50120130405012

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50120130405012

  1. 1. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING & ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME TECHNOLOGY (IJCET) ISSN 0976 – 6367(Print) ISSN 0976 – 6375(Online) Volume 4, Issue 5, September – October (2013), pp. 91-98 © IAEME: www.iaeme.com/ijcet.asp Journal Impact Factor (2013): 6.1302 (Calculated by GISI) www.jifactor.com IJCET ©IAEME MODELING AND SIMULATION OF PHYSICAL LAYER OF IEEE 802.22 OVER A MULTIPATH FADING CHANNEL Zarana Barot1 and Anil Kumar Sharma2 M. Tech. Scholar1, Professor & Vice Principal2, Department of Electronics & Communication Engineering, Institute of Engineering & Technology, Alwar-301030 (Raj.), India ABSTRACT IEEE 802.22, also known as Wireless Regional Area Network (WRAN), is the newest wireless standard developed for remote and rural areas. In this work, an overview of the standard, and more specifically its physical (PHY) layer is evaluated. For this purpose the PHY layer is modeled using SIMULINK tool and derived the received constellation mapping of the system for different code rates and modulation schemes with multipath noisy channel. In this paper Rayleigh multipath channel model is used in addition of AWGN channel to analyze the 802.22 PHY layer for likely practical conditions. Keywords: BPSK, IFFT, OFDM, VHF and WRAN. 1. INTRODUCTION A cognitive radio is a transceiver designed to use the best wireless channels in its vicinity [1]. Such a radio automatically detects available channels in wireless spectrum and accordingly changes its transmission or reception parameters to allow more concurrent wireless communications in a given spectrum band at one location. This process is a form of dynamic spectrum management. In response to the operator's commands, the cognitive engine is capable of configuring radio-system parameters. These parameters include "waveform, protocol, operating frequency, and networking". It functions as an autonomous unit in the communications environment, exchanging information about the environment with the networks it accesses and other cognitive radios (CRs). A CR "monitors its own performance continuously", in addition to "reading the radio's outputs"; it then uses this information to "determine the Radio Frequency (RF) environment, channel conditions, link performance, etc.", and adjusts the "radio's settings to deliver the required quality of service subject to an appropriate combination of user requirements, operational limitations, and regulatory 91
  2. 2. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME constraints". The Wireless Regional Area Networks (WRANs) are expected to operate primarily in low population density areas in order to provide broadband access to data networks.The WRAN systems will use vacant channels in the Very High Frequency (VHF) and Ultra High Frequency (UHF) bands allocated to the Television Broadcasting Service in the frequency range between 54 MHz and 862 MHz while avoiding interference to the broadcast incumbents in these bands. A typical application can be the coverage of the rural area around a village within a radius of 10 km to 30 km from the base station depending on its Equivalent Isotropically Radiated Power (EIRP) and antenna height. The Media Access Control (MAC) layer can also accommodate user terminals located as far as 100 km with proper scheduling of the traffic in the frame when exceptional RF signal propagation conditions are present. With the PHY implemented in this standard, WRAN systems can cover up to a radius of 30 km without special scheduling. in performance of their terrestrial television reception. Accordingly the use of IEEE 802.22 WRAN technology should enable more efficient use of the spectrum to be made as well as providing new services for users, especially in rural areas. A base station (BS) complying with this standard shall be able to provide high-speed Internet service for up to 512 fixed or portable customer premise equipment (CPE) devices or groups of devices within its coverage area assuming different quality of service (QoS) requirements for various CPEs, while meeting the regulatory requirements for protection of the incumbents. The standard includes cognitive radio techniques to mitigate interference to incumbents, including geo location capability, provision to access a database of incumbent services, and spectrum-sensing technology to detect the presence of incumbent services, other WRAN systems, and IEEE 802.22.1 wireless beacons.This work is based on the standard itself. In IEEE, before a standard is established proposal, for developing systems for newly developed technology, is discussed. A working group is formed which has many task groups working on a project related to the proposed technology. Ballot meeting are called to get vote on highly efficient implementation of the proposed technology. Finally, the standard is formed by taking vote of extinguished engineers, researchers, technical representatives of leading corporate bodies. Hence it is safe to say that the standard itself is very well tested. Still there can be many variations for testing methodologies. Under this assumption, this dissertation is done as an attempt to analyze the PHY layer for understanding behavior of PHY layer under various SNR values and channel variations 2. PHYSICAL LAYER OF 802.22 In order to meet the requirements for the overall 802.22 system, the physical layer maintains a high degree of flexibility. This is built in to the basic specification of the system. This work targets to analyze the PHY layer capabilities to survive in multipath environment [2]. One of the first characteristics is the modulation scheme. An OFDM (Orthogonal Frequency Division Multiplex) scheme has been adopted because the 802.22 WRAN system to provide resilience against multipath propagation and selective fading as well as a high level of spectrum efficiency and sufficient data throughput. To provide access for multiple users, OFDMA is used for both upstream and downstream data links [3][4]. OFDM is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. This means that when the signals are demodulated they will have a whole number of cycles in the symbol period and their contribution will sum to zero - in other words there is no interference contribution. The data to be transmitted is split across all the carriers and this means that by using error correction techniques, if some of the carriers are lost due to multi-path effects, then the data can be reconstructed. Additionally having data carried at a low rate across all the carriers means that the effects of reflections and inter-symbol interference can be overcome. It also means that single 92
  3. 3. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME frequency networks, where all transmitters can transmit on the same channel can be implemented [6]. IEEE 802.22 allows a variety of modulation schemes to be used within the OFDMA signal: QPSK, 16-QAM and 64-QAM can all be selected with convolution coding rates of 1/2, 3/4, and 2/3. The required modulation and error correction rates are chosen according to the prevailing conditions [4]. In order to meet the requirements for the individual users that may be experiencing very different signal conditions, it is necessary to dynamically adapt the modulation, bandwidth and coding on a per CPE basis. In order to be able to obtain the required level of performance, it has been necessary to the IEEE 802.22 to adopt a system of what is termed "Channel Bonding." This is a scheme where the IEEE 802.22 system is able to utilize more than one channel at a time to provide the required throughput. Often it is possible to use adjacent channels because in many countries the regulatory authorities and frequency planners allow two or more empty channels between stations transmitting high power signals as this prevents interference on the TV signals. These multiple free channels allow the use of contiguous channel bonding. In practice the maximum number of channels that are bonded is likely to be limited to three as a result of the front-end bandwidth limitations. To provide access for both upstream and downstream data, the form of duplex scheme that has been adopted is TDD. This has several advantages. First it only requires one channel to be used - FDD would not be viable because it would be more difficult to control two channels with sufficient transmit / receive spacing. Secondly the use of TDD enables dynamic change of the upstream and downstream capacity. The specification is for a system that uses vacant channels to provide wireless communication over a distance of up to 100 km, the propagation time over the first 30 km range being absorbed by the TTG at the PHY layer and the propagation time beyond 30 km being absorbed by proper MAC packet scheduling at the BS, as well as time buffers before and after the opportunistic bursts (ranging, BW request and UCS notification) and before and after the CBP burst [4].The OFDM System Design Requirements are available bandwidth, required bit rate, tolerable delay spread and Doppler values. The OFDM System design parameters are derived according to the system requirements. The requirement of the system design must be fulfilled by the system parameters. The various design parameters for an OFDM system are Number of subcarriers, Guard time (CP interval) and symbol duration, Subcarrier spacing and Modulation type per subcarrier. 3. PHYSICAL LAYER MODELING Fig 1. SIMULINK Schematic of IEEE 802.22 PHYSICAL Layer 93
  4. 4. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME Variable data rate block is used to generate random data input to the WRAN transmitter. The convolution encoder bank contains CC coders with different code rates. This block performs the Forward error correction operation on input data stream. Interleave Bank performs interleaving operation on the encoded bit stream. Modulator bank performs QAM modulation on the interleaved bit stream. It will output complex numbers assigned to a group of bits. Serial to parallel block is used to insert the pilot carriers and DC components to the bit stream and to convert the serial data into parallel data carriers which can be given as input to the IFFT block. The IFFT block computes the inverse fast Fourier transform (IFFT) of each channel of a P-by-N or length-P input, u. When the Inherit FFT length from input dimensions check box is selected, the input length P must be an integer power of two, and the FFT length M is equal to P. When the check box is not selected, P can be any length, and the value of the FFT length parameter must be a positive integer power of two. For userspecified FFT lengths, when M is not equal to P, zero padding or modulo-M data wrapping happens before the IFFT operation. Cyclic prefix insertion block adds the portion of input frame to its front end. Thus inserting a guard interval. The reshape function is used to convert the parallel data streams to serial bit stream. The wireless channel is used to insert noise in the OFDM modulated data. There are three options i.e. no noise, non dispersive multipath noise and dispersive multipath noise. The Multipath Rayleigh Fading Channel block implements a baseband simulation of a multipath Rayleigh fading propagation channel. This block is useful for modeling mobile wireless communication systems. The AWGN channel block adds white Gaussian noise to a real or complex input signal. When the input signal is real, this block adds real Gaussian noise and produces a real output signal. When the input signal is complex, this block adds complex Gaussian noise and produces a complex output signal. This block inherits its sample time from the input signal. Serial to parallel block at receiver performs inverse operation of parallel to serial block of transmitter. Cyclic prefix removes the cyclic prefix part from the input bit stream. FFT block performs the inverse operation of the IFFT block and will convert the time domain data to frequency domain. Disassemble OFDM frames converts the parallel data carriers to serial carrier. Demodulator Bank recovers digital bits from the modulation symbols. Deinterleaver Bank performs the deinterleaving operation on the demodulated data. Viterbi decoder Bank recovers the original information data inserted to by random data generator, by decoding the coded bitstream using viterbi decoder blocks SNR estimation takes input from demodulator bank and estimates Signal to Noise Ratio of the received signal. Mode Control takes input from SNR estimation block and changes the mode of the system accordingly. When SNR is higher then mode will be increased towards 8 and when SNR is lower the mode is decreased towards 1. Packet error rate calculation calculates the packet error rate by comparing the bits from random data generator and the Viterbi decoded data. This parameter shows the amount of information reached to the receiver. Manual mode control designed to configure the IEEE 802.22 Transmitter and Receiver according to the desired bit rate. There are total of 16 PHY modes [6]. For simplicity and compatibility check, in this work, only 8 modes are implemented. The change in mode is dependent on level of noise in the channel. The Transmitter and Receiver are configured to higher data rates if the channel noise is low and to lower data rates if the channel noise is high. 4. SIMULATION RESULTS The modes are designed to configure the IEEE 802.22 Transmitter and Receiver according to the desired bit rate. The change in mode is dependent on level of noise in the channel. If the noise is more in channel then the transmitter and receiver will use modes 1,2,3,4 for low data rates and if the noise is high in channel the transmitter and receiver will use 5,6,7,8 modes for higher Bit rates. The reason to use lower bit rates and modes for high noise in the channel is,if we send data with high bit rates in a channel when the noise is high, more bits will be lost. When we say transmitter and 94
  5. 5. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME receiver use Mode 1 we mean that the convolution encoder in Transmitter will be configured to code rate 1/2, modulator will use BPSK Modulation scheme and the data rate will be 4.54 Mbps. Similarly in Receiver the viterbi decoder will be configured to code rate 1/2 and the Demodulator will be configured to BPSK Demodulation. We have to use these modes in order to provide synchronization Transmitter and Receiver. If we don’t use any mode the transmitter may transmit data with different data rate and the Receiver may be configured to different data rate.Thus at Receiver we will not be able to recover any data from Transmitter. Table.1 shows the configuration of Physical blocks according to different modes [11]. Mode 1 Table-1-Configuration of Physical Blocks Code Rate Modulation scheme Bit rate (Mb/s) 1/2 BPSK 4.54 2 2/3 BPSK 6.05 3 3/4 QPSK 6.81 4 5/6 QPSK 7.56 5 2/3 16-QAM 12.1 6 3/4 16-QAM 13.61 7 2/3 64-QAM 18.15 8 5/6 64-QAM 22.69 After simulating model in 8 modes we get following results. By simulating different data rates we get result for different modes. Modes 1 and 2 are for BPSK modulation scheme and it’s code rate is 1/2 and 2/3 respectively. Bit rate is for Mode 1 is 4.54 and for Mode 2 are 6.05. The simulation corresponding to mode 1and 2 is shown in Fig. 2 and 3. Fig 2. Transmitted Constellation Fig 3. Received Constellation Modes 3 and 4 are for QPSK modulation scheme and it’s code rate is 3/4 and 5/6 Respectively. Bit rate is for Mode 3 is 6.81 and for Mode 2 is 7.56. The simulation corresponding to mode 3 and 4, is shown in Fig. 4 and 5. 95
  6. 6. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME Fig 4 Transmitted Constellation Fig 5 Received Constellation Modes 5 and 6 are for 16-QAM modulation scheme and it’s code rate is 2/3 and 3/4 Respectively. Bit rate is for Mode 5 is 12.1 and for Mode 6 is 13.61. The corresponding simulation is as shown in Fig. 6 and 7. Fig. 6 Transmitted Constellation Fig 7 Received Constellation Modes 7 and 8 are for 64-QAM modulation scheme and it’s code rate is 2/3 and 5/6 Respectively. Bit rate is for Mode 7 is 18.15 and for Mode 8 is 22.69. The corresponding simulation is as shown in Fig. 8 and 9. 96
  7. 7. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME Fig 8 Transmitted Constellation Fig. 9 Received Constellation 5. CONCLUSION AND FUTURE SCOPE In this paper the knowledge of WRAN technology is gained and also specifications of PHY layer of IEEE 802.22 are understood. We have studied the OFDM based technologies. We have developed and implemented a MATLAB SIMULINK based model of PHY layer of IEEE 802.22 to understand the PHY layer behavior in multipath environment. The Results are taken in the form of transmitted and received constellations. We can implement rest of 8 modes of PHY layer and also can perform a comparative analysis of other wireless standards like IEEE 802.11, 16 and 15 with IEEE 802.22 to exploit the future research scopes in the same direction. We can also implement the model in FPGA using HDL and Multiple Input Multiple Output (MIMO) architecture in IEEE 802.22 PHY for experimental study on performance. REFERENCES [1] [2] [3] [4] [5] [6] Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Policies and Procedures for Operation in the TV Bands (PDF). IEEE Std 802.11a, Part 22:Wireless RAN Medium Access Control (MAC) and Physical Layer(PHY) Specifications, Policies and Procedures for Operation in the TV Bands, 2011 N. Devroye, P. Mitran, and V. Tarokh, “Achievable Rates in Cognitive Radio Channels,” 39th Annual Conf. Info.Sci. and Sys., Mar. 2005. M. Ahmadi, E. Rohani, Pooya Monshizadeh Naeeni, and S. M. Fakhraie, “Modeling and performance evaluation of IEEE 802.22 physical layer,” in Proc., 2nd Internationadl Conference on Future Computer and Communication (ICFCC), Wuhan, China, pp. V3-62-66, May 2010. J. Mitola III and G. Q. Maguire Jr., “Cognitive Radio: Making Software Radios More Personal,” IEEE Personal Communications, vol. 6, no. 4, pp.13–18, Aug. 1999. S.Haykin, “Cognitive radio: brain-empowered wireless communications,” IEEE Journal on Selected Areas in Communications, vol. 23, Feb. 2005, pp. 201–220. 97
  8. 8. International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-6367(Print), ISSN 0976 - 6375(Online), Volume 4, Issue 5, September - October (2013), © IAEME [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] Mayank Mittal, Jaikaran Singh, Mukesh Tiwari, “Modelling and Performance Evaluation of Physical Layer of Wireless Regional Area Networks (IEEE 802.22) over AWGN Channel”, International Journal of Electrical, Electronic and Computer Engg., ISSN No: 2277-2626, 2012. J. M. Smith, “Adaptive Cognition Enhanced Radio Teams (ACERT),” May, 2005. Y. Zhao, L. Morales, J. Gaeddert, K. K. Bae, J. Um, and J. H. Reed, “Applying Radio Environment Maps to Cognitive WRAN Systems,” in Proc. of the Second IEEE International Symposium on Dynamic Spectrum Access Networks (DySPAN 2007), April 17–20, 2007, Dublin, Ireland. A. Sahai and D. Cabric, “Spectrum Sensing–Fundamental Limits and Practical Challenges,” Tutorial for 2005 1st IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Network. S. A. Fechtel, OFDM: From the Idea to Implementation, 2005. Luis Zarzo Fuertes, OFDM PHY Layer Implementation based on the 802.11a Standard and System Performance Analysis. B. Suresh Ram and Dr. P. Siddaiah, “Design of the Most Effective Method for Minimizing the Fading and Sep Analysis using Dpsk Over Rayleigh Fading Channel”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 3, 2013, pp. 227 - 231, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. Haritha.Thotakura, Dr. Sri Gowri .Sajja and Dr. Elizabeth Rani.D, “Performance of Coherent OFDM Systems Against Frequency Offset Estimation Under Different Fading Channels”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 3, Issue 1, 2012, pp. 244 - 251, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. Mostafa M. El-Said, “An Empirical Study to Compare Between IEEE 802.11p and Wave Protocols in Vanets Networks”, International Journal of Computer Engineering & Technology (IJCET), Volume 4, Issue 4, 2013, pp. 547 - 555, ISSN Print: 0976 – 6367, ISSN Online: 0976 – 6375. S.D. Giri and Prof. A. R. Salunke, “OFDM Based Wireless Lan Transmitter”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 2, 2013, pp. 469 - 476, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. Ami Munshi and Srija Unnikrishnan, “Performance Analysis of Radar Based on Ds-Bpsk Modulation Technique”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 2, 2013, pp. 137 - 143, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. P.Saravanaselvi and Dr.P.Latha, “Design and Analysis of Wimax Physical Layer”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 3, Issue 3, 2012, pp. 280 - 286, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. 98

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