The past few years have seen an explosion of new wireless transmission technologies: infrared transmission within rooms, ultra-low-power transmission e!ective over a few feet, and moreingenious coding techniques that give higher bandwidth. A mature mobile wireless technology holds out a lot of opportunities. These range from hand-held devices that support personal videoconferencing to self-con"guring desktop networks that use low-power wireless to identify and interconnect components. Moreover, the improvements in wireless have led to expectations that all of the services of wireline networks, including high-bandwidth multimedia, should be available in a wireless environment as well. Meeting those expectations will require a good deal of work over the next few years. Of course, rapid growth is likely as the price of the technology drops, standards are adopted, and people become accustomed to wireless solutions. Some predict a wireless market of around $2 billion# by the year 2001.
Novel research ideas as well as e$cient standardization e!orts are needed to enable such access techniques in broadband access architectures for mobile applications. In fact, emerging standards developments are taking the lead in this direction. Such emerging standards will no doubt enhance the chances of creating a generalized architecture for the newly born mobile broadband network industry. A synergy is therefore needed between current research and the ongoing standardization e!orts.
Four articles in the area of wireless access techniques in broadband networks in this special issue provide an insight into some issues in the "eld. They cover a range of topics that help readers in protocol performance, adaptive channel management schemes as well as guaranteed quality of service for wireless systems.
The "rst article by Znati and Kim presents a new class of adaptive channel management schemes. The objective is to provide a &better e!ort' quality of service (QoS) to new calls that risk being blocked when trying to minimize the hando! failure probability. Two di!erent schemes are discussed, the randomized Channel Assignment (rCA) scheme and the balanced Channel Assignment (bCA) scheme. The authors show that the latter approach alleviates the channel assignment scheme from a tight dependency on the underlying tra$c model and re#ects the dynamically changing load within a cell. Performance and comparison of both schemes to their counterparts are presented.
The second article by Chang and Chen proposes a generalized processor sharing algorithm for guaranteed QoS wireless access. The methodology is to serve constant-bit rate (CBR), variablebit rate (VBR), as well as available-bit rate (ABR) tra$c. This can also operate in a multiaccess channel with long propagation delay. The authors then suggest related important issues, such as a simple link control mechanism for CBR and VBR over unreliable channels.