Karina Fors

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.

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.

Electromagnetic environment mapping for the assessment of critical wireless services in ISM bands

Wireless technologies for critical societal functions is becoming more common today. Criminals have already recognized this vulnerability and used it in various types of crimes. Unintentional radiated electromagnetic interference can also be a big problem for these types of services. Before deployment of critical societal functions based on wireless technologies, mapping and analysis of the electromagnetic environment area is essential. In this work a cost efficient system for qualified mapping and analysis of the electromagnetic environment is described and demonstrated. The example results herein presents a methodology to identify areas with increase background interference. Furthermore, an example of a system that operates in an unlicensed ISM-band is given and based on the mapping data, its vulnerability to other transmitters is analyzed and qualified.

Electromagnetic interference on tactical radio systems from collocated medical equipment on military camps

On military camps for joint international operations, the intersystem interference can be highly unpredictable, and situation changes can occur very fast. For such situations it is highly important to perform intersystem interference analyses not only for intentional transmitters but also for electromagnetic interference from other electric equipment. One example of such an interference source to consider is medical equipment in field hospitals since the hospitals can contain a large amount of interfering equipment. In this article, we show examples of necessary safety distances between medical equipment and tactical radio systems at military camps for international missions. We give an example of how wideband electromagnetic interference can degrade the performance even for a wideband frequency hopping army combat radio.

Capacity benefits of airborne nodes in ad hoc networks with broadcast traffic

Tactical military networks are often ad hoc networks since it is a highly robust solution. The data rate in ground-based networks is often limited due to low antenna heights and a challenging wave propagation environment. In such networks it can be hard to achieve high enough data rate to support the requested services. A large portion of the traffic in tactical networks is broadcast or multicast traffic. Often, the used data rate is assumed to be the same for all links and tends to be low in order to reach all nodes in a network. A possible solution to improve the capacity is to add an airborne node to the network. In this paper, the performance of ground networks at 300 MHz is analyzed with and without an airborne node. The airborne node is positioned directly above and at a distance from the ground network. Also, both a detailed channel model including terrain data and a distance dependent channel model are considered. Results show the capacity improvement when adding an airborne node to an ad hoc network. Moreover, the use of a channel model with terrain considerations has a great impact on the results. For example, the required height of the airborne node, to achieve a certain capacity improvement, is severely underestimated when using the distance dependent model.

Interference impact on LTE from radiated emission limits

The society is becoming more and more dependent on Long Term Evolution (LTE-services) in a large variety of applications, which is why we must ensure it is secure and available when we need it. Like any wireless technology, it is vulnerable to radiated electromagnetic interference. In this paper, we show how the levels of standard radiated emission limits will affect the performance of LTE. The results show that the emission levels from EN 55022 can cause severe impact on co-location distances from approximately 20 meters and above. The levels of RE 102 in MIL-STD-461 will have impact at co-location distances in the order of one or a few meters.

Effects of interference between co-located frequency-hopping ad hoc networks

Traffic in military ad hoc networks are often broadcast or multicast traffic. A robust and efficient way to handle this type of traffic is the multi-point-relay (MPR) method. Furthermore, frequency spectrum is a scarce resource and must often be shared by several networks resulting in a risk for internetwork interference. The objective of this paper is to analyze the effects from internetwork interference in frequency-hopping (FH) ad hoc networks. Earlier work show that performance on a communication link can be degraded by interference between FH systems sharing the same spectrum resource. Results in this paper show that ad hoc networks are robust against FH interference in terms of a maintained high delivery ratio, but it is achieved at the cost of reduced capacity in the network. This reduction can in some scenarios be severe resulting in two networks with interference being less efficient than time-sharing between the networks.

A tool for coexistence planning in complex radio communication environments

Interference in the vicinity of a receiving radio system can cause serious degradation of the radio communication performance. This may even result in disruptions and lost calls. Existing analysis tools to analyze interference problems in advance are often specialized at certain radio technologies or so complicated that they can only be used by experienced specialists. To foresee and prevent such communication problems, a scenario based research tool for electromagnetic interference analysis has been developed. The tool is named GENESIS and can be used by larger user groups that are not experienced specialists. The tool can identify, by use of smart color-mapping, the regions where the risk for communication problems may arise, and the dominant interference sources can be identified. Moreover, the influence from different radio parameters, such as carrier frequency choice, out-of band emissions or frequency hopping band, can be analyzed and visualized. Hence, the effect of different EMC design strategies can be evaluated in the tool. In this paper, we specifically show how different requirements on out-of-band emissions can be analyzed for co-located frequency hopping systems and how the interference impact can be presented and visualized in several ways as a lower communication quality or reduced communication range.

The risk of coexistence problems between DAB and DVB-T2 and military services at the 225–240 MHz band

In Sweden, Digital Audio Broadcast (DAB) for radio broadcasts is allocated to the frequency band of 225-240 MHz. Recently, also television broadcasts based on the standard Digital Video Broadcasting - Terrestrial, version 2, (DVB-T2) has been proposed to use the frequency band of 225-230 MHz. Since this is the lower part of the harmonized military band intended for military radio systems, there may be a risk of interference issues between DAB, DVB-T2 and military systems planned for 225-400 MHz. For example, Have Quick II (HQII) and Saturn are two military radio systems that are allocated to this band. In this work, an analysis is performed whether the military systems HQII and Saturn can coexist with DAB and DVB-T2 without performance degradation of the civilian systems. The influence is quantified in terms of the necessary distance, which is a safety distance between the civil system and the military system. Safety distances of tens of kilometers are achieved for the land scenario. For the air scenario, it is stated that the required safety distance is, in some cases, exceeds the so-called line-of-sight (LOS) distance.