1. Wireless &Mobile Communications Chapter 9: 3G Cellular
What is 3G?
The ITU’s International Vision
The need/motivation for 3G
The Major Players
3G Architecture and Services
W-CDMA and CDMA2000 technologies

2. What is 3G? The current cellular system is referred to as 2G cellular.
It differs from the the first generation cellular in that the system is fully digital and provides roaming on a national or regional basis
The next generation cellular, 3G, is envisioned to enable communication at any time, in any place, with any form, as such, it will:
allow global roaming
provide for wider bandwidths to accommodate different types of applications
support packet switching concepts
The ITU named this vision: IMT-2000 (International Mobile Telecommunications 2000) with the hope of having it operational by the year 2000 in the 2000MHz range.
Ch9: 3G Cellular
Winter 2001

3. IMT 2000 Vision Common spectrum worldwide (2.8 – 2.2 GHz band)
Multiple environments, not only confined to cellular, encompasses: cellular, cordless, satellite, LANs, wireless local loop (WLL)
Wide range of telecommunications services (data, voice, multimedia, etc.)
Flexible radio bearers for increased spectrum efficiency
Data rates of: 9.6Kbps or higher for global (mega cell), 144Kbps or higher for vehicular (macro cell), 384Kbps or higher for pedestrian (micro cell) and up to 2Mbps for indoor environments (pico cell)
Global seamless roaming
Enhanced security and performance
Full integration of wireless and wireline
Ch9: 3G Cellular
Winter 2001

4. Major 3G Technologies Proposed for IMT 2000
W-CDMA backward compatible with GSM (called UMTS by the ETSI)
The IS-95 standard (CDMAOne) is evolving its own vision of 3G: CDMA2000
The IS-136 standard is evolving its own migration to 3G, Universal Wireless Communications, UWC-136 or IS-136 HS
Ch9: 3G Cellular
Winter 2001

5. Who will be first to offer IMT 2000?
The Japanese are leading the pack with their W-CDMA implementation. It is being rolled out in the year 2001.
The Koreans plan to have CDMA2000 up an running before the world cup in 2002.
The Europeans are pushing hard to UMTS up soon but the current push is fro 2.5G, a middle of the road to protect current infrastructure investments.
In the US no major push yet, some service providers are following in the footsteps of the Europeans by pushing a 2.5G solution.
Ch9: 3G Cellular
Winter 2001

6. IMT 2000 Services/Capabilities 1/2
All what 2G support including:
Registration, authentication and encryption
SMS
Emergency calling
Bit rates:
144Kbps or higher for vehicular (macro cell),
384Kbps or higher for pedestrian (micro cell) and
up to 2Mbps for indoor environments (pico cell)
Billing/charging/user profiles
Sharing of usage/rate information between service providers
Standardized call detail recording
Standardized user profiles
Ch9: 3G Cellular
Winter 2001

7. IMT 2000 Services/Capabilities 2/2
Support of geographic position finding services
For the mobile
For the network
Support of multimedia services
QoS
Assymmetric links
Fixed and variable rate
Bit rates of up to 2Mpbs
Support of packet services
Internet Access (wireless cellular IP)
Ch9: 3G Cellular
Winter 2001

8. IMT 2000 Family Concept
The IMT 2000 family concept defines some basic interoperability capabilities between different IMT 2000 technologies to enable global roaming!
Different Radio Access Networks (RANs):
CDMA2000
W-CDMA
UWC-136
Different Core Network standards
IS 41
GSM
ISDN
Ch9: 3G Cellular
Winter 2001

9. Challenge for the Family Concept
With IMT 2000 Standard Interfaces and Capabilities:
Any Family RAN could interface with any Family Core Network for some minimum set of features.
More advanced features are possible in limited regions where the Family RAN and the Family Core Network are optimally matched
The Core Network functionality should be kept independent of the Radio technology.
By maintaining independence, each can evolve separately based on needs
User Identity Modules (UIM) Plug-In modules could be used in locally rented handsets for Global Roaming with at least the minimum feature set. (similar to GSM SIMs)
Ch9: 3G Cellular
Winter 2001

10. UIM Roaming UIM cards should allow a subscriber to obtain:
Any IMT 2000 service/capability basic feature set on
Any IMT 2000 Network family member (W-CDMA, CDMA2000 and UWC-136)
UIM Card: will be a superset of the current GSM SIM
Contains all necessary information about the user’s service subscriptions
Supports user identity separate from handset identity:
Allows a user to use different handsets, with all usage billed to the single user
Allows a user to rent a handset in a foreign country/network and obtain instant service
Ch9: 3G Cellular
Winter 2001

11. To reach the IMT 2000 vision
Physical interfaces are being standardized:
UIM to handset interface
Radio/Air interfaces
RAN to Core Network
Network to Network Interfaces (NNI) between Core Networks
Radio independent functions are being standardized:
UIM to handset
Handset to Core Network
NNI
Ch9: 3G Cellular
Winter 2001

12. Key Technology Concepts for 3G
Higher bit rates required -> more bandwidth
Packet and circuit switched services
Coherent demodulation
TDD
Architecting for minimum required Eb/Io
Control Eb
Limit/Cancel Io
Smart antennas
Ch9: 3G Cellular
Winter 2001

13. Higher bit rates -> larger bandwidths
No free lunch!!!
For a CDMA system;
For 2-4Mbps you need around 20MHz channel
For 1-2Mbps you need around 10MHz channel
For 256Kbps-1Mbps you need around 5MHz channel
Ch9: 3G Cellular
Winter 2001

14. Packet and Circuit Switched Services
CS channels: 32 – 384 Kbps
PS channels: 64Kbps to 2Mbps
Circuit mode versus packet mode for data services:
Circuit mode
provides a dedicated channel for the duration of the call
Can mux control with data in same channel, can be a problem for data if bit stealing is used
Packet mode
Requires a scheduling scheme to control access to the shared channel
Generally supports a separate control channel
CDMA Packet Mode: two main approaches
Users share a dedicated channel (code):
Sequential access or scheduled on a need basis
Users share the allowable total interference for the carrier:
Each user gets a unique code
Users must be scheduled and transmissions controlled to limit the load in the system
Combination of the above two
Ch9: 3G Cellular
Winter 2001

15. Coherent vs Non coherent demodulation
Non coherent demodulation – where the receiver has no reference phase with which to compare the received signal
Coherent demodulation – where the receiver does have a reference pahse, supplied by the transmitted
A continuous Pilot ( or Reference) channel transmitted along with the signal (e.g. pilot channel in IS-95 for downlink)
A known sequence of Pilot (or Reference) symbols (or bits) embedded, periodically, in the signal bit stream (e.g. proposed for W-CDMA in both uplink and downlink channels, also CDMA2000 incorporates a pilot channel in reverse direction)
Ch9: 3G Cellular
Winter 2001

16. TDD All the standards naturally support FDD
Symmetric channels for up and down links
TDD can be added to allow transmission and reception in single frequency band.
Japanese W-CMDA supports an asymmetric TDD channel in addition to the FDD support
TDD allows for flexible spectrum usage, does not require paired frequency bands
Simpler, lower cost handsets – no need for duplex filters
More complex synchronization, the channel flips back and forth between uplink and downlink.
Ch9: 3G Cellular
Winter 2001

17. Architecting for Minimum Required Eb/Io
Eb/Io vs Eb/No vs C/SIR or SNR:
The former two refer to the energy per bit and are therefore more applicable to digital systems. The latter two are generally used to refer to analog systems.
Using I vs N basically has to do with what the noise source is, in cellular systems it is primarily due to interference so ``I” is the preferred term.
Eb =P/R
P is the power per bit in units of energy/sec
R is the signal bit rate in bits/sec
Eb is the received energy per bit of the signal, Io is the interference power density
Eb is directionally proportional to the received power of the signal
For CDMA: Eb/Io = (Pm/Itot) x (W/R) = SIR x Processing Gain
Eb/Io is the key parameter in determining the probability of receiving a bit correctly (I.e., the BER)
Ch9: 3G Cellular
Winter 2001

18. Techniques to keep Eb/Io low with higher bit rates
Maximize Frequency diversity – wider bands -> higher processing gains
Maximize Time diversity –
Rake receivers -> multiple signals with different delays at receiver,
interleaving with FEC
Maximize Space diversity –
diverse receive antennas at base station,
rake receivers -> different signal paths
Use FEC (forward error correction)
All of the above techniques come at a cost:
Higher bandwidth
More complex receivers (rake, multiple antennas)
More overhead bits (FEC) per signal
Ch9: 3G Cellular
Winter 2001

19. Controlling Eb
More power is required for the transmission of bits at higher bit rates over the same distance
Limit the distance over which high bit rates maybe sent
Using better antennas that will focus the beam so that:
The transmitter aims at the target without wasting energy in all directions
The receiver captures more of the signal as it is focused on a narrow beam
Fast power control to counteract changes in interference due to
Changing loads
Changing environments
Ch9: 3G Cellular
Winter 2001

20. Limit Io
Use better antennas with focused beams in conjunction with sectors
Use interference cancellation -> receive all signals and subtract all but the desired one from the total
Use more accurate and fasted power control techniques
To not transmit signals when there is a silence in the signal
Ch9: 3G Cellular
Winter 2001

21. Smart Antennas Switched beams: Adaptive Arrays:
Several antenna beams used to receive the signal
Use the antenna that receives the strongest signal
Not well suited to CDMA:
Switching will cause chip errors
Switching could disturb synchronization and demodulation
Works against the concept of the Rake receiver
Adaptive Arrays:
Narrow beam antenna which is steered to follow the mobile(s)
Better suited to CDMA but still have the Rake receiver problem
Ch9: 3G Cellular
Winter 2001