The 2012 International Conference on Advanced Technologies for Communications (ATC 2012)

Cooperative Communication Techniques for Cluster Size Expansion in Cluster Based Wireless Sensor Network Tuan-Duc Nguyen, Truong-Minh Nguyen Ngoc and Vo Nguyen Quoc Bao International University, Vietnam National University Post and Telecommunication Institut of Technology, Vietnam Email: [email protected]

Abstract—In the context of energy constrained wireless sensor networks where individual nodes can cooperate together to deploy the cooperative communications, Relay and cooperative Multi-Input Multi-Output (MIMO) techniques can be used to exploit the diversity gain to increase the performance or to reduce the transmission energy consumption. Based on the energy efficiency of cooperative communication, a new scheme of using cooperative MISO and Relay techniques for two way data transmission in cluster based Wireless Sensor Networks (WSN) is proposed in this paper. The energy consumption of the multi-hop, Relay and cooperative MISO transmission have been investigated in this paper. Simulation and energy calculation results show that the proposed cooperative scheme has a much lower energy consumption than the traditional multi-hop transmission scheme and the proposed scheme can be used to increase efficiently the size of WSN cluster.

I. I NTRODUCTION In distributed wireless sensor network where some individual sensor nodes can cooperate for the transmission and the reception in order to set up a cooperative communication, Relay techniques have been known as a simple and energy efficient technique to extend the transmission range due to their simplicity and their performance for wireless transmissions over fading channels [5], [9]. Beside the relay technique, cooperative MIMO technique can cooperate individual nodes in order to deploy a MIMO transmission using space time codes [3], [6]. Cooperative MIMO technique can exploit the diversity gain of space time coding in order to reduce the transmission energy consumption. It has been shown that cooperative MISO and cooperative MIMO techniques have a lower energy consumption than the traditional SISO and multi-hop SISO techniques [2], [7]. In WSN, cooperative communications can be used to reduce efficiently the transmission energy consumption which is important for medium to long distance transmission where transmission consumption is dominant in the total energy consumption. In various applications, such as environment monitoring, area surveillance for agriculture or intelligent transportation systems, middle and long range transmissions are indeed often required because of the weak density of the wireless sensor networks. Relay and cooperative MISO techniques are very useful for this wireless sensor network 978-1-4673-4352-7/12/$31.00 ©2012 IEEE

applications where the energy consumption is the important constraint. Clustering has been proved to be an energy-efficient method of network planning in many kind of WSN. The cluster based network is divided into many clusters, each cluster has a cluster head and many member sensor nodes. Energy efficiency of cluster based wireless sensor network have been reviewed in [8], [4]. In cluster based wireless sensor network, the size of cluster depends on the maximum transmission distance between the cluster header and outer wireless sensor node. The application of cooperative communication in cluster based WSN reduces not only the energy consumption, but also helps increase the maximum transmission distance of cluster head. The energy efficiency of cooperative MISO transmission in cluster based WSN has been studied in [10]. In this paper, we propose an energy-efficient cooperative transmission scheme in which cooperative MISO technique is used for data transmission from cluster head to sensor nodes and Relay technique is used for data transmission from a sensor node to cluster head. This proposed technique exploits the diversity gain of cooperative MISO va Relay techniques in order to reduce the energy consumption or increase the transmission distance between cluster head and sensor nodes. In cluster based WSN, this techinque helps increase the size of one cluster for the same energy consumption of all wireless sensor nodes. The rest of the paper is organized as follows. The cluster based wireles sensor network model and the proposed cooperative communication scheme are presented in section II. The energy comsumption model and the energy consumption calculation of multi-hop, cooperative MISO and Relay techniques are presented in Section III. In section IV, the result of performance simulation and energy consumption comparison of all cooperative techniques are shown. Finally, the conclusion is given in Section V.

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can cooperate with the cooperated node in order to deploy the cooperative MISO and Relay transmissions. As illustrated in Fig 2, consider that the cooperative node is nearby the head (it is easier to set-up a cooperative node nearby the cluster head than father from the cluster head). Instead of using 2 hops transmission (like in the top picture of Fig. 2), the proposed scheme uses cooperative MISO and relay transmission to send and receive data between cluster head and outer sensor node as illustrated in middle and bottom pictures of Fig. 2.

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Fig. 1.

Cluster based WSN

II. C OOPERATIVE C OMMUNICATIONS FOR C LUSTER BASED W IRELESS S ENSOR N ETWORK A. WSN Cluster Model As illustrated in Fig. 1, consider that one cluster in cluster based WSN has a head. Sensors in one cluster collect data and send its back to the cluster head and data communication between cluster head and sensors is two way communication. Cluster head play also as a role of network router in order to send data to other clusters. In this kind of cluster based WSN, the size of one cluster depends on the coverage area of the cluster head, ie. the maximum two way transmission range between the cluster head and outer wireless sensor nodes. The transmission distance depends on the maximum power consumption of cluster head and sensor nodes. As the transmission power increases with the power function of transmission distance and the power path loss factor k (k value is typically from 2 to 5 for wireless channel), transmission power is significant for medium to long distance transmission and dominates the total energy consumption of a wireless node. In order to reduce the transmission power consumption, multi-hop technique is a traditional approach to reduce the transmission consumption of wireless node. As illustrated in the top picture of Fig. 2, cluster head can send data to outer sensor node over 2 hops transmission through a middle sensor node between the cluster head and the destination sensor. B. Cluster Size Expansion using Cooperative Communication Beside the multi-hop transmission, cooperative communication likes cooperative MIMO or Relay techniques can also be employed in WSN in order to reduce the transmission power consumption. In this paper, we propose a cooperative transmission scheme using cooperative MISO and Relay technique for cluster based WSN of cluster head and wireless sensor nodes. Consider that one cluster has a head, and this cluster head can choose a cooperative node near it (cluster head is maybe generated randomly to form clusters and cluster head can choose a nearby node as a cooperative node). This cluster head

Fig. 2. Multi-hop, Relay and cooperative MISO transmissions between the cluster head and sensor node in cluster based WSN

In this proposed scheme, cluster head cooperates with cooperative node to deploy a cooperative MISO transmission using Alamouti STBC in order to sent data to sensor node for forward link transmission. There are two phases of communication: • Phase 1: cluster head sends a data sequence to the cooperative node in the first time slot. The cluster head and this cooperative node encode data sequence into space time code sequences. • Phase 2: Two nodes send this space time code sequence in the second time slot to the reception wireless sensor node node. The reception node combines the received space time sequence and decodes the signal. For reverse link (data transmission from sensor node back to cluster head), because the cooperative node is far from the sensor node, it is not efficient to deploy a cooperative MISO transmission. So that, the cooperative node will play as a relay node in order to deploy a relay Amplify and Forward transmission for data sending from sensor node back to the cluster head. There are also two phases of communication: • Phase 1: Sensor node sends data sequence to the cluster head and the cooperative node in the first time slot. • Phase 2: Cooperative node plays as a relay node and forwards it received signal to the cluster head by using the Amplify-Forward technique in the second time slot. Cluster head combine the received sequence from the sensor node and relayed sequence from the cooperative

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fc = 2.5 GHz Gt Gr = 5 dBi B = 10 kHz Pmix = 30.3 mW P¯b = 10−3 Pf ilt = Pf ilr = 2.5 mW Nf = 10 dB

η = 0.35 = −174 dBm/Hz β=1 Psyn = 50 mW 1 Ts = B PLN A = 20 mW ML = 40 dB

figure defined as Nf = Mn /N0 with N0 is the single-side thermal noise Power Spectral Density (PSD) and Mn is the PSD of the total effective noise at receiver input. Depending on the Power Spectral Density (PSD) of thermal noise N0 , ¯b,SISO can be calculated based on Eb /N 0 value given the E in Fig. 3 for a specific FER requirement. The power consumption Ppa can be approximated as

N0 2

TABLE I S YSTEM

PARAMETERS FOR THE ENERGY CONSUMPTION EVALUATION .

¯b,SISO ) ¯b,SISO ) = ( ξ )Pout (d, E Ppa,SISO (d, E η node by using Maximum Ratio Combining technique and decodes the signal. Fig. 2 illustrate two phases of communication of the cooperative MISO and Relay transmission technique. Continuous line and dash line are stand for the first and second phase of transmission. Cooperative MISO and Relay technique can exploit the diversity gain in order to increase the performance or reduce the energy consumption for the same performance. In comparison with multi-hop technique, It can increase the transmission distance for the same energy consumption. By using the cooperative MISO and Relay technique for two way communication in a cluster, the transmission distance between the cluster head and outer sensor node can be increased for the same energy consumption, leading to the cluster size expansion in cluster based WSN. III. E NERGY C ONSUMPTION M ODEL For energy consumption estimation, evaluation and comparison purposes, the reference power consumption model in [1] [7] is used in this paper as a reference. The system parameters of this model is presented in Table I. Let us consider multi-hop, cooperative MISO and Relay transmissions like in Fig. 2, the total energy consumption of each transmission is calculated in this section by using this reference consumption model. A. Consumption multi-hop transmission scheme Energy consumption of multi-hop transmission is the sum of the consumption of each hop. For each SISO transmission hop, the total power consumption consists of two components: the transmission power Ppa of the amplifier and the circuit power Pc of all RF circuit blocks of transmitter and receiver. Ppa depends on the output transmission power Pout . If the channel is considered as a square law path loss channel (power loss factor K = 2), the transmission power required for a transmission distance d can be calculated as ¯b,SISO ) = E ¯b,SISO Rb × Pout (d, E

(4πd)2 Ml Nf Gt Gr λ2

where ξ is the drain efficiency of the RF power amplifier and η is the Peak-to-Average Ratio (PAR) which depends on the modulation and the associated constellation size. Consider that the consumption of digital signal processing block of transmitter and receiver is small to the connsumption of other analof RF block, we neglect the consumption of this on the calculation of circuit consumption. The total circuit power consumption is given by Pc,SISO = Pc,transmitter + Pc,receiver ≈ (PDAC + Pmix + Pf ilt + Psyn ) +(PLN A + Pmix + PIF A + Pf ilr + PADC + Psyn ) (3) where PDAC , Pmix , PLN A , PIF A , Pf ilt , Pf ilr , PADC , Psyn stand respectively for the power consumption values of the digital-to-analog converter, the mixer, the low noise amplifier, the intermediate frequency amplifier, the active filter at the transmitter and receiver, the analog-to-digital converter and the frequency synthesizer. The total energy consumption of the transmission of Nb bits can be obtained as ¯b,SISO ) + Pc,SISO ) Ehop (d) = (Ppa,SISO (d, E

Nb Rb

(4)

Energy consumption of a multi-hop transmission is the sum of energy consumption of each hop. B. Consumption of Cooperative MISO transmission in forward link Energy consumption of a cooperative MISO transmission (with one cluster head and one cooperative node) is the sum of the energy consumption of two communication phases. Phase 1 uses a SISO transmission for data transmission from the cluster head to the cooperative node, so the the energy consumption of phase 1 can be calculated like the case of one hop transmission over a distance dm between cluster head and cooperative node. The energy consumption of phase 1:

(1)

¯b,SISO is the required mean energy per bit of SISO where E transmission for ensuring a given error rate requirement, Rb is the bit rate, d is the transmission distance. Gt and Gr are the transmission and reception antenna gain, λ is the carrier wave length, Ml is the link margin, Nf is the receiver noise

(2)

Ecoop (dm ) = (Ppa,SISO (dm ) + Pc,SISO )

Nb Rb

(5)

In phase 2, cluster head and cooperative node encode data sequence using Alamouti code and send it in same time to the destination sensor node. The transmission consumption of phase 2:

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2 ¯b,M ISO ) = ( ξ )E ¯b,M ISO Rb × (4πd) Ml Nf Ppa,M ISO (d, E η Gt Gr λ2 (6) ¯b,M ISO is the required mean energy per bit of where E MISO transmission which can be calculated based on Eb /N0 value given in Fig. 3 for ensuring a given error rate requirement. Neglecting the power conmsumption of space time encoding and combination process, the circuit consumption of phase 2:

Pc,M ISO ≈ 2(PDAC + Pmix + Pf ilt + Psyn ) +(PLN A + Pmix + PIF A + Pf ilr + PADC + Psyn ) (7) The energy consumption of phase 2: ¯b,M ISO ) + Pc,M ISO ) EM ISO (d) = (Ppa,M ISO (d, E

Nb (8) Rb

Nb Rb (13) So, the total energy consumption of Relay transmission is ¯b,Relay ) + Pc,SISO ) Erelay2 (dm ) = (Ppa,SISO (dm , E

ERelay (d) = Erelay1 (d) + Erelay2 (dm )

(14)

IV. S IMULATION RESULTS A. Performance of cooperative MISO and Relay techniques Simulations of cooperative MISO technique (using Alamouti code) and Relay technique are performed. The system uses an uncoded quadrature phase shift keying (QPSK) modulation, the channel is considered to be Rayleigh fading and independent for each frame of 120 symbols. For the reliability of result, 106 frames have at least been sent for assuring the frame-error-ratio F ER = 10−4 .

So, the total energy consumption of the cooperative MISO transmission is

SISO cooperative MISO Relay A−F

−1

10

EcoopM ISO (d) = Ecoop (dm ) + EM ISO (d)

(9) FER

C. Consumption of Relay transmission in reverse link For the reverse link transmission from sensor node back to the cluster head, there are two phase of Relay transmission: phase 1 of transmission from detination back to header and cooperative node (relay node), and phase 2 cooperative node use amplify and forward to send data to cluster head. The total energy consumption ERelay is the sum of the energy consumption of each transmission phase. The transmission power consumption and circuit power consumption of phase 1: 2 ¯b,Relay ) = ( ξ )E ¯b,Relay Rb × (4πd) Ml Nf Ppa (d, E η Gt Gr λ2

(10)

Pc,Relay ≈ (PDAC + Pmix + Pf ilt + Psyn ) +2(PLN A + Pmix + PIF A + Pf ilr + PADC + Psyn )(11) ¯b,Relay is the required mean energy per bit of Relay where E transmission, which can be calculated based on Eb /N 0 value given in Fig. 3 for ensuring a given error rate requirement. The energy consumption of phase 1: ¯b,Relay ) + Pc,Relay ) Nb Erelay1 (d) = (Ppa (d, E Rb

(12)

In phase two, cooperative node amplifies the received sequence and uses a SISO transmission for data forwarding to the cluster head. The the energy consumption of phase 2 can be calculated like the case of one hop transmission over a distance dm between cooperative node and cluster head. The energy consumption of phase 2:

−2

10

−3

10

10

15

20

25

30

35

Eb/No(dB)

Fig. 3. FER of SISO technique, relay technique and cooperative MISO technique, non-coded QPSK modulation, Rayleigh fading channel,power path loss factor k=2.

Fig. 3 represents the Frame Error Rate (FER) performance comparison of the traditional SISO technique, relay techniques (Amplify-and-Forward) and the cooperative MISO technique for two cooperative transmit nodes (one cluster head and one cooperative node). Fig 3. shows that performance of Relay and cooperative MISO techniques are better than the traditional SISO technique (for the same error rate requirement, received SNRs of relay and cooperative MISO is lower than SISO). At the typical error rate requirement F ER = 10−3 for Wireless Sensor Network, Eb /N0 of SISO, Relay and cooperative MISO techniques are respectively 36, 27, and 22 dB. For medium to long distance transmission, the transmission power consumption is usually much greater than the circuit consumption and dominates the total energy consumption. Cooperative MISO and Relay techniques help reduce the transmission consumption, leading reducing the total energy consumption of the transmission.

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B. Energy consumption comparison

6

x 10 14

The energy consumption were calculated by using the system parameters presented in Table I. The following figures represent the total energy consumption to transmit 107 bits with the error rate requirement F ER = 10−3 between a cluster head and a sensor node separated by a distance d. The channel is considered as a Rayleigh block fading channel with the channel path loss factor k = 2. The relative distance between cluster head and cooperative node is dm = d/10.

cooperative MISO Relay A−F Mutlti−hop

12

Energy Consumption (mJ)

10

8

6

4

6

x 10 3.5

SISO cooperative MISO Relay A−F multi−hop

2

0 100

120

140

2.5

160

180

200 220 Distance(m)

240

260

280

300

2

Fig. 5. Energy Consumption of multi-hop technique, relay technique and cooperative MISO technique, power path-loss factor k = 2. 1.5

1

0.5

0 10

20

30

40

50 60 Distance(m)

70

80

90

100

Fig. 4. Energy consumption of multi-hop technique, relay technique and cooperative MISO technique, power path-loss factor k = 2

Fig. 4 shows the total energy consumption (in function of transmission distance d) of the multi-hop (2 hops), relay and cooperative MISO techniques in comparison with traditional SISO technique (one hop transmission) for one way transmission from cluster head to destination sensor node. Multihop transmission has a lower energy consumption than SISO transmission. It is also obvious that the energy consumption of Relay and cooperative MISO techniques is lower than the multi-hop transmission technique. Fig. 5 shows the energy consumption of all techniques for longer transmission distance from 100m to 300m. The obvious advantage of the cooperative MISO and Relay techniques over multi-hop SISO technique is shown. For the case of the path loss factor k > 2, the transmission energy consumption will be greater than the case of k = 2. Cooperative techniques help saving the transmission energy consumption (because of the smaller Eb /N0 ), so that the advantage of cooperative MISO and Relay will be more significant.

to sensor node) and the proposed scheme where cooperative MISO and relay techniques are used for forward and reserve links. Based on the result of total energy consumption calculation of two way transmission, Fig. 6 shows the transmission distance in function of the total energy consumption of the proposed cooperative scheme and the traditional multi-hop scheme (using 2 hops and 4 hops transmission). Fig. 6 shows that, with the same energy consumption,the proposed cooperative scheme always has a longer transmission distance between the cluster head and wireless sensor node. ItÕs mean that, the cluster size can be expanded with the same total energy consumption of cluster head and sensor node. 600 Cooperative communication 2 hops transmission 4 hops transmission

550 500 450 400 Distance(m)

Energy Consumption (mJ)

3

350 300 250 200 150 100

C. Cluster size expansion using cooperative technique

0

Coverage area of one cluster depends on the maximum transmission distance between the cluster head and sensor node. Consider a 2 way transmission between the cluster head and sensor node (separated by a distance d), we calculate the total energy consumption of the mutlti-hop transmission scheme (2 hops and 4 hops transmission from cluster head

0.5

1 1.5 Energy Consumption (mJ)

2

2.5 7

x 10

Fig. 6. Transmission distance in function of the total energy consumption of cooperative scheme and multi-hop scheme.

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For example, if the cluster head uses 2 hops transmission in

order to send and receive properly the data to wireless sensor node and the cluster size (maximum distance) is 200m. For the same energy consumption, the cluster size can be increased to 500m by using the proposed cooperative scheme. If the cluster size of 2 hops scheme is 240m, the cooperative scheme can increase the cluster size to 600m for the same total energy consumption. It can be also observed that multi-hop scheme with 4 hops transmission has also a longer transmission distance than 2 hops transmission, but still shorter than the proposed cooperative scheme. Another drawback of 4 hops transmission is the transmission delay because it requires 4 phases of transmission instead of 2 phases of the proposed cooperative scheme.

[8] R. Saravanakumar, S. Susila, and J. Raja, “An energy efficient cluster based node scheduling protocol for wireless sensor networks,” in 10th IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT), 2010. IEEE, 2010, pp. 2053–2057. [9] A. Sendonaris, E. Erkip, and B. Aazhang, “User cooperation diversity. Part I. System description,” IEEE Transactions on Communications, vol. 51, no. 11, pp. 1927–1938, 2003. [10] C. Xi-biao, C. Hong-kui, Y. Ling, and N. Fang-lin, “Virtual miso based energy-efficient broadcasting in clustered wireless sensor networks,” in 6th International Conference on Wireless Communications Networking and Mobile Computing (WiCOM), 2010. IEEE, 2010, pp. 1–4.

V. C ONCLUSION Cooperative MISO and relay techniques provide attractive benefits for distributed wireless sensor network when diversity gain can be exploited to reduce the transmission energy consumption. The energy efficiency of cooperative MISO and Relay can be employed in cluster based WSN in order to increase the cluster size and the energy consumption in same time. The energy efficient scheme using cooperative MISO and Relay techniques for two way data transmission in cluster based WSN has been proposed in this paper. Simulation and energy calculation prove that the proposed scheme has a much lower energy consumption in comparison with the traditional multi-hop transmission scheme. In cluster based WSN context, the proposed scheme can increase the maximum communication distance between the cluster head and sensor nodes for the same energy consumption of multi-hop transmission scheme, so increases the cluster size of network. ACKNOWLEDGMENT This research was supported by the Vietnam’s National Foundationfor Science and Technology Development (NAFOSTED) (No. 102.01-2011.22). R EFERENCES [1] S. Cui, A. J. Goldsmith, and A. Bahai, “Modulation optimization under energy constraints,” Anchorage, AK, USA, May 2003, pp. 2805 – 2811. [2] S. Cui, A. Goldsmith, and A. Bahai, “Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks,” IEEE Journal on Selected Areas in Communications, vol. 22, no. 6, pp. 1089–1098, 2004. [3] M. Dohler, E. Lefranc, and H. Aghvami, “Space-time block codes for virtual antenna arrays,” in The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, vol. 1, 2002, pp. 414–417. [4] L. Guo, W. Wang, J. Cui, and L. Gao, “A cluster-based algorithm for energy-efficient routing in wireless sensor networks,” in International Forum on Information Technology and Applications (IFITA), 2010, vol. 2. IEEE, 2010, pp. 101–103. [5] J. Laneman and G. Wornell, “Energy-efficient antenna sharing and relaying for wireless networks,” in IEEE Wireless Communications and Networking Conference, WCNC, vol. 1, 2000, pp. 7–12. [6] ——, “Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks,” IEEE Transactions on Information Theory, vol. 49, no. 10, pp. 2415–2425, 2003. [7] T. Nguyen, O. Berder, and O. Sentieys, “Cooperative MIMO schemes optimal selection for wireless sensor networks,” 2007, pp. 85–89.

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