In intelligent reflecting surface (IRS) assisted communication systems, the acquisition of channel state information (CSI) is a crucial impediment for achieving the beamforming gain of IRS because of the considerable overhead required for channel estimation. Specifically, under the current beamforming design for IRS-assisted communications, KMN+KM channel coefficients should be estimated, where K, N, and M denote the numbers of users, IRS reflecting elements, and antennas at the BS, respectively. In this paper, we argue that since the BS-IRS channels are common channels among users, the number of channel coefficients being estimated can be reduced greatly by exploiting this special channel structure. Building on this observation, we propose a three-phase channel estimation framework for IRS-assisted uplink multiuser communications. Under this framework, we analytically prove that a time duration consisting of K+N+max(K−1,⌈(K−1)N/M⌉) pilot symbols is sufficient for the BS to recover all the channel coefficients.

This paper investigates a two-way relay channel operated with PNC between a controller and a robot. We particularly focus on a scenario where 1) the controller has more information to transmit than the robot; 2) the channel of the controller is stronger than that of the robot, and both users have nearly the same transmit power. To reduce the communication latency, we put forth an asymmetric PNC transmission scheme in which the controller transmits more information than the robot by exploiting its stronger channel gain. However, the current channel-coded PNC requires the two users to transmit the same amount of source information in order to preserve the linearity of the two users’ channel codes at the relay for successful decoding. To fill this gap, we propose a lattice-based encoding and modulation scheme. Our design is versatile on that the controller and the robot can freely choose their modulation orders based on their channel power, and the design is applicable for arbitrary channel codes, not just for one particular channel code.

This paper investigates noncoherent detection in a two-way relay channel operated with PNC. For noncoherent detection, the detector has access to the magnitude but not the phase of the received signal. For conventional communication in which a receiver receives the signal from a transmitter only, the phase does not affect the magnitude, hence the performance of the noncoherent detector is independent of the phase. PNC, however, is a multiuser system in which a receiver receives signals from multiple transmitters simultaneously. The relative phase of the signals from different transmitters affects the received signal magnitude through constructive-destructive interference. In particular, for good performance, the noncoherent detector in PNC must take into account the influence of the relative phase on the signal magnitude. Building on this observation, this paper delves into the fundamentals of PNC noncoherent detector design. To avoid excessive overhead, we do away from preambles. We show how the relative phase can be deduced directly from the magnitudes of the received data symbols.