A low-complexity feed-forward I/Q imbalance compensation algorithm

This paper presents a low-complexity adaptive feed- forward I/Q imbalance compensation algorithm. The feed-forward so- lution has guaranteed stability. Due to its blind nature the algorithm is easily incorporated into an existing receiver design. The algorithm uses three estimators to obtain the necessary parameters for the I/Q imbal- ance compensation structure. The algorithm complexity is low due to 1-bit quantization in the estimators. Simulations show that the compen- sation algorithm is able to attain an image-rejection ratio (IRR) of up to 65 [dB] under various imbalance conditions

Extracting cyclostationary features from single carrier signals

This paper contributes to the discussion about the usefulness of cyclostationary feature detection for the purpose of cognitive radio. From a simple but realistic radio signal model and an ideal channel, the power spectral density of the random signal component is derived, and compared with the periodical component that can be retrieved from the signal with a nonlinear operation

Coherence Filtering to Enhance the Mandibular Canal in Cone-Beam CT data

Segmenting the mandibular canal from cone beam CT data, is difficult due to low edge contrast and high image noise. We introduce 3D coherence filtering as a method to close the interrupted edges and denoise the structure of the mandibular canal. Coherence Filtering is an anisotropic non-linear tensor based diffusion algorithm for edge enhancing image filtering. We test different numerical schemes of the tensor diffusion equation, non-negative, standard discretization and also a rotation invariant scheme of Weickert [1]. Only the\ud scheme of Weickert did not blur the high spherical images frequencies on the image diagonals of our test volume. Thus this scheme is chosen to enhance the small curved mandibular canal structure. The best choice of the diffusion equation parameters c1 and c2, depends on the image noise. Coherence filtering on the CBCT-scan works well, the noise in the mandibular canal is gone and the edges are connected. Because the algorithm is tensor based it cannot deal with edge joints or splits, thus is less fit for more complex image structures

A Software-Defined Radio Simulation Method using Observer Patterns

A problem with object-oriented simulation models is that internal model states are hidden and cannot be monitored easily. Object-oriented models are essentially black-box models. This article describes a method to expose the internal states of an object-oriented simulation model. Exposure of the states is achieved though application of the Observer software pattern in the form of data sources. Data sources can be connected to a data sink which then receives data from the sources. Connections between data sources and sinks are made though a broker. The globally accessible broker holds information on the available data sources. Some implementation details of a simulation framework\ud based around the method are discussed. The framework is tested using a small simulation example on I/Q imbalance. Although the focus is on software-defined radio and communication systems, the concepts presented here can also be applied to other types of object-oriented simulation

Quantization Effects in OFDM Systems

The advantage of using orthogonal frequency division multiplexing (OFDM) over the single-carrier modulation is its ability to mitigate interference and fading without complex equalization filters in the receiver. OFDM systems have a high peak-to-average ratio (PAPR) which results in a high requirement for the resolution of AD converters. High-resolution AD converters are therefore widely used in OFDM receivers. However, the power consumption is proportional to the resolution of the AD converters. In this paper we investigate the quantization effects in OFDM systems. Quantization is a nonlinear function which happens in the time domain, so the quantization effect in the frequency domain (important for OFDM) is not simple. Here, we derive a model for the quantization effect in the frequency domain. Further, we investigate whether it is possible to apply low-resolution AD converters in reliable communications based on OFDM. Simulations with an AWGN channel reveal that the proposed model predicts the quantization noise in the frequency domain very well. Difference in $\sigma_\mathrm{q}^2$ between simulation outcomes and our model is less than 0.6\%. Also, simulations show that 5-bits AD resolution is required for OFDM communication over an AWGN channel

Reliable Download Delivery in a Terrestrial DAB Network

Reliable file transfer is important in broadcast networks. In this paper, we have investigated if it is useful to extend the DAB standard with Fountain codes. To evaluate this, results from measurements in a live Single Frequency Network (SFN) were used. Our results show that the existing error correction algorithms provide already reliable file delivery, so there is no need to extend the DAB standard

Modulation-Index Estimation in a Combined CPM/OFDM Receiver

In this paper we develop a blind modulation-index estimator for\ud a combined CPM/OFDMReceiver. The performance of the estimator\ud in an AWGN channel is assessed by simulation and analysis\ud and its suitability for our receiver is established

A (Simplified) Bluetooth Maximum a Posteriori Probability (Map) Receiver

In our software-defined radio project, we aim at combining two standards luetooth and HIPERLAN/2. The HIPERLAN/2 receiver requires more computational power than Bluetooth. We choose to use this computational power also for Bluetooth and look for more advanced demodulation algorithms such as a maximum a posteriori probability (MAP) receiver. The paper discusses a simplified MAP receiver for Bluetooth GFSK signals. Laurent decomposition provides an orthogonal vector space for the MAP receiver. As the first Laurent waveform contains the most energy, we have used only this waveform for our (simplified) MAP receiver. This receiver requires a E/sub b//N/sub 0/ of about 11 dB for a BER of 10/sup -3/, required by the Bluetooth standard. This value is about 6 dB better than single bit demodulators. This performance is only met if the receiver has exact knowledge of the modulation index

Three-dimensional reconstruction of stenosed coronary artery segments with assessment of the flow impedance

In this paper preliminary results of a study about the diagnostic benefits of 3D visualization and quantitation of stenosed coronary artery segments are presented. As is well known, even biplane angiographic images do not provide enough information for binary reconstruction. Therefore,a priori information about the slice to be reconstructed must be incorporated into the reconstruction algorithm. One approach is to assume a circular cross-section of the coronary artery. Hence, the diameter is estimated from the contours of the vessels in both projections. Another approach is to search for a solution of the reconstruction problem close to the previously reconstructed adjacent slice. In this paper we follow the first method based on contour information. The reconstructed coronary segment is visualized in three dimensions. Based on the obtained geometry of the obstruction the pertinent blood flow impedance is estimated on the basis of fluid dynamic principles. The results of applying the reconstruction algorithms to clinical coronary biplane exposures are presented with an indication of the assessed flow impedance

Undetected error probability for data services in a terrestrial DAB single frequency network

DAB (Digital Audio Broadcasting) is the European successor of FM radio. Besides audio services, other services such as traffic information can be provided.\ud An important parameter for data services is the probability of non-recognized or undetected errors in the system. To derive this probability, we propose a bound for the undetected error probability in CRC codes. In addition, results from measurements of a Single Frequency Network (SFN) in Amsterdam were used, where the University of Twente conducted a DAB field trial. The proposed error bound is compared with other error bounds from literature and the results are validated by simulations. Although the proposed bound is less tight than existing bounds, it requires no additional information about the CRC code such\ud as the weight distribution. Moreover, the DAB standard has been extended last year by an Enhanced Packet Mode (EPM) which provides extra protection for data services. An undetected error probability for this mode is also derived. In a realistic user scenario of 10 million users, a 8 kbit/s EPM sub channel can be considered as a system without any undetected errors (Pud = 6 · 10−40). On\ud the other hand, in a normal data sub channel, only 110 packets with undetected errors are received on average each year in the whole system (Pud = 5 · 10−13)