Interference Immunity

Interference Immunity for Artifact Free HD Video

Interference from other wireless networks is a notorious problem in wireless communications. HD video is particularly sensitive to interference, as it is not tolerable to any delay or jitter of traffic, which immediately translates to noticeable video artifacts. This is the reason why video traffic is usually delivered in the 5GHz band, where up to 13 different 40 MHz channels are available. However, it turns out that in dense deployments, even 13 channels are not nearly enough.

At Celeno, we believe the best interference mitigation technique is interference avoidance. To avoid interference, a video delivery system needs to make a smart initial channel selection, and to continue tracking interference status during operation, and change its operating channel accordingly.

The OptimizAIR™ channel selection algorithm scans the entire available spectrum and maps the interference condition in each channel. The algorithm accounts for adjacent channel interference, and even for interference from more remote channels, which in some cases can be more destructive than interference in the same operating channel. The problem with adjacent channel interference is that it is not recognized by the MAC protection mechanism, and is hence more prone to collisions. The channel that gets the best score in terms of both in channel and adjacent channel interference is selected.

Once video delivery operation has started, a special interference detection mechanism based on short term MAC errors and packet loss statistics kicks in. With Celeno’s channel aware rate selection, that predicts the exact over the air PER, excess PER due to interference is immediately detected, in many cases much before the video queue overflows and artifact is actually generated.

The Optimizer first decides if the interference condition is severe enough to justify an immediate action. A severe interference condition is one which is expected to result in system packet loss. If the interference is deemed tolerable, nothing is done, and interference tracking continues. In case severe interference is detected, the AP momentarily pauses traffic and performs a fast channel scan. Once an interference free channel is found, the AP commands all clients to change channel, and operation resumes in the new channel. In most cases, the channel change is done seamlessly, before any video artifact is actually generated, for a complete seamless video operation. The channel change procedure uses standard 802.11 protocols, and supports any 3rd party client.

So the key for interference mitigation is to avoid it completely. Seamless channel change based on fast and reliable channel aware interference detection is the means. Artifact free HD video is the result.