Kia Wiklundh

Relation between the amplitude probability distribution of an interfering signal and its impact on digital radio receivers

New emission limit requirements are needed to protect digital communication systems from radiated interference. Traditionally, standard emission requirements have focused on protecting analog amplitude modulated radio services. However, developments in digital technology require emission limit requirements adapted to protect digital radio communication services. The amplitude probability distribution (APD) of the envelope or the quadrature components of an interfering signal has been shown to be related to the bit error probability of some digital radio receivers. However, a general description of the APD of an interfering signal and its impact on digital coherent radio receivers has not been presented. The aim of this paper is to clarify this relationship for a larger group of digital radio receivers. A method of incorporating the APD in conventional error expressions developed for digital coherent radio receivers in additive white Gaussian noise is presented. Furthermore, the relation between the maximum error probability for different digital modulation schemes and the APD is described, which allows definition of emission requirements on the APD

Urban peer-to-peer MIMO channel measurements and analysis at 300 MHz

Multiple-input multiple-output (MIMO) systems operating at frequencies in the upper VHF and lower UHF region is attractive for peer-to-peer communication applications where robustness is of high importance, e.g., in tactical networks and emergency response systems. When designing and evaluating such systems, knowledge of realistic propagation conditions is required. This paper presents results from an urban MIMO measurement campaign at 300 MHz. Measurements are performed along 25 receiver routes and for three fixed transmitter locations, using antenna arrays mounted on two cars. Channel characteristics and ergodic capacity for the 7 times 7 MIMO channels are extracted from the measured data. A path-loss model is derived for the measured scenario, and the distributions of the large-scale fading, the Ricean K-factor, the delay spread, and the ergodic capacity are studied in detail. The correlation distance for the different channel parameters is also examined. Furthermore, the analysis reveals that several of the channel parameters are correlated, and also have a strong correlation with the capacity.

An improved method to estimate the impact on digital radio receiver performance of radiated electromagnetic disturbances

Present emission standards are developed with respect to analog communication services. Therefore, knowledge of how relating present standards to the impact on digital radio receivers must be available for system design purposes. For a digital radio receiver, the bit error probability (BEP) is often used to show the impact of the receiver performance from a disturbing signal. A simple, previously proposed method relates present emission standards to the BEP for broad-band (BE) disturbance. This method has to be modified for use on narrow-band (NB) disturbance such as the NB spectral components from periodic signals. A method based on a modification of the earlier method is presented for this NB disturbance. This represents typical disturbance from information technology equipment working with periodic signals. The conclusion is that the method presented delivers a useful value of the BEP, which can be used when radiated emission requirements are to be chosen on electronic equipment co-located to digital radio systems.

A new approach to derive emission requirements on APD in order to protect digital communication systems

Amplitude probability distribution (APD) has been proposed within CISPR as a measure of the emitted electromagnetic energy from electrical equipment. APD describes the envelope statistics of a disturbance from the IF filter of the measurement receiver and is in many ways a suitable model of nonGaussian noise, when determining its impact on a digital communication system. In an earlier paper, the connection between the APD of a disturbance and its effect on a digital receiver was presented. However, to derive a maximum allowed APD out of a maximum allowed bit error probability is a non-trivial problem. Unfortunately, this is exactly the issue when emission requirements should be related to the APD. This paper presents a possible way to put requirements on the APD in order to protect digital communication systems. By letting a measured APD of a disturbance lay below the requirements, the impact on a variety of receivers are guaranteed to not exceed the maximum bit error probability

An Approach to Using Amplitude Probability Distribution for Emission Limits to Protect Digital Radio Receivers Using Error-Correction Codes

New emission limits are needed to protect digital communication systems from radiated interference. Current standard emission limits were developed to protect amplitude- and frequency-modulated analog radio services. However, developments in digital technology require emission limits adapted to protect digital radio communication services. An approach to define emission limits on the amplitude probability distribution (APD) of the envelope of an interference source has been presented earlier. This approach is derived for coherent radio receivers utilizing no error-correction codes. However, since the most important digital radio systems today use error correction, it is necessary to develop the method to handle coded systems as well. This paper proposes a method to define emission limits on the APD of the interference to protect coded communication systems. The method is a further development of previously proposed emission limits derived for an uncoded system, which is modified in accordance with the coding gain.

Improved impulsiveness correction factor for controlling electromagnetic interference in dynamic spectrum access applications

Initiatives to open certain frequency bands for dynamic spectrum access (DSA) are ongoing. Examples are the wireless access policy for electronic communications services and white spaces coalition. A key issue in DSA is how to measure occupancy and interference in an open frequency band to decide whether or not it can be used for a certain service. Such measurement must be easy to perform and provide a result that can be used as decision metric. An earlier proposal, based on a so-called impulsiveness correction factor, with this purpose has been shown to work properly if the interference is dominated by a single pulsed signal. In this study, the former approach is extended to the case in which the interference signal consists of a multiple of interference signals. This extension is shown as a closed expression involving only parameters that can be determined from an interference measurement.

Band-limitation effect on statistical properties of class-A interference

The effect of band limitation on the statistical properties of Middletons class A noise model is investigated. It is found that a uniformly weighted sum of statistically independent and identically distributed class A random variables becomes a new class A random variable with reduced impulsiveness. It is also found that bandlimited noise becomes class A noise if the impulse response of the filter has a rectangular envelope waveform. Since matched filters employed by DS-SS (direct sequence spread spectrum) or OFDM (orthogonal frequency division multiplex) systems usually satisfy the above condition, the results can be widely applied to the evaluation of the error probability of signal detection in such communication systems subjected to class A interference.

A comparison between the impact of some signals on an MSK receiver

Transmitters and electrical equipment co-located to a radio system can, due to its radiated electromagnetic interference, cause serious degradation on the system performance. In real system design, when predicting the loss of performance, with a set of interferences of various signal types, there is a need of simple approximations that simultaneously describe the interferences in a proper manner. The focus of this paper is to show how different interfering signals will affect the performance of a radio system. Furthermore, the consequences of approximating these interference signals as additive white Gaussian noise are investigated.

A Simple Measurement Method to Derive the Impulsiveness Correction Factor for Communication Performance Estimation

Today, no simple methods are available for measurements of interference signals that give a proper indication of the impact in terms of the bit error probability (BEP) on a digital radio receiver. Such measure should quantify the corresponding impact and the measurements should be relatively easy to perform. By only using the root mean square (RMS) value of the interference average power the BEP can be underestimated with several magnitudes. To address this problem, an impulsiveness correction factor (ICF) has earlier been proposed to adjust for these errors. The ICF opens up for considerably more accurate BEP estimations whereas the simplicity in the calculations is maintained. However, how to determine the ICF for an arbitrary interference source through measurements has not earlier been known. In this paper, we show that the ICF can be obtained in two alternative ways. One way is to use the measured amplitude probability distribution (APD). The other way is to use the peak- and RMS values from standard measurement detectors. Both methods take the interference waveform properties into consideration and the BEP can thus be more accurately estimated.

A log-likelihood ratio for improved receiver performance for VLF/LF communication in atmospheric noise

Receiver-improving techniques are important for submarine communication at the LF/VLF bands, due to very demanding reception conditions. At the surface, the interference environment is dominated by the atmospheric noise, which is highly impulsive in character and may impede the reception of the radio signals. To handle the demanding channel and the impulsive interference environment, error correction and an adapted receiver are necessary. In this paper, we propose a log-likelihood ratio (LLR) as soft output from the demodulator suitable for atmospheric noise. The radio system is assumed to use minimum shift keying (MSK) and a low parity density check (LDPC) code. It is shown that the proposed interference-adapted LLR improves the performance substantially in atmospheric noise compared to when the LLR is designed for AWGN. The performance is also compared to a solution, where the soft output from the demodulator is simplified to a limiter, and to a solution when a larger system bandwidth is used in combination with a limiter. It is concluded that the proposed interference-adapted LLR achieves the best performance in the comparison, although the performance could probably be further improved, when compared to the obtained Shannon capacity of this particular interference.