With the set top coming up big in the news this wk it's a good time to reread this article. Nice charts.......OpenCable seems to be very important for CUBE/DIVI
It has become
effectively impossible for a single firm to handle the development load for a set-top box
with a large enough range of functions to be able to provide a variety of services.
nikkeibp.com
Set-Top Box Makers Push for
Common Standards
Common specifications are being developed for the digital set-top
boxes required to receive satellite, cable and terrestrial broadcasting,
ranging from the set-top box OS to the hardware architecture.
Digital set-top boxes (STB) are starting to attract considerable attention as the industry
moves towards digital broadcasting (Fig 1).
Now that terrestrial broadcasting and cable television (TV) networks are following in
the wake of satellite broadcasting by moving towards digital technology, a new
business opportunity is emerging and equipment manufacturers are keen to exploit it.
The basic function of the digital STB is to display digital broadcast images on existing
TV receivers. They are also expected to store and handle digital information received
through the high-capacity, high-speed "big pipe" that digital broadcasting provides,
serving as gateways for audio visual (AV) equipment and information terminals in the
home.
Pioneer Electronic Corp of Japan, in addition to being an original equipment
manufacturer (OEM) for French broadcaster CANAL+, now plans to begin shipping
products under its own name.
New Tie-Ups Reflect Interest
The high expectations the industry has for STBs are also apparent in new corporate
tie-ups (Fig 2).
An example of this are the succession of announcements, which began in April 1998,
from Sony Corp, Hitachi Ltd and Matsushita Electric Industrial Co, Ltd, all of Japan,
together with Microsoft Corp of the US. The three equipment manufacturers
announced their intent to use Windows CE in digital STBs under development.
Tie-ups like these are clearly laying the groundwork for the set-top boxes of the 21st
century. The functions of existing STBs can be provided by a relatively simple OS,
comprising rudimentary system software with monitor functions - sufficient for today's
services.
Receivers currently in use for communication satellite (CS)-based digital broadcast
services - SKYPerfecTV and DirecTV, for example - are STBs using extremely "light"
operating systems.
Joint Development Essential
Commercialization of multifunction STBs, however, is not possible with existing
development resources, according to most equipment manufacturers. It has become
effectively impossible for a single firm to handle the development load for a set-top box
with a large enough range of functions to be able to provide a variety of services.
If a multifunctional STB is the goal, then the first essential step is to beef up the OS and
the various types of middleware running on it. This is because the improved STB will
need the same resource management and communications control functions as a
personal computer (PC), such as microprocessor and memory management, file
management, and the ability to interface with a variety of terminals.
It is no easy task to develop and maintain all these functions, however, nor to develop
the applications. Limited development resources would have to meet simultaneous
demands for minimal time-to-market, and software quantity and quality.
NEC Corp of Japan, for example, has chosen to develop highly competitive products
in specific market niches, rather than trying to develop all the required software. As
Tomoo Yanase, assistant general manager of NEC Home Multimedia Development
Division points out, "Our personnel resources are limited, so we really have no choice
but to apply them to strategic sectors." For the time being, the firm plans to concentrate
on the graphical user interface (GUI).
Third Parties Join Market
While there are limits to in-house software development, the importance of independent
software vendors (ISV) is rising fast. ISVs have grown rapidly in the last few years,
developing a range of attractive applications for the PC and game software markets.
The same situation is about to occur in the STB market. According to Michiaki Koda,
deputy senior manager of Windows CE Accounts, Microsoft Corp, Ltd, OEM Sales,
"The PC market has hit a ceiling worldwide, and Taiwan manufacturers in the Windows
business are beginning to notice the potential of the Windows CE market." For STB
manufacturers, the involvement of third party developers is a major plus.
Universal OS Platform Sought
A number of common OS platforms are being considered. The major contenders are
Microsoft's Windows CE, the HAVi standard proposed by eight Japanese and
European consumer electronics manufacturers, and the PersonalJava application
programming interface (API) designed for STBs and other home networks, developed
by Sun Microsystems, Inc of the US (Fig 3).
There are, of course, differences between the platforms. The notable advantage of
Windows CE is that it is simple to port existing Windows applications (Win32
applications). This is because the Windows CE API is a subset of Win32. Equipment
manufacturers, however, will have to switch their own OS over to the Windows CE at
some time.
HAVi and PersonalJava are similar because they both run applications written in an
intermediate language (byte code) in an environment supporting byte code execution
(Figs 3b, 3c). Both offer the advantage of being able to continue using an existing
proprietary OS, but the overhead increases when byte code is used, which could have
an impact on realtime processing.
Common Architecture
Common hardware architectures are also attracting increasing attention. Digital TV
broadcasting schemes all use Moving Picture Experts Group phase 2 (MPEG-2) video
encoding, which incorporates multiplexing for audio and auxiliary data. This means that
the core hardware for all STBs, regardless of region, transmission medium or carrier, is
the same (Fig 4). If a common technology can be used in the other areas as well, then
only minimal work would be needed to support the various differences that exist due to
region or medium.
As competition in STB development progresses, products will no doubt appear which
are capable of receiving broadcasts from multiple sources, such as terrestrial and
satellite, or terrestrial and cable. If there is a common architecture in place, then
multiple sources can be supported with no change of core parts.
The ultimate goal is the universal set-top box: a device capable of receiving any type of
broadcasting from anywhere in the world, thanks to a common architecture.
"(Currently) we have to make set-top boxes for each individual service," says Reiji
Sano, managing director, member of the board, Matsushita Electric Industrial. "There is
no uniformity in broadcast format, aspect ratio, or number of scan lines. In the near
future, however, it will have to be able to receive all types of broadcasts anywhere."
STBs Need Common Specs
There is already concrete activity in the US towards achieving common specifications in
the industry for cable TV set-top boxes. Cable Television Laboratories, Inc
(CableLabs) of the US will release the OpenCable specification in the fourth quarter of
1998.
Until now, cable TV operators drew up their own specifications for STBs, ordered
manufacturers to produce to specification, and then rented them out to viewers. The
OpenCable specification will absorb the current differences in specifications used by
various cable TV operators, and will make it possible to sell STBs in retail outlets.
Retail STBs will reduce the facilities load on cable TV operators, and most observers
believe that equipment manufacturers will also provide support and services for retail
STBs.
The Association of Radio Industries Businesses (ARIB), which is involved in the
standardization of Japanese satellite and terrestrial digital broadcasting, is also looking
at a common architecture. The group hopes to create an STB capable of handling
everything: digital satellite broadcast, communication satellite broadcast, terrestrial and
cable TV.
Four Major Obstacles
There are, however, still a number of major obstacles to achieving a common
architecture (Fig 4).
First, a specification has to absorb differences in radio frequency (RF) signal
processing and error correction schemes. This would have to apply not only the
downlink from the broadcaster to the viewer, but to the uplink as well.
Secondly, it will be difficult to develop a common conditional access (CA) function
since, for security reasons, each broadcaster generally defines its own. It is important to
keep the CA function as a module and provide a standard interface for building it into
the common system as needed.
The third obstacle is the need for a common data processing software foundation,
handling both data broadcasting and the two-way service of tomorrow.
Lastly, a standardized interface will be needed to interconnect the STB to other AV
equipment.
Sub-Boards Mount Front-End
Two main types of front-end circuits are being considered to demodulate RF signals
received by the STB.
The first is to mount the front-end circuit on a sub-board and use a common
motherboard. This would mean, for example, that the STB would have to mount two
sub-boards to receive both terrestrial and satellite broadcasts.
"Most viewers would not install their own boards, but would instead rely on the set-top
box OEM vendor or retailer to select the appropriate sub-board and install it into the
common architecture. This would be quite different from PC extensions," predicts
Ganesh Moorthy, general manager, Digital Set-Top Computing Platforms, Intel Corp
of the US.
The other alternative is to rely on integrated circuit technology. Either multiple
demodulation circuits would be integrated on a single chip, or a programmable digital
signal processor (DSP) would be used to absorb differences in demodulation schemes
and reduce parts counts.
IC Makers Look to Integration
All IC manufacturers are beginning to think about single-chip solutions for multiple
demodulation schemes, according to Toshiba America Consumer Products, Inc of the
US. Broadcom Corp of the US, for example, is developing an IC jointly with Sony,
which will support both American terrestrial digital broadcasting and cable TV
broadcasting. The chip will be used in Sony STBs, processing both the 8-level vestigial
sideband (VSB) modulation used for terrestrial broadcasting, and the 64- or 256-level
quadrature amplitude modulation (QAM) scheme used for cable TV.
Other manufacturers are forging further ahead, such as Oren Semiconductor, Ltd of
Israel, which has developed the OR51220 demodulation and error correction chip,
which supports VSB, QAM and also the quadrature phase-shift keying (QPSK) used
in satellite broadcasting (Fig 5). Sample-shipment is slated to start in November 1998,
and it appears that Japanese AV equipment manufacturers are considering using it.
The chip will integrate analog-digital converter (ADC) circuits, a program-switchable
576-tap digital filter (including signal correction equalizer), programmable forward error
correction (FEC), and a DSP core. The DSP core will calculate the adaptive filter
coefficients and handle overall chip control. The firmware controlling all three
modulation schemes is said to have a capacity of about 64 Kbytes.
"We are even considering front-end boards for PCs," reveals Craig Wiley, director of
marketing at Oren. "If we use the PC microprocessor for MPEG-2 video and audio
demodulation, we should be able to make a front-end board for about US$100."
The firm is also developing the OR51320 IC for Europe, which will support the coded
orthogonal frequency division multiplexing (COFDM)-2K for terrestrial digital
broadcasting, cable TV QAM, and satellite broadcasting QPSK demodulations. The
prototype is expected in the second quarter of 1999.
CA Functions Kept Separate
The requirements for the CA function, which is the key to verification, are dependent
on transmission medium characteristics and the particular broadcast service involved;
for example, pay-per-view (PPV) vs flat-fee based broadcasting. If the goal is PPV or
video-on-demand (VOD), then verification will be needed on the uplink. For content
distributed for a fee via data broadcasting, it may be necessary to count user accesses.
There are many choices: cheap prepaid cards and multifunction (but more expensive)
PC cards may be preferable to the smart cards commonly used in existing CS digital
broadcasting.
For these reasons the movement toward common specifications is happening first in the
satellite broadcasting and cable TV industries, where most firms offer similar service
content. French CANAL+ and the other satellite broadcasters, for example, have
begun using the Common Interface (CI) architecture for CA to drive down the cost of
an STB. CI was drawn up by the Digital Video Broadcast (DVB) group in Europe.
Eventually, however, it seems likely that STBs will come with multiple slots for CA
modules. According to Toshiba America Consumer Products, in the worst case they
might need three slots: one for cable, one for satellite, and one either as a spare or for
terrestrial broadcasting.
The spare slot could be used for expansion service cards, such as an electronic banking
card to allow online payment of television shopping charges. This is possible
technically, but in order to use the card its internal specifications must be disclosed to
either the broadcaster or the bank, and a Pioneer spokesman warns that would be
difficult for security reasons.
Adding Security to PC Cards
The American cable television industry is currently working to implement the common
OpenCable specification. At present, there are two CA schemes in use: DigiCipher II,
developed by General Instrument Corp of the US and used by vendors like
Tele-Communications, Inc (TCI) of the US and Cox Communications, Inc of the US;
and PowerKEY, developed by Scientific-Atlanta, Inc of the US and used by Time
Warner Inc of the US and others.
OpenCable states that all vendor-dependent security functions must be integrated on a
single PC card, including the verification circuit, key data, descrambling circuit, and
media access control (MAC) layer circuit. This PC card is called the point of
development (POD) module (Fig 6). DVB's Common Interface also uses PC cards,
but does not require that they be used to hold all security functions.
High Degree of Safety
The design approach to the POD module follows guidelines from the Federal
Communications Commission (FCC) of the US to separate it from CA functions,
making it easier to prevent code cracking. Even if the key data is discovered, the POD
module can merely be replaced without any need to modify the set-top box itself.
Equipment manufacturers are also happy with the proposal, commenting: "With a clear
interface specification, set-top box design is simplified enormously because all we have
to do is to provide a slot." It seems likely, however, that the POD module itself will be
relatively expensive, making large-scale replacements of POD modules difficult.
The interface between the POD module and the set-top box is defined in the Point of
Development Module Interface Specification. According to the proposal made in June
1998, the POD module communicates with the head end at the station side via a
control channel called out-of-band (OOB) to handle verification processing. The
incoming bit stream, demodulated by the STB frontend circuit, is input to all POD
modules. If verification is received, then the POD module descrambles the bit stream
and passes the data to the STB.
HTTP vs MHEG-5
There is also a move to push for a unified standard in the middleware called the
"presentation engine." The presentation engine is the software responsible for assuring
that the multimedia data is displayed as the producer intended when it is played back
through the STB. In other words, the more viewers who use an STB with a given
presentation engine, the more people the broadcaster will be able to distribute
multimedia content to.
At the beginning of 1998 CANAL+ adopted Multimedia Hypermedia Experts Group
Level 5 (MHEG-5), as did UK terrestrial digital TV broadcasters and other firms
throughout Europe. In June 1998, DVB also adopted MHEG-5 in the Multimedia
Home Platform (MHP) specification for multimedia broadcasting.
In Japan there is little question that MHEG-5 will be adopted in the broadcasting
satellite (BS) digital data broadcasting specification to be finalized in the spring of 1999.
The US, however, takes the opposing position from Japan and Europe. At the end of
July 1998, the Advanced Television Enhancement Forum (ATVEF) was formed
consisting of a group of 14 broadcasters, set-top box manufacturers and PC
manufacturers (Table 1). The group claims that the presentation engine should instead
use hypertext markup language (HTML), which is standard on the Internet, and
Internet Protocol (IP) multicasting (Fig 7) |
