# 电子工程代写|数字信号处理代写Digital Signal Processing代考|ELEC3305

## 电子工程代写|数字信号处理代写Digital Signal Processing代考|Medium Access Control (MAC) Protocol Design

Medium Access Control (MAC) layer design has been extensively studied in the context of DSRC and 4G-LTE, while only a limited amount of literature has investigated solutions for other types of radios that are expected to be available in next-generation automotive systems. Conventional MAC solutions are suitable for situations in which the velocity/position of the vehicles can be accurately predicted. However, this may not be the case for V2X communication systems operating at high frequencies, mainly due to the intrinsic variability of the channel. Moreover, most recent solutions lack consideration of some important KPIs like reliability and delay. In particular, mmWave radio links require new schemes to enable vehicles and infrastructures to quickly determine the best directions to establish directional links. This functionality can be hardly supported by traditional communication protocols, which are often significantly affected by the high speed of the nodes and by the presence of frequent blockages on the propagation path.

The above discussion makes apparent the need for innovative MAC protocol design, specifically tailored to future vehicular networks, as represented in Fig. 2 . This objective can be achieved by enabling multi-connectivity, thus coupling a highfrequency data plane with a lower frequency control plane, to support the required rates, while increasing the robustness of the communication [9].

The authors in [5] present a beam prediction technique based on periodical speed and position information exchanged among network nodes through DSRC messages. Using the acquired information, the system is then able to estimate the vehicle’s trajectory and derive the optimal beam orientation accordingly.

Beam design optimization is also being considered as a solution to maximize the data rate [32]. Results are consistent with the intuition that narrower beams should be used for users near the cell edge, where coverage is weaker.

In [8], a location-aided beamforming strategy is proposed to achieve ultrafast connectivity between nodes. In particular, adaptive channel estimation based on location information allows the estimation time to be substantially reduced.

Efficient beam alignment schemes can also be designed by extracting information from radar signals [24]. Simulations confirm that radars can be a useful source of side information and can help configure the mmWave V2I links.

In conclusion, although mmWave communication is a viable approach to provide high-bandwidth connectivity to future intelligent vehicles, innovative MAC-layer solutions should be engineered to overcome the limitations that prevent the direct employment of traditional communication protocols on high-frequency links.

## 电子工程代写|数字信号处理代写Digital Signal Processing代考|Network and Routing Protocol Design

While the literature on network protocols ${ }^3$ for legacy vehicular scenarios is quite rich, little work exists regarding the communication performance of the network layer (especially routing) in a next-generation V2X context. More specifically, traditional routing solutions can be classified into two categories, as reported in Fig. 3: (i) topology-based routing protocols, and (ii) position-based routing protocols.
Topology-Based Routing Protocols. These schemes use link information within the network to send the data packets from the source to the destination. In particular, proactive routing protocols continuously maintain up-to-date routes for all the valid destinations, thus guaranteeing low-latency packet forwarding but suffering from scalability issues. Reactive routing protocols, instead, establish the path to follow for packet delivery only when a message needs to be actually exchanged, thus saving precious bandwidth resources but increasing the latency to find a reliable route.
Position-Based Routing Protocols. These schemes do not require routing tables, but only use the position information of neighboring nodes to determine the next forwarding hop to the destination. Since those protocols are based only on local knowledge, they are considered more scalable and robust against topological changes. However, they exclusively rely on position information that may be inaccurate or unavailable (e.g., in tunnels or where the satellite signal is absent) [23], and may suffer large overheads or additional delays caused by collision and contention of the underlying MAC protocols.

In this context, the propagation characteristics and the directional nature of mmWave links bring both challenges and opportunities for routing protocol design. For instance, due to the presence of communication blockages, the shortest path connecting two network nodes (in terms of geographical or topological distance) is not necessarily the best, and may actually yield lower throughput and higher packet loss than a longer path. It is thus important to make a judicious selection of relaying nodes, for example trying to keep the number of hops to a minimum when using multi-hop communications to overcome an impaired direct path.

Recently, some works tried to design network layer protocols specifically tailored to multi-hop systems with directional antennas. In [4], the authors proposed an $O p t i-$ mal Geographic Routing Protocol (OGRP) that selects the appropriate multi-hop relays considering the specific features of mmWave propagation. Other solutions implement some sort of multipath routing that allows a vehicular node to establish multiple connections through different access technologies, besides using device-todevice (D2D) transmissions.

In [25], a multi-hop concurrent transmission scheme is proposed and, by properly breaking one single-hop low-rate link into multiple shorter high-rate links and allowing non-interfering nodes to transmit concurrently, the network resources can be efficiently used to improve the network throughput.

## 电子工程代写|数字信号处理代写Digital Signal Processing代考|Medium Access Control (MAC) Protocol Design

[5] 中的作者提出了一种基于通过 DSRC 消息在网络节点之间交换的周期性速度和位置信息的波束预测技术。使用获取的信息，系统随后能够估计车辆的轨迹并相应地得出最佳光束方向。

## 电子工程代写|数字信号处理代写Digital Signal Processing代考|Network and Routing Protocol Design

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