Cellular Networks

1. Cellular Networks Lecture 6 Paul Flynn

2. Cellular Telephony - Architecture

4. Very Basic Cellular/PCS Architecture Mobility Database Public Switched Telephone Network Base Station Controller Mobile Switching Center (MSC) Radio Network Base Station (BS) Mobile Station

5. Duplex Communication - FDD • FDD: Frequency Division Duplex Base Station B Mobile Terminal M Forward Channel Reverse Channel Forward Channel and Reverse Channel use different frequency bands

6. Frequency Frequency Time Time Frequency Time Access Methods FDMA TDMA CDMA

7. Clusters • A cluster is a group of cells • No channels are reused within a cluster A seven Cell Cluster

8. Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service Reverse Channel Forward Channel 991 992 … 1023 1 2 … 799 991 992 … 1023 1 2 … 799 824-849 MHz 869-894 MHz Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 825.0 0.030(N-1023) + 825.0 Forward Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 870.0 0.030(N-1023) + 870.0 (Channels 800-990 are unused) Channel bandwidth is 45 MHz

9. Frequency Reuse • Only a small number of radio channel frequencies were available for mobile systems • Therefore engineers had to find a way to reuse radio channels to carry more than one conversation at a time • The solution the industry adopted was called frequency reuse. Implemented by restructuring the mobile telephone system architecture into the cellular concept

10. Frequency Reuse • The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area • Cells are assigned a group of channels that is completely different from neighbouring cells • The coverage area of cells is called the footprint and is limited by a boundary so that the same group of channels can be used in cells that are far enough apart

11. Frequency Reuse • Cells with the same number have the same set of frequencies Frequency Reuse

12. f2 f7 f3 f1 f6 f4 f5 Frequency Reuse using 7 frequencies allocations f2 f7 f3 f1 f6 f4 f2 f5 f2 f7 f3 f7 f3 f1 f2 f1 f6 f4 f7 f3 f6 f4 f5 f1 f5 f6 f4 f5 Each cell is generally 4 to 8 miles in diameter with a lower limit around 2 miles.

13. Cell Splitting • Allows urban centres to be split into as many areas as necessary for acceptable service levels in heavy-traffic regions, while larger, less expensive cells can be used to cover remote rural regions

14. Cellular Concept with Sectors frequency re-use base station

15. Hand-off • The final obstacle in the development of the cellular network involved the problem created when a mobile subscriber moved from one cell to another during a call

16. GSM infrastructureMSC, BSC, BTS, VLR, HLR, GSGN, GSSN

17. Compared to a fixed network Gateway MSC Transit exchang Local switches MSC BSC Subscriber stage Fixed phone MS

18. What’s new? • Radio access network • Encryption • Voice coding • Locate a mobile station • Identify and authenticate • Handle mobility during a call

19. A bird eye’s view GMSC Access Network MSC databases BTS BSC BSC BSC BTS MS BTS

20. ”Typical” Mobile operator • One to ten MSC per 1 M subscribers • Ten to one hundred BSC per MSC • Thousands of BTS per 1 M subscribers

21. Base Transceiver Station • Controls the radio link • encryption • error control • signal strength • 1 - 6 duplex carriers, for example: • two layers • 120o sectors • (6+8)*3 = 42 voice calls • Cost ~ 100 – 200 k$

22. Base Station Controller • communication with the mobile terminal • local hand-over • voice codecs • carrier allocation • paging to terminals • talks to the MSC • serves up to 40 BTSs • could be co-located with MSC

23. Mobile Switching Centre • Mobility management • identifies and authenticates • locates • switches between BSCs • Handover to other MSCs • 64 kbps regular voice channels

24. Radio Access network A carrier is divided into logical channels control channels CCH traffic channels TCH The first carrier holds 2 controll channels and 6 traffic channels. Additional carriers holds only traffic channels.

25. Control Channels • Broadcast • Frequency correction: to synchronize (FCCH) • Broadcast control: this is me, these are my neighbours (BCCH) • Common control • Paging: to notify a mobile station (PCH) • Random access: for the mobile to request service (RACH) • Access grant: reply with assigned dedicated control channel (AGCH) • Dedicated control • Standalone dedicated control: used during call set-up, SMS etc (SDCCH) • Slow associated control: power, time etc (SACCH) • Fast associated control: handover etc, uses the TCH (FACCH) • Cell broadcast: cell broadcast

26. Traffic Channels • Duplex • Error control • Forward Error Correction (FEC) • retransmission (ARQ) • Full rate (TCH/F) • 13 Kbps speech • 9,6 or 14,4 Kpbs data • Half rate (TCH/H) • 6,5 Kbps speech • 7,2 or 4,8 Kbps data

27. Logical channels Hyperframe: 2048 superframes 3h28m Superframe: 26 or 51 multiframes 6.12 s CCH CCH Multiframe: 26 or 51 TDMA frames CCH TCH 8 time-slot TDMA frame 4.143 ms

28. One TDMA frame 148 b 0.577 ms tail guard 8.25 tail training Normal burst 3 57 b 26 b 57 b 3 user data user data stealing flags Frequency correction burst Synchronization burst Dummy burst Access burst

29. Keeping track of a mobile station VLRvisiting location register Location area Location area update the VLR with newlocation area

30. Moving to a new MSC VLRwhich LA which MSC ? Location area Location area update the VLR with newlocation area and new MSC

31. but also…. HLRhome location register VLR update the home location register!

32. Home Location Register incomming call PSTN where is the mobile? GMSC HLR MSC How do we reach him? VLR

33. Mobile station numbers mobile subscriber ISDN number (MSISDN) i.e. the phone number PSTN GMSC HLR Mobile Station Roaming Number (MSRN). MSC VLR Temporary Mobile Subscriber Identity International Mobile Subscriber Identity

34. GPRS Internet Gateway GPRS Support NodeGGSN Access Network Packet Control Unit BTS BSC UDP/TCP tunnel Serving GPRS Support NodeSGSN BTS MS BTS

35. Looking to PCS from different Angles Internet PSTN (Telephone Network) Wireless Access Mobile Users • Laptop users • Pocket PC users • Mobile IP, DHCP enabled computers Mobile Users • Cell phone users • Cordless phone users Telecom People View Data Networking People View

36. Telecom and Data Networking Telecom Interest Data Networking Interest - Voice Transmission - Frequency Reuse • Handoff Management • Location Tracking • Roaming • QoS • GSM, CDMA, Cordless Phones, • GPRS, EDGE • Data Transmission • Mobile IP (integrating mobile hosts to internet) • Ad-hoc Networks • TCP over Wireless • Service Discovery • Radio Propagation • Link Characteristics • Error Models -Wireless Medium Access (MAC) - Error Control

37. Major Mobile Radio Standards - Europe

38. Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service Reverse Channel Forward Channel 991 992 … 1023 1 2 … 799 991 992 … 1023 1 2 … 799 824-849 MHz 869-894 MHz Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 825.0 0.030(N-1023) + 825.0 Forward Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 870.0 0.030(N-1023) + 870.0 (Channels 800-990 are unused) Channel bandwidth is 45 MHz

39. 2G Technologies

40. GSM Speech Signal Processing

42. GSM and CDMA Coverage Map Worldwide

43. Evolution

44. 1G TECHNOLOGY • 1G refers to the first generation of wireless telephone technology, mobile telecommunications which was first introduced in 1980s and completed in early 1990s. • It's Speed was upto 2.4kbps. • It allows the voice calls in 1 country. • 1G network use Analog Signal. • AMPS was first launched in USA in 1G mobile systems.

45. DRAWBACKS OF 1G • Poor Voice Quality • Poor Battery Life • Large Phone Size • No Security • Limited Capacity • Poor Handoff Reliability 1G Wireless System

46. 2G TECHNOLOGY • 2G technology refers to the 2nd generation which is based on GSM. • It was launched in Finland in the year 1991. • 2G network use digital signals. • It’s data speed was upto 64kbps. Features Includes: • It enables services such as text messages, picture messages and MMS (multi media message). • It provides better quality and capacity .

47. DRAWBACKS OF 2G • 2G requires strong digital signals to help mobile phones work. If there is no network coverage in any specific area , digital signals would weak. • These systems are unable to handle complex data such as Videos. 2G Wireless System

48. 3G TECHNOLOGY • 3G technology refer to third generation which was introduced in year 2000s. • Data Transmission speed increased from 144kbps- 2Mbps. • Typically called Smart Phones and features increased its bandwidth and data transfer rates to accommodate web-based applications and audio and video files.

49. FEATURES OF 3G TECHNOLOGY • Providing Faster Communication • Send/Receive Large Email Messages • High Speed Web / More Security Video Conferencing / 3D Gaming • TV Streaming/ Mobile TV/ Phone Calls • Large Capacities and Broadband Capabilities • 11 sec – 1.5 min. time to download a 3 min Mp3 song.

50. DRAWBACKS OF 3G TECHNOLOGY • Expensive fees for 3G Licenses Services • It was challenge to build the infrastructure for 3G • High Bandwidth Requirement • Expensive 3G Phones. • Large Cell Phones