DoCoMo's LTE is quick, but quickly disappoints

NTT DoCoMo's LTE (Long-Term Evolution) data network, launched in three of Japan's biggest cities on Dec. 24, promises speeds of up to ten times those of current 3G wireless. Over the last few days I've had a chance to test network performance in central Tokyo, and I found that while it does occasionally offer significantly faster downloads than 3G, the current LTE network generally under-performs and suffers from slow upload speeds.

DoCoMo began building the network in December 2009 and testing started in June 2010. Between April 2010 and March 2011, the company will invest ¥35 billion in the initial LTE roll-out and will follow that with an additional ¥270 billion investment by March 2013 to put LTE in major cities across Japan.

The service launched with two data modems, a USB device from LG Electronics similar to the one used by Verizon in the U.S., and an Express Card from Fujitsu. NTT DoCoMo provided the LG modem for the test.

I visited several locations in central Tokyo listed as having LTE coverage and attempted to connect via LTE. At all the locations I recorded the speed of downstream and upstream traffic by hitting Speedtest.net servers in Tokyo, Okinawa and Seoul. I also recorded comparable 3G speeds from the same locations with an LG 3G modem.

In most locations the LTE signal, when available, was strong. It typically measured three bars out of three on the PC software, but I didn't have to walk far from each area to see the signal drop or disappear completely. That's perhaps understandable for a new network and isn't disastrous because the modem falls back to an HSPA 3G connection when LTE isn't available.

A bigger area of concern was the connection speed.

NTT DoCoMo advertises the LTE service as offering outdoor download speeds of up to 37.5Mbps and upload speeds up to 12.5Mbps. Getting those speeds isn't expected in practice, but I was hoping for downloads at between 10Mbps and 25Mbps.

In most locations I didn't get even that.

Outside one central Tokyo railway station the fastest speed recorded to speedtest.net's Tokyo server was 5.9Mbps, and outside a second station it was 7.7Mbps. Outside NTT DoCoMo's headquarters in the Nagatacho district the connection peaked at 5.7Mbps.

For comparison I made connections over DoCoMo's 3G network in the same three locations and got speeds of 1.7Mbps, 3.8Mbps and 2.3Mbps respectively.

DoCoMo's 3G network is advertised as offering speeds of up to 7.2Mbps, so these three represent between 23 percent and 51 percent of the theoretical maximum. The LTE network was delivering between 15 percent and 21 percent of the top-speed.

But if downloads were on the slow side, the upstream connection to the network was a disaster.

In almost all tests the uploads on DoCoMo's LTE network were between 0.3Mbps and 0.7Mbps -- far slower than the "theoretical maximum" of 12.5Mbps -- and in three out of four locations the 3G network outperformed the LTE network.

Sometimes the gap between the two was considerable. At Tokyo's Shinagawa Station the LTE modem was repeatedly measured by speedtest.net at just 0.25Mbps. A 3G HSUPA connection to the same server was consistently clocked at around 1.7Mbps.

There was one area where the network performed to expectations.

Outside Shibuya Station, one of the busiest areas in Tokyo, the LTE broke free of whatever had been holding it back and I consistently saw download speeds of around 20Mbps to speedtest.net's Tokyo server. The fastest I managed to record was 22.39Mbps, which is much closer to my expectations of this technology. The 3G network hit 4.07Mbps at the same location.

Uploads were however poor with most registering at between 0.5Mbps and 0.7Mbps despite the fast downloads. I recorded an upload of 3.32Mbps to speedtest.net's Seoul server on one occasion, but I wasn't able to repeat it or even get close to that speed on subsequent attempts.

NTT DoCoMo won't comment on the results of such tests, but it's clear the carrier has some work to do in improving speeds on the LTE service. The weak upload is particularly troubling, and some local media have theorized its down to a bug in the network.

The company is offering unlimited use of the LTE service at a reduced rate of ¥4,935 (US$59.50) per month on two-year contracts signed between now and April 30, 2012. From May 2012 the service will cost ¥6,510 per month for 5GB of data, and ¥2,625 for each additional 2GB.

The company's 3G data service costs ¥5,985 per month with no data cap.

DoCoMo's LTE service has been commercial for less than a month, so it's still early days. If my experience outside Shibuya Station is to be typical, the LTE network will enable significantly faster mobile data networking in the future. DoCoMo has the network investment plan prepared, so it's just a matter of time.

Martyn Williams covers Japan and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com

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