**3.1 D2D communication architecture**

The LTE-V2X architecture has been developed to support diverse vehicular network services as discussed above. The architecture uses the new air interface PC5 along with the conventional Uu interface to support various services. The PC5 interface can offer enhanced network services such as device-to-device communication, normally supported by the ad hoc network architecture. The device-todevice communication services was introduced in Release 12 which was originally developed for the safety services [9]. The LTE Release 12 architecture is shown in **Figure 3**. The figure shows a new service function the Proximity Service located in the Evolved Packet Core which allows the devices to discover peer devices for D2D

**Figure 2.** *V2X communication architecture.*

### *An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks DOI: http://dx.doi.org/10.5772/intechopen.91948*

communication services. The ProSe function allows users to directly communicate and exchange data with neighboring devices by sending a registration message to the eNB with a ProSe application ID. The eNB organizes the communication between the devices using the control channels. Once the communicating devices are matched by the eNB, then they can directly communicate using the PC5 interface as shown in **Figure 3**. The PC interface functions are summarized in **Table 2**. Details of these interfaces can be found in [10].

The channels in the Uu and PC5 interfaces are organized as logical, transport, and physical channels. **Figure 4** shows the mapping structure of these channels used for the sidelink communication in the LTE standard. There are two logical channels introduced for sidelink communication: first is the SL Traffic Channel (STCH), and second is SL Broadcast Control Channel (SBCCH). The STCH is an interface to the Physical SL shared Channel (PSSCH), which transports the data carrying user information over the air. The SBCCH is used to broadcast control data, for synchronization in the out of coverage or partial coverage, or for the synchronization between UEs which are located in different cells. There is also a Transport and Physical Sidelink Control Channel carrying the SL control information (SCI). There is a new transport and physical channel for direct discovery: sidelink discovery channel (SL-DCH) and the physical sidelink discovery channel (PSDCH).

**Figure 3.** *LTE release 12 D2D reference network architecture [9].*


#### **Table 2.** *PC interfaces.*

**3. LTE-V2X standard**

The LTE standard is widely used in public and private mobile radio networks. LTE

technology has been identified to support vehicular network services using V2X architecture. The V2X service architecture is shown in **Figure 2**. As mentioned in the previous section, the V2X communication services include four different modes of communication (V2V, V2I, V2P, and V2N). These links are bidirectional. 3GPP study groups in collaboration with transport industries have started standardization activities on LTE-based vehicular networks in the working group 1. After several studies and developing several initial specifications on V2X services based on LTE, Release 14 was published in 2017 [8]. The standard is further developed in Release 15 in 2018 supporting enhanced V2X networking features. The enhancements go beyond the support of CAM and Decentralized Environmental Notification Messages (DENM) transmissions as shown in **Table 1**. The 3GPP specifications did not allocate any specific frequency band to support V2X services. European Telecommunications Standard Institute (ETSI) has allocated a 70 MHz spectrum in the 5.9 GHz band in which there is no overlap between V2X and conventional cellular network services. This separation of operating frequency will enable different operators to provide vehicular network services independent of conventional mobile operators. The 5.9 GHz LTE band will allow the system to coexist with IEEE 802.11p-based systems. However, the mobile operators can also use the licensed band to support the V2X services. The V2X services can use the conventional air interface as well as the newly developed D2D interface using the sidelink channel. The D2D communication archi-

*Moving Broadband Mobile Communications Forward - Intelligent Technologies for 5G…*

The LTE-V2X architecture has been developed to support diverse vehicular network services as discussed above. The architecture uses the new air interface PC5 along with the conventional Uu interface to support various services. The PC5 interface can offer enhanced network services such as device-to-device communication, normally supported by the ad hoc network architecture. The device-todevice communication services was introduced in Release 12 which was originally developed for the safety services [9]. The LTE Release 12 architecture is shown in **Figure 3**. The figure shows a new service function the Proximity Service located in the Evolved Packet Core which allows the devices to discover peer devices for D2D

tecture is briefly introduced in the following section.

**3.1 D2D communication architecture**

**Figure 2.**

**104**

*V2X communication architecture.*

LTE-V2X link is the subchannel in the frequency domain, corresponding to a multiple of the 12 subcarriers groups, and the TTI in the time domain. One packet normally occupies one or more subchannels in a TTI. To improve the system-level performance under high node density while meeting the latency requirement of a V2V link, a new classification of scheduling assignment and data resources is designed where the scheduling assignment is transmitted in sub-channel using specific Resource Blocks (RBs) across the time. More specifically, each data

*An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks*

*DOI: http://dx.doi.org/10.5772/intechopen.91948*

packet also known as Transport Block (TB) has an associated control message called the Sidelink control information (SCI). TB and the associated SCI must be transmitted in the same subframe but can be allocated in adjacent and nonadjacent

**Figure 6** depicts the overall network architecture enhancement in Release 16 for V2X services [13]. Two new entities are introduced: the V2X Application server and the V2X control function to support the V2X services. The V2X control function is the logical function that is used for network-related actions required for V2X. The parameters required for V2X communications can be obtained from V2X Application Server. It is also provision the UEs with Public Land Mobile Network (PLMN) specific parameters that allow the UE to use V2X in this specific PLMN. The V2X Application server incorporates the V2X capability for building the application functionality. It is responsible for receiving uplink data from the UE in the unicast mode, providing the parameters for V2X communications over the PC5 reference point to V2X control function. As per the network architecture, several new reference points (or interface) have been introduced. The roles of V2X reference points

To support the V2X communication, Release 14 introduced the new communication modes (mode 3 and mode 4) as shown in **Figure 7**. Mode 1 from Release 12 was enhanced to mode 3 for V2X communication; similarly, mode 2 from D2D was enhanced to mode 4 for V2X. In mode 3, the UEs' resource reservation and scheduling are performed by the eNB, while in mode 4 the UEs choose the radio resources autonomously. Mode 3 algorithms are not defined in the specifications and their implementation is left to vendors. In contrast, mode 4 can operate without cellular coverage and is therefore considered as the baseline V2V mode since safety applications cannot always depend on the availability of cellular coverage. In mode 4, also known as autonomous or out-of-coverage, each node selects the resources based on a sensing procedure and a semi-persistent scheduling (SPS) mechanism. Mode 4 includes a distributed scheduling scheme for vehicles to select their radio resources and includes the support for distributed congestion control. The detailed

resource blocks.

are summarized in **Table 3**.

**Figure 6.**

**107**

*Enhanced ProSe D2D sidelink architecture for V2X communications [13].*

**Figure 4.** *Mapping of channels for sidelink communication in 3GPP LTE.*

#### **3.2 Enhanced D2D communication architecture for V2X communications**

Recently, several fundamental modifications have been carried out to enhance the PC 5 interface in the Release 14 to support V2X operational scenarios and requirements as shown in **Table 1** [11]. The sidelink LTE-V2X employs the singlecarrier frequency division multiple access (SC-FDMA) which permits the UE to access radio resources in both time and frequency domains. In the frequency domain, the subcarrier spacing is fixed to 15 kHz, and subcarriers are utilized in groups of 12 (i.e., 180 kHz). To support different V2X operational requirements, the transmission channels may use a higher carrier frequency of 6 GHz with very high relative velocity. However, due to the high relative velocity and the use of higher carrier frequency, inter-carrier interference (ICI) due to higher Doppler shift and insufficient channel estimation due to shorter coherence time could be a problem compared to the legacy 3GPP systems.

To improve the performance in the presence of high Doppler shift, the sidelink interface has been tuned to counteract the severe Doppler shift experienced at high speed. In the time domain, additional demodulation reference signal (DMRS) symbols have been added in one subframe to handle the high Doppler shift associated with relative speeds of up to 500 km/h and the use of higher carrier frequency [12]. The new subframe structure is illustrated in **Figure 5**. Fourteen symbols form a subframe of 1 ms, also called transmission time interval (TTI), which include nine data symbols, four demodulation reference signal (DMRS) symbols, and one empty symbol for Tx-Rx switch and timing adjustment. The LTE-V2X has a large number of modulation and coding schemes (MCS), with 4-QAM and 16-QAM modulations, and an almost continuous coding rate. The minimum radio resource allocated to an

**Figure 5.** *V2V subframe for PC-5 interface structure [12].*

#### *An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks DOI: http://dx.doi.org/10.5772/intechopen.91948*

LTE-V2X link is the subchannel in the frequency domain, corresponding to a multiple of the 12 subcarriers groups, and the TTI in the time domain. One packet normally occupies one or more subchannels in a TTI. To improve the system-level performance under high node density while meeting the latency requirement of a V2V link, a new classification of scheduling assignment and data resources is designed where the scheduling assignment is transmitted in sub-channel using specific Resource Blocks (RBs) across the time. More specifically, each data packet also known as Transport Block (TB) has an associated control message called the Sidelink control information (SCI). TB and the associated SCI must be transmitted in the same subframe but can be allocated in adjacent and nonadjacent resource blocks.

**Figure 6** depicts the overall network architecture enhancement in Release 16 for V2X services [13]. Two new entities are introduced: the V2X Application server and the V2X control function to support the V2X services. The V2X control function is the logical function that is used for network-related actions required for V2X. The parameters required for V2X communications can be obtained from V2X Application Server. It is also provision the UEs with Public Land Mobile Network (PLMN) specific parameters that allow the UE to use V2X in this specific PLMN. The V2X Application server incorporates the V2X capability for building the application functionality. It is responsible for receiving uplink data from the UE in the unicast mode, providing the parameters for V2X communications over the PC5 reference point to V2X control function. As per the network architecture, several new reference points (or interface) have been introduced. The roles of V2X reference points are summarized in **Table 3**.

To support the V2X communication, Release 14 introduced the new communication modes (mode 3 and mode 4) as shown in **Figure 7**. Mode 1 from Release 12 was enhanced to mode 3 for V2X communication; similarly, mode 2 from D2D was enhanced to mode 4 for V2X. In mode 3, the UEs' resource reservation and scheduling are performed by the eNB, while in mode 4 the UEs choose the radio resources autonomously. Mode 3 algorithms are not defined in the specifications and their implementation is left to vendors. In contrast, mode 4 can operate without cellular coverage and is therefore considered as the baseline V2V mode since safety applications cannot always depend on the availability of cellular coverage. In mode 4, also known as autonomous or out-of-coverage, each node selects the resources based on a sensing procedure and a semi-persistent scheduling (SPS) mechanism. Mode 4 includes a distributed scheduling scheme for vehicles to select their radio resources and includes the support for distributed congestion control. The detailed

**Figure 6.** *Enhanced ProSe D2D sidelink architecture for V2X communications [13].*

**3.2 Enhanced D2D communication architecture for V2X communications**

*Moving Broadband Mobile Communications Forward - Intelligent Technologies for 5G…*

the PC 5 interface in the Release 14 to support V2X operational scenarios and requirements as shown in **Table 1** [11]. The sidelink LTE-V2X employs the singlecarrier frequency division multiple access (SC-FDMA) which permits the UE to access radio resources in both time and frequency domains. In the frequency domain, the subcarrier spacing is fixed to 15 kHz, and subcarriers are utilized in groups of 12 (i.e., 180 kHz). To support different V2X operational requirements, the transmission channels may use a higher carrier frequency of 6 GHz with very high relative velocity. However, due to the high relative velocity and the use of higher carrier frequency, inter-carrier interference (ICI) due to higher Doppler shift and insufficient channel estimation due to shorter coherence time could be a problem

compared to the legacy 3GPP systems.

*Mapping of channels for sidelink communication in 3GPP LTE.*

**Figure 4.**

**Figure 5.**

**106**

*V2V subframe for PC-5 interface structure [12].*

Recently, several fundamental modifications have been carried out to enhance

To improve the performance in the presence of high Doppler shift, the sidelink interface has been tuned to counteract the severe Doppler shift experienced at high speed. In the time domain, additional demodulation reference signal (DMRS) symbols have been added in one subframe to handle the high Doppler shift associated with relative speeds of up to 500 km/h and the use of higher carrier frequency [12]. The new subframe structure is illustrated in **Figure 5**. Fourteen symbols form a subframe of 1 ms, also called transmission time interval (TTI), which include nine data symbols, four demodulation reference signal (DMRS) symbols, and one empty symbol for Tx-Rx switch and timing adjustment. The LTE-V2X has a large number of modulation and coding schemes (MCS), with 4-QAM and 16-QAM modulations, and an almost continuous coding rate. The minimum radio resource allocated to an


application. The authors also compared those system performances with other decentralized clustering protocols. Remy et al. [21] propose a cluster-based VANET-LTE hybrid architecture for multimedia-communication services.

*An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks*

transmission of safety messages in the network.

*DOI: http://dx.doi.org/10.5772/intechopen.91948*

communication.

investigation.

**109**

**4. CBC-V2V system model**

In [22], the authors provide the delay performance analysis of hybrid architectures. Calabuig et al. [22] propose a hybrid architecture known as the VMaSC-LTE that integrates the LTE network with the IEEE 802.11p-based VANET network. In [22], the authors propose a Hybrid Cellular-VANET Configuration (HCVC) to distribute road hazard warning (RHW) messages to distant vehicles. In this hybrid architecture, cluster members (CMs) communicate with the cluster head (CH) by using the IEEE 802.11p link, and the CHs communicate with the eNB by using cellular links. However, this proposed 802.11p-LTE hybrid architecture increases the transmission delay at the same time as reducing the reliability when the IEEE 802.11p-based network needs to support higher node densities, leading to higher medium access delays. Toukabri et al. [23] propose a Cellular Vehicular Network (CVN) solution as a reliable and scalable operator-assisted opportunistic architecture that supports hyper-local ITS services for the 3GPP Proximity Services. A hybrid clustering approach is suggested to form a dynamic and flexible cluster managed locally by the ProSe-CHs. However, the authors do not focus on the

In [24–26], the authors compare the performance of the IEEE 802.11p and the LTE-V2X in terms of reliability. They mainly used simulation with a moving vehicle and consider the highway scenario to analyze the performance of two technologies. Some of them also include an urban Manhattan case [25, 26]. Bazzi et al. [27] compare IEEE 802.11p and LTE-V2V for cooperative awareness in terms of maximum awareness range and also provides analytical evaluation of the proposed schemes. Min et al. [25] introduce a resource scheduling algorithm known as Maximum Reuse Distance (MRD) for V2V communication under network coverage. The proposed scheduling algorithm is in-line with Cellular-V2X mode 3 with the aim of minimizing the interference and increasing the reliability and latency of V2V

Recently, a global alliance called the Fifth Generation Automotive Association (5GAA) has developed a model to assess the relative performance of LTE-V2X (PC5) and the IEEE 802.11p technologies with regard to improving the safety, focusing on direct communications [28]. This study indicates that the LTE-V2X (PC5) outperforms the 802.11p in reducing fatalities and serious injuries on European roads. All of the abovementioned works agree that LTE-V2X can provide better performance compare to IEEE 802.11p. This is due to a combination of the superior performance of LTE-V2X (PC5) at the radio link level for ad hoc/direct communications between road users. However, the use of LTE-V2X for vehicular applications is not mature yet. In particular, LTE-V2V devices are still under development, and the allocation (and management) of radio resources is still under

In this section, we present an LTE-based cellular network architecture for V2X communication using the PC5 interface of the LTE standard. We assume that all vehicles on the road are within the coverage of the eNB. A highway road traffic scenario is considered where traffic is flowing in both directions in a multilane road as depicted in **Figure 8**. We assume that each vehicle is equipped with a GPS device capable of providing accurate position measurements. The highway is partitioned

into fixed-size regions known as a cluster. Vehicles on the road with near

**Table 3.** *V2X interfaces.*

**Figure 7.** *V2X communication mode defined in release 14.*

description by 3GPP for mode 4 algorithm is presented in [14, 15]. The Global Navigation Satellite System (GNSS) is introduced to provide accurate timing and frequency references in the off-coverage scenario [16].

#### **3.3 Review on current research on LTE vehicular networks**

Since the LTE Release 14 was standardized, several studies have been carried out to compare the performance of IEEE 802.11p and LTE-V2X vehicular networks. In [17], comparative experiments with real devices were carried out, demonstrating improvement of the C-V2X system performance. The work demonstrated that the latency in C-V2X under congested conditions can be maintained under 100 ms.

The use of cellular technologies for vehicular networks has been investigated to meet the requirements of safety services in [5, 18, 19]. The work showed that traffic hazard warning messages are disseminated in less than a second. Hybrid architectures based on the LTE and the 802.11p standards have been proposed to exploit the benefits of both networks [20, 21]. Sivaraj et al. [20] present a cluster-based centralized vehicular network architecture which uses both the 802.11p and the LTE standards for well-known urban sensing application and floating car data (FCD)

#### *An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks DOI: http://dx.doi.org/10.5772/intechopen.91948*

application. The authors also compared those system performances with other decentralized clustering protocols. Remy et al. [21] propose a cluster-based VANET-LTE hybrid architecture for multimedia-communication services.

In [22], the authors provide the delay performance analysis of hybrid architectures. Calabuig et al. [22] propose a hybrid architecture known as the VMaSC-LTE that integrates the LTE network with the IEEE 802.11p-based VANET network. In [22], the authors propose a Hybrid Cellular-VANET Configuration (HCVC) to distribute road hazard warning (RHW) messages to distant vehicles. In this hybrid architecture, cluster members (CMs) communicate with the cluster head (CH) by using the IEEE 802.11p link, and the CHs communicate with the eNB by using cellular links. However, this proposed 802.11p-LTE hybrid architecture increases the transmission delay at the same time as reducing the reliability when the IEEE 802.11p-based network needs to support higher node densities, leading to higher medium access delays. Toukabri et al. [23] propose a Cellular Vehicular Network (CVN) solution as a reliable and scalable operator-assisted opportunistic architecture that supports hyper-local ITS services for the 3GPP Proximity Services. A hybrid clustering approach is suggested to form a dynamic and flexible cluster managed locally by the ProSe-CHs. However, the authors do not focus on the transmission of safety messages in the network.

In [24–26], the authors compare the performance of the IEEE 802.11p and the LTE-V2X in terms of reliability. They mainly used simulation with a moving vehicle and consider the highway scenario to analyze the performance of two technologies. Some of them also include an urban Manhattan case [25, 26]. Bazzi et al. [27] compare IEEE 802.11p and LTE-V2V for cooperative awareness in terms of maximum awareness range and also provides analytical evaluation of the proposed schemes. Min et al. [25] introduce a resource scheduling algorithm known as Maximum Reuse Distance (MRD) for V2V communication under network coverage. The proposed scheduling algorithm is in-line with Cellular-V2X mode 3 with the aim of minimizing the interference and increasing the reliability and latency of V2V communication.

Recently, a global alliance called the Fifth Generation Automotive Association (5GAA) has developed a model to assess the relative performance of LTE-V2X (PC5) and the IEEE 802.11p technologies with regard to improving the safety, focusing on direct communications [28]. This study indicates that the LTE-V2X (PC5) outperforms the 802.11p in reducing fatalities and serious injuries on European roads. All of the abovementioned works agree that LTE-V2X can provide better performance compare to IEEE 802.11p. This is due to a combination of the superior performance of LTE-V2X (PC5) at the radio link level for ad hoc/direct communications between road users. However, the use of LTE-V2X for vehicular applications is not mature yet. In particular, LTE-V2V devices are still under development, and the allocation (and management) of radio resources is still under investigation.

### **4. CBC-V2V system model**

In this section, we present an LTE-based cellular network architecture for V2X communication using the PC5 interface of the LTE standard. We assume that all vehicles on the road are within the coverage of the eNB. A highway road traffic scenario is considered where traffic is flowing in both directions in a multilane road as depicted in **Figure 8**. We assume that each vehicle is equipped with a GPS device capable of providing accurate position measurements. The highway is partitioned into fixed-size regions known as a cluster. Vehicles on the road with near

description by 3GPP for mode 4 algorithm is presented in [14, 15]. The Global Navigation Satellite System (GNSS) is introduced to provide accurate timing and

V1 The V2X application server can communicate towards an V2X application in the UE

*Moving Broadband Mobile Communications Forward - Intelligent Technologies for 5G…*

V3 The V2X control function can connect to the UE through the V3 interface

SGi An EPC can connect to the V2X application server through SGi interface

Packet Core in the 3GPP network through V4 interface

V2 The V2X application server can communicate with the V2X control function through V2

V4 The V2X control function connects with entity Home Subscriber Server (HSS) in Evolved

V5 A V2X application in UE can communicate towards a V2X application in different UEs

interface. The V2X application server may connect to V2X control function belonging to

Since the LTE Release 14 was standardized, several studies have been carried out to compare the performance of IEEE 802.11p and LTE-V2X vehicular networks. In [17], comparative experiments with real devices were carried out, demonstrating improvement of the C-V2X system performance. The work demonstrated that the latency in C-V2X under congested conditions can be maintained under 100 ms. The use of cellular technologies for vehicular networks has been investigated to meet the requirements of safety services in [5, 18, 19]. The work showed that traffic hazard warning messages are disseminated in less than a second. Hybrid architectures based on the LTE and the 802.11p standards have been proposed to exploit the benefits of both networks [20, 21]. Sivaraj et al. [20] present a cluster-based centralized vehicular network architecture which uses both the 802.11p and the LTE standards for well-known urban sensing application and floating car data (FCD)

frequency references in the off-coverage scenario [16].

*V2X communication mode defined in release 14.*

**Interface Main functions**

**Table 3.** *V2X interfaces.*

**Figure 7.**

**108**

through V1 interface

multiple PLMNs

through V5 interface

**3.3 Review on current research on LTE vehicular networks**

discovery [29]. For restricted discovery, the user entity is not allowed to be detected without its explicit permission. In this case, it prevents other users to distribute their information to protect user privacy. It suits social network applications (e.g., group gaming and context sharing with friends). For open discovery, a user entity can be detected as long as it is within another device's proximity. From the network's perspective, device discovery can be divided into two types: direct discovery and Evolved Packet Core (EPC) discovery. UE would search for a nearby device autonomously; this requires a UE device to participate in the device discovery process. Direct discovery work in both in-coverage and out-of-coverage scenarios. There are also provisions for EPC level discovery that notifies the terminal about other users detected in the vicinity based on the user interest information and the UE location information registered by terminals in the ProSe function [30]. All vehicles that need to use the D2D link must have the ProSe capability features: the ability to discover, to be discovered, and to communicate with discovered devices. Within the existing EPC level discovery model, the ProSe function authenticates the user by checking its credential with the HSS as to whether the user is permitted to utilize ProSe features. After successful authentication of the UE, the ProSe function creates an EPC ProSe Subscriber ID (EPUID) and assigned it to the registered device. Once a vehicle registered as a ProSe subscriber, it can run the applications that support proximity services, named as a ProSe-enabled applications. The application server allocates the user an Application Layer User ID (ALUID) to recognize him within the context of this particular application.

*An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks*

*DOI: http://dx.doi.org/10.5772/intechopen.91948*

However, these device discovery and the EPC level discovery models require significant control signaling or message exchanges such as announce requests, monitor requests, match reports, etc. [30, 31]. Our proposed discovery mechanism

diminishes network resource requirements. It assumes that every vehicle is equipped with a GPS receiver and can accurately determine its position and direction of movement. **Figure 9** appears the signaling diagram of the proposed EPC

1.When a new vehicle reaches an eNB coverage area, the downlink frame synchronization is accomplished once it has decoded the primary

synchronization signal (PSS) and the secondary synchronization signal (SSS) messages, which are accessible on the downlink broadcast control channel.

level discovery technique elaborated as follows:

*EPC level Sidelink peer discovery (ESPD) model for VANET.*

**Figure 9.**

**111**

**Figure 8.** *Highway scenario for proposed cluster-based V2V cellular (CBC-V2V) architecture.*

proximities form a cluster where they exchange the safety messages to each other using a CBC-V2V-based packet transmission technique.

We are considering two types of vehicles: the first type represents the user terminals capable of acting as a CH and supports D2D communication using the PC5 interface. The CH also manages the network resource usage among the group of devices communicating over D2D links. The second type of vehicles represents the network devices that can only act as CMs. These vehicles connect to the appropriate CH to assist them in establishing the D2D links to exchange messages. In this model, a vehicle uses two communication links: the conventional Uu channels and the D2D links using the PC5 interface. Cluster members can communicate with others using the PC5 links, whereas a CH communicates with the eNB using the Uu interface. Although the D2D channels enable two neighboring UEs to communicate directly, all signaling and data transmission processes should still be under the control of the eNB in order to comply with the LTE-Advanced architecture requirements.

## **4.1 Cluster-based cellular V2V (CBC-V2V) communication architecture**

We propose a cluster-based cellular V2V communication architecture that combines the new sidelink peer discovery model to support safety services. We propose to use a cluster topology where communication among cluster members is coordinated by the cluster shown in **Figure 8**. Vehicular networks are generally dynamic where vehicles may arrive new in a cluster location or may leave a cluster. For a newly arrived vehicle, it is necessary to find out necessary system information to join an appropriate cluster. In the following section, our proposed sidelink peer discovery model is presented. Following that discussion, our cluster-based cellular V2V communication mechanism combining with a round-robin scheduling technique is proposed to distribute the radio resources among the cluster nodes.

#### **4.2 EPC level sidelink peer discovery (ESPD) model**

For direct communication, two devices must be aware of each other. ProSe peer discovery is the first step to start a direct transmission. Since the introduction of D2D communication architecture in Release 12, many device/peer discovery techniques have been developed using two models defined in the standard. From the user's perspective, they can be classified into restricted discovery and open

### *An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks DOI: http://dx.doi.org/10.5772/intechopen.91948*

discovery [29]. For restricted discovery, the user entity is not allowed to be detected without its explicit permission. In this case, it prevents other users to distribute their information to protect user privacy. It suits social network applications (e.g., group gaming and context sharing with friends). For open discovery, a user entity can be detected as long as it is within another device's proximity. From the network's perspective, device discovery can be divided into two types: direct discovery and Evolved Packet Core (EPC) discovery. UE would search for a nearby device autonomously; this requires a UE device to participate in the device discovery process. Direct discovery work in both in-coverage and out-of-coverage scenarios. There are also provisions for EPC level discovery that notifies the terminal about other users detected in the vicinity based on the user interest information and the UE location information registered by terminals in the ProSe function [30].

All vehicles that need to use the D2D link must have the ProSe capability features: the ability to discover, to be discovered, and to communicate with discovered devices. Within the existing EPC level discovery model, the ProSe function authenticates the user by checking its credential with the HSS as to whether the user is permitted to utilize ProSe features. After successful authentication of the UE, the ProSe function creates an EPC ProSe Subscriber ID (EPUID) and assigned it to the registered device. Once a vehicle registered as a ProSe subscriber, it can run the applications that support proximity services, named as a ProSe-enabled applications. The application server allocates the user an Application Layer User ID (ALUID) to recognize him within the context of this particular application.

However, these device discovery and the EPC level discovery models require significant control signaling or message exchanges such as announce requests, monitor requests, match reports, etc. [30, 31]. Our proposed discovery mechanism diminishes network resource requirements. It assumes that every vehicle is equipped with a GPS receiver and can accurately determine its position and direction of movement. **Figure 9** appears the signaling diagram of the proposed EPC level discovery technique elaborated as follows:

1.When a new vehicle reaches an eNB coverage area, the downlink frame synchronization is accomplished once it has decoded the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) messages, which are accessible on the downlink broadcast control channel.

**Figure 9.** *EPC level Sidelink peer discovery (ESPD) model for VANET.*

proximities form a cluster where they exchange the safety messages to each other

*Moving Broadband Mobile Communications Forward - Intelligent Technologies for 5G…*

We are considering two types of vehicles: the first type represents the user terminals capable of acting as a CH and supports D2D communication using the PC5 interface. The CH also manages the network resource usage among the group of devices communicating over D2D links. The second type of vehicles represents the network devices that can only act as CMs. These vehicles connect to the appropriate CH to assist them in establishing the D2D links to exchange messages. In this model, a vehicle uses two communication links: the conventional Uu channels and the D2D links using the PC5 interface. Cluster members can communicate with others using the PC5 links, whereas a CH communicates with the eNB using the Uu interface. Although the D2D channels enable two neighboring UEs to communicate directly, all signaling and data transmission processes should still be under the control of the

eNB in order to comply with the LTE-Advanced architecture requirements.

**4.1 Cluster-based cellular V2V (CBC-V2V) communication architecture**

We propose a cluster-based cellular V2V communication architecture that combines the new sidelink peer discovery model to support safety services. We propose to use a cluster topology where communication among cluster members is coordinated by the cluster shown in **Figure 8**. Vehicular networks are generally dynamic where vehicles may arrive new in a cluster location or may leave a cluster. For a newly arrived vehicle, it is necessary to find out necessary system information to join an appropriate cluster. In the following section, our proposed sidelink peer discovery model is presented. Following that discussion, our cluster-based cellular V2V communication mechanism combining with a round-robin scheduling technique is proposed to distribute the radio resources among the cluster nodes.

For direct communication, two devices must be aware of each other. ProSe peer discovery is the first step to start a direct transmission. Since the introduction of D2D communication architecture in Release 12, many device/peer discovery techniques have been developed using two models defined in the standard. From the user's perspective, they can be classified into restricted discovery and open

using a CBC-V2V-based packet transmission technique.

*Highway scenario for proposed cluster-based V2V cellular (CBC-V2V) architecture.*

**Figure 8.**

**110**

**4.2 EPC level sidelink peer discovery (ESPD) model**

The vehicle at that point downloads the Master Information Block (MIB) from the broadcast channel. This channel incorporates the downlink and uplink carrier configuration information. Further, the vehicle utilizes the Downlink Shared Channel (DL-SCH) to download the system information block. The SIB2 block contains necessary parameters for the initial access transmission.


an SCH. SCH is the state the vehicle has no potential neighboring vehicle that can

*An LTE-Direct-Based Communication System for Safety Services in Vehicular Networks*

*DOI: http://dx.doi.org/10.5772/intechopen.91948*

Upon receiving the new proximity data in a neighboring table, an SV search the NVT during the time period *Tsearch* to check the vehicles in CH, SCH, and SE state. If none of the neighbor vehicles are recorded either as CH or SCH, the vehicle will check the neighboring vehicles in the SE states. If there are the vehicles in SE state in the NVT and the SV has the most reduced average speed and a maximum distance from its current location to the zone boundary (i.e., longest lifetime), at that point it becomes the CH. The algorithm for the CH and the SCH selection is presented in Algorithm 1. Each vehicle calculates its average speed periodically. If none of the neighbor vehicles are recorded either as CH, SCH, or SE, a source vehicle will take the role of SCH. In case the vehicle in the SCH state gets any joining request from a neighboring vehicle during the time period *TSCH*, then it will take the role of the CH. Otherwise, it will reach in the SE state and require a re-registration

1: while *Tsearch* 6¼ 0 && there is no potential neighbouring to connect

3: The SV will compare its *SSV* and *TLife* with other vehicles in NVL;

**4.4 Cluster head and semi-cluster head selection**

connect to it.

*CBC-V2V clustering approach.*

**Figure 10.**

to receive new proximity data.

2: if *VState* ¼ *ALLSE* then

(*VState* 6¼ *CHorSCH*) do

5: *SV* ! *CH*; 6: else

7: *SV* ! *SCH*; 8: end if 9: end if

**113**

**Algorithm 1.** CH and SCH selection

4: if *SSV* <*SALL* and *TLife* >*TALL* then
