When Sprint Nextel announced its decision to deploy a nationwide mobile WiMAX network in the US, much play was made of the fact that the carrier regarded this as the first step to 4G.
Whether mobile WiMAX lives up to that description seems doubtful at present, but it was another indicator of the growing interest in what might be termed technologies beyond 3G. There are various descriptions of these including 3.5G, 3.99G, Super-3G, etc.
Given that 3G itself is only just getting out of its starting blocks, it seems premature to be considering its successor. But there are good reasons for spending time and effort on developing post 3G solutions at this stage of the game. The most pressing is that 3G simply did not do what it said on the tin. The introduction of 3G was supposed to herald the arrival of true mobile broadband enabling users to surf the Internet, downloading files, films and music. The problem was that you could do all those things but only if you were prepared for a very long wait. Hence, the current high level of interest in High Speed Uplink/Download Packet Access (HSU/DPA), which was once famously described as being actually able to do what 3G said it was going to do.
HSxPA was always on the evolutionary roadmap, but its implementation has been brought forward to patch up the inadequacies of 3G. Whether it will be able to meet end-user expectations is another matter. For most users the benchmark is the bandwidth they get through their fixed-line broadband connection and that is typically between 2 and 8 Mbps.
The industry is promising that the first deployments of HSDPA will deliver 3.6 Mbps, and it is to be hoped that in real life this promise is fulfilled; the public is certainly getting fed-up with mobile industry hype.
Unfortunately, much of what is happening is largely like rearranging the deckchairs on the Titanic. Standards bodies and vendors are refining and extending an air interface that has severe limitations. The choice of W-CDMA as the air interface solution for 3G was always a compromise. Once the decision was made that 3G had to be backwardly compatible with GSM, then the choices became extremely limited. As an historical aside, it is interesting that when the wireless industry was sitting down in Paris in 1998 to decide what technology to go for, one of the options on the table was Orthogonal Frequency Division Multiplex (OFDM). The need for compatibility with GSM made OFDM an impossible choice so W-CDMA won the day. Now, OFDM is widely seen as the only way forward if the industry is to match the kind of data speeds that will be available in homes and offices in the future through technologies such as FTTH and ADSL2+.
A variant of OFDM is already being utilized in mobile WiMAX and hopefully will be the air interface of choice for 3G Long Term Evolution (LTE), the development project now being worked on by 3GPP and ETSI. There must be concern, given the existing huge GSM/3G subscriber base, and the investment already made in these technologies, that there will be pressure for 3G LTE also to be backwardly compatible to 3G. Such pressure must be resisted if the industry is going to be able to finally deliver the true mobile broadband experience that it has been threatening for so long.
Ian Channing Editor ([email protected])