Bøger af K. Riyazuddin

Revolutionary changes have been witnessed in the last decade in the field of wireless communications. 2G GSM based communication systems supporting data rates of 10 Kbps, are present and must see extinction. Number of enhanced wireless technologies have been industrialized in the past decade to allow broadband wireless access with data rates greater than 100 Mbps. These enhancements have successively led to the improvement and/or development of 3G and 4G wireless technologies like Worldwide Interoperability for Microwave Access (WiMAX), High Speed Downlink Packet Access (HSDPA), and Long-Term Evolution (LTE). This became possible by discovery of some wireless based technologies such as Orthogonal Frequency Division Multiplexing (OFDM), Code Division Multiple Access (CDMA), etc. These techniques form the basis of understanding in the realm of 3G/4G wireless communication systems. Wireless communications is the fastest budding section of the information communications industry. As such, it has bagged the public imagination and attention of the media. There is a tremendous growth in Cellular systems in the last few years. Certainly, the old wire line systems are supplanted by cellular phones which have become a dire business tool and also a part of the daily life in most of the developed countries. The future of wireless systems seems to be very bright because of an explosive growth in it united with the production of laptop and palmtop computers, both as stand-alone systems and being a part of a very big networking infrastructure. However, many technical challenges to be met while designing robust wireless networks which help in supporting some industrialized applications. OFDM has gained importance in recent years and it is the technique selected for wireless systems, such as Long-Term Evolution (LTE) for 4G communications systems, Wireless Local Area Networks (WLAN) or WiMAX. For this reason, OFDM systems have been under study in order to develop more accurate mobile stations positioning, both in outdoors and indoors environment. Nevertheless, OFDM systems require high timing synchronization accuracy in order to be able to receive the signal correctly, which makes timing synchronization estimation a key issue in OFDM receivers. Propagation is especially complicated over wireless channels, where the presence of multipath propagation, high level of interference signals or the obstruction of Line Of Sight (LOS) path make timing estimation even more difficult in indoor environment. The problem of multipath fading make timing estimation tough in outdoor environment also.