Analysis of BER v/s SNR at WiMAX Physical Layer Deepa.N.P Assistant professor, Dept of ECE DayanandaSagar College of Engineering, Bengaluru, ndia [email protected]

PriyaMudhol M.techstudent ,Dept of ECE Dayanandasagar college of Engineering Bengaluru, India [email protected]

ABSTRACT In this recent era wireless communication industries have focused on the uses of broadband system having high quality functions. Because of this issue new advances with high transmission capability technologies are designed.The broadband wireless access turns into the best approach to satisfy the high business interest for expanding the internet connection.WiMAX ("Worldwide Interoperability for Microwave Access") is a broadband wireless technology is developed to meet the growing demand of increased data rate and accessing the internet at high speeds as well as low cost maintnance. It isbased on the IEEE 802.16-2004 standard family. In this system allows using an efficient bandwidth in a wide frequency range, and last mile solution for broadband internet access. Basic application of WiMAX is for MAN/WAN base stations and link stations. It delivers the maximum range (50 km) and higher data rates (up to 75 Mbps) than Wi-Fi. The aim of this paper is to analyze and simulate WIMAX OFDM system using different modulation technique. MATLAB software is used to simulate and analyze the WIMAX OFDM system. The simulation results include the performance analysis based on bit error rate (BER) versus signal to noise rate (Eb/No). Keywords-WiMAX, OFDM, BER, SNR, Modulation schemes I.

INTRODUCTION

WiMAX (Worldwide Interoperability for Microwave Access) is a wireless broadband access in wireless Metropolitan area network. WiMAX belongs to IEEE 802.16 standard family [1].There are two types of WiMAX, Fixed WiMAX (IEEE 802.16d) and Mobile WiMAX (IEEE 802.16e) both work in Line of sight and Non line of sight wireless connectivity.IEEE 802.16 standard provides Wide range coverage and high speed communication for rural areas, security, sophisticateand last mile Broadband services. DSL or Cable infrastructures are not available to remote rural areas so Broadband wireless access provides flexible and cost effective solution for this issue. WiMAX offers wireless backhaul network it provides internet access to home, small and medium business customer, campus and also to Wi-Fi hot spots and base station.WiMAX provides data rates up to 70Mbps and large geographical area between base station (BS) and subscriber station (SS) covers up to 50km for fixed WiMAX and for Mobile WiMaX up to 5-10km [7]. WiMAX system comprises of two sections: A. WiMAX Base station: Base stations are frequently called WiMAX tower or Booster which comprise of an electronic device and work like as GSM network. The base station broadcasts radio frequency signal to the receiver end. Base station is may be transmitter or receiver provides services as a network hub. The WiMAX base station connected by one base station to another base station with high speed microwave link which is called as backhaul. Base station manages several subscriber stations. B. WiMAX receiver: WiMAX receiver receives the radio frequency signal from the WiMAX base station and provides connection to the WiMAX network. WiMAX receiver is all called as customer premises equipment (CPE); these devices are usually a Wireless USB modem, laptops, mobiles or computers. WiMAX subscriber can be indoor or outdoordepending on the available distance to the nearest WiMAX base station tower. WiMAX supports two types of services are Line of Sight which uses frequency range of 10-66GHz and Non-Line of Sight of 2-11GHz [2]. It works in point to point (P2P) and point to multi point (P2MP) modes. Physical layer and MAC layer (Medium access control) are the two layers of WiMAX system. The physical layer of WiMAX is based on OFDM. Several researchers thinks that WiMAX can bring the new dimension broadband network for wireless data transmission but there are some limiting factors for transmitting high data rates over medium including fading channel interference. The purpose of this paper is to implement the

WiMAXphysical layer based on OFDM and transmit data at lower bit error rate and higher efficient data over channel using forward error correction (FEC) as concatenation of Reed Solomon and convolution codingmethods to decrease the BER and improves its efficiency. The performance of system is increase by using coding technique, cyclic prefix and interleaving techniques. In this paper we concentrated initially to analyze the basic concept of WiMAX, its standards, and its other technologies. Performance WiMAX system is analyzed using different modulation technique such as BPSK, QPSK, QAM with different SNR and presented a curves of BER versus SNR. The OFDM modulation technique used is used in WiMAX system because of its spectrally efficient modulation due to its orthogonality principle. The main advantage of using OFDM are bandwidth efficiency, reduces intercarrier interference (ICI) and also reduces inter symbol interference (ISI).The performance analysis of WiMAX physical layer is done by using MATLAB software.

Figure 1: WiMAX Environment II.

BASICS OF WIMAX TECHNOLOGY

In 1998 the Institute of Electrical and Electronic Engineers (IEEE) group was introduced the WiMAX technology based on IEEE802.16 standardto develop an air-interface standard for wireless broadband. Initially this group was focused on the development of LOS based point to multipoint broadband system to operate in the frequency range of 10-66GHz millimeter wave band. The main goal was to develop WiMAX system to cover the rural areas where DSL and cable infrastructure in not available. In December 2001 the first version of the IEEE 802.16 standard was proposed and approved. The present version of standard IEEE 802.16d Fixed WiMAX was approved in June 2004with transmission scheme of single carrier and FFT size of OFDM 256 and 2048. The IEEE 802.16e Mobile WiMAX was approved in December 2005 and modified as scalable OFDMA with transmission scheme of single carrier, FFT size of OFDM 256 and scalable OFDMA of FFT size 128,512, 1024 or 2048. These variable sizes of FFT allow for optimum operation of system over a wide range of channel bandwidth and radio condition. A. Features of WiMAX  Interoperability: This is main future of WiMAX. WiMAX maintains and certified as IEEE standard 802.16 because it provides independency to selects the product from different customers and it will be deployed it to various Networks.  Long Range: It covers large geographical area of range around 50 Km for LOS and 10Km for NLOS.  Mobility: seamless handover is supported by mobile WiMAX and it also extends battery life by power saving mechanism.  Security: Advanced Encryption Standard (AES) is been used by WiMAX to provide robust privacy and key management, it also gives an authentication to any user by Extensible Authentication Protocol (EAP).  Last mile connectivity:DSL and cable infrastructure are not available in rural areas, this problem is solved by broadband wireless connection.  Quality of service: WiMAXsupports the multimedia application. Eachterminal consists of multipleconnections and it supports large number of users, these specifications are designed by WiMAX MAC. B. WiMAX Architecture The main components of WiMAX architecture are Base station and subscriber station and some other components are MS, ASN, CSN and CSN-GW etc. To achieve the conditions of the IEEE 802.16 standard air interference, the WiMAX Forum’s network working group proposed a network reference model. The network reference model is divided in to three parts to support the WiMAX Fixed, Nomadic and Mobile network.

Figure 2: WiMAX network architecture  Mobile station (MS): It is connected to end users who access the Mobile network.It is a convenient station ready to move to wide territories and perform information and voice communication. It has all the fundamentals of user equipment such as an antenna, amplifier, transmitter, receiver and tools required to perform the wireless communication. Some examples of the Mobile stations are GSM, CDMA and WCDMA.  Access service Network:It is under the Network Access Provider (NAP), produced with one or more base stations and ASN gateways which generates wireless access network.co-ordination between data and network element is maintained by ASN gateway. All services are accessed by ASN with Mobility and efficient scalability.  Connectivity service network: It connects the IP connectivity to the Internet or other public or corporate networks. It is provides each vendor policy management, address management, location management between the ASN and employs the QOS, roaming and security. III.

WIMAX PHYSICAL LAYER SIMULATION MODEL

In this paper we present the WiMAX IEEE 802.16e physical layer based on OFDM simulation model implemented by MATLAB software. The connection set up of physical layer is responsible for transmitting the bit sequence between the communication devices. There are two types of transmission techniques in WiMAX 802.16 PHY layer, they are OFDM and OFDMA and these both have frequency band of 2-11 GHz and uses the TDD and FDD. WiMAX based on OFDM provides high speed data transmission and for multimedia applications. The simulation model mainly consists of three stages, Transmitter, Channel and Receiver.

Figure 3: Work flow of WiMAX Physical layer

The specification of WiMAX physical layer based OFDM are given as the transmitter block consists of Randomized data, FEC, Modulation and OFDM transmitter (IFFT) and Additive White Gaussian Noise is used as channel and the receiver consist of OFDM receiver (FFT),Demodulator, Decoder (Viterbidecoder,RS decoder). A. Randomization: The first block of transmitter consists of randomization which generates the input data on each burst. The purpose of using randomization is to avoid long sequence of ones and zeroes. The Pseudo Random Binary Sequence (PRBS) is used to generate random input data by using a 15 stage shift register with generator polynomial and XOR gate. B. Forward Error correction: Forward Error correction is concatenation of Reed Solomon (RS) Coding and Convolution coding. The first layer is RS codes are block codes used for correcting burst of errors and second layer is convolution codes are used for correcting the random errors formed while transmission in multipath channels.  Reed Solomon code: The RS code in the format of (N, K, and T), where N is Number of Bytes, K is Data Bytes and T is Number of Bytes to be corrected. This process based on Galois Field of computation for calculating the redundant bits. Here WiMAX uses fixed RS encoding technique based of Galois field (28) which indicates as RS (N=255, K=239,T=8)  Convolution coding: it is used for correcting the random errors in transmission over channel. The code rate is ½, a constraint length is 7. At the receiver the convolution code is decoded by using Viterbi decoder. C. Modulation: Modulation technique is used to minimize the effect of communication channel noise by transforming signal waves. This is done in order to ensure that the received data can be demodulated to give back the original data. This is achieved by modulating the data by a desirable modulation technique. In this paper we use the following different modulation scheme Table 1: Mandatory channel coding per Modulation scheme

D. OFDM Transmitter: The OFDM transmitter consist of serial to parallel converter which converts data bits from serial to parallel form. Next the Inverse Fast Fourier transform (IFFT) is performed to convert the frequency domain signal to time domain, an IFFT converts the number of complex data points, of lengths of power of 2, in to the same number of point in time domain. The total number of sub bands in spectrum is determined by the number of subcarriers. To overcome the problem of Inter symbol Interference a cyclic prefix consists of copy of last N samples is appended at the beginning of the OFDM frame. E. Channel: This is channel in which data is transmitted in presence of noise and it effect the signal causes the distortion in the available data. Here we used an AWGN channel to simulate the noise. F. OFDM Receiver: At the receiver the cyclic prefix is removed and convert back to parallel to serial. Next the signal is sent to the Fast Fourier Transform (FFT) to convert it in to frequency domain. The output of FT is first M sample of the output. After conducting reverse FEC and Derandomizer, it retransmits the original transmit signal. G. Demodulator: This is technique in which original data retrieved from modulated signal which receives at receiver end.

H. Viterbi Decoder: The main purpose of Viterbi decoder is to decode the convolutional encoded data. The Viterbi algorithm reduces the computational load by taking advantage of the special structure of the trellis code. IV.

SIMULATION RESULTS

The various modulation techniques using BPSK, QPSK, QAM 16 and QAM64 are used to simulate the WiMAX model. The result graph of each case modulation is plotted bit error rate (BER) vs. Signal to noise ratio (EbNo). The results of simulation of WiMAX physical based on OFDM are shown in the following figure. The result gives the comparison BER vs. SNR for each modulation. The performance of WiMAX is determined by calculating the bit error rate and signal to noise ratio between the unmodulated signal data at the receiving end

Figure 4: Plot of BER VS SNR for BPSK-WiMAX

Figure 5: Plot of BER VS SNR for QPSK-WiMAX

Figure 6: Plot of BER VS SNR for QAM 16-WiMAX

Figure 7: Plot of BER VS SNR for QAM 64-WiMAX V.

CONCLUSION

In this paper firstly provide information about the WiMAX standard, architecture, specifications and proposes the Simulation of WiMAX physical layer model developed using MATLAB. This model represents the analysis of the WiMAX Performance by using AWGN channel with different modulation schemes and is evaluated over OFDM system. The proposed modulation schemes is based on the Eb/No (dB) of the channel. Receiver gets the originalinformation as transmitted from transmitter. The result gives the comparison of different modulation schemes used in WiMAX. Binary Phase shift keying (BPSK) provides less data rates, less bandwidth and very power efficient. Quadrature Amplitude Modulation (QAM 64) provides high data rates and requires high bandwidth. Quadrature Phase shift keying (QPSK) and QAM 16 provides the in between data rates of BPSK and QAM 64. In analysis of performance under BER conditions BPSK gives least values of BER, QAM 64 gives largest values of BER and QPSK AND QAM 16 gives the middle values of BPSK and QAM 64. So QAM 64 provides highest data rates. REFERENCES [1] [2] [3] [4]

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