Results

The distance in measurement (1) -- the maximum distance for zero-error reception -- was 0.50 miles.⁹ The distance in measurement (2) -- the maximum distance at which we could get packets at all -- was 0.87 miles.

The ``marginal zone'' is about 0.37 miles, or a 70 percent increase in distance if we can recover from received bit errors.

Figure 4: Fraction of packets lost versus error tolerance on the 0.55-mile one-way link. Note log-log scale.

The measurements on the 0.55-mile link were as follows:

1. 195 pings were transmitted, each with a 1,392-byte known payload.

2. 23 packets, or 12 percent of those sent, were lost entirely.

3. 63 received packets, or 32 percent of those sent, were received perfectly.

4. 10 received packets, or 5 percent of those sent, had 192 or more octets incorrect.

5. The remaining 99 packets, or 51 percent of those sent, had between 0 and 192 octets incorrect.

Figure 4 presents these data in graphical form: the fraction of packets with more than a given number of octets incorrect. Normal 802.11, which can only make use of perfectly-received packets, is at the left-hand side of the graph -- a loss rate of 100 - 32 = 68 percent.¹⁰ If we can salvage packets with up to 192 incorrect octets, we would instead have a loss rate of 100 - (32 + 51) = 17 percent.¹¹

These results -- a 70 percent increase in distance, a 75 percent decrease in packet loss rate -- convince us that adding redundancy so that the receiver can salvage errored packets can be a useful software-only addition to 802.11.