LITERATURE REVIEW

1. Performance Evaluation of Pseudo Random Noise and Hadamard-Walsh sequences for hamming coded WCDMA system over AWGN and Fading channels- M. Mehedi Islam, M. Mahabub Hossain, M. Sazzadur Rahman, M. Mostafizer Rahman-In this paper the impact of pseudorandom noise (PN) sequence code and Hadamard-Walsh sequence code on the performance of a WCDMA system with hamming code or without error correction and detection coding under QPSK modulation over AWGN and Fading channel is investigated.

2. Performance of WCDMA Spreading in Downlink for FDD Mode-Hassan Moradi, Masumeh Nasiri Kenari, Mahmoud Ahmadian, Ahmad Salahi-In this paper a simple WCDMA system in downlink and FDD mode is simulated that is an execution part of physical layer functions as layer 1,includes data modulation, spreading multipath channel, AWGN noise, data demodulation,de-spreading and Rake receiver. Simulation results are presented for varying spreading factor.

3. Orthogonal Code Generator for 3G Wireless Transceivers- Boris D. Andreev, Edward L. Titlebaum, and Eby G. Friedman-Orthogonal variable spreading factor (OVSF) codes are standard in third generation UMTS cellular systems. The efficient generation of these codes is essential for reducing the area and power of wireless transceivers. In this paper, the basic properties of this family of codes are analyzed and efficient code generation are presented.

4. Bit Error Rate Performance Analysis on Modulation Techniques of Wideband Code Division Multiple Access-M. A. Masud, M. Samsuzzaman, M. A.Rahman, JOURNAL OF TELECOMMUNICATIONS, VOLUME 1, ISSUE 2, MARCH 2010-In this paper the performance analysis of QPSK modulation and QAM modulation schemes for WCDMA system subjected to AWGN and fading channels are presented.

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5. Channel Estimation for a WCDMA Rake Receiver- Ahsan Aziz- In this paper the algorithms for channel estimation are discussed and the simulation results are presented.

6. Scrambling Code Generation for WCDMA-Imran Ahmed- In this paper the algorithms for scrambling code generation for WCDMA system are discussed.

7. Simulation Study of FIR Filter for Complexity Analysis in WCDMA-A S Kang, Vishal Sharma- This paper deals with simulation model of square root raised cosine pulse shaping filter for WCDMA with different parameters of the filter at 5Mhz.

8. Channel Estimation Algorithms for Third Generation W-CDMA Communication Systems-Khalid A. Qaraqe, Sonia Roe- In this paper, three approaches for channel estimation method are proposed and analyzed for third generation (3G) Wideband Code Division Multiple Access (W-CDMA) communication systems.

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CHAPTER 1

INTRODUCTION

Universal Mobile Telecommunications System (UMTS) is the European Standard of the third generation of mobile communications and its air interface is called WCDMA (Wide-band Code Division Multiple Access). In 1999 the mobile communication describes the characteristic by a diverse set of application using different standards of not compatible around the whole world. Third generation of mobile communication that provides high data rate multimedia services has been proposed by standards bodies and industrial interest groups and the final steps of its implementations was performed. Access to high bit rate services and higher spectrum efficiency is the important factor for accepting of third generation. In ITU the third generation systems is called IMT-2000, in Europe UMTS and in the United States UWC-136 and cdma-2000 [1]. The third generation systems are required to fulfills many objectives, the most important goals are high speed data services, flexibility, compatibility and low cost. High data rate services are also known as broadband services. Current examples of an application that utilizes such services are high speed internet access and multimedia type applications. A flexible wireless mobile system is one that can easily support new services after the system has been deployed. As would be expected, once the system is full and running, new services that are presently beyond one's imagination will be demanded by the end user. A successful system must be able to accommodate these future services. Backward compatibility with second generation systems is a vital requirement for the success of the system[2],[3],[4].The system is called the International Mobile Telecommunications-2000 in the International Telecommunications Union. Whereas in Europe, the system is called the Universal Mobile Telecommunications System (UMTS) .The standardization process was long and went through many disputes, discussions, and harmonization. Toward the end of 1998 two new organizations were established: the 3rd Generation Partnership Project (3GPP) and 3GPP2. The goal of 3GPP and also 3GPP2 was to harmonize the large number of the WCDMA based proposals submitted by different bodies into one system [5].Table 1-1 lists some of the proposed standards for the third generation mobile system to the ITU. Both the UTRA developed by 3GPP and cdma2000 developed by 3GPP2 are based on WCDMA technology.

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Table 1-1: Radio transmission technology proposals for IMT-2000

Proposal Description SourceDECT Digital Enhanced Cordless

TelecommunicationsETSI Project DECT

UWC-136 Universal Wireless Communications

USA TIA TR45.3

WIMS W-CDMA Wireless Multimedia and MessagingServices Wideband CDMA

USA TIA TR46.1

TD-SCDMA Time-division synchronous CDMA

China CATT

W-CDMA Wideband CDMA Japan ARIB

CDMA I1 Asynchronous DS-CDMA S. Korea TTA

UTRA UMTS Terrestrial Radio Access

ETSI SMG2

NA: W-CDMA North American: Wideband CDMA

USA TIP I –ATIS

cdma2000 Wideband CDMA (IS-95) USA TIA TR45.5

CDMA I Multi band synchronous DS-CDMA

S. Korea TTA

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BLOCK DIAGRAM

This is the complete block diagram of my project. In the receiver section first a single correlator receiver is considered, then a rake receiver with channel estimation using adaptive LMS algorithm and then Adaptive Channel equalizer is considered. The performance of each kind is analysed.

Figure 1-1 : Block diagram of WCDMA FDD Downlink system

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CHAPTER 2

CHARACTERISTICS OF UTRA(WCDMA) :

The WCDMA standard has two modes for the duplex method, Frequency Division Duplex (FDD) and Time Division Duplex (TDD). The frequency bands allocated for UTRA are shown in Figure 2-1 [6]. In UTRA there is one paired frequency band in the range 1920 -1980 MHz and 2110 - 2170 MHz to be used for UTRA FDD. There are two unpaired bands from 1900 -1920 MHz and 2010 – 2025 MHz intended for the operation of UTRA TDD. In this thesis we only consider the FDD mode of operation for the receiver [3].

Figure 2-1: The frequency spectrum allocations for UTRA

Table 2-1 [7] lists the most important parameters of the UTRA FDD.As can be seen in Table 2-1, the chip rate for the WCDMA standard is 3.84 Mcps and Spreading consists of two operations. The first operation is the channelization operation where the spreading code is applied to every symbol in the transmitted data. Thus the bandwidth of the data signal is increased. In this channelization operation, the number of chips per data symbol is called the Spreading Factor (SF). The second spreading operation is the scrambling operation, scrambling code is applied to the already spread signal. Both the

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spreading operations are applied to the so called In-phase (I) and Quadrature phase (Q) branches of the data signal. In the channelization operation, the Orthogonal Variable Spreading Factor (OVSF) codes are independently applied to the I and Q branches [8],[9]. The resultant signals on the I and Q branches are then multiplied by a complex-valued scrambling code, where I and Q correspond to the real and imaginary parts respectively.

Table 2-1: Standardized Parameters of WCDMA

Channel bandwidth 5 MHz

Duplex mode FDD and TDD

Downlink RF channel Direct Spread

Chip rate 3.84 Mcps

Frame length 10 ms

Spreading modulation Balanced QPSK (downlink) Dual-channelQPSK (uplink) Complex spreading circuit

Data modulation QPSK (downlink) BPSK (uplink)

Channel multiplexing in downlink Data and control channels time multiplexed

Spreading factors 4-256 (uplink), 4-512 (downlink)

Spreading (downlink)OVSF sequences for channel separationGold sequences 218-1 for cell and userseparation (truncated cycle 10 ms)

Spreading (uplink)OVSF sequences, Gold sequence 241 for userseparation (different time shifts in I and Qchannel, truncated cycle 10 ms)

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WCDMA Physical Layer

Physical layer or L1 functions are the data transmission and presentation of required service presentation to higher layer. In the other word, this layer executes the commands which come from higher layer only and has no deciding about data transmission quality [10]. In UMTS terrestrial radio access (UTRA), received information from higher layers in air interface has been carried by transport channel that mapped on physical channel in physical layer. Also physical layer must be support transport channel with variable rate for different services and multiplexing in a connection. The physical channels of the WCDMA systems are structured in layers of radio frames and time slots. There is only one type of downlink dedicated physical channel, the downlink Dedicated Physical CHannel (downlink-DPCH). The structure layout of the downlink dedicated physical channel (DPCH) of the WCDMA signal can be seen in Figure 2-2.

Figure 2-2 : The Radio frame structure downlink DPCH of WCDMA

As shown in the figure 2-2, every WCDMA radio frame is 10 ms long. Each frame is then divided into 15 slots i.e. 2560 chips/slot at the rate of 3.84 Mcps.

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In addition, every 72 frames constitute one super frame. The frame is a time multiplexed data and control bits from the Dedicated Physical Data Channel (DPDCH) and Dedicated Physical Control Channel (DPCCH). The DATA 1 and DATA 2 are data bits that belong to DPDCH, while bits of Transmit Power Control (TPC), Transport Format Combination Indicator (TFCI), and Pilot belongs to the DPCCH. The number of bits in each field vary with the channel bit rate. The exact number of bits in each field is shown in [40]. The TPC bits are used by the base station to command the mobile transceiver to increase or decrease the transmission power. TFCI bits are the indicators of slot format.The bit count shown in Figure 2-2 is the maximum possible number of data bits that can be transmitted in one slot. In a frame 15x 10x2K bits can be transmitted in every slot, where k is an integer in the range from 0 to 7. The parameter k is related to the Spreading Factor (SF):

............(1)

Thus the spreading factor SF may range from 512 down to 4 [11],[12].

Downlink Spreading and Modulation

In WCDMA, spreading is performed in two steps. In first step, a real code with a chip rate that equal to transmission chip rate is multiplied by data modulated sequence. In second step for spreading, one complex sequence with same chip rate is multiplied by complex spread spectrum signal. First step is called real or channelization spreading and second step is called complex or scrambling spreading. Quadrature Phase Shift Keying (QPSK) is applied for data modulation in the downlink. Each pair of two bits are converted serial-to-parallel and mapped to the I and Q branches respectively. The data in the I and Q branches are spread to the chip rate by the same channelization code. The channelization code is the OVSF codes. Figure 2-3 shows the spreading and modulation for a downlink user. The downlink user has a DPDCH and a DPCCH. Additional DPDCHs are QPSK modulated and spread with different channelization codes.

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Figure 2-3: Downlink Spreading and Modulation

The data modulation is QPSK in downlink whereas it is BPSK for the uplink. The data rates in the I and Q-channel are the same in the downlink whereas data rates in the I and Q-channel of the uplink may be different. The scrambling code is cell specific in the downlink, whereas it is mobile station specific in the uplink.

DOWNLINK SPREADING CODES

Different users are assigned different channelization codes for maintaining their orthogonality. Channelization codes that are used in WCDMA are orthogonal variable spreading factor (OVSF) codes. In these codes, even if use different spreading factors in their downlink physical channels, the orthogonality between codes is presence. Orthogonality between these codes is obtained from tree structural properties. Figure 2-4 shows this architecture. Orthogonal codes provide variable rate from their variable spreading factors that is used in both links. Every OVSF is represented in the form Csf, code number that code number is a row of its SF-dimensional square matrix that varies from 0 up SF-1. Due with attention to figure 2-4, every code can generate two orthogonal codes. In this case, generator code is called mother code and generated code is called child code that are not orthogonal and subsequently not used for channel separation. So, since users are separated by these codes, a channelization code can be allocated to a user if and only if codes that there are in the path to origin or in sub branches are not used by other users. This subject represents that the number of available channelization codes is not constant and depends on bit rate and spreading factor of the physical channel. Spreading code period is spreading factor and for a defined chip rate, depends on bit rate. So, number of usable code depends on bit rate.

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Figure 2-4: OVSF Code tree

DOWNLINK SCRAMBLING CODES

The downlink scrambling codes are used to maintain cell or sector separation. The total number of available scrambling codes is 512. These codes are divided into 32 code groups with 16 codes in each group. The grouping is done to facilitate fast cell search by the mobile [5]. Several scrambling codes might be assigned to one cell for the case adaptive antennas used to increase the capacity.The downlink scrambling codes is modulo2 sum of 38400 chips of two binary real m-sequences that generate from eighteenth order polynomial generator. Suppose X and Y are these polynomials of these two m-sequence. X is generated by primitive polynomial, 1+x7+x18 and Y is generated by1+x5+x7+x10 +x18 [7]. The sequence which is produced from modulo2 sum of these two sequences is a Gold code. Figure 2-5 shows the generation of downlink scrambling codes:

Figure 2-5: Generation of Downlink Scrambling codes

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Quadrature Phase-Shift Keying (QPSK) Modulation

In Phase-Shift Keying (PSK) , the phase of the carrier signal is shifted to represent data. For M-ary PSK, the number of bits to represent one symbol is given as:

..................(2)

where n is the number of bits per symbol and m is the number of possible levels to represent the signal. From the equation (2), we determine that the QPSK uses two bits to represent any one of its four-phasor symbols. Figure 2-6 shows the constellation diagram for QPSK and how these four levels of signal correspond to carrier phases, θ of 45°, 135°, 225° and 315°.

Figure 2-6: Constellation diagram for QPSK

Summary of the WCDMA Modulation

We can summarize the discussion on the modulation applied to the dedicated physical channels in the following table.

Table 2-2: Parameters of WCDMA Modulation

Spreading Modulation Dual Channel QPSK for ULBalanced QPSK for DL

Data Modulation BPSK for ULQPSK for DL

Spreading OVSF codes.4-256 spreading factor for UL4-512 spreading factor for DL

Scrambling Complex Scrambling

Frame Length 10 ms

Chip Rate Pulse Shaping

3.84 McpsRaised Cosine with 0.22 roll off

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CHAPTER 3

CHANNELS

Communication channels introduce noise, fading, interference and other distortions into the signals that they transmit. Different channels have different properties and are modeled differently. Here, we have considered-AWGN channel and Multipath Rayleigh Fading channel.

AWGN CHANNEL

Additive white Gaussian noise (AWGN) is a channel model in which the only impairment to communication is a linear addition of wide band or white noise with a constant spectral density and a Gaussian distribution of amplitude. The model does not account for fading, frequency selectivity or dispersion. However, it produces simple and tractable mathematical models which are useful for gaining insight into the underlying behaviour of a system before these other phenomena are considered. Wideband Gaussian noise comes from many natural sources, such as the thermal vibrations of atoms in conductors (referred to as thermal noise or Johnson-Nyquist noise), shot noise, black body radiation from the earth and other warm objects, and from celestial sources such as the Sun.Mathematically, thermal noise is described by a zero-mean Gaussian random process where the random signal is a sum of Gaussian noise random variable and a dc signal that is, z = a +n .................(2)A simple model for thermal noise assumes that its power spectral density Gn(f ) is a flat for all frequencies and is denoted as-

............(3)Where the factor of 2 to indicate that Gn(f) is a two-sided power spectral density. Since thermal noise is present in all communication systems and is a prominent noise source for most system, the thermal noise characteristics that are additive, white and Gaussian are most often used to model the noise in communication systems.

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FADING

Fading is the deviation or the attenuation that a carrier modulated signal experiences over certain propagation media. The presence of reflectors in the environment surrounding a transmitter and a receiver create multiple paths that a transmitted signal can traverse. As a result, the receiver sees the superposition of multiple copies of the transmitted signal, each traversing a different path. Each signal copy will experience differences in attenuation, delay and phase shift, which results in considerable degradation of the signal at the receiver. Since signal propagation takes place in the atmosphere and near the ground, apart from the effect of free path loss, Ls, the most notable effect of signal degradation is multipath propagation. The effect can cause fluctuations in the received signal's amplitude, phase and angle of arrival, giving rise to terminology multipath fading.Generally, there are two fading effects in mobile communications: large-scale and small-scale fading. Large-scale fading represents the average signal power attenuation or path loss due to shadowing effects when moving over large areas. On the other hand, small-scale fading refers to the dramatic changes in signal amplitude and phase that can be experienced as a result of small changes (as small as a half-wavelength) in the spatial separation between a receiver and transmitter.The received signal consists of large number of multiple reflective paths and there is no line of sight signal component. When there is a dominant non-fading signal component present, such as a line of sight propagation path, the small scale fading envelope is described by a Rician pdf.The mechanisms behind large scale fading and small scale fading are shown in figure 3-1. These mechanisms are reflection, diffraction and scattering.

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Figure 3-1: The three mechanisms in signal propagation in a multipath channel

Reflection

Reflection occurs when a propagating electromagnetic wave encounters a surface that is large relative to the wavelength of the propagating waves. This reflected wave as illustrated in figure 3-2 may interfere constructively or destructively at the receiver due to the change in phase shift after reflection. Sources for reflections include the surface of the earth, buildings and walls.

Figure 3-2: Reflection of a wave

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DIFFRACTION

Figure 3-3 shows that diffraction can occur at the edge of an impenetrable body or at a surface with sharp irregularities that is large compared to the wavelength of the radio wave. The secondary waves resulting from such edges or surfaces are partially reflected and retransmitted with a bend of waves around the obstacle. This allows the signal to be transmitted even when there is no LOS path between the transmitter and the receiver.

Figure 3-3: Diffraction of a wave

SCATTERING

Scattering occurs when the radio path between the transmitter and receiver consists of large amount of objects with dimensions that are small compared to the wavelength of the signal. Figure 3-4 shows that the scattered waves can be produced by rough surfaces or by other irregularities in the channel such as foliage and traffic signs.

Figure 3-4: Scattering of waves

Large-scale Fading

Large-scale fading is primarily attributed to path loss when the received signal strength decays over relatively large distances (several hundreds or thousands of

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meters) between the transmitter and the receiver as shown in figure 3-5. It is otherwise known as slow fading or shadowing, and is characterised by a long delay spread in figure 3-6.

Figure 3-5: Signal strength decays as the path distance increases

Figure 3-6: Large-scale and small-scale fading

Small-scale Fading

Small-scale fading as shown in figure 3-6, manifests itself as rapid fluctuations in the voltage envelope of the received signal over a short period of time or travel distance (a few wavelengths). It is caused by the interference between two or more versions of the transmitted signal arriving at the receiver with a spread of different times. These time-shifted signals are called multipath signals, which can be represented as ‘taps’ in an impulse-response model of a channel. Effects of multipath fading can be classified as flat or frequency

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selective. For flat fading, only the amplitude of the received signal can vary due to the constructive and destructive interference from the time-shifted signals. Frequency selective fading is due to the time dispersion of the received signal and is the cause of inter-symbol interference (ISI).

RAYLEIGH FADING CHANNEL

It is a statistical model for the effect of a propagation environment on a radio signal. Rayleigh fading model assumes that the magnitude of a signal that has passed through such a transmission media will vary randomly or fade according to Rayleigh distribution. Rayleigh fading is viewed as a reasonable model for tropospheric and ionospheric signal propagation as well as the effect of heavily built up urban environments on radio signals. It is most applicable when there is no dominant propagation along a line of sight (LOS) between the transmitter and the receiver.

DOPPLER SPREAD

The Doppler spread is a measure of the spectral expansion due to the time rate of change (time variant) of the channel parameters. It is the shift in frequency frequency due to the motion of mobile from the actual carrier frequency.The Change in frequency due to dopplers shift is given by

fd = (v/l) * cos(f)

If the mobile is moving toward the direction of arrival of the wave, the Doppler shift is positive (i.e. the apparent received frequency is increased), and if the mobile is moving away from the direction of arrival of the wave, the Doppler shift is negative (i.e. the apparent received frequency is decreased). In a typical multipath environment, the received signal arrives from several reflected paths with different path distances and different angles of arrival, and the Doppler shift of each arriving path is generally different from that of another path. The effect on the received signal is seen as a Doppler spreading or spectral broadening of the transmitted signal frequency, rather than a shift.

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CHAPTER 4

WCDMA Baseband Mobile Receiver

The work in this dissertation considers the Frequency Division Duplex (FDD) of the 3GPP WCDMA as a standard. In this section, I will examine the mobile baseband processing unit of the receiver. The mobile channel is a dynamic one, this behaviour gets aggravated for communication at higher data rates and worsens when communicating with a moving mobile terminal at higher speeds.

Figure 4-1: A block diagram of 3G receiver

Figure 4-1 outlines the block diagram of the complete receiver. As can be seen in the figure, after the signal has been received by the radio frequency unit with a frequency in the range of 2110-2170 MHz, the signal is then down converted to an Intermediate Frequency (IF) level of 270 MHz. The desired 5MHz channel is filtered by an IF band-pass filter. The IF signal is fed to the demodulator circuit where it is mixed with the fixed local oscillator frequency to produce the zero IF baseband in-phase and quadrature (I and Q) signals, these are then fed to the analog-to-digital converter. The output of the A/D converter is then fed to the baseband unit for processing.

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Figure 4-2: The baseband receiver front end

Figure 4-2 shows the block model of the receiver's baseband processing unit.The Figure shows more detail of the inner signal path in the front end of the baseband receiver. The analog signal is converted into a digital signal using wideband analogue to digital converter typically running at 4 times the chip rate and producing 8 bit resolution. The signal is then filtered using a Root Raised Cosine (RRC) filter with a roll-off factor of 0.22. The purpose of the root raised cosine filter is to reduce the inter-symbol interference. Subsequently the signal is fed to the RAKE receiver and searcher.Figure 4-3, shows a block diagram of the additional processing steps at the baseband of the WCDMA receiver. As shown in the figure, the incoming chips from the A/D converter are introduced to the RAKE receiver and to the searcher. The searcher provides an estimation of the multipath delays which are used by the RAKE receiver to resolve different paths signals. The maximal ratio combiner then weights the signals and sums them together.

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Figure 4-3: Complete block diagram of the receiver front end

Channel Estimation

Typically channel estimation is performed using one of three methods or a combination of these methods. The trade-offs between complexity and performance dictates the choice of algorithm:•Data Aided Channel Estimation: Known pilot symbols are transmitted. At the receiver end, the channel estimation algorithm operates on the received signal along with its stored symbols to generate an estimate of the transmission channel.•Decision-Directed Channel Estimation: A rough estimate of the channel is obtained using a suitable estimation method. Then this estimate is used to make symbol decisions. The channel estimate is further improved using the resulting symbols as “pilot symbols.” This type of estimation contains some inherent delay because the symbol decisions occur before the final channel estimate can be made. Also, there may be error propagations because any errors in the symbol decisions affect the final estimate.•Blind Channel Estimation: This estimation process relies not on pilot symbols or symbol decisions but rather on certain characteristics of the modulated signal. For example, the constant modulo algorithm (CMA) uses the amplitude of the signal as the criterion for estimating the channel. In constant energy modulation schemes such as Quadrature Phase Shift Keying (QPSK), the knowledge that all signals are transmitted with equal energy is used as the basis for obtaining the

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channel estimate. This type of algorithm typically requires a longer convergence time and usually has a higher mean square error (MSE) than the other two schemes. In a typical WCDMA rake receiver, channel estimates are used to combine the multipaths. Figure 4-4 shows how different paths are combined using Maximum Ratio Combining (MRC). In Figure 4-4, r(t) is the received signal, which is split into r(t-τi). Note that, g(t,τi) is the corresponding channel estimate for each path is r(t-τi). The objective is to estimate the channel phase and amplitude (denoted in Figure 4-4 as g(t,τi) ) for each of the identified paths. This information is then used for combining each path of the received signal.

Figure 4-4: Rake Receiver for WCDMA

As Figure 4-4 shows, the following steps occur in a WCDMA receiver (excluding the error correction coding):1. Descrambling- Received signals are multiplied by the scrambling code and delayed versions of the scrambling code. A path searcher determines the delays prior to descrambling. Each delay corresponds to a separate multipath that is to be combined by the rake receiver2. De spreading- The descrambled data of each path is de spread by simply multiplying the descrambled data by the spreading code. 3. Integration and dump- The de spread data is integrated over one symbol period, giving one complex sample output per QPSK symbol. This process is carried out for all paths to be combined by the rake receiver. 4. Symbol combining- The same symbols obtained via different paths are then combined using the corresponding channel information and a combining scheme such as MRC.

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5. The combined output is sent to a simple decision device to decide on the transmitted bits.The objective of the channel estimation block is to estimate the channel phase and amplitude (denoted in Figure 4-4 as g(t,ti) ) for each of the identified paths. Once this information is known, it can be used for combining each path of the received signal.

RAKE Receiver and Maximal Ratio Combining

The WCDMA communications system is based on the DS-SS baseband data modulation. This implies that the signal's spectrum is expanded, i.e. the signal energy is distributed over a much larger bandwidth than the minimum required for transmission. In direct sequence spread spectrum (DS-SS), the signal is spread by multiplying it with a PN sequence with a much higher chip rate. In the transmitter, the signal is multiplied by the spreading sequence which causes a spectral spreading of the original narrow band signal. At the receiver the signal is multiplied by the spreading sequence again. If the reference sequence of the receiver is synchronized to the data modulated PN sequence in the received signal, the original signal can be recovered.The RAKE is a special type of receiver that takes advantage of the multipath propagation. If the time spread of the channel is greater than the time resolution of the system then different propagation paths can be separated, and the information extracted from each path can be used to increase the signal to noise ratio (SNR). The time spread of the channel is given by the maximum delay between the arrivals of a transmitted signal on different propagation paths. The time resolution of the system is given by the inverse of the bandwidth of the radio frequency signal, or is equivalent to the chip period of the PN sequence.Figure 4-4 is a block diagram of L-arm RAKE receiver. The RAKE receiver is composed of two or more correlation arms, which extract the signals, arrived on different propagation paths. This is possible because the correlation between two versions of the PN sequence delayed by one or more chips is almost zero. Therefore the propagation paths are separable.As shown in figure 4-4, once the different paths are resolved, they are combined based upon their relative weights. Various techniques are known to combine the signals from multiple diversity branches. In Maximum Ratio combining each signal branch is multiplied by a weight factor that is proportional to the signal amplitude. Therefore, branches with strong signals are further amplified, while weak signals are attenuated.

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CHAPTER 5

SIMULATION FLOW CHART

Figure 5-1: Simulation flow chart for W-CDMA system models used in M files

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MATLAB SIMULATION MODEL

A communication-link level simulation in Matlab 7.10 was carried out for WCDMA model based on associated parameters, theories and formulae. Throughout this project, we set the bit rate of 384Kbps for the signal generator. Two W-CDMA wireless cellular system models used in this research are:-1. W-CDMA system in AWGN channel2. Multi-user W-CDMA system in AWGN and Multipath Rayleigh Fading (static and mobile)

SIMULATION RESULTS

In this dissertation we analysed the performance of QPSK modulation technique of WCDMA in AWGN Channel and Rayleigh fading channel, here in the receiver module rake receiver is not considered.

Performance Analysis of QPSK modulation technique of WCDMA in AWGNTable 5-1 shows the simulation result for evaluation on BER vs. SNR for AWGN Channel for single user.Table 5-1: Simulation result for evaluation on BER vs. SNR for AWGN channel for 1 user

Signal-to-Noise Ratio(Eb/No)

Number of Error Bit Error rate (BER)

0 0.078845 15769.01 0.05647 11294.02 0.038105 7621.03 0.02322 4644.04 0.012405 2481.05 0.0060 1200.06 0.00248 496.07 7.5E-4 150.08 1.75E-4 35.09 1.0E-5 2.010 0.0 0.0

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Figure 5-1: BER vs. EbNo for single user over AWGN Channel

Table 5-2 shows the simulation result for evaluation on BER vs. SNR for AWGN Channel for five users.

Table 5-2: Simulation result for evaluation on BER vs. SNR for AWGN channel for five user

Signal-to-Noise Ratio(Eb/No)

Number of Error Bit Error rate (BER)

0 0.082831 82831.01 0.061297 61297.02 0.042355 42355.03 0.027597 27597.04 0.016533 16533.05 0.008858 8858.06 0.004562 4562.07 0.001923 1923.08 7.56E-4 756.09 2.54E-4 254.010 5.0E-5 5.0

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Figure 5-2: BER vs. EbNo for five user over AWGN Channel

Performance Analysis of QPSK modulation technique of WCDMA in AWGN and Multipath Rayleigh Fading Channel (60 Kmph and 90 Kmph)

Table 5-3 shows the simulation result for evaluation on BER vs. SNR for AWGN and Multipath Rayleigh fading Channel for single user with terminal velocity 60 Kmph.

Signal-to-Noise Ratio(Eb/No)

Number of Error Bit Error rate (BER)

0 0.07868 15736.0

1 0.0567 11340.0

2 0.03784 7568.0

3 0.022765 4553.0

4 0.012465 2493.0

5 0.0060 1200.0

6 0.00227 454.0

7 6.7E-4 134.0

8 2.0E-4 95.0

9 2.5E-5 50.0

10 5.0E-6 10.0

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Figure 5-3: BER vs. EbNo for single user over AWGN and Rayleigh fading Channel with terminal velocity 60 KmphTable 5-4 shows the simulation result for evaluation on BER vs. SNR for AWGN and Multipath Rayleigh fading Channel for single user with terminal velocity 90 Kmph.

Signal-to-Noise Ratio(Eb/No)

Number of Error Bit Error rate (BER)

0 0.0842 16840.02 0.05315 10630.04 0.03285 6570.06 0.0217 4340.08 0.01215 2436.010 0.00905 1817.012 0.0072 144.014 0.0052 104.016 0.0042 84.018 0.0029 58.020 0.00215 43.0

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Figure 5-4: BER vs. EbNo for single user over AWGN and Rayleigh fading Channel with terminal velocity 90 Kmph

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CONCLUSION

The simulation result shows that QPSK modulation has better performance over AWGN channel than Multipath Rayleigh fading channel. It is also seen that when the number of user increases the performance degrades. When WCDMA system is subjected to dynamic environment with terminal velocity 60km/h and 90km/h the performance degrades.

FUTURE WORK

The results shown above can be improved by using rake receiver and channel coding. My future work will be to analyse the BER vs. SNR of conventional rake receiver and adaptive channel equalizers.

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REFERENCES

[1] T. Ojanpera, and R. Prasad, An Overview of Third-Generation Wireless Personal Communications: A European Perspective, IEEE Personal Commun. Mag., pp.59-65, Sept. 1998.

[2] R. Parsad, W. Mohr, and W. Konhauser, Third Generation Mobile Communication Systems, Artech House Publisher, Boston - London, 2000.

[3] W. Granzow, "3rd Generation Mobile Communications Systems," Course notes for Mobile Communication 11. Friedrich-Alexander-Universitat Erlangen- Niirnberg.

[4] E. Dahlman," WCDMA- The Radio Interface for Future Mobile MultimediaCommunications," IEEE Trans. on Vehicular Technology, Nov. 1998.

[5] 3rd Generation Partnership Project (3GPP);Technical Specification Group (TSG) Radio Access Network (RAN); Working Group 1 (WG1); Multiplexing and channel coding (FDD)- TS 25.212 V2.3.0 (1999-10)

[6] R. Steele, and L. Hanzo, Mobile Radio Communications Second and Third Generation Cellular and WATM Systems, John Wiley and Sons, New York, 1999.

[7] M. Zeng, A. Annamalai, and V. Bhargava, "Advances in Cellular WirelessCommunications," IEEE Communications Magazine, Sept. 1999

[8] [3GPP Technical Specification, "Spreading and Modulation (FDD)," 3GPPDocument no. 3G TS 25.213, Ver. 3.2.0, Mar. 2000.

[9] 3GPP Technical Specification, "Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD)," 3GPP Document no. 3G TS 25.211, Ver. 3.2.0, Mar. 2000.

[10] Performance of WCDMA Spreading in Downlink for FDD Mode-Hassan Moradi, Masumeh Nasiri Kenari, Mahmoud Ahmadian, Ahmad Salahi

[11] 3GPP Technical Specification, "Physical Layer Procedures (FDD)," 3GPPDocument no. 3G TS 25.214, Ver. 3.2.0, Mar. 2000.

[12] 3GPP Technical Specification, "Physical Layer General Description," 3GPP Document no. 3G TS 25.201, Ver. 3.2.0, Mar. 2000.

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