All digital phased arrays generate multiple beams concurrently through the digital beam forming technique, which features digital processing with multiple identical receiving/transmitting channels in RF or microwave frequencies. However, the performance of this process strongly depends on accurately matching the amplitude and phase of the channels, as mismatching is likely to degrade radar performance. In this paper, we present a method to calibrate receiving array by using NCO phase increasing algorithm, which simplifies array system by removing the external far-field calibration signals often needed in array systems. Both analysis and simulation results suggest that the proposed method attains better calibration performance than existing approaches, even with a low SNR input signal. Experiments also varify that the proposed calibration method is effective and achieves a desired radiation pattern. We can further boost calibration accuracy and reduce calibration time by programming NCO phase width and NCO phase resolution.

This paper presents the analysis on hidden node due to multiple transmission power level and its potential impact to system performance of White Space radio operating in the TV bands, a.k.a TV white space (TVWS). For this purpose, a generic interference model for determining the hidden node occurrence probability based on realistic physical (PHY) layer model is developed. Firstly, the generic hidden node interference model is constructed considering typical TVWS radio network deployment scenario. Emphasis is given on cases where the hidden node scenario involves multiple transmission power level. Secondly, the PHY layer design and channel propagation are modeled to analyze the realistic operating range of the TVWS radio. By combining the hidden node interference model and the PHY layer/propagation models, the realistic probability of hidden node occurrence is calculated. Finally, the performance degradation in the victim receiver due to interference generated by the potential hidden node is quantified. As a result, for urban environment, it is found that for networks consisting of devices with multiple transmit power level, the probability of hidden node occurrence is similar to that of networks consisting of devices with uni-transmit power level, provided that the interferer-victim separation distance in the former is 800 m farther apart. Furthermore, this number may increase to a maximum of 1.1 km in a suburban environment. Also, it is found that if the hidden node actually occurs, a co-channel interference (CCI) of -15 dB typically causes a degradation of 2 dB in the victim receiver.

In this paper, we present a coexistence protocol design for a coexistence information service to provide coexistence solutions among dissimilar or independently operated autonomous decision-making networks in a wireless communication environment over, specifically but not limited to, TV white space (TVWS) frequency bands. The designed coexistence protocol for the coexistence information service has three main functionalities: (1) To collect basic information of subscribed TVWS networks; (2) To support generating neighbor lists for the TVWS networks based on the geography information and/or propagation parameters; (3) To provide necessary information for TVWS networks to make coexistence decisions. Both theoretical analysis and simulation results show that the designed coexistence information service ensures harmonious communications among dissimilar networks and is able to achieve coexistence over an area with the limited number of available channels in white space.

This paper proposes a sensing method for TV signals of DVB-T standard to realize effective TV White Space (TVWS) Communication. In the TVWS technology trial organized by the Infocomm Development Authority (iDA) of Singapore, with regard to the sensing level and sensing time, detecting DVB-T signal at the level of -120 dBm over an 8 MHz channel with a sensing time below 1 second is required. To fulfill such a strict sensing requirement, we propose a smart sensing method which combines feature detection and energy detection (CFED), and is also characterized by using dynamic threshold selection (DTS) based on a threshold table to improve sensing robustness to noise uncertainty. The DTS based CFED (DTS-CFED) is evaluated by computer simulations and is also implemented into a hardware sensing prototype. The results show that the DTS-CFED achieves a detection probability above 0.9 for a target false alarm probability of 0.1 for DVB-T signals at the level of -120 dBm over an 8 MHz channel with the sensing time equals to 0.1 second.

This paper proposes an enhanced feature detection method for the OFDM signals of digital TV (DTV) standards, namely Digital Video Broadcasting-Terrestrial (DVB-T) and Integrated Services Digital Broadcasting-Terrestrial (ISDB-T). The proposed method exploits property of time-domain sliding correlation results of DTV signals with the pilots that are inserted into OFDM symbols. Some correlation outputs are much larger than the remaining outputs and are called correlation peaks here, and, the distance between their positions in the correlation output sequence keep constant regardless of the received DTV timings. The proposed method then derives sensing test statistic with improved SNR by aggregating the correlation peaks based on their positions. Performance of the proposed method is evaluated by both computer simulation and hardware implementation. Simulation results for DVB-T detection verify that compared to the optimal conventional sensing method, the proposed method achieves superior sensing performance. It reduces sampling time by about 25% for the same sensing performance while increasing computational complexity by around 0.0001%. Hardware performance further verifies that the proposed method is able to accurately detect ISDB-T at the low SNR of -14.5 dB by employing 8 OFDM symbol durations of samples.

This paper introduces a unified method of spectrum sensing for all existing analog television (TV) signals including NTSC, PAL and SECAM. We propose a correlation based method (CBM) with a single reference signal for sensing any analog TV signals. In addition we also propose an improved energy detection method. The CBM approach has been implemented in a hardware prototype specially designed for participating in Singapore TV white space (WS) test trial conducted by Infocomm Development Authority (IDA) of the Singapore government. Analytical and simulation results of the CBM method will be presented in the paper, as well as hardware testing results for sensing various analog TV signals. Both AWGN and fading channels will be considered. It is shown that the theoretical results closely match with those from simulations. Sensing performance of the hardware prototype will also be presented in fading environment by using a fading simulator. We present performance of the proposed techniques in terms of probability of false alarm, probability of detection, sensing time etc. We also present a comparative study of the various techniques.

Some key challenges remain to be overcome before spectrum sensing can be widely used to identify spectrum opportunities in the TV bands. To fulfill the strict sensing requirement specified by FCC, a comprehensive sensing algorithm, which produces high SNR gain and maintains sensing robustness under complex noise conditions, needs to be implemented. In addition, carefully designed physical features and improvement on cost performance ratio are also essential if a prototype is to be commercialized. To the best of our knowledge, no success has ever been announced in developing a sensing prototype that fulfills both FCC sensing requirement and the above mentioned features. In this paper, we introduce a recently developed sensing prototype for Japanese digital TV signals of ISDB-T. The prototype operates in the Japanese UHF TV band of 470-770MHz and can reliably identify presence/absence of an ISDB-T signal at the level of -114dBm in a 6MHz channel. Moreover, it has constrained size and weight, and is capable of accurately measuring power of an ISDB-T signal at an extremely low level. Efforts on reducing cost have also been made by avoiding the use of electronic components/devices of high price. Both laboratory and field tests are performed to evaluate its sensing performance and power measurement capability. In the laboratory test, sensing performance under conditions of adjacent channel interference and frequency offset, and power measurement accuracy, are checked. In field tests, the prototype is attached in a vehicle and is checked for its capability to identify the presence of purposely broadcasted ISDB-T signals at some fixed locations and also during movement of the vehicle.