Digitising VHF-FM sound broadcasting with DRM...

IEEE BMSB 2009, Bilbao, 13-15/05/2009 - 1 - Schad / Steil / Köhler / Feilen / Lehnert / Kilian / Hedrich

Digitising VHF-FM sound broadcasting with DRM+ (DRM Mode E)

Aspects related to compatibility, coverage and radio network planning

Felix Schad, University of Applied Sciences Kaiserslautern (FH-KL)


Introduction:DRM+: System, Global trial concept

First DRM + Field Trial (2008):Concept, Setup, Outcomes

Second DRM + Field Trial (2009):Concept, first Results




Overview


► DRM+: The system

• Digital Radio Mondiale: (C)OFDM-based digital broadcasting standard up to 30 MHz

• Extended up to Band II (120 MHz) by DRM+ ( = DRM Mode E) , currently undergoing ETSI‘s standarization process

4-/16-QAMSubcarrierModulation

96 kHzRF system bandwidth

2.25 ms + 0.25 ms guard interval

Symbol duration213No. Carriers / symbol

444 4/9 HzSubcarrier Spacing1 – 4 No. Channels / service

MPEG4 AAC+Audio Coding37-186 kBits/sNet data rate

Introduction

Motivation for our work:DRM+ is a high-potential candidate for digitising

analogue VHF-FM sound broadcasting


► DRM+: Things to look at before system‘s regular introduct ion

Introduction

Coverage aspects (2009), to be discussed in a few minutes more) � Lab�� 2nd field trial (2009)

Compatibility aspects:�� Lab (2007)

�� 1st field trial (2008, to be discussed next); VHF-FM, BOS

Compatibility to existing radio services:

� VHF-FM sound broadcasting (87.5 – 108 MHz, in Band)� Aeronautical services (ILS, VOR: above 108 MHz)� Emergency service (BOS: below 87.5 MHz)








Overview


► Objective and Concept

The 1st field trial (2008)

Objective:• Examine effects to existing FM-services with DRM+ ‚on air‘• Extend measurements (lab compatibility, 2007 vs. fieldcompatibility)

• Use two separate, (remote-)controlable transmitters:� ‚Victim‘ Tx radiating FM, variable frequency : Tx RB� ‚Interfering‘ hybrid Tx radiating either FM or DRM +, equal power for both modulations: Tx FH

• Study interference impact of Tx FH into Rx-signal qualityof Tx RB

Concept:


►Block schematics of hybrid Tx FH


Transmit EITHER FM OR DRM+ !!

DRM+

Modulator

Optimod

SMH

SMU 200A

RDS

Atten.

ZX60-33LN+22 dB

3dB-BW:±180 kHz

NP-501-1+66 dB

45 dBm ERP(35 W ERP) - ND

Audio �

+

GPIB

LAN

Audio Audio

Atten.

LAN

Audio

Audio WAN

Control ComputerFMDRM+

PBX

RFoff on

MPX-Limiter

IlS DRM/DRM+-Content-Server

RS 232HPA State monitoring


►Transmitter sites and activity spots at the core study are a



► Compatibility measurements: Key paradigm

• Relate RF-Signal-to-Noise and interference ratio to AF quality

• AF quality is characterized by p. e. SINAD of received signal• Compare quality degradation by switching interfering modulation @Tx FH

• Alternative indicators used:

– AF-S/N, phospometrically weighted, highly correlated to SINAD-values– Quality Rankings (mobile case only)

PI,∆f

∆f0 200KHz

variable:• ∆f• Pi (for ∆f)

constant:• Pv• PN• % / kHz

120kHz

PN

Pv

RF AF

Criteria:

• SINAD

• (weighted S/N)

RXMultipath portion %/kHz

Wanted power Pv

Interfering power PI

Channel-Noise PN

Frequency separation ∆f



► Example of stationary measurement result:

PI ,max

PI , min

Impact of different interferingmodulation on received SINAD


SINAD over RF-SNR as function of different modulations, channel spacings and interfering powers (TX FH)


► Key results of stationary and mobile measurements


Interference potential of DRM+ into FM higher as compared to FM, esp. due to time-varying amplitude.

DRM+ field compatibility to FM easier achieved as in lab

Comparison of AF-quality results at mobile reception in line with stationary results


• Trial‘s results are back to network planning, giving experimental prot. ratios• Investigation of two different scenarios for a few german VHF FM radio networks:

(1) Replacement scenario (RS): convert existing FM Tx to a DRM+-Tx(2) Integration scenario (IS): insert a new DRM+ station

• Predictions based on local regulatory rules (with adapted protection ratios) • RS:

– a Tx can be converted if it‘s power is lowered by 5 dB while improving coverage• IS:

– a Tx can only be added with low ERP‘s as compared to the high powerscommonly used for FM sound broadcast

– For local stations, good coverage can be achieved with even low powers• DRM+ coverage criteria based on theoretical assumptions

• Nonetheless: as long as nominal measurement and planning paradigma are not adapted, any digital broadcasting scheme is hardly to integrate into VHF-FM band II !!!!

► Consequences from a radio network planner‘s point of vie w


See paper for

details








Overview


► Objective and Concept

The 2nd field trial (2009)

Objective:• Assess DRM+-coverage in real radio environment• Propose first planning paradigms for DRM+

� Coverage criteria for DRM+ not defined yet

� No reference implementations (Tx/Rx) availableStarting

point:

• Preparative lab measurements:– Characteristic parameters of Tx-Rx chain

– Define measurement principles and quality ratingcriteria

– Protection ratios for DRM+

• Field trial to validate and extend lab results

Path to goal:


► Prototype receiver (in use since 2008)

separate wide- and narrowband controls




► Prototype receiver in the field

Early Rx-Implementationstage during 1st realtimeradio transmission using

DRM+ worldwide(April 23rd, 2008)

Measurement van FH KL, currentlybeing upgraded to a full grown mobile metering system(exterior view of rx-loc shown above)


► Measurement of essential Rx & Tx key parameters


Rx-characteristics:– Total Noise Figure: 11 dB– Total gain: 19 dB – High linearity: Shoulder distance of max. 54 dB – Phase noise: -75 dBc/Hz (worst value)

[-90 … -85 dBc/Hz] (typical value)– Sensitivity for BER = 1E-4:

• -1 dBµV (4QAM) • 6 dBµV (16QAM)

Tx-characteristics :– IP3@ subcarrier spacing: 60 dBm– Phase noise: -90 dBc/Hz @ 1st subcarrier

-110 dBc/Hz (typical value)Tx FH:Power Amp.,cavity filter


• Slight degradation due to hardware implementation• Rx-phase noise & Tx amplitude compression dominating factor @ higher SNR-values• BER = 1e-4 reasonable threshold for minimum reception quality• Measurements confirmed by sensitivity-values shown before


► AWGN-BER-Performance


► Visualization of the term protection ratio

ITU-R BS.641 interferer

• mono, col. Noise

• no compression

• no RDS

Stereo interferer

• lifelike for today‘s transmitters

• stereo, col. Noise, compressed

• RDS

PDS @ BER = 1E-4 (4-QAM; Coderate 2/5); Power difference (wanted – interfering signal): protection ratio

The 2nd field trial (2009)Please note: results too

new to be included in

the paper!

Att 0 dB*

A

*

*

3DB

RBW 1 kHz

VBW 10 kHz

SWT 600 ms

*1 RM

AVG

Ref -45 dBm

Center 95.15 MHz Span 600 kHz60 kHz/

-140

-130

-120

-110

-100

-90

-80

-70

-60

-50

SWP 20 of 20

1

Marker 1 [T1 ]

-58.12 dBm

95.200000000 MHz

2

Delta 2 [T1 ]

-59.98 dB

-200.000000000 kHz

Att 0 dB*

A

*

3DB

RBW 1 kHz

SWT 500 ms

*

*

VBW 10 kHz

Ref -35 dBm

Center 95.1 MHz Span 500 kHz50 kHz/

1 RM

AVG

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

SWP 20 of 20

1

Marker 1 [T1 ]

-45.37 dBm

95.150000000 MHz

2

Delta 2 [T1 ]

-70.22 dB

-150.000000000 kHz

-67

dB

-54

dB

150 kHz 200 kHz

Inte

rfer

ing

sign

al(F

M)

Wan

ted

sign

al(D

RM

+)


► Protection ratio measurements

FM-BC interferes DRM+, 16QAM; Coderate 1/3: C/I at beginning of interference

-80 dB

-60 dB

-40 dB

-20 dB

0 dB

20 dB

40 dB

60 dB

0 kHz 50 kHz 100 kHz 150 kHz 200 kHz 250 kHz 300 kHz 350 kHz 400 kHz 450 kHz 500 kHz

frequency offset

prot

ectio

n ra

tio

Loss of audio decoding, stereo interferer(compressed col. noise)

comparision: BER=1e-4, stereo interferer

BER=1e-4, interferer as defined in ITU-R BS.641 (FM into FM)

FM interfered by FM, planning curve (ITU-R. BS 412-9)

Please note:results too new to

be included in the

paper!


Points shown on previous slide


► Proceedings up to today


Next steps:� Stationary field-measurements� Compare BER / Audio dropouts at rx-loc. to FM audio

performance� Mobile measurements, compare DRM+ to FM

performance under fading conditions

� Key Tx- / Rx-Chain parameters assessed� DRM+-Coverage criterion defined� System immunity / Rx behaviour to interfering signals

known� Coverage predictions calculated, to be verified


These slides and more information covering the wholeof FH Kaiserslautern‘s and partners DRM activities can

be found at:

http://www.drm-radio-kl.eu

Final words

Digitising VHF-FM sound broadcasting with DRM...

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