NTT DoCoMo's 4G Tests Hit 300Mbps 259
haunebu writes "'Your brand-spankin'-new 3G phone is nearing obsolesence: NTT DoCoMo reveals the results from a new 4G test system.' says TheFeature. While in a car moving at 30kph, DoCoMo engineers managed a peak throughput of 300Mbps and a sustained transfer rate of 135Mbps with their new variable spreading factor orthogonal frequency code division multiplexing (WSF-OFCDM) downstream technology. Who comes up with these names, and how does Japan manage to stay lightyears ahead of everyone else in wireless?"
Names (Score:5, Informative)
Who comes up with these names...
Assuming the poster is referring to ``variable spreading factor orthogonal frequency code division multiplexing (WSF-OFCDM) downstream technology'', the name describes exactly how the technology works. Without reading a technical paper on the technology, I don't know the exact details, but I know what it is doing and what it isn't doing.
Population density helps (Score:5, Informative)
Rehtorical question? (Score:5, Informative)
Might have something to do with the fact that they have 130 Million people in an area slightly smaller than california [worldfactsandfigures.com].
Lot less area to provide coverage for. Not to mention 26 million people in Tokyo alone, making it the highest density city on the planet.
Re:their secret is... (Score:5, Informative)
Actually this is not funny. The United States is, for the most part, sparsely populated compared to most of Europe and Asia. This is why the U.S. carriers hesitated to adopt GSM in the early 90s, which has a fixed number of supported users/frequency and has a maximum cell size due to being time multiplexed. On the other hand, CDMA is able to create much larger cells at the expense of a higher noise floor (hence less users). It was promised to be better suited to sparsely populated areas, yet still tuneable to suit New York City and etc. Whether or not CDMA IS-95 met those goals is debateable.
Japan is indeed under less contraints. Their cell sizes are very small meaning the required transmission power is reduced. If anybody ever saw a Japanese PDC phone from 10 years ago, and was blown away at how small it was, this is the explanation.
Re:Total area to cover (Score:1, Informative)
There are countries which are less populated than the US and still have a much faster deployment of cell phone technologies.
(e.g. Nordic region)
Culture might also have something to say.
That said;
Even in the "home of nokia/Ericsson" nordic region we envy them their more advanced phones and networks.
Note: Requires L-O-S to the base station... (Score:3, Informative)
Re:their secret is... (Score:5, Informative)
As someone who worked with NTT.. (Score:3, Informative)
We tried launching Wireless access there in 2000 and 2001, and the endless meetings and forms were more than discouraging.
But the real answer to how NTT DoCoMo (a division of the monster) manages to turn around so fast is that their researchers work with cell researchers from KDDI, J-Phone (now Vodafone), and that other one who nobody uses (TUCA).
Where does all the funding for research come from? Well, in a country of now 135 million people, there are over 80 million cellular subscribers. A good portion of these are also cellular internet users, paying an extra 100 yen here, 100 yen there for different services.
There is a LOT more income on a monthly basis to Japanese cellular providers than there is in America, or anywhere else in the world.
The easy bottom line is that all this cash can be thrown at research, and that this research is further supported by companies like National/Panasonic, Toshiba, Sony, etc who make the phones for Japan.
The average turn-around time in phone ownership in Japan is 9 months. Your $150 top-of-the-line video-camera/mp3/digital still camera/phone is made obsolete in that short span of time. The furthering of technology by DoCoMo/Vodaphone/etc allows the phone manufacturers to move more units.
The consumer gets new features at the same monthly price (more or less), a new phone to show off to friends, and better service.
The providers and hardware manufacturers rake in the cash.
The cycle supports itself, and it makes everyone happy.
What VS-OFCDM is (Score:3, Informative)
CDMA has lots of advantages for ease of frequency-reuse, as you can have a lot of people on the same frequency, but each one spread with different codes.
OFDM has a lot of resistance against fading (i.e. signal going in and out as you move through diffracted and relected signal peaks and valleys), because you are putting out your signal on a wide range of frequencies. You also get additional frequency diversity from OFDM.
Put them together by doing CDMA spreading first and OFDMing the result, and as much like in the combination of peanut butter and chocolate that results in peanut butter cups, you get an excellent result!
This paper [chalmers.se] and this paper [kcl.ac.uk] gives some background.
VS-OFCDM changes the spreading factor adaptively based on cell structure, channel load, radio link conditions, etc.
Re:their secret is... (Score:3, Informative)
The Japanese were fairly brutal during the war.
They killed maybe more than hilter and Stalin - mostly east asians, chinese and Koreans
Nasty.
My Bad
Re:magic numbers? (Score:4, Informative)
Hmm. Perhaps you should consider the technology name. Much like the old quadrature based encodings, the orthogonal nature of the encoding will permit multiple bits per cycle. Othogonal carriers would be independent of one another, and therefore, be something that could be sampled independently.
Do not confuse what Nyquist has to say about sampling a single signal with the numbers presented. Each orthogonal component is a new axis upon which they can mux a data carrier (in the simplest sense).
Re:What it means (Score:3, Informative)
Are you sure you know what OFDM [wikipedia.org] is? It basically involves overlapping signals on a series of overlapping frequencies, but with different intensities at different frequencies. And each channels set of intensities is orthagonal to each other. Which makes the 'O' decidely non-redundant, as this is hardly traditional FDMA. Think of it as CDMA peformed on an FFT.
Your description of CDMA left a little to be desired as well, but its hard to express laymanwise, I agree.
Re:magic numbers? (Score:3, Informative)
Shannon's Law states the maximum error free digital bandwidth b bits/s of an a slice of spectrum c Hz wide is:
b = c.log2(1+s)
Where s is the signal-to-noise ratio. Thus, in this case, where b=300000000 and c=100000000 s = 7, or 8.5dB, not an unrealistic expectation.
Of course, no current form of error correction coding approaches the ideal Shannon's Law, however reasonably recently developed Turbo Codes [unisa.edu.au] have come reasonably close.
The sort of modulation/multiplexing technique they would be using is a Wideband CDMA technique, similar to that used by UMTS and CDMA2000 wideband technologies.
Putting it simply, the bits are mapped onto a constellation in the complex plane which rotates and changes the amplitude of the carrier. The signal is spread using 2 codes - an Orthogonal code which has poor autocorrelation properties (but ideal cross-correlation properties across codes - hence the orthogonal term), and finally a PN sequence which has excellent autocorrelation properties.
I'm not too familiar with this technology, but I can make some guesses how they might have gained speed improvements over UMTS would be:
- Very wideband - 100MHz vs 5MHz
- More precise QAM (Quadrature Amplitude Modulation) - UMTS allows upto QPSK (2 bits per symbol) or QAM-16 (4 bits per symbol). Perhaps this technology has extended this QAM-64 (6 bits per symbol).