Watching the Olympics, you might not have noticed an interesting spectrum policy point: Wireless microphones (mics) are being used widely without any technical problems in a spectrum policy environment very different from the US: wireless mic users like most other spectrum users in the UK (including military users) are paying for spectrum access!
As we enter the era of incentive auctions, one of the issues people in Washington do not want to talk about is the future of wireless mics and their current spectrum. Clearly wireless mics are a socially constructive and economically important use of spectrum for the entertainment industry, conference facilities, and other applications. But wireless mics developed in the US on the assumption that interstitial use of “vacant” TV channels was a “free good”. Under NTSC analog technology with the UHF taboos resulting from poor TV receiver technology, or at least poor predictions of TV receiver technology, this was mostly true. Of course, the questionable large scale marketing by companies like Shure, Inc. of wireless mics to users not legally eligible to use them only complicated the issue.
Similarly the unwillingness of the entertainment users of wireless mics to confront the legal contradictions of using the technology as a key building block of their shows until Docket 04-186 showed up was also irresponsible, (One wonders about Walt Disney Co. with respect to its dual roles as a TV broadcasters with multiple licenses and the owner of Broadway shows that violated the Communications Act through their illegal use of wireless mics until recently. Had their lawyers done a risk analysis of this issue?)
It does not take much of a crystal ball to see that in the long term wireless mic use of UHF-TV spectrum will become questionable as this spectrum is in greater and greater demand. While mire less mics are important, their use is very sparse in space and time and normal allocation models are not a good match.
In the UK, Ofcom’s “dedicated band manager” for “programme-making and special events”/PMSE is JFMG, which is now owned by Arqiva, the company that actually owns and operates broadcast transmitters in the UK - operated on behalf of the programming originators. JFMG buys spectrum at market prices and then leases it for PMSE uses such as wireless mics to users who pay according to the amount of resources they use.
As we have seen in the Olympics it works! I suppose NBC would have preferred the US system where spectrum access is free. But why is that so important? While marketplace forces do not work all the time for all applications, the UK-style system is probably a better way to handle the wireless mic problem and will ease the inevitable transition to new technologies in various bands. Does anything think FCC really has the patience to handle that well?
On October 28, 2011 FCC held a Public Forum on Indoor Deployments of Small Cell Sites in the Commission Meeting Room with live video online. The forum was organized by the Wireless Telecommunications Bureau, in conjunction with the FCC's Technical Advisory Committee (TAC) Small Cell working group and Spectrum Task Force. I have been somewhat critical of how little the TAC has been asked to do and how little it has accomplished since its formation, but this was certainly a positive move and the FCC staff and the TAC members certainly deserve credit for bringing public attention to this important issue.
The FCC PN on the event said,
Recent developments in technology offer an increasingly wide array of products to provide wireless coverage and capacity in limited or confined areas. Together, they offer potentially useful solutions to addressing the exploding demand for spectrum that is being driven by the exponential growth in wireless data services. The forum will provide an overview of small cell technologies currently available or soon to come on line, including software defined radios and enhanced Wi-Fi in both licensed and unlicensed spectrum. In addition, panelists will explore the business opportunities and challenges involved in expanding wireless data coverage. Finally, the forum will assess the potential economic impact of small cell deployments, particularly with respect to job creation, and explore possible policy approaches.
That is what was basically discussed and the forum dealt with both femtocells that act as tiny base stations for cells phones indoors and then connect to the network over the internet - effectively limiting CMRS spectrum use to very short distances - and Wi-Fi base station that extend the network to phones and smart phones that have both Wi-Fi and the more usual CMRS modulations. The cellular industry’s love/hate relationship with unlicensed in general and Wi-Fi will be the subject of a future post here - stayed tuned!
What was interesting to your blogger was also what was not discussed. This fell into two basic categories. Will the growth of indoor small cells impact the voracious demand for spectrum of the CMRS gang? Although the official CTIA party line is that spectrum is the only way to solve the “shortfall” and this is dutifully echoed in the FCC’s recent “infographic” , it would appear that the technologies discussed at the forum would also have an impact on spectrum needs. As we have stated before here, wireless capacity is a function of 3 factors: spectrum, technology, and infrastructure. The speakers successfully evaded this issue.
A second issue is whether femtocell technology should only be used for connections to the public switched network or Internet using standard CMRS modulations. Today’s cellular industry is focused on “killer apps” like iPhone that can affect there bottom line in massive ways and has little or no interest in niche markets. For several years your blogger has been trying to interest cellular carriers and manufacturers in using variants of femtocell technology to meet niche applications that otherwise would require dedicated bands.
Independently, Qualcomm began and R&D project exploring such an complementary use of cellular spectrum and earlier this year announced it as FlashLinq™which “operates in licensed spectrum as a managed service”. This is an example of using short distance links in CMRS spectrum to meet needs not served by traditional CMRS services such as short range communications. While unlicensed spectrum might be used for such uses, CMRS spectrum under carrier control offers the potential of much higher reliability. It would both fill the “white space” that is inevitable in an operational cellular spectrum and created new revenue for the carriers. Services that might be provided include wireless microphone services where a high density is required such as in theaters and concerts and medical information in hospitals where great reliability is needed. But such niche services are not “killer apps” in the eyes of the CMRS top leaders.
Well, here is another way to look at it: Niche markets like wireless microphones and medical uses all have as their preferred solution dedicated exclusive spectrum. We have seen more medical allocations in the US in recent years and other countries have dedicated wireless mic bands. Maybe the leaders of the CMRS community should not look at these applications and innovative technology such as FlashLinq not as a modest revenue source but as a way to eliminate spectrum competitors who are competing at FCC’s trough for the same spectrum the CMRS community seeks. So it may not matter if such applications are not “killer apps” if serving them in existing CMRS spectrum eliminates another roadblock to increased CMRS spectrum.
FlashLinq advances a concept known as proximal communications, whereby users can continuously connect, disconnect and communicate directly with other mobile users at broadband speeds based on their physical proximity. The technology is designed to complement traditional cellular-based services and serve as a scalable platform for new types of applications.“By expanding the operator model of managed services to the frontier of proximal communications, Qualcomm continues to demonstrate its leadership in wireless technology and innovation” said Ed Knapp, senior vice president of business development and engineering for Qualcomm. “FlashLinq’s direct discovery and distributed communications allows operators to naturally extend their cellular networks. The technology can efficiently support new and enhanced services in areas such as direct local advertising, geo-social networking and machine-to-machine communications.”
While wireless mics are not a large market product, their presence in TV spectrum with their present technology severely limits new spectrum options for this “beachfront property”. It is not just that wideband FM is not spectrally efficient - the same reason it is being phased out for Part 90, but the present equipment is very susceptible to intermodulation interference - remember NEXTEL/public safety? - and the only way to avoid it is to scatter wireless mic channels across large swaths of spectrum - limiting its use. Just as a trace of oil can contaminate a large amount of drinking water, a few wireless mics with FM can deny huge amounts of spectrum to other users. Wireless mics need and deserve spectrum access, but not the present access which may be unique in major industrialized countries.
When analog NTSC was the TV technology, its quirks resulted in such low spectrum use that wireless mics were not a problem. But with today’s demand for spectrum, the low density use limitation of wireless FM is getting to be a major burden for those who covet the spectrum - be they the CTIA crowd (Qualcomm’s traditional customer base) or the Silicon Valley-based TWBD advocates.
Now that an alternative wireless mic technology has a major player behind it, we hope that FCC and people interested in UHF spectrum start pressing harder for an orderly phase out of wideband FM except for small users who need only a handful of audio channels, e.g. small churches, conference rooms, MCs at weddings, etc.
The plot at left from Qualcomm’s briefing shows that with today’s analog wireless microphone technology, wideband FM dating back to Maj. Armstrong in the 1930s, capacity increases slowly with available spectrum. While this technology uses bandwidths of 100 kHz or more, the real limit in places requiring a high density of wireless mics - such as a theater stage - is intermodulation which generally results from receivers or antenna amplifiers that are not sufficiently linear.
Intermod in theaters can also result from wireless mic transmitters that are near each other (such as redundant mics on key players and actors who are standing next to or embracing each other) and interact with each other due to the lack of adequate RF isolation in their designs. While intermod could be corrected by improving analog FM equipment, today’s digital technology offers options that are intrinsically immune to intermod. The new Qualcomm chipset uses the same basic OFDMA technology used in WiMAX and LTE.
With the kind permission of PolicyTracker, here is their recent news report:
(Note that in UK-speak PMSE = program(me) making and special events = wireless mics)
Qualcomm announces chipset for digital wireless mic
©PolicyTracker Oct 27, 2010
by Martin Sims
Qualcomm says it has developed a chipset for an advanced digital wireless microphone with much greater spectrum efficiency than current analogue models. However, industry experts are sceptical about its likely power consumption.
While digital switchover will bring digital TV to everyone and more spectrum for mobile operators, wireless microphone users and the PMSE (programme-making and special events) community could lose out. In recent years, 790-862 MHz has been an “unofficial harmonised band”, according to Wolfgang Biltz of the Association of Professional Wireless Production Technology. “Travel all over Europe and you could always find a frequency which works for you – legally,” he said. However, 790-862 MHz will soon become the European mobile sub-band, meaning that many PMSE users will be looking for a new home.
The European Commission thinks that solving the problem requires action at the EU level and its recent digital dividend Communication called for the identification of harmonised bands. To help find these bands and to discuss other possible solutions, like the use of cognitive radio for PMSE and the transition to digital technologies for wireless microphones, the Commission held a worksop in Brussels on Tuesday 26 October.
Digital era closer than expected?
A move to digital could be one solution for wireless mics because increased spectral efficiency would mean that users could be accommodated in a smaller number of bands. So far the industry view has been that analogue mics will continue to dominate for many years to come. “We will see analogue transmissions for the next 10-15 years: it's efficient and higher quality and that is key to us,” Volker Schmitt of Sennheiser told the workshop.
This ought not to influence policy until it is embedded in a mic and being sold in a box
What surprised participants was Qualcomm's revelation that it had developed a chipset for a digital wireless microphone. Cyril Measson, a senior engineer at the company, said they were keen to partner with manufacturers and could make the chipset available to them in six months. “We are not talking about the future, we are talking about now,” he said.
Qualcomm's technology, which is intended for the professional wireless microphone market, is based on synchronous OFDMA and operates within existing 200 Khz channels. It uses the 2.4 GHz band and offers a range of up to one kilometre. Sound quality is 24 bit / 48 khz and it can pack 30 mics into 6 MHz.
Significantly, Measson said Qualcomm’s digital system could achieve the same latency as analogue systems: a delay of only three milliseconds at 100-200 metres. Latency, or the time it takes for the sound to be electronically processed and amplified, is crucial for PMSE users like musicians as playing or singling along is impossible if there is a significant delay in hearing the sound coming back.
Measson also said that the digital technology would enable the performer to transmit data back, allowing new ways of using wireless microphones. Qualcomm calls this its Interactive Venue Media System.
The power problem
Volker Schmitt of Sennheiser accepted that digital was the future and called Qualcomm's system “pretty amazing” but said there were great concerns about battery usage. “We have had a look at digital, we have looked at OFDM but it is not here yet because of power consumption,” he said. Schmitt said the problem came because of the need to use a special type of signal amplifier in order to achieve high audio quality with low latency. These linear RF amplifiers have very high power consumption, meaning that battery life would be too short and the battery packs would be too large for performers to wear. However, Measson said Qualcomm’s was a state of the art technology with an advanced power control system.
Digital mics may arrive more quickly than many people think
Like Schmitt, many attendees remained concerned about the battery life issue. “This is vapour-ware,” said one participant. “It ought not to influence policy until it is embedded in a mic and being sold in a box.”
Schmitt's view of the digital timescale was very different to Measson's. “Digital will come, but it's not around the corner,” he said. “We need three to five years for research, followed by extensive field tests...then two to three years for product development.”
Professor Georg Fischer, co-chairman of the ETSI group on cognitive PMSE systems, told participants that a move to digital alone would not resolve the issues facing the industry. He told the seminar that PMSE was not spectrally inefficient per se, considering the audio quality required, and he saw great possibilities in using the cognitive approach to analogue wireless mics.
It is also worth noting that manufacturers' pessimism about the development of digital wireless mics is not universally shared. “Digital mics are available, I have heard them in performances and they were perfectly acceptable,” one workshop participant said. “They may arrive more quickly than many people think.”
Note the key parameters in the above: 24 bit digitization (CD quality sound), 48 kHz sampling (resulting in 20+ kHz of audio, again CD quality), and < 5 ms latency/delay (important in live theater). There is some question about power consumption/battery life but it is hard to see that that is a key issue as actors do not stay on stage for hours at a time. I was amused by the quote: “ ‘This is vapour-ware,’ said one participant. ‘It ought not to influence policy until it is embedded in a mic and being sold in a box.’ “ How many times have I heard this thought? Regulators should wait under R&D people use private capital to develop products that have no market without regulatory action and not make any decisions until the technology is fully proven. Where would computer technology be if the Federal Computer Commission has to actively approve every new PC model’s technology under ill defined criteria in front of a crowd of competitors before it could be sold?
Compare the efficiency given by Qualcomm, “30 mics in 6 MHz” with the statement in the FCC’s newly adopted 15.713(h)(9) “As a benchmark, at least 6 – 8 wireless microphones should be operating in each channel used at such venues (both licensed and unlicensed wireless microphones used at the event may be counted to comply with this benchmark).” The Qualcomm technology could achieve 4-5 times what FCC recently viewed as a benchmark.
This new Qualcomm announcement may obsolete the recent decision before it is even published in the Federal Register!