ECE 4730: Lecture #25 1 Advanced Mobile Phone Service (AMPS) – 1G Analog FM IS-136 (aka USDC, IS-54) – 2G Digital TDMA Global System for Mobile (GSM)

ECE 4730: Lecture #25 1

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

Cellular Standards


USDC

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 DAMPS (Digital AMPS)


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)

IS54 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.


USDC Characteristics

/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


USDC Data Frame

Four data channel types simultaneously provided in TDMA frame : 1) DTC

2) CDVCC

3) SACCH

4) FACCH



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) Sent in every time slot by base and mobile 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



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



Pulse shaping 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 sec) since Bs was only 30 kHZ (AMPS) and usually < Bc



Channel Coding Extra protection for important speech data bits

260 bits/TS x 2 TS (full rate user) = 520 bits/frame1 frame = 40 msecSpeech + Channel Coding Data Rate = 520 / 40 msec = 13 kbps/user out of 16.2 kbps total


USDC IS-94 Evolution

IS94 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.



IS136 FVC/RVC same as USDC/IS-54 (frame structure, etc.) NEW:/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 (1.81.9 GHz) AT&T Wireless (PCS) and Cingular Wireless (AMPS)

» Major U.S. adopters of IS-136

IS-136 not adopted outside of U.S.



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!


Cellular Standards

1G2G

2G

2G - Obsolete2G - Obsolete

3G

3G

GSM-GPRS

EDGE

2G+

2.5G


Global System for Mobile (GSM) History :

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 1.82.0 GHz U.S. PCS band (e.g. T-Mobile, AT&T Wireless, Cingular)

GSM


Services and Features : 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

GSM


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: 935960 / 890915 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

GSM Characteristics


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!!

GSM Channels


Traffic CHannels (TCH) 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

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

GSM Channels


GSM BCH & CCCH


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!

GSM Channels

** Complex signaling and control protocols provide great flexibility and wide range of user services

Significant advantage over other systems


GSM Frame Structure


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)!

GSM Channels

Documents

ECE 4730: Lecture #25 1 Advanced Mobile Phone Service (AMPS) – 1G Analog FM IS-136 (aka USDC, IS-54) – 2G Digital TDMA Global System for Mobile (GSM)