8K UHDTV: How do you send a 48Gbps TV signal over terrestrial airwaves?

While the last 10 years have seen the rapid, consumerist adoption of HD everything -- from TVs to DVDs to digital cameras -- another far superior technology has been making the slow crawl from laboratory, to prototype, to the brink of public testing: Ultra High Definition TV, or UHDTV for short. With a resolution of 7680x4320 (8K or 4320p), UHD is comparable to IMAX -- and 16 times larger than HD's paltry 1920x1080. A single 8K frame consists of 33 million pixels -- higher resolution than almost every DSLR on the market.

UHDTV (also called Super Hi-Vision) has been entirely conceived and developed by NHK, Japan's public broadcasting organization. Starting in 2003, NHK effectively strapped 16 HDTV cameras together to create a single 30-minute UHD clip. In 2005, a UHD TV program was transmitted over a 240km (160 miles) fiber optic network -- and in 2010, NHK managed to transmit UHD from the UK to Japan, over the internet. Earlier in 2012, following various tech advances, NHK finally demonstrated the first shoulder-mounted UHDTV video camera -- and now, the Japanese broadcaster has successfully transmitted UHDTV 4.2km (2.6 miles) over conventional, UHF airwaves.

This is no mean feat: At 120 frames per second (UHD allows for 24, 25, 50, 60, and 120 fps), a raw 7680x4320 video feed clocks in at 48 gigabits per second (Gbps). The Super Hi-Vision spec (SMPTE 2036) supports 22.2-channel sound, too, which comes in at around 50Mbps. After compression (NHK has developed a special codec for Super Hi-Vision), the entire stream clocks in at around 500Mbps. To put this into perspective, a 1080p TV channel signal (over the air) is around 10Mbps. The new 802.11ac WiFi standard can reach similar speeds (500Mbps), but over tens of meters -- not 4.2km.

How does NHK transmit 500Mbps over a few miles, then? Using OFDM (orthogonal frequency-division multiplexing), MIMO (multiple-input, multiple-output, i.e. using more than one antenna), and two 8MHz UHF radio cahnnels. OFDM and MIMO, which are already used by many wireless technologies including digital terrestrial TV (DVB-T), 802.11ac and LTE, allow a vast amount of data to be squeezed into a single bandwidth block.

The huge transmission distance is simply a function of the transmission frequency and power. UHF channels in Japan fall between 400 and 800MHz, while WiFi generally uses 5GHz. Longer waves (VHF and UHF) can travel further without being attenuated by obstacles (such as houses) and atmospheric conditions. While we don't know the exact transmission power used by NHK, we're probably talking about 35 to 150 watts; WiFi is usually around 100 milliwatts -- and stronger signals travel farther. It might help to think of NHK's UDHTV broadcast as simply being a high-powered, one-way version of 900MHz LTE.

Moving forward, the main takeaway is that it's actually possible -- right now -- to transmit 8K television shows (and movies!) over the air. The main problem, though, is that there isn't a single commercial display on the market that's capable of displaying that resolution. Even 4K (2160p) televisions -- which have a quarter of the resolution of UHDTV -- are incredibly rare. Earlier this year at CES, Sharp showed off an 84-inch 8K TV (the world's first, apparently), and LG showed off a beautiful 4K OLED unit (which is due to launch in 2013).