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 CDMA2000 – 3G U.S./Qualcomm W-CDMA – 3G Europe ECE 4730: Lecture #25

USDC ECE 4730: Lecture #25 United States Digital Cellular (USDC) 2G Digital TDMA Standard Many evolutions/flavors: D-AMPS, IS-54, IS-94, IS-136 IS-136 was most recent version (IS = Interim Standard) Phased out by AT&T Wireless and Cingular Wireless around 2002 No vendor support to evolve from 2G to 3G!! System History : Developed in late 1980’s for AMPS band Meet increased demand for cellular service AMPS capacity not sufficient in major markets (e.g. Chicago, NY, SF) First U.S. digital cellular standard USDC also called DAMPS (Digital AMPS) ECE 4730: Lecture #25

USDC TDMA/FDD to provide 3 to 6 times current AMPS capacity 3 full-rate users (initial DSP and vocoder technology) 6 half-rate users (future DSP/vocoder improvement) IS54  USDC/AMPS dual-mode standard Gradual deployment of USDC in existing AMPS markets Key force in development of USDC standard Smooth transition from analog to digital in AMPS band Share same frequencies, frequency reuse plan, base stations, etc. ECE 4730: Lecture #25

USDC Characteristics ECE 4730: Lecture #25 p/4 DQPSK modulation on FVC/RVC 48.6 kbps channel data rate in 30 kHz RF BW (1.62 bps/Hz spectral efficiency) 16.2 kbps channel data rate/user (3 users) Forward and Reverse CC  same as AMPS to maintain compatibility 10 kbps FSK data signals in 30 kHz RF BW (0.33 bps/Hz!) Underutilized by USDC (10 kbps vs. 48 kbps!!) TDMA VC Data 6 times slots (TS) per frame 3 full-rate users  two TS/frame Staggered TS’s, e.g. user 1: TS 1/4, user 2: TS 2/5, and user 3: TS 3/6 6 half-rate users  one TS/frame ECE 4730: Lecture #25

USDC Data Frame Four data channel types simultaneously provided in TDMA frame : 1) DTC 2) CDVCC 3) SACCH 4) FACCH ECE 4730: Lecture #25

USDC Characteristics ECE 4730: Lecture #25 Digital Traffic Channel (DTC) Speech or user data (i.e. FAX) on forward/reverse link Coded Digital Verification Color Code (CDVCC) Sent in every time slot by base and mobile 12-bit coded message (8 data bits + 4 code bits) Base/mobile identification from co-channel base/mobiles Same purpose as SAT in AMPS Slow Associated Control Channel (SACCH) Communicate single message over multiple time slots (slow!) Power control and handoff initiation MAHO Report results to MSC of mobile unit monitoring of neighboring base station power levels ECE 4730: Lecture #25

USDC Characteristics Fast Associated Control Channel (FACCH) Steal frame of speech data and replace with other data Blank and burst transmission Used for important control or special traffic data More channel coding bits to protect information MAHO, call release, etc. Use idle DTC time slots to handle voice traffic internally! USDC/USDC phone call not passed thru PSTN MSC routes call over network to mobile user Flexibility and reduced provider cost ECE 4730: Lecture #25

USDC Characteristics ECE 4730: Lecture #25 Pulse shaping Equalization Raised cosine filtering Increase spectral efficiency and limit ISI Requires linear RF amplifiers to preserve spectral efficiency and limit ACI Poor DC-to-RF efficiency Reduced battery life in mobile unit Compensated somewhat by MAHO Equalization Specified for use in USDC but no specific algorithm chosen Use is up to provider and equipment manufacturer Deploy only in cities with large RMS delay spread (> 5 msec) since Bs was only 30 kHZ (AMPS) and usually < Bc ECE 4730: Lecture #25

USDC Characteristics Channel Coding ECE 4730: Lecture #25 Extra protection for important speech data bits 260 bits/TS x 2 TS (full rate user) = 520 bits/frame 1 frame = 40 msec Speech + Channel Coding Data Rate = 520 / 40 msec = 13 kbps/user out of 16.2 kbps total ECE 4730: Lecture #25

USDC IS-94 Evolution ECE 4730: Lecture #25 IS94 Add networking features to USDC to expand service capability Cellular interface directly with private branch exchange (PBX) Building or campus services Small base stations (microcells) placed in buildings Floor by floor if necessary One phone provides campus and city coverage Different rates for each service No need for wired phone service (ideally!) Deployed first in 1994 Some use in office building, hotels, etc. ECE 4730: Lecture #25

USDC IS-136 Evolution ECE 4730: Lecture #25 IS136 FVC/RVC same as USDC/IS-54 (frame structure, etc.) NEW: p/4 DQPSK modulation on FCC/RCC  48.6 kbps More efficient use of control channel spectrum Provide specialized PCS services Paging, short messages, caller ID, private group features, etc. Closed network capabilities like wireless PBX Local or campus type use Compete with GSM and IS-95 PCS band technology (1.81.9 GHz) AT&T Wireless (PCS) and Cingular Wireless (AMPS) Major U.S. adopters of IS-136 IS-136 not adopted outside of U.S. ECE 4730: Lecture #25

USDC IS-136 Evolution AT&T Wireless and Cingular Wireless Major U.S. adopters of IS-136 in 1998/99 “Dead-end” standard No vendor support for migration to 3G and higher data rate services Both carriers forced to migrate to new standard in 2001 and 2002 with upgrade path to 3G Both selected GPRS  2G+ GSM evolution Both upgraded to EDGE  2.5G GSM evolution Cingular purchased AT&T Wireless in late 2004 AT&T purchased Cingular in 2007! ECE 4730: Lecture #25

Cellular Standards ECE 4730: Lecture #25 1G 2G 2G+ 2G - Obsolete GSM-GPRS 2G - Obsolete 2G 2.5G 3G EDGE 3G ECE 4730: Lecture #25

GSM Global System for Mobile (GSM) History : ECE 4730: Lecture #25 First named “Group Special for Mobile” standard Developed in Europe in late 1980’s and first deployed in 1991 Well ahead of PCS type services in U.S. First cellular system to use digital modulation First cellular system to specify network features and services (texting) Most widely used standard for digital cellular systems in the world First operated in European 900 MHz band Versus 800 MHz for AMPS in US PCS version of GSM: PCS 1800 for 1.82.0 GHz U.S. PCS band (e.g. T-Mobile, AT&T Wireless, Cingular) ECE 4730: Lecture #25

GSM Services and Features : ECE 4730: Lecture #25 Teleservices: mobile telephony, FAX Data services: packet switched protocols (IP traffic), computer-to-computer communication 300 to 9600 bps ISDN services: call forwarding, closed user groups, caller ID, short messaging service (SMS) (alphanumeric paging messages) Subscriber Identity Module (SIM) Memory module that stores the brains of the phone Service features, ID, user-specific info; transferable to another phone Digital encryption  secure communication ECE 4730: Lecture #25

GSM Characteristics 0.3 GMSK modulation on forward/reverse links Gaussian baseband pulse shaping to improve spectral efficiency 270.8 kbps in 200 kHz RF BW (AFRCN) Forward/reverse link: 935960 / 890915 MHz TDMA/FDD 8 TS/frame 1 frame = 4.615 msec (~ Tc for mobile with v = 65 mph) 3 TS spacing between Tx/Rx on forward/reverse links No duplexer required User channel BW = 25 kHz; user channel data rate = 33.85 kbps ECE 4730: Lecture #25

GSM Channels Channel number (AFRCN) and TS define physical channel Many logical channels defined as well User, network, and control data Channel types : Traffic CHannel (TCH) Broadcast CHannel (BCH) Common Control CHannel (CCCH) Slow Associated Control CHannel (SACCH) Fast Associated Control CHannel (FACCH) Many others!! ECE 4730: Lecture #25

GSM Channels Traffic CHannels (TCH) ECE 4730: Lecture #25 Full or half rate  speech or user data Full rate speech = 14.4 kbps + coding = 22.8 kbps + frame overhead = 33.85 kbps Full rate data = 2.4, 4.8, or 9.6 kbps + coding = 22.8 kbps lower data rates have greater coding Half-rate speech or data = 6.6 kbps Built in to standard to anticipate further improvements in DSP Capitalize on DSP improvements to provide 16 users/frame!! Double system capacity ECE 4730: Lecture #25

GSM Channels Broadcast CHannel (BCH) and Common Control Channel (CCCH) TS 0 on first GSM Tx is set aside for base station broadcast and control Just like control channel in AMPS Additional base station Tx have TS 0 available for mobile users Broadcast, frequency, synchronization, paging, etc. all share TS 0 in repeating 51 frame sequence Fig. 11.8, pg. 558 ECE 4730: Lecture #25

GSM BCH & CCCH ECE 4730: Lecture #25

GSM Channels Slow Associated Control CHannel (SACCH) Steal 13th frame of speech data and replace with control data Power, handoff, and timing control Similar to blank and burst in AMPS Fast Associated Control CHannel (FACCH) Steal frames from other users’ TS not in use!! Urgent messages, MAHO, etc. Many other control channel types! ** Complex signaling and control protocols provide great flexibility and wide range of user services  Significant advantage over other systems ECE 4730: Lecture #25

GSM Frame Structure ECE 4730: Lecture #25

GSM Channels Frame Structure  Figure 11.10, pg. 562 Midamble  26 training bits for equalizer 13th and 26th frame in a multiframe used for control purposes (SACCH) Stealing flag indicates data or control GSM mobile unit uses 1 TS for Tx, 1 TS for Rx, and can monitor its base station and 5 other neighboring base stations signal power for MAHO! GSM encryption varies with time and depends on frame number in hyperframe which is 2,715,648 TDMA frames (duration 3 hr 29 min)! ECE 4730: Lecture #25