Management of interference in wireless networks (original) (raw)

2006, International Journal of Network Management

Wireless communication has become pervasive. As our reliance on wireless devices and networks increases, the complexity of the management problem is rapidly increasing. One of the key pieces of this problem is the management of interference. As wireless applications grow in terms of number, penetration, duty cycle, and performance demands, spectrum becomes the limiting factor. Although the spectrum has been fully allocated, the conundrum is that in most places much of the spectrum goes unused most of the time. More efficient spectrum utilization is necessary to meet the increasing application demands. Interference is a common theme of both technical and regulatory efforts aimed at addressing this issue, yet interference is not well understood. This special issue is aimed at highlighting some of the challenges posed by interference as well as the opportunities available through interference management. A dramatic change is occurring in the management of the radio frequency (RF) spectrum. The previous 80 years have seen an explicit control of the waveforms used in specific RF bands. This waveform control was established either through the stipulation of the waveforms by the regulatory agency itself to enable interoperability, or by providing a license to a specific entity which would then determine the best waveform to implement, given the dictates of the license. In all cases, the stipulations of the regulatory agency were provided to prevent new waveforms from interfering with existing, and previously licensed waveforms and their related systems. Interference, as defined by the regulatory agency, was to be structurally avoided! This tended to work very well until the most desirable spectrum was fully allocated. Over the past 20 years, two new developments have occurred to improve utilization of this increasingly valuable spectrum, namely policy changes defining unlicensed bands, and allowing advanced spectrum overlay and underlay radio techniques. These changes have begun to significantly impact the spectrum. First, unlicensed spectrum has permitted waveforms to be implemented with minimal oversight. This has created an in-band interference phenomenon, most pronounced in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, due to a multiplicity of devices, waveforms, and power spectral densities. This complexity is compounded by device mobility, especially in ad hoc networking environments. The in-band interference is highly dependent upon transmitter-receiver relationships and is not well understood. As a result, there is limited regulatory interference protection for unlicensed devices. The onset of advanced signal processing and wideband RF devices has provided the basis for the second major development in spectrum utilization. These new capabilities in waveform flexibility (i.e., modulation and carrier frequency) gave rise to both software-defined radio (SDR) and cognitive radio. In addition, an entirely different approach to wireless communications has emerged utilizing sophisticated electronics and broadband pulse-based emissions called ultra-wideband (UWB). These new methods have not yet been widely deployed. When deployed they will create a more complex RF environment. As a result, receivers will be required to cope with both in-band and out-of-band transmitters. These new methods create more complex interference across a broad spectral range including both licensed and unlicensed bands. This in turn has given rise to the problem of interference, causing a severe