BER Performance Analysis of Cognitive Radio Physical Layer over Rayleigh fading Channel

Transcription

1 Internationa Journa of Computer ppications ( ) Voume 5 No.11, Juy 011 BER Performance naysis of Cognitive Radio Physica Layer over Rayeigh fading mandeep Kaur Virk Dr. B R mbedkar Nationa Institute of Technoogy, Jaandhar, India jay K Sharma Dr. B R mbedkar Nationa Institute of Technoogy, Jaandhar, India BSTRCT In this paper we anayze the Bit Error Rate (BER) performance of Cognitive Radio Physica ayer over Rayeigh channe under different channe encoding schemes, digita moduation schemes and channe conditions. The system outperforms with moduation technique as compared to other digita moduation schemes and the system is highy effective to combat inherent interferences under Rayeigh fading channe. The system shows improved BER on using encoding schemes with error rate reduced by 10% using Reed Soomon (RS) encoding, 95% reduction on using Convoution encoding and 98% error reduction on appying RS with Convoution encoding. It has been anticipated from the simuation study that the performance of the communication system degrades with the increasing of noise power. Keywords Cognitive Radio, Bit error rate, dditive White Gaussian Noise, Reed Soomon encoding, Convoution encoding. 1. INTRODUCTION Wireess technoogy is embedded in our daiy routine aptops, ce phones, sensors a are wireess devices and use a finite amount of radio spectrum. s the number of devices increase, they compete for bandwidth and the service eve provided to them is degraded. Moreover, traditiona fixed spectrum aocation poicy can no onger meet the needs and services of the wireess users. ccording to Federa Communications Commission (FCC), tempora and geographica variations in the utiization of the assigned spectrum range from 15% to 85% in current spectrum aocation poicies [1]. So, we need to find out ways to aow wireess devices to efficienty share the airwaves. Cognitive Radio (Dynamic Spectrum ccess) has been proposed as a potentia soution for spectrum inefficiency probems []. Cognitive Radio paradigm shifts the way the spectrum is used and this presents many chaenges across various ayers of cognitive radio. Cognitive Radios are quite different from traditiona wireess radios, so the cognitive radio ayers perform additiona functionaity aong with functions of the conventiona wireess radios. This paper presents physica ayer anaysis of BER performance over a Rayeigh channe with WGN noise. We use a Time Division Mutipe ccess () system for icensed users aong with Orthogona Frequency Division Mutipexing (OFDM) and non- persistent Carrier Sense Mutipe ccess () system for unicensed users who opportunisticay use the ide icensed spectrum. Various digita moduation schemes used are,,,, and. RS and Convoution encoding schemes are used with varying vaues of Signa to Noise ratio (SNR) to compute Bit Error Rate (BER). The paper is organized as foows: Section describes the physica ayer of cognitive radio, Section 3 presents the simuation resuts and finay, the paper is concuded in Section 4.. PHYSICL LYER OF CR The physica ayer in cognitive ayer is responsibe for: 1) Spectrum sensing ) Reconfiguration 3) Change of operation parameters Figure 1. Cognitive Radio Layers Spectrum sharing is detecting unused spectrum bands. Reconfiguration is done when a icensed user appears whie unicensed user is using its frequency band and operation parameters (such as frequency, power and moduation) are changed to adapt to new operating environment [3]. Figure 1 shows the various ayers of cognitive radio aong with physica ayer functions. Cognitive radio (CR) promises to increase spectrum usage by supporting secondary users to share icensed bands [4]. Licensed users of CR are caed primary users and the unicensed users are caed secondary users. CR supports user access to the icensed spectrum as a secondary user when and where channes are detected ide [5]. 5

2 BER of BER of BER of overa channe Internationa Journa of Computer ppications ( ) Voume 5 No.11, Juy ccess Schemes Mutipe access schemes used in CR are: contention-based nonpersistent carrier sense mutipe access () for secondary users, and contention-free time division mutipe access () for primary users [6]. Orthogona Frequency Division Mutipex (OFDM) is considered the idea signa structure for wideband cognitive radio systems [7] In an OFDM system, the data is divided into mutipe parae sub streams at a reduced data rate, and each is moduated and transmitted on a separate orthogona subcarrier. This increases symbo duration and improves system robustness. is used to characterize the primary user who has the icense to access channe whenever they have information to send. is a contention-free mutipe access scheme which usuay empoys a centra entity (e.g. base station) to aocate capacity to individua users. It aows severa users to share the same frequency channe by dividing the signa into different time sots. It provides guaranteed reserved capacity and is commony used in packet-based communication systems, notaby sateites and in the GSM standard. The strict sot reservation process makes it a suitabe exampe of a primary user system mutipe access scheme. is used to describe the behavior of a CR secondary user that has the abiity to sense and access a free channe. is a contention-based mutipe access scheme where individua users make their own decisions on how and when to access a channe. The carrier frequency is sensed by each of mutipe stations, or nodes, to determine network avaiabiity before accessing the medium to transmit data. Each station must monitor the network to determine if a coision has occurred and the data require retransmission. In a non- persistent, a node transmits, if the medium is ide. If the medium is busy, the node waits a random amount of time before again sensing the medium. is naturay suited to distributed networks and is currenty empoyed in the IEEE WLN standard. The abiity to avoid ongoing transmissions through sensing makes it a suitabe exampe of a secondary user system mutipe access scheme [8]. 3. SIMULTION RESULTS The moduation schemes used for simuation are,,,, and. Forward error correction (FEC) encoding schemes used are convoutiona encoding and RS encoding. MTLB is used for simuation. The system is observed by separatey using convoutiona and RS encoding and then using them in combination using inter eavers. Simuation resuts are shown for, and overa channe. channe shows the resuts for and system combined together. In a the cases, the system provides degraded performance in 16 PSK and satisfactory performance in moduations. Figure through 5 show the BER performance of data through CR physica ayer under six types of digita moduation schemes on Rayeigh fading channe with WGN noise Figure. BER simuations for CR over Rayeigh channe for overa channe for system for system 6

3 BER of overa channe BER of BER of overa channe BER of Internationa Journa of Computer ppications ( ) Voume 5 No.11, Juy 011 Figure above shows the BER obtained at SNR vaues ranging from to 16 db. Figure gives the BER of overa channe and and perform better among a the moduation schemes with BER vaue x 10 - and x 10 - respectivey. Figure gives the BER vaues of system. BER of at SNR 6 db is x 10 - and for is x 10 - for. Figure shows the vaues of BER for a system and vaue of BER at SNR 6 db for better performing is x 10 - and for is.5466 x Figure 3. BER simuations for CR using RS encoded system over Rayeigh channe for overa channe for system for system Figure 3 above shows the BER obtained at SNR vaues ranging from to 16 db for RS encoded Rayeigh channe. Figure 3 gives the BER of overa channe and perform better among a the moduation schemes with BER vaue x Figure gives the BER vaues of system. BER of at SNR 6 db is 4.83 x 10 - for. Figure shows the vaues of BER for a system and vaue of BER at SNR 6 db for best performing is x perform better among a moduation schemes. The system shows 10% improvement using RS encoding. BER vaues for over Rayeigh channe is x 10 - and improved BER using RS encoding is x

4 BER of BER of BER of BER of BER of overa channe Internationa Journa of Computer ppications ( ) Voume 5 No.11, Juy Figure 4. BER simuations for CR using 1/3 convoutiona encoded system over Rayeigh channe for overa channe for system for system The simuation resuts for convoution encoded Rayeigh channe are shown in figure 4. Figure 4 shows the improved resuts for overa channe with the improved vaue of BER as 4.74 x. Improved vaue for system at SNR 6 db is 4.74 x and for system is 0 as shown in figure 4 and respectivey. The BER vaues for moduation scheme show improvement with vaue for Rayeigh channe as x 10 - and for convoution encoded system as 4.74 x. Convoution encoding removes bit errors and the system shows 95% improvement. The simuation resuts for RS and convoution encoded Rayeigh channe are shown in figure 5. Figure 5, and show the improved resuts for overa channe, and system with the improved vaue of BER as 0.53 x, x and 0 at SNR 6 db respectivey. RS encoding eiminates bock errors and convoution encoding removes bit errors and the system shows 98% improvement Figure 5. BER simuations for CR using RS and 1/3 convoutiona encoded system over Rayeigh channe for overa channe for system for system Tabe 1 beow shows the BER vaues obtained using various moduation and encoding schemes. The owest vaues of BER obtained are highighted. 8

5 Internationa Journa of Computer ppications ( ) Voume 5 No.11, Juy 011 Tabe 1. BER vaues for different moduation schemes for CR using Rayeigh BER vaues Rayeigh RS Encoding Convoution Encoding RS with Convoution Encoding SNR = 6 db x 10 - x 10 - x 10 - x 10 - x x x 10 - x x x 10 - x x x x x x 10 - x 10 - x x 4.74 x x x x x 10 - x 10 - x 10 - x 10 - x 10-5 x x 10-8 x x x x x x 10 - x 10-3 x x 10 - x x x 10-8 x x 10 - x 10-3 x x x 10-6 x x x 10-5 x x 10 - x 10 - x 10-9 x 10-5 x 10-9 x x 10-16Q M x 10 - x 10 - x 10 - x 10 - x 10 - x 10 - x 10 - x x 3.66 x x 10 - x CONCLUSION In this paper, the BER performance of data through CR physica ayer is shown using RS, Convoutiona channe coding and different digita moduation schemes. range of system performance highights the impact of digita moduations under RS and Convoution coding under Rayeigh fading channe with WGN noise. The system shows improved performance on using encoding schemes. The enhanced BER is 10% for RS encoding, 95% for convoution encoding and 98% for RS combined with convoution encoding scheme. In the context of system performance, it can thus be concuded that the impementation of moduation with RS and convoution channe coding technique together provides satisfactory resut among the digita moduation schemes with imited SNR. 5. REFERENCES [1] Danijea Čabrić, Robert W. Brodersen Berkeey, Physica Layer Design Issues Unique to Cognitive Radio Systems, Wireess Research Center, University of Caifornia at Berkeey, US. [] Wang Weifang, Denia of Service ttacks in Cognitive Radio Networks, nd Conference on Environmenta Science and Information ppication Technoogy,010 IEEE. [3] Mitoa J., Maguire G.: Cognitive radio: making software radios more persona, IEEE Pers. Communications, 1999, 6, (4), pp [4] Xueying Zhang, Cheng Li, The security in cognitive radio networks: survey,009. [5] Peha J. M.: pproaches to spectrum sharing, IEEE Communications Mag., 005, 43, (), pp [6] Pahavan k., evesque a.h.: Wireess information networks, Wiey Series in Teecommunications Signa. [7] Haiyun Tang, Some physica ayer issues of wideband cognitive radio systems, 005, IEEE. [8] Zhuo Yang; Yu-Dong Yao; Di Zheng,010 for primary users and for secondary users in a cognitive radio network, Wireess and Optica Communications Conference (WOCC), th nnua. [9] Zhuo Yang,, Investigations of mutipe access protocos in cognitive radio networks