Vehicle Ad-hoc Network (VANET) communication terminals, e.g., On Board Unit (OBU) and Road Side Unit (RSU), are crucial devices to facilitate the implementation of VANET systems. Based on the Wireless Access in the Vehicular Environment (WAVE) protocol stack and embedded development technology, we in this paper propose a complete designing approach to realize the VANET communication terminals in both hardware and software layer. The key feature of our proposed approach is that we adopt 802.11p module as the Radio Frequency (RF) front end, U-Blox8 as the Global Navigation Satellite System (GNSS) module and i.MX6 Dual Lite as the processing core. The designed VANET terminals can provide effective communications for both vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) connections, and thus enable the timely delivery of varied transport information.
This paper considers a cognitive radio inspired uplink communication scenario, where one primary user is allocated with one dedicated resource block, while $M$ secondary users compete with each other to opportunistically access the primary user's channel. Two new designs of NOMA schemes, namely hybrid successive interference cancellation with power adaptation (HSIC-PA) and fixed successive interference cancellation with power adaptation (FSIC-PA), are proposed. The significant advantages of the proposed schemes are two folds. First, the proposed two schemes can ensure that the secondary users are opportunistically served without degrading the transmission reliability of the primary user. Besides, the transmission robustness of the served secondary users can be guaranteed. Specifically, the outage probability error floors can be avoided for the secondary users, which is proved by asymptotic analysis in the paper. Extensive simulation results are also provided to demonstrate the superior performance of the proposed schemes.
The application of network non-orthogonal multiple access (N-NOMA) technique to coordinated multi-point (CoMP) systems has attracted significant attention due to its superior capability to improve connectivity and maintain reliable transmission for CoMP users simultaneously. Based on the concept of quasi-degraded channel for N-NOMA, this paper studies the precoding design for downlink N-NOMA scenarios with two base stations (BSs) equipped with multiple antennas. In specific, under quasi-degraded channels, simple linear precoding based N-NOMA can achieve the same minimal total transmission power as theoretically optimal but complicated dirty paper coding (DPC) scheme, when the users' target rates and minimal transmission power of each BS are given. In this paper, the channel quasi-degradation (QD) condition is first rigorously derived for the scenario with single CoMP user and two NOMA users. The closed-form optimal precoders for N-NOMA under quasi-degraded channels are also provided. Then, based on QD condition, a novel hybrid N-NOMA (H-N-NOMA) scheme is proposed, which is a mixture of N-NOMA and conventional zero-forcing beamforming (ZFBF) scheme. Further, for the scenarios with more users, a low-complexity QD based user pairing (QDUP) algorithm is proposed, which is then combined with H-N-NOMA to make a novel scheme termed H-N-NOMA/QDUP into being. Numerical results are presented to reveal the impact factors on QD channels, and also demonstrate the superior performance of the proposed H-N-NOMA/QDUP scheme. It is shown that the proposed H-N-NOMA/QDUP scheme can effectively exploit the benefit of multi user diversity.
In Ad-hoc networks, the MAC protocol based on time division multiple access (TDMA) has a wide application prospect in military and disaster relief emergency communications since it completely avoids access conflicts. However, the high-dynamic topologies of Ad-hoc networks force every node to conduct time synchronization frequently, which would inevitably cause substantial overhead. In this regard, this paper designs the fast layered-synchronization (FLS) algorithm, which is well-suited to high-dynamic network topologies owing to its low overhead. In the network access synchronization phase, FLS initially partitioned the nodes into different layers based on their locations. Then in every periodic synchronization phase, according to the theory of neighbor density, a series of synchronization reference nodes are selected from the network. The layer of each reference node is improved to the highest among all its neighbor nodes, and then provide time reference for them. The newly-accessed nodes also only need to exchange information with their nearest reference nodes to achieve synchronization, so that the overhead of synchronization can be reduced. Finally, in order to evaluate the performance of FLS, the wireless network card with TDMA mechanism is developed and the FLS algorithm is transplanted. The experimental results show that FLS can maintain microsecond-level synchronization accuracy with low overhead.
Autonomous vehicle has been one of the most active study with the potential to enhance safety and convenience. As one of the safety-critical tasks that must be executed by autonomous vehicle, the motion planning is generally divided into path planning and velocity planning. The main purpose of velocity planning is to determine a safe and comfortable velocity change mode for autonomous vehicle, which is a crucial task. A velocity planning method based on pre-set model is proposed in this paper. The exponential function model with undetermined parameters is constructed as the velocity planning model in this method. We take comfort and time-effectiveness as evaluation indexes and construct model functions respectively, and the objective function is constructed in the form of weighted sum to determine the optimal parameters of the velocity planning model in each scenario. The exponential model is suitable for most application scenes, and its closed form expression form is easy to implement in real-time applications. By analysis with actual data, the model is proved to be reasonable.
It has been well-recognized that clustered Interference alignment (IA) can provide remarkable interference suppression performance for the existing small cell networks (SCNs). There is also a tendency that full-duplex (FD) radios would replace the half-duplex radios at future small base stations (SBSs). In this context, the intra-cell and inter-cell interference in SCNs would become much more serious, where the performance of clustered IA has not been evaluated yet. In this paper, we explore the maximum achievable sum-rate of the FD-based SCNs when clustered IA combined with power control strategy is applied. To achieve this, a mixed-integer optimization problem is formulated, which is furtherly decoupled into two subproblems for ease of handling. Then we propose the minimized rate loss (MRL) algorithm to address the clustering subproblem and a convex approximation method to address the power control subproblem. The two subproblems are performed alternatively till the sum-rate gains convergence. Preliminary simulations clearly demonstrate that the achievable sum-rate is limited by the number of antennas at the users.
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