1. Cellular Networks
Lecture 6
Paul Flynn

2. Cellular Telephony - Architecture

3. 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

4. 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

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

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

7. 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
MHz
MHz
Channel Number
Center Frequency (MHz)
Reverse Channel 1 <=N <= 799
991 <= N <= 1023
0.030N
0.030(N-1023)
Forward Channel 1 <=N <= 799
991 <= N <= 1023
0.030N
0.030(N-1023)
(Channels are unused)
Channel bandwidth is 45 MHz

8. 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

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.

12. 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

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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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
MHz
MHz
Channel Number
Center Frequency (MHz)
Reverse Channel 1 <=N <= 799
991 <= N <= 1023
0.030N
0.030(N-1023)
Forward Channel 1 <=N <= 799
991 <= N <= 1023
0.030N
0.030(N-1023)
(Channels are unused)
Channel bandwidth is 45 MHz

20. 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

21. GSM Speech Signal Processing

23. GSM and CDMA Coverage Map Worldwide

24. 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

25. 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

26. 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:

27. 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

28. WiMax Deployment