1. Cellular Wireless Networks
First – Second and Third Generation Models

2. Lecture Learning Outcomes
At the end of the lecture, the student should be able to:
Understand the Principle of Operations of First Generation Systems using FDMA.
Understand the Principle of Operation of the 2nd Generation Systems using TDMA and CDMA
Understand the Objectives and Capabilities of 3rd Generation (3G) systems.

3. Class Index First-Generation Analogue Second-Generation TDMA
Spectral Allocation
Operation
AMPS Control Channel
Second-Generation TDMA
First and Second Generation Cellular Systems
Time Division Multiple Access
Design Considerations

4. Class Index Second-Generation CDMA Third Generation Systems
Global System for Mobile Communications
GSM Network Architecture
Radio Link Aspects
TDMA Format
Second-Generation CDMA
Code Division Multiple Access
IS-95
Third Generation Systems

5. First Generation Analogue
Analogue Transmissions using FM
Spectrum is shared through FDMA
Systems implemented:
AMPS: America and Australia (Advance Mobile Phone System
ETACS: Europe (European Total Access Communication System)
NTT: Japan (Nippon Telephone and Telegraph)

6. First Generation –Spectral Allocation
AMPS
ETACS
NTT
NTT Mod.
America &
Implementation
Australia
Europe
Japan
Channel Bandwidth
50 MHz
30 MHz
Forward Channel
Frequency Range
MHz
MHz
MHz
Reverse Channel
MHz
MHz
MHz
Channel Spacing
30 KHz
25 KHz
6.25 KHz
Total Channels per
operator
832
1000
600
2400
Data Rates
10 kbps
8 kbps
0.3 Kbps
2.4 Kbps

7. 1G - Operation Numerical Assignment Module Call Sequence
Telephone Number (Operator)
Serial Number (Manufacturer)
Call Sequence
Call Initiation
Phone Verification – Phone Authorization
Traffic Channel Assignment
MTSO sends a ringing signal to called party
MTSO establishes circuits on answer and starts billing
MTSO releases circuit when either party hangs up

8. 1G- Control Channels Reverse Control Channels Forward Control Channels
Mobile unit to BS
Forward Control Channels
BS to Mobile Unit

9. 1G- Control Channels Control Channels transmit digital data using FSK.
Data is transmitted in frames
Urgent Messages are sent through the voice channel.

10. Second Generation 2-G Higher-Quality Signals Higher Data Rates
Higher Transmission Capacity
Support of digital services.

11. 1-G and 2-G differences First Generation Second Generation
First Generation
Second Generation
Traffic Channels
Analogue
Digital
Traffic send in
Traffic Encrypted
Encryption
the clear.
to prevent
eavesdropping
Error Detection
Used and leading
and
Not Used
to very clear voice
Correction
reception
Channel
Access
FDMA
TDMA - CDMA

12. Convolutional 1/2 rate forward, 1/3 rate reverse
2-G Systems
GSM (Europe)
IS-136(US)
IS-95 (US)
Year Introduced
1990
1991
1993
Access Method
TDMA
CDMA
BS transmission band
MHz
MHz
Mobile transmission band
MHz
MHz
Spacing between forward and reverse channels
45 MHz
Channel BW
200 kHz
30 kHz
1250 kHz
Number of duplex channels
125
832 20
Mobile unit maximum power
20 W
3 W
0.2 W
Users per channel 8 3 35
Modulation
GMSK
/4 DQPSK
QPSK
Carrier bit rate
270.8 kbps
48.6 kbps
9.6 kbps
Frame size
4.6 ms
40 ms
20 ms
Error control coding
Convolutional ½ rate
Convolutional /2 rate forward, /3 rate reverse
Gaussian Filtered Minimum Shift Keying

13. Mobile - TDMA
In TDMA for mobile communications, each cell is allocated a number of channels, half reverse and half forward.
Each physical channel is further sub-divided into a number of logical channels.
Transmission is in the form of a repetitive sequence of frames, each of which is divided into a number of time slots.
Each slot positions across the sequence of frames forms a separate logical channel

14. TDMA Design Considerations
Number of Logical Channels: Minimum 8
Maximum Cell Radius: 35 Km
Frequency: Around 900 MHz
Bandwidth: Max 200 KHz (25 KHz/channel)

15. Global System for Mobile Communications (GSM)
Developed to provide a common 2-G technology for Europe
Same subscriber unit could be used throughout the continent.
Technology has been extremely successful. Most popular standard for new implementations.

16. Network Architecture

17. Mobile Station ME: Mobile Equipment SIM: Subscriber Identity Module.
Physical Terminal
SIM: Subscriber Identity Module.
Smart Card Stores Subscriber’s ID number, networks authorized to use, encryption keys.
Subscriber Specific Information.

18. Base Station Subsystem
BSS
Each BTS defines a single cell
BSC control one or multiple BTSs or cells
BSC reserves radio frequencies, manages handoff (inside the BSS), controls paging.

19. Network Sub-System
Home Location Register
Visitor Location Register
Link between Cellular Network and Public Switched Telephone Network
Controls Handoff between BSS
Authenticates Users and Validate Accounts.
Mobile Switching Centre:
Supported by 4 databases
Authentication Centre
Equipment Identity Registry

20. GSM Radio Link Aspects
25 MHz for BS transmissions and 25 MHz for Mobile transmissions
Access is throughout a combination of TDMA and FDMA.
RF carriers every 200 KHz provides 125 full duplex channels modulated at a data rate of kbps.

21. GSM-TDMA Frame Format Signals for Data or Stolen Control Signals
Sync of Transmission
Data
Training Sequence

22. Training Sequence
Used to adapt the parameters of the receiver to the current path propagation characteristics and to select the strongest signal in case of multipath propagation.
The training sequence is a known bit pattern that differs for different adjacent cells.
It enables the mobile units and the base stations to determine that the received signal is from the correct transmitter and not a strong interfering transmitter.

23. Training Sequence
In addition the training sequence is used for multipath equalization, which is used to extract the desired signal from unwanted reflections.
By determining how the known training sequence is modified by multipath fading, the rest of the signal is processed to compensate for these effects.

24. 2-G CDMA
As with FDMA, each cell is allocated a frequency bandwidth, which is split into two parts, half for reverse and half for forward.
Transmission is in the form of DSSS (direct sequence spread spectrum), which uses a chipping code to increase the data rate of the transmission, resulting in an increased signal bandwidth.
Multiple access is provided by assigning orthogonal chipping codes to multiple users, so that the receiver can recover the transmission of an individual unit from multiple transmissions.

25. CDMA Advantages for Cellular Networks
Frequency diversity: Because the transmission is spread out over a larger bandwidth, frequency-dependent transmission impairments have less effect on the signal.
Multipath resistance: In addition to the ability of DSSS to overcome multipath fading by frequency diversity, the chipping codes used for CDMA exhibit low cross correlation and low autocorrelation
A version of the signal that is delayed by more than one chip interval does not interfere with the dominant signal as much as in other multipath environments.

26. CDMA Advantages for Cellular Networks
Privacy: Because SS is obtained by the use of noise-like signals, where each user has a unique code, privacy is inherent.
Graceful degradation: With FDMA or TDMA, a fixed number of users can access the system simultaneously. However, with CDMA, as more users access the system simultaneously, the noise level, and hence the error rate increases; only gradually does the system degrade to the point of unacceptable error rate.

27. CDMA drawbacks
Self-jamming: Unless all the mobile users are perfectly synchronized, the arriving transmissions from multiple users will not be perfectly aligned on chip boundaries.
The spreading sequences of the different users are not orthogonal and there is some level of cross correlation.

28. CDMA drawbacks
Near-far problem: Signals closer to the receiver are received with less attenuation than signals farther away. Given the lack of complete orthogonality, the transmissions from the more remote mobile units may be more difficult to recover.
Soft handoff: A smooth handoff from one cell to another requires that the mobile acquires the new cell before it relinquishes the old. This is referred to as soft handoff and is more complex than the hard handoff used in FDMA and TDMA schemes

29. IS-95
Primarily deployed in North America, is the most widely used 2-G CDMA scheme.
Forward Link consists of up to 64 logical CDMA channels. Each occupying the same bandwidth of 1228 KHz.
Reverse Lind consists of up to 94 logical CDMA channels. Each occupying the same bandwidth of 1228 KHz.

30. IS-95 Forward Link Channel Sync Paging Traffic Rate Set 1
Data-rate (bps)
1200
4800
9600
2400
1800
3600
7200
14400
Code Repetition 2 1 8 4
Modulation Symbol
Rate (sps)
19200
PN chips/modulation
symbol
256 64
PN chips/bit
1024
128
512
682.67
341.33
170.67
85.33

31. IS-95 Forward Link (BSMU)
Pilot (Channel 0):Continous signal (all zeros).
Timing Information
Phase Reference for Demod.
Sync. (Channel 32): 1200-bps channel used to obtain ID info about the cellular.
Paging (Channels 1 to 7): Messages for mobile stations
Traffic: supported 9600 bps. Second set after revision bps

32. IS-95 Reverse Link Channel Access Traffic-Rate Set 1
Data Rate
4800
1200
2400
9600
1800
3600
7200
14400
Code Rate
1/3
Symbol Rate before
repetition (sps)
28800
Symbol Repetition 2 8 4 1
Symbol Rate after
Transmit duty cycle
1/8
Code symbol/modulation
symbol 6
PN chips / modulation
256
PN chips/bit
128
256/3

33. IS-95 Reverse Link – MUBS
94 Logical Channels.
Supports 32 Access Channels
Initiate call
Respond to paging channel
Location update
Supports 62 Traffic Channels
Traffic Channels are mobile unique.

34. 3-G Mobile Systems Objectives:
Provide High speed wireless communications.
Support Multimedia, Data and Video in addition to voice.
Driving Force is the trend towards universal personal telecommunications and universal communications access.

35. 3-G Systems
It is likely that they will be equipped with infrastructure to support Personal Communications Systems (PCSs):
Public Land Mobile Networks (PLMNs)
Mobile Internet Protocol (Mobile IP)
Wireless Asynchronous transfer mode networks (WATM)
Low Earth Orbit Satellite Networks

36. 3-G Capabilities
Voice quality comparable to the PSTN (public switched telephone network)
144 kbps data rate available to users in high-speed motor vehicles over large areas

37. 3-G Capabilities
348 kbps available to pedestrians standing or moving slowly over small areas.
Support (to be phased in) for Mbps for office use
Symmetrical and asymmetrical data transmission rates

38. 3-G Capabilities
Support for both packet switched and circuit switched data services
An adaptive interface to the internet to reflect efficiently the common asymmetry between inbound and outbound traffic.
More efficient use of the available spectrum in general

39. 3-G Capabilities Support for a wide variety of mobile equipment
Flexibility to allow the introduction of new services and technologies.

40. 3G Design Considerations
The dominant technology for 3G systems is CDMA.
Although three different CDMA schemes have been adopted, they share some common design issues:

41. 3G Design Considerations
Bandwidth: An important design goal for 3G systems is to limit channel usage to 5 MHz.
There are several reasons for this goal.
On the one hand, a bandwidth of 5MHz or more improves the receiver’s ability to resolve multipath when compared to narrower bandwidths.
On the other hand, available spectrum is limited by competing needs, and 5 MHz is a reasonable upper limit on what can be allocated for 3G.
Finally, 5 MHz is adequate for supporting data rates of 144 and 384 Kbps, the main targets for 3G services

42. 3G Design Considerations
Chip Rate: Given the bandwidth, the chip rate depends on desired data rate, the need for error control, and bandwidth limitations.
A chip rate of 3 Mcps (mega-chips per second) or more is reasonable given these design parameters.

43. 3G Design Considerations
Multirate: The term multirate refers to the provision of multiple fixed-data-rate logical channels to a given user, in which different data rates are provided on different logical channels.
Further, the traffic on each logical channel can be switched independently through the wireless and fixed networks to different destinations.
The advantage of multirate is that the system can flexibly support multiple simultaneous applications from a given user and can efficiently use available capacity by only providing the capacity required for each service.