Carrier Aggregation (CA) is investigated to address spectrum scarcity in 6G Integrated Sensing and Communication (ISAC) systems. However, inter-band phase offsets impose high complexity on achieving coherent gain across multiple bands. Furthermore, typical CA focuses on multi-frequency-band expansion, while multi-time-duration expansion has received limited attention. To address the above issues, this paper proposes a novel high-accuracy Multi-Band Joint Carrier Phase Sensing (MB-JCPS) framework that utilizes carrier phase information from multiple time-frequency bands to improve range and velocity sensing accuracy. A carrier phase extraction method is introduced based on oversampling Range-Doppler phase spectrum. The impact of non-ideal factors—including time, frequency, and phase offsets, as well as phase noise—on carrier phase is modelled, analyzed, and eliminated via an inter-path difference method. A Real-valued Multi-Carrier Ambiguity Resolution (RMCAR) algorithm is designed to resolve integer ambiguities in the range and velocity carrier phase models. The time-frequency selection problem is formulated as a constrained Rayleigh-quotient optimization problem and solved via successive convex approximation. The Cramér-Rao lower bound (CRLB) for the range and velocity estimation under phase offsets is derived, demonstrating the performance gain of CA in both frequency and time domains. Numerical simulations show that the proposed method achieves higher sensing accuracy with lower complexity than benchmark algorithms in 3GPP Uma-AV environments.

ABSTRACT Locally caching at base stations (BSs) can increase the network capacity as well as reduce the backhaul burden. However, it iremains an open problem whether it could increase energy efficiency (EE) for the future sixth‐generation (6G) network when the offloading link is in a deep fading condition. In order to analyse this problem, we attempt to analyse the energy efficiency of cache‐enabled wireless communication system assisted by reconfigurable intelligent surfaces (RIS), which is a new paradigm to increase EE. First, by considering the central limit theorem and Jensen's inequality, we obtain the approximated expression for EE when the number of RIS reflecting elements is very large. Secondly, due to the adoption of the RIS‐User/BS random association and a new BS‐RIS‐User wireless link, we analyse the performance between EE and the number of RIS reflecting elements under some condition. Finally, it is shown by full simulation that it is valid of our analysis, meanwhile, we gain the optimal cache capacity and the optimal transmission power of BS to maximize EE. Moreover, we show that the help of RIS can improve EE when the system is noise‐limited due to RIS can improve the signal power and has very low transmit power, but EE decreases in an interference‐limited system. Furthermore, we obtain the optimal number of BSs at the minimum EE in interference‐limited system, but EE decreases as the number of BS increases when the system is noise‐limited.

Wireless communication technology is one of the key technologies to achieve the key requirements of high reliability, low latency and mass connectivity in the Internet of Things (IoT). To meet these requirements, we apply the reconfigurable intelligent surface (RIS) in the wireless IoT networks. Specifically, we study a scheme that combines the joint beamforming design with RIS selection strategy for multi-RIS aided multi-cell wireless networks. In the joint beamforming design, we propose the control mode of “each base station (BS) controls its local RISs” for non-free propagation scenarios in wireless IoT networks, such as smart city and intelligent transportation system. Specifically, we give the details of algorithm for this control mode, and prove that it can achieve the performance comparable to the “all BSs jointly control all RISs” mode in the non-free propagation scenario, with lower algorithm complexity and control signaling overhead. Moreover, based on the joint beamforming design, we further propose a genetic algorithm-based RIS selection strategy to maximize the sum-rate under the constraint of limited RIS deployment. Finally, simulation results show that the proposed RIS selection strategy is effective and outperforms the existing schemes.

The widespread deployment of 5G networks has accelerated the development of Internet of Vehicles (IoV), laying the foundation for the development of intelligent transportation systems (ITSs) in future 6G networks. The unprecedented intelligence of 6G ITS is expected to enable the automation of vehicles, seamless collaboration, and intelligent management. High-volume information sharing plays a crucial role in this case, and its security and reliability becoming important cornerstones for 6G ITS. Without adequate security protection and trusted environments may result in unreliable and inefficient network services. In this article, we propose a reputation management-based blockchain, Info-Chain, for secure, trustworthy, and privacy-preserving information sharing in 6G ITS. Furthermore, to accommodate the distributed traffic environment in 6G ITS, we construct a novel consensus mechanism for Info-Chain, denoted as Proof of Reputation and sum (PoRs), which combines reputation with traffic environmental factors as competitive conditions. Finally, we propose a dynamic incentives and punishments mechanism that utilizes evolutionary game theory to guide vehicles to actively and honestly participate in information sharing. The security analysis shows that the proposed mechanism is capable of resisting common attacks, and the simulation result demonstrates that the proposed scheme not only enables efficient and secure information sharing in 6G ITS but also encourages vehicles to actively participate in information sharing.

In this paper, we propose a security-enhanced integrated sensing and communication (ISAC) system enabled by phase-coupled Intelligent Omni-Surfaces (IOS). The IOS, without the need for additional sensors, divides the entire space into two parts: a communication part and a sensing part. The IOS serves multiple users by providing communication services while also creating a virtual line-of-sight (LOS) link for target sensing. Moreover, the IOS is utilized to ensure physical layer security. Due to the possibility of the sensing target intercepting communication information, it is crucial to limit the information leakage rate. To achieve this, we jointly design the communication beamformers, sensing beamformer, and the IOS’s two phase-shift matrices. This joint design maximizes the sensing beam pattern gain towards the target, while meeting the requirements of the minimum signal-to-interference-plus-noise ratio (SINR) for communications and the maximum information leakage to possible malicious targets. To address this problem, we propose two types of alternative algorithms. The first type utilizes an independent phase-controlling model, while the second incorporates a coupled-phase model. Both algorithms aim to optimize the IOS’s phase-shift matrices.

Reconfigurable Intelligent Surfaces (RISs) have been considered as a promising technology for next generation communications. The existing works mainly focused on the single-connected RIS, which is always mathematically characterized as diagonal phase shift matrices, because that each element of traditional RIS separately controls its status and would not like to apply influence to any other elements. Although there exist some research on sub-array RIS, the grouping conception is based on the controlling strategy level but not on the hardware realization level. Fortunately, a new type of beyond diagonal RIS (BD-RIS) is proposed with its mathematical expression is symmetric and not limited to traditional diagonal phase shift matrices. BD-RIS model can fully cover the previous various types of RIS like: reflective RIS, refractive RIS, IOS (Intelligent Omni-Surfaces) or STAR-RIS (Simultaneously Transmitting And Reflecting RIS). In this work, a new model of BD-RIS is proposed to explain its working principle. Then, the quantization strategy for the new model BD-RIS is analyzed. Finally, the optimization algorithms for BD-RIS in single-user multi-input-multi-output (SU-MISO) systems and in multi-user multi-input-multi-output (MU-MISO) systems are proposed. Simulation results verifies the effectiveness of the the algorithms’ performance.

The routing algorithm will be the key issue in LEO satellite constellation with rapid development of the inter satellite links, especially for the space-based IOT networks. In this paper, a load-balancing strategy for routing technology based on historical traffic of satellite links was proposed. On the basis of the traditional snapshot-based satellite routing algorithm, the past traffic of each link is involved in calculating the optimal path, and the distributed of traffic load in the whole constellation network was considered to optimize. The network congestion and packet loss that caused by high traffic load burden in the some hot area of satellite network was alleviated significantly by the proposed algorithm. The simulation results show that this method can effectively improve the delay performance degradation caused by the unbalanced traffic load of the network under high load conditions, which also reduces the packet loss rate and optimizes the delay stability of the service.

This paper studies potential solutions for the beam switching issue based on a proposed beam-hopping LEO system. Different beam switching scenarios are considered, including beam switching within a satellite and beam switching between satellites. Also, different beam switching methods are discussed, including beam switching method with control beam, beam switching method with service beam, and beam switching method with hybrid beams. Analysis and simulation results show that control beam mechanism has the lowest overhead but the highest average delay, while hybrid beam mechanism can evidently decrease the average delay.

Recently, the ultra-dense low earth orbit (LEO) satellite constellation over high-frequency band has served as a potential solution for terrestrial data offloading owing to its seamless coverage and high-capacity backhaul. In this paper, we consider an integrated ultra-dense LEO-based satellite-terrestrial network where the terrestrial operator (TO) can offload its subscribed users to the LEO satellite network owned by the satellite operator (SO) for satellite-backhauled network access. However, data offloading consumes extra resources of the SO and degrades the quality-of-service of the SO's original users. Therefore, we aim to design a pricing mechanism based on the Stackelberg game to motivate both operators for data offloading, and the Stackelberg equilibrium is achieved by jointly optimizing the C-band user association, Ka-band spectrum allocation, and data service pricing. Simulation results show that our proposed pricing mechanism can motivate two operators for offloading efficiently. The influence of available frequency resources, data service prices, and the number of LEO satellites on the system performance are also discussed.

In this paper, based on 28 GHz indoor MIMO channel measurements, a cluster model based on Euclidean distance is analyzed. Moreover, according to QuaDRiGa (Quasi-Deterministic Radio Channel Generator) simulation platform, large-scale parameters like delay spread, ASA (Azimuth Spread of Arrival), Ricean K-factor and time evolution characteristics are simulated and validated. Results show that the cluster model describes the multipath environment physically. The QuaDRiGa simulation results fit quite well with measurement data. This verifies the applicability of the QuaDRiGa simulation model in millimeter wave bands. Received power and delay spread modeled as a function of distance in both LOS and NLOS cases, and the QuaDRiGa has better space-time continuity. The provided results are useful for design of 5G millimeter wave communication systems.

This paper proposes an adaptive relay selection method that exploits the social network and establishes a physical domain and social domain-based model named the Social-based device-to-device (D2D) relay selection model to address relay selection failure caused by the diversity of users cooperation willingness and the instability of communication links due to human mobility. Under the premise of tolerable interference caused to cellular users, the proposed approach synthetically considers the desired physical-relation factor and the social-interaction factor for the relay user. In particular, the reliability of the D2D link is obtained by considering the transmission stability of the link, assessed by the user encounter history and cooperation willingness characterized by user social distance, which is set as the criterion of relay selection, combined with the physical channel condition. Simulation results show that compared with the traditional socially blind method, the proposed method can increase the probability of relay selection success and reduce the burden of the cellular network to improve the system performance.

For the FDD massive MIMO system, the pilot overhead becomes a major problem, which may decrease the system performance. In this paper, a partial pilot transmission scheme and the corresponding two-dimension CSI acquisition methods are proposed. The downlink vertical pilot and horizontal pilot are mapped to one column and one row of the antenna array. CSI for the vertical and horizontal domain is fed back separately based on channel approximation algorithm. Compared with the full-dimension CSI acquisition method and the current passive antenna MIMO system (PAS), the proposed method achieves a compromise of the system overhead and the system throughput. Simulation result shows the effectiveness of the proposed method.

Dense small cells have been considered as a promising solution for improving system throughput in the future 5th generation networks. When a large number of small cells are overlapped, serious inter‐cell interference becomes one of the major technical challenges. Meanwhile, the energy efficiency (EE) of dense small cell networks (SCNs) attracts considerable concern, as well as the number of small cell base stations (SCBS)s in system, transmission power of each SCBS and caching capacity. Thus, the authors attempt to explore the potential of EE of cache‐enabled cooperative dense SCNs in this study. By deriving the closed‐form expression of the EE based on affinity propagation‐based clustering, the authors analyse the relationship between EE and the transmitter power, and that between EE and the number of SCBSs in system. Then, the optimal transmit power and the optimal number of SCBSs in the system are worked out under different antennas of each SCBS. Through numerical analysis and simulation, the authors demonstrate the feasibility and validity of their research.

In this paper, CSI feedback for massive MIMO system with planar antenna array is studied. A hybrid channel state information feedback mechanism is proposed. The proposed mechanism is based on combination of beamformed CSI-RS and non-beamformed CSI-RS transmission. Each codeword in the codebook for feedback regarding the non-beamformed CSI-RS is associated with a beamformed CSI-RS. By utilizing this association, accurate CSI feedback could be achieved without incurring overwhelming CSI-RS overhead while retaining CSI-RS coverage. Evaluation results are provided to confirm the effectiveness of the proposed mechanism.

In this paper, codebook design for massive MIMO systems with 32/64Tx transmit branches is investigated. Using the same parameterized codebook framework of LTE Rel-13 for 16Tx, 32/64Tx codebooks are discussed and evaluated through system level simulations. In addition, to deal with the larger feedback overhead, three codebook sub-sampling methods are discussed. These methods aim to achieve a tradeoff between the feedback overhead and the system performance. Simulation results prove the effectiveness of the proposed methods.

This paper presents wideband millimeter-wave channel characterization based on measurements at 26GHz with 1GHz bandwidth carried out in an open office at KeySight Beijing, China, which is a representative of an indoor hotspot scenario. In the time domain measurements, an omni-directional biconical horn is used as the transmitter, while at the receiver a 26dBi horn is applied and rotated with 5o angular step in the whole azimuth plane, and from -10o - 30o in the elevation plane with 10o angular step. Based on the line-of-sight (LOS) measured channel impulse responses at 39 locations, this paper investigates the directional and mean path-loss models and their relevant shadow fading. The channel parameters such as root mean square (RMS) delay spread, RMS angular spread at the azimuth and elevation planes, Ricean factor and power angular profiles (PAPs) etc. are analyzed for the purpose of channel simulations and propagation mechanism studies at 26GHz.

5G, the new generation of mobile networks, attracts lots of interests and attentions in wireless communication with its aggressive performance goals. To be able to provide much higher data rate than today, 5G mobile networks will operate at frequencies higher than the crowded frequency bands used today, with broader bandwidth. Understanding the propagation characteristics of the wireless channel under the new frequency bands is essential for the research of 5G mobile networks. This requires a channel sounder (CS) system for channel measurement and modeling. To meet the 5G performance goals, 5G channel sounder is required to support mmWave frequency bands, ultra-broad bandwidth and massive multiple-input/multiple-output (MIMO). These requirements can be very challenging for design and implementation. In this paper, we provide a novel mmWave channel sounder architecture which can use commercial Off-The-Shelf (COTS) instruments to set up the system with high performance and reliability to meet 5G channel sounder requirements. We show validation test results to prove the mmWave channel sounder system performance. 1GHz bandwidth SISO channel measurement campaign in open office has been done at 26GHz.

Massive multiple-input multiple-output (MIMO) is a promising technique to greatly increase the spectral efficiency and may be adopted by the next generation mobile communication systems. Base stations (BSs) equipped with large-scale antennas can serve multiple users simultaneously by exploiting the downlink precoding in time division duplex (TDD) mode. However, channel state information (CSI) of uplink transmissions cannot be simply used for downlink precoding, because the gain mismatches of the transceiver radio frequency (RF) circuits disable the channel reciprocity. In this paper, we focus on antenna calibration for massive MIMO systems with maximal ratio transmit (MRT) precoding to solve the channel nonreciprocity problem. A new calibration method, called mutual coupling calibration, is proposed by using the effect of mutual coupling between adjacent antennas. By exploiting this method, the BS can perform the calibration without extra hardware circuit and users' involvement. We also build up the model of calibration error and derive the closed-form expressions of the ergodic sum-rates for evaluating the impact of calibration error on system performance. Simulation results verify the high calibration accuracy of the proposed method and show the significant improvement of system performance by performing antenna calibration.

The increased number of antennas for massive MIMO system implies that the quantization codebook size needs to be significantly larger, which increases precoder search complexity accordingly. This paper compares the vertical/horizontal channel characteristics and finds that the vertical channel has a much longer coherence time than the horizontal channel. Based on these results, a two-dimension CSI quantization mechanism is proposed to allow decoupled vertical/horizontal domain quantization. The mechanism allows the vertical domain precoder search to be implemented at a slower rate than the horizontal domain, thereby enabling the network to separately control the feedback rate/granularity in different spatial dimensions. The proposed mechanism achieves significant UE complexity reduction and power consumption without compromising the system performance, demonstrated by realistic system simulation.

Femtocell has been considered as a promising solution since it can improve indoor coverage and the cellular system capacity in an economically viable way. When a large number of femtocells are overlapped, serious femto-femto interference becomes one of the major technical challenges. In this paper, we propose an inter-cell interference coordination scheme based on Quality of Service (QoS) hypergraph coloring algorithm.The hypergraph is used to model the cumulative interference relationships between femtocells, so as to mitigate interference more accurately. Taking into account the different QoS demand and greedy hypergraph coloring algorithm, all the femtocells are divided into different clusters, each of which has the maximum sum throughput. An effective resource allocation strategy is then gained by solving the optimisation problem of multi-user subchannels allocation. The simulation results demonstrate that the proposed scheme could enhance the user throughput and average throughput.

Device‐to‐device (D2D) is considered as a promising technique to increase resource utilisation and to provide new application in future wireless networks. This study reviews the standardisation progress of D2D in third‐generation partnership project. Three scenarios, in‐coverage, partial‐coverage and out‐of‐coverage, are defined. For these scenarios, channel model is obtained by the amendment of existing channel model. The function of D2D operation is divided into three building blocks: synchronisation, discovery and communication. The synchronisation procedure and synchronisation signal/channel are discussed first. Then the design aspects of D2D discovery and communication are discussed in detail, including channel structure design, resource allocation mechanisms, interference management and so on. Future works towards post Rel‐12 releases are also briefly outlined.

Multi-cell coordinated system is an attractive way of improving data rate, by serving one user through several base stations (BSs). BSs might share both data and their channel state information (CSI), but the demand on backhaul capacity makes it inflexible. In this paper, we consider the case with BSs sharing data dedicated to users but having only local CSI, and propose a decentralized nonlinear precoding algorithm for multi-cell coordinated system with multi-stream multi-antenna users. The proposed algorithm is designed to eliminate the inter-user interference and the inter-stream interference, and meanwhile to achieve equal performance for streams of each user. In the proposed algorithm, Tomlinson-Harashima precoding is applied to eliminate partial interference, and transmit space matrix is designed to eliminate the other interference. After the interference elimination, closed-form expression of the transmit and receive processing matrix are derived to maximize the minimum signal to interference plus noise ratio for streams of each user. Simulation results show that, compared with the decentralized linear precoding, the proposed algorithm achieves better performance.

In the open subscriber group (OSG) mode of heterogeneous network (HetNet), the inter macro-user interference is the main interference to macro user equipments (UEs), and the inter cell interference (ICI), containing the inter picocell interference and the cross-layer interference from macro base station (BS), is the main interference to pico UEs. In this paper, we propose an interference alignment (IA) scheme for such HetNet. The transceiver is designed as follows. Firstly, the precoding matrix for macro BS and the interference suppression matrices for macro UEs are used to eliminate the inter macrouser interference. Secondly, the precoding matrices of pico BSs are designed to align the inter picocell interference onto the space of the strongest cross-layer interference produced by macro BS. Finally, the aligned interference is removed by the interference suppression matrices of pico UEs. In addition, we introduce a power allocation scheme for the macro BS to further reduce the interference to pico UEs. The simulation results and the complexity analysis show that the proposed scheme can reduce the requirement of the receive antennas number and improve the system throughput of HetNet with lower complexity.

In this study, we consider the selective combining in hybrid cooperative networks (SCHCNs scheme) with one source node, one destination node and N relay nodes. In the SCHCN scheme, each relay first adaptively chooses between amplify‐and‐forward protocol and decode‐and‐forward protocol on a per frame basis by examining the error‐detecting code result, and N c (1 ≤ N c ≤ N ) relays will be selected to forward their received signals to the destination. We first develop a signal‐to‐noise ratio (SNR) threshold‐based frame error rate (FER) approximation model. Then, the theoretical FER expressions for the SCHCN scheme are derived by utilising the proposed SNR threshold‐based FER approximation model. The analytical FER expressions are validated through simulation results.

In this study, the authors introduce adaptive modulation and coding in a two‐way amplify‐and‐forward (AF) relay network to improve the system performance. They consider a cooperative system where two user nodes exchange information with the assistance of multiple two‐way AF relays. In the proposed scheme, the user nodes adaptively choose the appropriate modulation and coding scheme to ensure that the frame error rate (FER) satisfies the system requirement; all relays are utilised to forward the received signals to the user terminals. Furthermore, they provide a better approximation of the cumulative distribution function of the destination signal‐to‐noise ratio; and thus, derive more accurate expressions including average spectral efficiency and average FER in closed‐form, over Rayleigh fading channels. The theoretical analysis is verified by numerical results.

Let $\Gamma$ be a self-complementary circulant of prime power order. It is shown that either $\Gamma$ is a lexicographic product of two small self-complementary circulants or there exists a multiplicative automorphism of a regular cyclic subgroup that maps $\Gamma$ to its complement.

In this paper, the uplink sum-rate of the multi-cell multi-user massive MIMO system is studied under correlated Rayleigh fading channels. First, by considering pilot contamination effect, the equivalent system model of the massive MIMO is given with MMSE channel estimation. Then, the lower bound of the sum-rate is derived, and its asymptotical performance is studied when the base station antenna number goes to infinity. The result is general and is very accurate under the physical channel models.

Per-cell codebook based precoding is an effective transmission method in coordinated multi-point (CoMP) systems with the limited feedback constraint. There are two codeword selection methods for per-cell codebook, one is joint codeword selection (JCS) and another is independent codeword selection (ICS). In this paper, the system throughput obtained by the JCS and the ICS is analyzed firstly, which shows that JCS has a better trade-off between system throughput and feedback overhead. Then a codebook compression scheme for the JCS is proposed, which decreases the selection complexity of JCS by reducing the size of the codebook. Simulation results show that the proposed scheme can decrease the selection complexity greatly with tiny loss on performance and no additional feedback overhead.

The spectral efficiency of multi-cell multi-user distributed antenna system with imperfect channel state information (CSI) is studied in this paper. First, considering the pilot contamination and minimum mean-squared-error (MMSE) channel estimation, the equivalent channel model is presented and the sum-rate of the uplink transmission is derived. Under a physical channel model, the equivalent channel model can be seen as a special case of the joint correlated MIMO channel model proposed by Gao [1]. Then, the closed-form approximation of the spectral efficiency is derived. The spectral efficiency of the system with large number of antennas is also studied. Finally, the theoretical results are compared with Monte-Carlo simulation, and the performances of DAS and co-located massive MIMO are also compared. It is shown that similar to the systems with perfect CSIs, DAS still has large performance gains compared with massive MIMO.

One common and important task in urban modeling is the extraction of 3D building geometry. Detecting and describing rooftops is a key step. We propose a building roof detection and description method using airborne LiDAR data and orthorectified aerial imagery. Our approach makes no presumption of the shape that a building rooftop should exhibit. We use LiDAR to separate the building roof and its other significant features from other objects in the scene and estimate the strict outlines of these features. Imagery is processed using a robust segmentation and edge detection method to generate an edge map of the roof and then used to help refine the outlines obtained from LiDAR data. We will illustrate our approach by extracting several roof boundaries in the downtown region of Rochester, NY that exhibit simple and complex outlines.

The merit factor (MF) introduced by Golay has long been accepted as the standard criterion to evaluate and design binary sequences with good anti-multipath property in sonar, radar, and communication systems for its theoretical tightness and practical simplicity. In this paper, we first show that the MF is a biased anti-multipath performance evaluation metric in theory and, more importantly, is not a pertinent sequence design criterion in practice for most binary sequences of practical interest. Then we propose theweightedmeritfactor(WMF) based on a non-uniform weighting of the out-of-phase aperiodic autocorrelation function (ACF) that provides accurate measurement of self-generated interference for the constant amplitude complex-valued sequences and the nonconstant modulus ones. Based on the WMF, a list of "bad" (of low MFs) binary sequences (lengths 33-95) with better anti-multipath performance than the "best" (known) ones have been designed to verify its greater pertinence over the MF as a sequence design criterion for sonar, radar, and communication systems. Moreover, we extend the weighted correlation model of the WMF to the code-division multiple-access (CDMA) systems and propose theweightedcross-correlationfactor(WCF) to evaluate the sequence set's multiple-access interference (MAI) rejection property in the context of multipath propagation. Theoretical analysis corroborated by simulations confirms that the WCF provides greater practical pertinence and analytical tractability over the current standard criterion.