© Springer Nature Singapore Pte Ltd. and Science Press, Beijing, China  2019
Leibo Liu, Guiqiang Peng and Shaojun WeiMassive MIMO Detection Algorithm and VLSI Architecturehttps://doi.org/10.1007/978-981-13-6362-7_7

7. Prospect of the VLSI Architecture for Massive MIMO Detection

Leibo Liu1  , Guiqiang Peng2   and Shaojun Wei3  
(1)
Institute of Microelectronics, Tsinghua University, Beijing, China
(2)
Institute of Microelectronics, Tsinghua University, Beijing, China
(3)
Institute of Microelectronics, Tsinghua University, Beijing, China
 
 
Leibo Liu (Corresponding author)
 
Guiqiang Peng
 
Shaojun Wei

5G is a more advanced mobile communications network deployed in 2018 and later, which mainly includes the following technologies: the millimeter wave technology [1] (26, 28, 38, and 60 GHz) that is able to provide a transmission rate as high as 20 Gbit/s; the massive MIMO technology that can provide “a performance that is 10 times that of the 4G network” for the 5G communications network. As another important technology for 5G, “the low- and medium-frequency band 5G” (5G New Radio) that leverages the frequencies ranging from 600 MHz to 6 GHz, especially 3.5 to 4.2 GHz. Extended and evolved from 4G communications, 5G that represents the development tendency of new generation information communications is going to penetrate every field in the future society; thus, it will construct an omnidirectional user-oriented information ecosystem. This chapter prospects the future application scenarios and hardware development from three aspects: server, mobile terminal, and edge computing, which correspond to the subsequent sections.

7.1 Prospect of Server-Side Applications

7.1.1 Outline of 5G Communications Characteristics

The differentiation of application scenarios for 5G communications proposes the engineering requirements on communications services mainly from the perspectives of equipment quantity, communications bandwidth, and performance, i.e., deep coverage, ultra-low power consumption, ultra-low complexity, ultra-high density, ultimate capacity, ultimate bandwidth, deep ecological consciousness, strong security, ultra-high reliability, ultra-low latency, and perfect mobility, etc., as shown in Fig. 7.1.
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Fig. 7.1

Requirements and characteristics of 5G communications

On the premise of ensuring even improving the quality of service (QoS) for communications, high data rate, low latency and low power consumption are the most essential requirements. In terms of solutions for the establishment of 5G new radio, the key technologies arise such as massive MIMO [2], millimeter wave bands/visible light transmission, filter-bank-based multicarrier (FBMC) modem, dense networking and heterogeneous network, device-to-device (D2D) and in-vehicle network [3] and onboard network, software-defined networking (SDN) [4], cognitive radio networks, and green communications [5].

According to the report of GSMA, until 2025, 5G network will be commercially used in 111 countries and regions throughout the world. Before the 5G technology is laid in a large scale and provided for consumers, two transitions must be accomplished. First, the mobile operators must upgrade their network infrastructures into 5G equipment. Currently, the primary 5G equipment suppliers are Huawei and Zhongxing Telecommunications Equipment (ZTE) from China, Ericsson from Sweden, and Nokia from Finland. Second, the mobile phone manufacturers need to keep up with the pace to embed 5G wireless signal receivers into mobile phones, making full preparation for the 5G network.

At the early stage of the commercialization of 5G, operators will initiate extensive network construction. Revenues of equipment manufacturers from the investment on the 5G network equipment will become the primary source of direct economic output of 5G [6]. According to the White Paper of the Impacts of 5G on Economy and Society, it is estimated that the network equipment and terminal devices will bring the manufacturers a total revenue of approximately RMB 450 billion yuan in 2020, accounting for 94% of the direct economic output. In 2025, the middle stage of the commercialization of 5G, the expenditures from users, other industrial terminal devices and telecom services will grow constantly, which are expected to rise by RMB 1400 billion yuan and RMB 700 billion yuan, respectively, accounting for 64% of the direct economic output. In 2030, the middle and later stage of the commercialization of 5G, internet enterprises and information service industries related to 5G will become the backbone of the direct economic output, which will increase the economic output to RMB 2600 billion yuan, occupying 42% of the direct economic output.

In light of this, we can conclude that in the near future, the commercialization of 5G will result in a great revolution in the basic manufacturing industry and product substitution in equipment manufacturing industry, shining with extremely high commercial value and investment space. Thus, multiple national equipment manufacturers have devoted substantial human and material resources to industries related to 5G.

7.1.2 Outline of the Server-Side Characteristics

Server is a common name for the type of equipment working based on the network environment, which is usually undertaken by various kinds of computers. Unlike a terminal, a server acts as the control and service center of the network, which serves various terminal devices (usually undertaken by various kinds of computation equipment) that are connected to it; it has a high requirement for the computing performance. The three common server architectures include the cluster architecture, the load balancing architecture, and the distributed server architecture. The cluster architecture refers to integrating multiple servers to handle the same service, and it seems that there is only one server from the perspective of client. One advantage of the cluster architecture is that it can use multiple computers to conduct parallel computations to achieve a higher computing speed. The other advantage of the cluster architecture is that it can use multiple computers to backup, which ensures the proper operation of the entire system even if any machine is broken. Established upon the existing network structure, the load balancing architecture can offer a low-cost, effective, and transparent method to extend the bandwidth of network equipment and server, increase the throughput, strengthen the processing capability for network data, and enhance the network flexibility and availability. The distributed resource sharing server is a theoretical computing model server form that studies the geographic information distributed on the network and the database operations affected; it can distribute data and programs to multiple servers. The distributed architecture contributes to the distribution and optimization of tasks in the entire computer system, overcomes the defects in traditional centralized system where strained resources of central hosts and response bottlenecks occur, and addresses issues such as data heterogeneity, data sharing, and computing complexity in the geographic information system (GIS) of network, which is a significant progress in GIS. To ensure the security of important data, the cluster server architecture is mainly used in communications industry. The load balancing that aims at sharing the access loads and avoids temporary network traffic jam, is mainly applied in electronic business websites. The distributed servers are born to achieve the cross-sector high-speed access of multiple single nodes. At present, the distributed server is the first choice for the purpose like content delivery network (CDN).

As an exclusive communications system that a user sends files or accesses remote system or network through remote links, communications server can simultaneously provide communications channels for one or more users as per the software and hardware capabilities. Generally, communications servers are featured with the following functions: the gateway function that provides connections between the user and the host by converting data formats, communications protocols, and cable signals; the service access function that allows remote users to dial-in; the modem function that offers internal users with a group of asynchronous modems for dial-in access to remote systems, information services, or other resources; the bridge and router function that maintains the dedicated or dial-in (intermittent) links to remote local area networks (LAN) and automatically transmits data groupings among LANs; and the e-mail server function that automatically connects other LANs or electronic post offices to collect and transmit e-mails.

Since the performance of a server is crucial to that of the network, 5G and even beyond 5G communications raise the following requirements on the server: strong data processing capability for handling the access of the data in large flow, high stability, and reliability, have a full-functional system with ensured data security, and etc. As is mentioned in Chap. 1, from the perspective of hardware implementation, the main superiority of the ASIC method for implementing a data processing module is that it is able to obtain the optimum overall merit of performance and power consumption, which can satisfy the sharply rising computation capability required by massive MIMO detection chips, and achieve high throughput, high energy efficiency, and low latency. Nowadays, with the rapid development of mobile communications, the deficiency of flexibility prevents it from being further extensively applied. However, in the processing of compute-intensive data, reconfigurable processors cannot only achieve high throughput, low energy consumption, and low latency, but also exhibit unique advantages in flexibility and scalability. Additionally, benefiting from the reconfigurability of hardware, this architecture is possible to execute system update and error correction during the operation of the system, which poses dominant privileges in extending the service life and guaranteeing the release time of products. Thus, the reconfigurable processor becomes a significant and promising research subject in the development of communications in the future.

7.1.3 Server-Side Application

As the latest standard of the global communications, 5G does not confine its significance to a higher speed or improved mobile broadband experience, instead, its mission is especially to connect new sectors and encourage new services, e.g., advocating industrial automation, large-scale IoT, smart home, and autonomous driving, etc. Correspondingly, these sectors and services have higher requirements for the networks, which are higher reliability, lower latency, wider coverage, and higher security. Therefore, a flexible, effective, and scalable network is in urgent demand to meet different requirements from all walks of life.

In June 22, 2015, the conference of ITU-RWP5D held by International Telecommunications Union (ITU) defined the three main usage scenarios of the future 5G: the enhanced mobile broadband, the ultra-reliable and low latency communications, and the massive machine type communications. The specific scenarios cover Gbit/s mobile broadband data access, smart home, smart building, voice, smart city, three-dimensional video, ultra-high definition screens, work and play in the cloud, AR, industrial automation, mission-critical application, self-driving car, etc., as shown in Fig. 7.2.
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Fig. 7.2

Main usage scenarios of 5G communications

From October 26 to 30, 2015, when World Radiocommunication Conference 2015 (WRC-15) was held in Geneva, Switzerland, ITU-R officially approved three resolutions that were beneficial to the promotion of future research process of 5G and nominated the official name of 5G as “IMT-2020”. Out of the main usage scenarios, business requirements, and challenges of mobile Internet and IoT, “IMT-2020” recategorized the main usage scenarios of 5G into four based on the specific network function requirements: continuous wide-area coverage, high traffic capacity hotspot, low power consumption and a large number of connections, and low latency and high reliability, which are basically consistent with the three major usage scenarios of ITU. “IMT-2020” only further subdivides the mobile broadband into continuous wide area coverage and high traffic capacity hotspot, as shown in Fig. 7.3.
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Fig. 7.3

Continuous wide-area coverage and high traffic capacity hotspot scenarios

Continuous wide-area coverage and high traffic capacity hotspot scenarios are mainly designed to meet the mobile internet business requirements in 2020 and later, which are also primary traditional 4G scenarios. Continuous wide-area coverage is the fundamental coverage method of mobile communications targeting the assurance of users’ mobility and service continuity to offer seamless and high-speed service experience. Its primary challenge comes from the needs to ensure a 100 Mbit/s higher data rate for users anytime and anywhere, which is more obvious in harsh environments such as base station coverage edge and high-speed moving. The scenarios requiring high traffic capacity hotspot are mainly oriented at local hotspot areas to provide users with ultra-high data rate to satisfy the extremely high traffic density demands on the network, which need to be supported by multiple technologies. For instance, super intensive networking can effectively multiplex spectral resources and significantly promote frequency multiplexing efficiency in the unit area; full spectrum access can make the full use of low-frequency and high-frequency spectral resources to achieve a higher data rate.

The scenarios with low power consumption and a large number of connections, low delay, and high reliability (Fig. 7.4) mainly aim at IoT services, which are the scenarios newly extended in 5G dedicated to solving the problem that the conventional mobile communications cannot well support the IoT and vertical industrial applications. The scenarios with low power consumption and a large number of connections are generally for the circumstances where sensing and data collection are targeted and featuring with small data packets, low power consumption, and vast connections such as smart city, environmental monitoring, intelligent agriculture, forest fire prevention, etc. In these usage scenarios, a large number of terminals are widely distributed, which not only require the network to support over 100 billion connections to meet the connection density demand of 1 million/km2 but also guarantee an ultra-low power consumption and cost. The low latency and high-reliability usage scenarios are primarily leveraged for special application requirements of vertical industries such as internet of vehicles (IoV) and industrial control. These usage scenarios have extremely high requirements on latency and reliability; they need to provide users with end-to-end latency at millisecond level and close to 100% service reliability guarantee. Table 7.1 lists the main usage scenarios and key challenges of performance for 5G.
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Fig. 7.4

Scenarios with low power consumption and a large number of connections, and low latency and high reliability

Table 7.1

Main usage scenarios and key challenges of performance for 5G

Scenarios

Key challenges

Continuous wide-area coverage

100 Mbit/s user experienced data rate

High traffic capacity hotspot

User experienced data rate: 1 Gbit/s

Peak data rate: tens of Gbit/s

Traffic density: tens of Tbit/km2

Low power consumption and a large number of connections

Connection density: 106/km2

Ultra-low power consumption and cost

Low latency and high reliability

Air interface latency: 1 ms

End-to-end latency: at millisecond level

Reliability: close to 100%

The specific usage scenarios are introduced as follows.

7.1.3.1 IoV

As far as China is concerned, the national car ownership has reached 217 million up to 2017, which is increased by 23.04 million with a growth rate of 11.85% compared with that of 2016. Moreover, the proportion of automobiles in motor vehicles increases constantly from 54.93 to 70.17% in the recent 5 years; automobiles have become the main part of motor vehicles. In terms of distribution, there are 53 cities in China whose car ownership is more than a million, of which 24 cities amount to 2 million and 7 cities possess more than 3 million, Beijing, Chengdu, Chongqing, Shanghai, Suzhou, Shenzhen, and Zhengzhou. In western areas, the motor vehicle ownership reaches 64.34 million with the fastest growth rate. In 2017, motor vehicle ownership in eastern, middle, and western areas were 155.44, 90.06, and 64.36 million, accounting for 50.17, 29.06, and 20.77% of total motor vehicles in China, respectively. Among them, the automobile ownership of western areas in recent five years rises by 19.63 million with a growth rate of 19.33%, which is higher than the 14.61 and 16.65% of eastern and middle areas [7].

As you may know, international internet tycoons are rushing to control the driving cabs. It is possible that the significance that they march into onboard system is to reconstruct the ecosystem of the entire industry and establish a standard onboard operation platform, which is analogous to that once occurred to the smartphone. Some experts even predicted that the IoV will become the third internet entity, after PC-oriented internet and cell phone-oriented mobile Internet. A complete IoV involves a lot of links mainly including communications chip/module suppliers, external hardware suppliers, RFID and sensor suppliers, system integration suppliers, application equipment and software suppliers, telecom operators, service suppliers, automobile manufacturers, etc., as shown in Fig. 7.5. Thus, the automobile hardware market arising from the commercialization of 5G is also to be exploited.
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Fig. 7.5

Application of 5G in automobile industry

With the continuous and rapid increase of the motor vehicle ownership, the number of drivers also substantially grows synchronously, driving the annual increment of recent five years to 24.67 million. In 2017, the number of national motor vehicle drivers reached 385 million, of which automobile drivers accounted for 342 million. 30.54 million drivers occupying 7.94% of the total drivers had less than 1 year of driving experience. On one hand, the surge of automobile ownership and the improper management of parking lots aggravate the low utilization rate of parking space, which raises the “parking problem” to be solved. On the other hand, the high requirements on motor vehicles and sharp increased inexperienced drivers are endangering the traffic safety. Therefore, the research, development, and upgrade of the driving assistance even self-driving technologies are imminent.

To solve the parking problem, the cloud based parking management system (as shown in Fig. 7.6) is designed focusing on the remote control and management of parking locks. It achieves centralized management and decentralized control for parking space, which benefits the owner to lease the parking space while it is idle, and effectively mitigates the supply and demand issue of parking space and increases the urban park utilization rate. This is one of the typical usage scenarios of the low power consumption and large number of connections [8]. As a pivot component of the cloud-based parking management platform, the remote control system for parking locks is mainly responsible for the collection of parking space status information and the control of parking space permission. The system includes hardware and software parts, where the hardware mainly refers to the design of the built-in hardware control system tailored to realize the remote control of parking locks, while the software part involves the development of cell phone client and software at the server side (communications programs, data storage programs, etc.).
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Fig. 7.6

Architecture of the cloud-based parking management system

On the condition of satisfying the performance requirements such as power consumption, latency, and throughput, to cope with the increase of motor vehicle ownership by leaps and bounds, the data processing scale of massive MIMO signal detection chips will be certainly raised. In this scenario, the reconfigurable architecture is more suitable compared with the customized ASIC architecture.

Regarding autopilot technologies, in May 2016, Florida, USA, a Model S engaged in autopilot mode at full speed crashed into a white tractor trailer cutting across the highway and caused the death of the driver. In March 2018, Tempe city, Arizona State, USA, a self-driving Uber struck a pedestrian who died after being sent to the hospital. Apparently, these two accidents are caused due to different reasons. The autopilot accident was caused due to the failure in identifying the vehicle while the Uber accident occurred because of pedestrian identification fault. To deal with the shortcomings of current autopilot technologies, Tesla recently announced that the new version of in-house navigation and maps engine, “light-years ahead” will preliminarily complete the upgrade of software. Also, the software algorithms should be updated unceasingly. Figure 7.7 shows the autopilot diagram of Tesla.
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Fig. 7.7

Autopilot diagram of Tesla

In high-speed driving mode, real-time data processing and information interaction are extremely important [9], which is one of the typical usage scenarios of the low delay and high reliability. Thus, the low delay and high throughput are the most pressing performance demands. ASIC does not only have the natural strength in energy efficiency but also have low chip manufacturing cost due to the large volume of motor vehicle ownership (after mass production, one-time engineering cost can be amortized over all chips). Therefore, ASIC-based massive MIMO signal detection chips have an optimistic application prospect.

7.1.3.2 Cloud Computing

As network technologies are progressing, network size is increasing fast, and computer systems are growing complex, various novel systems and services spring up. Telecom operators and Internet application service suppliers are competing intensely with each other for attracting more users and achieving more profit. Recently, mobile Internet grows mature gradually, and numerous application service suppliers start to transform and develop over-the-top (OTT) services [6] to directly profit from users and advertisers without involving network operators. To tackle such challenge, although operators spend a lot on providing network services, they still do not find any effective solution, severely impacting their revenues. At the same time, application service suppliers attempt to break the technical barriers to obtain more network resources, resulting in issues such as “signaling storm” and the surge of terminal electricity energy consumption that dramatically harm the users’ interests. The blind contest and the lack of cooperation platform lead to the constantly intensifying of conflicts among operators, users and service suppliers (Fig. 7.8).
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Fig. 7.8

Three-layer model of cloud computing

Being the technical and development hotspot of the current Internet, cloud computing integrates infrastructures, application platforms, and application software into a complete network structure [10]. Based on the internet technologies, this system provides external services in self-service and on-demand manners; it is featured with broad network access, virtualized resource pooling, rapid elasticity, measured service, and multi-tenant, posing as an active reference for operators to improve their network application capabilities. According to different service modes, cloud platform can divided into three service modes, infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS). Using the technologies such as virtualization and distributed computing, cloud computing incorporates various computer resources into an address pool via a computer network, which is a new type of on-demand service mode [6]. Mobile cloud computing (MCC) has the characteristics including weakened limit for terminal hardware, more convenient data storage, personalized services, and ubiquitous availability [11], which should be supported by large-scale and prompt data quantity processing at the server side. In summary, in this scenario, the ASIC-based massive MIMO has a broad application prospect.

7.2 Prospect of Mobile-Side Application

Mobile computing terminal, which is by definition referring to the computer equipment used during movement, mainly including the wireless onboard terminal and the wireless handheld terminal. Thanks to the rapid progress of broadband wireless access technology and mobile internet technology, people are eager to ubiquitously obtain information and services easily even during movement. As the access interface to wireless network, mobile terminals witness a flourishing tendency with many kinds of mobile equipment (smartphones and pads) springing up. Current mobile computing terminals cannot only accomplish voice chat, voice videos, and photographing but also enable rich functions such as Bluetooth, GPS location, and information processing, which plays an ever more important role in human society. At Mobile World Congress 2018, “5G era” stood out as one of the spotlights. As the fifth generation of mobile communications network, 5G is capable of achieving the “internet of everything.” Compared with 4G communications technology, 5G has a much higher data rate, and achieves significant improvements in stability and power consumption; it will significantly affect the mobile computing terminals. Different from previous generations of communications technologies, the mobile computing terminals of 5G cover a more extensive range, generating many new products such as wearable devices and home networking devices. In addition, mobile computing terminals are more humanized to satisfy users’ requirements at faster information transmission rate. More importantly, 5G lays the foundation for the development of other related technologies because the fast data rate is universally required among big data, cloud computing, AI, and self-driving.

However, the development of mobile terminal still faces a series of challenges. Researches on the basic theories and key technologies have always been the concerns of researchers from either enterprises or academies. As one of the key technologies, massive MIMO can significantly improve the channel capacity and signal coverage range of mobile communications. Therefore, during the design of the massive MIMO detection processor, a better massive MIMO detection VLSI architecture means a lot for its high performance, low power consumption, low latency, flexibility, and scalability. In other words, seeking for an optimized MIMO detection architecture is vital to the development of the MIMO detection processor even the mobile terminal. Since the twenty-first century, relying on the proximity advantage, mobile terminals have already taken over the position where the competition is the intensest in marketing. As various technologies gradually mature, diversified mobile terminals step into the intelligent age featured with enriched functions, which evolve toward the integration of more functions. The development of global mobile communications terminal poses a forceful rising trend while the market has harsh performance requirements on the mobile terminal products. The performance and cost of mobile terminals mainly concentrate on the chip, in particular, baseband communications chip; thus, the primary link of terminal R&D focuses on the baseband chip [12]. The requirements of mobile terminals on baseband chips are mainly reflected in the following aspects.
  1. (1)

    Low power consumption. As the most essential part of mobile terminals, baseband chip mainly synthesizes baseband signals to be transmitted and decodes the received signals. During the transmission, it encodes signals into baseband codes that can be transmitted, while it decodes the received baseband codes into audio signals during the receiving. In the smart terminal market, the data processing on the baseband chip of smart terminals is becoming increasingly heavy, therefore, the low power consumption design of the baseband chip is significant to the development of smart terminals [13].

     
  2. (2)

    Low latency. A growing number of applications raise higher requirements on the path delay. In this case, baseband chip needs to process data in real time with a latency at millisecond level.

     
  3. (3)

    Low cost. In the fifth generation of ultra-intensive network, the size of a micro base station will be very tiny with short distances between stations. As the deployment density is very high, the cost of micro base stations is very important to the operators. The deployment should cover both the indoor and outdoor scenarios using low-cost CMOS power amplifiers to access nodes ranging from several meters to 100 m.

     
  4. (4)

    High capacity. Baseband chip needs to accomplish high capacity, energy efficiency, and spectrum efficiency.

     

As for the requirements of the baseband chip, massive MIMO detection VLSI architecture based on ASIC and the reconfigurable massive MIMO detection VLSI architecture may have a promising application prospect, from which aspects this section will be elaborated.

7.2.1 Application of ASIC-Based Detection Chips

In addition to supporting the mobile broadband development, 5G also supports numerous emerging application scenarios. Increasing numbers of applications promote higher requirements for data transmission, i.e., low latency and high throughput, which demands more for the design of massive MIMO detection chips. ASIC-based massive MIMO detection chips are endowed with the potential to meet the future application requirements in latency and throughput. The applications of ASIC-based massive MIMO detection are illustrated by taking the following future applications as examples.

7.2.1.1 VR and AR

VR and AR are revolutionary technologies that will radically change the content consumption of consumers and enterprise departments. VR is a shared and tactile virtual environment where several users are physically connected through a simulation tool to cooperate with each other via not only visual and but also tactile perception. Whereas, in AR, the real content and content generated by the computer is combined into the users’ line of sight to be visualized. Compared with the static information augment today, future AR application mainly aims at the visualization of dynamic content. The tactile feedback is the proposition of the interactions with high fidelity in the VR. Specifically, perceiving objects in the VR through haptic results in the dependency of high precision of programs, which can be realized only when the latency between the user and VR is lowered to several milliseconds. The addition of extra information to the users’ line of sight can boost the development of many assistance systems such as maintenance, driving assistance system, and education. With the tactile network, the content in the AR can be transferred from static to dynamic, enabling the virtual expansion of the user views in real time, and identifying and avoiding possible hazardous accidents. VR and AR technologies have extensive application prospects in the education industry by connecting the real world to the virtual one. Applying AR in the classroom deeply changes the traditional education mode, which enhances the teaching and learning effect (as shown in Figs. 7.9 and 7.10).
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Fig. 7.9

Application of VR in remote education

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Fig. 7.10

Subversion of VR in the traditional education

The perception capability of humans can be enhanced by using the AR-based driving assistance system (Fig. 7.11). First of all, the system adopts the virtual platoon control (VPC) to enable a real vehicle with passengers on to tightly follow a virtual one that is projected on the head-mounted display (HMD) manipulated from the objective view, which can ensure to drive without colliding with any obstacle [14].
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Fig. 7.11

AR-based driving assistance system.

©[2018] IEEE. Reprinted, with permission, from Ref. [14]

The wireless transmission plays a crucial role in VR and AR. For example, the tactile network in VR and AR must process data in real time to meet users’ demands. Under the circumstances where a large number of VR and AR terminals have data to be processed, massive MIMO detection needs to satisfy the requirements of high accuracy, low latency, and high throughput. Therefore, the ASIC-based massive MIMO is prospective particular for cases with the requirements of low latency and high processing rate.

7.2.1.2 Self-driving

Figure 7.12 outlines the driving assistance functions that will emerge in the near future. Most functions listed will involve radar sensors because they are relatively stable in different conditions such as rain, dust, and sunlight. However, there is no such a universal radar sensor that can satisfy all the functional requirements in the roadmap shown in Fig. 7.12. To meet the future demands, it is possible a good attempt to identify all key technologies required to apply in today’s radar sensors. In the real application scenario, the radar sensors usually demand high angular and speed resolutions, high reliability, high throughput, low cost, and small size. As one of the key technologies of radar detection, massive MIMO technology makes a great improvement in angular resolution and data throughput. Moreover, the design that applies plane frequency-modulated continuous-wave (FMCW) MIMO array and TDMA concept will maintain the dominance of MIMO and enhance the antenna gains at the transmission end to improve the overall SNR [15].
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Fig. 7.12

Roadmap of driving assistance function.

©[2018] IEEE. Reprinted, with permission, from Ref. [15]

In the massive MIMO detection system, the more optimal VLSI architecture can significantly improve the performance of the detection chip and lower the power consumption and latency of the system, which can better accomplish the real-time communications and achieve a higher safety in the self-driving field. This greatly benefits the reduction of traffic accidents and the improvement of the traffic congestion situation. In the current automobile security scenarios, the reaction time to avoid collisions is shorter than 10 ms, while the bidirectional data exchange of self-driving vehicles may require the latency be within 1 ms, which can be technically realized through tactile network and 1 ms end-to-end latency. Thus, full autopilot technology will definitely change traffic behaviors. In terms of the distance between vehicles, autopilot technology needs to detect the potential safety-critical conditions in advance, which can be supported by the future wireless communications system with high reliability and proactive predication [16]. With the increase of the self-driving terminals, data exchange is required among an increasingly number of users. For the self-driving terminal, how to cope with multiuser requirements and shield multiuser interference is a big challenge. The highly effective massive MIMO detection architecture can meet the high-speed processing requirements in the self-driving system to lower the latency. Meanwhile, massive MIMO detection architecture is capable of transmitting massive data and processing correspondingly to improve the system throughput. For the application scenarios with high interference and noise, the nonlinear massive MIMO detection architecture can enhance the detection precision while maintaining certain latency and throughput, which is very important for the security of self-driving. The ASIC-based massive MIMO detection architecture not only can meet the latency and throughput requirements but also poses certain advantages in power consumption. In addition, considering the high mobility of self-driving terminals, the massive MIMO detection architecture must adapt to distinct scenarios and requests.

The massive MIMO detector receives and restores information, which has great effects in improving the channel capacity and communications efficiency and ensuring instant communications of remote diagnosis. More importantly, a proper massive MIMO architecture can accelerate this process. Thus, designing a more optimal massive MIMO VLSI architecture has always been the research topic of many researchers. In 5G era, most communications systems of mobile terminals are inevitably associated with massive MIMO technology. The massive MIMO can fulfill not only high capacity and speed but also low power consumption and cost, which will contribute to the boost of further flourish of mobile terminals.

7.2.2 Application of Reconfigurable Detection Chips

In the future, more applications will emphasize high energy efficiency as well as flexibility and scalability to adapt to different algorithms, MIMO system scales, and detection performance requirements. To accommodate these features, the reconfigurable MIMO signal detectors have gradually become the hotspot in the academia in recent years. This is because the reconfigurable MIMO signal detectors can fully exploit and utilize the data parallelism in algorithms and dynamically reconfigure chip functions via configuration flow, which can achieve a certain tradeoff between efficiency and flexibility compared with GPP and ASIC. The following sections give examples to show the applications based on the reconfigurable massive MIMO detectors.

7.2.2.1 Intelligent Manufacturing (IM)

IM is a man–machine integration intelligent system composed of intelligent machines and human experts, which is capable of performing a series of intelligent activities, such as analysis, reasoning, judgment, conception, and decision-making (Fig. 7.13). With the cooperation between human and intelligent machines, the brainwork of human experts is enlarged, extended, and partly replaced. IM updates the concept of manufacturing automation and expands it to flexibility, intelligentization, and highly integration. Undoubtedly, intelligentization is the future development direction of manufacturing automation. AI technology should be widely used in almost each link of manufacturing. Expert system technology can be used in engineering design, process design, production scheduling, fault diagnosis, etc. Also, the advanced computational intelligence methodologies such as neural network (NN) and fuzzy control can be used in the product formulation, production scheduling, etc., to achieve IM. AI technology is especially suitable to solve extremely complex and uncertain problems. In the previous three industrial revolutions, the traditional manufacturing system mainly focused on its five core elements to pursue constantly technical upgrade, which include materials (including characteristics and functions, etc.), methods (including technology, efficiency, productivity, etc.), machines (including precision, automation, production capacity, etc.), measurement (including sensor monitoring, etc.), and maintenance (including utilization rate, fault rate, O&M cost, etc.). Throughout the whole human industrialized process, these five elements have always been the essentials. The logic of the IM is as follows. The issue occurs first; it is then analyzed according to the model, and the model is adjusted based on the five core elements. Then, solve the issue. Finally, accumulate the experiences according to the solved issues and retrospect the source of the issue to avoid similar issues later. In essence, IM is the process of knowledge generation and inheritance.
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Fig. 7.13

IM-related technologies

IM must make the most of communications means at the network layer to control and operate all the intelligent equipment by using wireless communications. In turn, massive MIMO detection in IM equipment must meet the requirements of high stability, flexibility, and scalability. Therefore, how to realize the above requirements will be a challenge for massive MIMO detection chip. Nevertheless, the reconfigurable massive MIMO detector shows certain advantages in these aspects, which is featured with very high potential application values. Moreover, with the popularization of IM, a growing number of industrial intelligent equipment will leverage wireless transmission systems, which raises the issues of upgrade and compatibility for equipment systems. Thus, the precision requirement for the design of massive MIMO detection chips will be increased. Therefore, how to reduce the interference between equipment and the impact of other environmental noise on the signal transmission, and improve flexibility and scalability will be the primary research directions for the design of reconfigurable massive MIMO detectors.

7.2.2.2 Wireless Medical

Communications technology is a key technology in wireless medical [17], as shown in Fig. 7.14. The remote diagnosis, remote surgery, and telerehabilitation using wireless communications and information technologies can ignore the geographical distance and provide effective, reliable, and real-time health services for patients [18]. In addition, in the remote surgeries assisted by robots, to promptly and accurately provide audio and video information and tactile feedback, e-health has very strict requirements for the reliability of the wireless connection. Especially in the remote surgeries and diagnosis, reliability is extraordinarily important. Unreliable connections may lead to the delay of imaging, and low image resolution may limit the remote handling efficiency of doctors. Furthermore, the accurate remote medical can only be realized by tactile feedback. Once human and machine can interact in real time, this demand can be achieved. However, the deterministic real-time act demanded is not supported by the existing communications systems. Human wearable devices can provide medical monitoring for the seniors, athletes, and children. Remote medical system offers a complicated communications environment for patients and healthcare professionals by monitoring patients via computer or cell phone technologies. Owing to its low cost, lightweight, and low maintenance frequency, wearable devices have an extensive application prospect in the medical data collection for patients, the establishment of connections between translation devices, tracking, rescue, etc. [16].
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Fig. 7.14

Wireless medical and monitoring system

In wireless medical, the reliability plays a vital role. To suit distinguished equipment and human characteristics, the hardware circuits with more flexible framework are required. Also, to adapt to the continuously developed and updated equipment requirements, the wireless baseband processing circuits should be scalable to lower the cost. Exactly, the reconfigurable massive MIMO detector will have a bright future regarding to these aspects. In addition, most massive MIMO detection algorithms are with deep parallel computing, and reconfigurable architecture shows its superiority in efficient processing of parallel computation [19]. Generally speaking, the higher the parallelism and the lower data dependency in the algorithm are, the more suitable it is to be accelerated using reconfigurable methods, which is also a reflection of the algorithm at the hardware level. Therefore, reconfigurable massive MIMO detector can effectively fulfill the computation with high parallelism.

7.3 Prospect of Applications of Edge Computing

As the continuous development of the socioeconomic level, people’s demand on mobile internet has shown a clear diversification trend. As for capacity, the massive application demands boost the application and development of emerging technologies such as IoT, D2D, and M2M, which promotes the continuous upgrade of mobile internet equipment and intelligent mobile equipment. The numbers of users and intelligent communications equipment in mobile internet are exploding, which will reach the order of tens of billions or even hundreds of billions according to the forecast. Correspondingly, the data traffic of 5G mobile communications will reach an unprecedented level along with the growth of the communications equipment. Some new application scenarios, i.e., self-driving, smart grid, AR and VR, propose higher requirements on the latency, energy efficiency, number of devices that can be accommodated, and reliability for the communications system [20]. Currently, the emergence of the applications such as online gaming, cloud desktop, smart city, environmental monitoring, and intelligent agriculture, puts the real-time computing capacity of mobile terminals under a harsh test. On one hand, limited by the reality factors such as volume, power consumption, and weight, the processing capability of existing terminal devices is far from meeting the requirements of the aforementioned applications in low latency, high energy efficiency, and high reliability, which severely affects the user experience. In this case, the MCC stands out as one of the effective solutions at present. MCC allows the user equipment to partially or completely migrate the local computation tasks to the cloud server for execution, which solves the problem of resource shortage of mobile equipment and saves the energy consumption of the locally task execution. However, offloading tasks to the core cloud server not only consumes the backhaul link resources and generates additional latency overhead but also impacts the reliability; thus, the requirements of low latency and high reliability are cannot meet for new application scenarios. Therefore, the emerging mobile edging computing (MEC) becomes the key to address this issue. Typical application scenarios of MEC are shown in Fig. 7.15. The basic idea of MEC is to migrate the cloud computing platform to the edge of mobile access network and allow the user equipment to offload computation tasks to the nodes at the edge of the network, e.g., base stations and wireless access spots. Apart from meeting the scalability requirements of the computing capability for terminal devices, MEC also makes up the shortcoming of MCC in long latency. Hence, MEC will become a key technology to assist 5G services to fulfill the technical indicators such as ultra-low latency, ultra-high energy efficiency, and ultra-high reliability [20, 21].
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Fig. 7.15

Typical MEC application scenarios

7.3.1 Concept of Edge Computing

The concept of MEC was first proposed by the European Telecommunications Standards Institute (ETSI) in 2014, and was defined as a new platform that “provides IT and cloud computing capabilities within the edge of mobile access network, the Radio Access Network (RAN) in close proximity to mobile subscribers” [22]. MEC offers cloud computing capabilities within the RAN. MEC connects the user directly to the nearest cloud-enabled edge network, which avoids the direct mobile communication between the core network and end users. Deploying MEC at the base station enhances computation and avoids the performance bottleneck and possible system failures [23]. As shown in Table 7.2, the comparison between MEC and traditional MCC shows that there are significant differences between MEC and MCC systems in terms of computing server, distance to end users, and typical latency, etc. Compared with MCC, MEC has the advantages of achieving lower latency, saving energy for mobile devices, supporting context-aware computing, and enhancing privacy and security for mobile applications [24]. First, MEC can lower the task execution latency. By migrating the cloud computing platform to the edge of access network, it narrows the distance between the computing server and user equipment. Since the task offloading does not need to travel through the backhaul link or core network, the transmission latency overhead is reduced. In addition, the computation capability of the edge server is significantly superior to user equipment, which dramatically lowers the task computation latency. Second, MEC can greatly improve network energy efficiency. Although IoT equipment can be widely applied to various scenarios such as environmental monitoring, group awareness, and intelligent agriculture, most deployed IoT equipment is powered by batteries. As MEC shortens the distance between the edge server and mobile equipment, it significantly saves the energy consumed by task offloading and wireless transmission, extending the service life of IoT equipment. Research results show that for different AR equipment, MEC can extend the battery service life ranging from 30 to 50%. Finally, MEC can provide a higher service reliability. Due to the distributed deployment, small-scale nature, and the less concentration of valuable information, MEC servers are much less likely to become the target of a security attack in contrast with the big data center of MCC, being able to provide more reliable services. And, most MEC servers are private-owned cloudlets, which shall ease the concern of information leakage [24] and ensure higher security. In general, the technical characteristics of MEC are mainly embodied in proximity, low latency, high bandwidth, and location awareness.
Table 7.2

Comparison between MEC and MCC

Comparison items

MEC

MCC

Server hardware

Small-sized data center requiring moderate resource [2, 9]

Large-scale data center (each possessing a lot of powerful servers) [10, 25]

Server location

Coexist with wireless gateway, Wi-Fi router, and LTE base station [2]

Installed in exclusive buildings with the scale comparable to several football courts [11, 26]

Deployment

Intensive deployment by telecom operators, MEC suppliers, enterprises, and family users participated and light configuration and plans required [2]

Deployed in a few places all around the world by IT corporations such as Google and Amazon with complicated configuration and plans required [10]

Distance to end user

Short (dozens of meters to several hundred meters) [26]

Long (probably across continents) [26]

Backhaul use

Infrequently used, alleviating congestion [12]

Frequently used, causing congestion [12]

System management

Layered control (centralized/distributed) [13]

Centralized control [13]

Supported latency

Less than tens of milliseconds [14, 26]

More than a 100 ms [15, 16]

Application

Compute-intensive applications with high requirements on latency, e.g., VR, self-driving, and online interactive games [2, 17]

Compute-intensive applications without high requirements on latency, e.g., online social, mobile commerce/healthcare/study [18, 19]

Proximity:

As MEC server is deployed proximal to the information source, edge computing is very suitable for capturing and analyzing the key information of big data. Moreover, edge computing can directly access user equipment; thus, specific business applications are easily derived.

Low latency:

As MEC server is proximal to or directly operating on the terminal devices, the latency is greatly lowered. This makes the application feedback faster, improves user experience, and dramatically reduces the possibilities of congestion incurred in other parts of the network.

High bandwidth:

As MEC server is proximal to the information source, it can complete simple data processing without uploading all data or information to the cloud, which reduces the transmission pressure of the core network, decreases network congestion, and enhances network transmission speed.

Location awareness:

When the network edge is a part of the radio access network, no matter Wi-Fi or honeycomb, local services can identify the specific location of each connection equipment with a relatively little information.

Figure 7.16 shows the basic system architecture of MEC. Note that, MEC server is closer to the end user than the cloud server. In this case, although the computing capability of MEC servers is weaker than that of the cloud computing servers, they still can provide better QoS for end users. Apparently, unlike cloud computing, edge computing incorporates edge computing nodes into the network. In general, the structure of edge computing can be categorized into three aspects, i.e., front-end, near-end, and far-end. The front-end mainly refers to the terminal devices (e.g., sensors, actuators) deployed at the front-end of the edge computing structure. The front-end environment can provide more interaction and better responsiveness for the end users. Nonetheless, due to the limited computing capacity of the terminal devices, most requirements cannot be satisfied at the front-end environment. In these circumstances, the terminal devices must forward the resource requirements to the servers. The gateway deployed in the near-end environment will support most of the traffic flows in the network. The reason why edge computing can provide real-time services for some applications is that it endows the near-end equipment with powerful computing capabilities. Edge severs can have also numerous resource requirements, such as real-time data processing, data caching, and computation offloading. In edge computing, most of the data computation and storage will be migrated to this near-end environment. In doing so, the end users can achieve a much better performance on data computing and storage, with a small increase in the latency. As the cloud servers are deployed farther away from the terminal devices, the transmission latency is significant in the networks. Nonetheless, the cloud servers in the far-end environment can provide more computing power and more data storage. For example, the cloud servers can provide massive parallel data processing, big data mining, big data management, machine learning, etc. [27].
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Fig. 7.16

Basic system architecture of MEC

7.3.2 Application of Detection Chips in the Edge Computing

In the current network architecture, the high deployment position of core network results in a long transmission latency, failing to meet the business requirement of ultra-low latency. Additionally, businesses ended at the cloud are not completely effective while some regional businesses that do not end locally waste the bandwidth and increase latency. Therefore, latency and connection number indicators determine that the ending point of 5G businesses is not all on the cloud platform at the rear end of core network. Fortunately, MEC fits the demands [28]. Figure 7.17 shows how MEC enhances the integration of data center and 5G. From one aspect, MEC is deployed at the edge. The edge service operating on the terminal devices feeds back faster, which resolves the latency issue. From another, MEC submerges computing content and capability, provides intelligent traffic scheduling, localizes services, caches content locally, and prevents part of regional services from the trouble of ending at cloud. As mobile network has to serve devices of different types and requirements, the cost is incredible if an exclusive network is established for each service. Network slicing technology allows operators to slice a hardware infrastructure into multiple end-to-end virtual networks. Each network slice is logically isolated from the equipment to the access network, to the transmission network to the core network, adapting to different requirements of various types of services, ensuring that from the core network to the access network including links such as terminals can allocate network resources dynamically, in real time and effectively to guarantee the performance of quality, latency, speed, and bandwidth. To a certain degree, the service awareness function of MEC is analogous to the network slicing technology. With low latency as one of the primary technical characteristics, MEC can support the most latency-sensitive services, which also means that MEC is the key technology for the slicing with ultra-low latency [29]. With the application of the MEC, the connotation of network slicing technology will be extended from purely slicing to slicing under different latency requirements to achieve multiple virtual end-to-end networks, which contributes to the development of 5G network slicing technology.
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Fig. 7.17

MEC enhancing the integration of data center and 5G

The key to achieving low latency and saving user equipment energy in MEC lies in the computation offloading, while a key to computing offloading is usually to decide whether to perform a computation offload. In general, there are three decisions with regards to computing offloading.
  1. (1)

    Local execution, in which the entire computation process is executed locally at the user equipment without offloading computation to the MEC, e.g., due to that the MEC computation resources are unavailable or the performance cannot be improved by offloading.

     
  2. (2)

    Full offloading, in which the entire computation is offloaded to be processed at MEC server.

     
  3. (3)

    Partial offloading, in which part of computation is executed locally while the left is offloaded to the MEC server for processing.

     

Computation offloading, especially partial offloading, is a very complicated process which will be impacted by multiple factors such as user preference, wireless and backhaul connection quality, user equipment computation capability, or utilizability of cloud computing capability. Application model/category is also one of the significant aspects of computation offloading because it determines whether full or partial offloading fits, which computations can be offloaded, and how these computations can be offloaded [27]. MEC server is able to provide more powerful computation capabilities than user equipment, offloading computation to MEC server for processing can shorten the data processing time and save the energy of terminal devices consumed for data processing. However, we cannot ignore the fact that offloading data to be processed by the user equipment to the MEC server (uplink) needs to consume transmission time and energy so does it when the MEC server transmits the processed data to the user equipment (downlink). When the computation amount of an application is not very huge, especially when the processing capability of user equipment satisfies the requirements, the aforementioned data transmission (uplink and downlink) may waste time and energy, causing the performance loss. Thus, a reasonable mechanism is required to make the decision of whether to perform computation offloading. MEC technology has relatively high requirements on uplink and downlink data transmission, which are mainly reflected in the low latency, high throughput, and low power consumption in massive MIMO detection. ASIC-based massive MIMO detection chips show outstanding performances in these aspects and can be implemented at the MEC terminal, to reduce latency and power consumption, and improve throughput.

In recent years, there are a large number of research results targeting at the computation offloading for MEC systems. However, there are still many emerging issues need to be addressed including mobility management for MEC, green MEC, and security and privacy issues for MEC. Mobility is an inherent feature of many MEC applications such as AR-assisted museum visit to enhance visitor experience. In this kind of applications, the movements and trajectories of users offer the MEC server with location and personal preference information, which improves the processing efficiency of user computation requests. Furthermore, mobility also poses a great challenge to the realization of universally reliable computation (i.e., without interruptions or errors) for the following reasons. First of all, MEC is usually executed in a heterogeneous network composed of multiple macro and small base stations, and wireless access points. Thus, the user movements should be frequently switched among small coverage MEC servers, as shown in Fig. 7.18, which becomes more complex due to the diversified system configurations and associated strategies between users and servers. Subsequently, serious signal interference and pilot pollution can be generated while users move among different base stations, dramatically deteriorating the communications performance. Finally, frequent switch increases computation latency, which affects the user experience [24]. To meet the communications performance demands, higher detection precision is required during the signal restoring by the detector. Hence, more optimal detector architecture is in demand, which shall be addressed by nonlinear or even more complicated detection algorithms. Therefore, how to support different algorithms and sizes of mobile terminal, and algorithm scalability should all be considered for the development of massive MIMO detection chips. Reconfigurable massive MIMO detectors ensure detection performance and can reach certain energy efficiency at the same time. Most importantly, this detector enables high flexibility, reliability, scalability, etc.
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Fig. 7.18

MEC terminal management

The MEC server is a small data center, and each data center consumes less energy than a traditional cloud data center. However, its intensive deployment mode causes serious problems in the energy consumption of the whole system. Therefore, it is definitely a key to developing innovative technologies to achieve green MEC. Compared with green communications system, the computation resources of MEC server must be appropriately allocated to realize the required computation performance, making traditional green wireless technologies no longer suitable. In addition, as the past researches on green data communications network has not considered wireless resource management, they are not applicable to green MEC. Besides, the highly unpredictable computation workload pattern in MEC server poses another big challenge for the resource management in MEC systems, calling for advanced estimation and optimization techniques [24]. What’s more, there are increasing demands for secure and privacy-preserving mobile services. While MEC enables new types of services, its unique features also bring new security and privacy issues. First of all, the innate heterogeneity of MEC systems makes the conventional trust and authentication mechanisms inapplicable. Second, the diversity of communication technologies that support MEC and the software nature of the networking management mechanisms bring new security threats. Besides, secure and private computation mechanisms become highly desirable as the edge servers may be an eavesdropper or an attacker. These motivate us to develop effective mechanisms [24]. We can also circumvent some power consumption and security related issues from hardware circuits. The reconfigurable massive MIMO detector is close to ASIC in energy efficiency, and can implement different algorithms and signals processing of different scales, demonstrating high flexibility and scalability. In addition, as the PEs and interconnect muddles inside the reconfigurable massive MIMO detector are relatively regular, it is difficult to obtain the algorithm information by observing the hardware architecture and circuit composition. This feature can improve the hardware security and avoid some MEC security issues.

Next, the practical application of the IoV is used as an example to demonstrate the advantages of MEC. The IoV has special requirements for the data processing. The first requirement is low latency, i.e., to achieve the early warning of collision when vehicles are moving at high-speed, the communications latency should be within several milliseconds. The second requirement is high reliability. For safe driving requirements, the IoV requires higher reliability compared with ordinary communications. Meanwhile, as vehicles are moving at high speed, signals must meet the high reliability requirements on the basis of being able to support high-speed motion. With the increase of networked vehicles, the data quantity of the IoV also grows and as a return, the requirements for latency and reliability are higher. After MEC technology is applied to the IoV, due to the location characteristics of MEC, the IoV data can be saved in places proximal to the vehicles to lower the latency, which is quite suitable for the service types with high latency requirements such as anti-collision and accident warning. Meanwhile, the IoV should ultimately be used to help in driving. The location information of vehicles changes rapidly when vehicles are moving at high-speed. Nevertheless, the MEC server can be placed on the vehicle to accurately sense the location change in real time, which improves the communications reliability. In addition, what the MEC server processes are the real-time IoV data with great values. The MEC server analyzes the data in real time and transmits the analysis results to other networked vehicles in the proximal area with ultra-low latency (usually in milliseconds) to facilitate the decision-making of other vehicles (drivers). This approach is more swift, autonomous, and reliable than other processing methods.