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  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 1 Dept. of ECE (2013-2014) 1. MOBILE COMMUNICATION 1.1 Revolution in telecommunication The telephone has long been important in modern living, but it use has been constrained by connecting wires. The advent of mobile radio telephony and particularly the cellular radio has removed this restriction and led to explosive growth in mobile throughout the world. The phone is really on move now.With the phenomenal and unprecedented growth of more than forty fold in just ten years a strong demand for mobile cellular services has created an industry which now accounts for more than one third of all telephone lines. 1.2 Concept of mobile communication The first wire line telephone system was introduced in the year 1877.Mobile communication systems as early as 1934 were based on Amplitude Modulation (AM schemes and only certain public organizations maintained such systems. The development of Frequency Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems began to witness many new changes. Mobile telephone was introduced in the year 1946. However, during its initial three and a half decades it found very less market penetration owing to high costs and numerous technological drawbacks. But with the development of the cellular concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising field of expanse which could serve wider populations. 1.3Mobile communication objectives The important objectives of mobile communications are Anytime anywhere communication Mobility& Roaming High capacity and subs density Efficient use of radio spectrum
  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 2 Dept. of ECE (2013-2014) Table 1.1: Different generations- Analog and Digital systems 1946-1960 1980 1990 2000 Appearance 1G 2G 3G Analog Digital Digital Multi Standard Multi Standard Unified Standard Terrestrial Terrestrial Terrestrial &Satellite The features and benefits expected in the new system Superior speech quality Low terminal, operational, and service costs A high level of security International Roaming Support of low terminal hand portable terminals A variety of new services and network facilities. 1.4Constraints in Implementation A host of services like teleservices supplementary services and value added services are being promised by GSM Networks. There are certain impairments in realizing an effective mobile communication system which has to meet the twin objectives of quality and capacity. (a) Radio frequency reuse High spectrum efficiency should be achieved at reasonable cost. The bandwidth on radio interface i.e. between the user equipment and the radio transceiver is to be managed effectively
  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 3 Dept. of ECE (2013-2014) to support ever increasing customer base with very limited number of radio carriers. For high BW services e.g. MMS as the GSM evolves towards 3G, more spectrums is demanded. (b) Multi path radio environment The most significant problem in mobile radio systems is due to the channel itself. In mobile radio systems, indeed,it is rare for there to exist one strong line of sight path between transmitter and receiver. Usually several significant signals are received by reflection and scattering from buildings etc. .And then they are Multiple paths from transmitter receiver. Fig 1.1 Multipath radio environment The signals on these paths are subject to different delays phase shifts and Doppler shifts and at the receiver in random phase relation to one another. The interferences between these signals give rise to a number of deleterious effects. The most important of these are Fading and Dispersion. Fading is due to the interference of multiple signals with random relative phase that causes variations in the amplitude of the received signal. This will increase the error rate in digital system since errors will occur when the signal-to noise ratio drops below certain threshold.
  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 4 Dept. of ECE (2013-2014) Dispersion is due to differences in the delay of the various paths, which disperses transmitted pulses in time. If the variation of delay is comparable with the symbol period delayed signals from an earlier symbol may interface with the next symbol causing Inter- symbol interference (ISI). (c) Mobility management Mobility management is concerned with how the network supports this function. When a call is made to mobile customer the network must be able to locate the mobile customer. Network attachment process which includes a location updating process is the answer for mobility management. In the location update process , the network databases are updated dynamically so that the mobile can be reached to offer the services if this process is not done efficiently it will result in poor call management and network congestion. (d) Services International roaming shall be provided. Advanced PSTN services should be provided consistent with ISDN services at limited bit rates only. Encryption should be used to improve security for both the operators and the customers. (f) Cost The system parameters should be chosen to limit costs particularly mobiles and handsets .In a competitive environment cost is the deciding factor for the survival of an operator.
  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 5 Dept. of ECE (2013-2014) 2. BANDWIDTH MANAGEMENT 2.1 INTRODUCTION Radios move information from one place to another over channels and radio channel is an extraordinarily hostile medium to establish and maintain reliable communications. The channelis particularly messy and unruly between mobile radios. All the schemes and mechanisms we use to make communications possible on the mobile radio channel with some measure of reliability between a mobile and its base radio station are called physical layer or the layer1 procedures. The mechanisms include modulation, power control, codingtiming, and host of other details that manage establishment and maintenance of the channel the radio channel has to be fully exploited for maximum capacities and optimum quality of service. Band width is a scarce natural resource. The bandwidth has to be managed for maximum capacity of the system and interference free communications. The spectrum availability for an operator is very limited .The uplink or downlink spectrum is only 25 MHz, out of this 25 MHz, 124 carriers of each 200 kHz are generated. These carriers are to be shared amongst different operators. And as a result each operator gets only a few tens of carriers making a spectrum management a challenging area. 2.2 Cellular structures and Frequency Reuse Traditional mobile service was structured similar to television broadcasting: One very powerful transmitter at the highest spot in area would broadcast in anarea radius of up to fifty kilometers. The scenario changes as the mobile density as well as coverage area grows. The answer to tackle the growth is the extensions based on addition of new cells.Thecellular concept structured the mobile telephone network in a different way.Instead of using one powerful transmitter many low-powered transmitter were placed throughout a coverage area. For example, by dividing metropolitan region into one hundred different areas (cells) with low power transmitters using twelve conversations (channels) each, the system capacity could theoretically be increased from twelve to thousands of conversations using one hundred low power transmitters while reusing the frequenciesThe cellular concept employs variable low power levels, which allows cells to be sized according to subscriber density and demand of a given
  • 3G UMTS HSPA RADIO NETWORK OPTIMIZAION 6 Dept. of ECE (2013-2014) area. As the populations grow, cells can be added to accommodate that growth. Frequencies used in one cell cluster can be reused in other cells. Conversations can be handed over from cell to cell to maintain constant phone service as the user moves between cells. Cells: A cell is the basic geographic unit of cellular system. The term cellular comes from the honeycomb areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending upon landscape. Because of the constraint imposed by natural terrain and man-made structures, the true shape of cell is not a perfect hexagon. (a) Cellular System Characteristics The distinguishing features of digital cellular systems compared to other mobile radio systems are: Small cells A cellular system uses many base stations with relatively small coverage radii (on the order of a 100 m to 30 km). Clusters and Frequency reuse The spectrum allocated for a cellular network is limited. As a result there is a limit to the number of channels or frequencies that can be used. A group of cells is called a cluster. All the frequencies are used in a cluster and no frequency is reused with in the cluster. And the total set of frequencies is repeated in the adjacent cluster. Like that the total service area, i.e. may be a country or a continent, can be served with a small group of frequencies. Frequency reuse is possible because the signal fades over the distance and hence it can be reused .For this reason each frequency is usedsimultaneously by multiple base-mobile pairs; located at geographically distant cells. This frequency reuse allows a much higher subscriber density per MHz of spectrum than other systems. System capacity can be further increased by reducing the cell size (the coverage area of a single base station), dow