Analysis and application of wireless HDMI Technology

Central topics:

• Broadband Wireless Technology
• Key wireless HDMI indicators
• Challenges for wireless HDMI

Solution:

• Ultra-low latency Technology
• 802.11n-based wireless HDMI applications

In recent years, the development of low-cost broadband wireless technology (such as 802.11n, UWB, and 60 GHz) makes it possible to transmit wireless data at a speed of 100 feet to or a wider range of Mbps. Barriers to high-speed wireless connection with HDTV, computer monitors, and projectors have been removed, and competition has shifted to providing solutions for wireless transmission of HD videos and graphics. This trend brings great benefits to consumers and enterprises. Obviously, for end users, replacing tedious video line connections with wireless transmission means a brand new experience.
With the rapid popularization of laptops with HD multimedia playback and portable/handheld devices, the connection between these devices and HD monitors has become a very popular feature. The features of wireless connection to adhoc bring great convenience to consumers.
Now the PS3 game console supports Bluetooth controllers, which allows consumers to have devices that can display game images anytime, anywhere. Similarly, Media Center device manufacturers will benefit from allowing consumers to control and view different video content wirelessly on any display device at home.
For enterprise applications, the absence of a video connection means that tedious operations to connect desktop docking stations and conference room projection devices will no longer exist.

Broadband Wireless Technology
At present, there are several broadband wireless technologies for HD monitors and projectors listed in table-1.

Table-1 only lists the four most popular wireless broadband technologies and does not intend to list them in detail. In addition, the maximum transmission rate listed in table-1 is physical layer data, and the actual data rate is usually lower than the overhead of the MAC layer.
Key wireless HDMI indicators
Wireless HDMI must provide the following non-cable HDMI repeater functions:
1. transmit video data;
2. transmit audio data;
3. Transmit edid (Extended display ID data) information;
4. Transmit CEC data;
5. Transmit clock information.
The goal of wireless HDMI is to provide the same user experience as wired HDMI. From this, we listed several key metrics of wireless HDMI in table-2:

The operation scope can cover only the minimum requirements for a single room. From the perspective of maximizing consumer benefits, they want to extend the coverage of wireless HDMI to the entire family.
Low cost does not mean that wireless HDMI will have the same price as wired HDMI. In the consumer's opinion, it is worthwhile to pay more for the convenience brought by wireless HDMI. However, in the early stages of the market, the retail price of wireless HDMI should not exceed $200 per transmission/receipt. When the market matures, the price should be less than 80 USD.
Challenges for wireless HDMI
Table-3 lists the bandwidth required to transmit various HD and SD video formats through wired HDMI.

At such a high bit rate, even the most Bandwidth Wireless Technology in table-1 still 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, compared with the uncompressed HD or SD video signal, the bandwidth required for the audio signal is still very low.

1) HRA = highresolutionaudio
2) Ma = masteraudio
Another challenge for wireless transmission is bandwidth fluctuations. Although the field of array signal processing and beam composition has made great strides, interference from other wireless signals in the same band and obstacles in transmission paths may still cause fluctuations in transmission bandwidth.

Compression or not?
From the perspective that the highest bandwidth of broadband wireless cannot support HD video transmission, the answer is obvious. But more importantly, to some extent, the bandwidth required by 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 that high-definition audio/video streaming can be sent to the Home Media Center on several display devices. Another example is the coming 2 k (24 and 48 FPS, 2048x1080 resolution) and 4 K (24 FPS, 4096x2160 resolution) digital cinema display and projector. A 48-bit/pixel 4kp24 uncompressed video stream requires a bandwidth of up to 12.8 Gbps.
Some may say that broadcasting compressed audio and video sources, such as DVD movies or cable TV programs, is enough. However, graphics overlay is always required for 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 unrealistic to transmit the compressed audio and video sources and uncompressed image information separately, and then re-combine them on the display end. In addition, the bandwidth required for uncompressed graph information is still high (see table-3 ).
H.264 video compression standard
Although there are already several video compression standards that can reduce the bit rate of the video signal to a reasonable range, the latest H.264 standard is obviously the best choice. To cover a wide range of application scenarios, H.264 defines a combination of multiple levels, levels, and coding tools. For example, you can adjust the quantization parameter to generate a reconstruction video that is almost the same as the original input. During the encoding process, only I frame can be used, or P frame or B frame can be used to improve the encoding efficiency by reducing the redundancy of the time domain.
H.264 can compress the YUV input in the format of or, as well as the 24-bit/pixel format and above. It even contains a lossless grade. The efficient H.264 encoder can reduce the bit rate of A 1080p60 HD video to about 50 Mbps. The compression rate is as high as 75: 1 compared with the 264 Gbps bit rate before compression. More importantly, H.264 has been widely used in the industry. Digital photo cameras and digital cameras have begun to use H.264 HD encoders, and their prices are quite low.
Latency-a huge challenge for Video Compression
The key challenge for video compression in wireless HDMI applications is how to reduce the latency brought by computing. When the resolution, frame rate, and color depth of a video are improved, the latency is further increased. This is a problem that all video encoding standards face, and H.264 is inevitable. In addition, bitrate control also increases latency. This is because the buffer used to smooth the output bit rate will lead to greater latency. Generally, the smaller the bit rate fluctuation, the better, to avoid bandwidth fluctuation and affect the quality of the decoded video. I frames always bring about significant fluctuations in bit rates. Even between two I frames, the bit rate may change significantly as the image complexity changes. Other factors such as pre-processing will also increase latency.
Ultra-low latency (SLL Technology)
In ww602 and ww108 ultra-low latency H.264 HD video codecs, wwcommunications solves the problem of low latency during video compression through architecture and algorithm innovation. Its ultra-low latency (SLL) technology in patent applications relieves bottlenecks in video processing and bit rate control. By using sll technology, the latency of video processing only depends on the video pixel clock. This means that the latency of processing the 1080p60 video signal is much smaller than that of processing the 480p60 video signal, because the pixel clock frequency of the 1080p60 video signal is much higher than that of the 480p60 video signal. In fact, sll technology can enable encoding and decoding of A 1080p60 video signal with a latency of less than 1 millisecond.
Sll technology uses methods such as intra-frame refresh of macro blocks to solve the latency caused by buffer I frames. Unlike compiling a complete I frame, I-macro blocks are distributed between several frames. This allows the I-frame encoding code stream to be smoothly output within the specified bit rate and latency. Another benefit of refreshing within a macro block frame is that it increases the error elasticity of the encoding code stream.
For wireless HDMI applications, sll technology has another significant advantage-lip synchronization. When using ww108 and ww602, even if there is no such technology as timestamp or other audio/video synchronization technology, as long as the audio signal has no significant delay, the problem of audio and video signal synchronization will no longer exist.
802.11n-based wireless HDMI applications
The 5 GHz band of 802.11n is usually used in WiFi products with low latency and high interactivity. In fact, other wireless standards in Table 1 will also be applied to wireless communication after the technology and market are mature. With its low power consumption, UWB has gradually become the first choice for the visible distance wireless communication solution, for example, implementing the "dongle" of wireless transmission ".
Compared with wireless communication with visual distance, 802.11n can achieve multi-media communication over a longer distance (non-visual distance). For example, audio and video between different rooms in the home can be played wirelessly. We use the standard 802.11 product for testing and prove that the robustness is very good. We can traverse the walls and concrete floors. Figure-1 shows the test environment and uses Sony's PS3 game machine as the HD video source, the distance between the source and display devices is 100 feet and the wall is crossed. The video content includes game and movie videos. Table 5 shows the test results. One group is a wireless device that uses 2x3mimo (two sending antennas and three receiving antennas) as the encoding and decoding ends, and the other group uses 2x3mimo as the encoding end, wireless devices with 2x2mimo receivers. The image quality of the 20 Mbps code stream for ww602 encoding can be higher than the image quality of 6-15 Mbps transmitted by HD cables.

Figure-1: ww602 802.11n-based wireless HDMI test environment
Note: The maximum codec speed is set to 65 Mbps.

Design a wireless HDMI Solution Using ww602 and ww108
The latest ultra-low latency H. the 264 HD video codec chips ww602 and ww108 support adaptive channel transmission rates, variable rates, and variable resolutions. these advanced features enable wireless HDMI to adjust the bit rate in real time to match the channel bandwidth under different working conditions, you can also change the HD content to adapt to devices that can only process low resolution and low bit rate. see table-5.
The powerful encoding Fault Tolerance Mechanism and decoding error masking mechanism in ww602 and ww108 chips can provide users with stable and reliable wireless video HDMI experience. the fault tolerance mechanisms on the encoding end include variable GOP, variable slice and intra-refreshsizes, forced I-frame and random I-block refresh (intra-Refresh ). the error masking mechanism at the decoding end is implemented in the macro block or shard-level skip mode.
The target market of w602 is low-cost, single-stream wireless HDMI applications, such as laptops, game consoles, DVD players, set-top boxes, DVRs, and portable media players. with its multi-code stream processing capability, ww108 targets mediahubs. With ww108, it can provide wireless channels to transmit different contents to different monitors at the same time.
Figure 2 shows the diagram of the ww602-based Single-stream wireless HDMI solution. Figure-3 shows a diagram of the ww108-Based Multi-code-stream wireless media hub solution. in these schemes, only videos are compressed and decompressed, while audio and control signals, such as hdmicec and edid, are directly transmitted through wireless channels.

Figure-2: frame diagram of ww602-based Single-stream wireless HDMI Solution

Figure-3: Diagram of the ww108-Based Multi-code-stream wireless media hub solution
After the introduction of HD videos to various aspects of content delivery, "video cutting" has become the cutting-edge technology of HD entertainment. Although various broadband wireless technologies compete for wireless channels for display, it is not difficult to find that the bandwidth is far from enough. The only feasible option is to adopt the compression technology, but now the best is to adopt the H.264 standard. The biggest challenge is to reduce the latency caused by codec channels. W & wcommunications, Inc. uses its own super lowlatencytechnology to prove that a well-designed Codec Chip can overcome latency troubles.