gical next step, given that 3G data services are popular there. However, by summer 2002, new developments, at least those reported in the news, ceased. In the United States, two 4G wireless initiatives were canceled. The standard for the multichannel multipoint distribution system (MMDS) is being reengineered. At the same time, Wi-Fi is showing some startling progress, even in mobile and cellular tests. As a result, the future of 4G may be slow or fast in coming, but it also may well not be based on any current CDMA telephony technology. The 4G concept includes some exciting possibilities, such as all-wireless backhaul and even mobile base stations mounted on trains or trucks. We do not mean base sta- tions that can be transported for emergency use or quick installation; we mean base stations on trains, providing active service to passengers and using a wireless uplink to fixed mobile switching centers even while the base station itself is in motion. Spec- ulation about the use of such service is even wilder, and we will not report it in an en- gineering text. 49.2.2 Spectrum allocation As we discussed earlier, North American spectrum allocation for cellular telephone ser- vice is already too small to meet demand easily and will be overcrowded before some relief arrives in 2008. This relief brings its own challenges, because engineers may face trouble developing cellular systems that operate well at 4 GHz. We also will have to reengineer our modeling tools, which make assumptions based on the transmission fre- quency. It is almost certain that more expensive multiband telephones will be needed. Meanwhile, Wi-Fi and 4G technologies are exploring uses of unlicensed spectrum. There is some thought of developing services at 40 or 60 GHz, well up in the microwave spectrum. The 60-GHz spectrum has a quality that is both an advantage and a disad- vantage for cellular services. Radiation is limited to about 1 mile due to absorption of this frequency by atmospheric oxygen. As a result, there would be less intercellular Do