Wireless transmission of HD-video and sound using video senders, digest - spring'12

    Dear friends, as planned, I continue the series of articles of 2012 (the first ), on current technologies and equipment for wireless HDMI transmission and high-quality audio-video signal.
    In this part, we will talk about the so-called video senders (see the detailed definition in one of the articles ), but if you are too lazy to follow the link, here is the general scheme for all video senders (light box - transmitter (transmitter), dark box - receiver (receiver) ):

    So, the fact that the video sender is a set of receiver and transmitter that imitate one or another cable for transmitting video and sound, I think everyone understands from the diagram. Since the most common HD hardware transmission interface is HDMI , in fact we will talkspecifically about its possible wireless implementations . Naturally, all standards use strong encryption , so I won’t even mention it further.

    The purpose of this article is to talk about the features of interaction within sets built to different wireless standards, as well as to outline and convey to the reader development prospects for each of these standards. As I promised earlier, the last article in the series will present a table comparing the characteristics of all known wireless standards for HD transmission.

    Oh, and a little caveat: if the kit contains a “whistle” for a computer that transmits a signal to a receiver using a special wireless standard, just as if this “whistle” is already built into a PC (it can be a Wi-Fi card on any because it’s a special chip, or a card of another wireless standard), this can’t be called a video sender, since there is no complete hardware simulation of an AV cable , and software is used for transmission, due to which the signal is broadcast.

    Let's start with the traditionally considered first ultra-wideband Wireless HD standard, which, relatively recently, has joined forces with the WiGig alliance aimed at creating a wireless multi-gigabit standard.

    WirelessHD / WiGig

    The company that invented WirelessHD and released chips is called SiBEAM, it was founded by immigrants from Berkeley in 2001. In 2011, SiBEAM was acquired by the notorious Silicon Image chip maker. Since then, Sil has been promoting the industry standard.

    About the relationship of WirelessHD and WiGig

    Once, even before the word “Tandem” appeared in 2007, WirelessHD (ieee802.15.3 was taken as the basis) appeared to satisfy the growing needs for transmitting high-quality (HD) signal to a TV. In 2009, however, the largest manufacturers scratched their turnips and created the WirelessGigabit alliance, correctly assuming that Wi-Fi speeds would soon become small. In fact, ieee802.11ac / ad was created under WiGig (see the detailed article by wiNIKA ), which allows you to “swing” the good old 802.11a / b / g / n into 2.4 and 5 GHz (802.11ac), and combine it with multi-gigabyte monstrous at 60 GHz (802.11ad) in the framework of one standard.
    No wonder WirelessHD later merged in ecstasyjoined WiGig, since the latter began to cover tasks and is very similar in principle to WiHD. Thus, we simplify the formula to the banal Wi-Fi + WirelessHD = WiGig .

    The WirelessHD standard is built on ultra-wideband broadcasting, which allows it to transmit zeros and ones with speeds up to 7 Gb / s (and drive FullHD 3D 7.1 without compression and delay), but only in direct line of sight. Such a wide strip cannot be “dragged” through the wall. But she copes well with small obstacles - furniture, people, animals; which technology allows you to "intellectually bend around."

    Returning to our sheep: unfortunately, little has been heard about video senders on WirelessHD recently. They reached a certain level - FullHD 1080p @ 60Hz, 3D and 7.1 sound, and all this without compression and delay, but it seems that the inability to transmit through the wall and the bulkiness of the transmitter (at least 6, even though built-in antennas) do not give adequate demand on the development of technology in the key of video senders.

    Although there is encouraging news on their website about the release of a new version of the standard - WirelessHD 1.1, with support for speeds of 10-28 Gbit / s, built-in antennas for mobile equipment, 4K x 2K resolution and an independent data channel - 1 Gbit / s, but about the new the gland has not heard anything at all.

    However, work in the WiGig camp is in full swing, from fresh - a prototype SD card with a WiGig adapter .
    The latest news about the next WirelessHD sender (over a year ago) - the Rocketfish video sender ;
    WirelessHD video sender clearly .


    • The fastest wireless channel;
    • No compression is used.


    • Works only in line of sight;
    • Bulky blocks due to antenna array.


    The next customer, traditionally, is WHDI. Created by the Israeli company Amimon, based on powerful MIPS chips with original firmware for HD transmission. It operates at a frequency of 5Ghz according to principles similar to 802.11a / n, but much faster - a wireless channel of 3 Gb / s. In order not to quarrel with the Wi-Fi slowly hanging out on 5Ghz, MIMO + OFDM technology and time slots are used, which allow us not to interfere with each other's WHDI and Wi-Fi.

    The current version of WHDI allows you to transfer FullHD 1080p @ 60Hz with 3D and multi-channel sound (simulated HDMI 1.4) through walls, with a transmission delay of less than 1 millisecond (less than that of LCD monitors) and with the forwarding of the infrared port and USB-HID.
    What do the latest spells mean? Forwarding the infrared port allows you to transmit signals from your remote to the signal source. Roughly speaking, you connected the receiver to the TV, and in another room you have a satellite receiver to which the transmitter is connected. You click the remote control from the satellite receiver to the receiver, which, in turn, transfers it to another room to the transmitter and from the transmitter the IR peephole looks at the satellite receiver and controls it. The original IR signal is transmitted through the video sender channel.
    USB-HID is about the same as IR forwarding, allowing you to connect the transmitter to the computer with an additional (in addition to HDMI) USB cable to control this PC using the keyboard and mouse (HID device) connected to the receiver. Roughly speaking, your TV has a receiver, a keyboard and mouse are connected to it, and you see / hear a signal from a computer and can control it.

    WHDI does not use compression as such, but there is a special, patented technology, Video Modem , which allows you to transmit a signal even in conditions of strong interference and significant bandwidth cuts. You can read about the old but good article in Russian here .

    There are currently two WHDI designs:

    Full - the transmitter and receiver the size of a router but without an antenna, there are 5-6 of them and they are built-in, communication is valid up to 30 meters with overcoming major obstacles;

    Compact (the so-called Stick) , 2-3 built-in antennas, the transmitter is slightly larger than a USB flash drive, the receiver is slightly larger than a computer mouse, both can receive power not only from a wall outlet but also from any USB port. Transmits to 10-15 meters with overcoming non-capital obstacles.

    Today, WHDI is one of the most promising standards, which is confirmed by large manufacturers, such as Asus, HP, Belkin, PowerColor, KFA2, etc., producing WHDI kits under their own brands. It is also worth noting LG, which has already introduced a TV with a built-in WHDI module (and many other monsters of the industry are also gathering), as well as Lenovo, which released a seven-inch Android tablet with a built-in WHDI module. A video with WHDI updates and a tablet demonstration on CES2012 can be seen here .

    WHDI's plans are to reduce power consumption, support simultaneous broadcasting by one transmitter to several receivers, support for 4K x 2K resolution, a wireless channel for data transfer, and combining WHDI and Wi-Fi into one chip.


    • A fairly fast wireless channel, respectively, compression is not used, no delay (1ms can be neglected);
    • It supports the highest possible HD-quality (with the exception of 4K x 2K, which was just born) and IR and USB forwarding functions;
    • Overcoming walls and the ability to use a compact design;
    • Ability to use several transmitters with one receiver (alternately).


    • It operates at a frequency of 5Ghz, which could potentially interfere with transmission during extreme spectrum overflow;
    • Embedded solutions and mobile devices require a separate WHDI module, in addition to Wi-Fi, until they release a combo chip.


    To date, there are such video senders that are successfully used for wireless HDMI transmission, it would seem that Wi-Fi is not specifically designed for this. However, such kits have their advantages, which often dominate the disadvantages.

    First of all, I’ll send you back to the first article of digest'12 . There are many and (I hope) clearly described the advantages and disadvantages of Wi-Fi, as a transport of video and sound wirelessly. Despite the fact that in that material, the transmitter is a Wi-Fi card built into the computer / smartphone, the principles are the same, only in cases with independent video senders you need more iron.

    So, the thesis:

    Features of the use of Wi-Fi in HD-video senders:
    • Wi-Fi has a bandwidth limit of 300-400 megabits (802.11n, of course);
    • To fit in such a band, the HD signal needs to be compressed (mainly H.264 is used);
    • Both for compression of content during transmission, and for decompression during reception, power and time are needed;
    • The result is powerful, sometimes dual-core (!) Processors based on Wi-Fi kits;
    • Another result is a delay; time required for compression - from 20 to 50ms;
    • The ubiquity of Wi-Fi and H.264 makes production quite economical.

    Now for the specifics (by the way, I will refer once again to another useful article on the topic ): almost all of today's Wi-Fi video senders have a LAN / PLC origin: initially, the HD stream was pressed by a codec to drive it over wires with a TCP / IP layer. When Wi-Fi 802.11n appeared, which, in fact, began to cover the 100-megabyte barrier, these same technologies "crawled" onto new tracks.

    The most interesting thing is that after compression, the HD stream needs a bandwidth of no more than 50 Mbit / s, well-known ip-technologies are successfully applied here: both rtp / rtsp , and Quality of Service (notorious, always disabled in the Windows list of QoS protocols ), and UDP and so on.

    Due to the full "standard" and long-term study of Wi-Fi from all sides, these senders successfully compete in overcoming distances and obstacles with specialized standards created exclusively for wireless HDMI transmission. The distance can be covered up to 40 meters, and obstacles are stitched, even being capital and in the amount of several pieces.

    But you can still unscrew the screws, climb inside the transmitter, there, remove the wiring from a miniPCIe Wi-Fi card to a standard antenna and tighten the reinforced ...

    There are 2 original manufacturers of reference iron: Itrio, Koreans, are still selling their famous video sender worldwide, back in 2008-2009, under different brands - Eminent, IOGear, Peerless and others. What’s great in the kit is that it contains both HDMI and VGA / component, and even composite and stereo-jack connectors. A kind of “Swiss Knife”:

    Since the model is relatively not young, hence HDMI support is only 1.3, which does not detract from all the advantages of FullHD, but sadly lacks 3D. Also, the single-core chip inside presses / decompresses more slowly than we would like - a transmission delay of 40-50ms (which, in general, is quite acceptable even for games, although not desirable).

    The second manufacturer, Cavium, introduced its latest variation of the video sender relatively recently - at the end of 2010. They called this technology (HD transmission over Wi-Fi) the word WiVu, and the chips, dual-core Arms with H.264 hardware support - PureVu. (Although in 2009 this technology was called NetHD and was focused on HD transmission, as already mentioned, via LAN and PLC). By the way, Linux is used as a platform for working with iron, and almost the entire opensource database / kitchen for compiling firmware can be downloaded from manufacturers' resources.
    This shaitan machine, due to all the power enclosed under its hood, easily transfers HDMI version 1.4a, with all 3D modes and with a 20ms delay compared to Itrio (my first LCD monitor had a delay of 16ms, it seems , for Windows ME it was quite acceptable;)). There is also a forwarding of the IR signal, USB keyboards, mice, joysticks, support for encrypted transmission of FullHD and 3D signal from the transmitter at the same time to 4 receivers.

    The reference design looks like this - a brochure .

    A kit based on WiVu, already produced and very popular among similar devices - actiontec mywirelesstv ( flash presentation , firmware sources ). By the way, mywirelesstv received an award at CES'12 for design and a successful engineering solution.

    About the prospects - as I wrote earlier, most recently Cavium announced a strategic partnership with Qualcomm and Intel. With Qualcomm, work will be aimed at creating a WiVi standard based on WiVu, while with Intel, cooperation will be in the production of WiDi receivers. So we are waiting for the next stage of integration of these technologies into modern devices. (HTC sets the pace with its latest, off-the-shelf MediaLink implementation )

    Advantages (with an asterisk in the beginning - applies only to Cavium-based)

    • Very far and armor-piercing;
    • * Support for the latest version of HDMI with 3D FullHD, USB forwarding;
    • IR transmission function and support for 4 receivers simultaneously;
    • * Ability to use several transmitters with one receiver (alternately);
    • Because of the standard components, you can intervene in the hardware / software and pick something out there;)


    • Potentially, the quality of the transmission may be reduced due to the debris of the Wi-Fi spectrum;
    • Compression is used, which requires powerful and non-compact equipment;
    • Due to compression, a transmission delay of 20ms or more occurs.

    PS: As a seasoned geek, I have some religious prejudices regarding the use of Wi-Fi video senders:
    Well, I can’t put up with the fact that already having my own Wi-Fi adapter, my PS3, itself, is powerful as lying in it based on an eight-core, or tri-core PowerPC 360th Xbox with a powerful graphics card, or, even worse, a PC with a multi-core processor (in which it is already integratedintel WiDi), they use two (!) (receiver and transmitter) Linux boxes to transfer video and sound to TV, comparable in power to a dual-core Andriod smartphone. It’s akin to some technologists releasing a super-duper flat screwdriver with an adjustable slot width in all dimensions and a horse-drawn power steering, and positioning it as a unique device for unscrewing cross bolts and screws. This feeling does not leave me ...

    That's all for today, it turned out a lot again, and who got to here, and even finds the strength to leave a sensible comment - I admire! And in order to support your spirit of young wrestlers with wires, I’ll say that I wrote the article for almost a week, in several approaches, and the material for it accumulated in general for years, so that you received only the most precious squeeze, without tinsel.
    As always, we indicate in the comments whether the topic should be further developed.

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