A BRIEF HISTORY OF CELLULARIN THE U.S.

Gary Kaatz March 28, 2016

PRE-CELLULAR: ØG

� FM Radio Telephones: Rural (Fixed) and Metro Areas (Car)� 1946: Mobile Telephone Service (MTS)

� Operator assisted, no direct dial, half-duplex (PTT), 60 kHz channel

� 9 channel pairs at low VHF, 11 at VHF

� 1964: Improved Mobile Telephone Service (IMTS)� Direct dial, in-band signaling using tones, 30 & 25 kHz channels

� Telco: 11 channel pairs at VHF and 12 at UHF (Frequency Division Duplex, FDD)

� RCC: 7 channel pairs at VHF and 12 at UHF (FDD)

� Severe limitation on the number of subscribers (3-year waiting list)

� Channels were taken over by paging services

THE CELLULAR CONCEPT

Cluster

� The core concept of cellular is frequency reuse

� A geographical area is divided into many cells: typically 7 cells per cluster

� A subset of the available frequencies is used in each cell

� Frequencies are reused in cells “far enough apart”

� Frequencies reused in the same cell color in adjacent clusters:

� Reuse distance: where N is the cluster size

� As the moving subscriber crosses cell boundaries, handoff is required to be

seamless

NRD 3=

CAPACITY

� If there are S channels assigned to a cellular operator:� Each cell is allocated k channels and if there are N cells per cluster

� If a cluster of N cells is replicated M times in a system, the total number of channels, C is a measure of the capacity

� Since S is fixed, only M (number of clusters) can affect capacity

� Capacity increases with cell splitting (R deduced by ½)

� Capacity increases with sectored cell site (a different way of cell splitting)

kNS =

MSMkNC ==

INTERFERENCE TRADEOFF

� If the cluster size N is reduced, M must increase, therefore capacity increases

� At the same time, co-channel interference increases because the reuse distance is smaller

� The signal to interference ratio is approximately:n

NS 3

� Where n is the path loss exponent (2-4) and m is the number of surrounding clusters

� So as N increases, the capacity decreases but S/I increases

� N can be 3, 4, 7, 12, 19, etc.

� System design task: for a required S/I, what is N?

n

m

N

I

S

≈

3

FIRST GENERATION: 1G

� 1983: Advanced Mobile Telephone Service (AMPS)� Analog FM for voice, 30 kHz channel (FDMA/FDD)

� 10 kb/s FSK control data (briefly mutes audio)

� Initially 666, in 1987 increased to 832 UHF channel pairs (824-849/869-894MHz)

� Two operators in each MSA/RSA (RBOC/RCC) each w/21 control & 395 traffic channels

� AMPS was standardized by EIA/TIA as IS-3, superseded by EIA/TIA-

553

� Major carriers: AT&T (Baby Bells), Cellular One

PROBLEMS WITH AMPS

� Can be easily monitored

� An eavesdropper with specialized equipment could

intercept a handset’s ESN and number and clone

them onto a different phone and steal air timethem onto a different phone and steal air time

� Led to the FCC banning scanners that covered the

cellular band and making interception of a cellular call

illegal

� AMPS had capacity issues at places like airports

(busy signals)

INTERIM CAPACITY FIX

� 1991:Motorola Narrow AMPS (NAMPS)

� Scaled bandwidth: 10 kHz channels� Signaling below 300 Hz, no audio blanking

� Falls back to AMPS where NAMPS is not available

� Tripled the capacity� Tripled the capacity

� Enhancements� SMS (Texting)

� Voice mail notification

� Superseded by 2G

� Legacy AMPS was shut down in 2008

SECOND GENERATION: 2G

� 1991: Digital (D-AMPS/USDC)� 24.3 kbaud/s π/4 DQPSK (2 bits per baud) in 30 kHz channels

� Non constant-envelope signal → inefficient linear RF PAs

� Voice centric

� TDMA/FDD with 6 time slots, each 6.67 ms (40 ms frame)� Each slot: 324 bits

� Each subscriber uses two of the 6 time slots, i.e. 1 & 4

� Triple the capacity of AMPS� Triple the capacity of AMPS� Later, 6X by going to half-rate (one time slot per subscriber)

� Speech coding (compression) with error correcting codes (260 bits in 20 ms: 13 kb/s, half-rate: 130 bits, 6.5 kb/s)

� No more monitoring

� Same control channel as AMPS

� Falls back to AMPS where DAMPS is not available

� Except for the AMPS fall-back, duplexer not required as the downlink and uplink channels are staggered in time

� EIA/TIA IS-54

2G EVOLUTION

� 1995: EIA/TIA IS-136� Equivalent to half-rate D-AMPS

� 6X the capacity of AMPS

� Digital control channel� Increased battery standby timeIncreased battery standby time

� Messaging and circuit-switched data

� AMPS compatible

� New PCS band was assigned for digital only� 1850-1910/1930-1990 MHz)

� Major Carriers: AT&T, Cingular

� D-AMPS was shut down along with AMPS in 2008

OTHER 2G AIR INTERFACES: GSM� GSM was deployed first in Europe in 1991

� First used in the U.S. in 2001 by AT&T to replace IS-136

� 270.833 kb/s 0.3 GMSK in 200 kHz channels� Constant envelope signal allows use of efficient RF PAs

� TDMA/FDD with 8 time slots, each 576.92 µs (4.615 ms frame)� Each slot: 156.25 bits, 8.25 bits guard time: 114 information-bearing bits

� Single-slot data rate: 24.7 kb/s (voice centric)

� Duplexer not required as the downlink and uplink channels are staggered in time� Duplexer not required as the downlink and uplink channels are staggered in time

� Speech coding rate: 13.4 kb/s

� 1.2X capacity of AMPS!

� Introduction of the Subscriber Identity Module (SIM)

� Standard maintained by European Standards Technical Institute (ETSI)� Many sub-standards: TS 45.xxx

� First world-standard cellular system

� Major carriers: AT&T, T-Mobile

OTHER 2G AIR INTERFACES: CDMA

� CDMA (cdmaOne) was deployed in the U.S. in 1993

� 1.2288 Mc/s QPSK in 1.25 MHz channels� CDMA/FDD

� 64 chipping codes per base station

� Other users of the same channel appear as noise

� Maximum 9.6 kb/s user rate (voice centric)

� Spreading factor of 128� Spreading factor of 128

� Downlink and uplink coded differently

� Every cell uses the same channels

� Not constant-envelope → inefficient linear RF PAs

� EIA/TIA IS-95

� 6-20X capacity of AMPS (varies with SNR)

� Major carriers: Verizon, Sprint, Alltel

OTHER 2G AIR INTERFACES: IRIDIUM

� Conceived in 1987 as a constellation of 77 LEO satellites; the number of electrons in the element Iridium. Operational in 1998. Deployed as 6 orbits of 11 satellites each.number of electrons in the element Iridium. Operational in 1998. Deployed as 6 orbits of 11 satellites each.

� Iridium SSC went bankrupt in 1999. Service was restarted in 2001 by acquiring company; Iridium Satellite LLC.

� 25 kbaud/s DE-QPSK in 31.5 kHz with 41.67 kHz channels to account for Doppler shifts� Non constant envelope signal and high power required exotic RF PAs

� TDMA/FDMA with an initial 20.32 ms for pagers and call paging, 4 uplink slots and 4 downlink slots, each 8.29 ms (90 ms frame)

� Speech coding rate: 2.4 kb/s

� 1618 – 1626.5 MHz: 184 channels

2G TRANSITION: 2.5G DATA!

� General Packet Radio Service (GPRS)

� GSM with use of up to four slots per subscriber to boost user data rate up to 115 kb/s (~2002)

� Enhanced Data Rates for GSM Evolution (EDGE/EGPRS) (2003)(2003)

� New modulation: 3π/8-offset 8-PSK with 3 bits per symbol and up to four slots boosts user data rate up to 384 kb/s

� IS-95B (~2001)

� Added 64 kb/s packet data capability

2G TRANSITION: 2.75G DATA!

� Evolved EDGE (~2008)

� 16 and 32-QAM, Reduced Transmission Time

Interval (RTTI), Downlink Dual Carrier (DLDC)

� 2002: CDMA 2000 1xRTT� 2002: CDMA 2000 1xRTT

� Replaced IS-95

� Although capable of higher rates, most

deployments are limited to a peak of 144 kb/s and

an average ~80 kb/s throughput

THIRD GENERATION: 3G MORE DATA!

� Although deployed in Europe and Japan since 2001, in 2004 AT&T deploys Universal Mobile Telephone System (UMTS)� 3.84 Mc/s WCDMA/FDD in 5 MHz channels

� 384 kb/s to 2 Mb/s depending on SINR

Standardized by 3GPP, an international organization, into � Standardized by 3GPP, an international organization, into multiple sub-standards: TS 25.xxx

� 2008: New AWS band 1710-1755/2110-2155 (T-Mobile)

� 2002: CDMA 2000 1xEV-DO rev 0� Downlink up to 2.4 Mb/s (3.1 Mb/s rev A)

� Uplink up to 153 kb/s (1.8 Mb/s rev A)

� Standardized by 3GPP2: TIA-856 Release 0

3G TRANSITION: 3.5 & 3.75G MORE DATA!

� 2008: T-Mobile UMTS-based HSPA, 2009 HSPA+� Downlink : 7.2 - 42 Mb/s

� Uplink : 384 kb/s – 11.5 Mb/s

� 2011: E-UTRA/LTE (Verizon) Hyped as 4G� New!: Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input-

Multiple Output (MIMO), scalable channel bandwidths (1.4 -20 MHz). OFDMA/FDD

Downlink : OFDMA up to 300 Mb/s (12 -35 avg)

∆f

� Downlink : OFDMA up to 300 Mb/s (12 -35 avg)

� Uplink : SC-FDMA (DFT-OFDM) up to 75 Mb/s (15 avg)

� Four new bands at 700 MHz for LTE

� 3GPP specifications TS 32.xxx

� AT&T, T-Mobile and Sprint now also have LTE

� Voice over LTE (VoLTE) deployed by Verizon and T-Mobile

� CDMA 2000 1xEV-DO rev B and EV-DV� Requires switch to 5 MHz channels

� Operators moving to LTE for higher data rates instead of rev B

Channel bandwidth (MHz) 1.4 3 5 10 15 20

Number of resource blocks 6 15 25 50 75 100

FOURTH GENERATION: 4G (NOW)

� 2014: E-UTRA/LTE Advanced deployed by AT&T,

2015: Sprint and T-Mobile

� Carrier aggregation in the downlink

� Inter-band and intra-band (contiguous and non-� Inter-band and intra-band (contiguous and non-

contiguous) up to 4 carriers

�Two inter-band carriers deployed by AT&T and Sprint

(Spark)

� Downlink up to 3000 Mb/s

� Uplink up to 1500 Mb/s

AIR INTERFACE: TIME AND FREQUENCY

OFDMA