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Non-interference topology scheme in wireless sensor networks
THE JOURNAL OF CHINA UNIVERSITIES OF POSTS AND TELECOMMUNICATIONS Volume 14, Issue 2, June 2007
MA Shu-hui, JI Hong, YUE Guang-xin
Noninterference topology scheme in wireless sensor networks CLC number TN929.5
Document A
Abstract A novel topology scheme, cell with multiple mobile sinks method (CMMSM), is proposed in this article for the collection of information and for the environment monitoring in wireless sensor networks. The system consists of many static sensors, scattered in a large scale sensing field and multiple mobile sinks, cruising among the clusters. Conservation of energy and simplification of protocol are important design considerations in this scheme. The noninterference topology scheme largely simplifies the full-distributed communication protocol with the ability of collision avoidance and random routing. The total number of cluster heads in such a topology was analyzed, and then an approximate evaluation of the total energy consumption in one round was carried out. Simulation results show that CMMSM can save considerable energy and obtain higher throughput than low-energy adaptive clustering hierarchy (LEACH) and geographical adaptive fidelity (GAF). Keywords sensor networks, energy consumption, topology design, multiple mobile sinks
1 lntroductlon In a typical wireless sensor network, sensor nodes are severely constrained by the limited amount of battery power and the limited capability of processors. On the contrary, sensor networks are application-oriented networks and are expected to function for long periods without external intervention in many applications, especially the application in a large scale field, for example, the battlefield surveillance and habitat monitoring [l]. Therefore, in such systems, reducing and balancing the energy consumption becomes .an important design consideration [2-51. Moreover, the protocol simplification is another key issue that must be considered, and requires the simple operation of sensor nodes. A great deal of complexity results from the broadcast Received date: 2006-10-14 MA Shu-hui JI Hong, YUE Guang-xin School of Telecommunication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876,China E-mail: skyhorseme9gmail.com
(w,
Article ID 1005-8885 (2007) 02-0007-07
characteristic of wireless channel and the distributed characteristic of sensor networks in the protocol design. In a traditional sensor network, the “sensor-to-sink” communication is achieved via multihop-short distance forwardings, which can save much transmission power and facilitate the aggregation of local data. However, the broadcast characteristic of wireless channel and the local connectivity bring large challenges to the protocol design, for example, the hidden terminal problem in medium access control (MAC) layer and the routing selection in network layer only with the local information. Otherwise, considering the prolonging of the lifetime of the network and satisfying the requirements of its application [5,6] also increases the complexity of protocol design. Several topology designs have already been proposed for wireless sensor networks, such as LEACH [7, 81, hybrid energy-efficient distributed clustering (HEED) [9], and GAF [lo]. They are all cluster-based schemes, in which the cluster heads perform the intracluster scheduling and data aggregation. LEACH randomly selects a few sensor nodes as the cluster heads and this function is performed in a cyclic manner to evenly distribute the energy load among the sensors in the networks. HEED is an improved version of LEACH that takes the residual energy of sensor nodes into consideration during the voting of cluster heads. GAF forms clusters based on the geographical location of sensor nodes and guarantees that arbitrary two nodes in the neighboring clusters are in each other’s radio range, the role of cluster head is rotated among the sensor nodes in the cluster. However, in a large-scale sensing field, the cluster heads report the sensing data to the remote sink directly or via multihop forwardings. The operation expends a large amount of energy, while the throughput is still low due to the many-to-one communication. This article aims to design a topology scheme, which will largely prolong the network lifetime, simplify the protocol design, and be scalable to satisfy the different quality of service (QoS) requirements. From this point of view, a hierarchical topology, CMMSM is proposed in wireless sensor networks. The function of CMMSM is to monitor the sensing filed and to collect the information. In this scheme, all the cluster heads are isolated and can transact simultaneously with
The Journal of CHUPT
8
the corresponding mobile sinks, which cruise among the clusters. It simplifies the full-distributed communication protocol with the ability of collision avoidance. Theoretical evaluation and simulation results show that CMMSM can save considerable energy and can improve the throughput compared with LEACH and GAF. The remaining sectionsof the article is organized as follows: the system model is described in Sect. 2. The motivation of this study is given in Sect. 3. The topology scheme CMMSM and the simple communication procedure are given in detail in Sect. 4. An approximate theoretical evaluation of energy cost is given in Sect. 5. In Sect. 6, the CMMSM is compared with LEACH and GAF by simulations. Finally, the conclusions are given in Sect. 7.
2 Syatemmodd
2007
8 Mottvcrtione LEACH and GAF are all cluster-based topology design and can be applied to accomplish this study. But the performance of energy efficiency and the throughput are not satisfactory. For example, in GAF, the neighboring cluster heads are connected to each other so that the data can be forwarded by cluster heads via multihop. However, the connectivity interferes with other neighboring cluster heads’ transaction. It is shown in Fig. 2. Cluster head (CH) “A” sends the data to the next hop CH “B”,and thus all other neighboring cluster heads, including CH LLC’-‘LL’’, cannot receive or transmit data successfully during the transaction between CH “A” and “B’. Obviously, considerable energy is wasted and the throughput is low. In LEACH, the long distance transmitted directly from the cluster head to the remote sink also expends much energy.
For better explanation, some definitions, which are described in Ref. [ll]: such as transmission range (Rh).carrier sensing range &), and interference range (Ri) are first reviewed. The analysis in Ref. [ l l ] shows that when the decay factor of signal is k, the interference range R~must satisfy R, 3
so that the ratio of signal to noise is above 10. A sensor network with many nodes randomly scattered in a large-scale field is considered. The task is to monitor the forest and to detect the occurrence of wild Fire. To achieve the goal, three levels of data transmission are operated. First, the intracluster data aggregation is performed in the cluster head and then many mobile sinks cruising among the clusters collect the needed information from the cluster heads. Finally, the mobile sinks transport all the harvest to the management server. Figure 1 shows an example of the system model. In this example, 100 nodes are randomly scattered in a 1 0 0 100 ~ m’area. The transmission radius Rt, of the cluster head is set to 10 m and the decay factor of the transmission signal is set to 4. Thus the interference range Ri of the cluster head is 17.8 m. The distance between the neighboring cluster heads is set to 40 m, which is highly sufficient to avoid the interference. Three mobile sinks move along the given track and transact simultaneously with the close cluster heads.
Fig. 2 One hop from CH “A” to CH “B’in GAF
To obtain higher energy efficiency, multiple mobile sinks are substituted [12-141 for the single static one that leads to the transmission of the data from the cluster head directly to the close sink which moves to the vicinity. The short distance transmission would decrease the power of cluster heads and prolongs the lifetime of the network. In addition, the mobility of multiple sinks would reduce the delay by increasing sink availability to a larger subset of sensors. The essence is to transfer considerable energy load to the sink nodes. However, the moving track and receiving position of the mobile sinks need to be elaborately designed. In LEACH and GAF, the CH is voted randomly in one cluster and the optimal position and amount of the cluster heads in the network are not considered. In this article, an optimal hierarchical topology, CMMSM, is presented to save considerable energy and to obtain higher throughput by designing a noninterference distribution scheme of the cluster heads. The distribution scheme is ideally integrated with the multiple mobile sinks method by settling the receiving position of the mobile sinks in each cluster.
4 CMMSM: cells wtth mufflple moblle .Ink ~ k r w l ~ ~ n r t w o r k . 4.1 How to deslgn the nonlnterferencedistrlbutlonscheme Fig. 1 An example of the system model
Initially, the necessary condition of a node pair transacting
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MA Shu-hui, et al.: Non-interference topology scheme in wireless sensor networks
successfiilly is analyzed, and then it is expanded to the first circle of neighboring node pairs and the topology scheme is designed to guarantee the noninterference of all the node pairs in the circle. Finally, we reexpand and get the noninterference distribution of node pairs in the entire network. 1) The necessary condition: assume that all the cluster heads and mobile sinks use a common range r for their transmissions, and I is the interference range of the transmission [15]. The decay factor of signal is k. When the cluster head Xitransacts with the sink Y, over the channel, this transaction is successfully done if a) The distance between Xi and yi is not more than r, i.e.,
9
this is the reason for the naming of CMMSM. The area surrounded by the dashed line is the equivalent of Fig. 3(a). Obviously, the distance between the adjacent white dots is only the interference range.
Fig. 4 Position of node pairs transacting simultaneously in the network (the white dots represent the cluster heads or sink nodes)
<1XJ- x
,p
4.2
The whole procedure
IX,-y;/bl <
lYJ - x
IY,
,p
-ypz
2) The procedure of formation of topology: a node pair is situated (one is the cluster head and another is the mobile sink) at the network center and then the two steps are followed that are given below. a) Find the nearest position of node pairs (one is the cluster head and another is the mobile sink) which conform to the necessary condition of successful transaction mentioned above. b) Repeat the first step until none of the positions of node pairs is found in the nearest circle. The result is shown in Fig. 3. It can be seen that at most four node pairs encircle the center if the decay factor of signal is 4, whereas fivenode pairs encircle the center for the decay factor of signal is 2.
(a) If the decay factor is 4,I = 1.78r
The whole procedure is split into three phases: network initialization, data transmission, and cluster alteration. During the network initialization phase, the cluster heads are determined and clusters are formed. The data transmission includes four steps: data sensing, intracluster data collection and fusion in the cluster head, mobile sinks data collection from the cluster heads, and finally the data aggregation in the management server after the transmission from all the sinks. To balance the energy consumption of nodes, the role of cluster head is rotated periodically and the clusters are formed again during the cluster alteration phase. 1) Network initialization: it should be recalled that during the procedure of formation of topology in Sect. 4.1, the cluster head have been settled as one of the node pairs, which means that half of the white dots shown in Fig. 4 are the cluster heads. One situation scheme of the cluster heads is shown in Fig. 5. Obviously, the situation of corresponding sinks is just in the vacant angle. To improve the energy efficiency and get benefit from the situation scheme of cluster heads, the directional antenna is used between the cluster head and the corresponding sink.
(b)Ifthe decay factor is 2, I = 3.16r
Fig. 3 The circle of node pairs transacting simultaneously (the dashed line indicates the edge of interference range and the bold line indicates the edge of transmission range)
c) Re-expand from the first circle, and then repeat the above steps until the position of node pairs are not found in the entire network. Figure 4 is the approximate equivalent of the result. The decay factor of signal is 4.It appears like numerous cells and
Fig. - 5 Position of cluster heads in the network (the dashed line is the edge of every circle and the white dots indicates the cluster heads)
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The Journal of CHUPT
The cluster heads send out the broadcast in the channel C1 and the transmission power of the cluster head is P I . Other nodes will choose the node from which the broadcast with strongest received signal is heard as its cluster head and adjust its transmission power according to the received signal strength. 2) Data transmission: the sensing data are reported systematically to the cluster head in the channel C1 , and then are aggregated in the cluster head. On completion of the data aggregation, the cluster head transmits the directional “report” signal in the channel C2 continuously. Sinks move randomly around the clusters and are heard in channel Cz. There is a possibility of two cases: a) If the “report” signal is heard, it will stop moving and send the queryhnterest message to the cluster head in the channel C2. The cluster head receiving the queryhnterest message will stop sending the “report” signal and transmit the needed information to the sink in the channel C2. The cluster head and mobile sink use the same transmission power P2 . The noninterference topology scheme permits the simultaneous transactions in each cluster head and guarantees the successful transactions. b) If the “report” signal is not heard by sink on the way, it will continue moving. The case means that the cluster heads on the way are being in transaction or have finished reporting the data. Finally, all the cluster heads are inquired and hand in what the sinks need. The data transmission of one round is over. 3) Cluster alteration: according to the topology forming method in Sect. 4.1, if the first node pair (cluster head and mobile sink) is situated in different position, the different situation of cluster heads can be obtained followed by the formation of the clusters once again.
2007
cluster head uses the transmission power P2, the average waiting time for the query/interest message is t, and all the aggregated data in the cluster heads are reported to the mobile sinks with the transmission rate v. In such case, the total energy consumption of one round in one cluster includes two parts. a) Intracluster nodes: Eclu*b-mm = ( N - MC,+ c,)F (3) b) Cluster head:
Ecluster_hesd = C,F + (N - l)CrF +
et + AEr +
wNF V
(4)
here, C,, C,, and C, are the sensing, receiving and transmitting cost of one bit, respectively. AEr represents the energy expended in receiving the querylinterest message from the mobile sink. To compute the energy consumption of the entire network, the number of cluster heads in the network is first evaluated. It should be noted that the number of the cluster heads in the network shown in Fig. 4 is equal to half of the number of dots. Assume that h is the total number of the dots in the area s and q is the radius of the area. From Fig. 4, the relation between h, s, and q can be obtained . q = q o , s=so, h = 7 q=2q0, s=4s0, h = 1 9 (5) q=3q0, s =9 s 0 , h=37 q=4q0, s=16s0, h = 6 1 here, qo and so are the radius and area of one cell unit, respectively, therefore, we can obtain the number of dots can be obtained 4 4a
h =c 6 x +1 x=l
The total number of cluster heads in the area s
I Anafysls of energy consumption In this article, the multiple mobile sinks are substituted for the single static sink and a large portion of energy load is transferred to the sinks. The main reason is that the mobile sinks can move out of the sensing field and their batteries can be expediently replaced. Therefore, the energy consumption of all the nodes placed in the sensing field is only used. Assume that the average number of nodes in one cluster is N , and every node senses the data traffic F in one round and then reports that to the corresponding cluster head. Data are aggregated in the cluster head and the compression ratio is w. On completion of the data aggregation, the cluster head transmits the directional “report” signal continuously until it receives the queryhterest message from the closer sink. Then the desired information is reported to the sink. Assume the
4 -
The total energy consumption of the entire network in one round Obviously, the radius qOof one cell unit represents the interference radius 1 of cluster head, and when the decay factor of signal is 4,the relation between qo and the transmission power P2 is
pz =w,4
(9)
here q is the noise factor. The relation between the interference radius 1 and the transmission radius R is given as
Z>@R (10) Figure 6 is the numerical simulation result of energy
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MA Shu-hui, et al.: Non-interference topology scheme in wireless sensor networks
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consumption in the entire network in one round while using the different transmission radius. It can be seen that there exists an optimal transmission radius of cluster head to obtain the minimal energy consumption of one round. 016 r
P
1 0
data traffic of 50 bit. Data are collected and aggregated in the cluster head with 10% compression ratio, and finally the fusion data are delivered to the sink (in CMMSM, that is the management server via multiple mobile sinks). The energy consumption over the number of rounds is shown in Fig. 8. It can be seen that the theoretical evaluation of energy consumption is a slightly lower than the actual value in CMMSM, whereas LEACH and GAF consume considerable energy than CMMSM. The main reason is that the transaction with the remote static sink in LEACH and GAF needs large transmission power or multihop forwardings; however, the transaction with the mobile sink in CMMSM needs only one-hopshort distance transmission.
r
I
5
10
15
20
25
30
35
R Im
Fig. 6 Energy consumption over differenttransmission radius
9t I
$ 8
6 SlmulaUonresults The OPNET10.0 can be used to compare CMMSM with LEACH and GAF in terns of communication energy costs, delay, and throughput in this section. In this simulation, 1 000 sensor nodes are randomly placed in the sensing field of I 000 x 1 000 mz square area. sink node (that is the management sewer in CMMSM) is 50 m away from the sensing field and the decay factor of the transmission signal is 4. In CMMSM, the transmission power PI of the broadcast from the cluster head is 15 mW and the cluster radius R,is 30 m; the transmission power P2 from the cluster head to the mobile sink is 10 mW, along with the transmission radius R2is 20 m. Five mobile sinks are used and the track of them is shown in Fig.7. In LEACH, the cluster radius is also 30 m and the transmission power from the cluster head to the intracluster nodes is also 15 mW, but the transmission power from the cluster head to the remote sink is 50 mW. In GAF, the communication radius between neighboring nodes is 10 m.
'1
A-CMMSM -v- Theoretical value of CMMSM
I
5
0
10
0 10 0 09
0 08
s 007
1:;
LEACH GAF A CMMSM -.I- Theorehd value of C W S M -B-
-0-
0
Fig. 7 The moving track of five mobile sinks
Assume that in a single round, each sensor node senses the
25
From Fig. 9, it can be seen that for the same traffk load in one round, CMMSM expends the minimal energy, which is almost equal to the theoretical evaluation.
0 01
5
20
Fig. 8 The comparison of energy consumption of LEACH, GAF, CMMSM and the theoretical evaluationof CMMSM
L5 002
4
15
Tim&
to03
*I -2 23
GAF
-0-
50
100 150 Rounds
200
250
Fig. 9 The comparison of energy consumption in each round of LEACH, GAF, CMMSM and the theoretical evaluation of CMMSM
Figure 10 shows that CMMSM can achieve over four fifths reduction in the delay of every round compared to LEACH and GAF. The main reason is that the topology design in CMMSM guarantees multiple simultaneous transactions
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between cluster head and mobile sink, whereas in LEACH only a single transaction between cluster head and the remote static sink is permitted at a time, and that multihop transmissions result in the long delay in GAF.
T
References
**+I
O0 0
40
20
60
80
100
120
1404 I&
Rounds
Fig. 10 The comparison of delay in each round in LEACH, GAF, and CMMSM
Figure 11 is the comparison of throughput in CMMSM, LEACH, and GAF. It also shows that CMMSM can achieve much more throughput than LEACH and GAF especially while using more mobile sinks. -.-LEACH -.-GAF - A-CMMSM (5 sinks) -r-CMMSM (2 s~nks)
*<
0.5 J
0
5
10
15
GAF, and moreover, it can reduce the delay becauses of the multiple mobile sinks compared with LEACH and GAF. Further, the noninterference distribution scheme of the cluster heads permits much more sinks to work simultaneously so that CMMSM is scalable to satisfy the QoS requirement. Acknowledgements This work is supported by the National Natural Science Foundation of China (60472070,60672124).
-m -LEACH -.-GAF A Ch4MSM
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25
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Timeis
Fig. 11 The comparison of average throughput in LEACH, GAF, and CMMSM
7 Condurlons In this article, a novel topology design scheme, CMMSM, for environment monitoring and data collection in a large-scale sensing field in wireless sensor networks is proposed. In CMMSM, a novel cluster head selection method is introduced. It simplifies the full-distributed communication protocol with the ability of collision avoidance and random routing. The CMMSM was compared with LEACH and GAF in terms of the performance of network such as the energy cost, delay, and throughput. Simulation results show that CMMSM is energy efficient and can save considerable energy than LEACH and
1. Akyildiz I F, Su W, Sankarasubramaniam Y,et al. A survey on sensor networks. IEEE Communications Magazine, 2002, 40(8): 102-114 2. Ye Wei, Heidemann J, Estrin D. Medium access control with coordinated adaptive sleeping for wireless sensor networks. IEEWACM Transaction on Networking, 2004,12(3): 493-506 3. Panchahhai A M, Baum C W. A node hibernation protocol utilizing multiple transmit power levels for wireless sensor networks. Proceedings of IEEE 60th Vehicular Technology Conference: Vol 4, May 17-19, 2004, Milan, Italy. Piscataway, NJ, USA: IEEE, 2004: 2808-2813 4. Cui Shu-guang, Goldsmith A J, Bahai A. Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks. IEEE Journal on Selected Areas in Communications,2004, 22(6): 1089-1097 5. Ma Shu-hui, Ji Hong, Yue Guang-xin. An energy-aware geographical forwarding protocol utilizeing adaptive sleeping in wireless sensor networks. The Journal of China Universities of Posts and Telecommunications,2006, 13(1): 15-19 6. Li Ning, Niu Xiao-hong. Power control mechanism in Ad-hoc networks. Journal of Chongqing University of Posts and telecommunications,2004, 16(6): 26-3 1 (in Chinese) 7. Heinzelman W R, Chandrakasan A, Balakrishnan H. Energyefficient communication protocol for wireless microsensor networks. Proceedings of the 33rd Hawaii International Conference on System Sciences, Jan 4-7, 2000, Maui, HI, USA. Los Alamitos, CA, USA IEEE Computer Society, 2000: 1-10 8. Heinzelman W R, Chandrakasan A, Balakrishnan H. An application-specific protocol architecture for wireless microsensor networks. JEEE Transactions on Wireless Communications, 2002, l(4): 660-670 9. Younis 0, Fahmy S. Distributed clustering in Ad-hoc sensor networks: a hybrid, energy-efficient approach. proceedings of the 23rd Annual Joint Conference of the IEEE Computer and Communications Societies WOCOM’O4), Mar 7-11, ux)4, Hongkong, China. Los Alamitos, CA, USA EEE Computer Society, 2004: 11-18 10. Xu Y, Heidemann J, Estrin D. Geography-informed energy conservation for Ad-hoc routing. Proceedings of the 7th Annual
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International Conference on Mobile Computing and Networking, (ACM MobiCOM’Ol), Jul 16-21,2001, Rome, Italy, New York, NY, USA: ACM Press, 2001: 70-84 11. Xu Ka-xin, Gerla M, Bae S. How Effective is the IEEE 802.11 RTS/CTS handshake in Ad-hoc networks? Proceedings of IEEE Global Felceomunications Conference: Vol 1, Nov 17-21, 2002, Taipei, China. Piscataway, NJ, USA: IEEE, 2002: 72-76 12. Oyman E I, Ersoy C. Multiple sink network design problem in large scale wireless sensor networks. Proceedings of E E E International Conference on Communications: Vol6, Jun 20-24, Paris, Frauce. Piscataway, NJ, USA: IEEE, 2004: 3663-3667 13. Song Liang, Hatzinakos D. Dense wireless sensor networks with mobile sinks. Proceedings of 2005 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSPOS): Vol 3, Mar 18-23, 2005, Pennsylvania, PA, USA. Piscataway,NJ, USA: IEEE Computer Society, 2005: 677-680 14. Ammari H M. Data dissemination to mobile sinks in wireless sensor networks: an information theoretic approach. Proceedings of the 2nd IEEE International Conference on Mobile Ad-hoc and Sensor Systems Conference,Nov 7-10,2005, Washington, DC, USA. Piscataway, NJ, USA: IEEE Computer Society, 2005: 1-8 15. Gupta P, Kumar P R. The capacity of wireless networks. KEEE Transactions on Information Theory, 2000,46(2): 388-405 16. Zou Shi-hang, Zhang Li-na, Cheng Shi-duan. An effeicient MAC protocol for mobile Ad-hoc networks. Journal of Beiing Universityies of Posts and Telecommunications, 2005, 28(1): 43-47 (in Chinese)
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17. Tian Hui, Xie Fang, Yang Ning, et al. Channel adaptive multi-path routing for Ad-hoc networks. Journal of Beiing Universityies of Posts and Telecommunications, 2005, 28( 1): 59-62 (in Chinese)
B i o g m p b MA Shu-hui,Ph. D. Candidate, Henan Province, School of Telecommunication Engineering, Beijing University of Posts and Telecommunications,interested in the research of wireless sensor networks and Ad-hoc network.
JI Hong, professor, Guangdong Province, School
of Telecommunication Engineering, Beijing University of Posts and Telecommunications, interested in the research of broadband wireless communicationand information networks.
YUE Guang-xin, professor, Guizhou Province, School of TelecommunicationEngineering, Beijing University of Posts and Telecommunications, interested in the research of communication theory, digital communication and high speed networks.
MA Shu-hui, JI Hong, YUE Guang-xin
Noninterference topology scheme in wireless sensor networks CLC number TN929.5
Document A
Abstract A novel topology scheme, cell with multiple mobile sinks method (CMMSM), is proposed in this article for the collection of information and for the environment monitoring in wireless sensor networks. The system consists of many static sensors, scattered in a large scale sensing field and multiple mobile sinks, cruising among the clusters. Conservation of energy and simplification of protocol are important design considerations in this scheme. The noninterference topology scheme largely simplifies the full-distributed communication protocol with the ability of collision avoidance and random routing. The total number of cluster heads in such a topology was analyzed, and then an approximate evaluation of the total energy consumption in one round was carried out. Simulation results show that CMMSM can save considerable energy and obtain higher throughput than low-energy adaptive clustering hierarchy (LEACH) and geographical adaptive fidelity (GAF). Keywords sensor networks, energy consumption, topology design, multiple mobile sinks
1 lntroductlon In a typical wireless sensor network, sensor nodes are severely constrained by the limited amount of battery power and the limited capability of processors. On the contrary, sensor networks are application-oriented networks and are expected to function for long periods without external intervention in many applications, especially the application in a large scale field, for example, the battlefield surveillance and habitat monitoring [l]. Therefore, in such systems, reducing and balancing the energy consumption becomes .an important design consideration [2-51. Moreover, the protocol simplification is another key issue that must be considered, and requires the simple operation of sensor nodes. A great deal of complexity results from the broadcast Received date: 2006-10-14 MA Shu-hui JI Hong, YUE Guang-xin School of Telecommunication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876,China E-mail: skyhorseme9gmail.com
(w,
Article ID 1005-8885 (2007) 02-0007-07
characteristic of wireless channel and the distributed characteristic of sensor networks in the protocol design. In a traditional sensor network, the “sensor-to-sink” communication is achieved via multihop-short distance forwardings, which can save much transmission power and facilitate the aggregation of local data. However, the broadcast characteristic of wireless channel and the local connectivity bring large challenges to the protocol design, for example, the hidden terminal problem in medium access control (MAC) layer and the routing selection in network layer only with the local information. Otherwise, considering the prolonging of the lifetime of the network and satisfying the requirements of its application [5,6] also increases the complexity of protocol design. Several topology designs have already been proposed for wireless sensor networks, such as LEACH [7, 81, hybrid energy-efficient distributed clustering (HEED) [9], and GAF [lo]. They are all cluster-based schemes, in which the cluster heads perform the intracluster scheduling and data aggregation. LEACH randomly selects a few sensor nodes as the cluster heads and this function is performed in a cyclic manner to evenly distribute the energy load among the sensors in the networks. HEED is an improved version of LEACH that takes the residual energy of sensor nodes into consideration during the voting of cluster heads. GAF forms clusters based on the geographical location of sensor nodes and guarantees that arbitrary two nodes in the neighboring clusters are in each other’s radio range, the role of cluster head is rotated among the sensor nodes in the cluster. However, in a large-scale sensing field, the cluster heads report the sensing data to the remote sink directly or via multihop forwardings. The operation expends a large amount of energy, while the throughput is still low due to the many-to-one communication. This article aims to design a topology scheme, which will largely prolong the network lifetime, simplify the protocol design, and be scalable to satisfy the different quality of service (QoS) requirements. From this point of view, a hierarchical topology, CMMSM is proposed in wireless sensor networks. The function of CMMSM is to monitor the sensing filed and to collect the information. In this scheme, all the cluster heads are isolated and can transact simultaneously with
The Journal of CHUPT
8
the corresponding mobile sinks, which cruise among the clusters. It simplifies the full-distributed communication protocol with the ability of collision avoidance. Theoretical evaluation and simulation results show that CMMSM can save considerable energy and can improve the throughput compared with LEACH and GAF. The remaining sectionsof the article is organized as follows: the system model is described in Sect. 2. The motivation of this study is given in Sect. 3. The topology scheme CMMSM and the simple communication procedure are given in detail in Sect. 4. An approximate theoretical evaluation of energy cost is given in Sect. 5. In Sect. 6, the CMMSM is compared with LEACH and GAF by simulations. Finally, the conclusions are given in Sect. 7.
2 Syatemmodd
2007
8 Mottvcrtione LEACH and GAF are all cluster-based topology design and can be applied to accomplish this study. But the performance of energy efficiency and the throughput are not satisfactory. For example, in GAF, the neighboring cluster heads are connected to each other so that the data can be forwarded by cluster heads via multihop. However, the connectivity interferes with other neighboring cluster heads’ transaction. It is shown in Fig. 2. Cluster head (CH) “A” sends the data to the next hop CH “B”,and thus all other neighboring cluster heads, including CH LLC’-‘LL’’, cannot receive or transmit data successfully during the transaction between CH “A” and “B’. Obviously, considerable energy is wasted and the throughput is low. In LEACH, the long distance transmitted directly from the cluster head to the remote sink also expends much energy.
For better explanation, some definitions, which are described in Ref. [ll]: such as transmission range (Rh).carrier sensing range &), and interference range (Ri) are first reviewed. The analysis in Ref. [ l l ] shows that when the decay factor of signal is k, the interference range R~must satisfy R, 3
so that the ratio of signal to noise is above 10. A sensor network with many nodes randomly scattered in a large-scale field is considered. The task is to monitor the forest and to detect the occurrence of wild Fire. To achieve the goal, three levels of data transmission are operated. First, the intracluster data aggregation is performed in the cluster head and then many mobile sinks cruising among the clusters collect the needed information from the cluster heads. Finally, the mobile sinks transport all the harvest to the management server. Figure 1 shows an example of the system model. In this example, 100 nodes are randomly scattered in a 1 0 0 100 ~ m’area. The transmission radius Rt, of the cluster head is set to 10 m and the decay factor of the transmission signal is set to 4. Thus the interference range Ri of the cluster head is 17.8 m. The distance between the neighboring cluster heads is set to 40 m, which is highly sufficient to avoid the interference. Three mobile sinks move along the given track and transact simultaneously with the close cluster heads.
Fig. 2 One hop from CH “A” to CH “B’in GAF
To obtain higher energy efficiency, multiple mobile sinks are substituted [12-141 for the single static one that leads to the transmission of the data from the cluster head directly to the close sink which moves to the vicinity. The short distance transmission would decrease the power of cluster heads and prolongs the lifetime of the network. In addition, the mobility of multiple sinks would reduce the delay by increasing sink availability to a larger subset of sensors. The essence is to transfer considerable energy load to the sink nodes. However, the moving track and receiving position of the mobile sinks need to be elaborately designed. In LEACH and GAF, the CH is voted randomly in one cluster and the optimal position and amount of the cluster heads in the network are not considered. In this article, an optimal hierarchical topology, CMMSM, is presented to save considerable energy and to obtain higher throughput by designing a noninterference distribution scheme of the cluster heads. The distribution scheme is ideally integrated with the multiple mobile sinks method by settling the receiving position of the mobile sinks in each cluster.
4 CMMSM: cells wtth mufflple moblle .Ink ~ k r w l ~ ~ n r t w o r k . 4.1 How to deslgn the nonlnterferencedistrlbutlonscheme Fig. 1 An example of the system model
Initially, the necessary condition of a node pair transacting
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MA Shu-hui, et al.: Non-interference topology scheme in wireless sensor networks
successfiilly is analyzed, and then it is expanded to the first circle of neighboring node pairs and the topology scheme is designed to guarantee the noninterference of all the node pairs in the circle. Finally, we reexpand and get the noninterference distribution of node pairs in the entire network. 1) The necessary condition: assume that all the cluster heads and mobile sinks use a common range r for their transmissions, and I is the interference range of the transmission [15]. The decay factor of signal is k. When the cluster head Xitransacts with the sink Y, over the channel, this transaction is successfully done if a) The distance between Xi and yi is not more than r, i.e.,
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this is the reason for the naming of CMMSM. The area surrounded by the dashed line is the equivalent of Fig. 3(a). Obviously, the distance between the adjacent white dots is only the interference range.
Fig. 4 Position of node pairs transacting simultaneously in the network (the white dots represent the cluster heads or sink nodes)
<1XJ- x
,p
4.2
The whole procedure
IX,-y;/bl <
lYJ - x
IY,
,p
-ypz
2) The procedure of formation of topology: a node pair is situated (one is the cluster head and another is the mobile sink) at the network center and then the two steps are followed that are given below. a) Find the nearest position of node pairs (one is the cluster head and another is the mobile sink) which conform to the necessary condition of successful transaction mentioned above. b) Repeat the first step until none of the positions of node pairs is found in the nearest circle. The result is shown in Fig. 3. It can be seen that at most four node pairs encircle the center if the decay factor of signal is 4, whereas fivenode pairs encircle the center for the decay factor of signal is 2.
(a) If the decay factor is 4,I = 1.78r
The whole procedure is split into three phases: network initialization, data transmission, and cluster alteration. During the network initialization phase, the cluster heads are determined and clusters are formed. The data transmission includes four steps: data sensing, intracluster data collection and fusion in the cluster head, mobile sinks data collection from the cluster heads, and finally the data aggregation in the management server after the transmission from all the sinks. To balance the energy consumption of nodes, the role of cluster head is rotated periodically and the clusters are formed again during the cluster alteration phase. 1) Network initialization: it should be recalled that during the procedure of formation of topology in Sect. 4.1, the cluster head have been settled as one of the node pairs, which means that half of the white dots shown in Fig. 4 are the cluster heads. One situation scheme of the cluster heads is shown in Fig. 5. Obviously, the situation of corresponding sinks is just in the vacant angle. To improve the energy efficiency and get benefit from the situation scheme of cluster heads, the directional antenna is used between the cluster head and the corresponding sink.
(b)Ifthe decay factor is 2, I = 3.16r
Fig. 3 The circle of node pairs transacting simultaneously (the dashed line indicates the edge of interference range and the bold line indicates the edge of transmission range)
c) Re-expand from the first circle, and then repeat the above steps until the position of node pairs are not found in the entire network. Figure 4 is the approximate equivalent of the result. The decay factor of signal is 4.It appears like numerous cells and
Fig. - 5 Position of cluster heads in the network (the dashed line is the edge of every circle and the white dots indicates the cluster heads)
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The cluster heads send out the broadcast in the channel C1 and the transmission power of the cluster head is P I . Other nodes will choose the node from which the broadcast with strongest received signal is heard as its cluster head and adjust its transmission power according to the received signal strength. 2) Data transmission: the sensing data are reported systematically to the cluster head in the channel C1 , and then are aggregated in the cluster head. On completion of the data aggregation, the cluster head transmits the directional “report” signal in the channel C2 continuously. Sinks move randomly around the clusters and are heard in channel Cz. There is a possibility of two cases: a) If the “report” signal is heard, it will stop moving and send the queryhnterest message to the cluster head in the channel C2. The cluster head receiving the queryhnterest message will stop sending the “report” signal and transmit the needed information to the sink in the channel C2. The cluster head and mobile sink use the same transmission power P2 . The noninterference topology scheme permits the simultaneous transactions in each cluster head and guarantees the successful transactions. b) If the “report” signal is not heard by sink on the way, it will continue moving. The case means that the cluster heads on the way are being in transaction or have finished reporting the data. Finally, all the cluster heads are inquired and hand in what the sinks need. The data transmission of one round is over. 3) Cluster alteration: according to the topology forming method in Sect. 4.1, if the first node pair (cluster head and mobile sink) is situated in different position, the different situation of cluster heads can be obtained followed by the formation of the clusters once again.
2007
cluster head uses the transmission power P2, the average waiting time for the query/interest message is t, and all the aggregated data in the cluster heads are reported to the mobile sinks with the transmission rate v. In such case, the total energy consumption of one round in one cluster includes two parts. a) Intracluster nodes: Eclu*b-mm = ( N - MC,+ c,)F (3) b) Cluster head:
Ecluster_hesd = C,F + (N - l)CrF +
et + AEr +
wNF V
(4)
here, C,, C,, and C, are the sensing, receiving and transmitting cost of one bit, respectively. AEr represents the energy expended in receiving the querylinterest message from the mobile sink. To compute the energy consumption of the entire network, the number of cluster heads in the network is first evaluated. It should be noted that the number of the cluster heads in the network shown in Fig. 4 is equal to half of the number of dots. Assume that h is the total number of the dots in the area s and q is the radius of the area. From Fig. 4, the relation between h, s, and q can be obtained . q = q o , s=so, h = 7 q=2q0, s=4s0, h = 1 9 (5) q=3q0, s =9 s 0 , h=37 q=4q0, s=16s0, h = 6 1 here, qo and so are the radius and area of one cell unit, respectively, therefore, we can obtain the number of dots can be obtained 4 4a
h =c 6 x +1 x=l
The total number of cluster heads in the area s
I Anafysls of energy consumption In this article, the multiple mobile sinks are substituted for the single static sink and a large portion of energy load is transferred to the sinks. The main reason is that the mobile sinks can move out of the sensing field and their batteries can be expediently replaced. Therefore, the energy consumption of all the nodes placed in the sensing field is only used. Assume that the average number of nodes in one cluster is N , and every node senses the data traffic F in one round and then reports that to the corresponding cluster head. Data are aggregated in the cluster head and the compression ratio is w. On completion of the data aggregation, the cluster head transmits the directional “report” signal continuously until it receives the queryhterest message from the closer sink. Then the desired information is reported to the sink. Assume the
4 -
The total energy consumption of the entire network in one round Obviously, the radius qOof one cell unit represents the interference radius 1 of cluster head, and when the decay factor of signal is 4,the relation between qo and the transmission power P2 is
pz =w,4
(9)
here q is the noise factor. The relation between the interference radius 1 and the transmission radius R is given as
Z>@R (10) Figure 6 is the numerical simulation result of energy
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MA Shu-hui, et al.: Non-interference topology scheme in wireless sensor networks
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consumption in the entire network in one round while using the different transmission radius. It can be seen that there exists an optimal transmission radius of cluster head to obtain the minimal energy consumption of one round. 016 r
P
1 0
data traffic of 50 bit. Data are collected and aggregated in the cluster head with 10% compression ratio, and finally the fusion data are delivered to the sink (in CMMSM, that is the management server via multiple mobile sinks). The energy consumption over the number of rounds is shown in Fig. 8. It can be seen that the theoretical evaluation of energy consumption is a slightly lower than the actual value in CMMSM, whereas LEACH and GAF consume considerable energy than CMMSM. The main reason is that the transaction with the remote static sink in LEACH and GAF needs large transmission power or multihop forwardings; however, the transaction with the mobile sink in CMMSM needs only one-hopshort distance transmission.
r
I
5
10
15
20
25
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35
R Im
Fig. 6 Energy consumption over differenttransmission radius
9t I
$ 8
6 SlmulaUonresults The OPNET10.0 can be used to compare CMMSM with LEACH and GAF in terns of communication energy costs, delay, and throughput in this section. In this simulation, 1 000 sensor nodes are randomly placed in the sensing field of I 000 x 1 000 mz square area. sink node (that is the management sewer in CMMSM) is 50 m away from the sensing field and the decay factor of the transmission signal is 4. In CMMSM, the transmission power PI of the broadcast from the cluster head is 15 mW and the cluster radius R,is 30 m; the transmission power P2 from the cluster head to the mobile sink is 10 mW, along with the transmission radius R2is 20 m. Five mobile sinks are used and the track of them is shown in Fig.7. In LEACH, the cluster radius is also 30 m and the transmission power from the cluster head to the intracluster nodes is also 15 mW, but the transmission power from the cluster head to the remote sink is 50 mW. In GAF, the communication radius between neighboring nodes is 10 m.
'1
A-CMMSM -v- Theoretical value of CMMSM
I
5
0
10
0 10 0 09
0 08
s 007
1:;
LEACH GAF A CMMSM -.I- Theorehd value of C W S M -B-
-0-
0
Fig. 7 The moving track of five mobile sinks
Assume that in a single round, each sensor node senses the
25
From Fig. 9, it can be seen that for the same traffk load in one round, CMMSM expends the minimal energy, which is almost equal to the theoretical evaluation.
0 01
5
20
Fig. 8 The comparison of energy consumption of LEACH, GAF, CMMSM and the theoretical evaluationof CMMSM
L5 002
4
15
Tim&
to03
*I -2 23
GAF
-0-
50
100 150 Rounds
200
250
Fig. 9 The comparison of energy consumption in each round of LEACH, GAF, CMMSM and the theoretical evaluation of CMMSM
Figure 10 shows that CMMSM can achieve over four fifths reduction in the delay of every round compared to LEACH and GAF. The main reason is that the topology design in CMMSM guarantees multiple simultaneous transactions
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The Journal of CHWT
between cluster head and mobile sink, whereas in LEACH only a single transaction between cluster head and the remote static sink is permitted at a time, and that multihop transmissions result in the long delay in GAF.
T
References
**+I
O0 0
40
20
60
80
100
120
1404 I&
Rounds
Fig. 10 The comparison of delay in each round in LEACH, GAF, and CMMSM
Figure 11 is the comparison of throughput in CMMSM, LEACH, and GAF. It also shows that CMMSM can achieve much more throughput than LEACH and GAF especially while using more mobile sinks. -.-LEACH -.-GAF - A-CMMSM (5 sinks) -r-CMMSM (2 s~nks)
*<
0.5 J
0
5
10
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GAF, and moreover, it can reduce the delay becauses of the multiple mobile sinks compared with LEACH and GAF. Further, the noninterference distribution scheme of the cluster heads permits much more sinks to work simultaneously so that CMMSM is scalable to satisfy the QoS requirement. Acknowledgements This work is supported by the National Natural Science Foundation of China (60472070,60672124).
-m -LEACH -.-GAF A Ch4MSM
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Timeis
Fig. 11 The comparison of average throughput in LEACH, GAF, and CMMSM
7 Condurlons In this article, a novel topology design scheme, CMMSM, for environment monitoring and data collection in a large-scale sensing field in wireless sensor networks is proposed. In CMMSM, a novel cluster head selection method is introduced. It simplifies the full-distributed communication protocol with the ability of collision avoidance and random routing. The CMMSM was compared with LEACH and GAF in terms of the performance of network such as the energy cost, delay, and throughput. Simulation results show that CMMSM is energy efficient and can save considerable energy than LEACH and
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17. Tian Hui, Xie Fang, Yang Ning, et al. Channel adaptive multi-path routing for Ad-hoc networks. Journal of Beiing Universityies of Posts and Telecommunications, 2005, 28( 1): 59-62 (in Chinese)
B i o g m p b MA Shu-hui,Ph. D. Candidate, Henan Province, School of Telecommunication Engineering, Beijing University of Posts and Telecommunications,interested in the research of wireless sensor networks and Ad-hoc network.
JI Hong, professor, Guangdong Province, School
of Telecommunication Engineering, Beijing University of Posts and Telecommunications, interested in the research of broadband wireless communicationand information networks.
YUE Guang-xin, professor, Guizhou Province, School of TelecommunicationEngineering, Beijing University of Posts and Telecommunications, interested in the research of communication theory, digital communication and high speed networks.