The wireless home network offers lots of promise for equipment providers, but they must be able to guarantee QoS.
Over the last five years, wireless data networks and the applications that access them have made our lives more convenient and provided us with precious flexibility. Wireless technologies have become so entrenched in our everyday life that they have now permeated into the home entertainment market. While consumers used to watch DVDs or video clips in front of a stationary TV at a single location in the house, they now want to share and access their growing pool of DVRs, mobile devices, laptops, and other entertainment resources anywhere in the home, at any time.
This presents a challenge for today's developers, which is to provide seamless networking for multimedia and entertainment convergence. Consumers want their wireless network and applications to be just as reliable as if they were wired. Unlike transporting general data over wireless networks, however, video applications can't tolerate bandwidth fluctuations, so the challenge is significantly more rigorous. There are many, many considerations to evaluate when pushing video content through a wireless network. Earlier wireless LAN technologies simply weren't up to the task, and the industry responded with the most recent IEEE 802.11n specification. Even this high-performance WLAN standard, however, isn't enough for transporting video, and requires supplementary technologies to provide the kind of high-quality entertainment experience that consumers demand.
A number of critical factors contribute to satisfactory performance as perceived by the consumer. These include bandwidth, latency, breadth of coverage, and quality of service (QoS).
Bandwidth is particularly important and is optimized through the use of MIMO (multiple-input multiple-output) and channel-bonding techniques. These techniques also contribute to QoS, because higher throughput improves immunity to interferences and makes it easier to handle degraded link conditions. In addition, any excess bandwidth can be traded for longer reach and better power efficiency--the more bandwidth, the better.
Not enough throughput
At the same time, though, raw bandwidth from higher PHY throughput isn't enough. What's needed is higher effective bandwidth at satisfactory levels for the given application, and this requires the additional step of substantially increasing media access controller (MAC) efficiency. This can be achieved using an aggregation mechanism that eliminates the overhead linked to each packet and replaces it with a common overhead. Aggregate exchange sequences are enabled with a protocol that acknowledges aggregated MAC protocol data units (A-MPDUs). As a result, there's a single block acknowledgement (Block ACK) instead of multiple ACK signals, and there's no need to initiate a new transfer for every MPDU. The result is a MAC efficiency of 70% as compared with typical 50% MAC efficiency ratings for IEEE 802.11a/b/g, as shown in Table 1.
Another key consideration is how far the network can reach; the gold standard is whole-house coverage. Although users can tolerate "dead spots" and limited coverage when using home data networks, dead spots and limited coverage aren't acceptable for wireless entertainment. Today's centralized multimedia storage devices are expected to serve as the source for all multimedia content, no matter where in the home it's being viewed or heard. This means that, unlike data networks, the bit rate can't drop with increased distance from the access point.
