersTasharie Williams 1004248Quacey Harris 1104091Anthony Brown 1007532Noel Brown 1101892
Table of Content
Overview of Gsm4
Transmission frequency of GSM.5
GSM Operating Spectrum7
Bandwidth of GSM...8Transmission Impairments of GSM..9GSM Modulation Scheme.10GSM Encoding Scheme.11Multiplexing Techniques used in GSM.12Spread Spectrum Techniques.13Achievable Channel Capacity14Uses/Application of the Technology.16Architecture17Limitations of GSM...20Suggested improvements...21Femtocell Frequency22Application of Femtocell Technology23Femtocell Operating Spectrum.24Limitation of Femtocell Technology25
Femtocell Bandwidth26
Femtocell Modulation Scheme.27
Femtocell Multiplexing Technique...28
Transmission Impairments Experienced by the Technology29Femtocell Architecture...30Achievable Channel Capacity31Suggested Improvements...32Comparative Analysis of Gsm Technology and Femtocell Technology...33References..35
Overview of GSMGSM (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 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 GSMAlthough 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, 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 usageThe 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 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.
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 MHz the Frequency band used for uplink (mobileto base) is 890 - 915 MHz and for the downlink (base to mobile) 935 - 960 MHz TheGSM has 124 channels with 200 kHz carrier spacing. When the mobile is assigned to an information channel, a radio channel and a time slot are also assigned. Radio channels are assigned in frequency pairs - one for the uplink path and one for the downlink path (also called reverse and forward channels respectively). Each pair of radio channels supports upto 8 simultaneous calls. So the GSM can support upto 992 simultaneous users with the full-rate speech coder, this number 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 between 1805 MHz and 1880 MHz. The duplex spacing is 95 MHz.
Transmission Impairments of GSMBandwidth 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.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 SchemeGSM 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 (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 Efficiency2. 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 SchemeAccording 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 = 160This 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 GSMIn 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 AccessTDMA is a technology used in digital cellular telephone communication that divides each 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 AccessFDMA 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 TechniquesFrequency hoppingFrequency-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 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 CapacityChannel 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 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 treatise GSM 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=-121dBmLet 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)=2.06MbpsThis 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.
Uses/Application of the TechnologyThe 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 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 stations Control 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 control If 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 controlopen 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.
ArchitectureGSM network architecture elementsThe 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)
Simplified GSM Network Architecture
Mobile stationMobile stations (MS), mobile equipment (ME) or as they are most widely known, cell ormobile phonesare the section of a GSMcellular networkthat 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 changed. It is accessed by the network during registration to check whether the equipment has been reported as stolen. The SIM orSubscriber Identity Modulecontains 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 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 GSMDropped 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 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 improvementsWe 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 qualityGSM 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 costsSignal 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.
DEFINITIONFemtocell 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.
Application of Femtocell Technology
DSL ModemThe 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 hardwired into the modem and can be given priority of voice calls to ensure improved performance.
Cable ModemMore 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.CellphonesFemtocells 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 3GPP2s program for femtocells for cdma2000 among others. Once activated, the femtocell connects to the MNOs 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 other femtocells.
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 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 regulatoryFemtocells 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 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 FemtocellQAM 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 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 FemtocellThe 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 FemtocellOFDM 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 TechnologyFemtocells 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 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 away macrocell. 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 by Talha Zahir, 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. In the 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 individual interfering femtocells.
Femtocell ArchitectureThe femtocell network architecture supports Service 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.
Achievable Channel CapacityFor 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
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).
Comparative Analysis of Gsm Technology and Femtocell TechnologyTechnologiesGSMFemtocell
Transmission frequency
Gsm operates on the four major frequency bands covering 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 TheGSM 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
Transmittion impairmentsIn 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.
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.
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
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 away macrocell. 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 Subsystem (OSS)
Common Elements of the Femtocell Network Architecture include: Femtocell Access Point (FAP), Security Gateway (SeGW) Femtocell Device Management System (FMS).
ReferencesRetrieved 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/gsm Access 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]
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Talha Zahir, Kamran Arshad, Atsushi Nakata, and Klaus Moessner, (Interference Management in Femtocells, Retrieved from: http://epubs.surrey.ac.uk/738896/1/talha_surv.pdf Accessed on [02/11/2013]
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