Wireless video products
There are several wireless standards that are vying for use driving displays. Wireless Home Digital Interface (WHDI) is an interface that uses the same 5GHz band as Wi-Fi, and is designed to transmit uncompressed HD video at data rates of up to 3Gb/s in a 40MHz channel. The range is said to be greater than 100ft, with a latency of less than 1ms.
WiGig (by the Wireless Gigabit Alliance) is a specification based on 802.11 that supports generic data transmission rates up to 7Gb/s. A different approach is being taken by WirelessHD, a specification that defines a wireless protocol that enables consumer devices to create a wireless video area network (WVAN) that can stream uncompressed audio and video up to Quad Full HD (QFHD, or4K) resolution, at 48-bit color and 240Hz refresh rates, with support for 3-D video formats. The specification, which is based on 802.15, supports data transmission rates at 10Gb/s to 28Gb/s.
The Wi-Fi Alliance has also announced a certification program, called Miracast, through which certified devices can make use of an existing Wi-Fi connection to deliver audio and video content from one device to another, without cables or a connection to an existing Wi-Fi network.
In another industry development, MHL is being used to connect tablets and smartphones to displays. MHL defines an HD video and digital audio interface optimized for connecting mobile phones and portable devices to HDTVs, displays and other home entertainment products. MHL features a single cable with a five-pin interface that is able to support up to 1080p60 HD video and 192kHz digital 7.1 channel audio, as well as simultaneously providing control and power (2.5W) to the mobile device.
Because MHL does not specify a unique connector, various mechanical interfaces have emerged, including five-pin and 11-pin MHL-USB connectors. MHL fully supports the HDCP specification (used elsewhere on DVI and HDMI interfaces) for the safeguarding of digital motion pictures, television programs and audio against unauthorized access and copying.
Maintaining high-speed networks
High-speed networks are challenging to maintain. When any of these high-speed interfaces are combined with long runs of cable, performance will degrade, primarily from inter-symbol interference caused by cable-based dispersion of different signal frequencies, as well as jitter caused by processing equipment, as shown in Figure 1. The result will be an increase in error rate at the receiving end.
To minimize this, video plants should be designed and maintained with equipment having low jitter and cable runs having the lowest length necessary, with repeaters used for lengths nearing maximum specifications. Adhering to these precautions will result in reliable operations.
—Aldo Cugnini is a consultant in the digital television industry.