Overcrowded Spectrum Effects

If you're fortunate enough to have a clean 2.4 GHz spectrum, you only need to worry about whether your wireless gear can provide enough bandwidth at the locations where you want to watch streaming video. Fortunately, this is the problem that most of the industry has been focused on, i.e. throughput vs. range.

The latest step in the battle to extend the throughput vs. rate curve is 802.11n, the high speed extension to the 802.11 standards, which raises raw throughput claims to over 200 Mbps and in some cases closer to 300 Mbps. So even if you cut the claimed data rates in half to start getting closer to what WLAN products deliver in usable throughput, the resulting 100 Mbps or so should be plenty for wireless streaming, right?

But a large percentage of those who want to use WLAN gear don't have an uncluttered spectrum. Certainly apartment and dorm dwellers run the highest risk of WLAN disappointment. But even suburbanites in developments with homes that snuggle up closely to their neighbors' can also feel the no-clear-channel pain. And even if you don't have other wireless LANs in range, the abundance of 2.4 GHz spewing gear that most homes unknowingly have often cause would-be WLAN owners to give up and ship their purchase back from whence it came.

So the 2.4 GHz band used by 802.11b/g is too crowded for successful video streaming. But what does "too crowded" mean and how is it different from the problems caused by wireless gear that just doesn't have the required throughput at the desired range?

The three main effects of spectrum overcrowding are:

• Bandwidth Loss
  Simply put, there are too many WLANs competing for too little spectrum. This causes not only a drop in available bandwidth, but usually also high bandwidth variation as neighboring WLANs compete for bandwidth.
• High Packet Loss
  High RF noise levels from adjacent channel and non Wi-Fi interference sources (microwaves, cordless phones, etc.) cause bandwidth loss as lost or damaged packets are re-sent. In the worst case, non-correctable errors occur.
• Unreliable Connection
  Wi-Fi users in crowded locations are very familiar with the problem of the client that keeps trying to connect to a neighbor's WLAN. This is usually due to the neighboring WLAN's access point (AP) or wireless router transmitting a stronger signal than your own AP. This coupled with the promiscuous default settings of Windows' built-in wireless utility usually results in a client that won't stay put.

It's obvious that if you run out of bandwidth or keep dropping a connection that any application won't work. But how much packet loss can streaming video withstand before it disturbs your viewing pleasure?

Tags: Tutorial, Video streaming, WiFi,

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