Multi-hop message forwarding based on geographic coordinates is a fundamental building block for vehicular communication. However, the unstable links and wide range of node densities make it challenging to design an algorithm suitable for vehicular use. We introduce DAZL, a new forwarding protocol that combines three concepts in a novel way. First, multiple nodes cooperate in packet forwarding. Compared with traditional single relay schemes, this provides robustness against changes in topology and packet delivery rates. Second, network-layer slotting is used to control duplication and contention in high density scenarios. Third, a distributed prioritization algorithm is used to opportunistically maximize hop length. Through both experiments and simulations, we show that DAZL provides improvements of up to 60% in throughput over single relay forwarding, while ensuring low latency and replication.

DAZL: Density-Aware Zone-based packet forwarding in vehicular networks

In current wireless networks, the radio systems are regulated by a fixed spectrum assignment strategy. This policy partitions the whole radio spectrum into a fixed number of radio ranges, each exclusively assigned to a specific user. Such a spectrum assignment strategy leads to an undesirable condition under which some systems only use a small portion of the allocated spectrum while the others have very serious spectrum insufficiency. The learning automata-based cognitive radio which is proposed in this paper is a highly potential technology to address the spectrum scarcity challenges in wireless ad hoc networks. This paper proposes a learning automata-based dynamic frame length TDMA scheme for slot assignment in clustered wireless ad-hoc networks with unknown traffic parameters, where the intra-cluster communications are scheduled by a TDMA scheme, and a CDMA scheme is overlaid on the TDMA to handle an interference-free inter-cluster communication. In this method, each cluster-head is responsible for a collision-free slot assignment within the cluster and determines the input traffic parameters of its own cluster members. It then takes these traffic parameters into consideration for an optimal channel access scheduling in the cluster. The medium access control layer in each cluster is based on a time division multiple access (TDMA) scheme, in which each host is assigned a fraction of the TDMA frame proportional to its traffic load. The simulation experiments show the superiority of our proposed slot assignment algorithm over the existing methods in terms of the channel utilization, control overhead, and throughput, specifically, under bursty traffic conditions.

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A Learning Automata-Based Cognitive Radio for Clustered Wireless Ad-Hoc Networks

In this paper, we propose a dynamic TDMA slot reservation (DTSR) protocol for cognitive radio ad hoc networks Quality of Service (QoS) guarantee plays a critically important role in such networks We consider the problem of providing QoS guarantee to users as well as to maintain the most efficient use of scarce bandwidth resources A dynamic frame length expansion and shrinking scheme that controls the excessive increase of unassigned slots has been proposed This method efficiently utilizes the channel bandwidth by assigning unused slots to new neighboring nodes and increasing the frame length when the number of slots in the frame is insufficient to support the neighboring nodes It also shrinks the frame length in an effective way Our proposed scheme, which provides both QoS guarantee and efficient resource utilization, be employed to optimize the channel spatial reuse and maximize the system throughput Extensive simulation results show that the proposed mechanism achieves significant performance improvement in multichannel cognitive radio ad hoc networks

Dynamic TDMA slot reservation protocol for cognitive radio ad hoc networks

This paper introduces a nonsmooth (NS) neural network that is able to operate in a time-dependent (TD) context and is potentially useful for solving some classes of NS-TD problems. The proposed network is named nonsmooth time-dependent network (NTN) and is an extension to a TD setting of a previous NS neural network for programming problems. Suppose $C(t)$ , $t \ge 0$ , is a nonempty TD convex feasibility set defined by TD inequality constraints. The constraints are in general NS (nondifferentiable) functions of the state variables and time. NTN is described by the subdifferential with respect to the state variables of an NS-TD barrier function and a vector field corresponding to the unconstrained dynamics. This paper shows that for suitable values of the penalty parameter, the NTN dynamics displays two main phases. In the first phase, any solution of NTN not starting in $C(0)$ at $t=0$ is able to reach the moving set $C(\cdot )$ in finite time $t_{h}$ , whereas in the second phase, the solution tracks the moving set, i.e., it stays within $C(t)$ for all subsequent times $t \ge t_{h}$ . NTN is thus able to find an exact feasible solution in finite time and also to provide an exact feasible solution for subsequent times. This new and peculiar dynamics displayed by NTN is potentially useful for addressing some significant TD signal processing tasks. As an illustration, this paper discusses a number of examples where NTN is applied to the solution of NS-TD convex feasibility problems.

Nonsmooth Neural Network for Convex Time-Dependent Constraint Satisfaction Problems

In this paper, we propose regularized block diagonalization (RBD) precoding using artificial noise (AN) for physical layer security in downlink multi-user MIMO wireless networks. We derive secrecy sum rate and asymptotic secrecy sum rate for the proposed scheme. The optimum power allocation for legitimate users and the AN signal are derived in closed form for optimal asymptotic secrecy sum rate. Our analysis shows that to achieve best performance, it is more efficient to degrade the performance of the eavesdropper than improving legitimate users’ rates. We also study the impact of error in channel estimation on the system and derive closed-form SINR and secrecy sum-rate expressions for this case. Simulations show that the secrecy sum rate of RBD precoding outperforms the secrecy sum rate of regularized channel inversion by 0.5 bits/s/Hz. We also show that in the presence of channel estimation error, our approximate closed forms for secrecy sum rate are very closed to the actual secrecy sum rate over a wide range of SNR and channel estimation error values.

Large-Scale Analysis of Regularized Block Diagonalization Precoding for Physical Layer Security of Multi-User MIMO Wireless Networks

This paper proposes an evolutionary-dynamic TDMA slot assignment protocol (E-DTSAP) for ad hoc networks. According to the topology density of the network and the bandwidth requirement, the proposed protocol changes the frame length and the transmission schedule dynamically. Moreover, it allows the transmitter to reserve one or more unscheduled slots from the set of unassigned slots in its neighborhood by coordinating the announcement and confirmation with the neighboring nodes up to two hops away. The important sections of the proposed protocol including frame format, packet format and slot assignment are presented and analyzed. The simulation results show that our proposed protocol is better than the conventional second category MAC protocols and 802.11.

An Evolutionary-Dynamic TDMA Slot Assignment Protocol for Ad Hoc Networks

This paper studies masked beamforming schemes for secure communication in broadcast multiple-input multiple-output (MIMO) systems with a passive multiple-antenna eavesdropper. Assuming no information about the eavesdropper is available at the transmitter, we aim to maximize the transmit power of the artificial noise while meeting mean square error (MSE) constraints at the legitimate receivers and the total power constraint at the transmitter. Based on imperfect channel state information (CSI) of the legitimate receivers at the transmitter, we present a worst-case robust masked beamforming algorithm. By exploiting alternating iterative optimization, the proposed algorithm recasts the non-convex optimization problem as two semidefinite program (SDP) based subproblems, which are solvable with interior-point methods. Simulation results are provided to illustrate the secrecy performance of the proposed algorithm.

Worst-case robust masked beamforming for secure broadcasting

The invention belongs to the technical field of wireless network communication, and specifically relates to a three-dimensional constellation-rotating encryption method based on wireless channel characteristics. The three-dimensional constellation-rotating encryption method based on the wireless channel characteristics comprises the following main steps: (S1) transmitting, by legal communication nodes, detection signals to each other, extracting an equivalent channel phase; (S2) performing, by a transmitting end, three-dimensional mapping on transmission data information to obtain constellation points in a three-dimensional space, utilizing the equivalent channel phase to perform rotating encryption on the constellation points; (S3) performing, by a receiving end, rotating decryption on the transmission data information by means of the equivalent channel phase; and (S4) performing demapping according to a least distance judgment method to obtain data information of the transmitting end. According to the three-dimensional constellation-rotating encryption method disclosed by the invention, the equivalent channel phase is extracted by means of reciprocity of a channel phase response, and a three-dimensional constellation is encrypted by utilizing the extracted equivalent channel phase, so that an eavesdropper cannot demodulate correct bit information, and therefore a safe communication effect can be achieved.

Three-dimensional constellation-rotating encryption method based on wireless channel characteristics

In this paper, we address the physical layer security problem for Wireless Sensor Networks in the presence of passive eavesdroppers, i.e., the eavesdroppers' channels are unknown to the transmitter. We use a multi-antenna relay to guarantee physical layer security. Different from the existing work, we consider that the relay works in full duplex mode and transmits artificial noise (AN) in both stages of the decode-and-forward (DF) cooperative strategy. We proposed two optimal power allocation strategies for power constrained and power unconstrained systems respectively. For power constrained system, our aim is to minimize the secrecy rate outage probability. And for power unconstrained systems, we obtain the optimal power allocation to minimize the total power under the quality of service and secrecy constraints. We also consider the secrecy outage probability for different positions of eavesdropper. Simulation results are presented to show the performance of the proposed strategies.

Full-duplex relay for enhancing physical layer security in Wireless Sensor Networks: Optimal power allocation for minimizing secrecy outage probability

In this paper, we propose an evolutionary time spread multiple access (E-TSMA) protocol which is independent of topology changes for ad hoc networks. Our proposed protocol is based on protocol threading technique and a novel contention schedule with reservation and carrier sense. According to the topology density of the network and the transmission requirement, our proposed protocol can control each node to utilize its assigned slots and its non-assigned slots effectively. The protocol improves upon the existing threaded time spread multiple access (T-TSMA) protocol while preserving the advantage of the topology transparency and eliminating the maximum nodal degree constraint. In this paper we present the protocol and analyze the performance of it. Simulation results show that our proposed E-TSMA protocol is better than the T-TSMA protocol.

Wei Li

Papers

An Evolutionary-Dynamic TDMA Slot Assignment Protocol for Ad Hoc Networks

Worst-case robust masked beamforming for secure broadcasting

Three-dimensional constellation-rotating encryption method based on wireless channel characteristics

Full-duplex relay for enhancing physical layer security in Wireless Sensor Networks: Optimal power allocation for minimizing secrecy outage probability

An Evolutionary Time Spread Multiple Access Protocol for Ad Hoc Networks