When deploying home networks, one question always seems to surface first: What wireless technology is “good enough” to support multiple streams of HD video—at the lowest cost? Although several wired options exist for the delivery of compressed video in home networks, including Multimedia over Coax (MoCA), Home Phoneline Networking Alliance (HPNA), and powerline communications (PLC), they don’t offer the same coverage and cost-effectiveness as wireless technology.
Among wireless technologies, emerging 60-GHz solutions lack the necessary reach and are fairly expensive. Thus, designers are left with 802.11n, particularly the 4x4 multiple-input multiple-output (MIMO) version, as the only solution that easily and economically spans every corner of the home.
Potentially, 802.11n can replace wired technologies to significantly extend home-networking coverage for just about every conceivable electronic consumer product, from TVs, residential gateways (RGWs), and set-top boxes (STBs) to game consoles, Internet Protocol (IP) phones, and mobile devices (Fig. 1).
Defining “Good Enough” For HDTV
“Viewing satisfaction” is a fairly complex and involved process to determine, taking into account both objective and subjective components. One specific, objective method that can help quantify and evaluate connection-quality scenarios has to do with measurements of long-term averages for packet loss ratio, also known as packet error rate (PER).
Consumers expect high-quality images at all times (e.g., watching TV for a long period of time without any glitches). This expectation translates into very low PER on the order of 0.01% to 0.001%—hence establishing the base parameter for watching quality HDTV.
Subjective components of viewing satisfaction tend to involve time-dependent, event-driven statistical properties of the system. These errors are fairly hard to simulate or measure directly. However, their combined effects can be seen on a TV screen due to the presence of residual errors that appear for a short time period—only long enough for the eye to see them.
Many parameters could influence subjective testing results. On the wireless physical-layer (PHY) side, however, they’re limited to just two: linear dynamic range of the system and signal-to-noise ratio (SNR) margin. Both are affected when random interfering events occurring in the air bombard the system.
Bandwidth Expectations
The data rate (also described as total capacity) achievable in a home environment is a product of time and bandwidth per user (i.e., how many megabits per second and for how long). It continues to climb with the move toward higher-quality flat-panel displays and higher-bandwidth and higher-resolution video content. The growth in TV size along with enhanced contrast ratio and color resolutions is driving demand for more bandwidth. Moreover, the transfer of quality HD content requires higher dynamic range.
Consequently, engineers turn to compression technologies such as H.264 to push HD content over the air. A few years ago, most flat panels displayed video content at 1080i-30 resolution, but that’s now shifting toward 1080P-60 resolution. Meanwhile, frame rates of 120/240 frames/s are becoming more commonplace. Couple that with the move to 3D TV, and the cry for more bandwidth becomes louder.
Viewing very high-quality HD content, such as the National Football League’s Super Bowl, on a 72-in. TV screen might require 30 Mbits/s or more of compressed H.264 performance. On that front, Quantenna’s labs demonstrated that using very high-speed H.264 encoders (with an average transfer rate of about 50 Mbits/s) enables compressed video to be displayed on a 60-in. flat-panel TV at a level of quality indistinguishable from Blu-ray uncompressed video.
Video gaming with HD content and low-latency system response creates even greater bandwidth requirements. With the advent of wireless technology using low-latency HD video encoding, all gaming gear can be stowed out of sight, in a central location, far from the flat-panel displays where the games are played. Today’s low-latency (sub-10 ms) video encoding/decoding technology requires that wireless technology deliver even higher bandwidth for low-latency HD video—as much as 60 Mbits/s for a fairly large size screen.
In general, two primary issues drive bandwidth requirements in the home: the amount of compressed video needed per HDTV screen, and the total number of TVs and wireless game consoles. Based on the aforementioned analysis, it’s reasonable to assume a 30-Mbit/s video-encoding rate is needed for each TV and about 60 Mbits/s for wireless gaming.
Of course, some HD compressed sources may have a much higher peak data rate than the average data rate. These rates are likely to be required across as many as three or four HDTVs as well as a variety of gaming gear.
It would be reasonable for service and content providers to allocate a sustained 120 Mbits/s of compressed HD video rates in the downstream direction from various sources, such as STBs, RGWs, and network-attached storage (NAS) boxes. This sustained bandwidth might require an even greater peak data rate when planning ahead for total home network capacity.