In recent years, the development of low-cost broadband wireless technologies such as 802.11n, UWB, and 60 GHz has made wireless transmission at 100 Mbps at 30 to 100 feet or more possible. The barrier to high-speed wireless connectivity to HDTVs, computer monitors, and projectors has been eliminated, and competition has turned to providing solutions for wireless transmission of high-definition video and graphics. The benefits this trend brings to consumers and businesses are enormous. Clearly, for end users, replacing wireless cable with cumbersome video cable connections means a whole new experience.
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With the rapid spread of notebooks and portable/handheld devices with high-definition multimedia playback capabilities, the connection of these devices to high-definition displays has become a very popular feature. The characteristics of wireless connection ad hoc bring great convenience to consumers.
Now the PS3 game console can support the Bluetooth controller, which makes consumers want to have a device that can display the game screen anytime, anywhere. Similarly, media center device manufacturers will benefit from being able to wirelessly control and view different video content simultaneously on any display device in the home.
For enterprise applications, no video cable connection means that the cumbersome operation of connecting desktop docking stations and conference room projection devices will no longer exist.
Broadband wireless technology
Currently, there are several broadband wireless technologies for high definition displays and projectors listed in Table-1.
Table-1 lists only the four most popular wireless broadband technologies and is not intended to exhaustively list all technologies. In addition, the maximum transmission rate listed in Table-1 is physical layer data, and the actual data rate is usually smaller than the value due to the MAC layer overhead.
Wireless HDMI Key Indicators
Wireless HDMI must provide the following cableless HDMI transponder features:
1. Transmitting video data;
2. Transmitting audio data;
3. Transmitting EDID (Extended Display Identification Data) information;
4. Transfer CEC data;
5. Transfer clock information.
The goal of wireless HDMI is to provide the same user experience as wired HDMI. So we list several key indicators of wireless HDMI in Table-2:
The operating range covers a single room with only a minimum requirement. From the perspective of maximizing consumer revenue, they are more likely to extend the coverage of wireless HDMI to the entire home.
Low cost does not mean that wireless HDMI will have the same price as wired HDMI. In the eyes of consumers, it is worth paying more for the convenience brought by wireless HDMI. Despite this, in the early days of the market, the retail price of wireless HDMI should not exceed $200 per transmission/reception. When the market matures, its price should be less than $80.
Wireless HDMI challenges
Table 3 lists the bandwidth required to transport various HD and SD video formats over wired HDMI.
At such a high bit rate, even the broadband wireless technology with the highest bandwidth in Table-1 cannot transmit uncompressed 24-bit/pixel 1080p60 video signals. As can be seen from Table-4, although the compressed multi-channel HD audio signal still requires a relatively high bandwidth, the bandwidth required for the audio signal is very low compared to the uncompressed HD or SD video signal.
1) HRA = High Resolution Audio
2) MA = Master Audio
Another challenge facing wireless transmission is the large fluctuations in bandwidth. Despite significant advances in the field of array signal processing and beamforming, interference from other wireless signals in the same frequency band and obstacles in the transmission path may still cause fluctuations in transmission bandwidth.
Compressed or not compressed?
From the point of view that the highest bandwidth of broadband wireless does not support HD video transmission, the answer is obvious. But more importantly, to some extent the bandwidth required for multimedia applications always exceeds the actual available value. Therefore, any future-oriented wireless HDMI solution must compress video and audio signals. An obvious example is the ability to stream high-definition audio and video to home media centers on several display devices. Another example is the upcoming 2K (24 and 48 frames per second, 2048x1080 resolution) and 4K (24 frames per second, 4096x2160 resolution) digital cinema displays and projectors. The 48-bit/pixel 4Kp24 uncompressed video stream requires a bandwidth of up to 12.8 Gbps.
Some people may say that broadcasting a compressed audio and video source, such as a DVD movie or cable TV program, is enough. However, graphics overlays are always required than program navigation or other interactions for Blu-ray DVDs. In the game console, this is even more obvious: all data is either pure graphics or a combination of graphics and video. Therefore, it is not practical to separately transmit the compressed audio and video source and the uncompressed graphics information and then recombine them on the display side. Moreover, the bandwidth required for uncompressed graphics information is still high (see Table-3).
H.264 video compression standard
Although several video compression standards are now available to reduce the bit rate of video signals to within reasonable limits, the latest H.264 standard is clearly the best choice. To cover a wide range of application scenarios, H.264 defines a combination of grades, levels, and coding tools. For example, by adjusting the quantization parameters, a reconstructed video that is comparable to the original input can be generated. In the encoding process, only I frames can be used, or P frames or B frames can be used to improve coding efficiency by reducing redundancy in the time domain. H.264 can compress YUV input in 4:2:2 or 4:4:4 format, as well as 24-bit/pixel and above formats, and it even includes a lossless grade. The efficient H.264 encoder can reduce the bit rate of 1080p60 HD video to around 50Mbps, with a compression ratio of 75:1 compared to the 3.6Gbps code rate before compression. More importantly, H.264 has been widely used in the industry. Digital cameras and digital cameras have also begun to adopt H.264 HD encoders, and their prices are quite low.
Delay – a huge challenge in video compression
The key challenge for video compression in wireless HDMI applications is how to reduce the latency caused by computing. When the resolution, frame rate, and color depth of the video are increased, the delay is further increased. This is a problem that all video coding standards will face, and H.264 is also inevitable. In addition, rate control also introduces an increase in latency. This is because the buffer used to smooth the output bit rate results in a larger delay. Generally, the smaller the code rate fluctuation is, the better it is to avoid the bandwidth fluctuation and affect the quality of the video at the decoder end. I frames always cause large fluctuations in the code rate. Even between two I frames, the code rate may vary considerably as the complexity of the image changes. Other factors such as pre-processing will also increase the delay.
Ultra low latency technology (SLL technology)
WW Communications solves the problem of low latency in video compression through WW602 and WW108 ultra-low latency H.264 HD video codec through architecture and algorithm innovation. Its ultra-low latency technology (SLL technology) in patent applications eases bottlenecks in video processing and rate control. By using SLL technology, the latency of video processing depends only on the video pixel clock. This means that the latency of processing a 1080p60 video signal is much less than the latency of processing a 480p60 video signal because the pixel clock frequency of a 1080p60 video signal is much higher than a 480p60 video signal. In fact, SLL technology can make encoding and decoding a 1080p60 video signal with a delay of less than 1 millisecond.
The SLL technique uses a method such as macroblock intra refresh to resolve the delay caused by buffering I frames. Rather than compiling a complete I frame, the I-macroblock is distributed between several frames. This allows the encoded code stream of the I frame to be smoothly outputted within a prescribed code rate and delay. Another benefit of macroblock intra-frame refresh is the increased error resiliency of the code stream.
For wireless HDMI applications, SLL technology has another significant advantage - lip sync. When using WW108 and WW602, even if there is no such technology as time stamp or other audio and video synchronization technology, as long as the audio signal has no significant delay, the problem that the audio and video signals are out of sync will no longer exist.
802.11n-based wireless HDMI application
The 5GHz band of 802.11n is commonly used in low-latency, interactive WiFi products. In fact, the other wireless standards in Table 1 will also be applied to wireless communications after the technology and market mature. Among them, UWB is gradually preferred as the wireless communication scheme for visible distance with its low power consumption characteristics, such as "dongle" for wireless transmission.
Compared to the application of wireless communication with visual distance, 802.11n can realize more distant (non-visible distance) multimedia communication, such as audio and video between different rooms in the home through wireless play. We use standard 802.11 products for testing, which proves to be very robust and can pass through walls and concrete slabs. Figure-1 is a test environment diagram, using SONY's PS3 game console as a high-definition video source, source and display device. At a distance of 100 feet and across 6 walls, the video includes games and movie videos. Table 5 shows the test results. One group is a wireless device with 2x3 MIMO (2 transmit antennas and 3 receive antennas) on both the encoder side and the decoder side, and the other set uses 2x3 MIMO on the encoder side and 2x2 MIMO on the receive side. The image quality of the WW602 encoding with 20 Mbps stream can exceed the image quality of 6-15 Mbps transmitted by HD cable.
Figure-1: WW602 802.11n-based wireless HDMI test environment
Note: The maximum codec rate is set at 65Mbps.
Designing Wireless HDMI Solution with WW602 and WW108
The latest ultra-low latency H.264 HD video codec chips WW602 and WW108 support channel adaptive transmission rate, variable rate and variable resolution. These advanced features enable wireless HDMI to adjust the bit rate in real time to match different types. The channel bandwidth under working conditions can also transform HD content to accommodate devices that can only handle lower resolutions and lower bit rates. See Table-5.
The powerful code-side fault-tolerant mechanism and the error-masking mechanism on the WW602 and WW108 chips provide users with a stable and reliable video wireless HDMI experience. The code-side fault tolerance mechanism includes variable GoP, variable slice and intra-refresh sizes, and mandatory I. Frame and random I block refresh (intra-refresh). The error concealment mechanism at the decoder side is implemented in macroblock or SK level SKIP mode.
The WW602's target market is low-cost, single-stream wireless HDMI applications such as notebooks, game consoles, DVD players, set-top boxes, DVRs, portable media players, etc. WW108 targets media hubs with its multi-stream processing capabilities (media) Hubs), Media Hubs With the WW108, you can provide wireless channels that simultaneously transfer different content to different displays.
Figure 2 shows a block diagram of a single-stream wireless HDMI solution based on the WW602. Figure-3 shows a block diagram of a WW108-based multistream wireless media hub solution. In these scenarios, only video is compressed and decompressed, while audio and control signals, such as HDMI CEC and EDID, are transmitted directly over the wireless channel. .
Figure-2: Block diagram of a WW602-based single-stream wireless HDMI solution.
Figure-3: Block diagram of a WW108-based multistream wireless media hub solution.
in conclusion
After the introduction of high-definition video into all aspects of content distribution, "cutting the video line" became the technological frontier of HD entertainment. Although there are various broadband wireless technologies competing for the wireless channel of the display, it is not difficult to find that the bandwidth is not enough. The only viable option is compression, and now the best is the H.264 standard. The biggest challenge is to reduce the latency caused by the codec channel. W&W Communications, Inc. has proven its codec chip to overcome latency by using its own low-low latency technology (Super Low Latency Technology).
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