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
CDMA2000 – 3G U.S./Qualcomm
W-CDMA – 3G Europe
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2. 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)
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3. 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.
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4. 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
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5. USDC Data Frame
Four data channel types simultaneously provided in TDMA frame :
1) DTC
2) CDVCC
3) SACCH
4) FACCH
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6. 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
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7. 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
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8. 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
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9. 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
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10. 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.
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11. 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.
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12. 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!
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13. Cellular Standards ECE 4730: Lecture #25 1G 2G 2G+ 2G - Obsolete
GSM-GPRS
2G - Obsolete 2G
2.5G 3G
EDGE 3G
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14. 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)
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15. 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
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16. 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 = 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 = kbps
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17. 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!!
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18. 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 = 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
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19. 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
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20. GSM BCH & CCCH
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21. 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
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22. GSM Frame Structure
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23. 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)!
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