A Review of Digital Mobile Radio Modulation Technologies

February 27, 2016, Sendai

Yoshihiko Akaiwa

Emeritus Professor of Kyushu University

Workshop for celebrating Prof. Adachi Retirement

Analog Cellular Systems and Digital Pager

Digital Modulation for Analog Systems

POCSAG Paging System Specifications

Post Office Code Standardization Advisory Group

The First Stage (’78): Two-way Digital Mobile Radio

Two-way Digital Mobile Radio

- Police & Military CommunicationsDigital-Voice Scrambling

- Digitization of Analog FM Radio in 25kHz Channel Spacing

Digital Modulation :Power Efficiency Constant Envelope Modulation

- Tamed FM (de Jager & Dekker, ’78)- GMSK (Hirade & Murota, ’79)- Multilevel FM (Akaiwa et al., 79), - PLL-QPSK (Honma et al., 79)

Voice Coding :- Adaptive Delta Modulation (CVSD)

CMOS, One-chip codec (Motorola & Harris)

GMSK: Gaussian Filtered Minimum Shift Keying

modulator

m = 0.5NRZ

FM GMSKdata

{1,0}1 LPF

Gaussian

The Second Stage (’85): Digital Cellular Systems

- Spectrum Efficiency- System Cost- Handheld Terminal

Proposed Systems for the GSM System

System Company MultipleAccess Modulation Bit RateChannelSpacing

S900D Bosch/Ant/Matra TDMA 4-levelFSK 128

kbps

250kHz

DMS90 Ericsson TDMA GMSK 340 300

SFH900 LCT/TRT TDMA/CDMA GMSK 200 150

CD900 SEL/AEG/ATR/SAT/ITALTEL

TDMA/CDMA QPSK 4,000 6,000

MATS-D TeKaDe/TRT QAM 1,218 1,250

GTFM 19.5 25

GSM System (’87)

The first TDMA system (8-time slot : 270 kbps)Base Station Cost, implicit path-diversity effect (with adaptive equalizer), mobile-assisted hand-off, variable data rate

- Adaptive Equalizer DPM+Viterbi Eql. (Maseng, ’86)GMSK+DFE (Raith, Stjenrvall & Uddenfeldt ’87)

- GMSK- RPE - LPC (16kbps, Phillips)

Error Rate Results by Field Experiments

without equalizer(256 kbps, discriminator detection)

with decision feedback equalizer

- GMSK modulation

(Stjernvall, Hedberg & Ekemark, Proc. VTC’87)

(340 kbps)

Hand-Portable Properties

GSM-TDMA Analog 900 MHz Analog 900 MHz(1993) (1987)

(1993)

Operating time 25 h 5h 9h(hours) (300 mAh cells) (500 mAh cells) (300mAh cells)

Weight (grams) 160 g 600 g 250 g

Volume(cc) 161 cc 610 cc 251 cc

Relative cost 0.5 1 0.5

(Rydbeck, Hedberg & Uddenfeldt, Int. Conf. on Digital Land Mobile Radio Communications, Venice 1987)

ADC(IS-54, ’90) and PDC (’91)

- Very Narrow Band TDMA(3-channel)30 kHz (ADC:AMPS), 25 kHz (PDC:NTT) channel spacingChannel speed: 48.6 kbps(ADC), 42 kbps(PDC)

- Compatibility with analog systems- No adaptive equalizer but diversity reception(PDC)

- linear Modulation ( /4 shifted QPSK: Akaiwa & Nagata ’85)Feed-forward Common Power Amplifier (Nojima et

al ’93)

- VSELP (13 kbps: IS-54, 11.2 kbps: PDC)

Power Spectra for Linear Modulation

Frequency

without non-linear distortion output of power amplifier(= power efficiency)

-80

-70

-60

-50

-40

-30

-20

-10

0

10

-4 -3 -2 -1 0 1 2 3 4

Pow

er S

pect

ral D

ensi

ty (

x 1/

Ts) [

dB

Frequency (1/Ts)

4-level FMQPSK

0 20-20 40 60 80 100 kHz-40-60-80-100

Frequency Departure

0

-20

-40

-60

-80

-10

-30

-50

-70

Rel

ativ

e Po

wer

Spe

ctru

m D

ensi

ty (d

B)

=41%

%

%

Power Amplifier Non-linearity Compensation with Negative Feedback

without feedback with feedback

Adaptive Feed-forward Amplifierpilot signal

vectoradjust

main amp.

sub amp.

controlcircuit

vectoradjust

without compensation with compensation

(Uebayasi et al. NTT Review,1999)

CDMA System (IS-95, Qualcom, ’93)

The first Spread-Spectrum System in Cellular Telephony

- Rake receiver against multi-path fading- Soft Hand-off (one-frequency reuse: short- and -long codes)- Fast and Precise Transmit Power Control (the near-far problem)- Variable rate voice coder

The Third Stage (’00) : IMT-2000 ( 3G )

- Mobile Multimedia Serviceshigher data rates, wireless IP

- Global Roaming

TDMA Evolution

EDGE : GSM Evolution

- higher data rate (2.86 x 270 kbps) in a GSM Spectrum Mask- GMSK high level linear modulation

IS-136+ : Evolution from IS-136 (IS-54)

- higher data rate (64 kbps) in the IS-136 Spectrum Mask- /4 - shifted QPSK 8PSK- improved voice quality (12.2 kbps US 1)

W-CDMA- high data rates : 2 Mbps (indoor), 384 kbps (mobile)- Coherent Detection, Multiple Spreading-factor,

Non-synchronized base stations

MC-CDMA (cdma 2000)- HDR- 3-carrier system

CDMA Evolution

W-CDMA System Specifications

Wired v.s. Wireless

Wired : ISDN, ADSL, CATV, FTTHWireless : WLL, Wireless LAN, IMT-2000, Wireless (Mobile) IP

WLL, IMT-2000(2Mbps)

(low cost base station)

Router IP Network

(WDM optical fiber)

AMP

DSP

(Keynote speech at VTC 2000, Tokyo)

The Fourth Stage (’05 ?) : The Fourth Generation System

Narrow sense: LTE-Advanced and WiMAX 2Wide sense: LTE, WiMAX and HSPA+ in addition to the above

HSPA+ (or Evolution)- MIMO (2x2): 23.4-28Mbps (down)- 64QAM (down): 21Mbps, 16QAM (up): 11Mbps

LTE (long term evolution) - maximum data speed: 300Mbps (down), 75Mbps (up)- radio transmission delay (one way) : less than 5ms

- frequency-and time-domain multiplexing : MC-OFDM (down: a resource block of 12 continuous subcarriers

with 15kHz spacing, number of resource block: 6-100)- Adaptive channel resource allocation (scheduling) depending onuser channel condition (user diversity)

LTE-Advanced - maximum transmission rate of 1Gbps (down), 500Mbps (up)

with bandwidth expansion up to 70MHz with carrier aggregationand 4x4 MIMO

WiMAX- OFDM (down & up)- maximum transmission rate: 70Mbps (down & up)

WiMAX 2- bandwidth more than 20MHz with carrier aggregation

to meet the IMT-Advanced requirement of 1Gbps

Increase of PAPR (peak to average power ratio)

PAPR- constant envelope modulation (digital FM) : 0 dB- linear QPSK : 3.5 dB- increases with number of multiplexed signals (CDM, OFDM, CA)- causes difficulties for power amplifier

Counter measures against high PAPR - PAPR reduction method such as peak clipping and filtering- nonlinearity compensations for power amplifier

(feedback, feed forward, pre-distorter)

Complementary cumulative distribution function of normalized power

PWRDET

BPF

TABLE

algorithm

Digital Signal Processing

t G AMP X

In Out

f 0

f 0'

-100

-80

-60

-40

-20

0

20

-8 -6 -4 -2 0 2 4 6 8

Pow

er S

pect

ral D

ensi

ty [d

B]

Normalized Frequency

originalcompensated

Adaptive Pre-distortion Power Amplifier

- Adaptive with digital signal processing- High power-efficiency- Closed in RF band

The Doherty Power Amplifier

W.H. Doherty, 1936

Output power and power efficiency vs. input powerfor a Doherty power amplifier

Courtesy of Prof. Honjyo of the UEC

Measured performance of the GaN Transistor Doherty power amplifier with digital predistorter

Transmit power: 40W, The final stage power efficiency: 50〜60％

Courtesy of Hitachi-Kokusai Co. Ltd.

Power consumption