Chapter 3 Cellular Networks. Wireless Network and Mobile Computing Professor: Dr. Patrick D. Cerna

Transcription

1 Chapter 3 Cellular Networks Wireless Network and Mobile Computing Professor: Dr. Patrick D. Cerna

2 Objectives! Understand Cellular Phone Technology! Know the evolution of evolution network! Distinguish the characteristics of GSM, 2G, 3G, 4G and LTE! Share a Mobile Data Connection with Your PC! Differentiate Mobile Data Versus Wi-Fi:! Learn to co-exixtmobile Service and Bluetooth!

3 Understanding Cellular Phone Technology! Signals carrying voice, text, and digital data are transmitted via radio waves from one device to another.! In the case of cellular networks, the data is transmitted not to a central hub in a small network of devices (as it is with Wi- Fi) or even directly from device to device (as it is with Bluetooth), but through a global network of transmitters and receivers.

4 Cells in a Network! a mobile phone network is divided into thousands of overlapping geographic areas, or cells.! It can be envisioned as a mesh of hexagonal cells, as shown in Figure 3.1, each with its own base station at the center

5 Figure 3.1. Cells in a cellular network.

6 ! The base station at the center of each group of cells functions as the hub for those cells not of the entire network, but of that individual piece of the network! RF signals are transmitted by an individual phone and received by the base station, where they are then retransmitted from the base station to another mobile phone. Transmitting and receiving are done over two slightly different frequencies.

7 ! Base stations are connected to one another via central switching centers which track calls and transfer them from one base station to another as callers move between cells.! Each base station is also connected to the main telephone network, and can thus relay mobile calls to landline phones.

8 Carrying a Two-Way Radio! A mobile phone is actually a two-way radio, containing both a low-power transmitter (to transmit data) and a receiver (to receive data).! The typical cell phone includes a dual-strength transmitter, capable of transmitting either 0.6-watt or 3-watt signals (while AM 5,000 50,000 watts)! Reason is that they re transmitting within a relatively limited range within the current network cell.

9 How Does a Mobile Network Work?! cellular network, employs the use of radio frequencies that can be used simultaneously by several callers at one and the same time Types of Mobile technologies: 1. GSM (Global System for Mobile Communication) 2. GPRS (General Packet Radio Service), 3. CDMA (Code Division Multiple Access), 4. EDGE (Enhanced Data Rates for GSM Evolution), 5. iden (Integrated Digital Enhanced Network) and 6. EV-DO (Evolution-Data Optimized).

10 Transmission! The transmissions of a base station and the phones within its cell do not make it very far outside that cell.! The same frequencies can be reused extensively across the city.! The power consumption of the cell phone, which is normally battery-operated, is relatively low. Low power means small batteries, and this is what has made handheld cellular phones possible.!

11 Cont. transmission! A typical large city can have hundreds of towers. But because so many people are using cell phones, costs remain low per user.! Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO).! This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.!

12 Roaming! If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming! A system identification number (SID) is broadcast by one or more base stations to identify a cellular network in a certain area (usually contiguous).! The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid

13 ! Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells

14 Cell Phones and CBs! Citizens Band radio (also known as CB radio) in many countries, a system of short-distance radio communications between individuals on a selection of 40 channels within the 27 MHz (11 m) band.

15 Full-duplex vs. half-duplex! Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time.! However, A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.

16 Channels! A walkie-talkie typically has one channel! A CB radio has 40 channels.! A typical cell phone can communicate on 1,664 channels or more!!

17 Range -! A walkie-talkie can transmit about 1 mile (1.6 km) using a 0.25-watt transmitter.! A CB radio, because it has much higher power, can transmit about 5 miles (8 km) using a 5-watt transmitter.! Cell phones operate within cells, and they can switch cells as they move around. Cells give cell phones incredible range.! Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.

18 Along Comes Digital! Digital cell phones use the same radio technology as analog phones, but they use it in a different way! Many digital cellular systems rely on frequencyshift keying (FSK) to send data back and forth over AMPS.! FSK uses two frequencies, one for 1s and the other for 0s, alternating rapidly between the two to send digital information between the cell tower and the phone

19 ! Clever modulation and encoding schemes are required to convert the analog information to digital, compress it and convert it back again while maintaining an acceptable level of voice quality

20 Cellular Access Technologies! Frequency division multiple access (FDMA)! Time division multiple access (TDMA)! Code division multiple access (CDMA)! The first word tells you what the access method is. The second word, division, lets you know that it splits calls based on that access method

21 ! FDMA puts each call on a separate frequency.! TDMA assigns each call a certain portion of time on a designated frequency.! CDMA gives a unique code to each call and spreads it over the available frequencies. The last part of each name is multiple access. This simply means that more than one user can utilize each cell

22 Telecommunication Systems! GSM - GSM (Global system for mobile communications) is the standard by which the vast majority of mobile handsets work in Europe and is becoming dominant in other parts of the world with over 2 billion people currently using the system.! The majority of GSM networks use 900MHz and 1800MHz but in the US the 850MHz and 1900Mhz are prominent.!

23 GSM! Most GSM phones are primarily used for voice but can be used for mobile internet access via the GPRS Core Network.

24 GPRS! GPRS or General Packet Radio Service is a system used to transmit data at speeds of up to 60 kbits per second and is a battery friendly way to send and receive s and to browse the internet but in these days of broadband connectivity it will be seen as slow by some.

25 ! To set up GPRS connections on your smartphone you will need to obtain specific information from your mobile provider to input into your phone.! Most are happy to provide this information and some manufacturers such as Nokia offer pre-configured files that you can install onto your phone for your network.

26 EDGE! EDGE (Exchanged Data rates for GSM Evolution) is a recent development based on the GPRS system and has been classified as a '3G' standard due to the fact that it can run at up to kbits per second.! It can be used for heavy mobile data transmission such as receiving large attachments and browsing complex web pages at great speed.

27 1G! Analog cellphones uses Advanced Mobile Phone System (AMPS) standard, which operated in a range of frequencies between 824MHz and 894MHz, dubbed the 800MHz band.! Because analog phones could transmit only analog voice data, not digital data, they couldn t be used to access the Internet or transmit text messages.

28 2G! 2G networks and phones were used to transmit non-voice data. This ushered in the era of text messaging, in the form of Short Message Service (SMS) and, later, Multimedia Message Service (MMS).! It also enabled access to the Internet, for , web browsing, and the like.! the original analog voice signal is digitized into a series of 0s and 1s; the resulting digital signal is then compressed and transmitted across the assigned frequency band.

29 2G Standards 1. Code Division Multiple Access (CDMA). - This standard operates in the same 800MHz band used by the previous analog transmissions and is employed by Sprint and Verizon. 2. Global System for Mobile Communications (GSM). This standard operates in the 1,900MHz band and is used by AT&T and T-Mobile.!

30 3G! 3G networks feature increased bandwidth and transfer rates that better accommodate the transfer of digital data necessary for Internet access and the use of web-based applications! Today s 3G networks boast transfer speeds up to 2Mbps; in contrast, 2G phones can only transfer data at around 144Kbps.

31 3G Standards! CDMA2000 is an evolution of the previous CDMA standard. It s used by Sprint and Verizon.! Universal Mobile Telecommunications System (UMTS) is an evolution of the GSM standard used by AT&T and T-Mobile.

32 4G! Carriers are just starting to roll out 4G networks, and suppliers are just starting to produce 4G smartphones! 4G promises data transmission rates in excess of 1Gbps,! LTE Advanced is a mobile communication standard and a major enhancement of the Long Term Evolution (LTE) standard. It was formally submitted as a candidate 4G system

33 4G Standards! Long Term Evolution (LTE). This standard promises data download rates to mobile users up to 300Mbps. It s used by AT&T and Verizon.! Evolved High Speed Packet Access (HSPA+). This standard promises data download rates up to 168Mbps, although current rates top out at 42Mbps. It s used by T-Mobile.! Worldwide Operability for Microwave Access (WiMax). This standard promises data download rates of 128Mbps. It s used by Sprint.

34 Data Transmission Comparison

35 Sharing a Mobile Data Connection with Your PC! 3G s maximum 2Mbps data download speed is close to that offered by many home Internet service providers (ISPs); DSL, for example, typically delivers speeds in the same 2Mbps range.! Naturally, when we re talking 4G networks with speeds approaching 300Mbps, cellular Internet is suddenly faster than what you get at home or sitting in your local Wi-Fi hotspot.! With that in mind, why not use your smartphone to provide Internet access for your computer?

36 ! Most cellular providers offer external data modems that provide access to their 3G or 4G cellular-data network.! These modems are small and portable and connect to your computer via USB; they let you access the cellular network with your PC, just as you do with your phone.

37 Figure 3.3 Sharing a cellular data signal via physical tether

38 Tethering Your Smartphone! This process is called tethering, and it s a great way to share a connection and an existing data service plan.! Not all carriers support this type of tethering, however, and those that do may charge extra for it in addition to the normal data usage plan.

39 ! A Wi-Fi tether turns your smartphone into a portable Wi-Fi hotspot.! You establish an ad-hoc Wi-Fi network with your phone as the router, and then connect your computer to that network to share the phone s Internet connection

40 ! Some manufacturers make what they callmobile broadband routers that receive a 3G (or, in some instances, 4G) mobile signal and then convert it into Wi-Fi.! The Wi-Fi signal is then broadcast throughout your home, same as with a wireless router, and all of your Wi-Fi-enabled devices can connect to it to access the Internet.

41 Mobile Broadband Router/Pocket WIFI

42 Mobile Data Versus Wi-Fi: Choosing One or the Other! Your smartphone can connect to the Internet either via Wi-Fi or via your cellular service s network. Most phones are configured to use the nearest Wi-Fi signal by default, as Wi-Fi is both faster than 3G data connections and doesn t rack up charges against your phone s data plan

43 ! This default-to-wi-fi behavior makes a lot of sense, especially if you consume a lot of media online. Checking your won t necessarily eat up your available data plan, but viewing a lot of photos on web pages or consuming streaming music or video will. If you use your phone to watch a lot of streaming movies or TV shows, chances are you ll blow through your data plan much sooner than you d like, and be liable for costly overage charges.

44 ! Naturally, you can, at any time, switch off your phone s Wi- Fi, which then forces your phone to connect to the cellular network to access the Internet. In most instances, however, you probably want to use Wi-Fi when it s available and fall back on your 3G network only when you have to.

45 Mobile Service and Bluetooth: Learning to Co-Exist! there s the issue of Bluetooth wireless, which is also built into most smartphones.! Bluetooth is typically used to connect your phone to cordless headsets and your car s built-in phone/audio system.! In this respect, Bluetooth and cellular wireless co-exist quite nicely; in fact, you can easily flow one wireless connection through the other.

46 ! You can see this co-existence in action when you connect to your phone s data network while your phone is connected to another Bluetooth-enabled device.

47 Summary! Cellular telephone networks are so-named because they re built from a series of adjoining cells; as a phone travels from one point to another, its signal is handed off from cell to cell.! There have been four generations of cell phone technology: 1G (analog), 2G (original digital), 3G (faster digital), and 4G (even faster digital, designed specifically for smartphone and streaming video use).! Using a smartphone to access the Internet is painful on older 2G networks, acceptable on 3G networks, and downright enjoyable on the latest 4G networks.! Most smartphones can connect to the Internet via either Wi-Fi or cellular data networks; Wi-Fi is faster than 3G cellular (but not as fast as 4G) and doesn t use up your monthly data plan.! Smartphones can connect to cellular and Bluetooth networks simultaneously, in order to beam cellular voice calls to a Bluetooth-enabled device.

48 References! [1] Beaulieu, Marck (2002). Wireless Internet, Applications and Architecture. Addison-Wesley! [2] Goldsmith, Andrea (2005). Wireless communications. Cambridge, UK: Cambridge University Press! [3] [4] [5]