An ultra-wideband (UWB) system usually occupies a large frequency band, which may overlap with the spectrum of a narrow band system. The latter is referred to as a victim system. To effectively use frequency, a UWB system may create a notch in its spectrum to accommodate the victim signal for interference avoidance. Parameters of the notch such as the depth and the width of a notch need to be decided in accordance to victim systems. In this paper, we investigate the effective UWB avoidance by examining the suitable notch based on experimental evaluation. In the experiments, 3GPP LTE, Mobile WiMAX, as well as an IMT Advanced Test-bed are respectively employed to represent different types of victim systems. The UWB system is set up based on WiMedia specifications and operates at the UWB low band of 3.1–4.8 GHz. A notch is fabricated by nullifying the related subcarriers of the UWB signal. In addition, a filter or a window function is formed and employed to further smooth the notch. Bit error rate (BER) or packet error rate (PER) performances of victim systems are measured and used to evaluate the UWB interference. Our results show that when a notch is properly formed, the interference level introduced by UWB can be below the permitted level by regulations.

The paper presents capability of signal detection for realizing coexistence between broadband wireless access (BWA) systems and ultra wideband (UWB) devices. The capability is experimentally evaluated for baseband signals of downlink (DL) in both mobile WiMAX and 3GPP LTE. An UWB receiver based on fast Fourier transform (FFT) compliant with MB-OFDM standard is implemented as a detector of the BWA signals. The capability is evaluated in terms of elapsed time required to achieve signal detection with probability of 99% by the implemented FFT-based UWB receiver at different conditions of the receiver. Decisions on the signal detection are made by the simplest method which is by setting a threshold which is determined by noise floor of the receiver as reference. The experiments have been conducted though baseband signals for both AWGN and multipath fading channels without any synchronization between the DL signals and UWB receiver. In AWGN environment, results show that the elapsed time depends on the duty ratio of the DL signal to be detected, however, the correlation between the required time and duty ratio is not linear since their envelopes of the DL signals are not constant. In multipath fading environments based on channel models commonly employed as mobile radio environments, the required time for the signal detection becomes as 17 times longer than that in AWGN due to its signal attenuation. For robust signal detection in multipath fading environments, it has been revealed that the number of quantization bits at ADC is crucial through the experiments.