IJEETC. InternationalJournalof. ElectricalandElectronicEngineering& Telecommunications.

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1 IJEETC InternationalJournalof ElectricalandElectronicEngineering& Telecommunications

2 Int. J. Elec&Electr.Eng&Telecoms Jaspreet Kaur and P S Sharma, 2015 Research Paper ISSN Special Issue, Vol. 1, No. 2, July 2015 National Conference on Emerging Trends in Electronics & Communication (ETEC-2015) 2015 IJEETC. All Rights Reserved TURBO - CODED IDMA FOR UWB TECHNOLOGY Jaspreet Kaur 1 * and P S Sharma 2 *Corresponding Author: Jaspreet Kaur, bajwa.jass15@gmail.com In this paper the extended study of IDMA system is done by implementing it in UWB environment. Interleaving Division Multiple Access, briefly IDMA, is an evolution of CDMA -Multiplex transmission method for digital signal transmission and is the solution of multiple access interference (MAI) and various other issues with the already available techniques. With IDMA, different users are solely distinguished by user specific interleavers. These interleavers can be selected randomly and orthogonality is not essential. The IDMA-UWB system is tested on different parameters such as channel modes, coding gain, BER and number of iterations. From the simulation results it is evident that the insertion of UWB channel in IDMA results in higher coding gain due to turbo encoding used in IDMA. Keywords: IDMA, CDMA, UWB, MAI, Modes, Iterations, BER INTRODUCTION Since its evolution from 1980 the communication era specifically known as telecommunication is growing rapidly and this is due to development in scientific field. This progress is particularly striking for mobile radio communications with the appearance of different generations of mobile telephony. At the same time, applications that are benefitted from this technology have continued to evolve and diversify. OWDM (Orthogonal Wavelength- Division Multiplexing) is considered to be promising[1]. IDMA (Interleave Division Multiple Access) is a special case of random CDMA that is mainly limited by MAI (Multiple Access Interference) and ISI (Inter Symbol Interference). Indeed with IDMA, different users are, solely, distinguished by user-specific interleaves. These interleavers can be selected randomly and orthogonality is not essential. Turbo type iterative MUD (Multi-User Detection) has been extensively studied to mitigate MAI and ISI, and significant progress has been made. In this paper, a turbo coded IDMA in UWB channel is proposed and implemented by using Simulink tool of MATLAB. This technique can alleviate the problem of Multiple Access 1 Assistant Professor, Department of ECE, Quantum Global Campus, Roorkee, Uttarakhand, India. 2 Department of ECE, DIT University, Mussoorie Diversion Road, Dehradun, Uttarakhand , India. 161

3 Interference (MAI) as well as improves the coding gain. The system performance is analyzed by analyzing the resultant Bit Error Rate (BER) obtained from the IDMA-UWB system. The further sections of the paper are organized as follows: Section given general introduction of Interleave Division Multiple Access technology, section III discussed about transmitter and receiver models for IDMA technology. Section IV for Ultra Wide Band channel model and section V is provided IDMA on UWV system implementation. INTRODUCTION TO THE SIMULATED TRANSMITTER AND RECEIVER OF IDMA Transmitter Structure The transmitter structure of the conventional IDMA scheme is shown in Figure Considering the transmitter, with K users transmitting simultaneously, for anyone of the users denoted by k, the input data array is first encoded using a Forward Error Correction (FEC) code generating a sequence. The assigned interleavers are randomly generated and a chip sequence results [14]. This process represents an important part of the multicarrier IDMA scheme, as the interleavers are the sole means of identifying different users in the system, ensuring ease of separation of signals coming from the various users at the receiver. Using the same approach we have simulated the IDMA transmitter as shown in Figure 1. We have used a low rate code the Hadamard code to improve the power efficiency as well as the coding gain. Figure 1: IDMA Transmitter where N represents the subcarrier length [14]. The low-rate FEC technique, which replaces the spreading operation carried out in MC-CDMA, is used for controlling errors in the input data propagation over the fading channel and to increase the coding gain of the multiuser system. Each of the chips are then assigned distinct interleavers represented as The IDMA Receiver The IDMA scheme has a unique sub-optimal receiver structure [15], which consists mainly of the Elementary Signal Estimator (ESE) and a posteriori probability decoders (DECs). At the transmitter, the resulting sampled radio signal is transmitted over the multipath channel after the Inverse Fast Fourier Transforms 162

4 (IFFT) process, and the received signal is given as: where h k (n), is the fading channel coefficient for an active user k, (n) is the additive white Gaussian noise with zero mean and variance 2. The symbol represents the multiuser interference due to other users combined with the Gaussian noise (n), with respect to user k and can be expressed as: The ESE, which operates on a chip-by-chip order and a posteriori probability (APP) decoders are present at the receiver of system model for each active user k [15]. Figure 2: IDMA Receiver Using the same approach we have simulated the IDMA receiver as shown in Figure 2. INTRODUCTION TO UWB AND UWB CHANNEL Ultra wideband (also known as UWB or as digital pulse wireless) is a wireless technology for transmitting large amounts of digital data over a wide spectrum of frequency bands with very low power for a short distance. According to the FCC definition [13], a UWB device is any device where the fractional bandwidth is greater than 25% of its center frequency or occupies 1.5 GHz, whichever is less. The fractional bandwidth is defined as 2(F H -F L )/ (F H +F L ) where F H and F L are the upper and lower frequency of the -10 Db emission level. The short duration pulses also offer immunity to multipath fading and a much lower fading margin, which gives multipath resolution. There are three types of UWB pulses usually referred as Gaussian pulse, Gaussian monocycle (first order derivative of Gaussian pulse), and Gaussian doublet (second order derivative of Gaussian pulse) To develop a UWB simulator we first needed to define a pulse shape. In order to compare results we adopted the pulse shape seen at the receiver suggested in [13]. This pulse shape, called g(t), was suggested to be the second derivative of the Gaussian function: 163

5 Indoor channel environments are classified as CM1, CM2, CM3, and CM4 following IEEE a standard based on propagation conditions as follows [13]. The classification of the different indoor channels of UWB is depicted in tabular form as shown in Table 1. Table 1: Indoor Channels of UWB Table 2: Specifications for IDMA-UWB Model Parameters Modulation Values BPSK Samples per frame 64 Encoding Signal bandwidth Filtering Turbo and Hadamard Tunable Selective Figure 3: Simulation of IDMA-UWB System CM1 describes a line-of sight (LOS) scenario with a maximum distance between transmitter and receiver of less than 4 m. CM2 describes the same range as of CM1, but this is for a non-line-of sight (NLOS) situation. CM3 describes a NLOS medium for separation between transmitter and receiver of range 4-10 m. CM4 describes an environment of more than 10 m with strong delay dispersion, resulting in a delay spread of 25 ns with NLOS medium. THE IDMA-UWB SIMULATION MODEL On the basis of specifications given in Table 2 we have generated the model for IDMA-UWB system as shown in Figure 3. RESULTS AND DISCUSSION We have tested the model on various parameters such as coding, type of modulation, different channel modes of UWB channel. The simulations are performed in all the channel modes. The BER display helps to analyze the whole system performance. From the display it is clear that number of iterations can be increased to improve the performance of IDMA-UWB system. Since the simulations are done in Simulink, the results are discussed taking various parameters. Further the results can be analyzed from Table 3 which gives the comparison between the two schemes. The table gives detailed description of the results and the performance of the two schemes. 164

6 Table 3: Parameters and Results S. No. Parameters IDMA-UWB 1. Channel modes All the three modes shows uniform improvement from CM1, CM2 and CM4 but CM3 performs better. 2. Coding gain High 3. BER Improves number of iterations is increased 4. Modes The channels behave uniformly. 5. Spreading low rate coding such as Hadamard coding helps to achieve high gain 6. MAI and ISI mitigated with additional circuitry 7. No. of iterations helps to improve gain Channel Modes To perform the simulation we have taken all the four UWB channels (CM1, CM2, CM3, and CM4) and have tested them on the IDMA model. From the display of the bit error rate (BER) in the display box it seen that the channels shows an uniform improvement from CM1, CM2 and CM4 but CM3 performs better than all the three channels approaching the Shannon s limit. Coding Gain We have employed the turbo Hadamard code that can achieve performance close to the ultimate Shannon limit in AWGN Channels. The code is constructed using the Simulink tool of MATLAB. The advantage of such a low rate code is verified by using the AWGN channel AND the low rate code. It is seen that there is a coding gain of about 1dB due to higher coding gain of the turbo Hadamard code [27]. The power efficiency improvement can be directly translated into spectral efficiency improvement in cellular systems. Since the performance of cellular sytems is mainly limited by the interference among users. Lower transmission power from each user leads to reduced interference, and consequently a larger number of simultaneous users can be supported. No. of Users In the IDMA-UWB the performance of the system improves as we increase the no. of users. At display 1 the BER is and at display 2 the BER is about so the performance of IDMA-UWB improves as we increase the number of users. This concept can be applied to sensor systems or the low power systems Mitigation of MAI and ISI W ith IDMA, different users are solely distinguished by user-specific interleavers. These interleavers can be selected randomly and orthogonality is not essential. In our model we have used the interleaver indices as [64:- 1:1]. This model can be tested for various other interleavers which have been explained in chapter three of the thesis. The performance of IDMA-UWB is improved depending on the choice of interleavers. No. of Modes The various channels of UWB can be operated to behave under different modes such as 100 Mb/s, 200 Mb/s, 250 MB/s, etc., the performance of IDMA-UWB system becomes better as we increase the number of modes. The model of IDMA-UWB is also tested for various other parameters such as the type of modulation and the number of iterations. Based on these and the parameters which are discussed above we find that coded 165

7 IDMA-UWB performs better as shown in Figure 4. REFERENCES Figure 4 1. Chang R W (1966), High-Speed Multichannel Data Transmission with Band Limited Orthogonal Signals, Bell Systems Tech. J., Vol. 45, December, pp Ian Oppermann, Matti Hamalainen and Jari Linatti (2004), UWB: Theory and Applications, pp , Wiley Press. 3. Jayalath A D S and Tellambura C (2000), The Use of Interleaving to Reduce the Peak-to-Average Power Ratio of an OFDM Signal, Proc. IEEE GLOBECOM 2000, Vol. 1, pp Jones A E, Wilkinson T A and Barton S K (1994), Block Coding Scheme for Reduction of Peak to Mean Envelope Power Ratio of Multicarrier Transmission Schemes, Electronics Letters, Vol. 30, No. 25, pp Kusume K, Bauch G and Utschick W (2012), IDMA vs. CDMA: Analysis and Comparison of Two Multiple Access Schemes, IEEE Trans. Wireless Commun., Vol. 11, pp Li Ping, Lihai Liu, Wu K Y and Leung W K, On Interleave-Division Multiple- Access, Department of Electronic Engineering, City University of Hong Kong. 7. Li Ping, Liu L, Wu K Y and Leung W K, Interleaved-Division Multiple-Access, IEEE Trans. on Wireless Communication, Vol. 4, pp Mahafeno I, Langlais C and Jego C (2006), OFDM-IDMA versus IDMA with ISI cancellation for quasi-static Rayleigh fading multipath channels, in Proc. 4th Int. Symp. on Turbo Codes & Related Topics, Munich, Germany, Apr. 3-7, Maria-Gabriella Di Benedetto and Guerino Giancola (2004), Understanding Ultra Wide Band Radio Fundamentals, Pearson. 10. Molisch A (2011), Orthogonal Frequency Division Multiplexing (OFDM), Wiley- IEEE Press ebook Chapters, 2nd Edition, pp Necker M and Stuber G (2002), Totally Blind Channel Estimation for OFDM over Fast Varying Mobile Channels, in Proc. of International Conference on Communications, IEEE, April 28-May 2, NY, USA. 12. Ochiai H and Imai H (2000), Performance of the Deliberate Clipping with Adaptive Symbol Selection for Strictly Band-Limited OFDM Systems, IEEE Journal Select. Areas Commun., Vol. 18, No. 11, pp

8 13. Tellado J (2000), Multicarrier Modulation with Low PAR: Applications to DSL and Wireless, Kluwer Academic Publishers, Massachusetts, USA. 14. van Nee R and Prasad R (2000), OFDM Wireless Multimedia Communications, Artech House, Boston. 15. Weinstein S B and Ebert P M (1971), Data Transmission for Frequency- Division Multiplexing Using the Discrete Fourier Transf orm, IEEE Trans. Commun. Tech., Vol. 19, No. 5, pp

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