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Wireless &Mobile Communications Chapter 9: 3G Cellular  What is 3G?  The ITU’s International Vision  The need/motivation for 3G  The Major Players.

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Presentation on theme: "Wireless &Mobile Communications Chapter 9: 3G Cellular  What is 3G?  The ITU’s International Vision  The need/motivation for 3G  The Major Players."— Presentation transcript:

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 Winter 2001Ch9: 3G Cellular9.2 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.

3 Winter 2001Ch9: 3G Cellular9.3 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

4 Winter 2001Ch9: 3G Cellular9.4 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

5 Winter 2001Ch9: 3G Cellular9.5 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.

6 Winter 2001Ch9: 3G Cellular9.6 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

7 Winter 2001Ch9: 3G Cellular9.7 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)

8 Winter 2001Ch9: 3G Cellular9.8 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

9 Winter 2001Ch9: 3G Cellular9.9 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)

10 Winter 2001Ch9: 3G Cellular9.10 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

11 Winter 2001Ch9: 3G Cellular9.11 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

12 Winter 2001Ch9: 3G Cellular9.12 Key Technology Concepts for 3G  Higher bit rates required -> more bandwidth  Packet and circuit switched services  Coherent demodulation  TDD  Architecting for minimum required E b /I o  Control E b  Limit/Cancel I o  Smart antennas

13 Winter 2001Ch9: 3G Cellular9.13 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

14 Winter 2001Ch9: 3G Cellular9.14 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

15 Winter 2001Ch9: 3G Cellular9.15 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)

16 Winter 2001Ch9: 3G Cellular9.16 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.

17 Winter 2001Ch9: 3G Cellular9.17 Architecting for Minimum Required E b /I o  E b /I o vs E b /N o 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.  E b =P/R  P is the power per bit in units of energy/sec  R is the signal bit rate in bits/sec  E b is the received energy per bit of the signal, I o is the interference power density  E b is directionally proportional to the received power of the signal  For CDMA: E b /I o = (P m /I tot ) x (W/R) = SIR x Processing Gain  E b /I o is the key parameter in determining the probability of receiving a bit correctly (I.e., the BER)

18 Winter 2001Ch9: 3G Cellular9.18 Techniques to keep E b /I o 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

19 Winter 2001Ch9: 3G Cellular9.19 Controlling E b  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

20 Winter 2001Ch9: 3G Cellular9.20 Limit I o  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

21 Winter 2001Ch9: 3G Cellular9.21 Smart Antennas  Switched beams:  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


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