Sri Krishna College of Engineering and Technology, Coimbatore. Sri Krishna College of Engineering and Technology, Coimbatore.

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1 ENERGY EFFICIENT COEXISTENCE PROTOCOL FOR COGNITIVE RADIONETWORKS 1 M.S.Rihana, 2 Mr.N.Sathish 1 PG Student, Department of ECE, Sri Krishna College of Engineering and Technology, Coimbatore. 2 Assistant Professor, Department of ECE, Sri Krishna College of Engineering and Technology, Coimbatore. Abstract-Due to increased spectrum utilization, one prominent way to minimize its scarcity is by using Cognitive Radio (CR) Network. Cognitive radio works smartly by helping secondary user to access the unused spectrum without causing any disturbances to the primary user. This strategy of cognitive radio is utilized in the networking sector to achieve efficiency giving rise to CR networks. The protocols designed for the CR networks provide great challenge in improving the efficiency of the entire network. In this paper an energy efficient protocol is designed for coexistence model of primary and secondary system employing Hybrid Automatic Repeat Request (HARQ) technique in block fading channel. When the primary system retransmits the data signal, the secondary system serves as a relay for the retransmission of the primary system and simultaneously transmits its data signal. Energy of signal transmission of this protocol is further reduced by incorporating minimum energy property used in Simple Minimum Energy for Communication Network (SMECN) protocol. The experimental results shows this coexistence protocol significantly reduces energy consumption and enhances lifetime of the network. Throughput, end to end delay and transmission energy of signal are also analyzed. (FCC) defines a cognitive radio as a radio that can change its transmitter parameters based on interaction with the environment in which it operates [3].CR is evolved from the Software Defined Radio (SDR) whose functions depend on the program codes and incapable of acting on its own. The idea for Cognitive Radio (CR) has come out of the need to utilize the radio spectrum more efficiently, and to be able to maintain the most efficient form of communication for the prevailing conditions[2] [3]. A cognitive radio may be defined as a radio that is aware of its environment and the internal state and with knowledge of these elements and any stored pre-defined objectives can make and implement decisions about its behavior. When Primary user (licensed user) is not using the licensed band Cognitive Radio senses spectrum hole [3] and allows the secondary user (unlicensed User) to access the licensed band of primary without causing any interference to primary. Index Terms Cognitive Radio,CR network, HARQ, Minimum energy property, Energy efficient protocols. A. Cognitive Radio I. INTRODUCTION Cognitive Radio tops the recent trends in civil, military and network fields due to its capability to adapt itself into the environment it works in.the Federal CommunicationsCommission 189

2 Improved coverage: By setting up cognitive radio network, it is possible to relay data from one node to the next. In this way power levels can be reduced and performance maintained. There are three basic operational models used to implement the CR networks: Overlay model Underlay model Cooperation model Fig. 1.Cognitive Radio and Spectrum Hole A spectrum hole is a band of frequencies assigned to a primary user, but, at a particular time and specific geographic location, the band is not being utilized by that user. Advantages of CR over conventional radio are Highly reliable communication whenever and wherever needed; Efficient utilization of the radio spectrum. Cognitive radios have the ability to monitor, sense, and detect the conditions of their operating environment, and dynamically reconfigure their own characteristics to best match those conditions. B. Cognitive Radio Network Cognitive radio networks (CRN) are an innovative approach to wireless engineering in which radios are designed with an unprecedented level of intelligence and agility. This advanced technology enables radio devices to use spectrum in entirely new and sophisticated ways. It can identify potential impairments to communications quality, like interference, path loss, shadowing and multipath fading. They can then adjust their transmitting parameters, such as power output, frequency, and modulation to ensure an optimized communications experience for users. It is a wireless communication in which the transmission or reception parameters are changed to communicate efficiently without interfering with licensed users (Primary User). The use of a cognitive radio network provides a number of advantages when compared to cognitive radios operating purely autonomously: In the Overlay model, the secondary system senses the temporal spectrum holes in the licensed bands, and then uses these holes to avoid interference to the primary system [1]. Although this approach can improve the spectral efficiency, the improvement depends on the accuracy of spectrum sensing. In the underlay model, the secondary system coexists with the primary system and can simultaneously use the licensed bands while the primary system occupies the bands [1]. In this case, the secondary system works under the interference constraint of the primary system to preserve the quality of service (QoS) requirement of the primary system. In the cooperation model, the secondary system cooperates with the primary system and improves the QoS of the primary system by using cooperative diversity. As compensation for cooperation, the secondary system can access the licensed bands of the primary system [1]. This model corresponds to less interference; hence it is widely used than other models. C. Hybrid Automatic Repeat Request In wireless communication systems, the Automatic Repeat Request (ARQ) and Hybrid ARQ (HARQ) have been considered to be principal techniques to provide high reliability to users. The HARQ is a retransmission technique that employs forward errorcorrection (FEC) code to improve reliability. The HARQ is the use of conventional ARQ along with an Error Correction technique called 'Soft Combining', which no longer discards the received bad data (with error). With the 'Soft Combining' data packets that are not properly decoded are not discarded anymore. The received signal is stored in a 'buffer', and will be combined with next retransmission. In fig.2, the transmission continues, and is sent a package (2). The package (2) arrives, but let s considers now that it arrives with errors. If the package (2) arrives with errors, the receiver sends a 'NACK'. Improved spectrum sensing: By using cognitive radio networks, it is possible to gain significant advantages in terms of spectrum sensing. 190

3 that H-ARQ provides a significant rate advantage relative to a system not using HARQ at reasonable SNR levels. Moreover using HARQtechnique improves Long-time average Throughput (LAT) which improves the efficiency of the network. D. Problem Statement Fig. 2. HARQ Only now this package (2) (bad) is not thrown away, as it is done in conventional ARQ. Now it is stored in a 'buffer'. Continuing, the transmitter send another package (2.1) that also (let's consider) arrives with errors. We have them in a buffer: bad package (2), and another package (2.1) which is also bad. By combining these two packages ((2) + (2.1)) we have the complete information thus ACK is send. The authors of [5] has proposed a cooperateandaccessspectrum sharing protocol is proposed where the secondary system alternates between cooperation and access modes. In the cooperation mode, the secondary system serves as a relay to assist the primary transmission, and in return accumulates credits. The credits allow the secondary system to gain spectrum access by exploiting the ARQ retransmissions of the primary system. We show analytically that through the proposed credit system, as long as the credits accumulated in cooperation mode compensate for the degradation in primary performance during access mode, an equal or higher average throughput is achieved for the primary system than in the case without spectrum sharing, while providing spectrum access opportunities for the secondary system. There are two widely-used HARQ schemes inducing the buffer to store and combine the received information: HARQ with Chase Combining (HARQ-CC) Improving the overall efficiency of the CR networks is stilla challenge though many protocols are designed to suit different scenarios. Reducing the energy consumption in CR networks is one way to improve efficiency. A protocol is designed such that when primary is unable to send its data secondary comes into action help primary, in return secondary can send its data as well, yielding better performance. Here Secondaryacts as relay is assumed to senses the NACKsend by primary. The remainder of this paper is organized as follows. In Section II, proposed system is presented. In Section III, Coexistence protocol implementation. In Section IV, simulation resultsare given.in Section V, conclusions are drawn.in Section VI, future scope is given. II. PROPOSED SYSTEM The CR network considered here has primary system with Primary Source (PS) and Primary Destination (PD) and secondary system with Secondary Source (SS) and Secondary Destination (SD) over block-fading channel. Primary system employs a HARQ. The network consists of a pair of PS and PD and a pair of SS and SD as shown in fig 3. HARQ with Incremental Redundancy (HARQ-IR) In the HARQ-CC scheme, the source sends the same coded data packet for (re)transmissions. The destination stores the coded data packets for the (re)transmission and combines them before decoding [6]. In the HARQ-IR scheme, the source transmits different parity of the coded data packet for each (re)transmission, and the destination accumulates the parities of the coded data packet during the (re)transmission. HARQ-IR generally achieves higher performance and data rates than HARQ-CC [7]. The use of HARQ with 'Soft Combining' increases the received Eb/Io effective value for each retransmission, and therefore also increases the likelihood of correct retransmissions decoding, in comparison to conventional ARQ. Authors of [7] [10] has studied performance of HARQ and proved Fig. 3. System Model The secondary systems SS is assumed to correctly estimate the channel of SS-PD, SS-SD, and PS-PD links from reporting channels. The nodes perfectly decode the ACK and NACK signals and that ACK/NACK feedback delay is ignored. It is assumed that continuous modulation scheme and a capacity achieving channel coding are used The CSIs are perfectly estimated by all the receiving 191

4 nodes and the reporting signals are successfully decoded. All the links among the PS, PD, SS and SD are represented as normalized Rayleigh channels with block-fading, i.e.,channel gains in the initial transmission and retransmission are independent. When the primary destination fails to decode the data send by primary source, secondary user helps by retransmitting the primary data. In return for this favor, primary user lends the spectrum for transmitting secondary s data creatind a win-win situation. The overall goal of this design is toimprove the efficiency of the network by reducing energy consumption of the signals in addition to secondary s spectrum utilization. III. IMPLEMENTATION AND ANALYSIS Fig. 4. Secondary overhears A. Protocol Description The coexistence protocol for this network consists of following description. During the transmission of primary source to destination, the secondary system overhears the ACK/NACK signals of the primary to evaluate the channel quality of the primary system. The protocol works as follows: During initial transmission, the PS transmits a data signal; the PD, SS and SD receives it. If the PD fails to decode the data signal, it sends an NACK signal to report the failure. After the SS and SD overhear the NACK signal of the PD, the SD decodes the data signal of the PS for the initial transmission. If decoding is successful, the SD sends an ACK signal to the SS as shown in fig. 4. If the SS successfully decodes the data signal, it is ready to cooperate with the primary system. During retransmission, while the PS transmits the additional parity of the data signal, the SS transmits the coded parity of the PS data signal and its own data signal simultaneously as shown in fig. 5. Fig. 5. Secondary sends data to SD as well as primary s data to PD B. Parameter Analysis To calculate the performance of the network certain parameter like throughput, delay and transmission energy must be analyzed. These parameters give inference about the network model that is under study. Throughput is defined as the transmission rate (R) over the number of (re)transmissions until the data signal is successfully decoded. If the decoding of the data signal fails for the retransmission, the throughput is zero. The average throughput of the primary system with the secondary system should be no less than that of the primary system alone. Network Delayis an important design and performance characteristic of a computer network or telecommunications network. The delay of a network specifies how long it takes for a bit of data to travel across the network from one node or endpoint to another. It is typically measured in multiples or fractions of seconds. Delay may differ 192

5 slightly, depending on the location of the specific pair of communicating nodes. Delay is the difference between the time at which the sender generated the packet and the time at which the receiver received the packet. Σ ( arrive time send time ) / Σ Number of connections The lower value of end to end delay means the better performance of the protocol. Energy of Signal Transmission Energy modeling is a key element in wireless network simulation. In several simulation scenarios, the energy consumption at a particular node, or at a particular component of a node, is of interest. Further, energy consumption is an important metric for evaluating the performance of wireless network protocols. Also, if a protocol is energy-aware, i.e. its operation depends on the energy level, it cannot be effectively simulated without an energy model. The initial Energy is given in Joules (but you need not specify the unit) and the txpower, rxpower, sleeppower and idlepower are given the units in Watts (here also no unit need to be specified). Energy = Power * time Fig. 6.Throughput Throughput of the network is plotted against time (ms) and is shown in fig 6.Fig 7 shows the delay plotted for this model End to end DelayThe average time taken by a data packet to arrive in the destination is end to end delay. It also includes the delay caused by route discovery process and the queue in data packet transmission. Only the data packets that successfully delivered to destinations that counted. IV.RESULTS The coexistence protocol is implemented in Network Simulator 2.The simulation is time stamped for 50 seconds and the scenario consists of transmission of primary followed by the intervention of secondary nodes and slowly as time progresses the secondary node comes into action by transmitting data of its own as well as primary s data. As the time progress the secondary nodes try to send its data and its transmission of data packets to primary. This scenario presents few active secondary nodes in action to reduce the complexity. The analysis for this network is carried out by estimating various characteristics like throughput, end to end delay and transmission energy and graphs are plotted. Fig. 7. End to end delay The energy of signal transmissionis shown in fig

6 minimum energy property and through relay reduces the transmission signal energy and traffic to a considerable rate. To prove that total signal transmission energy of the network and other important parameters of network improve the efficiency better than existing model, analysis will be carried out and compared with existing network model. REFERENCES Fig. 8. Transmissiion Signal Energy V. CONCLUSION A protocol for the coexistence of the HARQ based primary and secondary systems over block-fading channels was implemented in NS2. In this protocol, if the PD fails to decode the data signal of the PS in the initial transmission, the SS serves as a relay for the primary system simultaneously transmits its data signal in the retransmission of the primary system. Analysis of the average throughput of the primary and secondary systems is carried out through their LATs. The closed-form solutions of the transmission rate and the fraction of the transmit power of the PS and SS is also obtained. The graph obtained by comparing throughput, power and transmission rate between PS, PD, SS and SD indicates by adjusting the fraction of the transmit power, the secondary system can provide the additional average throughput gain to the primary system. VI. FUTURE WORK The coexistence protocol implemented here consumes more energy in transmission of packets from source to destination. This affects power consumption and efficiency and hence reduces lifetime of the network. In order to overcome this problem, advanced location based routing protocol Small Minimum Energy Communication Network Protocol (SMECN) protocol is proposed. This protocol with [1] M Moon-Gun Song, Young-Jin Kim, Eun-Yeong Park, and Gi- Hong Im,(2014) Rate Adaptation and Power Allocation for Cognitive Radio Networks with HARQ-Based Primary System Senior Member, IEEE [2] S. Haykin, Cognitive radio: brain-empowered wireless communications, IEEE J. Sel. Areas Commun., vol. 23, no. 2, pp , Feb [3] J. Mitola, Cognitive radio: An integrated agent architecture for software defined radio, Dissertation, Royal Institute of Technology, [4] D. Kim, Y. Choi, S. Jin, K. Han, and S. Choi, A MAC/PHY crosslayerdesign for efficient ARQ protocols, IEEE Commun. Lett., vol. 12,no. 12, pp , Dec [5] Q. Li, S. H. Ting, A. Pandharipande, and M. Motani, Cooperate-andaccessspectrum sharing with ARQ-based primary systems, IEEE Trans.Commun., vol. 60, no. 10, pp , Oct [6] J.-F. Cheng, Coding performance of hybrid ARQ schemes, IEEETrans. Commun., vol. 54, no. 6, pp , Jun [7] P. Wu and N. Jindal, Performance of hybrid-arq in block-fading channels: a fixed outage probability analysis, IEEE Trans. Commun.,vol. 58, no. 4, pp , Apr [8] R. Narasimhan, Throughput-delay performance of half-duplex hybrid- ARQ relay channels, in Proc IEEE International Conference on Communications, pp [9] M. Levorato, U. Mitra, and M. Zorzi, Cognitive interference management in retransmission-based wireless networks, IEEE Trans. Inf.Theory, vol. 58, no. 5, pp , May [10] Q. Li, S. H. Ting, A. Pandharipande, and M. Motani, Cooperate-and access spectrum sharing with ARQ-based primary systems, IEEE Trans.Commun., vol. 60, no. 10, pp , Oct