An introduction to SEAMCAT

A key goal in the ECC strategic plan for the period 2015-2020 is to provide expertise in managing scarce resources, notably the radio spectrum. The higher penetration of wireless communications in recent years has led to increased congestion in the radio spectrum. As a result, radiocommunication systems must find a way to share the resource efficiently. For this purpose, sharing and compatibility studies need to be carried out to investigate the possibilities for systems to coexist in the same or in adjacent frequency bands.

Figure 1: Example of radio spectrum occupancy in Europe¹

To manage the spectrum resource in an effective and efficient manner, it is necessary to develop methods and tools that are capable of modelling complex compatibility scenarios realistically. They in turn will determine if coexistence between different systems can be achieved.

In that context, SEAMCAT (Spectrum Engineering Advanced Monte Carlo Analysis Tool) has been developed since the late 1990s to respond to the need for a common spectrum engineering analysis tool. The aim is to have a recognised, flexible and reliable platform for assessing the compatibility among various radio systems.

1. SEAMCAT: what is it and how does it work?

A free of cost, open-source² software tool, SEAMCAT performs calculations based on the Monte Carlo simulation method for statistical modelling of different radio interference scenarios. It has been developed to analyse a diverse range of complex spectrum engineering and radio compatibility problems. It aims to obtain close-to-reality results, increasing the chances of using the radio spectrum efficiently.

1.1. The Monte Carlo method

In general, Monte Carlo methods refer to a set of computational algorithms that allow using randomness to solve problems that might be difficult to solve using a deterministic approach. They allow solving problems that have a probabilistic interpretation and are very useful for simulating systems which involve many variable parameters.

This is particularly the case with radiocommunication systems, which are defined by many parameters that vary in real operating conditions. Furthermore, if the aim is to assess the interaction of many systems, the number of variables involved in the exercise substantially increases.

For the purpose of explaining the basics of the Monte Carlo method, let’s consider a simplistic scenario involving just one radiocommunication system. Let’s imagine that we want to calculate the mean power of the signal received in a system composed of:

• a fixed transmitter operating at constant frequency and power; and

• a moving receiver.

In this basic scenario, the physical location of the transmitter will be fixed while the position of the receiver may vary. Therefore, the power of the received signal may also vary.

In the Monte Carlo method, parameters that vary can be defined as random variables with a given distribution. The basic principle of a Monte Carlo simulation is the random sampling of these distributions at each simulation run (i.e. simulation event) in order to perform a given calculation.

Continuing with our example, all possible positions of the moving receiver are defined as a random variable with a given distribution. In a simulation event, one of the possible positions of the receiver will be chosen randomly across the distribution. This value will then be used to calculate the received signal power for that specific event.

In a Monte Carlo simulation, results of calculations obtained at each event can then be averaged across the total number of events. The number of events required to produce a statistically representative result depends on the number of random variables included in a given scenario.

In our example, after having simulated all events, we can then average all values of the received signal power calculated at each event in order to obtain the resulting mean received power.

1.2. Using the Monte Carlo method with radio systems in SEAMCAT

Calculations performed in SEAMCAT involve one victim system and one or several interfering systems. The radio parameters and locations of the transceivers in each system can be customised.

In the schematic scenario depicted in the figure below the receiver of the victim system gets its wanted signal from its corresponding transmitter. The victim receiver operates amongst a population of one or more interfering transmitters. Therefore, the victim receiver also gets interfering signal(s) originated at the interfering transmitter(s), as indicated in Figure 2 below.

Figure 2: Schematic compatibility scenario

In a SEAMCAT simulation, it is possible to assess the effect of interference into the victim system by comparing what happens before and after the introduction of one or more interfering system(s). At each simulation event, the received signal strengths for each link are calculated. The wanted and interfering signal strengths are compared according to a given criterion (i.e. interference criterion, protection ratio³, network capacity or bitrate specifications). The final results are typically defined in terms of probability of interference, or indeed average capacity/bitrate loss, averaged over all simulated events. Other results are also provided and may be used for further analysis, such as the distributions of the wanted and interfering signal strengths across all events.

The main interference mechanisms that can be analysed in SEAMCAT are the unwanted emissions of interfering transmitters, the selectivity and overloading of the victim system receiver and the effect of intermodulation products. Figure 3 below depicts the two main interference mechanisms typically analysed (i.e. unwanted emissions and receiver selectivity).

Figure 3: Unwanted emissions and receiver selectivity

Comprehensive information on SEAMCAT, including full details of settings, parameters, computation algorithms and results, is contained in the SEAMCAT handbook. This document was reviewed by the CEPT and was published at the end of April 2016 as ECC Report 252⁴.

2. SEAMCAT development and user community

SEAMCAT is developed under the mandate of the CEPT’s Electronic Communications Committee. The SEAMCAT Technical Group⁵ (STG), under the direction of the Working Group Spectrum Engineering, is the responsible body that proposes, discusses and validates corrections and enhancements to the software and the handbook. The group cooperates closely with other ECC working groups and project teams, to respond to their SEAMCAT-related needs, and to inform relevant sharing and compatibility studies within these groups.

It is important to note that SEAMCAT is not only used within the CEPT, but also worldwide in administrations, industry and academia. These sectors comprise the so-called SEAMCAT community, whose focal point is the ECO⁶, and who work together to improve the tool.

3. SEAMCAT key development objectives

The main objectives in SEAMCAT development are to provide a recognised, flexible and reliable platform. That platform enables realistic modelling of complex scenarios for the compatibility assessment involving various radio systems, using the Monte Carlo method. Furthermore, users also expect a tool that is comfortable to use and performs simulations at a satisfactory speed.

3.1. Increase its flexibility

In the context of SEAMCAT development, flexibility refers to the capability of the tool to adapt to emerging needs in terms of availability of input parameters and output results. This also means that it should be able to include new system definitions without requiring radical changes to the program each time a new system is introduced.

One way to achieve this type of flexibility is through a variety of input parameters, which can be specified in SEAMCAT workspaces, and through the availability of a wide range of output results.

Flexibility is also provided through the use of libraries. We can distinguish among two main types of libraries:

• Libraries for system components and parameters. SEAMCAT is distributed with a pre-defined set of libraries (see Figure 4 below), which contain system parameters. For example, there are libraries for generic and cellular systems, spectrum emission masks, receiver blocking masks, transceivers, etc. Also, users can build customised libraries for their own requirements, which can then be shared.

  

  Figure 4: SEAMCAT system parameters and plugin library

• Plugin libraries. Plugins are software components that can perform specific calculations, access intermediate results of simulations and enable the customisation of final results. SEAMCAT contains built-in plugin libraries for propagation models, antenna patterns and coverage radii. Additionally, specific types of plugins - event processing plugins - allow defining specific calculations based on the intermediate results of simulations. These are accessible from the computational core of the tool. With this new feature SEAMCAT functionalities can be extended to implement customised algorithms but still use a shared interface.

3.2. Improve its reliability

Reliability in this context means the degree of confidence that users can have in the accuracy of simulation results. This is intrinsically related to the design and functionalities provided in SEAMCAT.

Several features have been developed to make SEAMCAT more reliable:

• Sharing SEAMCAT workspaces and simulation results. This enables users to verify input parameters, compare and reproduce results and therefore inform discussions to define necessary sharing conditions and regulations.

• Running simulations in debug mode. This provides a report containing all variables involved in a given simulation and interim simulation results.

• Play/replay feature. Users can analyse parameters and calculations for each event in a specific simulation run.

3.3 Enhance its computation speed and user-friendliness.

The regular maintenance of SEAMCAT aims to produce a software tool that is faster and easier to use

Computation speed has been improved in recent versions with the introduction of parallel processing, which uses the capability of multi-core computers, and with the optimisation of complex algorithms. Continued increases in computation speed are expected in the upcoming releases.

One of the challenges that needs to be further addressed in the upcoming releases is the improvement of the tool’s user-friendliness. This can be achieved by improving the graphical interface, by extending the consistency checks for parameters entered in workspaces and by regularly updating the documentation accessible through the program and available in the SEAMCAT handbook.

4. Promoting the use of SEAMCAT

The promotion of SEAMCAT is also an important objective in the ECC strategic plan for the period 2015-2020. In response to this goal, the ECO organises free of charge workshops on a regular basis. They are intended for SEAMCAT users with different levels of expertise, from beginners to experienced users. Additionally, the ECO frequently introduces the tool and its most recent features at international conferences. All these efforts are intended to increase the use of SEAMCAT. In the CEPT context, it is frequently used by spectrum engineering project teams for the preparation of their deliverables. This intensive use can be observed in the number of documents - more than 30 ERC and ECC reports⁷ - containing compatibility studies based on Monte Carlo simulations using SEAMCAT.

José Carrascosa, European Communications Office,
SEAMCAT project manager and chairman of the SEAMCAT Technical group.

¹ Radio spectrum applications in Europe in the 440 – 942 MHz range , obtained from the ECO Frequency Information System (EFIS): view
² The source code can be downloaded free of charge after signing a licence agreement. Further information is to be found at the SEAMCAT Source Code page: view
³ A protection ratio is the minimum value of the wanted-to-unwanted signal ratio, usually expressed in decibels, at the receiver input, determined under specified conditions so that a specified reception quality of the wanted signal is achieved at the receiver output (c.f. Nr. 1.170, ITU Radio Regulations).
⁴ ECC Report 252: SEAMCAT handbook. It can be downloaded here
⁵ Further information on the SEAMCAT technical group (STG) can be found here: here
⁶ The ECO (European Communications Office) is the permanent office of the CEPT to which it provides advice and support in order to help it to develop and deliver its policies and decisions. ECO further supports CEPT member countries and other stakeholders providing a forum to debate and advance European communications policy for the benefit of all Europe’s citizens
⁷ SEAMCAT workspaces used in ERC and ECC Reports are made available in zip files in the ECO documentation database: www.ecodocdb.dk