This paper explores the use of reconfigurable intelligent surface (RIS) in the integrated terrestrial-space network (ITSN) to mitigate co-channel interference between low earth orbit (LEO) satellite systems and terrestrial base stations (BS), with a focus on minimizing total power consumption. An alternating optimization framework is developed, decomposing the problem into three subproblems: BS beamforming design solved via second-order cone programming (SOCP) with interior-point methods or zero-forcing (ZF) method with water-filling algorithm, RIS phase-shift optimization addressed through semi-definite relaxation (SDR) combined with Gaussian randomization to handle non-convex unit-modulus constraints, and LEO satellite transmit signal power optimization addressed by water-filling algorithm. Simulation results show that compared to conventional non-RIS architectures, the proposed system achieves significant power reductions: 14–16 dB for BS and 8.68 dB for satellites. Compared to the WMMSE-based method, it reduces interference at BS users by 4–6 dB and at SU by 15–20 dB. When the satellite power is fixed, it still reduces the power consumption of the BS by 6-8 dB. The proposed methodology enables harmonious coexistence between terrestrial BSs and LEO satellite service zones under strict power budgets through enhanced interference decoupling capabilities.

The sixth-generation (6G) communication networks target peak data rates exceeding 1Tbps, necessitating base stations (BS) to support up to 100 simultaneous data streams. However, sparse pilot allocation to accommodate such streams poses challenges for users’ channel estimation. This paper presents channel estimation considerate precoding (CECP), where BS precoders prioritize facilitating channel estimation alongside maximizing system throughput. To address the computational complexity of 6G large-scale multi-input multi-output (MIMO) systems, we propose a computationally-efficient space-time block diagonal channel shortening (ST-BDCS) precoding scheme. By leveraging the sparse Toeplitz property of orthogonal frequency division multiplexing (OFDM) channels, this time-domain precoding design effectively mitigates multi-user interference in the downlink and shortens the effective channel’s temporal length. Consequently, users can estimate the channels using sparse pilots. To enable fast implementation, we develop a generalized complex-valued Toeplitz matrix QR decomposition algorithm applicable to various space-time signal processing problems. Simulation results demonstrate that the ST-BDCS precoding method approximates the spectral efficiency performance of conventional subcarrier-by-subcarrier precoding schemes. However, it offers the advantages of accurate effective channel estimation for users and significantly reduced computational complexity for the BS.

The wireless in-band full-duplex (IBFD) technology can in theory double the system capacity over the conventional frequency division duplex (FDD) or time-division duplex (TDD) alternatives. But the strong self-interference of the IBFD can cause excessive quantization noise at the output of the analog-to-digital converters (ADCs), which hampers its real implementation. Fortunately, the reconfigurable intelligent surface (RIS) can reconfigure the wireless channels by dynamically adjusting the reflection coefficients, which makes it a promising solution to self-interference mitigation (SIM) for the IBFD system. This paper considers a RIS-assisted IBFD (RAIBFD) system where a full-duplex base station (BS), assisted by a co-located RIS, receives and transmits signals on the same frequency band simultaneously. We propose to jointly design the DL precoding matrix and the RIS coefficients to mitigate the strong self-interference before the ADCs of finite bit resolutions. To gauge the performance of the proposed RAIBFD system, we also consider an idealistic RIS-assisted IBFD (I-RAIBFD) system with ADCs of infinite bit resolutions and RIS-assisted FDD (RAFDD) system, and take them as performance benchmarks. The effectiveness of the proposed RAIBFD system is verified by simulation studies, even if the phases of the RIS have only finite resolutions.

This paper proposes a novel scheme for mitigating strong interferences, which is applicable to various wireless scenarios, including full-duplex wireless communications and uncoordinated heterogeneous networks. As strong interferences can saturate the receiver’s analog-to-digital converters (ADC), they need to be mitigated both before and after the ADCs, i.e., via hybrid processing. The key idea of the proposed scheme, namely the Hybrid Interference Mitigation using Analog Prewhitening (HIMAP), is to insert an$M$-input$M$-output analog phase shifter network (PSN) between the receive antennas and the ADCs to spatially prewhiten the interferences, which requires no signal information but only an estimate of the covariance matrix. After interference mitigation by the PSN prewhitener, the preamble can be synchronized, the signal channel response can be estimated, and thus a minimum mean squared error (MMSE) beamformer can be applied in the digital domain to further mitigate the residual interferences. The simulation results verify that the HIMAP scheme can suppress interferences 80dB stronger than the signal by using off-the-shelf phase shifters (PS) of 6-bit resolution.