John Grosspietsch

Geo-Location Database Techniques for Incumbent Protection in the TV White Space

The opening of the television bands in the United States presents an exciting opportunity for secondary spectrum utilization. Protecting licensed broadcast television viewers from harmful interference due to secondary spectrum usage is critical to the successful deployment of TV white space devices. A wide variety of secondary system operating scenarios must be considered in any potential interference analysis, as described below. Several different types of licensed television transmitters currently exist in the TV bands, along with secondary licensed services, such as wireless microphones. All licensed services must be adequately protected from harmful interference, which can readily and reliably be achieved with the described geo-location database methods. Specific implementation details of geo-location databases are discussed, including several complexity reduction techniques. Geo-location database techniques are also shown to more efficiently utilize available spectrum than other spectrum access techniques.

Energy Detection Using Estimated Noise Variance for Spectrum Sensing in Cognitive Radio Networks

In this paper, we analyze the performance of spectrum sensing based on energy detection. We do not assume the exact noise variance is known a priori. Instead, an estimated noise variance is used to calculate the threshold used in the spectrum sensing based on energy detection. We propose a new analytical model to evaluate the statistical performance of the energy detection. We claim some characteristics of this model, and analyze how these characteristics affect the performance of spectrum sensing. The analytical results are verified through numerical examples and simulations. Through these examples, we demonstrate the effectiveness of our analytical model: we show how it can be used to set the appropriate threshold such that more spectrum sharing can be facilitated, especially when combined with cooperative spectrum sensing method.

Spectrum Sensing Using Cyclostationary Spectrum Density for Cognitive Radios

Cognitive radios (CR) are proposed to alleviate the spectrum scarcity problems facing wireless service providers. In US, the FCC is considering spectrum regulation changes by allowing unlicensed operation in the TV broadcast bands provided that no harmful interference is caused. In this paper, we discuss the spectrum sensing aspects of cognitive radios. We particularly focus on the detection method based on cyclostationary spectrum density (CSD) estimation. The advantage of CSD is its relative robustness against noise uncertainty compared with energy detection methods. CSD estimation is a two dimensional transformation; therefore it is computationally complex. We transform the algorithm from the two dimensional space to a one dimensional case, therefore making the real time implementation more feasible. Through analysis and simulation, we identify the features with highest SNR to be used for CSD based detection. Based on the simulation results, we further propose dedicated hardware implementation architecture for CSD estimation using field programmable logic array (FPGA). Our implementation can achieve greater than 90% detection probability on BPSK signals with SNR of -18 dB, when the probability of false alarm is less than 10%.

A carry-free 54b/spl times/54b multiplier using equivalent bit conversion algorithm

An equivalent bit conversion algorithm (EBCA) is proposed to eliminate the need for final carry propagation in the redundant binary (RB) to normal binary (NB) conversion step for RB multiplication. The multiplication process helps with the carry-free conversion step by eliminating certain combinations of RB product. When the EBCA is applied, conventional power-consuming carry-propagating adders are replaced by simple, minimum-sized carry-free converters, and the entire multiplication process can be made free of carry propagation from input to output. The method employed in this work reduces 40% of the total power and 30% of the total multiplication time in the final adder stage of traditional multipliers. The prototype fabricated in 0.35-/spl mu/m CMOS demonstrates that the 54 b/spl times/54 b multiplier consumes only 53.4 mW at 3.3 V for 74-MHz operation.

An FPGA Based All-Digital Transmitter with Radio Frequency Output for Software Defined Radio

This paper presents the architecture and implementation of an all-digital transmitter with radio frequency output targeting an FPGA device. FPGA devices have been widely adopted in the applications of digital signal processing (DSP) and digital communication. They are typically well suited for the evolving technology of software defined radios (SDR) due to their reconfigurability and programmability. However, FPGA devices are mostly used to implement digital baseband and intermediate frequency (IF) functionalities. Therefore, significant analog and RF components are still needed to fulfill the radio communication requirements. The all-digital transmitter presented in this paper directly synthesizes RF signal in the digital domain, therefore eliminates the need for most of the analog and RF components. The all-digital transmitter consists of one QAM modulator and one RF pulse width modulator (RFPWM). The binary output waveform from RFPWM is centered at 800MHz with 64QAM signaling format. The entire transmitter is implemented using Xilinx Virtex2pro device with on chip multi-gigabit transceiver (MGT). The adjacent channel leakage ratio (ACLR) measured in the 20 MHz passband is 45dB, and the measured error vector magnitude (EVM) is less than 1%. Our work extends the digital implementation of communication applications on an FPGA platform to radio frequency, therefore making a significant evolution towards an ideal SDR

Digital Modulation Classification using Temporal Waveform Features for Cognitive Radios

This paper presents a novel digital modulation classification system for cognitive radios using only temporal waveform features. Temporal features extraction is desirable for cognitive radios because it is easy to implement them compared to the extraction of other features types such as spectral features. The features used for classification are extracted from instantaneous amplitude and phase of the digitized intermediate frequency signal. A hierarchical approach is used to first make separations into intermediate subclasses, where some of the subclasses can consist of more than one modulation type. Then a second classifier is used to discriminate between higher order modulation schemes using additional features. Compared to alternative methods, the simulation results show the overall effectiveness of the proposed method in the presence of noise, especially for higher order digital modulations. Particularly, the overall success rate for the classification of seven common digital modulation schemes exceeds 95% at signal to noise ratios ranging from 10 dB to 80 dB.

Comments on "A carry-free 54 b/spl times/54 b multiplier using equivalent bit conversion algorithm"

For original paper see ibid., vol. 36, no. 10, p. 1538-1545 (Oct. 2001). In the aforementioned paper by Kim et al., a multiplier is presented which produces the result in radix-2 signed-digit representation. It is claimed that this representation can be converted into conventional magnitude representation by an algorithm which has no carry propagation. To the commenters this algorithm seems incorrect. The critical situation is a string which consists of a sequence of zeros followed by a -1; in such a case a carry is needed and the algorithm proposed is deemed incorrect. Consequently, it is pointed out that the proposed algorithm produces a correct multiplication result in conventional magnitude representation only if the signed-digit string does not have a sequence of 0s followed by a -1. The commenters show a multiplication example using the proposed conversion algorithm in which this situation occurs.