To land_cruisin:
First of all, I have to make it clear that I'm not investing in MCOM. Nor did I spend time in studying their technology therefore I'm not qualified to make any comments regarding their claims in the white paper. My friend Caxton pointed me to your message and as he said he doesn't really care about MCOM's claim, just my opinion about your assessments about HDR. So please treat this post as a discussion regarding HDR and nothing else. I may or may not spend more time into MCDN in the future however that would be a different issue.
Now I would like to comment on some of the points you made in that post.
1) In short, you may be receiving 144kbps from a CDMA tower, but if you were to do a bandwidth test, you may find that you are only receiving 56kbps of actual internet data, which is all you care about.
Absolutely, how ever I think you should know that internet traffic can be very different from different applications such as FTP, Web surfing, Email, voice/video streaming etc. They all have different traffic characteristic, QoS, overhead etc. Therefore I have never seen anybody, I mean anybody ever try to give their customers what should be the real data throughput other than the Raw data speed. Because simply put, that's impossible to do.
2) There are time gaps between your packets that when accounted for, will dilute your sustained data rates. By quoting burst speeds, you can pretend that those periods of DEAD TIME, where no data is passed, don’t exist. In the real world, quoting burst speeds inflate your data rates by 15% or more..
And that's the nature of internet data traffic, which is bursty all the time. HDR's claim of peak rate quote is rather about what's the max speed you can get, which is also a very important parameter of your system.
3) Theoretical numbers mean nothing because the ideal conditions that they assume never exist. Theoretically, a 1.25MHz CDMA channel can support 64 voice users. In reality, it often tops out at 20 users. Limitations of the electronics as well as adverse RF conditions stemming from multipath, a noise floor, and fading will drag down your numbers.
Again good point although I'm not sure about that 20 users tops out part. One thing I would like to point out is that it's all about statistics, which itself is a meassurement of what would happen in the real world in most of the cases. Throughout that white paper and your post, worst cases are often brought up to attack HDR, which, I would say is another way to confuse people. Although I would say the performence of a wireless system is really depends on the radio environment. No doubt about it.
4)QCOM tries to insinuate otherwise by saying that there should be a 50-100% increase in voice capacity with 1X but this is pretty sketchy based on their reasoning and even the CTO of AT&T Wireless has questioned this. I think Moore’s Law has spoiled people into thinking every technology will increase in performance exponentially. Unfortunately, increasing spectral efficiency is much harder than increasing the number of transistors on a computer chip.
The spectral efficiency is improved due to better encoding, power control, modulation etc. Remember CDMA is a game of power, with all multiple methods you lower the interferences between users therefore the increased capacity. Keep in mind that CDMA itself is still in its evolving stage, cdmaOne is far from perfecting the CDMA technology therefore there are still a lot of rooms for improvement.
As for AT&T's comment. I think you, as obviously putting your time into CDMA study, should know how much of credibility they have as far as CDMA concerned:-)
5)Your comments about 1x etc(pretty long comments). Again you tend to use worst case scenario to conclude its capacity and speed etc, please see my point 3) and 4). However in recent trial with SprintPCS and Samsung. Qcom demonstrated 35 voice calls and 144Kbps simultaneously. Also please keep in mind that this is still the early phase of 1x, which is not fully implementing some of the features in CDMA2000 such as number of Supplement channels and certain modulation scheme. Therefore I think the capacity and throughput will more than likely go up in the future.
6)About your HDR comments(also a little longer than I want to copy here). First of all, that 600Kbps is NOT Lab data but rather OTA number in a very real radio environment(some even very tough)with very realistic mobile user environment. The theoritical 2.4Mbps max speed is no doubt the peak and max rate. Also keep in mind that it's only about one sector for a tower. As for your comments about users take roud robin etc. As you and I both know, we use throughput to describe internet traffic rather than individual user. This is the case when you are talking about a LAN, a router, or even a computer bus. There got to be some kind of multiplexing somewhere. And I think your own "DEAD TIME" example should come pretty handy here. As for how HDR get off the ground, Korea and Japan have clear objective in when they will start the service. The networks upgrade can be real cost effective, it really depends on the market and capacity demand. Oh and another thing, HDR just got standardized, which is why it picked up great momentum lately(such as Nortel fully engagement).
6) Bottom line, MCOM’s quote of 128kbps uses none of the “cheats” mentioned above and the latencies are comparable to that of DSL or cable and far better than the latencies you would see with dial up, 3G, HDR, or any other voice based technologies. Instead of “killing” Ricochet, I’d bet that 3G and HDR will bring it more respect when people see how poorly the competing technologies really perform when/if they show up.
As I said since I'm not familiar with MCOM technology so I'm not qualified to comment on that 128kbps is really all- time-bad-or-good-environment-no-matter-how-many-users-and-after-raw-data.
Oh and BTW, HDR is not voice technology, and that's why we have HDR. |
