With respect to digital radio, Europe is known as a 100 percent DAB Eureka-147 area, and the image of in-band, on-channel digital in Europe is very poor. Unproven arguments against IBOC are disseminated, like “technically not feasible in Europe because of many differences in the FM system,” and there is confusion of FM with AM HD Radio questions.
Based on large DAB investments and a European digital FM system (DRM+) on its way to finalization, it is understandable no one is really interested in a “foreign” FM digital alternative.
However, not even one European country has a commercially profitable DAB operation yet (with the eventual exception of the United Kingdom, where there is the chance to become profitable some years from now; CGap, the biggest U.K. operator predicts “digital break even” for 2010).
Moreover, some thousands of local and regional (single-program) broadcasters are no longer so sure that a multiplex technology is the proper solution for them; perhaps more feasible and economically viable systems with a slow evolution path to digital should be found.
That’s why the Swiss Federal Office of Communications (OFCOM) and the Association of Private Broadcasters (VSP) started to support our initiative to do some HD Radio field trials, and to follow any other kind of FM digital system that could be an alternative.
The Swiss OFCOM granted the first European HD Radio test license at the end of 2005 for two years to Ruoss AG/Radio Sunshine. This license was extended until the end of 2008, and a total of three different frequencies are now allowed to be tested simultaneously.
(click thumbnail)Fig. 1: Simplified map of critical field test areaSince field testing began, and especially after the successful HD Radio days in Lucerne in October 2006, HD Radio has begun to gather a lot of positive interest in Europe. The “false statements” about HD Radio have started to fade away, piece by piece.
A good example of such false statements was that European FM deviation will have to be reduced below 50 kHz peak deviation, and the audio multiplex power to –6 dBr, to make it work. This argument has now completely disappeared.
FIELD AND LAB TEST SETUP
For IBOC field testing, the main transmitter of Radio Sunshine (88 MHz, located at around 400 meter height above average terrain, with mountains approximately 7, 13 and 25 miles behind the coverage area) is used in a high-level combined standard hybrid mode with 3,500 watts analog and 35 watts digital power. The main coverage area is the town of Zug and vicinity; Radio Sunshine has a total of 16 transmitters to cover Central Switzerland (see Fig. 1).
The content transmitted in 24/7 multicast mode is:
- Radio Sunshine analog FM
- Radio Sunshine digital (HD1) 48 kbps
- Radio Energy Zurich digital (HD2) 32 kbps
- Service digital (HD3) 15 kbps, voice, traffic, weather, sport, events
- PAD HD-display 1 kbps
A second transmitting setup together with other FM test equipment is used for lab simulations and testing. For the first part of the trial, a number of JVC, Sanyo and Kenwood car receivers are used together with some tabletop radios from Polk and Boston Acoustics. ADA receivers are used for audio quality reference.
(click thumbnail)Fig. 2: Measurement of typical peak deviation and audio multiplex power used at the Radio Sunshine transmitter network. The recorded values are at the ‘edge’ of what is allowed in Switzerland.Twelve FM receivers were used for lab testing: three Walkman radio/cellphone-type, three car radios, four portable and two compact HiFi.
DEVIATION AND MPX POWER ISSUES
The FM system in the United States uses 75 µsec pre-emphasis, a maximum deviation of 75 kHz and multiplex power above 0 dBr.
Europe uses 50 µsec pre-emphasis, a 75 kHz maximum deviation and maximum MPX power levels ranging from 0 dBr to “some dBr” depending on country and “best practice.” Some European countries only allow a maximum of 0 dBr MPX audio power while other countries like Switzerland allow +3 dBr, and some countries use even higher MPX levels. See Fig. 2 for typical peak deviation and MPX power for all HD Radio lab and field testing [Ed. Note: For European radio broadcasters, the International Telecommunications Union established a modulation density specification that uses the integrated value of the power in the audio modulation of the FM signal to define “peak” modulation levels. This reference of 0 dBr is equal to a 19 kHz average deviation over a 60 second integration interval, which is typically much lower than modulation used by an FM station in the United States.]
All our testing so far shows clearly that “the European values” of peak-deviation, pre-emphasis and MPX power levels (up to 6 dBr) do not give any relevant limitations for the use of the HD Radio system.
Is the European receiver universe different from that of the United States? Not really, but in most countries in Europe, portable and indoor listening of FM radio is much more important than in the U.S.
Actual figures from Switzerland show that approximately 2/3 of all radio listening is indoor/portable. This means that portable receivers have to be tested as well as car receivers. Home stereos are a bit less important nowadays because they are mostly connected to cable systems and no longer to an antenna.
(click thumbnail)Fig. 3: SNR (in dBA) of typical European FM receiversEarlier receiver studies from Nozema (Netherlands, 1998) and the Swiss OFCOM in 2002 indicated that a greater part of the portable receivers are not even able to meet the minimum signal-to-noise ratio requirement and the minimum RF-Selection criteria as recommended by the ITU-R BS.412-9, BS.415-2 and ITU-R BS.641 rules. Fig. 3 shows the S/N performance (with and without HD signal) of a sample of typical European FM receivers.
The S/N influence of the two digital HD Radio sidebands on Europe’s FM receiver universe at the time of operational introduction of HD Radio should be very minimal, and the commonly used planning criteria on minimum S/N performance can be met. No influence on RDS-AF function was detected so far.
EXTENDED HYBRID AND MULTICAST
Simple lab measurements and comparisons with extended hybrid operation did not show any relevant differences to the measurements made in the United States.
(click thumbnail)Fig. 4: Measured coverage quality of the analog FM signal of Radio Sunshine’s main transmitter at 88.0 MHz. The different colors represent the 5-Grade CCIR scale for audio quality.However, to get best possible S/N protection for some of the existing high-performance FM receivers, I would actually recommend delaying full extended hybrid operation until after initial operational introduction in European radio markets to minimize any potential interference to existing receivers. Looking from a marketing perspective, of course, multicast is a must, right from beginning.
I. FIELD TEST RESULT
Digital Coverage in the FM Coverage Area
Within the FM coverage area the digital coverage for all digital content is perfect and 100 percent stable with car receivers. For examples see Fig. 5.
It also can be seen that coverage extension happens in areas where FM analog is unusable (black/blue and green in Fig. 4) because of strong multipath reception, as long as there is sufficient field strength and off-spectrum protection.
(click thumbnail)Fig. 5: Digital coverage at the fringe and outside of FM analog coverage area. In strong multipath areas (like the sections with the black color on analog graph) there is much better digital than analog coverage.Fig. 4 shows the FM analog quality (ITU, five-grade scale) of almost the complete reception area of the 88 MHz transmitter. Almost all of the green/blue and black parts will have digital reception with some blending to analog. The coverage area for the multicast content is smaller than for the host program because there is no blending feature. These results are not yet validated for complete indoor reception in all of the areas where car reception is good.
RDS-AF Functionality/Host Compatibility
In the first nine months of operation with the HD Radio signal during our testing, not one complaint was received from a listener (more than 50,000 FM receivers on 88 MHz) about S/N reduction from HD Radio sidebands.
Nor were there any complaints about RDS Alternate Frequency function, which is very important in the test area (more than four different frequencies are needed for FM analog coverage around Lucerne/Zug). This is a clear indication that HD Radio can be introduced on existing FM transmitters in a European frequency planning environment.
Indoor Portable Reception
At this moment, few indoor reception tests have been done. Extensive indoor testing with 40 or more portable receivers distributed to listeners in the fringe area of the 88 MHz transmitter will take place in the second part of the trial. We already know that outdoor field strength in the fringe areas gives us around 15–20 dB “headroom” for digital reception.
Based on the commonly used factor of 14 dB for FM building penetration, we are confident the indoor results will be promising, with the exception that we cannot yet quantify the influence of today’s typical indoor noise environment on digital reception in the FM band. To achieve deep indoor reception, approximately 60 dBuV/meter at 2 meters (commonly used in Switzerland for actual FM planning) will be necessary.
HD Robustness at High Speeds
Because 88 MHz is relatively “well protected” (in respect to ITU 412-9 recommendation), additional “artificial” interferers on both sides of 88 MHz were needed to simulate digital reception robustness in fast moving vehicles.
Compared to actual lab results some degradation could be recognized, but at maximum allowed ITU-412 interfering levels the digital reception still is robust. More quantifiable work will be done on this issue in Part II of the trial.
II. LAB TESTING RESULTS
For lab testing the ITU 412-9 and ITU-R BS.641 Recommendation for FM Planning and Measurement is taken as the basic reference. Because FM HD Radio hybrid operation is a mixture between an analog and a digital system, and because the two HD sidebands are redundant, some of the recommended procedures are not useful anymore.
(click thumbnail)Fig. 6: RF spectrum measurements for hybrid and extended hybrid operation during the HD Radio field trial in Switzerland.Also today’s station audio processing produces somewhat other spectral densities than at the time the recommendations were made. For judging the HD Radio system we must have a different set of protection ratios for the following interfering situations: D to A (Digital to Analog), an HD station interferes with an analog-only FM station; A to D, an analog-only station interferes with an HD station; and D to D, interference between digital hybrid stations.
For A to D and D to D, one also will need different protection ratios for stationary/portable and reception in fast-moving vehicles. To get realistic numbers, both sidebands have to be interfered at the same time. Some subjective evaluation of the difference between an FM signal interfering with an analog FM signal and an OFDM HD signal interfering with an analog FM signal at the typical HD signal differences has to take place.
Fig. 6 shows the typical RF spectrum for hybrid and extended hybrid operation.
Critical Spectrum Issues?
For the D to A measurements, the same receivers as for the host compatibility tests were used. For A to D and D to D measurements, HD Radios from Sanyo, JVC and Kenwood were used. Co-channel and 400 kHz interfering situations are not critical at ITU limits and the same as in the United States, so no special additional attention is necessary for these situations.
Fig. 7 shows European 100 kHz Interferer at ITU 412-9 limit. This allocation condition is not critical for D to A, A to D and D to D interference. The analog interference is always stronger than the interference from the digital sidebands. Depending on the FM receiver, more than 10 dB of headroom was measured on the ITU limit.
(click thumbnail)Fig. 7, at top, shows European 100 kHz interferer at ITU 412-9 limit. Fig. 8, middle, is the European 300 kHz interference situation at ITU 412-9 limit. Fig. 9 is worst-case spectrum allocation condition for Europe, both sidebands interfered with an HD Signal at ITU 412-9 limits (same as in U.S.)Fig. 8 shows the 300 kHz interference situation at ITU 412-9 limit. This constellation is not critical for D to A, A to D and D to D interference. The headroom to ITU 412-9 limits is only “some dBs” depending on the receiver, and symmetrical interferers, both strong at same time, can be critical in fast-moving vehicles.
Fig. 9 shows the worst possible constellation for Europe with both HD sidebands interfered with at ITU limits. This is the most critical situation in the field (same as in the U.S.) and is fortunately not standard practice in most European countries. It is uncommon to find stations with strong interferers at both +200 kHz and –200 kHz adjacent channels.
D to A Interference
When the listener does not use an HD Radio, the maximum stereo S/N can be reduced well below the recommended value. In practice, almost all of today’s car receivers will blend to mono (producing approximately 20 dB better S/N) during this kind of strong interference, and the average listener will not notice.
Home stereos with individual aerials, which these days exist only in rare cases, will have degraded noise performance, and “old” receivers with poor RF selectivity (and missing low-pass filter after demodulator) will have analog interference before they notice the additional noise from the OFDM signal. Therefore it is recommended that special attention be paid in 200 kHz interferer situations, especially when both sidebands are affected, to protect the existing FM receivers.
A to D and D to D interference at ITU limits will produce stable HD Radio reception for the wanted signal.
New FM HD Radio Planning Rules?
If the ITU 412-9 recommendations are respected as was “common practice” for earlier FM planning in Europe, and if estimated future average FM receiver performance is used, no new rules are necessary to implement HD Radio in Europe.
The following provisions may apply:
- Avoid symmetrical, (and same time/same location) 200 kHz interferers in the coverage area.
- Provide some headroom at 200 kHz frequency difference; average 7 dB would be great.
- Use 60 dBuV/meter at edge of coverage area.
- Correct earlier non-conforming 200 kHz interferers in the coverage area.
In Europe, the same interferers (+/- 200 kHz) are the HD Radio system limit for the existing analog FM receiver universe as in the United States!
Fig. 10 shows typical lab test configurations as they were used for preliminary protection ratio measurements.
Coming as no big surprise, all tested car HD Radio receivers had very good sensitivity and very good FM analog performance as well. HD Radio uses the same proven FM radio RF front end as current radio receivers. The car receivers we measured so far worked in digital mode a bit below 30 dBuV at the receiver antenna input. The first generation tabletop radios are a few dB less sensitive.
(click thumbnail)Fig. 10: Typical lab test configurations with ‘European 100 and 300 kHz interferers’ as they were used for preliminary protection ratio measurementsHow selective are today’s FM receivers? Unfortunately not all receivers in the existing FM radio universe have the same performance when it comes to selectivity. As Fig. 11 shows, there are dramatically big differences between receivers.
As an example at 200 kHz frequency separation, a relevant part of the receiver universe (BAKOM Study 2003) is more than 20 dB worse than the ITU recommendation (portable/mobile), but another group of receivers — especially car receivers — is up to 50 dB better than the ITU-R is looking for.
The good news is that with the exception of 100 kHz interferers the actual FM receiver chips built in cheap portable receivers and cell phones are much better as some years ago, and are reaching ITU 412-9 minimum performance.
HD Radio as ETSI Standard?
The initial steps have already been taken to make HD Radio a European Technical Standard Institute standard. An important part of this process will be the inclusion of the European RDS standard with the AF-Functionality (Alternate Frequencies), because in contrast to the United States, an average private broadcaster has a high number of translators and not just one main transmitter.
Other FM HD Radio Trials in Europe
HD Radio’s growing popularity in Europe has led to some “HD Radio tourism” to our location in central Switzerland for a test drive and a laboratory demonstration of all critical protection ratio issues.
Almost all unbiased visitors, who previously had only heard of and read about HD Radio in the United States, become real fans of the digital FM idea after demonstrations in the lab and field.
Some of the leading OEMs for the German automotive industry and some German car manufacturers have started to use central Switzerland as the test bed for their HD Radio equipment.
(click thumbnail)Fig. 11: Three groups of receiver performance, according to ITU 412-9 specifications are shown. Group 1 is almost worse than the minimum specification. Group 2 is a bit better than the ITU Reference and Group 3 is much better than the ITU 412-9 minimum performance. The difference at first adjacent can easily be greater than 1:1000 (60 dB!).Examples of car manufacturers include BMW, Daimler, Harmann Becker, Visteon and more. Even after the announcement by the World DAB Organization about the arrival of the far more efficient new DAB+ (with AAC+ audio codec, which is similar to the HDC used by HD Radio and with better error correction) the interest from regulating bodies and private broadcasters in Europe in HD Radio is still growing strongly.
In France, Towercast and NRJ-Group, with backing from SIRTI, have been doing intense testing since April 2006 in the Paris area with two HD transmitters on the air, in a critical European frequency assignment. Poland and Ukraine also are running some HD Radio tests.
Since Dec. 3, 2007 the first German HD Radio field trial has been on air with the Radio Regenbogen high-power transmitter in Heidelberg. The practical subjective results after the first weeks of operation are promising, even though it was predicted that the spectrum jam around Heidelberg will never allow a successful practical operation of HD Radio.
Other new plans for HD Radio trials and interest in HD Radio in Europe that we know of include Austria (Krone-Hit-Vienna and others); Italy (RVR with some broadcasters in north Italy, Aeranti Corallo-Radio Association); Romania; Czech Republic; and Bosnia.
Even with the positive results so far, more detailed investigations in the lab and in the field are necessary before regulatory agencies can start issuing operational licenses for HD Radio.
Following are the major steps in our trial project:
- Comparison between FM and HD Radio indoor coverage
- Support for OFCOM lab measurement of HD Radio protection ratios for all major allocation conditions and receiver segments
- Determine the consequences (if any) on FM planning for FM HD Radio implementation in Switzerland (and Europe), and a comparison with U.S. and ITU 412-9 recommendations
- Translators and single frequency network boosters for HD Radio in the field (and RDS-AF functionality test)
- Implementation and operation costs in comparison to FM operation and other digital platforms
- Implementation comparison with other digital FM systems like DRM +
- Support of timely creation of operational HD Radio operational licensing guidelines
- More general awareness in Europe for FM HD Radio, including at the receiver manufacturer level for multi-platform receivers
The Key Advantages of FM HD Radio
HD Radio can become the optimum path to the digital radio age for European single-program broadcasters.
The advantages are obvious. The broadcaster can continue to use almost all of his existing transmitter and translator sites and equipment. Compared to the total operating cost of an FM distribution network, only minor reinvestment for the startup of the digital operation is needed.
As our actual experience so far shows, not all translators have to be modified to digital. Radio Sunshine has a total of 16 sites. For a minimum of 80 percent HD Radio coverage approximately 10 sites will be needed to be modified to HD Radio technology. In contrast to the United States where one licensee has only one transmitter per program stream, a typical European private broadcaster has an average of more than five translators per program stream. This further use of the existing broadcast infrastructure gives the broadcaster the unique chance for a controlled slow evolution to digital at low cost.
To be able to use the same FM channels for the programming and other content is an extremely valuable marketing advantage for the broadcaster.
As additional advantages the broadcaster will get better quality of service within his coverage area and good indoor reception. Portable and indoor reception is important in Europe because it counts for more than 2/3 of total radio listening hours.
For the success of HD Radio in Europe it is critical that broadcasters and the industry begin to show interest in this technology and its development. This is the reason we founded the European HD Radio Alliance, or EHDRA.
More information about the HD Radio Field Trial in Switzerland can be found at www.hd-radio.ch. For more information about EHDRA, visit www.ehdra.org.