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Cellular Standards

Cellular Standards. A dvanced M obile P hone S ervice (AMPS) – 1G Analog FM IS-136 (aka USDC, IS-54 ) – 2G Digital TDMA Global System for Mobile (GSM) – 2G Digital TDMA European IS-95 CDMA – 2G Digital CDMA U.S. / Qualcomm 2.5G Standards – TDMA/CDMA CDMA2000 – 3G U.S./Qualcomm

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Cellular Standards

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  1. Cellular Standards • Advanced Mobile Phone Service (AMPS) – 1G Analog FM • IS-136 (aka USDC, IS-54) – 2G Digital TDMA • Global System for Mobile (GSM) – 2G Digital TDMA • European • IS-95 CDMA – 2G Digital CDMA • U.S. / Qualcomm • 2.5G Standards – TDMA/CDMA • CDMA2000 – 3G U.S./Qualcomm • W-CDMA – 3G Europe ECE 4730: Lecture #26

  2. IS-95 CDMA • CDMA Digital Cellular Standard (IS95) • System History • Developed first for AMPS band as alternate 2G technology to USDC • Theoretical capacity advantages over TDMA technology • No need for frequency planning • Macroscopic spatial diversity advantages • RAKE Rx (forward link) and Soft Handoff (reverse link) • Dual-mode CDMA/AMPS operation (Verizon) • 1.81.9 GHz version (JSTD 8) available for U.S. PCS band (Sprint PCS) ECE 4730: Lecture #26

  3. IS-95 CDMA • System Characteristics • AMPS band, 45 MHz F/R channel separation • 1.25 MHz RF channel BW (after spreading) • AMPS providers only willing to “risk” 1.25 MHz (10% of overall spectrum allocation) on new technology • 1.23 MHz for user + 0.27 MHz guard spectrum • 10 RF channels in 12.5 MHz AMPS spectrum/provider • User data rate changes in real time depending on voice activity • 1200 to 9600 bps • Low data rate for silent period • Data repeated multiple times for low rates to obtain constant 19.2 kbps (including channel coding; ½ rate) ECE 4730: Lecture #26

  4. IS-95 CDMA • Forward link • QPSK modulation • Base station simultaneously transmits all data for mobile units in a cell • Users share common channel • Unique PN sequence for each user • Spreading sequence chip rate = 1.2288 Mcps = 128 x 9600 bps • Spreading factor of 128 • Pilot code also embedded in transmission at higher power level • Base station ID • Power signal measurement to determine if handoff needed • Coherent Rx demodulation in mobile Rx ECE 4730: Lecture #26

  5. IS-95 CDMA • Forward link • RAKE Rx exploits macroscopic spatial diversity by combining signals from multiple base stations if present • Data processed in 20 msec blocks called frames • don’t confuse with TDMA! • Power control commands included in frames for “rapid” power control • 800 bps stolen from speech data (16 bits in one 20 msec frame) • Tightly control power to eliminate near/far problem ECE 4730: Lecture #26

  6. IS-95 CDMA • Reverse link • OQPSK modulation • Non-linear RF amps for longer mobile battery life !! • PN spreading code for each mobile user • 1.2288 Mcps (same as forward link) • Variable data rate transmission from 1200 to 9600 bps • Cycle Tx on/off (DTX) for lower data rate transmission • Reduce PN interference for other mobile users • All 3rd Generation (3G) proposed wireless standards have some form of CDMA as integral component • Flexible user BW for multi-rate, multi-type data services ECE 4730: Lecture #26

  7. 2G Standards • Widespread adoption of wireless communications accelerated in late 1990s • Governments everywhere opened PCS bands (1.8-2 GHz) • PCS bands : • Increased competition (e.g. AMPS duopoly) • Spurred deployment of 2G digital systems • Especially in U.S. • 1995  80M users • 2001  800M users • 2006  2B users • 2011  4.6B users!! ECE 4730: Lecture #26

  8. 2G Standards • Three major 2G digital standards • GSM, IS-136 (NADC), IS-95 (CDMAOne) • All 2G standards designed before widespread use of internet (pre-1995) • Circuit-switched data modems limited to single voice channel • Data throughput rate is approximately the same as the speech coding data rate for all three 2G standards • Typically 10 kbps data rate for single user • Very limited internet browsing and email functionality ECE 4730: Lecture #26

  9. 2.5G Standards • 2.5G Standards • Goal was to retrofit 2G standards to allow higher data rate transmissions • Support modern internet applications • More “data-centric” standards • Overlay on existing 2G networks for gradual deployment • Base station upgrades (software and/or hardware) • Software upgrade only is least expensive • New mobile unit software • Provide intermediate solution for migration to fully data-centric 3G standards for high-speed data transmission ECE 4730: Lecture #26

  10. 2.5G Upgrade Appropriate 2.5G upgrade path must match previous 2G technology to prevent wholesale equipment change at base station ECE 4730: Lecture #26

  11. 2.5G TDMA Standards • 2.5G Standards : HSCSD, GPRS, and EDGE • High Speed Circuit Switched Data (HSCSD) • Circuit switched (not data centric!) upgrade for GSM • GSM speech coder data rate was14.4 kbps (plus channel coding  22.8 kbps ) • GSM original speech data rate was 9.6 kbps (plus data error coding  14.4 kbps plus channel coding  22.8 kbps ) • HSCSD : • Eliminates original GSM data error coding • Individual users allowed to use up to 4 consecutive GSM time slots in a given frame (same radio channel) • Max data rate = 4 x 14.4 = 57.6 kbps • Good for real-time/dedicated internet access (circuit-switched) • BS only needs software upgrade; New mobile handsets required ECE 4730: Lecture #26

  12. 2.5G TDMA Standards • General Packet Radio Service (GPRS) • Upgrade for GSM or IS-136 (sort of) • Multi-user packet based (more data centric) • Multi-user network sharing of radio channels and time slots • Supports many more users than HSCSD but in bursty manner (not dedicated) • Best suited for non-real time internet • Email, fax, asymmetric web browsing • Asymmetric?  download rate is greater than upload • Retains original 2G TDMA (GSM or IS-136) modulation • Completely redefined air interface for packet network ECE 4730: Lecture #26

  13. 2.5G TDMA Standards • GSM GPRS • 21.4 kbps raw (no channel coding) data rate per TS • If all 8 GSM time slots are dedicated to GPRS then maximum instantaneous data rate is 8 x 21.4 =171.2 kbps • GSM channel data rate is 270 kbps • 270 – 171 = 99 kbps  frame overhead • Applications can provide own error coding as needed • Data throughput for individual user decreases substantially when • More users added to network • Propagation conditions degrade • Retransmission of lost data packets!! • 50 kbps average data throughput routinely achieved ECE 4730: Lecture #26

  14. 2.5G TDMA Standards • GSM GPRS • New IP routers and gateway hardware at BS • New BS software for packet network air interface • No new RF (Tx/Rx) BS hardware • New GPRS mobile handsets • Originally developed for GSM only but NADC operators (e.g. AT&T and Cingular) requested GPRS be extended to include IS-136 as well • IS-136 GPRS developed but not actually deployed!! • U.S. IS-136 carriers switched to GSM-GPRS!! • Not a seamless upgrade as originally intended!! • Significant cost to upgrade (wholesale RF hardware change) ECE 4730: Lecture #26

  15. 2.5G TDMA Standards • GSM GPRS • Most widely used 2.5G standard • Much more popular than HSCSD • Packet vs. Circuit Switched • Multi-User vs. Single-User • 100 million users in 2001 • T-Mobile first to deploy in U.S. • AT&T Wireless and Cingular switched in 2001 • Upgraded to 2.5G EDGE in 2003 and 2004 • AT&T completed nationwide upgrade to EDGE in late 2003 ECE 4730: Lecture #26

  16. 2.5G TDMA Standards • Enhanced Data for GSM Evolution (EDGE) • More advanced upgrade to GSM standard • Requires new RF hardware at BS unlike GPRS • New digital modulation standard 8-PSK (Octal PSK) used in addition to standard GMSK • Higher order modulation  more bits/symbol  larger spectral efficiency  larger data throughput • Nine different air interface formats • Rapidly and adaptively selectable • Variable data rates and error coding • Multiple Modulation and Coding Schemes (MCS) ECE 4730: Lecture #26

  17. 2.5G TDMA Standards • EDGE MCS • Each MCS state can use low (GMSK) or high (8-PSK) data rate modulation • Each mobile unit adaptively determines best MCS setting for user data needs and channel conditions • Stronger S / I then higher data rate • Selected data rate decreases as one moves away from BS • Adaptive selection of best MCS  “Incremental Redundancy” • Quickly negotiate the optimal coding and data rate • Ensures each user will rapidly reach condition with maximum data rate, minimum error coding, minimum BS, and minimum power drain • Ultimately maximizes system capacity for multi-rate users ECE 4730: Lecture #26

  18. 2.5G TDMA Standards • EDGE Data Rate • Assuming: • All 8 GSM TS are used by single user • No error coding • Max instantaneous data rate is 384 kbps (2.2X larger than GPRS) • Multi-user sharing yields maybe ~100-120 kbps average data rate under nominal conditions • Multi-Carrier Transmissions  3G EDGE • Specified in EDGE for further data rate enhancement • Allows multiple RF channels to be used • Increases throughput to 1-2 Mbps for single user and 300-500 kbps for multiple users ECE 4730: Lecture #26

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