Uplink Positioning for PASS in Multipath Environments

Pinching-antenna systems (PASS) enhance wireless propagation by activating or placing pinching antennas (PAs) near users. Therefore, accurate uplink positioning is essential for efficient communication. In this paper, an uplink multi-carrier positioning framework is established for PASS in multipath environments. Matrix pencil (MP)-based and low-complexity Rank-1 ranging algorithms are proposed to estimate the distances between the PAs and the user. For the MP-based ranging algorithm, the line-of-sight (LoS) component is separated from non-line-of-sight components by exploiting the shift-invariance property of the Hankel matrix, thereby enabling accurate distance estimation. For the Rank-1 ranging algorithm, the dominant LoS delay is directly isolated through truncated singular value decomposition, thereby avoiding matrix inversions. Subsequently, a two-stage weighted nonlinear least-squares (WNLS) positioning algorithm is designed to estimate the three-dimensional user position. To gain further insights, a comprehensive theoretical performance analysis of the proposed ranging and positioning algorithms is conducted. The closed-form ranging variances and position error bound (PEB) are derived to reveal the error propagation mechanism. Numerical results demonstrate that: i) The MP-based algorithm achieves higher accuracy and robustness than the Rank-1-based algorithm, while the Rank-1-based algorithm has lower computational complexity. ii) The positioning error of the MP-based algorithm follows the same trend as the derived PEB, whereas the Rank-1 algorithm exhibits an error floor due to multipath bias. iii) The positioning accuracy of the MP algorithm improves as the number of subcarriers increases.

Pinching-Antenna Systems (PASS)-Based User-Side Navigation: An Anchor-Line-based Approach

Pinching-antenna systems (PASS) are capable of dynamically reconfiguring wireless channels by flexibly repositioning pinching antennas (PAs) along the waveguides to establish short-range line-of-sight links. In this paper, a user-side navigation framework for PASS is proposed, where mobile users determine their own positions using only downlink broadcast signals without any prior knowledge of the PA positions. First, a Lambert W function-based PA positioning and pseudorange estimation (LWF-PAP) algorithm is developed, in which the closed-form expressions for both the PA positions along the waveguide and the PA-user pseudoranges are derived. Second, a weighted least squares-based PASS navigation (WLS-PAN) algorithm is formulated, where the nonlinear PASS-based navigation equations are transformed into a closed-form linear system, and the optimal weight matrix is derived, achieving minimum-variance unbiased estimation. Third, the PA-derived position dilution of precision (PA-PDOP) metric is further defined to characterize the theoretical accuracy bound. Simulation results demonstrate that centimeter-level positioning accuracy is achieved for both PAs and users within the breakpoint distance. It is also shown that uniform PA deployment and a moderate increase in the number of PAs effectively improve navigation accuracy, thereby validating the effectiveness and robustness of the proposed framework for distributed real-time user-side self-navigation.

On the Performance of Pinching-Antenna Systems (PASS) Under Dynamic Channels with Blockages

The performance of pinching-antenna systems (PASS) is fundamentally affected by line-of-sight (LoS) blockage in practical environments. In this paper, PASS is investigated under realistic, obstacle-induced blockage by jointly considering the LoS and non-LoS (NLoS) components, rather than relying on a LoS channel or a probabilistic blockage model. A geometry-aware blockage model is adopted, where a blockage region on the waveguide is defined according to the actual locations and geometric features of obstacles, such that a pinching-antenna (PA) located within the blockage region is unable to establish a LoS link to the user equipment (UE). The channel models of PASS are developed by jointly accounting for in-waveguide attenuation and spatial propagation loss. To quantify the impact of channel factors on PASS performance, a single-PA single-UE scenario is studied under Rayleigh and Rician fading channels. Closed-form expressions for the outage probability are derived for both cases. For the ergodic rate, a closed-form expression is obtained in the Rayleigh case, while a complete analytical expression and an approximate closed-form expression are derived in the Rician case. Analytical expressions are derived for the endpoints of the blockage region, and the deployment criteria of optimal PA are provided. Simulation results validate the analysis and reveal that: i) NLoS scattering has a twofold effect on PASS performance, potentially degrading the outage performance while improving the rate performance under Rician fading; ii) Sufficiently strong NLoS scattering can still sustain communication in the presence of LoS blockage; iii) The optimal PA position is jointly determined by the environment geometry and the interplay between spatial propagation loss and in-waveguide attenuation.

Constrained Pinching Antenna Array Design for Sum-Rate Maximization in Multi-User PASS

Pinching antenna systems (PASS) have recently emerged as a promising architecture for flexible indoor wireless communications. However, most existing pinching antenna (PA) array designs for multi-user PASS either offer limited beam adaptation accuracy or require prohibitively high deployment cost. In this paper, we investigate a more practical constrained pinching antenna array (C-PAA)-assisted downlink PASS, where multiple PAs are grouped into a movable array and can be finely adjusted within the array at the wavelength scale. To improve the system spectral efficiency, a sum-rate maximization problem is formulated by jointly considering the array-center position and the fine-grained antenna distribution within the C-PAA. First, the structural properties of the C-PAA are characterized, and an explicit upper bound on the array aperture is derived. Then, tractable approximations for the effective channel gain and the achievable user rate are developed. Furthermore, the optimization problem of the multi-user sum-rate is analyzed, where the system sum-rate function is shown to exhibit a favorable unimodal behavior under practically relevant conditions, which enables an efficient one-dimensional search for the optimal C-PAA position. To further reduce the computational complexity, a closed-form approximate solution for the near-optimal array-center position is derived. Numerical results verify the accuracy of the developed analysis and demonstrate that the proposed C-PAA scheme closely approaches the ideal upper bound and significantly outperforms conventional fixed-spacing and existing PA array benchmarks.

Integrated Positioning and Communications for PASS: A Robust Approach

The pinching-antenna systems (PASS), which dynamically activate and relocate the pinching-antennas (PAs) along the dielectric waveguide, offer unprecedented potential for integrated positioning and communication. The multi-waveguide-based uplink positioning approaches for indoor environments are first proposed in this paper, and the downlink communication performance is analyzed. Two possible scenarios, multi-waveguide single-PA (MWSP) and multi-waveguide multi-PA (MWMP), are considered under the assumptions of line-of-sight channels and a single, stationary user. For the MWSP scenario, the received signal strength indication (RSSI)-based ranging method and the MWSP-based least square (LS) positioning algorithm are developed. To gain deeper insights, a comprehensive error analysis of the LS positioning algorithm is conducted. Subsequently, for the MWMP scenario, the closed-form expression of the superposed signal is derived. According to the signal power, the MWMP-based grid search algorithm is proposed and the estimation error of proposed algorithm is analyzed. Then, based on the user's positioning result, the PAs are relocated to provide downlink communication service, and the achievable data rate of MWSP and MWMP scenarios are analyzed. Numerical results validate the correctness of our analysis, which show that: i) For the MWSP scenario, a smaller geometric dilution of precision (GDoP) leads to a lower average positioning error. Furthermore, even when the GDoP is large, the regions where the distances to PAs are nearly equal achieve the best accuracy. ii) For the MWMP scenario, non-parallel waveguide deployment improves positioning accuracy, although errors increase with the number of PAs. iii) The noise has a serious double-impact on data rate. There is a trade-off between positioning accuracy and communication performance.

Multi-/Uni-Cast Non-Orthogonal Multiple Access-Based INAC

With the rapid development of satellite communication and navigation, there is an urgent need to integrate both technologies to achieve reliable communication and precise navigation services within the same satellite system. By combining multi-/uni-cast (MUC) and non-orthogonal multiple access (NOMA) technologies, we propose a novel MUC-NOMA-based integrated navigation and communication (INAC) signal structure, in which the navigation and communication signals share a common pseudo noise (PN) sequence, thereby integrating satellite communication and navigation at the signal level. According to different power allocation strategies, two scenarios are defined: multi-cast-oriented (MO-) INAC and uni-cast-oriented (UO-) INAC, where a greater portion of power is assigned to either the multi-cast or the uni-cast signal, respectively. To mitigate co-channel interference, we employ successive interference cancellation (SIC) at the receiver and design a signal processing algorithm for the proposed INAC signal. Then, closed-form expressions are subsequently derived for the bit error rates (BER) of both the navigation and communication signals, along with the positioning accuracy of the navigation signal. To gain further insights, the impacts of power allocation factors and communication rates are evaluated. Our analysis results show that: i) In the MO-INAC scenario, the positioning and BER performance of navigation signal are excellent when more power is assigned to the multi-cast signal; ii) In the UO-INAC scenario, interference in the shared resources is reduced when more power is assigned to the uni-cast signal; iii) The ranging accuracy decreases as the communication data rate increases. Numerical results confirm the superior BER and positioning accuracy of the MO-INAC scenario for MEO satellites.

tuGEMM: Area-Power-Efficient Temporal Unary GEMM Architecture for Low-Precision Edge AI

General matrix multiplication (GEMM) is a ubiquitous computing kernel/algorithm for data processing in diverse applications, including artificial intelligence (AI) and deep learning (DL). Recent shift towards edge computing has inspired GEMM architectures based on unary computing, which are predominantly stochastic and rate-coded systems. This paper proposes a novel GEMM architecture based on temporal-coding, called tuGEMM, that performs exact computation. We introduce two variants of tuGEMM, serial and parallel, with distinct area/power-latency trade-offs. Post-synthesis Power-Performance-Area (PPA) in 45 nm CMOS are reported for 2-bit, 4-bit, and 8-bit computations. The designs illustrate significant advantages in area-power efficiency over state-of-the-art stochastic unary systems especially at low precisions, e.g. incurring just 0.03 mm^2 and 9 mW for 4 bits, and 0.01 mm^2 and 4 mW for 2 bits. This makes tuGEMM ideal for power constrained mobile and edge devices performing always-on real-time sensory processing.

Performance Analysis of NOMA-RIS aided Integrated Navigation and Communication (INAC) Networks

Satellite communication constitutes a promising solution for the sixth generation (6G) wireless networks in terms of providing global communication services. In order to provide a cost-effective satellite network, we propose a novel medium-earth-orbit (MEO) satellite aided integrated-navigation-and-communication (INAC) network. To overcome the severe path loss of MEO satellites, we conceive a network for simultaneous serving navigation and communication for ground users by adopting the non-orthogonal multiple access (NOMA) technique and the reconfigurable intelligent surface technique. Based on the power allocation strategies, communication-oriented (CO-) and navigation-oriented (NO-) INAC scenarios are proposed. We first derive the closed-form expressions for the new channel statistics, outage probability and channel capacity of the INAC-user. For gleaning further insights, the diversity orders and navigation accuracy are evaluated for illustrating the performance of the INAC networks. According to our analysis, when RIS elements are sufficient, the proposed INAC network can perform better than conventional terrestrial communication networks in terms of channel capacity. Numerical results are provided for confirming that the NO-INAC and CO-INAC scenarios have superior performance for communication in the low signal-to-noise-ratio (SNR) regimes and high SNR regimes, respectively, which indicates a hybrid CO/NO-INAC network is preferable.