Due to overshadow and channel fading, many mobile users are unable to receive the signal transmitted from satellite directly. Hence, some relay stations should be set to help this type of users to receive signals reliably. In this paper, we present a novel cognitive hybrid satellite-terrestrial model, where two cognitive relays forward their received signal for a mobile user successively. Furthermore, we address its achievable rate maximization. We first convert the co-channel interference threshold into transmit power constraints, and then formulate the maximization of the achievable rate as an optimization problem. Based on Karush–Kuhn–Tucker conditions, the optimization problem is decomposed into four cases, each of which is solved in closed form. Simulation study with different system settings is presented, and the efficiency of the proposed power allocation scheme is shown.

Achievable Rate Maximization for Cognitive Hybrid Satellite-Terrestrial Networks With AF-Relays

With the uninterrupted revolution of communications technologies and the great-leap-forward development of emerging applications, the ubiquitous deployment of Internet of Things (IoT) is imperative to accommodate constantly growing user demands and market scales. Communication security is critically important for the operations of IoT. Among the communication security provisioning techniques, physical layer security (PLS), which can provide unbreakable, provable, and quantifiable secrecy from an information-theoretical point of view, has drawn considerable attention from both the academia and the industries. However, the unique features of IoT, such as low-cost, wide-range coverage, massive connection, and diversified services, impose great challenges for the PLS protocol design in IoT. In this article, we present a comprehensive review of the PLS techniques toward IoT applications. The basic principle of PLS is first briefly introduced, followed by the survey of the existing PLS techniques. Afterwards, the characteristics of IoT are identified, based on which the challenges faced by PLS protocol design are summarized. Then, three newly-proposed PLS solutions are highlighted, which match the features of IoT well and are expected to be applied in the near future. Finally, we conclude the paper and point out some further research directions.

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A Review of Physical Layer Security Techniques for Internet of Things: Challenges and Solutions.

Energy harvesting (EH)-powered wireless communications have attracted great attention from both industry and academia. However, the available energy, which relies on EH efficiency, will become another nonnegligible factor when we do research on EH-powered wireless communications. This paper studies the resource allocation problems in terms of spectrum and energy under EH-powered Device-to-Device (D2D) Communication underlaying Cellular Network (EH-DCCN). In this network, D2D pairs powered by EH are allowed to reuse the spectrum resources occupied by Cellular Users (CUs). To investigate the resource allocation problems, a sum-rate maximization problem of the whole cellular network with consideration of Quality of Service (QoS) and available energy constraints is formulated. The maximization problem is a nonconcave mixed-integer nonlinear programming (MINLP) problem, which has been proved to be NP-hard. To solve the problem, we first relax it with a concave lower bound on the original problem and then obtain the theoretical performance of the lower bound by Outer Approximation Algorithm. Moreover, a heuristic algorithm, an Energy-aware Space Matching approach (ESM), is proposed to acquire a suboptimal solution with low computational complexity. Finally, numerical simulation results indicate our considered resource allocation strategy is more effective than the strategy only based on channel state information under the EH-DCCN. Moreover, the performance in aspects of the sum rate and the matching probability shows that the ESM can approximately obtain the theoretical performance of the lower bound on the original problem under the scenarios with higher ratio of CU and EH-powered D2D numbers.

Resource Allocation for Energy Harvesting-Powered D2D Communication Underlaying Cellular Networks

As multihomed terminals are equipped with multiple interfaces and allowed to access heterogeneous networks, transferring data simultaneously through all the available paths becomes possible and also brings many benefits. Multipath TCP (MPTCP) has been proposed to distribute an application stream over different TCP connections. However, due to the disparate latencies of different paths, the problem of existing out-of-order packets usually occurs at the receiver. Large number of these packets exhaust the limited receiving buffer and make the receive window be stalled, which greatly degrade the throughput. Thus, an efficient scheduling mechanism will play an important role to keep in-order delivery. However, almost all of the previous intelligent scheduling mechanisms ignored packet losses, and didn't consider window changes of the congestion control algorithm and utilize the feedback information, which cannot perform well in the lossy heterogeneous networks. In this paper we propose a new scheduling algorithm: Forward Prediction based Dynamic Packet Scheduling and Adjusting with Feedback (DPSAF). DPSAF first utilizes maximum likelihood estimation in TCP modeling to estimate the data amount sent on other paths simultaneously, which takes packet loss rate and time offset into consideration, then gets feedback information from SACK options and fixes the scheduling value. From the simulation, we can see that our mechanism obviously improves throughput and reduces cache occupancy at receiver in lossy heterogeneous networks.

DPSAF: Forward Prediction Based Dynamic Packet Scheduling and Adjusting With Feedback for Multipath TCP in Lossy Heterogeneous Networks

The past, present, and future of transport-layer multipath

As terminals are equipped with multiple interfaces and allowed to access heterogeneous networks, transferring data simultaneously through all the available paths becomes possible and also brings many benefits. Multipath TCP (MPTCP) distributes an application stream over different TCP connections. Since different paths have disparate latencies, out-of-order packets problem occurs at receiver. Large number of these packets exhaust the limited receive buffer and make the receive window stall, which greatly degrade the throughput. Thus, a scheduling mechanism plays an important role to keep in-order delivery. Previous intelligent scheduling mechanisms schedule data independently each time and doesn't utilize the feedback carried in acknowledgements, which lose flexibility. Our Offset Compensation based Packet Scheduling (OCPS) mechanism gets feedback information from SACK options and gains the knowledge of whether last scheduling round still causes out-of-order problem. Then it modifies the scheduling next round accordingly by using an offset. The simulation results illustrate our mechanism enhance throughput and reduce cache occupancy at receiver.

OCPS: Offset Compensation based Packet Scheduling mechanism for multipath TCP

This paper proposes a generalized interrelay interference cancelation (gIRIC) scheme for a two-path relay model in multisource systems. Both the sources and the relay adopt complex field network coding (CFNC) to remove the interrelay interference (IRI) caused by the two-path relay. Furthermore, we introduce two detecting modes (gIRIC-noSD and gIRIC-SD) for destination in our scheme. Two switching rules are given to select a suitable detecting mode between treating the signal of a direct link as noise (gIRIC-noSD) and utilizing the direct link to assist signal detection (gIRIC-SD). The bounds of average symbol error probability (SEP) and throughput of our scheme are derived.

Generalized Interrelay Interference Cancelation for Two-Path Successive Relaying Systems

Device-to-device (D2D) communication is proposed as a vital technique to enhance system capacity in cellular networks, which requires efficient interference modeling and managements to improve spectral efficiency. In practice, even when two wireless connections share the same resources, the interference between them may not always exist if there is no conflict at packet-level transmissions. To explore the real effect of interference, in this paper, we establish a cross-layer model for D2D communications underlaying cellular network and derive the closed-form stable throughput region. Then, we formulate an optimization problem to obtain the maximal achievable packet rate for cellular link, which determines whether the D2D pair can share the same resources with a specific cellular link. By dividing the original optimization problem into several simplified subproblems, the optimal solution can be calculated with low complexity. Subsequently, our model is extended to a generalized scenario where multiple D2D pairs share the same resources with one cellular link. Due to the complexity of obtaining closed-form expressions on stable throughput regions, we propose an algorithm to determine whether the transmissions of the cellular link and the multiple D2D pairs can satisfy the QoS requirements simultaneously. Furthermore, a low-complexity dynamic admission control strategy is introduced to deal with the admission process for new D2D requests. As a consequence, the cellular spectrum can allow access of many more D2D pairs than what the conventional model can. The significant improvements are verified by numeral simulations.

Stable Throughput Region and Admission Control for Device-to-Device Cellular Coexisting Networks

Relay-based cooperative communication has become a research focus in recent years because it can achieve diversity gain in wireless networks. In existing works, network coding and the two-path relay scheme is exploited to deal with the increase in network size and the half-duplex nature of relay, respectively. To further improve bandwidth efficiency, we propose a novel cooperative transmission scheme which combines network coding and the two-path relay scheme together in the multi-source system. Due to the utilization of two-path relay, our proposed scheme achieves full-rate transmission. Adopting complex field network coding (CFNC) at both the sources and the relays ensures that symbols from different sources are allowed to be broadcasted in the same time slot. We also adopt physical-layer network coding (PNC) at the relay nodes to deal with the inter-relay interference caused by the two-path relay. With careful process design, our scheme can achieve the ideal throughput up to 1 symbol per source per time slot (sym/S/TS). Furthermore, the theoretical analysis provides a method to estimate the symbol error probability (SEP) and throughput in complex additive white Gaussian noise (AWGN) and Rayleigh fading channels. The simulation results verify the improvements achieved by the proposed scheme.

High-Throughput Cooperative Communication with Interference Cancellation for Two-Path Relay in Multi-Source System

Two-path relay networks can be deployed to achieve full-rate transmissions. In this paper, we introduce stable throughput analysis into decode-and-forward (DF) two-path relay networks. We establish the queueing model and take outage probabilities into consideration to characterize the packet-level cooperation and derive the closed-form stable throughput region. Based on the stable throughput region, we also propose a power-allocation scheme between the source node and relays to maximize the achievable packet rate. The maximal achievable packet rate determines the admission control of certain cooperation (i.e., when to cooperate) under a specific interrelay interference (IRI) cancellation technique. The power allocation is utilized to illustrate how to cooperate between the source node and relays. Three IRI responses are considered, and the system behaviors under various circumstances are presented through simulations.

Hao Lu

Papers

OCPS: Offset Compensation based Packet Scheduling mechanism for multipath TCP

Generalized Interrelay Interference Cancelation for Two-Path Successive Relaying Systems

Stable Throughput Region and Admission Control for Device-to-Device Cellular Coexisting Networks

High-Throughput Cooperative Communication with Interference Cancellation for Two-Path Relay in Multi-Source System

Analysis on Decode-and-Forward Two-Path Relay Networks: When and How to Cooperate