Abstract- This paper characterizes interference in 802.11 Wireless Fidelity (Wi-Fi) systems that utilize Barker codes as spreading sequences. Particularly, detailed spectral analyses are performed. These studies result in exaxt power spetral densities (PSDs) for 1 Mbps and 2 Mbps signaling schemes that define their spectral signatures. Investigation of the leakage of interference power into adjacent 802.11 channels , which can be useful for the deployement of cognitive radios, is presented. The theoretical and computer simulation results for the Wi-Fi signal PSDs are verified through experimental measurements and emulation.

Abstract—This paper describes the high value of cognitive radio technology and characterizes the opportunity space in four distinct classes. A Chicago-based spectrum occupancy study illustrates the opportunity showing that 82.6% of the spectral capacity is unused. A set of spectral signatures is presented for common devices in the unlicensed frequency band with the view that this technique can be widely deployed across the spectrum. The limitations of current network simulation tools in an interference environment are identified. Finally, the paper briefly discusses several of the non-technology related issues that impact the deployment of cognitive radio techniques.

Abstract- Some devices not used for data communications radiate in the 2.4 GHz Wireless-Fidelity (Wi-Fi) band, thus causing unintentional interference that degrades the performance of IEEE 802.11 wireless systems. An analytical model for radio emissions from one of the most common unintentional interferers, the residential microwave oven, is developed from laboratory measurements. Simulation of the analytical model results in a power spectral density and spectrogram that are in good agreement with experimental data. An interference mitigation technique is proposed for the microwave oven emission.

Abstract- An investigation into the utilization of radio frequency spectrum for wireless communication is undertaken. The spectrum range falls in the range of 960-2500 MHz. Using test equipment, the electromagnetic energy was measured in several frequency bands over a period of several minutes on November 18, 2005, in downtown Chicago. The data was tabulated to estimate the occupnancy in each band. The issues affecting an estimate of spectrum utilization are discussed. We conclude that certain bands in the spectrum are heavily utilized and others which appear to be under utilized, particularly in the L-band above 1 GHz. There exist some opportunities for reallocation of spectrum, but there is a need for a better metric of spectrum utilization than spectrum occupancy which can lead to erronious conclusions as the the availability of free spectrum.

Client Channel Selection for Optimal Capacity in IEEE 802.11 Wireless Networks, John T. MacDonald, Udayan Das, Dennis A. Roberson, IEEE Conference on Dynamic Spectrum Access Networks, Dublin, Ireland, April 2007

Abstract—In wireless networks, clients are often presented with several access points to open a channel to the infrastructure network. A client can optimize its channel performance by selecting the access point that registers the lowest interference. The interference metric in wireless networks depends on several
factors including: the signal quality of the access point, the competing clients associated with the access point, and the impact of other adjacent networks in the same spectrum space. In this paper we demonstrate radio scene analysis in terms of the spatial geometry of networks, the spectrum occupancy in the band, and
the temporal load of multiple clients in the network, to evaluate the interference metric. We use this criterion to optimize the client channel capacity. A case study is evaluated in a congested 802.11 wireless local area network. This has implications for wireless network optimization and efficient spectrum utilization.

Abstract—Interference temperature is a measure of how well a radio operating with a particular protocol and modulation scheme can tolerate interference in its spectrum space. We consider this tolerance metric for the IEEE 802.11 protocol for
wireless networking. In experiments with off-the-shelf devices in the laboratory, we characterize the tolerance of the protocol to interference at various frequencies and power levels. Using the results of the experiment, we compute the interference temperature limit that the system will tolerate. We find that the interference temperature limit of the devices is much lower than the upper bound predicted by theory. The interference temperature limit of the protocols is not proportional to the data capacity, hence factors in the physical implementation play an important role in the robustness of the channel.

Abstract—This paper describes research on the development of an appropriate support structure for the analysis of the spectral environments to support the successful deployment and utilization of a cognitive radio system in specific high value spatial domains (e.g. urban centers). Specifically the paper discusses the opportunity to use a system of spectrum observatories augmented by wireless sensor networks to provide guidance to the discrete radios within a cognitive radio system on the most likely available spectral channels and bands. Toward this end, the paper separates and characterizes the spectral opportunity into four distinct classes. The paper also discusses four criteria for identifying and separating spectral bands into these classes.

Generic implementation requirements for a Spectrum Observatory are identified and illustrated with the embodiment at IIT’s Chicago campus. The paper discusses various academic and research opportunities afforded by the availability of a
Spectrum Observatory. Finally, the potential for the full deployment of a “spectrum traffic” system is discussed along with the requirement for continuing research efforts.