Frequently Asked Questions

Colosseum Hardware and Computation Capabilities

Q: Is it possible to run/install packages using the internet?

A: It is possible to set up appropriate proxies and you can access the wide internet, but it is currently restricted. We encourage users to install software on their local system due to reasons including using Colosseum resources primarily for experiments and not be limited by Colosseum reservation time.

Q: How much storage is available for each team on the NAS server?

A: There are quotas for each team, it can be specified according to your needs. At the moment the quota is 500 gigabytes per team, but we are planning to increase the storage space.

Q: Are the SRNs synchronized at the RF TX port to build the MIMO model using multiple SRNs?

A: Yes, they are synchronized through Octoclocks (clock/PPS signal).

Q: For the mMIMO case, what is the maximum number of time and phase coherent antennas/radios?

A: The current maximum is 32 SDRs.

Q: I assume you can build a MIMO channel model using multiple SRNs, especially for more than 2 layers, is this right?

A: Yes, you can build a MIMO system using different SRNs.

Q: Is there any guideline regarding the maximum sample rate that can be supported by the host (assuming default FPGA images at USRPs)?

A: Each USRP has an independent host/server, so your only bottleneck is the speed of the single host. Also see:

Q: What are the available bandwidth sub bands? Is it possible to make use of 5G bands 3.4Ghz and 3.5Ghz? Are 30GHz available too?

A: Any frequency supported by UBX daughterboards can be used for your experiment.

Q: Do users have full access to UHD settings in each USRP?

A: Yes, you can basically flash the FPGA, but access is only through JTAG and power cycling is not permitted.

Q: Can we physically access the SDRs to perform some real measurements?

A: Users have full access to the SDR software and the host server. At this time users do not have “physical” access to the SDR. This may be considered on a case by case basis in future.

Q: Can we plug in RF components like filters, amplifiers, etc., between the user SDR and simulator SDR RF channels to measure the impact of real RF components in the loop? Is it possible to hook up real WIFI devices (e.g. commercial access points) into the Colosseum infrastructure to generate traffic? Can we make use of SDR outputs and connect them to our own RF/mmWave Components to do some more advanced measurements?

A: At this time, BYOD is not supported directly. However, we do plan to allow this sometime in the future.

Q: Can you have a receiver to transmit feedback?

A: It is possible for over-the-air emulation. There is also a collaboration network where each node can connect to each other through Ethernet.

Q: Can we account for the "true" hardware impairments of the RF front-end or is this a baseband-in-the-loop simulation?

A: Yes, the signal transmitted travels through a physical radio’s pipeline which allows for true hardware impairments. Everything is Colosseum is "real", so you can emulate from traffic to waveform, including all the real-world imperfections you get in a real system

Q: Is it possible to have half a wavelength at 60 GHz?

A: This will be allowed in around 18 months.

Q: What are the constraints of each SDR? E.g., what is the number of Tx/Rx antennas per supported per node? What is the range of operating frequency/bandwidth? Are there any constraints on the frequency range?

A: Each SDR is an X310, with 2  daughterboards. So all the constraints are the same as the X310. See

Q: What is the clock/sample rate in the FPGA channel emulator?

A: MCHEM samples at 200 MS/s, see

RF Emulation Scenarios and Capabilities

Q: Can channel emulation happen in the RF or it happens in the “baseband” and will be fed back into RF?

A: Channel emulation happens in baseband.

Q: Is it possible to simulate phased array antennas for directional mmWave research?

A: Technically it is possible to simulate phased array antennas but not at mmWave.

Q: Is flexible antenna arrangement (ULA, URA,...) available for massive MIMO application?

A: Users can define appropriate GPS coordinates of the radios in a custom created scenario (Alleys of Austin does have a linear set of moving nodes). We do not have a circular placement yet. Each node can be time synchronized to a common reference clock (we have this ready today for one Quadrant, i.e., 32 nodes).

Q: Regarding the beam-forming testing in both simulation and experiment, can we flexibly configure the separation between inter-antennas (or inter-channels) of SDRs?

A: Yes, you can assign different positions to different antennas by defining GPS coordination; Hence the granularity will be the GPS one.

Q: How many taps can be specified for the channel model?

A: It is 512 taps for each link. You can emulate up to 256x256 channels. You can specify taps for each individual link.

Q: Can scenarios be defined by 3D models?

A: Yes, GPS coordinates are specified. Both 2D and 3D.

Q: How is the physical 3D map of a scenario defined?

A: Each scenario specifies GPS coordinates (3D) of each node, e.g., you can have flying UAVs and terrestrial nodes in the same scenario. The coordinates are specified in the scenario used for the specific experiment.

Q: Does the 4-tap filter emulator incorporate both the delay due to path loss and any small-scale fading?

A: The 4 taps are complex numbers and can be used to model any channel effect (path-loss, fading, multi-path, etc…). Each path delay is accounted for. Small-scale fading can be emulated according to your specific scenario (for example, with a ray tracer).

Q: Does MCHEM support the channel model specified by 3GPP for 4G & 5G, especially MIMO channel model with different spatial correlation and beam-forming models?

A: The limitation is 4 non-zero taps of a 512-tap vector for each FIR filter. So far there is no attempt to specifically map the 3GPP channel to a 4-tap channel.

Q: Are UAV scenarios also available at this point? UAVs that are also equipped with SDRs? If yes, what kind of SDR is that? Ettus B205 mini or B210? How flexible are UAVs scenarios regarding mobility, collision avoidance, number of drones and autonomy?

A: All SRNs are X310. There is no “UAV” with a hovering channel model etc. The SRN moves in a circular pattern to emulate a UAV motion in the Alleys of Austin scenario. The channel is straight line FSPL at this point. The UAV motion (basically any motion in Colosseum) has to be predetermined. So, you cannot change the motion/location on the fly once emulation starts as a result of some local action, e.g, interference.

Q: Does Colosseum support only UDP flows for now? Why is that? Any plans for TCP support?

A: Colosseum supports UDP and TCP in different ways.

Q: (in the webinar demo) Is the TCP/IP connection built on a real wireless channel or just a wired end-to-end channel?

A: Nothing on Colosseum is wireless, but the MCHEM emulates a wireless channel based on the selected scenario.

Q: Is Wi-Fi unicast working (i.e., ACKs return in time?)

A: You can always use the channel as a feedback to get the IDs. No base container has this capability currently, but users can implement it in their own codes.

Q: How are the channel models for the 5G wireless environments modeled (in Rome, Boston, etc.)? Are they based on actual measurements/mathematical models/raytracing, etc?

A: They are dependent on the scenarios. There are scenarios in development based on ray tracing and it is certainly possible to be able to be based on actual measurements/mathematical models.

Q: Does Colosseum support hybrid terrestrial-satellite communication

A: It does support hybrid aerial communications. The delay that can be modeled by Colosseum is limited to what you would see in a scenario with 1 km of distance. As of now, satellite communication is not supported by Colosseum but maybe possible in the future.

Q: Can users design their own scenarios?

A: As of now, users are only provided set scenarios and are not able to design their own scenarios. We are open to working with users to create a scenario if the existing scenarios do not satisfy the users’ needs.

Q: Can users create their own custom protocol stack? (from APP to PHY)

A: Yes, users have freedom to create a fully customized protocol stack.

Q: What is the end to end (TX process to RX process) delay?

A: Colosseum generates a real wireless signal over the SDR which is passed through a wire and the wire’s propagation delay in near real time. It is as fast a radio can process an RF signal and as fast as the propagation can happen. We account for waveform propagation delay as well.

Q: Are the SDRs connected 1-to-1 or is there a multi-path component in RF analog also?

A: The SDRs are connected to the channel emulator physically. The channel matrix that we enter at the emulator takes into account multiple signals. On the receiver side, the receiver takes in the intended transmission and transmission interference from the rest of the other transmitters which adds to the complexity capabilities of Colosseum 4-tap model.

Q: How realistic is it to only have 4 non-zero taps?

A: We had to make a compromise between feasibility/cost and fidelity. Colosseum supports up to 512 taps per link. 4 taps is a good compromise between complexity and accuracy. This is something we inherited from DARPA/APL. In most cases the system so far has been used with path loss and propagation delay only (no multi path). We are developing a pipeline to approximate propagation profiles generated with ray tracers with a sparse 512-tap filter with 4 nonzero taps. Feedback from the community is very much appreciated. Introducing additional taps will require substantial changes in the channel emulator. Basically, it is the FPGA space needed to emulate the entire 256x256 mesh.

Q: What about having 4 non-zero taps at the mmWave level?

A: mmWave will be a new, redesigned quadrant with longer channels and only 16x16 mesh.

Q: How fast are the taps updated?

A: Scenarios are generated with 1 second resolution, then interpolation occurs, and resolution is one millisecond. So, for every millisecond we update the channel information.

Q: The channel taps can be changed, but is the number of taps fixed?

A: The number of taps is always fixed but they change every 1 ms. Scenarios can be made where the channel will update at various speeds or to be fixed.

Q: Is it possible to reduce the total number of taps from 512 to something like 64-80 while each tap can be populated?

A: Only 4 taps can be non-zero. The 4 taps are generated according to your RF scenario and are completely customizable. They are stored inside Colosseum and are automatically retrieved and processed whenever you launch a reservation. We are working on releasing a general tool that can generate the 4 taps given coordinates of nodes and the location of the region where they are placed. To enter these taps implies making a new scenario. This feature is not available to general users as of now as a directly accessible capability but we can work with individual teams on scenario building if the existing scenarios do not satisfy the users’ needs.

Colosseum Containers

Q: What is the process for using specific packages for custom experiments?

A: A custom LXC container must be created and all packages and changes must be made on your local machine and then saved to the image and uploaded to the experiment’s reservation website.

Q: Would the container management framework support something like Kubernetes or Kubevirt?

A: Not right now, but we are planning on supporting them.

Q: Can users have a snapshot of the image within the container using the Colosseum CLI?

A: Yes, and it will be saved in the images folder of your team directory.

Q: Does it support LXC YAML configuration files or similar?

A: Yes, you can configure the LXC container as you desire.

Q: Are Colosseum containers using Ubuntu 16.04 or newer version required?

A: Ubuntu 16.04 as well as newer versions work with Colosseum. Your LXC container can run any Ubuntu version. You can build one entirely from scratch, if you so desire, but Colosseum provide base images with all the requirements and users can customize these base images based on their needs.

Q: Do the containers have access to the internet? Or do I have to download the container to install software?

A: By default, containers do not have access to the internet. At the moment, internet connection is restricted., the best practice to install new software is by downloading the base image on your computer and modify it as you wish, and then upload it back to Colosseum

Q: There is currently a Container that is accessible at Colosseum to carry out srs-LTE experiments there. Are there any plans to update any specific Wi-Fi based container very soon or we need to create our own container locally and upload it?

A: There is currently a basic srs-LTE container on the website that can be downloaded, customized and uploaded back to Colosseum. There are also Wi-Fi based containers available. You can use the basic containers for general purpose experiments or customize any of the above containers.

Q: What is usually included in the container exactly? Everything running on SRN?

A: A container includes your own code to process the incoming traffic. The base containers come with the UHD drivers, Colosseum CLI, and all other requirements needed to connect to the USRPs, the MCHEM, and other components of the system.

Q: Has there been benchmarking done to compare the potential overhead of running code in container instead of native machine? Any implications on types of experiments supportable?

A: LXC containers give you bare metal access to hardware. So, the overhead should be negligible. The code is running locally on the SRN host. Each SRN has its own blade server.

Legacy Scenarios Support, PAWR Integration and Future Upgrades

Q: Are you going to resurrect the mandated outcomes and collaboration channel from the SC2 competition?

A: For the time being, we are not working on resurrecting the mandated outcomes. The feature is archived at the moments as the current focus is not for competition-based experiments.

Q: To what extent can Colosseum currently serve as a stepping-stone to in-field experimentation on the existing PAWR platforms?

A: For the past several months, we have onboarded a large set of lead users including participants from the DARPA SC2 competition and other lead user communities with prior experience with Colosseum which include some NSF researchers. These teams developed the containers ansible tool chains to extend the containers that we use for Colosseum and that can be used for existing PAWR platforms. While the process is still being optimized, there is capability for instantiating the Colosseum LXC containers on the PAWR compute fabric that will allow them to connect to the SDRs that are available for PAWR.

Q: Are there any in-field PAWR scenarios currently modeled in Colosseum?

A: Colosseum has 2 scenarios from the PAWR platform that were based on measurement campaigns that would be run statically and remotely by the Northeastern team to develop. Recently, the PAWR team itself has run a measurement campaign and we will be releasing to the public, the data set at multiple frequencies. These frequencies (CBRS and 2.5) are currently being annotated and will be released to the community.

Q: What is the timeline for the Evolution of Colosseum? When can we expect the upgrades?

A: The computing/networking/GPU upgrades are first to be completed in one year. The 100km2 capability and mmWave are to be completed in 18 months.