iPhone 3GS Upstream Transfers Limited to 384 Kbps

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Macworld reports that while the iPhone 3GS does support the improved 7.2 Mbps download transfer speed now currently being deployed in the U.S. by AT&T and already available in other parts of the world, it will not support the correspondingly improved upload transfer speeds of 1.4 or 1.9 Mbps generally available on such networks and will be limited to the same 384 Kbps upload speed available on the iPhone 3G.

I had supposed that Apple took the opportunity to build HSUPA on the upstream side, at either 1.4 or 1.9 Mbps speeds that are supported in many European networks that have already rolled out 7.2 Mbps HSDPA. But it turns out, Apple didn't. . .

After my HSPA article ran, reader Nick Dunklee pointed out in e-mail that a teardown at RapidRepair of an iPhone 3GS shows that it has a UMTS/HSDPA chip. UMTS is the earliest 3G standard deployed on GSM networks, and it tops out at 384 Kbps. It's easy to test, if you have an iPhone 3GS. Go to any speed tester, like Testmyiphone when you're outdoors with a good signal. Downstream, you might hit well over 1 Mbps; upstream, under 384 Kbps.

Macworld's report is a follow-up to a previous article that discussed the ins and outs of the High Speed Packet Access (HSPA) network standard and how AT&T's offerings compare to that standard.

HSPA (High Speed Packet Access) is actually two separate standards: HSDPA (for downstream) at a raw rate of 7.2 Mbps and HSUPA (for upstream), likely at raw rates of 1.4 Mbps or 1.9 Mpbs, the two most popular upload speeds deployed by existing 7.2 HSPA carriers. The 7.2 Mbps downstream and 1.4/1.9 Mbps upstream rates represent the full bandwidth available in a given HSPA channel, but don't translate to what an individual user will see.

For AT&T's current HSPA system, the company claims range from 700 Kbps to 1.7 Mbps downstream, and 500 Kbps to 1.2 Mbps upstream.

So while the iPhone 3G was unable to even take full advantage of existing upstream transfer speeds, the iPhone 3GS suffers from the same limitation. But the limitation is not unique to the iPhone, as the new report mentions that other GSM smartphones are also utilizing the older UMTS standard at a maximum of 384 Kbps.

Dunklee examined the specs on a number of GSM network smartphones, and found none included HSUPA. It's possible that there could be a firmware update from UMTS to HSUPA, but thats unlikely. There's usually a reason for using an older standard, which is related to power consumption, chip size, or cost.

Smartphones using competing CDMA technology, such as those on Sprint and Verizon, however, do take advantage of the full upstream capacity, suggesting that the limitation is related to the use of GSM technology as the basis for these cellular networks.

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