Enrique LaRoche writes: > I am sure 11a is 4 times faster at up to 50 feet > At 500 it might just be a bit slower.
Lots of people who got a 'B' in high school physics are 'sure' that the only important factor here is the difference in frequency, and forget that OFDM is a *much* more sophisticated modulation than CCK. Some even forget that the lowest rate for 802.11a is 6Mbps, so if you're getting through at all, you're running faster than 11b's 5.5Mbps CCK modulation. Further, the noise floor in 5GHz is almost always going to be lower than it is in 2.4GHz. The "cleaner spectrum" argument is almost always true. If you carefully read the Atheros paper, they measure an indoor (read, moderate to high multipath) environment. OFDM kicks butt in this situation due to its ability to not use carriers where high interference is present. I don't recall reading the Mobilian paper. Outdoors, it is true that the free space loss at 2.4 is much less than at 5GHz. Basic physics states that: Free Space Loss = 20Log10(Frequency (MHz)) + 20Log10 (Distance (Miles)) + 36.6 and this would tend to favor 2.4GHz. Plugging a few friendly numbers here, a 5 mile link at 2.400 GHz has 118.2 dB of free space loss, while the same link at 5.850 GHz (the top of the band, so worst case) has 125.9 dB of loss. At 20 miles, the 2.4GHz 'path' will yeild 130.2 dB of loss, and at 5.850 GHz, 20 miles will set you back 138 dB. But all the world is not built of 5 mile (plus) links, think 'mesh routing' here. Further the part 15.407 rules allow the same tx power as 15.247 (1W), but in 5GHz, you're allowed essentially *unlimited* antenna gain for point-to-point applications, vs. 6dBi of gain @ 1W of tx power in 2.4GHz. I don't know if the original poster wanted to talk about power consumption, or RF power as compared to distance, or spectral power (roughly the ability for two simultaneous signals in the same frequency to be heard by a pair receivers). They're all different questions. The reasons the papers differ in viewpoint is that they're not written from a position of neutrality. Both organizations are attempting to present their products in the best possible light. In short, they're both selling. Jim -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
