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- 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.

Abstract- The MicroWave Oven (MWO) is a commonly available appliance that does not transmit data, but still radiates signals in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band. The MWO thus acts as an unintentional interferer for IEEE 802.11 Wireless Fidelity (Wi-Fi) communication signals. An analytic model of the MWO signal is developed and studied in this paper. Based on this model, an interference mitigation technique is developed that incorporates cognitive radio paradigms allowing Wi-Fi devices to reliably transmit information
while a residential MWO is operating. This technique is applied in the experimental case where Barker spread Wi-Fi signals carry data in the presence of MWO
emissions. Bit error rate is evaluated to provide a performance metric for the mitigation technique.

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.