TelcoTV: Here Comes 802.11ac

TelcoTV, the largest video conference focused on the U.S. service provider market, celebrated its tenth anniversary in New Orleans this week. The three day conference included vendor-hosted workshops, a Cloud Services summit, TelcoTV learning tracks, and keynote presentations.

Nir Shapira, CTO of Celeno Communications, explains the latest WiFi standard – 802.11ac – in Converge. It will likely be the preferred wireless tv delivery method in homes.

The 802.11n standard, utilizing Multiple Input, Multiple Output (MIMO) technology, has become the cornerstone of many IPTV home networks, since it boosts speed significantly over earlier WiFi standards.

While 802.11n was the first standard to introduce the concept of MIMO, 802.11ac will offer several improvements over 802.11n.

The main 802.11ac benefit is better throughput. The committee targeted compressed video delivery on multiple channels. Compressed video streaming usually does not require more than ~80Mbps of aggregate throughput (assuming an average HD video stream is compressed to 10-20 Mbps), but it needs to deliver this relatively modest throughput to the edge of the home.

The main improvement in 802.11ac is wider bandwidth (BW) channels. A mandatory 80 MHz bandwidth mode has been defined, doubling the maximum of 40MHz BW supported by 802.11n.

With mandatory 80Mhz BW, operation in the 2.4GHz band is practically impossible, so 802.11ac is targeted to operate solely in the 5GHz band. At 5 GHz, spectrum is available to accommodate up to four non-overlapping 80MHz channels in Europe and five 80MHz channels in the US.

It is yet to be seen how efficient the usage of 80MHz channels will be in dense environments. Where operation runs into problems, it will fall back to 40MHz. An optional 160MHz BW mode was also defined which is less able to handle interference.

A high level of performance can be achieved with less transmit or receive antennas compared with 802.11n, resulting in more cost-effective devices.

The expected PHY throughput for various BW and MIMO dimension options. However, 2×2 80 MHz is still inferior to 3×3 40MHz. It is therefore expected that 802.11ac devices targeting video delivery applications will not rely on 2×2 or 1×1 radio configurations and will consist of at least 3 radios on the video source side of the link.

Similarly to 802.11n, 11ac will support the optional features of LDPC coding and beamforming. LDPC is an advanced coding method that typically achieves an additional gain of 2dBs compared with the mandatory convolution code that was inherited from the legacy 802.11a/g standard and is usually still used by most 802.11n devices.

Beamforming is a method by which a multi-antenna transmitter focuses the transmitted energy towards the target device antennas, and is the theoretically optimal transmission scheme in a MIMO channel. Instead of blindly emitting energy in all directions, the transmitter uses a concrete channel estimation to shape the transmission. Beamfoming gain is significant across all the relevant signal-to-noise (SNR) range and is at least 5dBs.

The new multi user (MU) mode is considered a true breakthrough. Termed MU-MIMO (distinguished from the single-user (SU) beamforming mode inherited from 802.11n, this new mode can deliver several simultaneous data streams to several different users simultaneously.

While in SU-MIMO mode (as in 802.11n), three spatial streams required three receive antennas, in MU-MIMO mode three spatial streams can be delivered simultaneously to three single antenna users, thus reducing dramatically the overall complexity of a home network.

The main promise in 802.11ac might be the adoption of optional modes in 802.11n like beamforming and LDPC. These technologies are already being used successfully in a handful of video delivery devices today on top of 11n, so the main benefit from 11ac is interoperability. Together, these two technologies can quadruple link performance in a typical home environment and significantly improve reach and robustness.

In-Stat estimates that nearly 350 million routers, client devices and attached modems with 11ac will ship annually by 2015, following a sharp curve up from about 1 million units in 2012, probably the first year when 11ac products will be sold, Dickson said.

But even in 2015, shipments of 11n will outnumber sales of the new technology, with an expected 1.5 billion products equipped with 11n, more than double the estimated 700 million in 2011. The 802.11ac standard will be backward compatible with 11n, and products are likely to support both.

Posted by Sam Churchill on .

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