<OFDM offers better spectral efficiency and interference immunity. First consider the interference within a cell. Clearly, in any given symbol period, different mobiles in a cell use different tones. From the orthogonality discussed previously, there is no interference between mobiles within a cell. Recall that CDMA is not orthogonal. This property gives flash-OFDM a capacity of almost three times that of CDMA, and provides additional advantages of supporting bursty data traffic. >
Thanks for posting that Kent. Okay, capacity is 3x not 30% more than CDMA. That's the same advantage that CDMA has over GSM and GSM's sales advantage is going to have lasted for a whole decade! A decade during which the prices of minutes were very high and sensitivity to minute price was consequently high.
If we check QUALCOMM's white paper on data, qualcomm.com we see data in 1xEV is expected to cost 2c a megabyte. That is just the network costs and depreciation, not spectrum or marketing costs, which will make it much higher.
If we assume that OFDM gizzards would be similarly expensive per megabyte, we need to calculate the savings on spectrum afforded by OFDM. Maybe I've got the wrong end of the stick, but my understanding is that as with GSM versus CDMA, the cost of the electronic gizzards is much the same, but the capacity, ie the spectrum efficiency, is 3x as good for OFDM.
However, WackyWireless rules dictate that we could reduce those costs by a factor of 3 because those costs make assumptions about network loading, and those assumptions are based on typical loadings, which are deliberately kept at a low average to avoid too many busy signals, which make subscribers grumpy.
The QUALCOMM white paper says: <The cost per megabyte in Table 2 reflects the network operating costs and depreciation on capital investment required to design a network to support a given busy hour traffic load. For comparison purposes, we evaluate the cost to deliver data traffic in low, medium, and high data traffic density regions given 5 MHz of spectrum available for data traffic. We assume 15% of total traffic demand occurs in the busy hour.
Based on the busy hour traffic demand, we optimized the network configuration for each technology...blah, blah, blah...>
So, we are really dealing with network costs of less than 1c per megabyte for 1xEV and 0.3c a megabyte for OFDM.
0.7c a megabyte is a bit of Gaussian noise in service provider charges. I get 400 megabytes a month included with my ADSL monthly fee. I don't use it all and I click on anything which takes my fancy. BUT, I do instruct my spendthrift offspring to NOT download MP3 music [though a bit of it is okay]. 400 megabytes a month = $4 a month with CDMA or, I could save $3 a month and go with OFDM. But that assumes I'd use the whole 400 megabytes.
With a mobile device, there is no way I'd get anywhere near 400 megabytes a month without gobbling multimedia. Most mobile applications are transient requirements which don't involve multimedia needs. Sometimes they will, so the facility will be needed, but usually not, so the total demand will be only part of a person's total demand. Most usage will still be back at base, with a cup of tea at hand, a big screen, a big keyboard, a heater and a comfy chair.
But $3 a month is still $36 a year and I might as well have it! But I'll not be in too much of a hurry to trade in my CDMA Anita[TM] device for a 5G version with OFDM included to save $36 and get data even faster. My guess is that somewhere around 2008 I'll be wanting an OFDM version.
That's based on the fact that it has taken from 1991 to 2001 for CDMA to wend its way from San Diego to Auckland, despite secret signals from my QCP820 back to Q! HQ 3 years ago. We are still full of analogue and GSM signals here and that's despite the high cost of voice calls where the savings of CDMA are very large.
Reducing costs by a factor of 3 matters a LOT at $1 a minute, but not much at 10c a minute.
Back to the spectrum savings. $500 per person purchase price seems to be about right in rich, densely populated countries. That would require subscriber payments of $100 per year or $8 a month [depending on how long the service provider's rights to the spectrum last]. If OFDM can cut that to $3 a month, that's good too, but much of that spectrum will be for voice, so the saving isn't that great - CDMA seems okay for voice.
But in Kiwiland, all the 3G spectrum and a lot of 2G spectrum too, sold for a total of about US$60 million. That's $US20 per kiwi. We've got spectrum to burn!! A lot of countries are like that.
So yes, there are significant savings from using OFDM. People who want a lot of data will be clamouring for it. Most of us will struggle by on cdma2000 1xEV until 2010 [or VW40 if they ever get it running].
We are also bumping up against another issue, which is brain capacity. I don't know about you others, but mine is right up to the limits. I don't have the capacity to absorb OFDM signals full of data.
So, OFDM is excellent, just as CDMA is compared with GSM. But subscribers won't flock by the billion for a factor of three capacity improvement, just as they haven't for CDMA from GSM.
I hope that makes sense, because it's how I'm betting my money. When OFDM is timely, I'm sure QUALCOMM [Spinco] will buy a licence and incorporate OFDM in their ASICs for Anita [TM] 5G devices.
Mqurice
PS: This post will have blocked a few brains too!! |
