DiBcom Diversity Technology [2009-12-22 – 09:29:41]

One of the most innovative technologies during the past few years in the DVB area has been DiBcom’s "Diversity Technology", at least in my opinion. It aims at improving the sensitivity of COFDM modulated signals (e.g. DVB-T/DVB-H) and compensating the Doppler effect for more robust reception in borderlands and/or mobile applications. It does so by smartly combining the signals received by multiple (small bar) antennas. Figure 1 illustrates the ideas behind the technology.

Figure 1 - Diversity Technology Overview

Several COFDM demodulators (e.g. DVB-T) are daisy-chained to each other. The Maximum Ratio Combining algorithm (MRC) inside weights the signals received by all of them in "real-time" with respect to their Signal-to-Noise Ratio (SNR) and smartly "sums them up" to one single improved signal. According to DiBcom, a two-antenna MRC system can achieve a sensitivity improvement (increase in SNR) of up to 3 to 10 dB.

Theory and exercise often tell a different story. The reason for me to take a look at the practical site of the technology is because I am living in DVB-T borderland here in Austria. ORS, Austria’s leading broadcaster, recommends using a roof antenna properly aligned to the transmitter for clean reception, see figure 2 for their coverage map in my region.

Figure 2 - ORS Coverage Map

Marked red is the location of testing. Light blue color indicates that proper reception is only possible with a roof antenna, the area not colored is not covered by DVB-T at all. The darker blue it gets, the better the signal conditions in this very area. Judging from that, it should be quite obvious that conditions are not at their optimum with lots of dead spots.
The coverage map only tells the story for ORS multiplex A and B (DVB-T.at) from the transmitter Pfaender, which are aired with an ERP of 71 kW.
Also aired from the transmitter Pfaender is a SRG SSR multiplex with only 9 kW (see table 1).

	ORS MUX A	ORS MUX B	SRG SSR MUX
Carrier	498 MHz	474 MHz	578 MHz
Polarization	Horizontal	Horizontal	Vertical
Bandwidth	8 MHz	8 MHz	8 MHz
Modulation	16 QAM	16 QAM	16 QAM
Guard Interval	1/4	1/4	1/8
FEC Coderate	3/4	3/4	3/4
Netto Datarate	14.93 MBit/s	14.93 MBit/s	16.59 MBit/s
ERP	71 kW	71 kW	9 kW

Table 1 - ORS Transmitter Pfaender

The strong ORS muxes did not seem to be much of a challenge for Diversity, so I concentrated on properly receiving even the 9 kW SRG SSR mux where I am pretty sure no coverage would be attested at all in the above map region.

To evaluate the performance of Diversity, I used TransEdit to analyze the digital data (on TransportStream level) delivered by a TerraTec T5 USB DVB-T receiver with a Diversity enabled DiBcom DIB7700 chipset for about half an hour in both, single and dual antenna environments and compared the TS packet loss (also including broken packets which could not be repaired by the FEC circuit).
Also evaluated was the impact of the antenna alignment (position and horizontal/vertical mounting). The small bar antennas, those that came with the T5, were placed outside the window. A region that is not covered is enough to deal with. So I decided to eliminate the bad impact of a well isolated house.

Figure 3 - Single Antenna Setup 1

Figure 4 - Single Antenna Setup 2

Figure 5 - Diversity Setup

Single antenna setup performance ranges from bad (lots of garbled data, see figure 4) to very bad (no evaluable data at all, see figure 3), pretty much depending on the alignment of the antenna.
The Diversity setup (figure 5) was pretty close to perfect, not as much depending on the alignment of the antennas as the single antenna setup. The signal is clean most of the time, only every now and then, short error bursts are introduced, causing some packets to be lost and/or broken. Garbled video packets in the double-digit area leads to only little video information being lost (in the area of KBit), which in real-life translates to subtle video artefacts for only a split second, depending on the error concealment of the video format and decoder.

Unfortunately, the DiBcom driver (3.12a) does not offer the possibility to monitor the SNR, but only propagates a meaningless quality percent indicator via the IBDA_SignalStatistics interface. 0%-20% vs. ~80% sounds like a huge impact, which the performance analysis confirmed in an impressive manner, but it does not give the least idea of the real SNR.

Cool thing is, that no special software support is required. DiBcom driver is pure BDA, providing two DVB-T BDA tuner filters. If the DVB application only opens one tuner, Diversity is used automatically. If both are opened (if PiP or parallel recordings are allowed), the DiBcom chipset is configured as dual tuner, adding the possibility to lock two frequencies simultaneously. No Diversity is used in this case. So if you are living in DVB-T borderland, you better disable one tuner for DVB applications supporting multiple of them.

So finally someone came up with something practical concerning the DVB-T reception problem. Compared to active antennas, which amplify the power of a signal (often only resulting in more noise), Diversity improves its quality (SNR), effectively resulting in a less erroneous stream.

Review: anysee E7 PS2

anysee has been around for quite some time now, focusing their efforts on DVB solutions for PC. At least in the western civilization, their success seemed to be somewhat attenuated. This may change with the DVBSHOP soon providing the E7 series, quite an interesting CI solution by anysee. I had the oportunity to have a look at the E7 PS2.

The E7 PS2 is an internal expansion card. It can either be mounted to a PCI or PCIe slot. These connectors are purely mechanical however. The electrical interface is realized via USB 2.0. Like front USB panels, the card is connected to a standardized 9 pin socket on the mainboard. The 500mA that USB can deliver of course is not enough to power the E7 PS2, so a further connection to the PSU via 4-pin molex has to be established.

On the left hand side picture, one may see a selfmade cable to connect the E7 PS2 via an external USB type A plug.








The card is very well made and when having a closer look, one may find quite some quality parts, for example the Samsung can tuner which is well shielded against electromagnetic interference. It is based on STmicroelectronics RF (STV6110) and demodulator (STV0903). In theory this means that the tuner is capable of performing a full band blindscan. Anysee is not providing software support for this feature however, so there is no possibility to activate it and no API to read back the correct parameters (modulation, symbolrate a.s.o.) from the hardware.

The USB bridge, a Cypress EZ-USB FX2LP, is nothing to write home about, known to work reliably however. One may find Cypress USB bridges inside TechnoTrend and TeVii products as well. As is the case with all USB DVB devices, also the E7 PS2 acts a bit sluggish, taking a bit longer to initialize or delivering a stream after tuning. We are talking about few hundreds of milliseconds however, so nothing that the average user will recognize.

On the back of the PCB one may find the most exciting part, a Xilinx CPLD, which may be running the CI stack in hardware. The great CAM compatibility of the E7 PS2 supports this theory, even working flawlessly together with more exotic modules like the unicam or Diablo Light/Diablo2, definitely one of the better CI products I tested so far.


From a hardware point of view the E7 PS2 is a pretty sophisticated product. But the best hardware is nothing without a decent BDA driver. I used a recent driver from the anysee homepage, dated 2011-03-25. Installation is quite easy. Users don't have to mess with the device manager. An installer takes care of all this stuff. After installation, the card worked flawlessly inside WMC, including a transparent operation of the CI.
A nice addition is the tray tool, adding the possibility to access the CAM menu via CI MMI.

The card also passed my TransEdit tests by reliably locking transponders and delivering a clean stream, even the bigger ones on Hot Bird (e.g. 12476H, 8PSK, 27500 KS/s, 3/4).

Something I do not like about the E7 PS2 is that LNB voltage is not switched off, when the tuner is not in use, which means that multiswitch and LNB are fully powered, in my case drawing more than 10W.
[Update 2011-05-01]
anysee has just released a new driver version (dated 2011-04-21), adding the possibility to turn off LNB voltage after a user-defined timeout.

Cypress and STmicroelectronics parts may have also been a good pick when it comes to Linux support, as drivers already exist.

Thoughts on Apple TV

The second generation of Apple TV has just been announced at Apple's music event in September and has already started shipping. It's time to have a look at the ideas and concepts and develop some thoughts on the future of TV. Apple definitely is up to something other than just a hobby.


Hardware Platform

The new Apple TV builds on top of the iOS device platform used within latest generation iPhone, iPad and iPod Touch, featuring Apple's A4 SoC, integrating an ARM based CPU and OpenGL ES 2.0 capable PowerVR graphics. Using mobile technology results in a low power consumption of typically 2-3W (which is about as much as most stationary electronic devices draw in standby) and allows for a small footprint even with the power supply built-in.

Another advantage of this platform decision is a low end consumer price.

The interfaces (Wi-Fi N and 100BASE-T Ethernet) and the 8 GB small NAND flash indicate that the new Apple TV is solely meant to be used as a streaming client, using the flash memory only to store the operating system and as a smoothing condenser (cache) in case the provided bandwidth does not meet the requirements of the requested stream.

The connection to the HD TV screen is established via HDMI. Due to today's TV sets featuring multiple HDMI inputs, Apple TV can be used in parallel to other media sources or set-top boxes. Apple TV is most likely meant to be hidden somewhere, being powered and reachable 24/7.


Video on Demand

During the four years of Apple TV being a hobby, Apple allegedly learned quite a few things. According to them, the number one thing that people want is most recent Hollywood movies and TV shows. They want it in high quality (HD), on demand and preferably at a low price. Sounds reasonable. Movie and TV show rentals through the iTunes Store seem to fulfill exactly these requirements, being a very convenient alternative to video rental stores, not fully replacing existing TV networks however due to yet limited content deals for TV show rentals. Only ABC and FOX provide their shows an a rental basis for $.99 each so far.
Another problem with this service to really take off and make the Apple TV a success is that it is not available in a lot of countries. Some countries are already preparing their iTunes Stores for movie renting and purchasing however.
To attract more people, Apple has to find a way to bring prices down outside the United States. Renting a first-run Hollywood movie in HD is $4.99 in the United States vs. €4.99 in German speaking countries for example. Going to the video rental store around the corner, the same movie on Blu-Ray costs €1.50 per calendar day.

The HD video format of Apple's joice is H.264 main profile @ level 3.1, which basically means 720p resolution at up to 30 frames per second. Unlike many people's opinion, I think that it is quite a handy format for web streaming, and even the nominal bitrate of approx. 4 mbps should result in some nice pictures (remember that we are mainly dealing with 24 fps progressive movie content here) certainly way above DVD quality.

Another quite popular on-demand video streaming service that can be used with a pre-installed app on Apple TV is Netflix which again is limited to few countries (United States and Canada).


iTunes Streaming (Home Sharing)

Apple’s Home Sharing is pretty similar to DLNA (also known as UPnP AV). Besides advanced syncing, it adds the possibility to browse and stream media content from several iTunes music/video/photo libraries located on PC’s within a local network.

The concept behind this is more mentionable than it seems at first sight, finally getting rid of the rather complicated media syncing mechanism. People don't have to manage storage on an Apple TV any longer. The rental model supports this new philosophy.


AirPlay

Coming with iOS 4.2 in November, a feature called AirPlay will add additional value to the Apple TV. The idea is to establish a wireless connection between any iOS device (or iTunes) and the Apple TV, and therefore the TV, for media streaming/playback. AirPlay is push oriented in contrast to iTunes library browsing and streaming, hence the differentiation. Any media content that is played via the iOS mobile’s integrated audio/video playback interface can be streamed to the Apple TV with only one or two taps of a finger. The big deal about it is that this includes any HTML5 embedded H.264 video on the web (which according to lastest statistics make up over 50% of all web videos and growing rapidly) as Safari of course uses the integrated player. It starts to make more and more sense why Apple pushed those technologies.

Going the way via iOS mobiles, which are intended to pull web content, may prevent media content providers from being able to shut down their services on an Apple TV explicitly which we currently see happening to Google TV.

It remains to be seen however whether 3rd party players will integrate the AirPlay mode, especially thinking about protected subscription based content players (like Hulu Plus), or whether the output device can be configured globally within iOS.

The Skyfire browser on iPhone even adds access to an additional few million Flash videos on the web. It does so by using Skyfire's cloud technology which translates Flash video to HTML5/H.264 on-the-fly.

Human Interface

 

Bundled with the Apple TV comes an infrared remote control. If done right the remote does not necessarily have to be in line of sight with the receiver. The big advantage of the technology is that its implementation is inexpensive.
The input possibilities are pretty limited, basically only consisting of a navigation cross. The intuitive graphical user interface is optimized for this kind of input.

Connecting the iOS mobile wirelessly to the Apple TV enables people to use it as an input device. This comes in quite handy when dealing with text input. The virtual remote screen can be set up adaptively to the context, for example popping up the keyboard when attempting to find a movie on the iTunes Store (or a video on YouTube).

Google TV co-developer Sony is putting in the hands of users what seems to be a computer keyboard. Do people really want to mess with another computer in their living room? Do we really need to be able to browse the web on the TV in an era where mobile devices like smartphones or tablets have already been well established as being the best experience to do so?


Apps

From a software point of view, iOS may open the app market for Apple TV. AirPlay already kind of brings apps to the Apple TV even though actually running on an iOS mobile device. The long-term goal however should be to move apps directly to the Apple TV which would make the product more attractive to people who are not in possession of an iOS mobile device.

3rd parties (e.g. film studios) could extend their business model and contribute apps to provide their media content, just like the current built-in apps (Netflix, YouTube, Podcasts, MobileMe, Flickr), slowly establishing the Apple TV + Internet as a real alternative to cable network subscriptions. Apps may become the channels/stations/bouquets of the future and even turn the Apple TV into a gaming console. One should not expect miracles from the A4 processor's 3D capabilities however when being hooked up to a screen with HD resolutions.

Another interesting addition could be support for media servers other than iTunes, like the AirPlayer app being a DLNA client (currently available for iOS mobile devices, not to confuse with Apple's AirPlay protocol) or a ported VLC player, extending the rather small list of supported container formats, with MKV and TS/M2TS being the more popular among those missing. Hopefully Apple will add an API to access the dedicated PowerVR video decoder hardware as the mentioned players currently have to use the up to 1 GHz fast ARM core to decode video, most likely disqualifying any HD content from being played back smoothly, also draining the battery order of magnitude faster. The PowerVR video decoder is said to not go much beyond H.264 main profile @ level 3.1 without dropping frames either, not to mention other formats. Apple TV is not meant to be this comprehensive allround media player though.

Due to an A4 SoC bootrom exploit, first apps are already showing up for jailbroken Apple TV's. NitoTV's weather forecast and RSS reader have already been demoed. So even if Apple does not open the app market for Apple TV, the jailbreaking scene may add quite some value to those boxes.


Final Words

The whole Apple TV concept is not about bringing web browsing to the TV, which is an important cornerstone of the Google TV concept, but to seamlessly integrate into the iOS device ecosystem and to provide valuable content, establishing the Internet as an alternative medium to cable and satellite networks.

Apple sold 250k second generation Apple TV's during the first six weeks which is quite a success already comparing the numbers to first generation Apple TV and Roku sales, which at this time is most likely mainly due to its low price. Despite its low price, Apple earns more per unit sold compared to the old model which is due to a pretty economical platform decision which as mentioned also has its drawbacks.

Bringing the iTunes Store movie and TV show rental service to more countries, establishing deals with more content providers (especially when it comes to TV shows) and putting the Apple marketing machine in place for AirPlay may make the Apple TV quite a successful product. Not to forget the impact that certain 3rd party apps may have. By supporting Netflix, Apple seems to have realized that the success of their TV not just depends on their own services. Thanks to the popularity of iOS devices, the availability of services and content by 3rd parties for this platform is growing constantly.

So there is still a lot of yet unused potential that may elevate the Apple TV from being a hoppy to a serious product.