Performance analysis is performed for a wireless communication system with a single transmitter and multiple receive antenna diversity over a Rayleigh fading channel with Turbo error correction coding. The analysis includes the development of bit error rate (BER) expression analytically considering different types of Turbo codes. Performance results are evaluated in terms of bit error rate (BER) as a function of signal-to-noise ratio (SNR) for different system parameters such as number of receive antennas, fading parameters and doppler frequency shift along with different clear distance of the code.
It was found that there is a significant improvement in receiver performance compared to the Rayleigh fading channel due to the inclusion of turbo coding in the presence of receiver diversity with maximum ratio pooling. The improvement appears in terms of lowering the BER bottom, which cannot be lowered even by increasing the number of receiving antennas. For a given BER, 10-3, the amount of coding gain is found to be 2 dB to 20 dB, depending on the system parameter values and the free code distance.
It is also noted that the coding gain is higher when the doppler shift frequency is larger and the free spacing of the code is higher and the number of antennas is smaller. The results will be used in the design of the SIMO wireless communication system with Turbo coding.
CHAPTER!
- Introduction to Communication System
- Digital CommunicationSystem
- General Features of Wireless Communication
- Challenges In Wireless Communication Networking
- Historical Review of OFDM
- Orthogonal Frequency Division Multiplexing (OFDM)
- Orthogonal Frequency Division Multiple Access (OFDMA)
- Advantages of OFDM Transmission Scheme
- Disadvantages of OFDM Transmission Scheme
- Diversity Schemes
- Time Diversity
- Frequency Diversity
- Polarisation Diversity
- Multiuser Diversity
- Antenna Diversity
- Transmit Diversity
- Diversity Reception
- Diversity Combining Schemes
The binary sequence at the output of the channel encoder is transferred to the digital modulator. The primary purpose of the digital modulator is to map the binary information sequence into signal waveforms. During the early years of the evolution of OFDM research the contributions due to the efforts of.
OFDMA is a multi-user version of the popular Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. At the receiver end, it is very difficult to locate the start of the FFT symbol. Multiple versions of the same signal may be transmitted and/or received and combined at the receiver.
Time diversity is multiple versions of the same signal being transmitted at different times. The use of diversity techniques at both ends of the link is called space-time coding.
SIMO Technology
Different Forms of SIMO
Until now, Single-antenna SIMO (or Single user MIMO) technology has mainly been developed and is implemented in some standards, e.g. Multiple-input and one-output (MISO) is a degenerate case where the receiver has a single antenna. Single-input and multiple-output (SIMO) is a degenerate case where the transmitter has a single antenna.
MIMO
SIMO
- Applications of SIMO
- Review of Previous Works
- Objectiveof the Thesis
- Organization ofthe Thesis
Spatial multiplexing techniques make the receivers very complex, which is why they are typically combined with Orthogonal Frequency Division Multiplexing (OFDM) or with Orthogonal Frequency Division Multiple Access (OFDMA) modulation, where the problems created by multi-path channel are effectively handled. MIMO is also planned to be used in mobile radiotelephony standards such as recent 3GPP and 3GPP2 standards. Numerous research works have been carried out during the last few years on the performance evaluation of an Orthogonal Frequency Multiplication (OFDM) system both analytically and also through simulations [I ]-[20].
Wireless communications and networking, including coding, differential multiplexing and multiple access, forms of diversity, and many topics related to wireless communications are well covered in [2] and [3]. [4] also discusses error-correcting coding, including turbo coding, spread spectrum, diversity techniques, and multiple access. Wireless system designers face many challenges such as limited spectrum availability, complex spatio-temporal variable wireless environment, increasing demand for higher data rates, better quality of service, increased network capacity, etc [I] & [2].
Single-Input Multiple-Output (SIMO) systems rely on the use of no. more than two antennas at the receiver to achieve diversity [2] and [3]. Turbo code is the most exciting and potentially important development in coding theory, which is able to achieve near Shannon capacity performance [4] &[5]. Recently, space-time block coding has been shown to be an effective means of anti-fading in a multipath propagation environment [6].
In a multipath propagation environment [7] and [8], the use of two transmit antennas and multiple receive antennas and space-time block coding (STBC) [9] and [10] have been found to provide remarkable improvement. Instead of using STBC, wireless performance can be further improved by using turbo coding in a SIMO configuration. Verifying the performance improvement using turbo coding in SIMO configuration is very important for the next generation wireless communication system, which is yet to be reported.
The possible result of the research will fmd applications in the design of high data rate wireless communication system. Salient highlights of the wireless system development, the challenges of the wireless system and various fading are briefly discussed in this chapter. The BER performance of the system in the presence of A WGN, fading and timing jitter is analyzed with and without turbo coding and receive diversity.
THEORETICAL ANALYSIS OF A SIMO OFDM SYSTEM
- System Model
- Analysis of OFDM Systems
- Analysis of BER
- QPSK and 7l / 4 - DQPSK
- M-ary Phase Shift Keying (MPSK)
- Coherent Reception in a Flat Slow Rayleigh Fading Channel: HER Analysis
- HER Analysis
- Carrier-to-Noise plus Interference (CNIR) Power Ratio
- Channel Coding
- General Convolutional Coder
- Turbo Codes
- System Block Diagram of Turbo Encoder and Decoder
- Bit Error Rate Performance of Turbo Code
A block of N serial symbols is converted into a block of N parallel modulated symbols, each of which has a duration T=NTs• If the effective channel delay range (J,N is chosen so that NTs » (Jr, ,This means fighting interference between symbols due to the temporal dispersion of the channel. In the frequency domain, the bandwidth of each subband signal is lIN times that of the original signals. If the bandwidth of the original signal is large compared to the coherence bandwidth of the channel, so that the channel exhibits frequency selective fading, N can be chosen appropriately , so that the channel seen by each of the subbands in OFDM shows flat fading.
Vn(t) is the complex envelope of the transmitted signal in the nth subband and is given by. The output sequence of the AID converter is also divided into blocks of length N and demodulated block by block, The corresponding block fork=0 has N samples taken next. Since the detection of the odd digit is independent of that of the even digit, the probability of getting the symbol correctly is
In general, the probability of the error for MPSK with coherent demodulation is given by [35]. We consider a stationary flat and slowly fading channel where (a) the delay spread introduced by the multipath propagation environment is negligible compared to the symbol interval (hence, the channel does not introduce intersymbol interference) and (b) channel fading status does not change not. many over a number of symbol intervals. The first condition means that the effect of the channel can be represented by a complex gain art) expljO(t)}, where a(t) is the amplitude fading and O(t) the phase distortion. In an A WGN channel, for a large value of Y b, the probability of error decreases exponentially with respect to Y 2b • In a Rayleigh fading channel, however, the probability of error decreases with respect to Yb for Yb» 1 .
When the signal is in deep fading (ie, a(t) « l), the instantaneous bit SNRI drops significantly, resulting in a very high chance of transmission error, although in most cases the instantaneous value Y b of the received signal is greater than the corresponding one in an AWGN channel. Therefore, the output of the lth branch demodulator at the end of the Kth symbol interval is. This is because maximum ratio combining uses the signal components in all diversity channels, and the average SNR per bit increases linearly with L. However, in selective diversity, at any time, only the signal from the best channel is used for detection .
The analysis of the bit error probability in a Rayleigh fading channel can be extended, for example, by diversity, so that . Where 1;,lr(x) is the conditional bit error probability given that the received SNR per bit is r =x. This is because for the same value of Tb, Tc for L =8 is 3dB less than Tc for L =4 with low. The effect of the much higher channel noise in the case of L =8 on the BER is stronger than the gain diversity effect achieved by increasing L from 4 to 8.
The following observation can be made: (a) Comparing the BER curve of an A WON channel with that of the fading channel without diversity (L=1), the transmission performance is seriously degraded by the Rayleigh fading; (b) Selective diversity can greatly improve the BER performance; (c) The performance improvement is more significant when L is increased from 1 to 2 than it is when Lis is further increased from 2 to 4 and to 8. Note that the superior performance of BPSK with maximum ratio combining is obtained under the assumption that that the receiver can have accurate estimates of the diversity channel gains alk expU Blk) and can then. It is a point to note that the two interference effects should be included in the CNIR of the received Rayleigh wave, since these interferences are caused by Rayleigh fading.
RESULTS AND DISCUSSION
Results and Discussion
It is noted that there is an improvement in receiver sensitivity as the number of receiving antennas L increases. For example, the sensitivity of the receiver at a BER of 10-3 with L=2 without turbo coding is approximately 29 dB and approximately 22.5 dB when turbo coding is applied.
34; IIJ)
The improvement in BER performance for receive diversity with Turbo coding is shown in Figures 3.8 to 3.11. It is observed that the sensitivity of the receiver is significantly improved by increasing the free distance code for the Doppler frequency fd= 100 Hz. So, in Turbo coding, the gain of the receiver increases as the free distance code increases.
For the different number of receiving antennas, the gain is calculated for increasing the db and fd= value.
CONCLUSION AND FUTURE WORK
Conclusion
Suggestions for Future Works
January 2002
26] Steendam, H., Moeneclaey, M., "Analise and Optimization of the performance of OFDM on Frequency-Selective Time-Selective Fading Channels", IEEE Transaction on Communication, Vol-47, No.12 Desember 1999. S., "A systematic approach to the detection of OFDM signals in a faded channel", IEEE Transaction on Communication, Vol-48, No. 28] Fumihito Sasarnori, Shiro Handa and Shinjiro Oshita, "A Simple Method of BER Calculation in DPSKlOFDM Fading Channel Galaxies", IEICE Transaction Fundamentals, VoI.E88-A, No-I, bladsy 366-373, January 2005.
Sollenberger, "Transmit diversity for OFDM systems and its impact on high-speed wireless data networks," IEEE J.
