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Subscription Radio Gets Real

We conclude our examination of the remaining unknowns of IBOC with a look at RadioGuard, the conditional access system proposed by Ibiquity Digital for use on HD Radio subscription services, which if the FCC’s final IBOC rules permit, could be the primary mechanism for radio subscription service delivery.

We conclude our examination of the remaining unknowns of IBOC with a look at RadioGuard, the conditional access system proposed by Ibiquity Digital for use on HD Radio subscription services, which if the FCC’s final IBOC rules permit, could be the primary mechanism for radio subscription service delivery.

First, a word about conditional access, or CA: This is a generic term for any technology used to block access to a broadcast channel. Its original development was largely enabled by the analog cable TV industry, where it has been used to distinguish premium (“pay”) channels from basic cable services for many years.

Today’s digital cable and satellite TV systems offer further CA sophistication, but the basic concept remains the same as always: Premium channels are protected by encryption when broadcast from the head end, and individual receivers in the homes of customers who subscribe to these services are authorized via communications from the head end to selectively decrypt the appropriate channels.


The fundamental functions of a CA system therefore involve 1) the encryption of protected content, and 2) the management and delivery of “keys” to allow the decrypting hardware at the customer’s premises to appropriately decode a given channel’s audio and video signals. (These keys are often referred to as “entitlements.”) An interface to subscription and billing systems typically is also required, of course.

Most CA systems break an encrypted channel’s content into a sequence of short, contiguous elements, generally each a few seconds long, and encrypt them separately, with each section requiring a different key. This prevents a protected channel from being hacked by the cracking of a single key, and thus requires the flow of entitlement data to be nearly continuous throughout the viewing period for that channel.

Naturally, this entitlement data takes up bandwidth on the delivery system, so there is a value to its minimization. On the other hand, the more data that is applied to the entitlement (i.e., the longer the keys), the less vulnerable the channel will be to hacking. Thus today’s CA systems earn their salt by providing an appropriate balance between robustness and efficiency.

Note also that many of today’s television CA systems take advantage of the return path offered by the telephone modem on the receiver, or via a bidirectional cable system.

Lastly, it is important to distinguish between CA and digital rights management or DRM systems, the latter of which are typically used by music download services. CA limits a receiver’s access to certain channels on a multichannel service, whereas DRM is bound to a particular piece of content, and controls the user’s access to that content for playback.

So while often considered together, CA and DRM are quite different in their application: For example, DRM can prevent a downloaded song to be copied or played on an unauthorized device, while CA can prevent a receiver from outputting content carried on a channel to which it is tuned. Further, CA typically is limited to the consumer’s terminal device (receiver), whereas DRM is intended to be continuously bound to content as it passes through the consumer’s digital media ecosystem.

Radio is different

While the basic premise of CA could easily apply to radio, it needs some tweaking to function properly there. Ibiquity has worked with one of the top names in the CA world, a Rupert Murdoch company named NDS, to produce the RadioGuard system for HD Radio.

First, this system assumes that there will never be a back channel (i.e., return path) available. Unlike most of NDS’s other implementations such as DirecTV, which are large, wideband, multichannel video services from a single provider and head end, the RadioGuard system must operate in an environment where each program channel it is used on typically originates from a separate service provider and transmitter. Thus there is no economy of scale for overhead (i.e., no bundling of channels as in a cable or satellite TV system), and bandwidth is far more constrained in general.

The RadioGuard system therefore places very high priority on efficiency and scalability, while also attempting to keep latency low. (In a CA context, the latter refers to the time it takes between signing up for a subscription service and the protected audio signal playing on the new subscriber’s radio.)

Like other CA systems, however, RadioGuard adds two new elements to an IBOC multicast signal: encryption and entitlements. Ibiquity claims that the encryption will add about 1 kbps to the audio signal, while another 1 kbps or so is reserved for the channel’s entitlements. The latter should handle tens of thousands listeners/hour, with a latency target on the order of several seconds to a few minutes.

Regarding latency, this could become another issue specific to radio, in cases where an announcement on (free) air about availability of an event on a subscription multicast channel (e.g., a live concert) causes a rush of listeners to momentarily flood the system. Such “impulse buying” is rare in the TV world, but could become common for radio, so the system is designed to accommodate this without excessive latency by temporarily increasing the bandwidth allocated to entitlements. Ibiquity and NDS are still working on real-world modeling of this system aspect.

Of course, it is always possible to avoid this rush by stations’ announcing (and listeners’ subscribing) in advance of any event. Entitlements for specific events (as opposed to full-time channels) can be stored and will be maintained on the authorized receiver in non-volatile memory.

Putting it to use

Besides the obvious pay-channel or pay-event application, some have considered the use of a subscription service as a free “frequent listeners” perk, whereby audience members who sign up (and provide demographic or other data, for example) on the station’s Web site are rewarded with exclusive access to certain content, either full time or occasional, and probably commercial-free. Public radio’s “pledge-free channel” during on-air fundraising periods is a similar concept.

Regarding entitlement logistics, NDS will handle key management centrally, but all listener subscriptions will be handled by individual stations (or third parties they may assign to this purpose), using the sign-up method of their choice — call-in (automated DTMF or live operator), Web page, etc. All such public-facing elements will in turn use a private, secure Web-based interface to the central NDS key management system, which will return authorizations, also via Internet connection, to each station’s entitlement generator — a 1 RU device that stations will need to purchase from NDS and interface to their IBOC data importer. (Ibiquity will not charge additional licensing fees beyond the standard HD Radio data license for use of RadioGuard.)

At the listeners’ end, the sign-up process requires the input of their radios’ ID number, which will either be printed on the receiver’s box or labeled on its chassis, and/or it can be displayed on the receiver through a series of menu commands. Alternatively, when a user with a RadioGuard-enabled receiver tunes to a protected service, the display will render a message such as, “Call 1-800-555-NNNN to activate …Your radio ID is 123456789.”

Importantly, users with legacy receivers that cannot access such services will not display this or any other notification that a subscription service is available. This avoids the poor user experience that would result from listeners knowing something is being broadcast that their receivers cannot access.

Finally, regarding product availability, Ibiquity reports that software is complete and new HD Radio chips that include RadioGuard will be ready for implementation in receivers by later this year. Some first-generation devices will require an add-on chip to provide the radio’s ID number, but it is expected that by mid-2008, most if not all HD Radio chips will simply include RadioGuard as standard — just as multicast was incorporated into all HD Radio receivers from the second generation onward.

If all goes according to plan, yet another pipe dream may become part of radio’s routine reality soon.