Wireless communication devices become ever more crucial parts of people’s everyday lives. We also put ever tightening demands on the networks the devices use: an example of this is that we want the delays to be minimal. One solution to this particular issue is to employ simultaneous transmit-and-receive (STAR) operation.
“This, however, leaves the device’s receiver susceptible to what is known as self-interference, since the device’s transmitted signal is also being received by the same device,” says Vesa Lampu.
“The self-interference can be much more powerful than the signals from other devices. My dissertation focuses on digital methods to cancel the self-interference from the received signal, in two different duplexing schemes. This allows the actual signals-of-interest to be deciphered,” he continues.
Novel models to efficiently cancel self-interference in traditional STAR systems
Traditional STAR systems mitigate the self-interference problem by operating the transmitter and receiver on different frequencies, in a scheme called frequency division duplex (FDD). Despite this precaution, a phenomenon called intermodulation may introduce self-interference to the receiver’s frequency. If the cause of the intermodulation is a passive element, such as a switch or a connector, the phenomenon is called passive intermodulation (PIM).
The focus of Vesa Lampu’s dissertation is the digital cancellation of PIM caused by external metallic objects, that are not part of the physical transmitters or receivers. Moreover, the cancellation of the PIM is studied in scenarios, where multiple transmitters and receivers operate in parallel, at the same time.
“This complicates the mathematical modeling of the system. In my dissertation, I propose various algorithms that attempt to lower the complexity of the cancellation models, which in turn lowers the energy requirements to execute the algorithms. Extensive simulations and measurements and indicate that the proposed cancellers can bring the residual self-interference close to the thermal noise floor of the receivers,” Vesa Lampu says.
Bringing in-band full-duplex closer to reality
Recently, the interest in STAR system research has shifted towards in-band full-duplex (IBFD), where the transmitter and receiver operate on the same frequency, at the same time. IBFD can therefore theoretically double the spectral efficiency compared to traditional duplexing schemes, such as FDD. IBFD is envisioned to be an enabling technology for 6G communications, but it is reliant on high-fidelity self-interference cancellation.
“The contribution of my dissertation to the field of IBFD is the introduction of two low-complexity self-interference cancellation algorithms, one of which was implemented on a real-time platform. Real-time implementations are a crucial step in making the IBFD technology viable for the future communications networks,” says Vesa Lampu.
Overall, Vesa Lampu’s dissertation provides several solutions to the self-interference cancellation problem in two distinct operational scenarios. The proposed solutions are evidenced to provide high levels of self-interference suppression, which is achieved at lowered computational cost compared to the reference methods.
Public defence on Friday 29 August
The doctoral dissertation of M.Sc. (Tech) Vesa Lampu in the field of communications engineering entitled Digital Self-Interference Cancellation Methods in 5G and Beyond STAR Systems will be publicly examined on Friday 29 August 2025 at 12.00 noon at Hervanta campus, Tietotalo, auditorium TB109. The Opponent will be Professor Mario Huemer from Johannes Kepler University Linz, Austria. The Custos will be Professor Mikko Valkama from Tampere University, Tampere, Finland. The work has been co-supervised by D.Sc. (Tech) Lauri Anttila from Tampere University.
The doctoral dissertation is available online.
The public defence can be followed via remote connection.