About 60 operators worldwide currently offer HSPA (High-Speed Packet Access) commercially, more than 50 percent of them using Ericsson equipment. And there are more than 50 different HSPA devices, from handsets to laptops, on the market.
"So far we have commercially reached 3.6Mbps for the downlink and 384kbps for the uplink," says Andrei Dulski, Ericsson's marketing manager for 3G systems.
"In a couple of months we will make the second phase of HSPA generally available, where networks will able to offer up to 14Mbps downlink and - thanks to the newly introduced Enhanced Uplink technology - 1.8Mbps uplink. Maximum speeds experienced by end users will however be limited initially to 7.2Mbps because of terminal limitations."
This upgrade will also provide increased system capacity, so each cell can serve more users simultaneously.
This is just the beginning: Ericsson demonstrated the future evolution of HSPA earlier this year at CTIA in Las Vegas, with data rates in excess of 20Mbps.
Jan Färjh, director at Ericsson R&D, explains that evolved HSPA is now being standardized in 3GPP for the existing 5MHz spectrum. The standard will be released next year and products will be available during 2008.
"Instead of today's 16QAM modulation for the downlink, we propose that it uses 64QAM, which means a 50 percent improvement," Färjh says. "The uplink will use 16QAM instead of QPSK, which means a doubled rate."
3GPP is also discussing the use of multiple antennas for the downlink - MIMO (multiple input, multiple output) - in this case two at the base station and two at the terminal, which will double the bit rate.
Evolved HSPA requires new terminals but the base stations are already prepared for this upgrade.
Then we will go from today's 14Mbps to 42Mbps," Färjh says.
Using advanced receivers (G-RAKE) in base stations and terminals, and by cutting the latency in the network (the round trip from terminal to IP server to terminal) from 50 to 25 milliseconds by using better protocols, the system will provide a substantially improved total performance and user experience.
Facts
QAM (Quadrature Amplitude Modulation) is a modulation scheme where information is conveyed by changing the amplitude of two carrier waves. The two carrier waves are in quadrature - they are out-of-phase with each other by 90 degrees. The signal constellation is made up by shifting the amplitude independently of the two carrier waves according to a predefined number of levels. The total number of signal constellation points decides the level of the QAM: for example, in 16QAM, one symbol will take the value of one out of 16 constellation points. With 16 different constellation points, four bits per symbol can be conveyed; correspondingly in 64QAM, each symbol will convey six bits of information.
Increasing the number of levels means more bits can be conveyed per symbol, resulting in a higher transmission speed. But the transmission will also be more susceptible for noise and interference, which usually results in a need for more complex receivers. |
