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Wireless &Mobile Communications Chapter 9: 3G Cellular

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. What is 3G?. The current cellular system is referred to as 2G cellular.

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Wireless &Mobile Communications Chapter 9: 3G Cellular

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  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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

  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 Ch9: 3G Cellular

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