1. Cellular Networks

2. Overview Data Rates 1980 1990 2000 2010 Years 2 Mbps 3G 1 Mbps
(144Kbps to 2Mbps)
1 Mbps
100 Kbps
2.5G
(10-150Kbps)
10 Kbps 2G
(9.6Kbps)
1 Kbps 1G
(<1Kbps)
1980
1990
2000
2010
Years

3. Cellular networks: From 1G to 3G
1G: First generation wireless cellular: Early 1980s
Analog transmission, primarily speech: AMPS (Advanced Mobile Phone Systems) and others
2G: Second generation wireless cellular: Late 1980s
Digital transmission
Primarily speech and low bit-rate data (9.6 Kbps)
High-tier: GSM, IS-95 (CDMA), etc
Low-tier (PCS): Low-cost, low-power, low-mobility e.g. PACS
2.5G: 2G evolved to medium rate (< 100kbps) data
3G: future Broadband multimedia
144 kbps kbps for high-mobility, high coverage
2 Mbps for low-mobility and low coverage
Beyond 3G: research in 4G

4. Issues Vital to cellular
Frequency allocation
Licensed
Many providers
Multiple Access
Many users
Wide area of coverage
Traffic management
Location management
High mobility (in cars, trains)
Multiple suppliers
Handoff management, roaming
General principles
Handled differently by different generations

5. Multiple Access Techniques: How to allocate users
Session4
Session3
Session1
Session2
Session3
Session4
Frequency
Session2
Frequency
Session1
Time
Time
Time Division
Multiple Access (TDMA)
2G TDMA
3G TDMA
Frequency Division
Multiple Access (FDMA)
1G Cellular (AMPS)
All sessions
based on a
code
Frequency
Time
2G CDMA (IS-95)
3G CDMA
Code Division
Multiple Access (CDMA)

6. A Cellular Network Cell 1 Cell 2 Mobile Telephone Switching Center
(MTSC)
Public
Switched
Telephone
Network
(PSTN)
Cell 2
HLR
VLR
Base Transceiver Station (BTS)
Mobile User
Cordless connection
HLR = Home Location Register
VLR = Visitor Location Register
Wired connection

7. Overview of Location Services
Cell-id based location.
assigned an id of the cell that you are in.
cell-id is stored in a database.
As you move from one cell to another, you are assigned a different cell-id and the location database is updated.
most commonly used in cellular networks. (HLR, VLR)
Neighborhood polling: Connected mobile units only move to adjacent cells
Angle of arrival (AOA). the angle at which radio waves from your device "attack" an antenna is used to calculate the location of the device.
Time taken. In this case, the time taken between the device and the antenna is used to calculate the location of the device.
Network assisted Global Positioning System (GPS). a GPS chip is installed inside a phone and thus the location of the user is tracked.

8. Cellular System Handoffs (typically 30 mseconds):
Public
Switched
Telephone
Network
(PSTN)
Mobile
Switching
Center
(MTSC)
Cell 1
Cell 2
HLR
VLR
Handoffs (typically 30 mseconds):
1. At any time, mobile station (MS) is in one cell and under the control of a BS
2. When a MS leaves a cell, BS notices weak signal
3. BS asks surrounding BSs if they are getting a stronger signal
4. BS transfers ownership to one with strongest signal
5. MTSO assigns new channel to the MS and notifies MS of new boss

9. 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

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

11. Frequency Reuse using 7 frequencies allocations
Each cell is generally 4 to 8 miles in diameter with a lower limit
around 2 miles.

13. Problem with Smaller Clustersize
Interfering cells are closer by when clustersize is smaller.

16. 0G Wireless
Mobile radio telephones were used for military communications in early 20th century
Car-based telephones first introduced in mid 1940s
Single large transmitter on top of a tall building
Single channel used for sending and receiving
To talk, user pushed a button, enabled transmission and disabled reception
Became known as “push-to-talk” in 1950s
CB-radio, taxis, police cars use this technology
IMTS (Improved Mobile Telephone System) introduced in 1960s
Used two channels (one for sending, one for receiving)
No need for push-to-talk
Used 23 channels from 150 MHz to 450 MHz

17. First-Generation Cellular
Advanced Mobile Phone Service (AMPS) invented at Bell Labs and first installed in 1982
Used in England (called TACS) and Japan (called MCS-L1)
Key ideas:
Exclusively analog
Geographical area divided into cells (typically 10-25km)
Cells are small: Frequency reuse exploited in nearby (not adjacent) cells
As compared to IMTS, could use 5 to 10 times more users in same area by using frequency re-use (divide area into cells)
Smaller cells also required less powerful, cheaper,smaller devices

19. Cell Design E D F E A D F C G A C B G E B D F A C G B
Cells grouped into a cluster of seven
Letters indicate frequency use
For each frequency, a buffer of two cells is used before reuse
To add more users, smaller cells (microcells) are used
Frequencies may not need to be different in CDMA (soft handoff)

20. Cellular Network Organization
Cell design (around 10 mile radius)
Served by base station consisting of transmitter, receiver, and control unit
Base station (BS) antenna is placed in high places (churches, high rise buildings) -
Operators pay around $500 per month for BS
10 to 50 frequencies assigned to each cell
Cells set up such that antennas of all neighbors are equidistant (hexagonal pattern)
In North America, two 25-MHz bands allocated to AMPS
One for transmission from base to mobile unit
One for transmission from mobile unit to base

21. Approaches to Increase Capacity
Adding/reassigning channels - some channels are not used
Frequency borrowing – frequencies are taken from adjacent cells by congested cells
Cell splitting – cells in areas of high usage can be split into smaller cells
Microcells – antennas move to buildings, hills, and lamp posts

22. Security Issues with 1G Analog cellular phones are insecure
Anyone with an all band radio receiver can listen in (many scandals)
Theft of airtime:
all band radio receiver connected to a computer
can record 32 bit serial number and phone number of subscribers when calling
can collect a large database by driving around
Thieves go into business - reprogram stolen phones and resell them

23. Second Generation Cellular
Based on digital transmission
Different approaches in US and Europe
US: divergence
Only one player (AMPS) in 1G
Became several players in 2G due to competition
Survivors
IS-54 and IS-135: backward compatible with AMPS frequency allocation (dual mode - analog and digital)
IS-95: uses spread spectrum
Europe: Convergence
5 incompatible 1G systems (no clear winner)
European PTT development of GSM (uses new frequency and completely digital communication)

28. Advantages of Digital Communications for Wireless
Voice, data and fax can be integrated into a single system
Better compression can lead to better channel utilization
Error correction codes can be used for better quality
Sophisticated encryption can be used

29. Differences Between First and Second Generation Systems
Digital traffic channels – first-generation systems are almost purely analog; second-generation systems are digital
Encryption – all second generation systems provide encryption to prevent eavesdropping
Error detection and correction – second-generation digital traffic allows for detection and correction, giving clear voice reception
Channel access – second-generation systems allow channels to be dynamically shared by a number of users

30. Integrating Data Over Cellular
Direct access to digital channel
Voice and data using one handset
PCS 1900 (GSM-1900)
9.6 kbps circuit switched data
14.4 kbps under definition
Packet mode specified
Short message service
IS-95-based CDMA
13 kbps circuit switched data

31. GSM (Global System for Mobile Communications)
Completely designed from scratch (no backward compatability)
Uses 124 channels per cell, each channel can support 8 users through TDM (992 users max)
Some channels used for control signals, etc
Several flavors based on frequency:
GSM (900 MHz)
GSM 1800 (called DCS 1800)
GSM 1900 (called DCS 1900) - used in North America
GSM 1900 phone only works in North America.
In Europe, you can transfer your SIM (Subscriber Identity Module) card to a phone of the correct frequency. This is called SIM-roaming.

38. GSM (2G-TDMA) Circuit mode data Short message service
Transparent mode
Non-transparent mode using radio link protocol
Data rate up to 9.6kb/s
Short message service
Limited to 160 characters
Packet mode data: Plans for GSM Phase 2+
Architecture specification very detailed (500 pages)
Defines several interfaces for multiple suppliers

40. Mobile Station and Base Station Subsystem (BSS)
Mobile station communicates across Um interface (air interface) with base station transceiver in same cell as mobile unit
Mobile equipment (ME) – physical terminal, such as a telephone or PCS
ME includes radio transceiver, digital signal processors and subscriber identity module (SIM)
GSM subscriber units are generic until SIM is inserted
SIMs roam, not necessarily the subscriber devices
BSS
BSS consists of base station controller and one or more base transceiver stations (BTS)
BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging

41. Network Subsystem Center
Mobile Switching Center (MSC) is at core; consists of several databases
Home location register (HLR) database – stores information about each subscriber that belongs to it
Visitor location register (VLR) database – maintains information about subscribers currently physically in the region
Authentication center database (AuC) – used for authentication activities, holds encryption keys
Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station

42. GSM Location Services 6 2 9 Terminating MSC Gateway MTSC BTS 10 Public
Switched
Telephone
Network
(PSTN) 1 10 10 9 10 7 8 5 3 4
VLR
HLR 10 5
6. Call routed to terminating MSC
7. MSC asks VLR to correlate call to
the subscriber
8. VLR complies
9. Mobile unit is paged
10. Mobile unit responds, MSCs convey
information back to telephone
1. Call made to mobile unit (cellular phone)
2. Telephone network recognizes number
and gives to gateway MSC
3. MSC can’t route further, interrogates
user’s HLR
4. Interrogates VLR currently serving user
(roaming number request)
5. Routing number returned to HLR and
then to gateway MSC
Legend: MTSC= Mobile Telephone Service Center, BTS = Base Transceiver Station
HLR=Home Location Register, VLR=Visiting Location Register

43. GSM Protocol ArchitectureCM CM MM MM
BSSMAP
BSSMAP
RRM
BTSM
BTSM
RRM
SCCP
SCCP
LAPDm
LAPDm
LAPD
LAPD
MTP
MTP
Radio
Radio
64 Kbps
64 Kbps
64 Kbps
64Kbps
Base Station
Controller
Mobile
Station
Base Transceiver
Station
Mobile Service
Switching Center
MM = Mobility Management
MTP = Message Transfer Part
RRM = Radio Resources Management
SCCP = Signal Connection Control Point
BSSMAP = BSS Mobile Application part
BTSM = BTS management
CM = Connection Management
LAPD = Link Access Protocol, D Channel

44. Functions Provided by Protocols
Protocols above the link layer of the GSM signaling protocol architecture provide specific functions:
Radio resource management: controls setup, termination and handoffs of radio channels
Mobility management: location and security (MTSO)
Connection management: connects end users
Mobile application part (MAP): between HLR,VLR
BTS management: management base system

45. 2G CDMA Cellular IS-95 is the best known example of 2G with CDMA
Advantages of CDMA for Cellular
Frequency diversity – frequency-dependent transmission impairments have less effect on signal
Multipath resistance – chipping codes used for CDMA exhibit low cross correlation and low autocorrelation
Privacy – privacy is inherent since spread spectrum is obtained by use of noise-like signals
Graceful degradation – system only gradually degrades as more users access the system

46. Drawbacks of CDMA Cellular
Self-jamming – arriving transmissions from multiple users not aligned on chip boundaries unless users are perfectly synchronized
Near-far problem – signals closer to the receiver are received with less attenuation than signals farther away
Soft handoff – requires that the mobile acquires the new cell before it relinquishes the old; this is more complex than hard handoff used in FDMA and TDMA schemes

47. Types of Channels Supported by Forward Link
Pilot (channel 0) - allows the mobile unit to acquire timing information, provides phase reference and provides means for signal strength comparison
Synchronization (channel 32) - used by mobile station to obtain identification information about cellular system
Paging (channels 1 to 7) - contain messages for one or more mobile stations
Traffic (channels 8 to 31 and 33 to 63) – the forward channel supports 55 traffic channels

48. Forward Traffic Channel Processing Steps
Speech is encoded at a rate of 8550 bps
Additional bits added for error detection
Data transmitted in 2-ms blocks with forward error correction provided by a convolutional encoder
Data interleaved in blocks to reduce effects of errors
Data bits are scrambled, serving as a privacy mask
Power control information inserted into traffic channel
DS-SS function spreads the 19.2 kbps to a rate of Mbps using one row of 64 x 64 Walsh matrix
Digital bit stream modulated onto the carrier using QPSK modulation scheme

49. Enabling Technologies
Wireless Network Evolution to 3rd Generation 3G
2 Mbps
CDMA2000
3XRTT
(UMTS)
CDMA Migration
W-CDMA
(UMTS)
1G-2G Migration
500 kbps
TDMA Migration
2.5G
EDGE
150 Kbps
CDMA-2000
1XRTT
100 Kbps
GPRS 2G
50 Kbps
10 Kbps 1G
IS-95
GSM
1 Kbps
AMPS
1999
2000
2001
2002
2003
1980

50. Fig 8-13

51. Table 8-3

52. 2G Technologies cdmaOne (IS-95) GSM, DCS-1900 IS-54/IS-136 PDC
Uplink Frequencies (MHz)
(Cellular)
(US PCS)
MHz (Eurpe) (US PCS)
800 MHz, 1500 Mhz (Japan)
Downlink Frequencies
MHz (US Cellular) MHz (US PCS)
(Europa)
(US PCS)
MHz (Cellular) (US PCS)
800 MHz, 1500 MHz (Japan)
Deplexing
FDD
Multiple Access
CDMA
TDMA
Modulation
BPSK with Quadrature Spreading
GMSK with BT=0.3
p/4 DQPSK
Carrier Seperation
1.25 MHz
200 KHz
30 KHz (IS-136) (25 KHz PDC)
Channel Data Rate
Mchips/sec
Kbps
48.6 Kbps (IS-136) 42 Kbps (PDC)
Voice Channels per carrier 64 8 3
Speech Coding
CELP at 13Kbps EVRC at 8Kbps
RPE-LTP at 13 Kbps
VSELP at 7.95 Kbps

53. Alternatives to 3G Cellular
Major technical undertaking with many organizational and marketing overtones.
Questions about the need for the additional investment for 3G (happy with 2.5G)
Wireless LAN in public places such as shopping malls and airports offer options
Other high-speed wireless-data solutions compete with 3G
Mobitex low data rates (nominally 8 Kbps), it uses a narrowband (2.5KHz) as compared to 30 KHz (GSM) and 5 MHz (3G).
Ricochet: kbps data rates. Bankruptcy
Flash-OFDM: 1.5 Mbps (upto 3 Mbps)

54. Major Mobile Radio Standards USA
Type
Year
Intro
Multiple Access
Frequency Band
(MHz)
Modulation
Channel BW
(KHz)
AMPS
Cellular
1983
FDMA FM 30
USDC
1991
TDMA
DQPSK
CDPD
1993
FH/Packet
GMSK
IS-95
Cellular/PCS
CDMA
QPSK/BPSK
1250
FLEX
Paging
Simplex
Several
4-FSK 15
DCS-1900 (GSM)
PCS
1994
200
PACS
Cordless/PCS
TDMA/FDMA
300

55. Major Mobile Radio Standards - Europe
Type
Year
Intro
Multiple Access
Frequency Band
(MHz)
Modulation
Channel BW
(KHz)
ETACS
Cellular
1985
FDMA
900 FM 25
NMT-900
1986
12.5
GSM
Cellular/PCS
1990
TDMA
GMSK
200KHz
C-450
20-10
ERMES
Paging
1993
FDMA4
Several
4-FSK
CT2
Cordless
1989
GFSK
100
DECT
1728
DCS-1800
Cordless/PCS
200

56. IEEE vs 3G Cellular

57. 4G Systems
Wireless networks with cellular data rates of 20 Mbits/second and beyond.
AT&T has began a two-phase upgrade of its wireless network on the way to 4G Access.
Nortel developing developing features for Internet protocol-based 4G networks
Alcatel, Ericsson, Nokia and Siemens found a new Wireless World Research Forum (WWRF) for research on wireless communications beyond 3G.
Many new technologies and techniques (multiplexing, intelligent antennas, digital signal processing)
Industry response is mixed (some very critical)

58. Engineering Issues Steps in MTSO controlled call TDMA design
CDMA design
Handoff
Power control
Traffic engineering

59. Steps in an MTSO Controlled Call between Mobile Users
Mobile unit initialization
Mobile-originated call
Paging
Call accepted
Ongoing call
Handoff
Call blocking
Call termination
Call drop
Calls to/from fixed and remote mobile subscriber

60. Mobile Wireless TDMA Design Considerations
Number of logical channels (number of time slots in TDMA frame): 8
Maximum cell radius (R): 35 km
Frequency: region around 900 MHz
Maximum vehicle speed (Vm):250 km/hr
Maximum coding delay: approx. 20 ms
Maximum delay spread (m): 10 s
Bandwidth: Not to exceed 200 kHz (25 kHz per channel)

61. Mobile Wireless CDMA Design Considerations
Soft Handoff – mobile station temporarily connected to more than one base station simultaneously
RAKE receiver – when multiple versions of a signal arrive more than one chip interval apart, RAKE receiver attempts to recover signals from multiple paths and combine them
This method achieves better performance than simply recovering dominant signal and treating remaining signals as noise

62. What is WiMax? Worldwide Interoperability for Microwave Access
Last mile wireless broadband access
Alternative to cable and DSL
Deliver data, voice, video
Support hundreds to thousands of homes/business

63. Defined by IEEE as
Typical target environment:
Targets fixed, portable, and mobile stations
Environments with and without line of sight
Cell radius of 3-10 kilometers
Capacities of up to 40 Mbps per channel
Mobile network deployments of up to 15 Mbps, 3 km radius

64. Builds on and Extends WiFi Technology
Advantages of WiFi are:
Easy to deploy, unlicensed spectrum, low cost
Supports (limited) mobility
But WiMax needs to address the following:

65. WiFi limitations Susceptible to interference
targets short-range indoor operation (mostly)
Security is a concern
Limited level of mobility
WiMax is intended to complement WiFi
WiMax Forum: promotes WiMax and looks after interoperability

66. WiMax Deployment