Assignment 2 - High-Tier LicencedMobile Systems

MID260 Wireless Communication

Shahed Farid

University of Stavanger

October 24, 2011

2G (GSM)

GSM (Global System for Mobile Communications) is a digital mobile telecommunicationsystem for cellular network systems. It replaced the analog 1G systems that existedbefore (e. g. NMT). When established, the primary goal for GSM was to provide amobile system that allowed roaming in the whole of Europe and that provided voiceservices that were compatible with e. g. ISDN-systems. Today, it is the most successfulcellular communication system in the world.

GSM networks are designed to be able to use numerous frequency bands, as listed intable 1.

System Downlink (Hz) Uplink (Hz)GSM 900 935-960 890-915GSM 1800 1805-1880 1710-1785

Table 1: Frequency bands in GSM

For channel access, TDMA (Time Division Multiple Access) is used. TDMA allowsmultiple users to share the same frequency channel by dividing the signal into differenttime slots. The frequencies are divided into eight timeslots and then grouped into aTDMA frame. Synchronization between sender and receiver is required to be able touse the correct time slots. GSM focuses mainly on voice, but data services, such as textmessaging (SMS), are also possible. SMS-messages are not sent through the same networkthat handles e. g. conversations, but through the signalling channels [1, 2].

2.5G (GPRS)

GPRS (General Packet Radio Service) is a standard for data communication over theGSM. It introduced packet switching to the GSM. GPRS provides higher data speeds(theoretically up to 171.2 kbps). This technology uses the resources (of the GSM network)that are not being used for conversations and provides a "always on" mode, no connectionhas to been set up prior to the transmissions. The existing GSM network has to beupgraded with both new hardware and software to be able to offer GPRS. All GPRSservices can be used in parallel to the regular network services GSM provides [1, 7].

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Figure 1: GPRS

3G

3G is a set of standards for mobile communication. It evolved from the previous genera-tions, adding (amongs other functionalities) higher data speeds and enhanced audio andvideo capabilities. 3G is based upon higher bandwith than 2G. This makes 3G systemscapable of simultaneous transmission of voice and data [1, 4].

The following technologies are included in the 3G standard:

• EDGE (Enhanced Data rates for GSM Evolution)

EDGE is a technology that improved the data transmission rates and is a backward-compatible extension to GSM. An existing GSM network can be updated withEDGE by using software. There is no need for any hardware changes. The sameTDMA frame structure as GSM is used, as well as the same 200 kHz carrier band-width [5].

EDGE can achieve higer data transmission rates because it uses more efficient cod-ing shemes and modulation techniques. It also uses adaptive algorithms that adaptthe coding and modulation according to the quality of the transmission channel.EDGE can offer data rates of up to 384 kbps. [1, 5, 7].

• CDMA2000 (Code Division Multiple Access)

CDMA2000 is a set of standards that uses the CDMA technology for mobile com-munication. In CDMA, several transmitters can send data simultaneously over asingle channel, but unlike TDMA, which divides access by time, CDMA dividesaccess by code.

This technology is very efficient and robost. Some advantages are increased security,increased voice capacity, higher data troughput, frequency band flexibility and fullbackward-compatibility [6].

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• UMTS (Universal Mobile Telecommunications System)

UMTS is a standard that uses CDMA technology for radio but TDMA for routingof conversations. By using CDMA the technology gives better spectral efficiency.The first version of UMTS offered data rates of up to 384 kbps. Later, HSPA (HighSpeed Packet Access) was introduced. If UMTS is used in conjunction with HSPA,the theoretical speed can be up to 45 Mbit/s. By using HSPA, the efficiency andlatency can be approved.

4G

4G is a cellular network technology that is the successor to the 2G and 3G technologies.4G is not built on the previous ones, it is an all IP-based tecnhology (the same networkstructure as in the internet). This means that new eqipment has to be installed. Some ofthe reasons for choosing an all IP-based infrastructure is scalability and fault tolerance.Data networks are evolving at a very high rate. The network needs to be scalable tobe able to cope with increased traffic as more and more technically demanding contentis beeing provided to customers. Using IP, it is more easy to add extra eqipment thatcan act like e. g. a base station controller via Ethernet. Also, With IP, traffic canautomatically be routed to another device on the network if one device fails. IP-networksare also very reliable [10].

Figure 2: One world, one device

4G uses OFDMA (Orthogonal Frequency-Division Multiple Access) as its access tech-nique. OFDMA splits the data signal into multiple, smaller sub-signals which then aretransmitted simultanously at different frequencies. The space between the frequenciesare precisely controlled and provides the orthogonality. OFDMA is very resistant againstnoise and interference. Compared to CDMA, high spectral efficiency is achieved. How-ever, OFDMA requires very accurate freqency synchronization between sender and re-ceiver to be able to use the ortghogonal functionality [8].

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In 4G, MIMO (Multiple-Input and Multiple Output) technology is used in conjunctionwith OFDMA. MIMO utilizes multiple antennas at both the transmitter and receiver toacheieve better communication performance and to minimize error. It takes advantage ofa phenomenon called multipath, where transmitted signals bounces of different objects(e. g. walls and floors) and arrives at different locations at different times. By usingmultiple antennas, the "bounced off" signals can be received, making the transmissionsmore efficient [9].

Figure 3: MIMO

3G vs 4G

The biggest difference between 3G and 4G is the speed. 4G can offer theoretical speedsof up to 1Gbps. 4G can utilize frequency bands that are higher up in the spectrum range.Since 4G is all IP-based, it is fully packet swithed, 3G have some circuit and some packetswitching. The overall through-put of 4G networks are greater because it uses forwarderror correction (FEC) techniques that allows larger data packets to be transmitted andat the same time reduces the bit error rate (BER). Also, 4G uses more efficient accessmethods and utilized MIMO-technology [11].

The future

As more demanding content is beeing offered and as more and more devices are beeingcapable of running advanced, bandwith consuming application, the networks driving thesedevices needs to be scalable and reliable. 4G can handle these issues better than oldergenerations of networks. I think that this technology has a lot of potensial to cope withthe demands of future communication.

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1 References

[1] Schiller J. (2003). Mobile Communications (2nd ed.). Addison Weley

[2] http://www.cse.wustl.edu/~jain/cse574-08/ftp/j_fwan.pdfVisited: October 12, 2011.

[3] http://encyclopedia2.thefreedictionary.com/3G+cellular+networkVisited: October 12, 2011.

[4] http://www.wirelessinternet.org/3G-network.phpVisited: October 12, 2011.

[5] http://www.telecomspace.com/datatech-edge.htmlVisited: October 12, 2011.

[6] http://www.telecomspace.com/3g-cdma2000.htmlVisited: October 12, 2011.

[7] http://www.3gpp.org/article/gprs-edgeVisited: October 13, 2011.

[8] http://www.wave-report.com/blog/?p=72Visited: October 13, 2011.

[9] http://www.intel.com/support/wireless/sb/CS-025345.htmVisited: October 13, 2011.

[10] http://www2.electronicproducts.com/Migrating_to_an_all_IP_network-article-OCTMOT1-oct2003-html.aspxVisited: October 17, 2011.

[11] http://mobileinsight.blogspot.com/2008/01/3g-vs-4g.htmlVisited: October 17, 2011.

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Figure 1: http://wiredcpu.com/what-is-gprs/Visited: October 17, 2011.

Figure 2: http://cecfoces.wordpress.com/2010/06/06/fourth-generation-4g-mobiles/Visited: October 17, 2011.

Figure 3: http://connectedplanetonline.com/wireless/technology/mimo_ofdm_091905/Visited: October 17, 2011.

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