Anyone in the radio business knows that one of the medium’s chief assets is its portability. Radio broadcasts can originate from and be listened to almost anywhere. This immediacy and near-ubiquity differentiates radio from other mass media, and is largely responsible for its resilience and sustained popularity.
Most of us can remember our first “transistor radio,” which the solid-state revolution first enabled during the 1960s. Radio was already well established in the home and car by then, and this trend added a third axis of use – the handheld, pocket-sized, portable receiver. These devices further leveraged the value of radio’s wireless delivery, and made radio’s popularity even stronger among the key constituency of young listeners. This not only fortified radio’s current audiences of the day but ensured its future success, particularly for the then-fledging FM service, by capturing the hearts and minds of future prime demographics.
Portable receivers back then were not without their challenges, though. Antenna design (particularly for AM) was tricky, and audio quality was well below what radio listeners were used to at home or even in the car. Battery life was also an issue, but the newly popular 9V brick battery provided a reasonable and affordable solution. Headphone (or “earplug”) listening was not much in vogue back then, so all portable radios had a small speaker, and given both speaker-size and amplifier-power constraints, fidelity was not impressive. Nevertheless, portability was so important to consumers that the devices quickly became popular, and the handheld audio device movement was born.
This form factor remained a radio-only device until the late 1970s, when the Sony Walkman added cassette playback. After that, a sequence of other storage formats – analog and digital – followed, but radio (usually AM/FM stereo) often remained coupled to the device.
In the last few years, of course, the computer-peripheral RAM device has taken over this category, allowing cheap, random-access high-fidelity storage of a huge number of compressed digital audio files, for playback on speakerless handhelds equipped with low-power, high-quality amplifiers and efficient, high-fidelity headphones.
While these devices’ electronics consume somewhat more power than their predecessors, optimized chip design and advances in rechargeable battery technology such as nickel metal-hydride and lithium-ion (driven mostly by the needs of concurrently popular laptop computers) again provided viable solutions. Their lack of motors or speakers also helps moderate their power consumption.
But something was lost in translation: the radio tuner. Very few among the current crop of RAM audio players include a radio receiver of any kind. So just as the transistor radios of the 1960s brought new, young listeners into the radio camp, broadcasters may rightly fear that trends in today’s handheld audio devices may be pushing potential future listeners away from the medium.
Although the common wisdom among consumer electronics manufacturers holds that tired old analog radio has no place in slick new digital handhelds, a recent survey of handheld users found that radio was their most wanted additional feature. So it would make perfect sense that next-gen handhelds incorporate new digital radio formats, and thus they could find their way into the hearts and minds of future audiences. It all sounded great – except for one big, and largely unforeseen problem: the heavy power consumption of digital tuners.
This dirty little secret is simultaneously being discovered in the terrestrial digital broadcast, satellite radio and wireless telecom/mobile TV environments. The broadband OFDM receivers that virtually all of these devices use are current hogs – at least in their current implementations.
Put in its simplest terms, this is the price paid for robustness in OFDM, which achieves its magic by spreading payload data across of hundreds or thousands of separate, narrowband, closely spaced individual carriers within a broadcast channel. The receiver necessarily requires significant parallel processing to demodulate and decode these many separate small streams all at the same time. There are plenty of available microprocessor platforms that can handle this today, but it’s difficult to get them to do it without sucking down a lot of power in the bargain. It’s simply a function of the MIPS involved, and the need for low latency in a real-time broadcast receiver (i.e., you can’t really serialize your way around the process).
Initially OFDM tuners were developed on generalized DSP platforms, which of course weren’t usable for battery-powered application, and were never intended to be. But even the subsequently developed application-specific (and format-optimized) OFDM tuner chips are relatively power hungry. Naturally, this only becomes an issue in handheld receivers, but these are becoming an ever more important sector of today’s consumer electronics business – particularly for audio-only devices.
Solutions remain elusive
This is actually not a new discovery to everyone. Several years ago it influenced the development of new digital broadcast standards, such as DVB-H, the handheld variant of the European digital terrestrial TV format known as DVB-T. Even though DVB-T was from the start designed for mobile reception, it required an OFDM tuner with very high current drain. So the DVB-H variant was created with its primary design parameter being the reduction in processing demands on the receiver (accomplished by reducing bandwidth, optimizing video for small-screen display and “time-slicing,” which substantially reduces the duty cycle of the receiver’s operations).
Even with this effort, however, the first generation of DVB-H receivers is not getting particularly high marks for battery life.
Of course, most digital handhelds include display screens, always known to be prime battery killers. Some of these screens are relatively large, bright, high-resolution and full-color capable, so it’s expected that they would put significant strain on battery life.
However, given the huge marketplace for such technologies (the billions of wireless phones sold each year now include them), development of power-efficient screens has come a long way lately, and technologies like the white LED show even greater promise for the near future. Also, these screens can be set to shut off their backlights or turn off entirely after a few seconds when not in use (particularly in an audio-only device, where the screen is used only for navigation/control), whereas the OFDM tuner needs to stay on at essentially full power whenever the radio is in use.
Power-efficient screen technology has already progressed to the point that the OFDM tuner is the highest power-consuming component in the most recent handhelds. The screen is still up there, but generally in second place (sometimes a distant second, and trending lower still). In any case, these two components together make it difficult for a handheld digital broadcast receiver to provide much more than a couple of hours of continuous use between charges.
One interesting result has been the quoting of two different typical battery-life specs for multipurpose devices (such as satellite radio + MP3 players) – one with the tuner in use, and one without. So far, the latter number has ranged to about twice the former.
Naturally it can be assumed that this problem will be reduced over time, as more efficient and portable-optimized OFDM receiver designs are developed. But as screens also continue to drop in current drain, the OFDM tuner is likely to remain at the top of the current budget for these devices, which will do little to entice consumer electronics manufacturers to include a lot of digital broadcast receivers in their handheld products.
Moreover, the relatively small number of developers working on HD Radio tuner chipsets implies that a handheld receiver in this format remains many years away.
Not a pretty picture
This is tough to swallow for radio, a medium that has touted its ubiquity via easy portability of its receivers.
In recent years, this trend has accelerated, with ever smaller and cheaper portable analog radios becoming available. These AM/FM receivers are quite power efficient, as well, but the handheld form factor is arguably the worst case for multipath interference, given the increased audibility of its distortion and stereo image instability when wearing headphones, and the typical use of an often wildly moving headphone cord as the FM antenna.
So it is with great irony that while the handheld receiver provides perhaps the strongest argument for the value of HD Radio’s multipath immunity, such a device remains just out of reach due to battery-life constraints.
As a result, the lack of handheld HD Radio receivers – at least for the next few years – will keep the fledgling technology from becoming a player in the increasingly important portable audio industry. Given the strength and projected growth of that sector, this absence could have significant impact on HD Radio’s success, as well as to the radio industry’s overall relevance to future audiences.
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