Video-grade Wi-Fi – A Requirement for TV Everywhere
A new wave of Wi-Fi innovation is underway.
In recent years, Wi-Fi has become the de facto home networking technology due to its flexibility and ease of use for Internet surfing and data connectivity. Interestingly, a key element of the success of Wi-Fi – the use of a particular segment of unlicensed spectrum – is also its Achilles heel.
Operating mostly in the 2.4 GHz radio spectrum, Wi-Fi spectrum is quite narrow and supports very few channels, leading to congestion in urban areas with neighboring Wi-Fi systems. Compounding the problem, Wi-Fi shares the same frequency as microwaves, cordless phones and other appliances, which in many cases leads to limited throughput or spotty reception.
And although Wi-Fi is designed to share many devices on the same radio channel using a collision avoidance technique (CSMA), the mechanism is inadequate for high-bandwidth applications such as video. While applications such as Web browsing and email can operate using traditional Wi-Fi solutions, as more demanding applications such as video and multimedia streaming are introduced into the market, more appropriate solutions are clearly needed.
WHY VIDEO-GRADE Wi-Fi?
These characteristics are becoming increasingly problematic as IP-based video content becomes increasingly available and consumers are increasingly using Wi-Fi to distribute that video.
Multichannel video programming distributors (MVPDs) are offering tripleplay packages in order to compete with each other. Among MVPDs, the telcos have thus far demonstrated greater interest in how to exploit Wi-Fi for in-home video distribution.
The telcos’ bundles are based on IPTV, effectively digitized video that is compressed and packaged as IP packets. AT&T’s U-verse service, for example, leverages H.264 video compression down to about 10 Mbps for HD streams.
AT&T and other telcos are looking at Wi-Fi home networks for distributing live channels from the DSL gateway to the IP set-top boxes. In fact, Cisco has created a set-top (the ISB7005) for AT&T U-Verse that was designed with a Wi-Fi video interface.
Despite the known problems with Wi-Fi, the advantages of Wi-Fi networking remain compelling; they include easy, fast and cost-effective installation, as well as the flexibility to place STBs and TVs anywhere in the home not limited by coax jacks locations.
Carriers realized very quickly that conventional Wi-Fi in the congested 2.4 GHz band was not up to the task of distributing HD video throughout the home, and that a new breed of Wi-Fi solution was necessary. In particular, the shift to the 5 GHz radio band to avoid the crowded 2.4 GHz radio band was absolutely mandatory. While this was a first step in the right direction, in itself it was not enough.
Most conventional Wi-Fi implementations are optimized for best-effort, peakrate data streaming and don’t deal well with video traffic’s unique requirements. Video is very sensitive to packet loss, and consumers don’t tolerate the resulting artifacts on their screens. For many services, low latency and jitter are also important in order to improve the user experience.
Also, whole-home coverage and a consistent signal becomes mandatory – consumers may have their STB and TV located in many corners of the home and can’t be expected to move them around to get a better signal, and they also won’t tolerate flicker on their screen when someone crosses the room and blocks the radio signal momentarily, for example.
The solution to problems such as these is to use video-grade Wi-Fi that is optimized for the unique requirements of video streaming in the home. It provides whole-home coverage, a consistent signal, very low packet loss and bounded jitter, as well as interference mitigation techniques. Video-on-demand, multi-room DVR and over-the-top (OTT) content are services based on IP-based video that push the envelope further for Wi-Fi connectivity in the home.
TV EVERYWHERE IS PUSHING THE BAR EVEN HIGHER
The proliferation of iPads and other tablets means that these devices are quickly becoming multimedia consumption tools. Service providers are pushing for TV Everywhere, especially on the iPad and laptops, in an effort to get control over the secondary screens in the home. Cablevision, Comcast and Time Warner Cable notably have done this.
Subscribers will expect a crystal-clear picture on their iPads and portable display devices, and they will also want the freedom to move around their homes as they watch TV. Video-grade Wi-Fi meets these demands.
Designing a Wi-Fi system that streams HD video to any portable device is twice as hard as streaming HD video to a wireless STB manufactured by a service provider. Service providers have very little control over the quality and capabilities of the Wi-Fi design of the portable devices. Therefore, they need “smart enough” Wi-Fi access point technology that works well with any third-party device.
In order to meet these requirements, service providers are designing a new breed of home gateway that includes concurrent dual-band operation at both the 2.4 GHz and 5 GHz bands (see Figure 1). These home gateways support data and legacy devices on the 2.4 GHz band and video-grade Wi-Fi on the 5 GHz band in order to support a high video user experience on a wireless STB, iPad or other portable screen.
VIDEO-GRADE Wi-Fi DEFINED
A video-grade Wi-Fi access point needs to stream high-bandwidth HD movies simultaneously to multiple portable screens and STBs in the home effectively while maintaining a flicker-free picture. This must be accomplished perfectly, without any proprietary “secret sauce,” enabling a good user experience on all portable devices, which typically do not have embedded video-grade Wi-Fi.
Wi-Fi PERFORMANCE REQUIREMENTS
Range and throughput consistency are two of the most important parameters of video-grade Wi-Fi. Subscribers can’t be expected to move their STB out of dead spots or be bound with their iPads to certain locations in the home in order to watch a movie with a decent experience.
A video-grade Wi-Fi system has to be able to deliver consistent video streams concurrently to multiple locations throughout the house (see Figure 2).
• Throughput and coverage – Videograde Wi-Fi must support multiple simultaneous HD streams, with an overall bandwidth requirement of at least 60 Mbps to 100 Mbps (or more depending on the IPTV encoding of the HD streams) to the edge of the house. The AP may be located in the basement or in the attic, while the client can be located up to four rooms, or up to two floors or ceilings, away from it.
• Consistency – Unlike data services, where performance is benchmarked by measuring average throughput, video and IPTV distribution systems simply cannot lose packets. Incoming traffic is typically multicast, and therefore lost packets cannot be retransmitted, which means that any lost packet is immediately translated to a visual artifact on the TV screen.
MEETING THE REQUIREMENTS
A combination of digital beamforming and antenna diversity has proven an effective combination of performance and cost for video-grade Wi-Fi technology. While a conventional 802.11n MIMO system transmits from multiple antennas, a digital beamforming-enabled Wi-Fi system does so while controlling the phase of the transmitted signals – electronically – to gain coherent signal summation at the client location, effectively increasing the received power on the iPad or STB.
The technique is comparable to a laser beam, focusing the energy on one spot, versus a light bulb, effectively radiating light all over. The implementation of digital beamforming in a smart way that does not require any collaboration from a smart Wi-Fi client is the key to achieving gains when transmitting HD video to portable devices.
Streaming to multiple client devices is more difficult, and quality of service (QoS) becomes an important consideration in this scenario. Clients must not interfere with each other. For example, a deteriorating viewing condition on a moving iPad must not affect the viewing experience in the main living room wireless STB. A video-grade access point must have a scheduled access, “slicing up” air time into well-calculated “time slots,” ensuring that each client receives the required bandwidth.
While the previous algorithms optimize performance dramatically, a second line of defense is required against unexpected interference or colliding neighboring Wi-Fi networks. Various signal processing techniques or antenna attenuation techniques don’t provide robust enough isolation, as interference can sometimes overshadow the video traffic in excess of 30 dB. The best approach is to move away from a noisy channel to a clean channel in a fast channel hop. The key to a successful video-grade implementation is doing so in real time, and fast enough, without affecting the user experience.
Two mega-trends – the proliferation of IP-based video content and changing consumer habits, with more users purchasing iPads and tablets – have increased the need for video-grade Wi-Fi systems. Service providers are delivering a new breed of home gateway that supports concurrent dual-band Wi-Fi solutions that simultaneously operate in the legacy 2.4 GHz band, as well as the 5 GHz band, to support wireless STBs, connected TVs and tablets. Video-grade Wi-Fi is required to support the new gateways and provide a superior viewing experience that is comparable to that of wired TV sets.