HSDPA Speed, Lab Versus Real World
Here’s the deal. The 3.6 Mbps number is real, but you as a user will never see it. It is based on using the highest order modulation available (16 Quadrature Amplitude Modulation), and five high-speed codes allocated to the same device. Even then, it is at the link layer, meaning that it does not take into account IP and TCP packet overhead, though this is likely less than 10%. It is effectively the capacity of most of the cell site directed at one user under optimal radio conditions. But even if you were the only user in that cell sector with an excellent signal, while the radio could deliver this throughput, the bottleneck in the real world is the backhaul connection to the base station, which is typically based on T1 circuits that are limited to 1.5 Mbps of throughput. I can guess that Nortel has a fiber connection to their test cell site in Chateaufort, but that’s not the real world, though to be fair, some cell sites are on fiber. But most are not.
The reason you’ll see actual throughputs in the 400 to 700 kbps, as quoted by Cingular, is two fold. One, as just mentioned, is the real world constraint of backhaul capabilities, which by the way is no different for Wi-Fi hotspots. The other is that multiple users will be active in the cell, sharing the radio capacity. So beware of the inflated speed claims. While they may represent the real capabilities of individual devices, and the theoretical capabilities of the technology, they will not necessarily be what you will experience.