Abstract – A wireless communications willalways be affected by fading, interferences or hidden terminal problems. Forvehicle, an urban scenario is centre stage to roam around the concrete jungle.Beaconing message is the most common communications which has an ability to letthe vehicle know about its neighbouring vehicle in order to choose a rightforwarder for non-safety or safety message. However, a congestion that resultingin low messages and overhead beacon that caused by the influx of the broadcastmessages were give a negative impact for a low reception message and in excessivedelay. An emergency messages may be affected from the street beacon andresulting in interferences. In this paper scheme were proposed in order tocancel an interferences by using adaptive transmission control because of theproblem caused by communications of inter-street beacons, while at the sametime maintaining the application layer of the transmission range throughnetwork coding and forwarding multi-chop beacon. From the simulation, it showthat the scheme produced is much higher in packet delivery ratio and also have higher successful channel utilizationcompared with the CSMA/CA protocol.Keywords- Control of congestion,Interference, Coding network,Beacon.
I. INTRODUCTION It has been witnessed from the industry such ascommunication in vehicular network as well as academia. This because of manyapplications such as, traffic monitoring, driver assistance infotainment andcollision notifications. From the research conduct it can be conclude that the Internetand cloud has a negative influence where it is encouraged a cyber penetration ina big way in a vehicular network.
A lot of data application required for thevarious intelligent transportation systems (IPTS) in order to be able tocommunicate between ‘Vehicle-to-Vehicle’, (V2V) and also witha Vehicle Infrastructure networks (V2I). Based on 3 it is say that beaconingis one of the important necessity to cater a safety applications for DSRC/WAVE.The bacon must can go to 10 beacons per seconds so it can be able to deal withthe changes of direction for the rear end and head collision of the vehicle. Toimprove the accuracy of the neighbourhood information a frequent beaconing isneed to be done.
A time needed to be considered if commuting by using a publictransport or private transport. A connection mayestablish between the vehicle and the base station through a mobile gateway ordirectly 27. Vehicular network may also being used in cellular service inorder to give access services from mobile offloading 28 into the travellingpassenger that follows a private or public transport. A data were forwardedbased on the multi-hop since the sensing in the vehicular network is sensiblebecause of the plethora incidents. A high bandwidth requirements were had byall this communications. We can conclude that since by assuming the future WIFIand mobile communications will exploits the vehicular network it will needed alot of MAC and also network layer protocol. Vehicular network has its owntechnical challenge such as, high mobility of vehicle, reliability requirements3 of real time applications, large differences in vehicle speeds;inter-street interferences 29 and stringent delay.
To ensure a considerableoverload only can affect the control channel performances 1 a several kind ofmessage were generate. The approaching were made based on the interference ofthe other vehicle in this paper, where it reduced the interference by loweringnode of each transmission power when the vehicle is not part of the samesegment of the road. Transmission power is reduced for the safety of thetransmission power application and in order to obtain much lower transmissionranged from the original transmission range needed. Separated by certaindistances, a separated preselecting process need to be done for the forwarding nodes.The process of rebroadcasting a resulting message were done from the oppositedirection when the forwarder were receive the beacon message. This process willcontinues until the beacon message is forwarded anymore and when the range forthe application layer is reached. When transmission power for the beaconmessage is reduced, the interference can be negate and it can manage congestioncontrol.
There is several section in this paper, and each section has explain adifferent things where, section II present a discussion about the challengesand state of art, section III described about the protocol that being proposed,section IV is about the evaluation based on the simulation and the performanceof proposed approach and the final section V is about the conclusion of thispaper and about future work.II. RELATED WORKS Using a single and separated allocatedchannel in order to control the message 14. Bydepending on various active safety precautions 12 we can get the accuracy ofthe beacon message. When beaconfrequency increase its accuracy also increase, but as a result channel for thecommunication became congested because of the higher rate of the beacon. Thechannel busy time problem were occur because of the increasing on the nodedensity and at the same time it cause decreasing on the reception probabilityof beacon 1. In 2, extremely saturated scenario, a reduction in beaconprobability is demonstrated. An obstacles suchas buildings had a major role in vehicular network since it can alterperspective all together.
Many realistic model have been develop forsimulations in this recent years 30. The attenuation were add by these modelto receive the signal. Map and building structures were used to compute theattenuation. But, the attenuation values varies drastically based upon thebuildings structure and maps. The packet reception is usually much lower forthe city scenario compare to highway scenario 30. Many proposal has been madein loss recovery model 25 in vehicular network. Sub layer also were proposed based onthe paper 24 to optimize the broadcasting for VANETs.
VANETs can be used toreduce congestion using rebroadcasting ofmessage. In 25 a proposal regarding wirelessbroadcast transmission using random network were done. Based on the proposal acombining packets were combine into one source code by linear network codingfor retransmission while the original packets is decode by the receivers. In26 it explained that the author has discovered that Network coding has abenefit in improving performance for a repetition based loss recovery in safetycommunications. Multi-hop and one-hoponly can be supported after the hidden terminal problem is eliminate and byusing implicit acknowledgement 20. Vehicles were move into the oppositedirection because of the node mobility on the control channel, and this causedby disjoint assigning set of time slot, thus transmission collision is reducedfor road side unit.
As thetopologies became more, higher the control for the congestion became more,harder because of the change of the network size became more frequent. Fourmain approached is adopted in order to reduce the effect of the 81518. Contentionwindow is considered as ineffective for broadcast message 4 however due todynamic variation it enchance the network performance. Inorder to adapt with the problem a formulae called as empirical formulae isproposed, where it functioning based on the received beacons during las fewseconds from neighbours 11. By increasing beacon ratemore accurate data can be gain about the neighbours, but at the cost of higherprobability. Number of nodes wereinfluenced by change in transmission power where it share a same bandwidthchannel in the fixed beacon frequency. In theliterature most of the proposal is about a transmission power mechanisms whichhas the ability to adapt with the node density. From17 it show that a proposal done by Artimy where the proposal is about a transmission power control scheme toestimate a density for a local traffic in each node then from there a suitabletransmission range will be determine, but the main objective is actually tomaintain the connectivity.
At 19 a proposal about a fair power adjustment weremade by Torrent-Moreno. The proposal propose a power management of VANET wherebased on the proposal a vehicle can adjust its transmission power and at thesame time keep the beacon load within. Becauseof this, a situation where the bandwidth always enables to be reserved is occurand usually for the driven messages, but the disadvantage is more overhead ishappen cause by the multi-hop is used. If itwere seen based on the congestion scenario, a transmission control mechanismscan work well, but as a side effect a scalability issue were occur caused bythe congestion 14 Inthis paper we can see the proposed technique can be considered as unique sinceit has the ability to reduce transmission power in order to reduce and get ridthe congestion and also the interferences. The proposal indicate that, duringforwarding beacons the channel will be reduced 22.III. CODINGNETWORK FOR PROTOCOL INTERFERENCE FREE Interference Free (NC-IF) protocol is aproposed protocol with objective to get rid of the interference due to hiddenterminals problems and inter street communications.
The proposal were archivedby fulfil the following objective which by reducing the vehicle transmissionrange. By doing this it can solve two types of purpose, which is: (a) theintra-street communications were free allowed by the interferences; and (b)reduces congestion (beacon load). By assuming the system is aware of thedigitals map a distance between nearby vehicle with the street can becalculated.
In the proposal a power control transmission module were used inorder to deal with the range of the adaptive transmission. In order to archivethe transmission layer range a multi-hop transmission beacon were used, as thetransmission range is reduced; a network coding forwarder must be preselectedas one of the forwarding nodes. The delay mayincrease substantially as the hop-counts increase; beacons is allowed forward for a quickest time aslong as the timer and delay control the module.
Figure 1.Show Inter-street interferenceA.Motivations From Figure 1 above, it seen that when ‘S’Node send a beacon, it’s received by the other nodes at the neighbourhood. Thisbeacon messages is important to be received by nodes 1,2,3,4,5,6 and 7 becauseit’s shared same road segment with node S. Thebeacon messages may be receive successfully send by F neither by nodes A,B,C,E and F, or aninteresting signal will be received.
Because of the various obstacles come fromthe buildings the beacon has no choice but come through it and resulting in aseveral attenuated signal even though the nodes in within the S transmissionrange. Since beacon S shared same bandwidth with the others nodes (A,B,C,E,F)it is not a very good phenomena even some of the node successfully in receivingthe beacon messages. Thus the transmission power for node ‘S’ need to bereduced and multi-hop beacon is send in order to ensure it reach the same roadsegment for the neighbouring node.B.Power Control of Dynamic Transmission It is required about 300m for thetransmission range layer (R) by the DSRC based active-safety application 21.Forwarding nodes is needed in order to forward beacon in multi-hop, and at thesame time it will allow for the vehicles to receive the beacons sending fromthe other vehicle (R vehicle) in apart distance. To take care the forwardingthere is a forwarding node.
After the power is reduced one of the forwarder isput within the transmission range. ‘T’ is denoted as the transmission rangewhere it should be at least 50 meters at most R. A distance between the nearbyroad segment with the vehicle is considered as D. Initial value of T can bedefined as:T= + D (1) Multiple of D is transmission range, T. Thelowest transmission range a node poses is the initial value of, T. Usually aproblem such as terminal problem is a lesser importance since the neighbouringconnectivity is more important in a case when the scenario is lower.
The transmission range still increase eventhere is a few packets of beacon getting drop because of the hidden terminaland inter street interference problem. The new transmission range can go up toT=R as it became T=T+D. ‘T’ will be computed by using equation in (1) if thesituation change for example is density. C.Selection of NC-Forwarders Inorder for every vehicle can send its beacon between the R, transmission range itmust be preselected so that the multi-hop forwarding can be used.
In forwarding node selection it is must be donewithout interfere the communications of inter-vehicle. The forwarding nodesknown as Network coding forwards or also known as NC-Forwarders. The distancebetween these forwarders must be at least 50m which is same with M. Selectionmust be made start from the extreme south west point in the road segment. Weconsider that the road segment is lies from left to right horizontally as inthe example where the nodes P in the left side get declared as a NC-Forwarders. After the beacon message is received there is another node which declares itself as aNC-Forwarder known as node Q where after receive a beacon message it lies inthe right side of P.When nodes receive a declaration from node Q it cannot declare itself in thearea of the neighbourhood P as NC-Forwarder. Whenthe process continue into the right side of Q the moving direction of allNC-Forwarders is moving at the same direction as P.
A new node will take overafter the NC-Forwarder leaves the road segment.D.Network Coding of forwarding Multi-hop beacon By using Multi-hop the power transmission ofthe vehicle were reduced and at the same tie the messages were also forwardingby Multi-hop. A transmission range willbe reduced as a result from overhead where every vehicle will broadcast thebeacons, thus a significant delay problem will occur for the multi-hop andfinally the beacon message cannot be lowered. By adopting theefficient forwarding mechanisms hop delay can be reduced as explained in Esection. As a result the contention delay will be lowered and as the number forthe packet transmission can be reduced the queuing delay also is.
Maximumbenefits of reducing transmission range and to overcome the issue can beachieve by exploiting the packet level of the network coding 22. Forwarding algorithm: Has a function toimprove the overall throughput where the packet level network coding wereapplied. To take appropriate coding decisions each of the nodes maintain acoding table along with the neighbours table. In neighbours table it is containof position, id, transmission power and speed of neighbours. Beacon receivedfrom a node and NodeID are include in each entry of the coding table.
The position of the senderwith the transmission power were used in orderto determine the forwarding region from receiving the beacon when the nodes istypes NC-Forwarder. If it is inside the forwarding region it will became one ofthe candidates which has a function to forward the beacon. Tochoose the node as a forwarder it must fulfil the condition where it must bethe farthest NC-Forwarder where it must in within the forwarding region andalso must from the sender among all the NC-ForwardersFigure 2.Show forwarding and network coding for multi-hop. Thebeacon only can be coded when the sender is not within the range between eachother, where this applied when there is two received beacons.
Here we let the beacon be terms as a partner beacon.A suitable partner will be search by the node in its coding table. In order to locate the neighbour entry a Node ID isused for every entry based on the table code. Update position were update usingneighbours dynamics such as position, speed and acceleration. For the neighbourto have an ability to serve as a partner beacon the update for the position isneeded. When the partner beacons is found a coded beacon will be formed betweennode XORs and the received beacon.
If not, the node ID with the sender ID willbe put away into the table coding and will be stored there until a partner forthe beacon is received. From Figure 2 it can beseen that the transmission range R of the application layer were in node S. As the transmissionrange is reduced the beacons is forwarded through X,Y and Z to the one end. Theleft side of node S is replicated in this process. The broadcasted beacon messagesfrom S were all received by the neighbours including node X and S. Beaconmessage might be received from the right for node X. Herenode X has a function to apply network coding into the packet then rebroadcastthe node. Besides that, the network will be rebroadcast when node X has extractthe beacons sent by S.
The applying network coding will only will getrebroadcast when node Z receives the packets for the network coded. Coded packetA XOR B were created after node Z performs the XOR operations, thus finallybroadcast it when it receiving a packets from A and B. When X and Y receivedthe network packet a it still can obtain thepackets from each other just by XOR-ring again with their own packet. Forwarderwill receive two packets of beacons as a result of opposing direction in orderto make a maximum benefits from the network coding. If forwarder not receiveany beacon packets or only receive a packets from one direction only then itwill start to starve.
Total delay will increase in this forwarding. It is impossible for the network to receive a packetfrom one direction while the others packets also follow from other direction.Forwarder will not wait for another packets in order to form a network codingpackets since it will forwards the packets immediately when it is in approach.
E.Timer and delay control NC-Forwardersbroadcast its network coding packets along with its beacon message. A scheduling mechanisms is required for such highnumber of message exchange. All of the idleperiod were keep in track by sensing the medium of the NC-Forwarders. When the beacon message is received for a newvehicle the NC-slots will update if not a new message for the vehicle will notexist.
When NC-Forwarders receive more than onebeacon message from opposite site a new network coding need to be applied thusa new packet will be scheduled so it can be broadcast. When the situation wherethe a new packet is not receive a new packet were receive will be broadcast directlywithout need to apply a network coding. F. Coding Gain Estimation Packetfor (1-p) is forwarded without using a network coding based in the proposedscheme. The number of vehicle between transmission range is given by n/h, wheren is defined total vehicle in the road segment (2) (h-1) (3) Ncand Nwc based on the equation above is defined as a number of transmission.Since P=3/4 gain given by Nwc/Nc became very high. IV.
EVALUATION OF PERFORMANCEA. Metrics of the performances 1) Packet Delivery Ratio: Can be defined as a number of vehicle thatcan receive a beacon into the total expected receivers. Dissemination is one ofthe important criterion in beacon transmission system where it is worth tocompare it with the packet delivery ratio CSMA/CA proposed in this paper. 2) Successfulchannel busy time: Average time period can be defined as a channel which isbusy receiving a beacons in the state of average period of time. A measurementwere done for each node where it is set to 1 sec for every measurement. Inorder to ensure the message reception is successful it is action take inmeasure of the channel utilization.3) AverageBeacon Forwarding Delay: Can be defined as a nodes within the applicationlayer (between nodes to another nodes) in a transmission range which also canbe known as average delay for beacon to be received.
4) Coding gain: Can be defined as a ratio of the transmitted networkpacket to the ratio of the network coding transmitted packets.Table1: Simulation of Parameters Data Rate 3Mbps Transmission Range 50m,100m,150m,200m ,250m,300m Model of channel Two Ray Ground Number of Streets 4 Road Length 1km Velocity 10m/s-20m/s Size packet 200Bytes Random noise 5dB-26dB Bacons numbers 10 Beacons/sec B. Simulation Setup Matlab were used to perform the simulation.The simulation were done to find out about the NC-IF protocol performance.Information (parameter) in order to run the simulation can be seen on the Table1. The simulation were run in the environment where a 1km lanes is separatedwith distance, 100m. In the simulation, when the receiver is not belong to thesegment where the beacon is forwarded an attenuation (a random one) will be putat the end of the receivers. For the simulation Ns-2 is choose.
C. Result and Discussion As can be seen on Figure 3 a result from thesimulation for varying node density for the packets delivery ratio werepresented. From the simulation done we can see that there is a decreasing in both of the protocol for thepacket delivery ratio as the node density is increase. It is shown that, theCSMA/CA is suffering from the congestion and collision where it can be saidthat it happen as one of the impact from the interference. When the NC-IF hasno interferences thus we know that the packets is free from the collisionproblem.
Based on the simulation we learn that with high densities a PDR inCSMA/CA has a very high degradation problem. From the observation, when there is a lot of collision occur it willresulting in many vehicles which choose a same beacon interferences-(cause ofsuch severity). Fromthe simulation we were presented in Figure 4 is a delay protocol (NC-IF)compared with the CSMA/CA. To remove the interference during the simulation amultiple hop were choose, but in case of CSMA/CA one hops were used to get ridthe interferences. Even the interferences were getting rid a number of vehiclesis not much changing, this because of the position where it much close to theold position since the delay is so low.
An identical channel can be seen from theresult of the simulation for both of the protocol as can be seen in Figure 5.We want to conclude that, most of the packets were received successfully eventhough extra packet were send. As result NC-IF is not changed even at the busytime. Coding gain is shown in Figure 6. From the graphsimulate it can be seen that a 1.
3 coding gain high where it is around 30%. Besidesthat, the gain is increased when there is increasing in node density. When nodedensity is increasing we learn that the power of the transmission also reducedadaptively while at the same time when the node density increase the number ofhops also increase. Thus, as the node density increased the gain ishigher.
Figure3: Ratio of Packet DeliveryFigure4: Delay of Beacon Transmission within Transmission Distance of ApplicationLayer (i.e 300m)Figure5: Channel successful in busy time (Timeof node spend in successfully receiving packets)Figure6: NC-IF coding gainV. FUTURE WORKS AND CONCLUSION The benefit of the network coding and the power control of theadaptive transmission power is evaluated in to reduce overhead beacon and inter-streetinterferences. By reducing the transmission range of the beacons the channelcontention also reduce. For transmission range specified in safety applicationsthe beacons can be delivered into the receivers placed with exploiting thelevel for the network coding packet.
The basic CSMA/CA were outperform in termsof packets ratio delivery in the proposed scheme and it same with the channelsuccessful in busy time as can be seen on the simulation conduct. The multi-hopdelay beacon is under control as shown from the simulation as an evident. It is confirmed that the nodes has the ability tosend a beacon into the significant number of receivers at the high densityscenario.