TECH TALK: Next-Generation Networks: 3G and 4G

WiMaxs opponents (led primarily by Qualcomm) point to 3G as the ultimate solution for high-speed wireless networking. Technologies like EV-DO are already offering hundreds of kilobits per second for people on the move. 3G already has been deployed in some European and Asian countries. Discussion has also started in India about the allocation of spectrum for 3G services to the existing mobile operators.

Here is a tutorial from Russell Beattie (Dec 2003) on the evolution to 3G technologies:

First, here’s the deal about CDMA vs. GSM. The way that GSM works is really an extension of the old TDMA analog system. GSM adds digital technology to divide up the frequency allotments into 8 channels, which are then time shared across those channels. CDMA on the other hand uses the same piece of spectrum and separates the calls by encoding each one uniquely, allowing your phone to disregard other transmissions on the same frequency.

Okay, so the basic CDMA that most people uses right now is now called “cdmaOne”. The next generation is the move to “CDMA2000 1x RTT.” This is what Verizon is spending all their money buying. The 1x stands for “single channel” and the RTT (which Qualcomm doesn’t like to use any more, though it was written in the article that way) stands for “radio transmission technology.” Even though the speeds of this new standard are really what has been considered 2.5G, the technology is the base for higher speeds and has been deemed 3G by marketing higher ups, so you’ll see it referred to that way.

The 1x is the important part: CDMA2000 uses from one to three 1.25 MHz carriers. This first rev of CDMA2000 uses just one of those three. cdmaOne already uses this frequency, which is why CDMA2000 is considered “backwards compatible” and I guess what the CDMA2000 standard adds is more efficient use of that spectrum. The next steps in CDMA are then CDMA2000 1xEv which uses a second channel (1xEv phase one uses the second channel only for data only: “1xEv-DO” and phase two uses both channels together “2x”), and 3x which uses all three channels as a single 3.75Mhz carrier. You can see how adding channels and infrastructure will naturally cause data bandwidth to go up, though, it’s important to note that unlike the GSM route, this allocation seems backwards compatible and isn’t just for data, but also for voice calls as well.

The GSM path goes to GPRS next, which can dedicate one or more of the channels in the GSM spectrum to packet data only. It works, but has lots of provisioning problems and bandwidth constraints. I’m not sure about this, but it seems to me that if you’re enabling GPRS, you’re cutting off at least one channel, and this must affect the GSM voice service. After GRPS is EDGE which works in a similar way, but uses a newer “modulation scheme” which allows higher data rates. I have no idea what a “modulation scheme” is, actually, but it’s easy to get the idea: same general functionality, but with faster moving bits.

After this, however, the GSM guys have to scratch all that equipment and move to WCDMA, which is a version of the CDMA technology and divides up calls by uniquely encoding them.

So that’s the general idea. The pairs are roughly cdmaOne/GSM, CDMA2000 1x/GPRS, CDMA 1xEv/EDGE, CDMA2000 3x/WCDMA .

Wikipedia adds: The International Telecommunication Union (ITU) has defined the demands for third generation mobile networks with the IMT-2000 standard. An organisation called 3GPP has continued that work by defining a mobile system that fulfils the IMT-2000 standard. This system is called Universal Mobile Telecommunications System (UMTS) The UMTS system is based on layered services, unlike GSM. On the top there is the services layer, which will give advantages like fast deployment of services and centralized location. In the middle there is the control layer, which will help upgrading procedures and allow the capacity of the network to be dynamically allocated. On the bottom is the connectivity layer where any transmission technology can be used and the voice will transfer over ATM/AAL2 or IP/RTP.

Tomorrow: 3G and 4G (continued)

TECH TALK Next-Generation Networks+T

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Rajesh Jain

An Entrepreneur based in Mumbai, India.