Mobile equipment maker Ericsson was able to reach real-world speeds of 100 Mbps in the latest tests of its Long Term Evolution (LTE) cellular data gear, engineers write in the company's house journal, Ericsson Review. On the street using 2.6 GHz base stations and commercial antennas, engineers pulled in 170 Mbps in raw throughput with the optimum antenna and channel configuration, and they also tested a method that delivered 130 Mbps but could use double the bandwidth with no alterations for 260 Mbps. Actual net throughput was far less, but still 20 to 100 times current typical 3G network rates.

LTE is the next generation of cellular data networking for GSM networks. In the U.S., AT&T has already committed to it, while Verizon Wireless will switch from its traditional use of Qualcomm's CDMA standard to deploy LTE as it develops more advanced networks. LTE is part of a set of loosely defined fourth-generation (4G) standards that will carriers hope will leapfrog today's 3G networks, and offer real competition to wired services, including today's fiber-to-the-home and fiber-to-the-node deployments. Sprint opted for WiMax, which currently delivers far lower speeds than are projected for LTE, but it works today and has a roadmap for improvements.

While carriers are claiming they'll be ready to deploy LTE in the U.S. starting in 2010, every previous new generation of cell data technology has been announced with equal ambition, and then much delayed. On the other hand, each refresh, such as EVDO Rev. A for Verizon and Sprint, has ultimately provided far higher and reliable speeds than the preceding flavor.

Ericsson's engineers were partly testing the efficacy of different multiple antenna configurations. MIMO (multiple-in, multiple-out) antenna arrays have become a basic part of wireless networking, where antenna diversity allows beam steering, which allow signals to be selectively focused on receivers, and spatial multiplexing, which allows multiple streams of data to be sent by separate radio chains using different reflective paths. More antennas and radios have a few other advantages, as well: they allow transmissions over greater distance without increasing interference among devices as beams are focused, and they provide greater receive sensitivity, allowing formerly too-distant senders to be "heard." MIMO is a basic requirement in all 802.11n WiFi devices, and it's part of WiMax's evolution as well.

The company tested a host of arrays, with from one to four transmitting antennas and two or four receiving antennas (in combinations of 1x2, 2x2, and 4x4, in MIMO parlance). The more antennas, the greater the speed over longer distances, of course, but increasing antennas increases manufacturing costs and battery drain, and will limit what kinds of arrays are put in handheld mobile devices as opposed to laptop adapters or automotive systems. The engineers tested at various distances while in motion on foot and by car, and while stationary.

Engineers tested 20 MHz and 40 MHz channels, an enormous increase in bandwidth over all currently deployed cellular technology. In the U.S., Verizon and Sprint's 3G networks using EVDO Rev. A require 1.25 MHz per channel (upstream and downstream) to achieve raw rates over 3 Mbps downstream, while AT&T has deployed HSPA, which uses paired 5 MHz channels to achieve a raw 7.2 Mbps rate. (Both standards have speed bumps ahead: EVDO Rev. B could hit 46 Mbps downstream using a total of 20 MHz, and HSPA's future flavors should hit 42 Mbps using the same total of 10 MHz.)

With current 3G services, Verizon and Sprint claim about 800 Kbps to 1.4 Mbps downstream in real-world uses, while AT&T says its service runs between 700 Kbps and 1.7 Mbps downstream. By contrast, Ericsson engineers were able to achieve real-world rates (using TCP) of over 40 Mbps during half percent of their tests with 20 MHz allotted, and 100 Mbps over 10 percent of the time. They managed 100 Mbps of throughput at 100 km/h with the best signal conditions, but dropped to 40 Mbps at 4 km from the base station.

AT&T and Verizon recently spent billions to acquire licenses in the 700 MHz band, which will allow them to have 5 MHz and 10 MHz channels, depending on locations. LTE can handle channels from 1.4 MHz to 20 MHz in width, according to Ericsson. (Verizon won the choicest block: 22 MHz nationwide in two 11 MHz pairs. AT&T and Verizon bought plenty of paired 6 MHz channels, too.)

Ericsson's results should keep the carriers happy, since they're the ultimate purchasers of the company's gear and they face pressure as users demand more bandwidth for downloading video and gaming.