the radio of the future

THE RADIO OF THE FUTURE

Natarajan.P

No. 17

S7 Electronics & Comm. PTDC

College of Engineering, Thiruvananthapuram

DEFINE DRM DRM is the world’s only

non-proprietary Digital AM Radio Systems for SW,MW, and LW with

ability to use existing frequencies and bandwidth.

DRM covers the broadcasting band below 30 MHz. College of Engineering,

Thiruvananthapuram

TRANSITION FROM ANALOGUE

• Fairly easy to start digital broadcasting• Difficult to stop analogue broadcasting

(because of the many millions of analogue radio and TV sets owned by consumers)

• The real benefits of spectrum efficiency can be achieved only when the analogue services stop

• As many countries have introduced digital TV, plans are being made for analogue TV switch-off

• Analogue radio switch-off will take a long time– starting DIGITAL services early is the best

mechanism for stopping ANALOGUECollege of Engineering, Thiruvananthapuram

– it uses the spectrum much more efficiently than analogue broadcasting

– digital transmitters operate at lower power– the number of radio & TV services can

increase– it offers improved quality, especially on

mobile and portable receivers– it offers new features, such as interactivity

DIGITAL BROADCASTING

is important because:


DRM & DAB• Two digital radio systems:

– DRM for use in the AM bands (LF, MF & HF)– Eureka 147 DAB for use in VHF & UHF bands

• The EBU has endorsed both systems because they are complementary– DRM is designed for use in the narrow channels

currently used for AM radio– DAB is a broadband system carrying multiple radio

services (and video services)

• Some broadcasters will use DAB or DRM– others will use both DAB and DRM


ADVANTAGES OF DRM

• DRM signals fit within the 9 kHz or 10 kHz channels used by traditional AM signals – simplifying frequency planning– permitting existing AM transmitters to be

reused for digital radio services with relatively minor modifications

• Broadcasters are attracted by the re-use of expensive hardware, such as high power transmitters and transmitting antennas College of Engineering,

Thiruvananthapuram

DRM .. advantagesDRM .. advantages

• Large coverage areas • Four operating modes for reliability:- Ground

wave mode, Sky wave mode, Highly robust modes 1 and 2

• Superior sound quality with AM reach • No change in listening conditions• Easy receiver tuning : by frequency, station

name or program


DRM FeaturesDRM Features

• Non proprietary standards

• Compatibility with existing AM channels

• Workable migration from analog to fully digital

• Multi mode operation depending propagation

• Provision for Data broadcasting

• SFN capabilityCollege of Engineering, Thiruvananthapuram

DRM System ArchitectureDRM System Architecture

Audio data

stream

Source

Encoder(s)

Data

stream

Source

Encoder(s)M

ultip

lexe

r

Energy

dispersal

Channel

encoder

Cell inter-

leaver

OF

DM

cel

l map

per

OFDM

Modulator

Pilot

generator

Coder,interleaver Energy dispersal

Coder,interleaver Energy dispersal

FAC

information

SDC

information

MSC

Signal Out


DRM MultiplexDRM Multiplex

Up to 4 Audio +Data

Channel parameters, Spectrum,modulation

interleaving….

Multiplex,CA,freq, schedule,time/date, region, coding,SBR,

PAD,Mod etc

MSC

FAC

SDC

MULTIPLEX

To OFDM


Source CodingSource Coding

AACStereo

HigherBit-rates-48 kbps

Audiosignal

SBR

AudioSuper

framing

Mux

& c

hann

el c

odin

g

AACStereo

NarrowbandCELP

NarrowbandCELP

StandardMode -20 kbps

Ultra robustMode-10 kbps

Low bitrateMode 8 kbps


Frame structureFrame structure

Frequency

Kernel carriers4.5kHz for FACin every frame

SDC2 OFDM symbols

Time

Core partOf SDC

Additional partsOf SDC

Frame400ms

Super-frame 1200ms

Frame 400ms

Frame 400ms

1 2 3


For this, there are the following properties:Frame length: 40 msAAC sampling rate: 24 kHzSBR sampling rate: 48 kHzAAC frequency range: 0 – 6.0 kHzSBR frequency range: 6.0 – 15.2 kHzSBR average bit rate: 2 kb/s per channelCollege of Engineering,

Thiruvananthapuram

DRM-Modes

Mode A B C DExpectedModulation

64QAM 64/16QAM 16QAM 64/16QAM

TypicalApplication

Groundwave

(MW,LW)

Sky-wave(MW, SW)

Difficultsky-wave

(SW)

Verticalincidence

(SW)Interleave Short Long Long Longest

Bit rate High Medium Med/Low Low

AudioQuality

High Medium Med/Low Low

Robustness Medium High High/V.High Very High


Guard Interval for different ServicesGuard Interval for different Services• System immunity against Fading, Doppler effect• For SFN Operation

Parameter MW SW

Duration Tu 24ms 21.33ms

Carrier spacing1/Tu

41 2/3 46 7/8Hz

Guard interval Tg 2.66ms 26.66ms

Tg/Tu 1/9 ¼

Symbols/frame 15 15


ImplementationImplementation

• Need a DRM exciter to generate QAM-COFDM symbols, in I and Q Channel

• Need a Digital Frequency Synthesizer to phase and amplitude modulate the carrier

• Linear amplifiers can take these signals directly • Non Linear older transmitters need to be linearised

or are to be modulated separately in amplitude and phase

• New MW transmitters using digital modulation techniques can easily take DRM.


Implementing DRM in Linear Implementing DRM in Linear TransmittersTransmitters

DRM Digital

Modulator

Digital RF

Synthesizer

Output

RF Circuits

Linear RF AmplifierTo

Antenna

RF Amplifier

Pre-amplifier

I

Ph

ase

an

d A

mp

litu

de

Mo

du

late

d R

F

Q

Audio + Data


Implementing DRM in Non-Linear Implementing DRM in Non-Linear TransmittersTransmitters

Digital

Pre-correction

Digital RF

Synthesizer

Digital

Demodulator

High Level

Modulator

Output

RF Circuits

Modulated HV

To Antenna

RF Amplifier

Corrected

I

Corrected

Q

I

Q

I DemodulatedQ Demodulated

Modulated

RF Sample

Corrected Amplitude

DRM Digital

Modulator

Digital RF

Synthesizer

I Q

Audio + Data


Other implementation issuesOther implementation issues

• Flat Spectrum response of the output circuit of transmitters

• Non uniform Phase change in amplifiers

• Antenna Tuning unit band width

• Band width of antenna( wide-band/dual band)

• Matching system / VSWR


ADVANCEMENT

The DRM consortium voted in March 2005 to begin

the process of extending the system to the

Broadcasting Bands up to 120 MHz

The design development and testing phase are

expected to be completed by 2007 – 2009


CONCLUSIONS

• Digital Radio Mondiale has achieved great technical success in developing the DRM system

• Synergy between DAB and DRM must be exploited

• The big challenge is now to achieve successful implementation– persuading broadcasters– persuading regulators– persuading receiver manufacturers– persuading consumers


the radio of the future

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