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J Med Syst (2015) 39:192 DOI 10.1007/s10916-015-0336-x
MOBILE SYSTEMS
Design of QoS-Aware Multi-Level MAC-Layer for WirelessBody Area Network
Long Hu1 ·Yin Zhang2 ·Dakui Feng3 ·Mohammad Mehedi Hassan4 ·Abdulhameed Alelaiwi4 ·Atif Alamri4
Received: 3 November 2014 / Accepted: 7 September 2015© Springer Science+Business Media New York 2015
Abstract With the advances in wearable computing andvarious wireless technologies, there is an increasing trendto outsource body signals from wireless body area network(WBAN) to outside world including cyber space, healthcarebig data clouds, etc. Since the environmental and physio-logical data collected by multimodal sensors have differentimportance, the provisioning of quality of service (QoS) forthe sensory data in WBAN is a critical issue. This paper
This article is part of the Topical Collection on Mobile Systems
� Dakui Fengfeng [email protected]
Long [email protected]
Mohammad Mehedi [email protected]
Abdulhameed [email protected]
Atif [email protected]
1 School of Computer Science and Technology, HuazhongUniversity of Science and Technology, Wuhan, China
2 School of Information and Safety Engineering, ZhongnanUniversity of Economics and Law, Wuhan, China
3 School of Naval Architecture and Ocean Engineering,Huazhong University of Science and Technology, Wuhan,China
4 Chair of Pervasive and Mobile Computing, Collegeof Computer and Information Sciences, King Saud University,P.O. Box 51178, Riyadh 11543, Saudi Arabia
proposes multiple level-based QoS design at WBAN mediaaccess control layer in terms of user level, data level andtime level. In the proposed QoS provisioning scheme, dif-ferent users have different priorities, various sensory datacollected by different sensor nodes have different impor-tance, while data priority for the same sensor node variesover time. The experimental results show that the proposedmulti-level based QoS provisioning solution in WBANyields better performance for meeting QoS requirements ofpersonalized healthcare applications while achieving energysaving.
Keywords Healthcare · Body area network · QoS
Introduction
In recent years, provisioning of human-centric servicesthrough WBAN is continuously attracting extensive atten-tion from both academia and industry. In WBAN, the sen-sors worn on human body are used as the end devices, asshown in Fig. 1. Typically, the body sensors do not directlycommunicate with access points (APs), instead, a personalserver (PS) is used as the bridge between body sensors andAPs [1]. PS can be a smartphone. In addition to routing bodysignal and sensor data, there are other functions supportedby PS, such as
1. data fusion for reducing the size of body signal;2. acting as the ZigBee network coordinator for the body
sensors.
Differing from the characteristic of QoS provisioningin wireless sensor network (WSN), WBAN has stricterrequirements for specific QoS, including time constraintsand reliability [1]. In addition, QoS is required to be
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Fig. 1 The illustration of a typical WBAN architecture during patient care
customized for different WBAN application scenarios. Forexample, in a typical scenario at hospital where sensory datafrom different patients are transmitted over limited band-width, the transmission priority should be differentiated toprovide situation-aware healthcare services. Motivated bythe practical situation at hospital, this paper considers thefollowing three levels of priorities for QoS design:
1. priority of user (PoU), indicates that different usershave different priorities. For example, the sensory dataof seriously ill patients should have higher priority forfaster delivery than that of the patients with chronicdisease;
2. priority of data (PoD), means that heterogeneous sen-sory data collected from various sensor nodes (belongsto one user) should have different priorities. For exam-ple, electrocardiogram (ECG) data should be sent priorto temperature data;
3. priority over time (PoT), represents the priority of sen-sory data collected by of the same sensor node may varyover time. For example, the blood sugar data are usuallygiven lower priority; however, if the blood sugar is toohigh or too low, high priority should be given.
Existing work of MAC layer design for QoS provisioningin WBAN are either based on IEEE 802.15.4 non-beaconenabled mode or beacon enabled mode. For example,NDNC-BAN [2] aims to provide QoS by adaptive band-width scheduling based on the non-beacon mode in bodysensor network. Most of the proposed schemes are basedon beacon enabled mode. In [3], the superframe structure inbeacon enabled mode is fine tuned to implement the QoS
framework for WBAN with a star topology. In [4], Rah-man et al. design ATLAS to dynamically adjust contentionaccess period (CAP), contention free period (CFP), andinactive period (IP) in superframe for QoS provisioning interms of energy and delay. In [6], a collect-and-send schemenamed CoSenS is proposed to overcame the weakness ofCSMA/CA (Carrier Sense Multiple Access with CollisionAvoidance) mechanism. However, the above mechanismsdid not consider the QoS provisioning of sensory data deliv-ery at multiple levels in WBAN. In addition, most of theproposals are implemented in a star topology based WBAN.
This paper proposes a level-based QoS framework basedon the IEEE 802.15.4 beacon-enabled mode in WBANwith a tree topology. Compared to the existing work, thecontributions of this paper are described as below:
– QoS mechanism implemented in the tree topology ismore applicable for a large-scale network than the startopology.
– The level-based QoS framework provides guaranteedservices in three levels in terms of PoU, PoD andPoT, which is more flexible than a single level-basedproposal.
– In a tree structured network, the router node betweenterminal node and the coordinator adjusts dynamicallyaccording to the instant priority of terminal sensornodes, which allocates the limited bandwidth for deliv-ering sensory data among different patients who share asingle coordinator in a more balanced fashion.
The simulation results verify the effectiveness of themulti-level QoS provisioning in WBAN:
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1. the implementation of PoU guarantees the user withhigher priority access the resource of guaranteed timeslot (GTS) first;
2. when employing PoD, the dispatcher queue delay is 50% lower than the case without priority;
3. the use of PoT yields 29 % lower end-to-end delay thatwithout priority.
IEEE 802.15.4 MAC Protocol and tree topology
IEEE 802.15.4 Beacon-enabled mode
IEEE802.15.4 provides two operating modes: beacon modeand non-beacon mode. In the non-beacon mode, unslottedCSMA/CA mechanism is used for communication, which issimpler than slotted CSMA/CA in the beacon mode, with allnodes access to the channel in a competitive mode. The bea-con mode is more applicable to real-time data transmission,periodic data transmission, and the realization of QoS[5]in WBAN. This Paper mainly researches the network com-munication under the beacon mode. There is a significantconcept in the beacon mode: superframe, which is a periodictime structure and divided into active period and optionallyinactive period. Every coordinator has its own superframe,with the superframe structure shown in Fig. 2. The coordi-nator periodically transmits the beacon frame and the nodesimultaneously runs via the beacon frame. The time inter-val between two adjacent beacon frames is called beaconinterval (BI). During the active period, the node opens thereceiver to receive data or prepare to receive data. During theinactive period, the node sleeps to save energy. The durationof the superframe is expressed in SD (Superframe Dura-tion) which is divided into 16 equal aNumSuperframeSlots.The entire active period is also divided into CAP and CFP.During CAP, the node accesses the channel with slottedCSMA/CA. During CFP, the node conducts communicationwith TDMA (Time Division Multiple Access). The time slotresource is described with Guaranteed Time Slot (GTS).During CFP, there are one or several GTSs and the GTS
assigned to an equipment includes one or several time slotsfor the communication with the coordinator.
BI and SD are separately decided by Beacon Order (BO)and Superframe Order (SO), with the computing methodshown in Formula (1) and Formula (2). SO and BO mustmeet: 0 ≤ SO ≤ BO ≤ 14
BI = aBaseSuperf rameDuration × 2BO
SD = aBaseSuperf rameDuration × 2SO
aBaseSuperf rameDuration = aBaseSlotDuration
×aNumSuperf rameSlots = 60 × 16 = 960symbols
The Slotted CSMA/CA mechanism has three impor-tant parameters: NumberofBackoff (NB), Content Windows(CW), and BackoffExponent(BE). Thereinto, NB means thenumber of backoff, with the initial value of 0 and the max-imum value of 4. When the node completes random delayand supervises busy channel, NB is increased by 1; if NBsurpasses the maximum value, the transmission fails. CWmeans content windows, expressing times of channel idle-ness to be acknowledged prior to data transmission, with thedefault value of 2. When the channel idleness is acknowl-edged to be successful once, CW is decreased by 1. WhenCW is 0 and the network channel is idle, data starts tobe transmitted. BE means backoff exponent, expressingthe random backoff time prior to the detection of chan-nel idleness, with the value range of 0 5 and the defaultvalue of 3.
IEEE802.15.4 protocol does not compulsorily but veryflexibly set values of NB, BE, and CW with which maybe adjusted according to actual conditions. In future, theseparameters will be appropriately adjusted to meet QoSdemands. During CFP, under IEEE 802.15.4 beacon mode,guaranteed time slot (GTS) is used to provide channel visitfor access devices. Before equipments access the channel,GTS must be applied and the frame format of GTS requestcommand is shown in Fig. 3.
When the node (End Device or Router) utilizes GTSto transmit data, it must transmit GTS allocation requestcommand frame to its parent node (router or coordi-nator). In addition, when CharacteristicsType domain in
Fig. 2 Superframe structure
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Fig. 3 GTS request command frame structure
the command frame is 1, it means GTS application.GTS Length means the number of applied time slots.The parent node transmits acknowledgement frame afterreceiving GTS request command. When the parent nodeis allocating GTS, it must meet the following threeconditions:
– The number of the remaining time slots of the currentsuperframes in the parent node is more than GTS lengthof node request (inclusive);
– The number of allocated GTS in the parentmode is less than 7 (7 GTS at most for everysuperframe);
– After GTS allocation, the CAP length in the parent nodeis more than the value of aMinCAPLength (inclusive)(the minimum CAP length provided in IEEE802.15.4,with the value of 440 symbols).
When the bandwidth resource allows, the parent nodeallocates GTS for nodes in the principle of first-come-first-service and saves GTS allocation in the GTS domain of thebeacon frame. The node which requests GTS analyzes thereceived GTS domain of beacon frame within a stipulatedbeacon cycle to judge whether GTS is allocated. If the par-ent node allocates GTS for itself, it may transmit data withina stipulated GTS time slot scope. Or else, GTS allocationrequest fails.
Tree topology structure
Tree addressing is a default address allocation mechanismin ZigBee. During the use of tree addressing, we must spec-ify three network parameters in advance: maximum numberof child nodes (Cm), maximum number of routers in childnodes (Rm), and maximum network length (Lm). The depthof a coordinator is provided to be 0, the depth of an addressis 0, and the depths of sub-equipments of the coordinator are1, with length increased by 1 for per next level. When youhave determined values of Cm, Rm, and Lm, you may cal-culate the addresses of leaf nodes (i.e. non-router nodes andcoordinators) according to Formula (3) and Formula (4).The
allowable maximum address in the network is calculatedaccording to Formula (5).
An = Aparent + Cski(d) × Rm + n (1)
Cskip(d) ={1 + Cm × (Lm − d − 1) , if Rm = 11+Cm−Rm−Cm×R
Lm−d−1m
1−RmOtherwise
(2)
Amax = Cskip(0) × Rm + Cm − Rm (3)
Cskip(d) in Eqs. (1–3) and Algorithm (1-2) mean addressintervals among sub-equipments of coordinators in the childnodes of nodes of a router with the depth of d. n means theavailable n terminal equipment with the scope of 1 (Cm-Rm). Amax means the maximum available address numberand the number surpassing Amax could not be used. Forexample, when Cm=7, Lm=5, and Rm=5, the address inter-vals among sub-equipments of routers in child nodes of acoordinator is (d = 0) Cskip(0) = 1+7−5−7×55−0−1
1−5 =1093. Since Rm=5, there are only five child nodes of routersunder the coordinator and their addresses must be R1=1,R2=1094, R3=2187, R4=3280, and R5=4373. That is tosay, every router may accommodate 1093 descendant nodes.Since Cm=7, there are also two 7 − 5 = 2 terminal nodesunder the coordinator and their addresses are calculatedto be 5466 and 5467 by the use of Eq.(3). However, weshall notice that the coordinator usually allocates addressaccording to the adding sequence of routers to the networkand from small to big, and the coordinator also allocatesaddresses according to the adding sequence of terminalnodes to the network and from small to big. The maxi-mum address of the network in this example is Amax =1093 × 5 + 7 − 5 = 5467, and addresses more than 5468(inclusive) will be wasted. Similarly, we may calculate theaddress allocation of child nodes of other routers such asR1. Seen from the above example analysis, we know the treeaddressing has the following shortages:
1. address space is wasted, specifically: the address spaceover Amax is wasted.
2. Since the tree address allocation is a pre-allocationmechanism, during network planning, we shall care-fully select the three parameters including Lm, Cm, andRm.
Once such parameters are determined, the equipmentaddresses are determined and then network topology isalso determined. If the network topology structure needsto be changed, it may be easily limited by address space.Therefore, such addressing way is not flexible enough. Treeaddressing is characterized with a simple routing algorithm
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and is closely related to the tree routing algorithm. The rout-ing utilized in the tree topology structure is called tree rout-ing or hierarchical routing. In the tree routing, data packetsare spread along the tree route and relies on tree addressing.After a router compares the target address with its address,the router may know next-hop node address. In the treeingaddressing, the address field reserved for child nodes of arouter is calculated with CSkip(d) function. If the targetaddress is not in the address field, it indicates that the nodeof the target address is not its descendant node and then, nextaddress shall be the parent node of a router. For example,assuming the target address is D, the depth of a router is d,the address of a router is A, when DA or DACSkip(d1), therouter transmits data packets to the parent node. If ADAC-Skip(d1), the data packets should be transmitted to a childnode of the router. If D > A + Skip(d) × Rm, it indi-cates the target node is the terminal child node type of therouter and, in next-hop, directly arrives in the target node,or else, the target node is a child node of the router. Sinceevery child node of a router occupies CSkip(d) addressfield, | [D−(A+1)]
CSkip(d)|1 means the address field that the target
node belongs to a child node of a router, and in next-hop, theaddress shall beA+1|[D− A+1
CSkip(d)|×CSkip(d), where |x|
means the maximum integer within x. It can be seen that thetree routing is not required to save other infoRmation exceptsome necessary network parameters, which features simplecalculation and is suitable for the low-power consumptionapplication in WBAN.
Level-based QoS framework
This section proposes a tree topology structured wirelessbody sensor network QoS framework, as based on the IEEE802.15.4 beacon mode. The framework is integrated withthe IEEE 802.15.4 beacon-enabled communication mode,and uses tree topology and tree routing. The frameworkdivides the service into three levels, Level I is the servicedifferentiation of patient level, where priority is determinedaccording to the degree of urgency of the patient’s diseaseor the payment situation, the communication of the highpriority patient is guaranteed, and is called the priority ofpatient. Level II is the priority of the internal sensor of thepatient. Generally, the human body carries multiple sen-sor nodes (e.g. EEG, ECG) in WBAN, these sensor nodesusually have different priorities according to practical sit-uations, for example, the priority of the ECG sensor of apatient with heart disease should be higher than that of othersensors, when the heart disease becomes active, the ECGdata must be sent out prior to other sensor nodes. Level IIIis the priority of data in the sensor node, where the priorityof data frames in the sensor node to be sent is differentiatedaccording to the degree of urgency, thus, ensuring important
urgent data are sent first, for example, when heart diseasebecomes active, the data information must be sent to themedical center immediately. We use the CAP and CFP in theIEEE 802.15.4 beacon mode to implement the three levelsof priority.
PoU-based QoS implementation
Each patient carries with them equipment called PS, whichis in charge of receiving the sensor data of the patient andforwarding the data. The PS has the tree routing function.
In medical application, some sensor data of some patientsshould be transmitted first, thus, the priority of data is dif-ferentiated. For example, in urgent medical treatment, thedata of seriously ill patients are given higher transmissionpriority. Two digits are used in the Reserved for GTS Char-acteristics field, as shown in Fig. 3, to designate the priorityof data, which can designate 00˜03 priorities.
The medical care personnel set the priority of nodeor router according to the physical circumstances of thepatient, when the node applies for GTS, priority is set in theReserved field. When the father node (router or coordina-tor) receives a GTS request, it is inserted in the GTS queueaccording to the priority of Reserved requests. The parentnode GTS queue is in ascending order of priority. The GTSis allocated from the end of queue to the front, as shown inFig. 4.
When inserted in the queue, the father node reallocatesthe GTS in descending order of the GTS queue priority,thus, the low priority GTS may lose the time slot, and theGTS without a time slot becomes ”Waiting GTS”, whichwaits for the high priority GTS to release the time slotresource. When the high priority GTS node releases GTS,the father node reallocates GTS, and the following ”WaitingGTS” may recover the time slot resource.
In the tree structure, when the node priority under therouter is changed, the priority of the router is changedaccordingly; the priority of the router is the weighted aver-age of various subnode priorities.
The steps are detailed below:
1. The terminal node sends a GTS request to the router;2. The router returns an ACK frame to the terminal node;
Fig. 4 GTS queue schematic diagram
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3. The router allocates time slot to the terminal node, andupdates its priority;
4. If the router priority changes, a new GTS request is sentto the coordinator;
5. If the router has allocated GTS, the coordinator updatesits GTS information, otherwise the coordinator allo-cates a GTS time slot according to router priority;
6. The router sends a beacon frame with new allocationinformation to the terminal node;
7. The coordinator sends a beacon frame with the newallocation information to the router;
When the terminal node receives the beacon frame, itstops sending data if its GTS initial time slot is -1, till GTSis reallocated to the beacon frame (initial time slot is not -1)before data transmission.
When the router priority is changed, a new GTS requestis sent to the coordinator, which updates its GTS queueaccording to the priority of the router, and then, notifies therouter via the beacon frame, where the processing procedureis similar to the router.
PoD-based QoS implementation
There may be multiple sensor nodes (e.g. EEG, ECG) onthe human body. There are two methods for QoS imple-mentation between sensor nodes: the first is the BackoffExponent (BE) of CAP in the time slot-based CSMA/CAmechanism. The second is the GTS mechanism of CFP,which function has been integrated into the PoU-based QoSimplementation. The first method is specified, as follows.
The BE represents the random backoff waiting time ofthe node when the detection channel is in the busy or idlestate, its value is set according to the battery life exten-sion parameter macBattLifeExtPeriod. If this attribute valueis TRUE, BE=min (2,macMinBE), i.e. the minimum valuebetween 2 and macMinBE. If this attribute value is FALSE,BE=macMinBE. As the replacement of the node battery inthe body area network is relatively easy, we assume the mac-BattLifeExtPeriod attribute value to be FALSE, which is tosay, the value of macMinBE is the value of BE, where T rep-resents the random backoff waiting time, and R representsrandom integers within 0 ∼ (2BE − 1).
It is obvious that the selection of the BE value directlyinfluences random backoff time T, the range of BE is 0˜mac-MaxBE, and the value of macMaxBE is 0˜5. A smaller BEvalue means the equipment is more likely to use the channelto send data first. Thus, it can be seen that if the nodes havedifferent BE’s, they have different chances of occupying theCSMA/CA mechanism access channel. We implement theservice differentiation by regulating the BE value of eachEnd Device, where a smaller BE represents a higher priorityof the End Device, thus, guaranteeing QoS in the CAP.
PoT-based QoS implementation
There are multiple types of data to be sent inside each sensornode, such as, periodically sent nonurgent data, urgent dataof accident, data requiring confirmation, data not requiringconfirmation, and the command frame of the MAC layer. Inorder to ensure urgent accident data can be sent successfullyand immediately, service differentiation is required for thedata to provide QoS assurance.
When the data flow forms in the node, the internal pro-cessing program sets the priority according to the data type,and then adds the data in the CAP dispatcher queue, if thequeue is empty, the data is directly added in the queue. If thequeue is not empty, the data packet is inserted in the queueaccording to the priority of the data packet, where data pack-ets with high priority are ranked in front of data with lowpriority to be sent first.
Performance evaluation
The performance of the proposed QoS framework andimplementation algorithm is evaluated by computer simu-lation. The OPNET Modeler simulation tool [7] and IEEE802.15.4/ZigBee OPNET simulation model of open sourcecode [8] are used. The proposed level-based QoS frameworkand algorithm are implemented. The tree routing algorithmin the simulation model is modified to meet the QoS require-ment, and the GTS scheduling algorithm supporting QoS isadded.
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BE-based QoS simulation
If the patient carries three sensor nodes, the three sensornodes must communicate with PS. There are two cases ofBE values for the three sensor nodes, node 1, node 2, andnode 3: Case I, the BE values of three sensor nodes are 3;Case II, the BE values of three sensor nodes are 1, 2, and3, respectively. The three sensor nodes have the same flowstart time in the CAP, the flow rate is set as 100 bits/0.03s,and the simulation time is 50s. The CAP queue delay time
simulation results of two kinds of BE values are shown inFig. 5a and 5b. When the nodes have identical BE values,the delay time of the data to be sent by the three nodes in thequeue centers at 0.005s˜0.010s. When different BE valuesare set, the queuing delay of node 1 is 0.003s˜0.004s, thequeuing delay of node 2 is 0.006 s˜0.008 s, and the queu-ing delay of node 3 is 0.008s˜0.012s. The simulation resultsshow that the delay in the data transmission of the threenodes increases with the BE value, which implements theeffect of sending data according to priority.
Fig. 5 The CAP queue delaytime simulation results
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Fig. 6 Network load simulationresults
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GTS-based QoS simulation
Six subnodes are set under one router, the BO is set as 6, theSO is set as 2, the interval between subnode packets is 1s,the packet size is 500 bit, and the simulation time is set as60s.
If four nodes apply for the same GTS priority beforemodification, node1˜node6 apply for four time slots, thesimulation result is as shown in Fig. 6a.
It is observed that, according to the FCFS principle,node1 to node3 have obtained four time slots, as limited tominimum CAP, the CFP can be divided into 13 time slots at
most, node4 obtains one time slot, and as there is no avail-able time slot when node5 and node6 apply for time slots,they always fail in application.
When the GTS allocation algorithm is improved, thesimulation result is shown in Fig. 6b, and the variance in theGTS queue of router in the simulation process is shown inFig. 7.
Figure 7 shows the family diagram of the variation ofthe father node GTS queue, with the start and end of datatransmission of node5 and node6 (16th sec-50th sec), whennode4 begins to send data. When node4 applies for a GTStime slot, it is allocated with four time slots first, and node2
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Fig. 7 Change of the GTSs’ priority
and node3 occupy four time slot, respectively, as node2 hasthe lowest priority, it has only one time slot. The GTS queueis shown in Fig. 7a.
When node5 has applied for four time slots at the 20thsecond, node2 is deprived of GTS and enters the waitingstate. Figure 6 shows that the network output load of node2becomes smooth at the 20th second, and node1 has only onetime slot. The GTS queue is shown in Fig. 7b.
When node6 has applied for four time slots at the 24thsecond, node1 is also deprived of GTS and enters the wait-ing state. The GTS queue is shown in Fig. 7c, and thenetwork output load of node1 in Fig. 6 becomes smooth.
Node5 reaches the end time at the 40th second andreleases GTS, and node1 recovers one time slot GTS, theGTS queue is shown in Fig. 7d. The network output load ofnode5 in Fig. 7 becomes smooth, node1 begins to send dataagain, and the network output load begins to rise.
Node6 reaches the end time at the 50th second andreleases GTS, node1 has three additional time slots, andthus, it has four time slots. Node2 recovers one time slot inGTS, and the GTS queue state is restored to Fig. 7a, whichincreases one time slot in GTS, the GTS queue is shown in
Fig. 7d. The network output load of node6 in Fig. 6 becomessmooth, node2 begins to send data again, and the networkoutput load rises.
The aforesaid results prove that we have implementedresilient transmission of data with different GTS prioritiesin CFP.
The priority of the router is the weighted average of allGTS time slot priorities, and when the GTS queue changes,the priority of router changes accordingly. The priority ofthe router is shown in Fig. 8. If the router priority changes,a GTS assignment request is sent to the coordinator.
As the priority of node1 and node2 is 1 at the 4th andthe 8th second, there is no change. When node3 beginsto apply for GTS at the 12th second, the average priorityof the router is 1.3, when node4˜node6 begin to apply forGTS, the average priority approaches to 3. When node5and node6 quit GTS at the 40th and the 50th second, theaverage priority is a little lower than 2. According to Algo-rithm 2, the total number of time slots is 13, the routerpriority is (4*3+4*2+4*2+1*1)/131.9, meaning the changein the priority of node results in changes in the priority ofthe router.
Simulation of QoS in node
At Algorithm 2, ← denotes an assignment operation.As the settings of QoS in the node and data transmission
are only related to the sensor and PS, in order to simplifythe setting process and analyze the simulation result, weset only one sensor node for communication with the PS.As the ratio of MAC command frames to the overall com-munication is low, we only simulate ACK and NO ACKflows. The ACK and NO ACK flows of the sensor node aresent at intervals of 0.01s (exponentially distributed), the datapacket size is 100 bits, the transmission time is 0.2s˜4.0s,and the simulation time is 5s.
Fig. 8 Change of the routers’priority
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Fig. 9 The end to end delaytime simulation results
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The simulation result of the average End to End Delayof data frames without priority is shown in Fig. 9a. Thesimulation result of priority is shown in Fig. 9b. The aver-age End to End Delay of ACK flow and NACK flow,without priority, centers at 0.007s˜0.009s; when priority isset, the average ETE delay of the ACK flow centers at0.004s, and the average ETE delay of the NACK flow cen-ters at 0.014s˜0.018s, meaning priority setting guaranteespreferential transmission of ACK data to the destination.
Conclusion
Providing effective QoS assurance mechanism in the bodywireless sensor network is very important for the popular-ization of WBAN. This study used IEEE 802.15.4 beaconmode and the tree routing based on tree topology to imple-ment the level-based QoS framework, ensuring the trans-mission of data with high priority at three different levels. Itis completely compatible with the existing communication
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protocols while the QoS is implemented, and the proposedQoS framework is validated by computer simulation.
Acknowledgments This work was funded by the National Plan forScience, Technology and Innovation (MAARIFAH), King AbdulazizCity for Science and Technology, Kingdom of Saudi Arabia, AwardNumber (12-INF2885-02).
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