Speed of different cellular networks. E- Business Prof. Eduard Heindel

Transcription

1 Speed of different cellular networks E- Business Prof. Eduard Heindel By: Ahmed Hefny

2 Hereby I declare that I have prepared this term paper by myself without anyoneʼs help and all the sources I used has been citied as footnotes and bibliography. Ahmed Hefny 2

3 Table of Contents 1. WHAT IS CELLULAR NETWORKS? CONCEPT FREQUENCY REUSE MOVEMENT FROM CELL TO CELL AND HANDOVER EXAMPLE OF A CELLULAR NETWORK: THE MOBILE PHONE NETWORK SPEED OF DIFFERENT CELLULAR NETWORKS G G... 7 COMPETING 2G TECHNOLOGIES / 3G... 8 "TRUE" 3G G FUTURE OF CELLULAR NETWORKS CONCLUSION BIBLIOGRAPHY

4 1. What is Cellular Networks? A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Cellular networks offer a number of advantages over alternative solutions: Increased capacity Reduced power use Larger coverage area Reduced interference from other signals An example of a simple non-telephone cellular system is an old taxi driver's radio system where the taxi company has several transmitters based around a city that can communicate directly with each taxi. 1.1 Concept In a Cellular radio system, a land area to be supplied with radio service is divided into regular shaped cells, which can be hexagonal, square, circular or some other irregular shapes, although hexagonal cells are conventional. Each of these cells is assigned multiple frequencies (f 1 - f 6 ) that have corresponding radio base stations. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells, as that would cause co-channel interference. The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission. If there is a single plain transmitter, only one transmission can be used on any given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency. In the simple case of the taxi company, each radio had a manually operated channel selector knob to tune to different frequencies. As the drivers moved around, they would change from channel to channel. The drivers knew which frequency covered approximately what area. When they did not receive a signal from the transmitter, they would try other channels until they found one that worked. The taxi drivers would 4

5 only speak one at a time, when invited by the base station operator (in a sense TDMA). 1.2 Frequency Reuse The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must use different frequencies, however there is no problem with two cells sufficiently far apart operating on the same frequency. The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, D is calculated as Where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. 1 Depending on the size of the city, a taxi system may not have any frequencyreuse in its own city, but certainly in other nearby cities, the same frequency can be used. In a big city, on the other hand, frequency-reuse could certainly be in use. Recently also OFDMA based systems such as LTE are being deployed with a frequency reuse of 1. Since such systems do not spread the signal across the frequency band, inter-cell radio resource management is important to coordinates resource allocation between different cell sites and to limit the inter-cell interference. There are various means of Inter-cell Interference Coordination (ICIC) already defined in the standard 2. Coordinated scheduling, multi-site MIMO or multi-site beam forming are other examples for inter-cell radio resource management that might be standardized in the future. 1.3 Movement from cell to cell and handover In a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed. If a communication was interrupted due to a loss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency. In a cellular system, as the distributed mobile transceivers move from cell to 1 J. E. Flood. Telecommunication Networks. Institution of Electrical Engineers, London, UK, chapter V. Pauli, J. D. Naranjo, E. Seidel, Heterogeneous LTE Networks and Inter-Cell Interference Coordination, White Paper, Nomor Research, December

6 cell during an ongoing continuous communication, switching from one cell frequency to a different cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the handover or handoff. Typically, a new channel is automatically selected for the mobile unit on the new base station which will serve it. The mobile unit then automatically switches from the current channel to the new channel and communication continues. The exact detail of the mobile systemʼs move from one base station to the other varies considerably from system to system (see the example below for how a mobile phone network manages handover). 1.4 Example of a cellular network: the mobile phone network The most common example of a cellular network is a mobile phone (cell phone) network. A mobile phone is a portable telephone which receives or makes calls through a cell site (base station), or transmitting tower. Radio waves are used to transfer signals to and from the cell phone. Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that a limited number of radio frequencies can be simultaneously used by many callers with less interference. A cellular network is used by the mobile phone operator to achieve both coverage and capacity for their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in that area. All of the cell sites are connected to telephone exchanges (or switches), which in turn connect to the public telephone network. In cities, each cell site may have a range of up to approximately ½ mile, while in rural areas, the range could be as much as 5 miles. It is possible that in clear open areas, a user may receive signals from a cell site 25 miles away. Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS (analog), the term "cell phone" is in some regions, notably the US, used interchangeably with "mobile phone". However, satellite phones are mobile phones that do not communicate directly with a ground-based cellular tower, but may do so indirectly by way of a satellite. 3 3 Bernhard H. Walke. Mobile Radio Networks: Networking, protocols and traffic performance. John Wiley and Sons, LTD West Sussex England, Chapter 2. 6

7 2. Speed of Different Cellular Networks 1G First generation services were analogue services for cell phones. These were (and are) for voice only; the technology didn't provide for SMS or other data services. 1G is circuit switched. This means that when you place a call, a connection is established for you, and is maintained until you hang up. You are billed for the duration of the call, regardless of how much talking occurred. This is appropriate for voice communication where one person or the other is talking at any point in time. 2G Moving from 1G to 2G saw the transition from analogue to digital. As in other areas, the impact of going digital was revolutionary. The transition provided the ability to store, copy, encrypt and compress data, and allowed data transmission without loss and with error-correction. It provided wireless cellular data services such as internet access, with speeds of 14.4.kbps (theoretical), 9.6 kbps kbps (real). In addition, voice quality improved. 2G was also circuit-switched; you still paid for total connection time. This is less appropriate for data than voice, as data is often "bursty", with periods of transmission activity and then periods of silence. This is not a good deal for the consumer or the carrier. The consumer has to pay for dead time, and the carrier has to reserve a slice of spectrum which could be sold to someone else. 4 Competing 2G Technologies The generic term for 2G services is PCS (Personal Communications services). There are two 2G technologies in Canada, GSM and CDMA, that are incompatible with each other in every respect. This incompatibility explains some things about the evolution of the market and carrier relationships. GSM stands for Global System for Mobility. It is based on a time-sharing process in which a slice of spectrum is shared between multiple users, by dividing creating small time-slices and allocating a slice to each user in turn. One of the big benefits of GSM is its coverage. It is the standard 2G technology in Europe, with the potential for roaming 90+ countries with same 4 Greyfriars Consulting Group 7

8 phone. Globally, 70% of the world's digital subscribers are on GSM. Both Rogers Wireless and Microcell use GSM. CDMA stands for Code Division Multiple Access. It is an elegant technology, but also a complicated one that cannot be described in a few words. Both Bell Mobility and Telus Mobility use CDMA. 2.5 / 3G Moving from 2G to 2.5G / 3G introduced another revolutionary change, the introduction of packet switching for data rather than circuit switching. Packet switching is an unlikely seeming technology that breaks a message into pieces and sends each piece individually across the network, together with control information on whether it is the first, second, etc packet in the set. The packets travel through the network to their destination, possibly taking different paths depending on network conditions, where they are reassembled in the correct order. For the consumer, packet switching provides two benefits. First, the commodity being sold is packets, not network time connected, so the pricing model becomes more data oriented. The consumer does not have to pay for dead time. Carriers provide a large variety of data oriented plans, just as they do with basic cell phone plans. For example, 1MB of data sent might cost up to $6-7. Each packet requires a significant amount of control information to route and sequence the packet, so your actual data may be less than 1MB. The second benefit to the consumer is that the internet is "always-connected" or "always-on". There is no need to make a connection or hang up; users experience constant connection to the internet, just like home subscribers of ADSL or cable internet connection. There is another benefit to consumers of 2.5 / 3G services, and that is speed. They have a theoretical maximum speed of 115 kbps, with real speeds around 56 kbps (a common speed for dial-up connections to the internet). The two 2G technologies in Canada extend to two 2.5G technologies, GSM/GPRS and 1XRTT, likewise incompatible in every respect. GPRS stands for General Packet Radio Service, and is a data-oriented technology extending the GSM voice services. Rogers and Microcell use GSM/GPRS. Microcell was the first player out of the gate in June 2001, but is now wondering if it can stay in business. Rogers AT&T Wireless provides GPRS coverage to more than 93% of the Canadian population. This does not mean coverage of 93% of the Canadian geography, due to the concentrations of population, and there are many places where coverage would be desirable but is unavailable, such as in the oil patch and rural areas. 1XRTT is an abbreviation for CDMA2000 1XRTT and is usually abbreviated further to 1X. It is the current generation system used by Bell and Telus. Bell launched their service early in 2002 in the greater Toronto Area early Bell claimed cruising speeds of 86 kbps, compared to 56 kbps for dialup modems. 5 5 Greyfriars Consulting Group 8

9 "True" 3G Third-generation specifications call for even higher speeds 144 kbps in vehicles, 384 Kbps for pedestrians outdoors, and 2.48 Mbps in indoor offices. Some carriers are calling their current deployments 3G. This is contested by others as being the lowest rung of the 3G specification, and hence prefer to use the term 2.5G. As expected, each of the 2.5G technologies has a forward path to the 3rd generation. EDGE (Enhanced Data Rates for Global [or GSM] Evolution) is the true 3G offering along the GSM path. It provides data rates three times greater than GSM/GPRS, with speeds in the range kbps (up to 200 kbps in bursts). EDGE was rolled out across Canada in Being an extension of GSM/GPRS, EDGE will be widely available internationally, and supported by network operators in many countries, and over 60 network operators in over 40 countries have committed to EDGE for their next generation services. There are a couple of forward paths from CDMA2000 offering substantially higher data rates. Neither of the CDMA based carriers (Telus Mobility, Bell Mobility) had announced offerings or pilots at the time or writing. 4G In telecommunications, 4G is the fourth generation of cellular wireless standards. It is a successor to the 3G and 2G families of standards. In 2009, the ITU-R organization specified the IMT-Advanced (International Mobile Telecommunications Advanced) requirements for 4G standards, setting peak speed requirements for 4G service at 100 Mbit/s for high mobility communication (such as from trains and cars) and 1 Gbit/s for low mobility communication (such as pedestrians and stationary users). One of the key technologies for 4G and beyond is called Open Wireless Architecture (OWA), supporting multiple wireless air interfaces in an open architecture platform. A 4G system is expected to provide a comprehensive and secure all-ip based mobile broadband solution to laptop computer wireless modem, smartphones, and other mobile devices. Facilities such as ultra-broadband Internet access, IP telephony, gaming services, and streamed multimedia may be provided to users. 6 IMT-Advanced compliant versions of LTE and WiMAX are under development and called "LTE Advanced" and "WirelessMAN-Advanced" respectively. ITU has decided that LTE Advanced and WirelessMAN-Advanced should be accorded the official designation of IMT-Advanced. On December 6, 2010, ITU recognized that current versions of LTE, WiMax and other evolved 3G technologies that do not fulfill "IMT-Advanced" requirements could nevertheless be considered "4G", provided they represent forerunners to IMT- 6 Greyfriars Consulting Group 9

10 Advanced and "a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed." 3. Future of Cellular Networks 5G (5th generation mobile networks or 5th generation wireless systems) is a name used in some research papers and projects to denote the next major phase of mobile telecommunications standards beyond the 4G/IMT-Advanced standards effective since At present, 5G is not a term officially used for any particular specification or in any official document yet made public by telecommunication companies or standardization bodies such as 3GPP, WiMAX Forum, or ITU-R. New standard releases beyond 4G are in progress by standardization bodies, but are at this time not considered as new mobile generations but under the 4G umbrella. With multiple air-interface support capabilities and higher cell densities, future cellular networks will offer a diverse spectrum of user services. The resulting dynamics in traffic load and resource demand will challenge present control loop algorithms. In addition, frequent upgrades in the network infrastructure will substantially increase the network operation costs if done using current optimization methodology. This motivates the development of dynamic control algorithms that can automatically adjust the network to changes in both traffic and network conditions and autonomously adapt when new cells are added to the system. 7 7 Borst, Buvaneswari, Drabeck,

11 4. Conclusion Wireless communications is, by any measure, the fastest growing segment of the communications industry. As such, it has captured the attention of the media and the imagination of the public. Cellular systems have experienced exponential growth over the last decade and there are currently around two billion users worldwide. Indeed, cellular phones have become a critical business tool and part of everyday life in most developed countries, and are rapidly supplanting antiquated wireline systems in many developing countries. In addition, wireless local area networks currently supplement or replace wired networks in many homes, businesses, and campuses. Many new applications, including wireless sensor networks, automated highways and factories, smart homes and appliances, and remote telemedicine, are emerging from research ideas to concrete systems. The explosive growth of wireless systems coupled with the proliferation of laptop and palmtop computers indicate a bright future for wireless networks, both as stand-alone systems and as part of the larger networking infrastructure. 11

12 Bibliography J. E. Flood: Telecommunication Networks. Institution of Electrical Engineers, London, UK, chapter 12 V. Pauli, J. D. Naranjo, E. Seidel: Heterogeneous LTE Networks and Inter-Cell Interference Coordination, White Paper, Nomor Research, December 2010 Bernhard H. Walke. Mobile Radio Networks: Networking, protocols and traffic performance. John Wiley and Sons, LTD West Sussex England, Chapter 2 Greyfriars Consulting Group, Simon C. Borst, Arumugam Buvaneswari, Lawrence M. Drabeck, Michael J. Flanagan, John M. Graybeal, Georg K. Hampel, Mark Haner, William M. MacDonald, Paul A. Polakos, George Rittenhouse, Iraj Saniee, Alan Weiss, and Philip A. Whiting: Dynamic Optimizationin Future Cellular Networks