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

A Monitoring Network for Spectrum Governance

Dynamic Spectrum Access (DSA) is an exciting new technology, which has introduced a paradigm shift in spectrum access. As a result it also changes the role of the regulator. On one hand the scarce radio spectrum should be used in an optimal way, so that society is best served. On the other hand interference between users and between networks should be avoided. For that reason rules have to be defined for spectrum use. This topic is called spectrum governance. For evaluation and to check whether devices obey the rules, a monitoring system is needed. In this paper, we propose to use a fleet of mobile monitoring vehicles for this purpose.\u

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

Channel selection requirements for Bluetooth receivers using a simple demodulation algorithm

In our Software Defined Radio (SDR) project we combine two different types of standards, Bluetooth and HiperLAN/2, on one common hardware platform. SDR system research aims at the design, implementation and deployment of flexible radio systems that are reprogrammable and re-configurable by software. Goal of our project is to generate knowledge about designing the front end of an SDR system (from the antenna signal to the channel bit stream) where especially an approach from both analog and digital perspective is essential. This paper discusses the channel selection requirements for the Bluetooth standard. The standard specifications specify only the power level of the interferers, the power level of the wanted signal and the maximum allowed Bit Error Rate (BER). In order to build a radio front-end, one has to know the required (channel) suppression of these interferers. From [1] it is known that the required SNR for a Bluetooth demodulator is 21 dB, but by which value should interferers be suppressed? This paper will validate if the SNR value needs to be used for the suppression of adjacent channels. In order to answer this question a simulation model of a Bluetooth radio front-end is built

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