Recent years have brought many advancements for hardware-in-the-loop testing. Gone are the days when a single device could be connected at once and the amount of simulated wireless links couldn’t cover the number of antennas found in a modern day MIMO device. Modern channel emulators allow the connection of numerous devices simultaneously, but the number of wireless links have risen into thousands of links.
Why have interest in this kind of development? The biggest reason—new numbers enable many things that were impossible a few years ago. Imagine modelling the battlefield environment for the communications of a full army battalion. Not only would you save field testing time, but you would also gain visibility for every single radio link, no matter if it is a tactical radio link to the nearest individual, or a strategic link from a company to fire command. You can also apply any kind of radio environment for each part of the battlefield and record and playback the conditions, as needed, to clarify disturbances.
The extended capabilities of a modern channel emulator enable multi-system testing within a single test run. Independent controllable link characteristics also enable simultaneous testing of tactical radios and satellite links. This brings laboratory testing one step closer to tangible field testing, allowing simulated inter-system operations. Also, modelling whole satellite constellations has become within reach of channel emulators. In a laboratory, the end-to-end signal chain from ground station through multiple satellites and back to earth is possible.
Why is a Channel Emulator Needed?
Depending on the size of the emulator, the latest generation of devices typically enable a minimum of 16 simultaneous connected devices with full mesh connectivity. Full mesh is a connection, where all radios are fully connected to one another and without changing any connections or cabling, can communicate with each other. This kind of setup requires N(N-1) signal routes in between radios. Let’s say we want to connect 32 radios in one testing-round. The amount of needed internal connections is already as high as 992, which requires a very powerful channel emulator.
Tactical radios—check. What about vehicular networks, flight control, and satellites? The longer the distance between radios, the more delay there will be in receiving transmitted signals. Luckily, Moore’s Law works to our benefit here as well as on the processing power side. The amount of memory in modern devices is easily tens of gigabytes—even high bit-rate signals can be recorded for a relatively long time for delay and playback. Big memory together with powerful processors, enable modelling of any actual space and satellite use cases.
The latest channel emulators host many exciting features, such as IQ record/playback for every channel. Also, frequencies for connected devices can be set independent of each other, providing an efficient way to test inter-network operations and frequency conversions in between radios.
Multipurpose Tool—As Efficient and Precise as Special Purpose Tools?
Many times, a multipurpose tool is a compromise. It fits many purposes, but not as well as a tailored solution. Modern channel emulators can host a wide variety of applications—from commercial wireless to military communications, from aerospace to terrestrial radios, and from single link to network level testing—all with the same precision and accuracy. How is this possible?
One way to keep things accurate and repeatable is to use a file-based channel emulation. This means the radio propagation emulation is defined and stored in a file. The benefit is the emulation can be copied, replicated, and run again—anytime with the same results. Many times, this also means the file can be read and edited outside the emulator, but this depends on the philosophy selected in the design of the channel emulator.
Characteristics of a modern, file- based, open architecture channel emulator:
- File -based emulation ensures accuracy and repeatability.
- Open interfaces ensure interoperability with any 3rd party tools.
Wireless Development Challenges
The modern wireless communications within all industry segments are getting more and more alike: involving advanced technologies, such as MIMO and multi-user transmission, beamforming, and concatenating narrowband transmissions into a single wideband. What justifies the added system level complexity is the higher end user throughput. Even before the latest wireless innovations, it has been challenging to cover all the functionality in testing. With the latest features, it seems inevitable the most complex systems are launched immature.
The more complex the system, the more thoroughly it needs to be tested before operational phase. One very good example is satellite communications. You don’t want to find your system lacking performance after it is launched into orbit. Even more critical is the tactical radio; the operations must be robust right from the start—lives depend on it.
During the past 10 years, the wireless world has become fully dependent on the software side of the implementation—today through software, there are antenna-elements which that can change their characteristics and operational frequency. The high level of configurability the software has enabled means the number of configurations that require testing has exploded. New features brought into systems by software might totally change how the hardware behaves. It is essential to have a test environment which that combines testing of the software and hardware, as early as possible, to avoid heavy and long-lasting SW-HW integration toward the end of the development cycle.
Channel Emulator Answers Toughest Challenges
Maturing a wireless system requires both hardware and software (figure Figure 1) to go through various conditions the system may experience when it is operational. Finding the edge where inevitable loss of signal hits the user means, that additional to normal use the system need to be exposed to some abnormal radio conditions.
The common way to test system operations is to take the radios into the field, find various environments, and operate the equipment as it will be utilized by the end user. The biggest technical problem with field testing is the lack of repeatability. There are no identical conditions, especially in the urban environment. The interference and radio propagation conditions might be totally different from yesterday. Next, the biggest problem is money. Travelling with radios and test staff, finding good test environments and conditions is expensive. Even worse, if the intended use of the radio system is to provide a link in between vehicles, for example, tanks or jet fighters, there is a limited amount of field testing available to verify if the system works in decent radio conditions.
Channel emulators can emulate the actual field conditions by replacing the signal path from antenna-to-antenna with programmable logic. Emulation can be very accurate and radios cannot distinguish whether they are out in the field or connected to a channel emulator device in the laboratory. Channel emulators apply all radio propagation effects into signal path, such as: signal delay, caused by the distance of radios; frequency Doppler shift, caused by the movement of the radios; and various interference, caused other operation radio systems and nature. Even the locations and antenna orientation of the radios can be emulated to fake the equipment regarding where they are, where they are going, and where there are neighboring radios.
Taking Advantage of the Channel Emulator
Emulating authentic radio conditions in a controlled laboratory setup provides clear benefits. Repeating the same radio conditions for various radio and software versions, or even different radio manufacturer’s units, provide objective data regarding how well the system performs when compared to the next one.
Is it difficult to setup and use a channel emulator environment? Some suggestions would be to look for a solution where testing can start as soon as cables are attached to the channel emulator unit. Ensure available ready-made channel models are added in between radios with a couple of mouse clicks. With intuitive user interface guarantees, the most complex setup is possible with additional experience.
The advantage of knowing how the radio works, starting from the very first prototype, saves a lot of effort in the later phases, reflects higher end customer satisfaction, and over time, protects multiple times the investment in reduced developmental costs.
