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Qualcomm OFDMA Chipset Promises Efficiency Breakthrough for Wireless Mics

Still depending on Comm Daily for all your spectrum news? My friends at PolicyTracker, a London-based spectrum management newsletter, published a surprising story last week that has not received any coverage on this side of the Pond. At a recent European Commission spectrum management meeting in Brussels Qualcomm announced a new product that could have a huge impact on the wireless microphone market and regulations in the US.

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!