Parametric Comparison of various Fading Channels using MATLAB Simulation

International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 Parametric Comparison of various Fading Channels using MATLAB Simulation Hemant Dhabhai1, Dr. Ravindra Prakash Gupta2, Anand Jain3 1 Ph.d Scholar. Pacific University,Udaipur(Raj.) 2 Principal, MIT, Bikaner (Raj.) 3 Scholar, M. Tech., Digital Communication, Sri Balaji College of Engineering & Technology, Jaipur, India Abstract— Fading is caused by reflection, diffraction Direct Sequence Spread Spectrum (DSSS), Frequency and scattering of transmitted signal so that multiple Hopping Spread Spectrum (FHSS). copies of the signal with varying delays can be received 1.1 WIRELESS CHANNEL MODELING at the receiver with different phases. Wireless communication is one of the most active areas of We have evaluated the performance of transmission technology development and has become an ever-more modes by calculating the probability of Bit Error Rate important part of our everyday life. Hence,simulation of (BER) versus the Signal Noise Ratio (SNR) under the wireless channels accurately is very important for the various wireless channel models i.e. Gaussian, Rayleigh, design and performance evaluation of wireless Rician and Nakagami. We consider the data modulation communication systems and components. Fading or loss and data rate to analyze the performance that is BER vs. of signals is a phenomenon that related to the Wireless SNR. We also consider multipath received signals. The Communications Field. This leads us to the fading models simulation results had shown the performance of describing the fading patterns in different environments transmission modes under different fading channel and conditions. As no model can perfectly describe an models. Based on simulation results, we observed that environment, they strive to obtain as much precision as some transmission modes are not efficient for digital possible. The better a model can describe a fading communication. environment, the better can it be compensated with other signals. Hence, on the receiving end, the signal is error Keywords – Fading, Gaussian, Rayleigh, Rician and free or at least close to being error free. Our main object Nakagami in the paper is to compare all the parameters as BER, I. INTRODUCTION Power delay profile, outage capacity and distortion. The performance of wireless communication devices Important issue is in wireless application development is needs to be evaluated by considering the transmission the selection of fading models. characteristics, wireless channel parameters and device 1.2 FADING AND MULTIPATH structure. Also, performance of data transmission over Fading refers to the distortion that a carrier-modulated wireless channels is well captured by observing their telecommunication signal experiences over certain BER, which is a function of SNR at the receiver. Several propagation media. In wireless systems, fading is due to models have been proposed and investigated to calculate multipath propagation and is sometimes referred to as SNR. All such models are function of the distance multipath induced fading. To understand fading, it is between the transmitter and the receiver, the path loss essential to understand multipath. In wireless exponent and the channel gain. Several probability telecommunications, multipath is the propagation distributed functions are available to model a time-variant phenomenon that results in radio signals' reaching the parameter i.e. channel gain. We have presented the four receiving antenna by two or more paths. Various Causes important and frequently used distributions in this paper. of multipath include atmospheric ducting, reflection from Those are Gaussian, Rayleigh and Rician and Nakagami terrestrial objects, such as mountains and buildings, models. The signal is detected and decoded by employing ionosphere reflection and refraction. These propagation several replicas of the received signal. So, we consider mechanisms are responsible for multipath propagation multilink receiver structure. which includes constructive and destructive interference, As per IEEE 802.11 standard, each communication device and phase shifting of the signal. This distortion of signals should use a wireless transmission technique among caused by multipath is known as fading. In other words , Orthogonal Frequency Division Multiplexing (OFDM), multipath occurs when there is more than one path available for radio signal propagation. The phenomenon Page | 91 International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 of reflection, diffraction and scattering all give rise to The wave travels through the medium consists of smaller additional radio propagation paths beyond the direct LOS dimension objects compared to the wavelength and path between the radio transmitter and receiver. having larger volumes of obstacles per unit volume, then 1.2.1 FADING CHANNELS scattering will occurred. Due to rough surfaces, small A Fading Channel is known as communications channel objects and irregularities in the channel scattered waves which has to face different fading phenomenon during are produced. In practice, in mobile communications, signal transmission. In real world environment, the radio electrical poles and street signs etc. induces scattering [8] propagation effects combine together and multipath is in communication. generated by these fading channels. Due to multiple 1.2.3 TYPES OF FADING signal propagation paths, multiple signals will be received According to the effect of multipath, there are two types by receiver and the actual received signal level is the of fading vector sum of the all signals. These signals are impinging a) Large Scale Fading: In this type of fading, the from any direction or angle of arrival. In multipath, some received signal power varies gradually due to signals aid the direct path and some others subtract it. signal attenuation determined by the geometry of 1.2.2 CAUSES OF FADING the path profile. Fading is caused by many factors which are as follows:: b) Small Scale Fading: If the signal moves over a A. Doppler Shift distance in the order of wavelength, in small scale When a mobile is moving at a constant velocity v along a fading leads to rapid fluctuation of the phase and path, vs is the velocity of the source, f’ is the observed amplitude of the signal. frequency and f is the emitted frequency. All these terms There are two types of fading according to the effect of will be related by the following equation: Doppler Spread. = a) Slow fading: When the coherence time of the ± channel is large relative to the delay constraint of (1) the channel then slow fading will occurred. The From the above equation, the detected frequency amplitude and phase change imposed by the increases for objects moving towards the observer and channel can be considered roughly constant over decreases when the source moves away. This the period of use. The event such as shadowing, phenomenon is known as the Doppler Effect [6]. where a large obstruction as hill or large building B. Reflection obscures the main signal path between the When a propagating electromagnetic wave impinges on transmitter and the receiver, causes the slow object which has generated large dimensions wave length, fading. when compared to wavelength of the propagating wave, b) Fast fading: When the coherence time of the then Reflection will occurred. Actually we know that if channel is small relative to the delay constraint of the plane wave is incident on a perfect dielectric, part of the channel causes the fast fading. The amplitude the energy is transmitted and part of the energy is and phase change imposed by the channel varies reflected back into the medium. If the medium is a perfect considerably over the period of use. conductor, all the energy is reflected back. Reflections 1.2.4 TYPES OF SMALL SCALE FADING occur from the surface of the earth and from buildings There are many models that describe the phenomenon of and walls. In practice, not only metallic materials cause small scale fading. Out of these models, Rayleigh fading, reflections, but dielectrics also cause this phenomenon Ricean fading, AWGN and Nakagami fading models are [5]. most widely used. C. Diffraction a) Rayleigh fading model: The Rayleigh fading is The sharp irregularities (edges) of a surface between primarily caused by multipath reception [8]. Rayleigh transmitter and receiver and obstructs the radio path then fading is a statistical model for the effect of a propagation diffraction will occurred. The bending waves around the environment on a radio signal. It is a reasonable model for obstacle, even when a Line of Sight does not exist troposphere and ionospheres‟ signal propagation as well between transmitter and receiver the secondary waves will be spread over the space. Diffraction looks like a as the effect of heavily built-up urban environments on reflection at high frequencies depends on the amplitude, radio signals. Rayleigh fading [11] is most applicable phase and polarization of the incident wave and geometry when there is no line of sight between the transmitter and of the object at the point of diffraction. receiver. D. Scattering b) Ricean fading model: The Ricean fading model [8] is similar to the Rayleigh fading model, except that in Page | 92 International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 Ricean fading, a strong dominant component is present. presence of fading, Doppler spread, interference This dominant component is a stationary signal and is and thermal noise. commonly known as the LOS (Line of Sight Component). • Spectral Efficiency: The modulated signals c) Additive White Gaussian Noise Model: It is the power spectral density should have a narrow simplest radio communication environment in which a main lobe and fast roll-off of side lobes. Spectral wireless communications system or a local positioning efficiency is measured in units of bit /sec/Hz. system or proximity detector based on Time of- flight will • Power Efficiency: saving of Power is one of the have to operate is the Additive-White Gaussian Noise critical design challenges in portable and mobile (AWGN) [6] environment. AWGN is the commonly applications. Nonlinear amplifiers are usually used to transmit signal while signals travel from the used to increase power efficiency. However, channel and simulate background noise of channel. The nonlinearity may degrade the bit error rate mathematical expression in received signal is - performance of some modulation schemes. r(t) = s(t) + n(t) (2) Constant envelope modulation techniques are used to prevent the re growth of spectral side that passed through the AWGN channel where s(t) is lobes during nonlinear amplification transmitted signal and n(t) is background noise. 1.3.1 DIGITAL MODULATION As compared to Analog modulation, Digital modulation schemes transform digital signals into waveform that are compatible with properties of the communications channel. One process uses a constant amplitude carrier and the other carries the information in phase or frequency variations (FSK, PSK). A major transition is from the simple amplitude modulation (AM) and frequency modulation (FM) to digital techniques such as Quadrature Phase Shift Keying (QPSK), Frequency Shift Fig. 1 Block Diagram of AWGN Channel Keying (FSK), Minimum Shift Keying (MSK) and Quadrate Amplitude Modulation (QAM). In this paper, An AWGN channel adds white Gaussian noise to the signal that we have simulate the BER using various modulation passes through it. It is the basic communication channel technique. model and used as a standard channel model. The A. Quadrature Amplitude Modulation: transmitted signal gets disturbed by a simple additive Quadrature Amplitude Modulation (QAM) is a method white Gaussian noise process. for transmitting two separate channels of information d) Nakagami Channel: The Nakagami-m distribution using a single carrier. has gained a lot of attention due to its ability to model a QAM is both an analog and a digital modulation scheme. wider class of fading channel conditions and to fit well It conveys two analog message signals by modulating the the empirical data. It has gained a lot of attention in the amplitudes of two carrier waves, using the amplitude-shift modeling of physical fading radio channels. Nakagami-m keying (ASK) digital modulation scheme or amplitude is more flexible and it can model fading condition from modulation (AM) analog modulation scheme. worst to moderate. 64-QAM is same as 16-QAM except it is 64 possible 1.3 MODULATION signal combinations with each symbol represent six bits The easiest way to send the low frequency audio signal (26 =64). 64- QAM is a complex modulation technique over long distance is to change a transmittable signal but gives high efficiency. This digital frequency according to the information in the message signal. This modulation technique is primarily used for sending data alteration is called modulation, and it is the modulated downstream over a coaxial cable network. It is very signal that is transmitted. The receiver then recovers the efficient, can support up to 28-mbps peak data transfer original signal through a process called demodulation. rates over a single 6-MHz channel. It's susceptibility to Modulation techniques are expected to have three positive interfering signals makes it ill suited to noisy upstream properties: transmissions. • Good Bit Error Rate Performance: Modulation schemes should achieve low bit error rate in the Page | 93 International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 SNR is the ratio of the received signal strength over the noise strength in the frequency range of the operation. It is an important parameter of the physical layer of Local Area Wireless Network (LAWN). Noise strength, in general, can include the noise in the environment and other unwanted signals (interference). BER is inversely related to SNR, that is high BER causes low SNR. High BER causes increases packet loss, increase in delay and decreases throughput. The exact relation between the SNR and the BER is not easy to determine in the multi Fig. 2 Constellation Diagram for 64-QAM channel environment. Signal to noise ratio (SNR) is an indicator commonly used to evaluate the quality of a 1.3.2 BIT ERROR RATE (BER) communication link and measured in decibels and The BER, or quality of the digital link, is calculated from represented by Eq. (5). the number of bits received in error divided by the SNR = 10 log10 (Signal Power / Noise Power) dB (5) number of bits transmitted. BER= (Bits in Error) / (Total bits received) (3) 1.3.4 Eb/N0 In digital transmission, the number of bit errors is the Energy per bit to Noise power spectral density number of received bits of a data stream over a ratio(Eb/N0) is an important parameter in digital communication channel that has been altered due to noise, communication or data transmission. It is a normalized interference, distortion or bit synchronization errors. The signal to- noise ratio (SNR) measure, also known as the BER is the number of bit errors divided by the total "SNR per bit". It is especially useful when comparing the number of transferred bits during a particular time bit error rate (BER) performance of different digital interval. BER is a unit less performance measure, often modulation schemes without taking bandwidth into expressed as a percentage. We can sense the bit error rate account. Eb/N0 is equal to the SNR divided by the (BER) of existing link and implement modulation to "gross" link spectral efficiency in (bit/s)/Hz, where the data rate and apply Forward Error Correction (FEC), bits in this context are transmitted data bits, inclusive of which is used to set the BER as low error rate for data error correction information and other protocol overhead. applications. BER measurement is the number of bit error When forward error correction (FEC) is being discussed, or destroys within a second during transmitting from Eb/N0 is routinely used to refer to the energy per transmitter to receiver. Enviourment noise may affect the information bit (i.e. the energy per bit net of FEC BER performance. Quantization errors also reduce BER overhead bits); in this context, Es/N0 is generally used to performance, through incorrect or ambiguous relate actual transmitted power to noise. reconstruction of the digital waveform. The accuracy of the modulation process and the effects of the filtering on II. SIMULATION RESULT signal and noise bandwidth also effect quantization errors. BER can also be defined in terms of the probability of In this paper, we have simulated and analyzed the concept error (POE) and represented in Eq. (4). of fading by the approach available in MATLAB. The results obtained from the MATLAB simulations are POE = ( − ) / (4) discussed in this section.. It is necessary to explore what happens to the signal as it travels from the transmitter to Where erf is the error function, Eb is the energy in one bit the receiver. Then it is very easy to understand the and N0 is the noise power spectral density (noise power in concepts in wireless communications. As explained a 1Hz bandwidth). earlier, one of the important aspects of the path between The error function is different for the each of the various the transmitter and receiver is the occurrence of fading. modulation methods. The POE is a proportional to Eb/N0, MATLAB provides a simple and easy way to demonstrate which is a form of signal-to-noise ratio. The energy per fading taking place in wireless systems. bit, Eb, can be determined by dividing the carrier power The different fading models and MATLAB based by the bit rate. As an energy measure, Eb has the unit of simulation approaches will now be described. joules. N0 is in power that is joules per second, so, Eb/N0 is a dimensionless term, or is a numerical ratio. TABLE 1 – Parameters used for Matlab simulation 1.3.3 SIGNAL TO NOISE RATIO (SNR) Page | 94 International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 S. Parameter Values NO. 1. Modulation B-PSK, PSK, BFSK,Q-PSK, BFSK,Q Scheme 4-QAM, QAM, 8-PSK, 8 & 16- PSK 2. Nakagami 1, 2, 2.28, 3, parameter(m) 3.77, 4, 5 and 9 3. Rayleigh When k=0 in rician and m=1 in nakagami TABLE 2 - BER in AWGN, Rayleigh and Rician fading channels in 64-QAM QAM modulation scheme Fig. 4 Error performance of N-Nakagami channel using BPSK modulation technique Fig. 5 Performance of Rayleigh and Rician ,Nakagami ,N under BPSK Modulation Scheme Figure 5 indicates the performance of Rayleigh and Rician ,Nakagami under BPSK Modulation Scheme. Rayleigh fading channel corresponds to K=0 in Rician and m=1 in nakagami fading channel. It is represented by solid line in Fig. 5. Fig. 3 Comparative Study of AWGN, Rayleigh and Rician We know that , the relationship between the Rician fading in 64-QAM QAM Modulation Scheme factor ‘K’ and the Nakagami-m Nakagami fading factor ‘m’ is given by- m2 − m k 2 + 2K + 1 k= ,m = (6) m − m2 − m 2K + 1 It has been observed that performance of the system is better in case of Nakagami faing channel as compared to other fading channel under BPSK and in other modulation schemes . Page | 95 International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-5, Oct.- 2014] ISSN: 2349-6495 Communications, 2009, Vol. 3, Issue 8, pp 1333- III. CONCLUSION 1342. From the simulation results, the Bit Error Rate (BER) of a [9] Yahong Rosa Zheng and Chengshan Xiao, digital communication system is an important figure of “Simulation models with correct statistical properties merit which used to quantify the integrity of data for Rayleigh fading channels”, IEEE Transactions on transmitted through the communication system. By communications, Vol. 51, No. 6, June 2003. implementing the different modulation techniques, the [10] Lightwave Magazine, September 2004 article on criterion is comparison of the variation of BER for “Explaining those BER testing mysteries”. different SNR. It is observed that the BER is minimum [11] James E. Gilpy, Transcript International Inc., August for AWGN and maximum for Rayleigh and Rician fading 2003, “Bit Error Rate Simulation using Matlab” channel. For Rician it is found that the BER is less than [12] BER Performance of Dual Predetection EGC in AWGN and Rayleigh for QAM. For higher values of Eb / Correlative Nakagami-m Fading George K. N0, the BER is decreasing in all the fading channels for Karagiannidis, Member, IEEE, Dimitris A. Zogas, different modulation schemes. The decay in Average bit Student Member, IEEE, and Stavros A. Kotsopoulos error probability with respect to average S/N ration per bit for different value of N statically independent random variables for BPSK modulation. Furthermore, at higher M-PSK schemes, more carrier power is needed to modulate the signal in order to give low error performance; and in order to maintain the error performance of a scheme,the carrier power must be increased. Here we can observe that Nakagami fading performance is better in comparison with other fading channels. REFERENCES [1] Theodore S. 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