**4.3 Cluster formation**

After the peer discovery, each vehicle needs to select an appropriate Cluster Head (CH) to associate with it. Using the peer discovery model, after successful registration, each vehicle updates its Neighborhood Table (NVT) in its VIR with the new proximity data (i.e., a list of neighbor vehicles) along with the vehicle ID, total number of vehicles, and current state of the each vehicle in the list. Once the new proximity data received, the vehicle will reach in the Selection State (SE). As shown in **Figure 10**, a vehicle in the selection state first tries to connect to the existing cluster to minimize the number of clusters. Hence, the source vehicle (SV) first checks the total number of vehicles, their position conjointly, and the state of each vehicle in its NVT.

If the vehicle finds a cluster head in its NVT, and the number of members in the cluster is lower than the maximum number of members allowed, the SV will attempt to connect to the existing CH. In the NVT, if none of the neighboring vehicles are listed as CH or the vehicle is unable to connect to any of the neighboring CHs, the vehicle inspects the neighboring vehicles in the semi-cluster head (SCH) state. If there are vehicles in the SCH state in its NVL, the source vehicle tries to connect the existing semi-cluster head. If none of the neighbor vehicles are listed as CH or SCH, the SV checks the neighboring vehicle in Selection State. If the SV discovers the vehicles in SE in NVT and it has the lowest average speed and the maximum distance from its current location to the zone boundary (i.e., longest lifetime) among them, then it will take the role of CH. Otherwise, the SV becomes

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

**Figure 10.** *CBC-V2V clustering approach.*

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.

discovery, the vehicle sends its location information in the registration request

2. In the initial state, each vehicle on the road must register itself with the eNodeB using its current GPS position. Unlike the existing EPC level

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

to the eNodeB instead of using the ProSe function for user (vehicle) registration. The vehicles will forward their information (such as ALU\_ID, current GPS location, an average speed of the vehicle, discovery range, and vehicle ID) in the registration request message utilizing the Random Access Channel (RACH) to the eNB. The eNB acknowledges the registration request and broadcasts the registration response back to vehicles along with the current traffic profile over the broadcast channel. The vehicle's traffic profile contains an EPC ProSe Subscriber ID, zone information (i.e., to which zone it currently belongs), neighboring vehicle list, and the vehicle's remaining

3.After accepting the information supplied in the registration response, the vehicle collects all the data in its Vehicle Information Register (VIR), a repository that stores vehicle and surrounding information. For D2D

After the peer discovery, each vehicle needs to select an appropriate Cluster Head (CH) to associate with it. Using the peer discovery model, after successful registration, each vehicle updates its Neighborhood Table (NVT) in its VIR with the new proximity data (i.e., a list of neighbor vehicles) along with the vehicle ID, total number of vehicles, and current state of the each vehicle in the list. Once the new proximity data received, the vehicle will reach in the Selection State (SE). As shown in **Figure 10**, a vehicle in the selection state first tries to connect to the existing cluster to minimize the number of clusters. Hence, the source vehicle (SV) first checks the total number of vehicles, their position conjointly, and the state of each

If the vehicle finds a cluster head in its NVT, and the number of members in the

cluster is lower than the maximum number of members allowed, the SV will attempt to connect to the existing CH. In the NVT, if none of the neighboring vehicles are listed as CH or the vehicle is unable to connect to any of the neighboring CHs, the vehicle inspects the neighboring vehicles in the semi-cluster head (SCH) state. If there are vehicles in the SCH state in its NVL, the source vehicle tries to connect the existing semi-cluster head. If none of the neighbor vehicles are listed as CH or SCH, the SV checks the neighboring vehicle in Selection State. If the SV discovers the vehicles in SE in NVT and it has the lowest average speed and the maximum distance from its current location to the zone boundary (i.e., longest lifetime) among them, then it will take the role of CH. Otherwise, the SV becomes

vehicle will require re-registration to update its VIR.

communication, each vehicle updates its neighborhood table with a new list of neighboring vehicles and builds knowledge of its local environment. The global mobile location center (GMLC) keeps vehicle locations tracked. Once the vehicle comes to a new zone or crosses the boundary of the zone, the location alert, i.e., the Location Service (LCS) report, will be received and

distance from its location.

**4.3 Cluster formation**

vehicle in its NVT.

**112**

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

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

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 to receive new proximity data.

#### **Algorithm 1.** CH and SCH selection

1: while *Tsearch* 6¼ 0 && there is no potential neighbouring to connect (*VState* 6¼ *CHorSCH*) do 2: if *VState* ¼ *ALLSE* then 3: The SV will compare its *SSV* and *TLife* with other vehicles in NVL; 4: if *SSV* <*SALL* and *TLife* >*TALL* then 5: *SV* ! *CH*; 6: else 7: *SV* ! *SCH*; 8: end if 9: end if

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

10: if *TSCH* 6¼ 0 then 11: *SCHi* receive any joining request from neighbouring vehicle; 12: *SCH* ! *CH*; 13: else 14: *SCH* ! *SE*; 15: end if 16: end while

#### **4.5 V2X sidelink channel structure**

Using communication mode 3, we suggest the 3GPP standard-based V2V sidelink channel structure as shown in **Figure 11**. The figure shows that an eNB reserves 10 D2D subframes on uplink cellular traffic channels in the time division multiplex (TDM) manner. The D2D subframe repetition rate is 100 ms. Each subframe contains two slots; hence a single carrier offers 20 slots for sidelink communications. The RBs are used to transmit data and control information. The data is transmitted using transport blocks (TBs) over the Physical Sidelink Shared Channels. Sidelink control information messages are transmitted over the Physical Sidelink Control Channels (PSCCH) [16]. The number of RBs in a slot depends on the bandwidth of an LTE-V network cell. Using a 3 MHz transmission bandwidth, there will be 15 RBs in 1 slot available for the D2D communication.

> Radio resources are initially allocated to the CH for each cluster of nodes. The CH then conducts round-robin resource scheduling among its CMs (i.e., vehicles) based on the vehicle ID. The round-robin scheduling approach is based on the idea of being fair to all active users in the long term by granting an equal number of physical resource blocks (PRBs). Our proposed resource allocation scheme is operated by dynamically assigning the same slot to the multiple users, in turn, using node IDs in ascending order. Subsequently, members of a cluster can share the same

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

As shown in **Figure 11**, 10 subframes for D2D communication show up in every 100 ms which are shared between different clusters. Since each cluster is designated one slot, the same subframe will support two clusters. In the example, slot 1 is assigned to *CHA*<sup>0</sup> and slot 2 is assigned to *CHB*0. When the resource is allocated, the CH chooses PRBs within the available slot to transmit its posses CAM to its CMs in the multicast mode. A ProSe-enabled node cannot receive and decode the D2D message while it is transmitting, due to the half-duplex nature of most transceiver designs. Therefore, in the cluster, when one vehicle is transmitting, the rest of the vehicles will receive the CAM from the transmitting vehicle. Each safety message can be accommodated utilizing four PRBs based on the selected modulation and coding scheme and the packet size. On completion of the transmission from the CH, it will assign the same slot to its CMs. The next vehicle *VA*<sup>1</sup> is thereby allocated the same slot on its turn based on its vehicle ID. Then *VA*<sup>1</sup> multicast its own safety message to its neighboring vehicles. The same procedure will follow by the

remaining vehicles in the cluster. To maximize reuse of the spectrum, the same D2D

In this architecture, the inter-cluster communication is required to share safety messages by vehicles which are found at the edge of the two neighboring clusters. In the example, vehicle *VB*<sup>1</sup> is in the neighbor list of *VA*<sup>1</sup> but out of range of its *CHA*0. Therefore, direct communication is not conceivable between *VA*<sup>1</sup> and *VB*1. In this case, *CHA*<sup>0</sup> collects the safety message from its cluster member *VA*<sup>1</sup> over the D2D Physical Sidelink Shared Channel and transmits to the eNodeB over the LTE interface in the unicast mode. At that point, the eNodeB conveys the safety traffic message to a

resource can be assigned to different nonoverlapping clusters.

slot in turn to transmit their own CAM.

*CBC-V2V communication over sidelink channels.*

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

**Figure 12.**

**115**

#### **4.6 CBC-V2V communication**

Our proposed CBC-V2V communication for safety message transmission is shown in **Figure 12**. As seen, the intra-cluster communication procedure between cluster members *VA*<sup>1</sup> and *VA*<sup>2</sup> belongs to a cluster *CHA*<sup>0</sup> and inter-cluster communication from *VA*<sup>1</sup> to the vehicle *VB*<sup>1</sup> which belongs to a neighbor cluster *CHB*0. For the rest of the vehicles in the network the same procedure will follow. A CH acts as a ProSe gateway node for vehicle-to-infrastructure (V2I) and infrastructure-tovehicle (I2V) communication. The CH utilizes the Physical Uplink Shared Channel (PUSCH) uplink grant allocated during the random access procedure to send the RRC connection request along with the data structure called cluster\_info. In the cluster\_info, each CH keeps the information such as the *CHID* and the number of CMs attached to it. Based on the cluster\_info in the RRC connection request, an eNB dynamically allocates resources to a CH for D2D communication. At the cluster level, each cluster head further schedules the resources among its CMs using the new cluster-based round-robin scheduling as described below.

**Figure 11.** *V2V sidelink subframe structure.*

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

**Figure 12.** *CBC-V2V communication over sidelink channels.*

10: if *TSCH* 6¼ 0 then

12: *SCH* ! *CH*;

14: *SCH* ! *SE*; 15: end if 16: end while

**4.5 V2X sidelink channel structure**

**4.6 CBC-V2V communication**

**Figure 11.**

**114**

*V2V sidelink subframe structure.*

13: else

11: *SCHi* receive any joining request from neighbouring vehicle;

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

Using communication mode 3, we suggest the 3GPP standard-based V2V sidelink channel structure as shown in **Figure 11**. The figure shows that an eNB reserves 10 D2D subframes on uplink cellular traffic channels in the time division multiplex (TDM) manner. The D2D subframe repetition rate is 100 ms. Each subframe contains two slots; hence a single carrier offers 20 slots for sidelink communications. The RBs are used to transmit data and control information. The data is transmitted using transport blocks (TBs) over the Physical Sidelink Shared Channels. Sidelink control information messages are transmitted over the Physical Sidelink Control Channels (PSCCH) [16]. The number of RBs in a slot depends on the bandwidth of an LTE-V network cell. Using a 3 MHz transmission bandwidth,

Our proposed CBC-V2V communication for safety message transmission is shown in **Figure 12**. As seen, the intra-cluster communication procedure between cluster members *VA*<sup>1</sup> and *VA*<sup>2</sup> belongs to a cluster *CHA*<sup>0</sup> and inter-cluster communication from *VA*<sup>1</sup> to the vehicle *VB*<sup>1</sup> which belongs to a neighbor cluster *CHB*0. For the rest of the vehicles in the network the same procedure will follow. A CH acts as a ProSe gateway node for vehicle-to-infrastructure (V2I) and infrastructure-tovehicle (I2V) communication. The CH utilizes the Physical Uplink Shared Channel (PUSCH) uplink grant allocated during the random access procedure to send the RRC connection request along with the data structure called cluster\_info. In the cluster\_info, each CH keeps the information such as the *CHID* and the number of CMs attached to it. Based on the cluster\_info in the RRC connection request, an eNB dynamically allocates resources to a CH for D2D communication. At the cluster level, each cluster head further schedules the resources among its CMs using the

there will be 15 RBs in 1 slot available for the D2D communication.

new cluster-based round-robin scheduling as described below.

Radio resources are initially allocated to the CH for each cluster of nodes. The CH then conducts round-robin resource scheduling among its CMs (i.e., vehicles) based on the vehicle ID. The round-robin scheduling approach is based on the idea of being fair to all active users in the long term by granting an equal number of physical resource blocks (PRBs). Our proposed resource allocation scheme is operated by dynamically assigning the same slot to the multiple users, in turn, using node IDs in ascending order. Subsequently, members of a cluster can share the same slot in turn to transmit their own CAM.

As shown in **Figure 11**, 10 subframes for D2D communication show up in every 100 ms which are shared between different clusters. Since each cluster is designated one slot, the same subframe will support two clusters. In the example, slot 1 is assigned to *CHA*<sup>0</sup> and slot 2 is assigned to *CHB*0. When the resource is allocated, the CH chooses PRBs within the available slot to transmit its posses CAM to its CMs in the multicast mode. A ProSe-enabled node cannot receive and decode the D2D message while it is transmitting, due to the half-duplex nature of most transceiver designs. Therefore, in the cluster, when one vehicle is transmitting, the rest of the vehicles will receive the CAM from the transmitting vehicle. Each safety message can be accommodated utilizing four PRBs based on the selected modulation and coding scheme and the packet size. On completion of the transmission from the CH, it will assign the same slot to its CMs. The next vehicle *VA*<sup>1</sup> is thereby allocated the same slot on its turn based on its vehicle ID. Then *VA*<sup>1</sup> multicast its own safety message to its neighboring vehicles. The same procedure will follow by the remaining vehicles in the cluster. To maximize reuse of the spectrum, the same D2D resource can be assigned to different nonoverlapping clusters.

In this architecture, the inter-cluster communication is required to share safety messages by vehicles which are found at the edge of the two neighboring clusters. In the example, vehicle *VB*<sup>1</sup> is in the neighbor list of *VA*<sup>1</sup> but out of range of its *CHA*0. Therefore, direct communication is not conceivable between *VA*<sup>1</sup> and *VB*1. In this case, *CHA*<sup>0</sup> collects the safety message from its cluster member *VA*<sup>1</sup> over the D2D Physical Sidelink Shared Channel and transmits to the eNodeB over the LTE interface in the unicast mode. At that point, the eNodeB conveys the safety traffic message to a concerned neighbor *CHB*<sup>0</sup> over the LTE interface. The *CHB*<sup>0</sup> multicasts the safety message to its cluster members *VB1* and *VB2* via the LTE-D2D PC5 interface.
