Comparative Performance Evaluation of DVB-T using Advance Design System (ADS)

Wireless technologies have brought a rapid growth to digital video broadcasting and as such, has played (and still playing) a vital role in communication systems. Orthogonal frequency division multiplexing (OFDM) has also become so popular in wireless communication systems reason been that it has high spectral efficiency, high throughput, high data capacity and resilience to multipath fading. In addition to these, it is very robust to channel impairment; a quality which has made it preferable and ideal in wireless communication systems. This paper evaluates DVB and compares its performance across three different channels (AWGN, Rayleigh and Ricean) and three different modulation techniques (QPSK, 16 QAM and 64 QAM) is employed. DTV_DVB in 2K Mode carriers is transmitted across AWGN, Rayleigh and Ricean and a comparison of BER performance of the different modulation schemes was considered. At the end of the simulation results and analysis, it was found that AWGN in 16QAM carrier modulation is considered the best modulation technique for DVB_T. Keywords: modulation, channel, digital television, digital video broadcasting

Reduction of peak to average power ratio in OFDM and OFDM-CDMA system

High Peak to Average Power Ratio is a main problem in Orthogonal Frequency Division Multiplexing(OFDM) system and Orthogonal Frequency Division Multiplexing -Code Division Multiple Access (OFDM-CDMA) system. Considering a compensated High Power Amplifier(HPA), in order to keep linearity for amplification, Input Back-Off(IBO) of the HP-A, has to be increased for handling a high PAPR. Higher 1130 will make HPA less efficient. Additionally, a signal with high PAPR will suffer clipping when PAPR is larger than 1130 of the HPA. Clipping can cause the distortion of the signal and deteriorate the performance of the system. Reduction of PAPR is a main issue for OFDM and OFDM-CDMA application. In this thesis, some coding schemes are discussed to reduce PAPR. Of all possible code words for transmission, some code words with lower PAPR are chosen for transmission. Some redundancies are added to the end of the original code words to form these lower PAPR code words, though the net bit rate will decrease as a tradeoff. To reduce PAPR block coding scheme and cyclic coding scheme are discussed first. An odd parity bit is added as a redundancy bit. Also the code rate is 3/4. A novel block coding scheme with bit position control is discussed, where the position of the redundancy bit in the original code words is chosen by a feedback selection. For multiuser application, OFDM-CDMA is discussed. Walsh- Hadard (WH) and Complementary (CP) and Gold code sequences are used as the spreading sequences. These coding schemes used in OFDM system are also used before spreading to reduce PAPR in OFDM-CDMA system

Laboratory and field trials evaluation of transmit delay Diversity applied to DVB-T/H networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The requirements for future DVB-T/H networks demand that broadcasters design and deploy networks that provide ubiquitous reception in challenging indoors and other obstructed situations. It is essential that such networks are designed cost-effectively and with minimized environmental impact. The use of transmit diversity techniques with multiple antennas have long been proposed to improve the performance and capacity of wireless systems. Transmit diversity exploits the scattering effect inherent in the channel by means of transmitting multiple signals in a controlled manner from spatially separated antennas, allowing independently faded signals to arrive at the receiver and improves the chances of decoding a signal of acceptable quality. Transmit diversity can complement receive diversity by adding an additional diversity gain and in situations where receiver diversity is not practical, transmit diversity alone delivers a comparable amount of diversity gain. Transmit Delay Diversity (DD) can be applied to systems employing the DVB standard without receiver equipment modifications. Although transmit DD can provide a gain in NLOS situations, it can introduce degradation in LOS situation. The aim of this thesis is to investigate the effectiveness in real-word applications of novel diversity techniques for broadcast transmitter networks. Tests involved laboratory experiments using a wireless MIMO channel emulator and the deployment of a field measurement campaign dedicated to driving, indoor and rooftop reception. The relationship between the diversity gain, the propagation environment and several parameters such as the transmit antenna separation, the receiver speed and the Forward Error Correction Codes (FEC) configuration are investigated. Results includes the effect of real-word parameter usually not modeled in the software simulation analysis, such as antenna radiation patterns and mutual coupling, scattering vegetation impact, non-Gaussian noise sources and receiver implementation. Moreover, a practical analysis of the effectiveness of experimental techniques to mitigate the loss due to transmit DD loss in rooftop reception is presented. The results of this thesis confirmed, completed and extended the existing predictions with real word measurement results

MIMO-OFDM Optimal Decoding and Achievable Information Rates Under Imperfect Channel Estimation

Optimal decoding of bit interleaved coded modulation (BICM) MIMO-OFDM where an imperfect channel estimate is available at the receiver is investigated. First, by using a Bayesian approach involving the channel a posteriori density, we derive a practical decoding metric for general memoryless channels that is robust to the presence of channel estimation errors. Then, we evaluate the outage rates achieved by a decoder that uses our proposed metric. The performance of the proposed decoder is compared to the classical mismatched decoder and a theoretical decoder defined as the best decoder in the presence of imperfect channel estimation. Numerical results over Rayleigh block fading MIMO-OFDM channels show that the proposed decoder outperforms mismatched decoding in terms of bit error rate and outage capacity without introducing any additional complexity

Diversity gain for DVB-H by using transmitter/receiver cyclic delay diversity

The objective of this paper is to investigate different diversity techniques for broadcast networks that will minimize the complexity and improve received SNR of broadcast systems. Resultant digital broadcast networks would require fewer transmitter sites and thus be more cost-effective and have less environmental impact. The techniques can be applied to DVB-T, DVB-H and DAB systems that use Orthogonal Frequency Division Multplexing (OFDM). These are key radio broadcast network technologies, which are expected to complement emerging technologies such as WiMAX and future 4G networks for delivery of broadband content. Transmitter and receiver diversity technologies can increase the frequency and time selectivity of the resulting channel transfer function at the receiver. Diversity exploits the statistical nature of fading due to multipath and reduces the likelihood of deep fading by providing a diversity of transmission signals. Multiple signals are transmitted in such a way as to ensure that several signals reach the receiver each with uncorrelated fading. Transmit diversity is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here comply with existing DVB standards and can be incorporated into existing systems without change. The diversity techniques introduced in this paper are applied to the DVB-H system. Bit error performance investigations were conducted by simulation for different DVB-H and diversity parameters

Performance Enhancement in SU and MU MIMO-OFDM Technique for Wireless Communication: A Review

The consistent demand for higher data rates and need to send giant volumes of data while not compromising the quality of communication has led the development of a new generations of wireless systems. But range and data rate limitations are there in wireless devices. In an attempt to beat these limitations, Multi Input Multi Output (MIMO) systems will be used which also increase diversity and improve the bit error rate (BER) performance of wireless systems. They additionally increase the channel capacity, increase the transmitted data rate through spatial multiplexing, and/or reduce interference from other users. MIMO systems therefore create a promising communication system because of their high transmission rates without additional bandwidth or transmit power and robustness against multipath fading. This paper provides the overview of Multiuser MIMO system. A detailed review on how to increase performance of system and reduce the bit error rate (BER) in different fading environment e.g. Rayleigh fading, Rician fading, Nakagami fading, composite fading

Performance evaluation of fixed WiMax physical layer under high fading channels

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system

Analysis of MIMO Communications Systems Based on Experimentally Observed Channels

This thesis presents an analysis of multiple-input/multiple-output (MIMO) communications systems where the objective is to provide a unified solution to the problems of (i) crosstalk coupling in transmission line channels (ii) multi-path fading in the time variant high frequency wireless channel. In the case of transmission line channels, a comparative analysis is presented of the performance of MIMO communications systems based on balanced CAT 5 twisted-pair transmission lines, balanced twisted-pair telephone transmission lines scheme as well as unbalanced flat-pair transmission lines. The unbalanced flat-pair transmission lines are viewed as a model for digital subscriber lines (DSLs) which may be deemed out-of-range for high speed internet connections because of the circumstances of poor balance, high insertion losses and high degrees of crosstalk. This comparative analysis is then extended to examine effect of imperfect knowledge of the transmission line channels on MIMO communications system performance. In the case of wireless channels, an analysis is presented which investigates the effect of both the Rayleigh and Ricean channels on MIMO communications system performance. Again the analysis of the wireless channels is extended to examine the effect of imperfect knowledge of the channel on MIMO communications systems performance. All of the analyses in this work are based on experimentally observed channels. In the case of the transmission line channels, it is concluded that MIMO communications systems do offer the possibility of high speed internet connectivity on transmission lines that, hereto, would have been considered out-of-range for such services. Considering the CAT 5 transmission line channels, it is concluded that the MIMO communications system provide enhancement at frequencies above 50 MHz and therefore the possibly of extending length and coverage above the standard 100 metres is proposed. On the other hand, the improved performance of the twisted-pair telephone transmission lines is consistent over the range from 300 kHz to 100 MHz when the MIMO system is applied. For all the transmission line channels that are examined, the extent of imperfect knowledge of the channel that can be allowed while maintaining a reasonable MIMO communications system performance is indicated. In the case of the wireless channels, it is concluded that MIMO communications system performance is better in the case of Rayleigh channel than in the case of Ricean channel provided that the degree of correlation of the multi-path channel impulse response components is equivalent. Also, as the number of transmitters and receivers, N T, increases the effect of a given degree of imperfect knowledge of the wireless channel becomes more detrimental on MIMO communication system performance. This work thus indicates the extent of imperfect knowledge of the wireless channel that can be allowed while maintaining a reasonable MIMO communications system performance. The trade-off between increased capacity gain and decreased accuracy of knowledge of the channel as the dimension, N T, was increased is highlighted