Testing finds HSPA+ speeds still no match for LTE
While some operators are looking to HSPA+ as an alternative to LTE, independent testing from Spirent and Signals Research finds that HSPA+ speeds aren’t quite as fast as advertised.
Spirent Communications and Signals Research have put to the test recent industry claims that high-speed packet access plus can deliver comparable download speeds to 4G technologies, and they’ve concluded that HSPA+ may not be as fast as its proponents claim. Testing currently available HSPA+ chipsets over live HSPA+ networks, Spirent and Signals found that while HSPA+ can deliver tremendous amounts of bandwidth under certain static conditions, as subscribers become more mobile, download speeds quickly drop off, leaving them with connections significantly slower than those anticipated on the first long-term evolution networks.
Using Spirent instruments Signals Research tested Qualcomm’s (NASDAQ:QCOM) HSPA+ chipset, Sierra Wireless’ (NASDAQ:SWIR) data card (which uses the Qualcomm chipset) and an early pre-commercial platform from ST-Ericsson (NYSE:STM, NASDAQ:ERIC) in the field over several commercial HSPA+ networks. It found that when sitting directly under the cell site immobile, the platforms were able to deliver at the physical layer peak speeds of 19 Mb/s, near the theoretical maximum of 21 Mb/s for HSPA+. But as soon as mobility was introduced, those speeds rapidly fell off.
In what Sierra Wireless called pedestrian mode — moving around at a walking pace — peak speeds fell to 8.5 Mb/s and went as low as 3 Mb/s near the cell edge. In truly mobile conditions — in a car at freeway speeds — data rates dropped further, ranging from 2.5 Mb/s to 4 Mb/s. Similar tests performed on today’s typical HSPA networks — which theoretically support up 7.2 Mb/s — produced speeds in pedestrian conditions ranging from 1 Mb/s to 3.5 Mb/s and in mobile conditions from 500 kb/s to 2.3 Mb/s.
The bottom line, said Nigel Wright, vice president of wireless for Spirent, is that while HSPA+ can theoretical deliver three times the capacity of a regular HSPA network, in real-world conditions it delivers only double the speed. In a few unique situations, though, its true promise does shine, almost tripling HSPA’s best speed of 6.9 Mb/s, Wright said.
“HSPA+ can deliver speeds approaching 21 Mb/s, but you have to be static under the base station at 3 o’clock in the morning to get anywhere close to that,” Wright said. “I can imagine there are some cases where that happens, say businessmen at their hotel rooms downloading files late at night. But those aren’t your typical conditions.”
The reason for the widely varying results on HSPA+ is its modulation scheme, Wright said. HSPA+ depends on higher-order modulation for its capacity boost, but it’s very difficult for the network to maintain that scheme as a device becomes more mobile, forcing it to "downshift" to a lower-order modulation and give up capacity gains to most subscribers. “The first iteration of HSPA+ uses 64 [quadrature amplitude modulaton], which is very delicate,” Wright said. “You have to be fairly close to the center of the cell for the device and the base station to shift up to that modulation, so the network isn’t in that mode for the majority of the time.”
T-Mobile (NYSE:DT) has begun marketing its HSPA+ network as capable of delivering “4G speeds,” while wireless consulting firm Aircom International is advising its customers that HSPA+ will deliver much of the speed gains of LTE networks at a fraction of the cost. Spirent and Signals numbers, however, show that HSPA+ still has a long to way to go close the bandwidth gap between 3G and 4G. Verizon Wireless (NYSE:VZ, NYSE:VOD) hasn’t yet launched its LTE network, but it claims it is achieving peak speeds of 50 Mb/s in field trials and speeds between 5 Mb/s and 12 Mb/s in typical network conditions. Independent testing of TeliaSonera’s live LTE network in Stockholm recorded average download speeds of 25 Mb/s.
Those aren’t apples-to-apples comparisons, and so far Spirent and Signals have not conducted similar tests on LTE networks because the only commercial LTE system, TeliaSonera’s, is so under-loaded it wouldn’t yield any meaningful comparisons, Wright said. But he added that he anticipates that commercial LTE networks will be able to support much higher data rates far more consistently because of the nature of the technology. Unlike HSPA+, which uses a single high-speed wideband CDMA carrier, LTE uses orthogonal frequency division multiplexing access, which splits the transmission into numerous small sub-carriers that are far less dependent on the particular conditions of the network at any given time to maintain their connection speeds, Wright said.
Wright, however, did concede one advantage to HSPA+. In all of its tests, speeds never dropped below 2 Mb/s, which is more than enough to power even the most robust smartphone applications and provide adequate mobile broadband speeds for all but the most bandwidth-hungry PC applications. In that sense, HSPA+ delivers enough capacity to create a comparable experience to 4G networks for many applications, even if it’s unlikely to match LTE’s raw bandwidth, he said.
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© 2013 Penton Media Inc.
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