Research Article Dynamic Subchannel Assignment-Based...

Hindawi Publishing CorporationJournal of Computer Networks and CommunicationsVolume 2013 Article ID 962643 9 pageshttpdxdoiorg1011552013962643

Research ArticleDynamic Subchannel Assignment-Based Cross-Layer MACand Network Protocol for Multihop Ad Hoc Networks

Khanh Nguyen Quang1 Van Duc Nguyen1 and Hyunseung Choo2

1 School of Electronics and Telecommunications Hanoi University of Science and Technology Hanoi Vietnam2 Sungkyunkwan University School of Information amp Communication Engineering Republic of Korea

Correspondence should be addressed to Khanh Nguyen Quang khanhnq1vmscomvn

Received 19 April 2013 Accepted 23 July 2013

Academic Editor Youyun Xu

Copyright copy 2013 Khanh Nguyen Quang et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Thepaper presents a dynamic subchannel assignment algorithmbased on orthogonal frequency divisionmultiple access technologyoperating in the time division duplexing and a new cross-layer design based on a proposed routing protocol jointed with the MACprotocolTheproposed dynamic sub-channel assignment algorithmprovides a new interference avoidancemechanismwhich solvesseveral drawbacks of existing radio resource allocation techniques in wireless networks using OFDMATDD such as the hiddennode and exposed node problems mobility and cochannels interference in frequency (CCI) Besides in wireless networks whena route is established the radio resource allocation problems may decrease the end to end performance proportionally with thelength of each route The contention at MAC layer may cause the routing protocol at network layer to respond by finding newroutes and routing table updates The proposed routing protocol is jointed with the MAC protocol based on dynamic sub-channelassignment to ensure that the quality of service in multihop ad hoc networks is significantly improved

1 Introduction

The cochannel interference (CCI) is one of the major chal-lenges in wireless networks for multihop communicationsThis interference is introduced when two different radiostations simultaneously use the same frequency It is mainlycaused by the spectrum allocated for the system being reusedmultiple times in TDMA network CCI is one of the majorlimitations in cellular and personal communication serviceswireless telephone networks since it significantly decreasesthe carrier-to-interference ratio In addition it makes thediminished system capacity more frequent handoffs anddropped calls IEEE 80211 distributed coordination func-tion operation is based on conventional carrier mechanism(CSMACA) in order to prevent channel collisions CCIand provide the communication between multiple pairs ofindependent mobile nodes without access points or basestations such as mobile ad hoc networks [1 2]

Recently orthogonal frequency division multiplexing(OFDM) has been intensively investigated for wireless datatransmission in broadband cellular and ad hoc networks

The multiple access technique for these networks is OFDMA[3] The concept of this technique is to assign different usersto different sub-channels in order to avoid interference

Dynamic sub-channel assignment algorithm based onorthogonal frequency division multiple access (OFDMA)technology operating in time division duplexing has beenstudied in [4ndash7] However in most of the previous worksMAC layer is still transparent from physical layer

In our previous work [7] we proposed a DSA algorithmbased on orthogonal frequency division multiple access(OFDMA) technology operating in time division duplexing(TDD) This algorithm can maximize overall throughput ofnetworks as well as solve some drawbacks existing in cellularnetworks such as hidden node and exposed node problemsHowever in this work a concept of multihop networkswas not considered The performance of the proposed DSAtherefore was not presented in such networks In thispaper we improve the DSA algorithm and apply it to theconcept of multihop networks In addition we propose asimple routing protocol jointed with MAC model for mul-tihop ad hoc networks based on OFDMA technology using

2 Journal of Computer Networks and Communications

the proposed DSA algorithm The cost of a route in theproposed routing protocol refers to not only the distance butalso the throughput of the route By using the new concept ofcost the routing protocol aims to transmit data in a routewiththe balance of the distance and performance of the networkin terms of throughput

The paper is organized as follows In Section 2 we brieflyreview sub-channels allocation methods Section 3 describesthe proposed DSA algorithm In Section 4 the proposedrouting protocol is presented Simulation schemes numericalresults are discussed in Section 5 Finally conclusions aredrawn in Section 6

2 Review of Subchannels Allocation Methods

21 OFDM-FDMAFix Allocation Thefixed allocationmeth-od of OFDM-FDMA formultiuser communications was pro-posed [8] In such method different users will be fixedlyassigned to different sub-channels Therefore this methodhas not any anti-interference mechanism

22 OFDM-FDMA Random Allocation The OFDM-FDMArandom allocation method is based on the idle and busyof sub-channels allowing users to account different sub-channels [9] However it does not have any attention to thenetwork interference Once a sub-channel is selected a userstarts transmitting using the selected sub-channel Duringa transmission process if a sub-channel does not meet therequired QoS it will be released and assigned to a new userAlthough the method is simple and it offers an adaptivemechanism it does not provide CCI avoidance

3 Proposed DSA Algorithm

Co-channel interference (CCI) is crosstalk from more thanone different radio transmitter using the same frequency inwireless networks Reducing CCI is very important since itmakes the poor throughput performance To avoid CCI andcollisions we propose a novel channel allocation algorithmcalled DSA which supports simultaneous transmissions invehicle ad hoc network among nodes In this section theproblem of CCI in OFDMATDD in wireless networks isdiscussed in detail Then we present the proposed dynamicsub-channel assignment (DSA) algorithm

31 CCI inOFDMATDDSystem To illustrate the problemofCCI a simple scenario consisting of two base stations (BSs)and four mobile stations (MSs) is depicted in Figure 1 Let usassume an example of exchanging data among BSs and MSsas followsThemobile station MSRx

1 MSRx2 andMSRx

3receive

data frombase station BSTx1 while at the same time themobile

station BSTx2

transmits its data to the base station MSRx4 In

such scenario BSTx2

causes CCI to receive the data of MSRx1

MSRx2 and MSRx

3 the base station BSTx

1causes CCI to receive

the data of MSRx4 Note that CCI only exists in TDD mode

Interference signalDesired signal

MSRx2

BSTx2

MSRx1

MSRx3

BSTx1

MSRx4

Figure 1 Cochannel interference in OFDMATDD system

If a node can select appropriate sub-channels in availablesub-channel set before the data transmission CCI is mini-mized and thus increases the throughput of the network

32 Subchannel Selection Based on Busy Signals In the previ-ous example CCI was introduced and it badly affects thereceiving data of MSRx

1 MSRx2 and MSRx

3 To avoid this inter-

ference MSRx1 MSRx2 and MSRx

3have to broadcast a busy

signal when they receive data Before data transmission BSTx2

will first hear busy signals in all channels and then comparethe received signal power with a predetermined thresholdIf the power of busy signal in a channel is lower than thethreshold BSTx

2can select the channel for data transmission

33 Dynamic Subchannel Assignment Algorithm In this sec-tion we propose an algorithm for downlink and uplink trans-missions based on incorporation of the sub-channel selectionbased on busy signalsmechanism inOFDMATDDnetworkThe proposed algorithm is illustrated in Figure 3 The busysignal sent an in-band signaling before data transmissionData sub-channels are mutually orthogonal and used fortransmitting OFDM symbols

Figure 2 shows data transmitting and receiving in viewpoint from BS and MS respectively [4] The structure ofthe uplink frame is similar to that of the downlink frameEach subframe includes a busy signal channel (an OFDMsymbol) used for signaling busy signal MAC frame length ischosen corresponding to the time correlation of the channelInitially the sub-channel is selected by only the transmitterOn the other hand the adaptive period is adjusted by bothtransmitter and receiver We define two kinds of signal

(i) busy signal transmitted only in a channel by MSreceiver

(ii) data signal transmitted only by BS transmitter

Journal of Computer Networks and Communications 3

Frequency

Transmissiondirection of a BS

Busy tone OFDMAsymbol for downlink

Time

Frequency

Transmissiondirection of MS

Downlink

Time

12

3

4

1

23

4

Uplink

Received busy signal Transmitted data symbolTransmitted busy signal Received data symbol

Selected grid for downlink

th MAC-frame MAC-frame(i minus l) i-th

Figure 2 Structure of the MAC frame for DSA algorithm

In Figure 3 the proposed algorithm includes the twofollowing steps

(1) Link Initialization Link initialization occurs when119898th BSneeds to transmit data to 119896th MS in the network Firstly119898thBS listens to all busy signals and compares each of these busysignals with a given threshold to obtain a set of available sub-channel for data transmission called set A A sub-channelsis available if the power of the received busy signal is belowthe threshold The 119898th BS will start transmiting its data toreceiver using a set of available channel at the (119894 minus 1)th MACframe We propose a mathematical model (1) where 119886119896119898

119897119894minus1

denotes the sub-channel assignment for 119897th sub-channel atthe (119894 minus 1)th MAC frame of the link between119898th BS and 119896thMS If the sub-channel is assigned to the link between119898th BSand 119896th MS then 119886119896119898

119897119894minus1= 1 otherwise 119886119896119898

119897119894minus1= 0 The outcome

of this channel assignment is obtained by comparing the busysignal with the threshold as follows

119886119896119898

119897119894minus1=

1 if 10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th

0 otherwise(1)

119868th is a threshold being a measure for the interference thatthis transmission would effect to other coexisting transmis-sions Set A is all sub-channels having channel assignment by(1)

(2) Dynamic Subchannel Assignment At the (119894 minus 1)th MACframe 119896th MS estimates the SINR on each sub-channel of setA Based on the given QoS requirement for the transmission119896th MS will decide to maintain or release the respective sub-channel of set A 119896th MS will only broadcast the busy signal

on the remained sub-channels If the sub-channel is specifiedthen 119887119896119898

119897119894minus1is assigned 1 otherwise 119887119896119898

119897119894minus1= 0

We propose a mathematical model (2) where 119887119896119898119897119894minus1

denotes the reservation of 119897th sub-channel for the 119894th MACframe 120574119896

119897119894minus1 120574req are SINR estimated by 119896th MS and required

QoS

119887119896119898

119897119894minus1=

1 if (10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th) ( 120574

119896

119897119894minus1ge 120574req)

0

(2)

Since the 119894th MAC frame the condition for the sub-channel assignment on the desired or new link between 119898thBS v 119896th MS for subsequent MAC frames is given as follows

119886119896119898

119897119894=

1 if (119886119896119898119897119894minus1

10038161003816100381610038161003816119861119898

119897119894

10038161003816100381610038161003816le 119868th) or 119887

119896119898

119897119894minus1= 1

0 otherwise(3)

where 119861119898119897119894is the busy signal received at the119898th BS on the 119897th

sub-channel at the 119894th MAC frame and

119886119896119898

119897119894minus1=

1 if 119886119896119898119897119894minus1= 0

0 otherwise(4)

Since the 119894th MAC frame set A includes all maintainedsub-channels (set B of (119894 minus 1)th MAC frame) and newrespective sub-channels if the power of their received busysignal is below the threshold

4 Proposed Routing Protocol Description

In multihop ad hoc networks a node transmits its data toa destination node via an optimal route In order to find


Set A determination based on the received busy signal

Frame transmission on all of set A

Set B determination based on SINR estimation

Broadcast busy signal on in set B

Set A detemination based on received busy signaland set B for the next frame

Data transmissionis continued

End

Start

Y

N

Link initialization

Synamic subchannelassignement

Figure 3 Flowchart of the proposed DSA algorithm

the optimal route the routing is implemented In this sectionwe propose a new routing protocolwhich can be easily jointedto the MAC protocol based on the DSA algorithm Thecorporation between the routing and the MAC protocol notonly ensures the mobility and multihop but also gains theperformance in terms of throughput in the multihop ad hocnetworks

The routing protocols working in wireless networksdepend on the radius of coverage of nodes The connectionamong all nodes changes fastly over time The principal costof the proposed routing protocol is the combination of thedistance among nodes and the throughput of a route Thefinding of the shortest route in the proposed protocol is basedon the shortest route finding algorithms and the radius ofcoverage of nodes in the network To ensure the mobility andthe performance in terms of throughput of the network theMAC provides the number of selected channels of a route tothe routing protocol This value is compared with a proposedthreshold called Channel threshold in order to update theoptimal route for the transmission

Before describing the flowchart of this protocol we definethe following

(i) 119877119894is the radius of coverage of 119895th node in the network

(ii) The network is supposed to be a graphwith nodes andedges of the network

(iii) The connection among nodes is described in a con-nection matrix called connection matrix

We propose a mathematical model which is based onmodel (5) for the connection matrix

119872119894119895=

distance (119894 119895) if distance (119894 119895) le min (119877119894 119877119895)

0 otherwise(5)

where119872119894119895and distance (119894 119895) are the connection state and the

distance between node 119894 and node 119895 respectively


Build the connection matrix

End

Start

Data tranmission based DSA at MAC

N chgtChannel threshold

N route = 0

Select the route for thetransmitting data

Y

N

N

Y

route loop = 0

No route isselected for

thetransmitting

data

Y N

Select theshortest

route for thetransmitting

data

Step 1

Step 4

Step 3

Step 2

route loop = 0

Increase route loop by 1

Find the shortest route andof available routes (Nroute)

by using matrix andthe algorithm

Calculate the numberof selected (Nch) of

the shortest route basedon the DSA algorithm

Remove the route from routeavailable paths set of algorithm

Figure 4 Flowchart of the proposed routing protocol

In Figure 4 the proposed routing protocol finds the routeusing the following three steps

Step 1 The input of this step is the radius of coverageof all nodes and the distances between all node pairs inthe network The connection matrix is built based on theproposed mathematical model (5) The value of init loop isinitially set 0

Step 2 In this step the shortest route and the number ofavailable routes (iNP) are obtained by using the Dijkstraalgorithm and shortest route algorithm see [10]The inputs ofthe step are the positions of the destination and source nodeand the connection matrix

Step 3 This step aims to find the optimal route for the trans-mitting data Firstly iNP is checked If iNP is nonzero thereis at least one available route between the source node and thedestination nodeThe number of selected sub-channels (iSC)

Table 1 OFDM system parameters

Parameters ValuesBandwidth (119861) 20MHzSampling interval (119905

119886= 1119861) 50 ns

FFT length (119873FFT) 256OFDM symbol duration (119879

119878) 128120583s

Guard interval (119879119866) 2120583s

Frequency (119891119888) 19 GHz

Modulation scheme 16-QAMSINRmin (120574req) 16 dBChannel threshold 42

of the shortest route is derived by using the proposed DSAalgorithm If iSC is larger than the given Channel thresholditmeans that the route ensures the requirement of throughputof the system Consequently the shortest route is selected asthe optimal route for the transmission data Otherwise theroute does not satisfy the requirement of the system Wetherefore have to find another route The init loop is set to1 which points that there is at least one available route notsatisfying the requirement of throughput of the networkThestep is directed to the beginning of Step 2 and the shortestroute is excluded in the Dijkstra algorithm At the end ofStep 1 if iNP is zero these two cases can happen the first caseis that there is no available route between the source node andthe destination node (init loop is 0) hence the transmissionis stopped and it has to delay for some time to transmit thedata In the other case there is at least one route availableHowever all of the nodes do not satisfy the requirement ofthroughput of the network In this case the shortest node isselected for the transmission data

Step 4 In this step the data transmission based on the DSAalgorithm at MAC layer will occur

5 Simulation Model

In the simulation scheme OFDM parameters are selected inTable 1 16-QAMmodulation is selected for all sub-channelsWe will present the performance in terms of throughput ofthe networks of our proposed method in three scenariosIn the first scenario the performance of the proposed DSAis demonstrated in single-hop ad hoc networks withoutthe proposed routing protocol Then the proposed DSAalgorithm and the proposed routing protocol are appliedin the scenario of multihop ad hoc networks However inthis case the routing is implemented without selecting theoptimal route in terms of throughput of the route Finally theproposed routing protocol that cooperated with the proposedMAC protocol based on DSA algorithm is fully carried out inmultihop ad hoc networks

51 Throughput of Single Hop Ad Hoc Networks

511 Analysis Model We consider a model including twotransmitter-receiver pairs depicted in Figure 5 where Txand Rx are the transmission mode and the receive moderespectively TDD mode is used In this model the distance


O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2

Figure 5 A simple circumstance for single-hop ad hoc network

minus400 minus300 minus200 minus100 0 100 200 300 4000

50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels

= minus70dBm= minus80dBm= minus90dBm

= minus60dBm= minus40dBm

120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth

Figure 6 The number of selected sub-channels with differentthresholds and conventional OFDM-FDMA

between two nodes in each pair is constant and these pairsmove in the opposite direction

512 Numerical Results In this evaluation the throughputin terms of the number of selected sub-channels is consid-ered for two methods OFDM-FDMA fixed allocation andproposed DAS algorithm It can be seen from Figure 6 thatthe throughput of network using the proposed DSA dependson the value of different threshold 119868th as well as the distancebetween pairs in the network When the distance betweenpairs is high the proposed method demonstrates a high per-formance Since in OFDM-FDMA fixed allocation methodsub-channels are fixedly allocated to users its throughput isconstant and much less than the one of the proposed DSAmethod On the other hand the proposed method offers CCIavoidance mechanism based on busy signal The selection ofsub-channel consider to given threshold thus the throughput

MS2

MS1

MS3

MS4

MS5

MS6

Connection path

Figure 7 Initial state of networks used in simulation in the case ofmultihop ad hoc networks

depends on the selection of threshold From the results inFigure 6 the suitable threshold for the proposed method isminus60 dBm

52 Throughput of Multihop Ad Hoc Networks Based on Onlythe Proposed DSA Algorithm and MAC Structure

521 Analysis Model In this scenario the performance ofthe proposed DSA algorithm and the MAC structure isevaluated in a multihop ad hoc network considering theeffect of the length of selected routes and 119868th Therefore therouting protocol used in this model is not the proposedrouting protocol presented in Section 4 It is just the principlerouting which considers only the distance of a route asthe cost of this route The shortest route being selectedas the optimal route for transmitting data is obtained byusing the Dijkstra algorithm The input of the Dijkstraalgorithm is the connection matrix of the network Beforeeach transmission section the connection matrix is built asproposed in Section 4 Then the shortest route output fromtheDijkstra algorithm is selectedThedatawill be transmittedthrough the selected route We consider a vehicles networkVANET that includes 6 mobile stations (MSs) indexed from 1to 6 with the initial state depicted in Figure 7 MS

1 MS5 and

MS6are running step by step while the other mobile stations

are fixed The running step length is set to 5 meters MS5and

MS6run in the same direction being opposite to the running

direction ofMS1While themobile stations are runningMS

1

is transmitting its data to MS5 After each step to throughput

of whole network is obtained Figure 8 gives an example of theconnection state of the network It can be seen from Figure 8that the shortest route (MS

1rarr MS

2rarr MS

4rarr MS

5) is

selected for the transmitting data

522 Numerical Results Figure 9 plots the length of routefrom MS

1to MS

5with respect to running steps Since the

routing protocol is not based on 119868th the length of routes forthe three cases of 119868th is the same We truncate the processinto three groups A B and C In each group we can see that


MS2

MS1

MS3

MS4

MS5

MS6

Connection routeRoute from MS1 to MS5 found by routing protoccol

Figure 8 An example of the route fromMS1to MS

5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)

Figure 9 Length of route fromMS1to MS

5

lengths of routes seem to be the same When the length of aroute is high it means that the number of intermediate nodesis also high Therefore the data is transmitted through manysections In some sections some sub-channels do not meetthe QoS Hence the channel is not fullfilled thus making thedecrease of throughput This conclusion is backedup fromgroup A and B where the lengths of routes are high andthroughput is small in Figure 10 On the other hand when thelength of a route is small the number of intermediate nodesis also small Data can be directly transmitted from source todestination or through few intermediate nodes In such casethe effect of interference exposed node and hidden nodeis reduced and the channel is fullfilled Consequently thethroughput of the network is significantly increased It canbe seen from group C that the length of the route at eachstep is small and the throughputs would therefore be highThroughput also depends on 119868th which decides a sub-channelbe selected for transmission data or not When 119868th is smallthe probability that a sub-channel is selected is high Hencethroughput is also high The effect of 119868th is clear when thelength of a route is high (in A and B groups) since it affectsthe selection of sub-channel in many intermediate sectionsOn the other hand when mobile stations are close (in groupC) the role of 119868th is not so important Therefore throughputs

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth

Figure 10Throughput of the network whenMS1sends data toMS

5

seem to be similar for the three cases of 119868th of minus20 minus40and minus60 dBm It is clear that the throughput of the networkdepends on the distance between the source and destinationnodes as well as 119868th

53 Throughput of Multihop Ad Hoc Networks Based onthe Proposed Routing Protocol

531 Analysis Model The performance of the proposedrouting protocol is evaluated in this sectionWe implementedthe routing protocol jointed with the MAC layer on thenetwork as the one presented in Section 52 However weconsider the transmission data fromMS

1toMS

6The channel

allocation for the transmission data between nodes in thenetwork is based on the proposed DSA algorithm Thethreshold Channel threshold is experimentally set to 42 Amathematical method for deriving the optimal thresholdwill be proposed in our future work 120574min and 119868th are setto minus80 dBW and 16 dB respectively An example of a routefound by using the proposed routing protocol is drawn inFigure 11 In this state the shortest route was found bythe Dijkstra algorithm The route however does not meetthe requirement of the number of selected sub-channelsHence it was not selected for the transmitting data On theother hand our proposed protocol derived another routewhich has a longer length than the shortest route Since thenumber of selected sub-channels of this route is larger thanChannel threshold it was selected as the optimal route

532 Numerical Results The performance of the proposedrouting protocol is depicted in Figures 12 and 13 where onlyconventional routing protocol is the principle routing basedon the Dijkstra algorithm It can be seen from these resultsthat the throughput of the network depends on the distancebetween the source node and the destination node as in theconclusion in Section 52 In group A where the destinationand the source node are far the number of intermediate nodesis high Hence the transmission significantly suffered from


MS2

MS1

MS4

MS5

MS6

Connection route

MS3

Route from MS1 to MS6 found byrouting protocol

Route from MS1 to MS6 found byconventional routing protocol

Figure 11 An example of a route from MS1to MS

6found by using

the proposed routing protocol

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step

Proposed routingConventional routing

CBA

= minus80 dBm 120574min = 16 dB

Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr

Figure 12 Length of the route fromMS1toMS

6using the proposed

routing protocol and the conventional routing protocol

the CCI as well as the hidden and exposed node problemsConsequently the number of selected sub-channels of allavailable routes is smaller thanChannel thresholdThereforethe proposed routing selected the shortest route as theoptimal route to transmit the data and there is no differenceof throughput the proposed routing protocol and the conven-tional oneOn the other hand in groupC since the source andthe destination are very close they transmit its data directlyor via a few of intermediate node The effect of the CCIand the hidden and exposed node problems is considerablyfell thus making the increase of the number of selected sub-channels The number of selected sub-channels for all routesis larger than Channel threshold Therefore as in group Athe proposed routing protocol selected the shortest routeas the optimal route In this group the proposed routingand conventional routing protocols demonstrate the sameperformance In group B some routes have the number ofselected sub-channel being larger than threshold while oneof the other routes is smaller than threshold In some case

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB

= minus80dBm 120574min = 16 dBIthr

Figure 13 Throughput of the network using the proposed routingprotocol and the conventional routing protocol

the shortest route does not meet the requirement of theselected sub-channels hence it is not selected as the optimalroute Our proposed find another route satisfy the require-ment with longer length of route Therefore in this groupthe proposed method outperforms the conventional routingprotocol in terms of throughput of the network

6 Conclusions

In this paper we present a dynamic sub-channel assignmentalgorithm based on OFDM and a new routing protocol Aconcept of multihop ad hoc networks based on the DSAalgorithm is simulated with the proposed routing protocolThe proposed algorithm has an interference avoidancemech-anism so the throughput of the network can be maximizedThe problems of cellular networks such as hidden nodeand exposed node are solved A routing protocol which isjointed to the MAC protocol is proposed The proposedrouting protocol improves the throughput of multihop adhoc networks as well as ensures the mobility multihop ofad hoc and multihop networks In the future we will studythe mathematical model for Channel threshold parameternetwork layer and transport layer integration to improve andoptimize QoS of multihop ad hoc networks

Acknowledgments

This research is funded by the Vietnam National Founda-tion or Science and Technology Development (NAFOSTED)under the grant number 10202-201115 and the VietnamMinistry of Science and Technology (MOST) under the grantnumber KC010511-15

References

[1] G Kulkarni and M Srivastava ldquoSubcarrier and bit allocationstrategies for OFDMA based wireless ad hoc networksrdquo inProceedings of the IEEE Global Telecommunications Conference(GLOBECOM rsquo02) pp 92ndash96 November 2002


[2] V Venkataraman and J J Shynk ldquoAdaptive algorithms forOFDMA wireless ad hoc networks with multiple antennasrdquoin Proceedings of the Conference Record of the 83th AsilomarConference on Signals Systems and Computers pp 110ndash114November 2004

[3] S W Kim and B-S Kim ldquoOFDMA-based reliable multicastMAC protocol for wireless ad-hoc networksrdquo ETRI Journal vol31 no 1 pp 83ndash85 2009

[4] V-D Nguyen H Haas K Kyamakya et al ldquoDecentralizeddynamic sub-carrier assignment for OFDMA-based adhoc andcellular networksrdquo IEICE Transactions on Communications volE92-B no 12 pp 3753ndash3764 2009

[5] J M Torrance and L Hanzo ldquoOptimisation of switching levelsfor adaptive modulation in slow Rayleigh fadingrdquo ElectronicsLetters vol 32 no 13 pp 1167ndash1169 1996

[6] S Skiena Implementing Discrete Mathematics Combinatoricsand Graph Theory With Mathematica Addison-Wesley Read-ing Mass USA 1990

[7] VDNguyen P EOmiyi andHHaas ldquoDecentralised dynamicchannel assignment for cellular OFDMTDD networksrdquo inProceedings of the International OFDM Workshop (InOWorsquo05)vol 3 pp 255ndash2259 August 2005


[9] M Stemick and H Rohling ldquoOFDM-FDMA scheme for theuplink of a mobile communication systemrdquo Wireless PersonalCommunications vol 40 no 2 pp 157ndash170 2007

[10] C Y Wong R S Cheng K B Letaief and R D MurchldquoMultiuser OFDM with adaptive subcarrier bit and powerallocationrdquo IEEE Journal on Selected Areas in Communicationsvol 17 no 10 pp 1747ndash1758 1999

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the proposed DSA algorithm The cost of a route in theproposed routing protocol refers to not only the distance butalso the throughput of the route By using the new concept ofcost the routing protocol aims to transmit data in a routewiththe balance of the distance and performance of the networkin terms of throughput

The paper is organized as follows In Section 2 we brieflyreview sub-channels allocation methods Section 3 describesthe proposed DSA algorithm In Section 4 the proposedrouting protocol is presented Simulation schemes numericalresults are discussed in Section 5 Finally conclusions aredrawn in Section 6

2 Review of Subchannels Allocation Methods

21 OFDM-FDMAFix Allocation Thefixed allocationmeth-od of OFDM-FDMA formultiuser communications was pro-posed [8] In such method different users will be fixedlyassigned to different sub-channels Therefore this methodhas not any anti-interference mechanism

22 OFDM-FDMA Random Allocation The OFDM-FDMArandom allocation method is based on the idle and busyof sub-channels allowing users to account different sub-channels [9] However it does not have any attention to thenetwork interference Once a sub-channel is selected a userstarts transmitting using the selected sub-channel Duringa transmission process if a sub-channel does not meet therequired QoS it will be released and assigned to a new userAlthough the method is simple and it offers an adaptivemechanism it does not provide CCI avoidance

3 Proposed DSA Algorithm

Co-channel interference (CCI) is crosstalk from more thanone different radio transmitter using the same frequency inwireless networks Reducing CCI is very important since itmakes the poor throughput performance To avoid CCI andcollisions we propose a novel channel allocation algorithmcalled DSA which supports simultaneous transmissions invehicle ad hoc network among nodes In this section theproblem of CCI in OFDMATDD in wireless networks isdiscussed in detail Then we present the proposed dynamicsub-channel assignment (DSA) algorithm

31 CCI inOFDMATDDSystem To illustrate the problemofCCI a simple scenario consisting of two base stations (BSs)and four mobile stations (MSs) is depicted in Figure 1 Let usassume an example of exchanging data among BSs and MSsas followsThemobile station MSRx

1 MSRx2 andMSRx

3receive

data frombase station BSTx1 while at the same time themobile

station BSTx2

transmits its data to the base station MSRx4 In

such scenario BSTx2

causes CCI to receive the data of MSRx1

MSRx2 and MSRx

3 the base station BSTx

1causes CCI to receive

the data of MSRx4 Note that CCI only exists in TDD mode

Interference signalDesired signal

MSRx2

BSTx2

MSRx1

MSRx3

BSTx1

MSRx4

Figure 1 Cochannel interference in OFDMATDD system

If a node can select appropriate sub-channels in availablesub-channel set before the data transmission CCI is mini-mized and thus increases the throughput of the network

32 Subchannel Selection Based on Busy Signals In the previ-ous example CCI was introduced and it badly affects thereceiving data of MSRx

1 MSRx2 and MSRx

3 To avoid this inter-

ference MSRx1 MSRx2 and MSRx

3have to broadcast a busy

signal when they receive data Before data transmission BSTx2

will first hear busy signals in all channels and then comparethe received signal power with a predetermined thresholdIf the power of busy signal in a channel is lower than thethreshold BSTx

2can select the channel for data transmission

33 Dynamic Subchannel Assignment Algorithm In this sec-tion we propose an algorithm for downlink and uplink trans-missions based on incorporation of the sub-channel selectionbased on busy signalsmechanism inOFDMATDDnetworkThe proposed algorithm is illustrated in Figure 3 The busysignal sent an in-band signaling before data transmissionData sub-channels are mutually orthogonal and used fortransmitting OFDM symbols

Figure 2 shows data transmitting and receiving in viewpoint from BS and MS respectively [4] The structure ofthe uplink frame is similar to that of the downlink frameEach subframe includes a busy signal channel (an OFDMsymbol) used for signaling busy signal MAC frame length ischosen corresponding to the time correlation of the channelInitially the sub-channel is selected by only the transmitterOn the other hand the adaptive period is adjusted by bothtransmitter and receiver We define two kinds of signal

(i) busy signal transmitted only in a channel by MSreceiver

(ii) data signal transmitted only by BS transmitter


Frequency



Time

Frequency


Downlink

Time

12

3

4

1

23

4

Uplink







119897119894minus1


119897119894minus1= 1 otherwise 119886119896119898



119886119896119898

119897119894minus1=

1 if 10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th

0 otherwise(1)





119897119894minus1= 0




QoS

119887119896119898

119897119894minus1=

1 if (10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th) ( 120574

119896

119897119894minus1ge 120574req)

0

(2)


119886119896119898

119897119894=

1 if (119886119896119898119897119894minus1

10038161003816100381610038161003816119861119898

119897119894

10038161003816100381610038161003816le 119868th) or 119887

119896119898

119897119894minus1= 1

0 otherwise(3)



119886119896119898

119897119894minus1=

1 if 119886119896119898119897119894minus1= 0

0 otherwise(4)











End

Start

Y

N

Link initialization










119872119894119895=


0 otherwise(5)





End

Start



N route = 0


Y

N

N

Y

route loop = 0


thetransmitting

data

Y N

Select theshortest


data

Step 1

Step 4

Step 3

Step 2

route loop = 0














119886= 1119861) 50 ns


119878) 128120583s

Guard interval (119879119866) 2120583s

Frequency (119891119888) 19 GHz




5 Simulation Model





O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2



50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels



120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth




MS2

MS1

MS3

MS4

MS5

MS6

Connection path





1 MS5 and





1



1rarr MS

2rarr MS

4rarr MS

5) is



1to MS




MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Frequency



Time

Frequency


Downlink

Time

12

3

4

1

23

4

Uplink







119897119894minus1


119897119894minus1= 1 otherwise 119886119896119898



119886119896119898

119897119894minus1=

1 if 10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th

0 otherwise(1)





119897119894minus1= 0




QoS

119887119896119898

119897119894minus1=

1 if (10038161003816100381610038161003816119861119898

119897119894minus1

10038161003816100381610038161003816le 119868th) ( 120574

119896

119897119894minus1ge 120574req)

0

(2)


119886119896119898

119897119894=

1 if (119886119896119898119897119894minus1

10038161003816100381610038161003816119861119898

119897119894

10038161003816100381610038161003816le 119868th) or 119887

119896119898

119897119894minus1= 1

0 otherwise(3)



119886119896119898

119897119894minus1=

1 if 119886119896119898119897119894minus1= 0

0 otherwise(4)











End

Start

Y

N

Link initialization










119872119894119895=


0 otherwise(5)





End

Start



N route = 0


Y

N

N

Y

route loop = 0


thetransmitting

data

Y N

Select theshortest


data

Step 1

Step 4

Step 3

Step 2

route loop = 0














119886= 1119861) 50 ns


119878) 128120583s

Guard interval (119879119866) 2120583s

Frequency (119891119888) 19 GHz




5 Simulation Model





O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2



50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels



120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth




MS2

MS1

MS3

MS4

MS5

MS6

Connection path





1 MS5 and





1



1rarr MS

2rarr MS

4rarr MS

5) is



1to MS




MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation
















End

Start

Y

N

Link initialization










119872119894119895=


0 otherwise(5)





End

Start



N route = 0


Y

N

N

Y

route loop = 0


thetransmitting

data

Y N

Select theshortest


data

Step 1

Step 4

Step 3

Step 2

route loop = 0














119886= 1119861) 50 ns


119878) 128120583s

Guard interval (119879119866) 2120583s

Frequency (119891119888) 19 GHz




5 Simulation Model





O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2



50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels



120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth




MS2

MS1

MS3

MS4

MS5

MS6

Connection path





1 MS5 and





1



1rarr MS

2rarr MS

4rarr MS

5) is



1to MS




MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











End

Start



N route = 0


Y

N

N

Y

route loop = 0


thetransmitting

data

Y N

Select theshortest


data

Step 1

Step 4

Step 3

Step 2

route loop = 0














119886= 1119861) 50 ns


119878) 128120583s

Guard interval (119879119866) 2120583s

Frequency (119891119888) 19 GHz




5 Simulation Model





O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2



50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels



120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth




MS2

MS1

MS3

MS4

MS5

MS6

Connection path





1 MS5 and





1



1rarr MS

2rarr MS

4rarr MS

5) is



1to MS




MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










O

X

Y

MSRx1

MSTx2BSRx

1

BSRx2



50

100

150

200

250

300

Distance (m)

Sele

cted

sub

chan

nels



120574min = 16 dB

OFDM-FDMAIthIthIth

IthIth




MS2

MS1

MS3

MS4

MS5

MS6

Connection path





1 MS5 and





1



1rarr MS

2rarr MS

4rarr MS

5) is



1to MS




MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










MS2

MS1

MS3

MS4

MS5

MS6



5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1620406080

100120140160180200

Step

BA C

Leng

th o

f rou

te fr

om M

S 1to

MS 5

(m)


5


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

255075

100125150175200225250

BA C

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)

120574min = 16 dB


IthIthIth


5




1toMS

6The channel




MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










MS2

MS1

MS4

MS5

MS6

Connection route

MS3




6found by using


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20110120130140150160170180190200

Step


CBA


Leng

th o

f rou

te fr

om M

S 1to

MS 6

(m) Ithr


6using the proposed



0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 9510035404550556065707580

Step

Thro

ughp

ut (b

itsO

FDM

sym

bol)


A CB




6 Conclusions


Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Research Article Dynamic Subchannel Assignment-Based...

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