Spectrum efficiency and network planning [message from the Editor-in-Chief]

2 ith the scarce availability of wireless spectrum in commercial networks, and the increase in number of users and their corresponding traffic volume, one of the most important challenges for wireless system engineers is to have high spectrum efficiency in order to accommodate as many users as possible in a limited frequency spectrum range. It is also important to plan the network carefully so that network resources can be used as optimally as possible while making network operation highly reliable. The spectrum limitation has redirected wireless systems toward the use of unlicensed spectrum and cooperative networks of heterogeneous wireless systems. So the spectrum efficiency and network planning has found a new direction in handling simultaneous use of licensed and unlicensed frequencies as well as dealing with cooperation of heterogeneous protocols at higher layers for mobility and traffic management, among other issues. Different from homogeneous networks, in a heterogeneous environment interference cancellation, multiple access optimizations, handoff control, and other technical issues in network and spectrum planning are becoming very complicated. In heterogeneous networks not only should traditional planning and resource allocation be considered, but also interaction among protocols of different natures and co-interference due to the existence of multiple systems must be dealt with. Consideration of a wide range of parameters and their unexpected mutual interactions could be a great problem to tackle in nextgeneration wireless networks. This issue of IEEE Wireless Communications starts with the special topic of 3G/4G/WLAN/WMAN Planning and ABBAS JAMALIPOUR ME S S A G E FROM T H E ED I T O RI N -CH I E F