The Eureka 147 digital audio broadcasdting system adapted to the U.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 83-85).by Nupur Gupta.M.Eng

Design of an OFDM Physical Layer Encryption Scheme

This paper presents a new encryption scheme implemented at the physical layer of wireless networks employing orthogonal frequency-division multiplexing (OFDM). The new scheme obfuscates the subcarriers by randomly reserving several subcarriers for dummy data and resequences the training symbol by a new secure sequence. Subcarrier obfuscation renders the OFDM transmission more secure and random, whereas training symbol resequencing protects the entire physical layer packet but does not affect the normal functions of synchronization and channel estimation of legitimate users while preventing eavesdroppers from performing these functions. The security analysis shows that the system is robust to various attacks by analyzing the search space using an exhaustive key search. Our scheme is shown to perform better in terms of search space, key rate, and complexity in comparison with other OFDM physical layer encryption schemes. The scheme offers options for users to customize the security level and the key rate according to the hardware resource. Its low complexity nature also makes the scheme suitable for resource-limited devices. Details of practical design considerations are highlighted by applying the approach to an IEEE 802.11 OFDM system case study

Design Implementation of Next Generation Wireless LAN for Mass Digital Cinema

We have been designing an over 1.2 Gbps throughput wireless for next generation WLAN system conform with IEEE802.11TGac’s requirements. It reaches 33 meter propagation distance by using 80MHz of bandiwdth on 5GHz band. 4x5 antennas configuration contribute 2nd-order diversity gain and maintain both the high throughput and performance. The Greenfield format preamble was proposed for its high efficiency. Novel phase rotation is employed to lower the PAPR signal. Run test for transmitting 90 frames of 40961714 pixels/frame under in-door channel model proves that the proposed system shall be considered for providing an excellent performance mass digital cinema. Index Terms—Gigabit wireless LAN, IEEE802.11 TGac, digital cinema transmissio

Performance Analysis and Enhancement of Multiband OFDM for UWB Communications

In this paper, we analyze the frequency-hopping orthogonal frequency-division multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless personal area networks (WPANs) based on ultra-wideband (UWB) transmission. Besides considering the standard, we also propose and study system performance enhancements through the application of Turbo and Repeat-Accumulate (RA) codes, as well as OFDM bit-loading. Our methodology consists of (a) a study of the channel model developed under IEEE 802.15 for UWB from a frequency-domain perspective suited for OFDM transmission, (b) development and quantification of appropriate information-theoretic performance measures, (c) comparison of these measures with simulation results for the Multiband OFDM standard proposal as well as our proposed extensions, and (d) the consideration of the influence of practical, imperfect channel estimation on the performance. We find that the current Multiband OFDM standard sufficiently exploits the frequency selectivity of the UWB channel, and that the system performs in the vicinity of the channel cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading algorithm improve the system power efficiency by over 6 dB at a data rate of 480 Mbps.Comment: 32 pages, 10 figures, 1 table. Submitted to the IEEE Transactions on Wireless Communications (Sep. 28, 2005). Minor revisions based on reviewers' comments (June 23, 2006

Feasibility study of 5G low-latency packet radio communications without preambles

This thesis deals with the feasibility of having lower latency for radio communication of short packets, which is the major traffic in the fifth generation (5G) of cellular systems. We will examine the possibility of using turbo synchronization instead of using a long preamble, which is needed for Data-Aided (DA) synchronization. The idea behind this is that short packets are required in low-latency applications. The overhead of preambles is very significant in case of short packets. Turbo synchronization allows to work with short or null preambles. The simulations will be run for a turbo synchronizer which has been implemented according to the Expectation Maximization (EM) formulation of the problem. The simulation results show that the implemented turbo synchronizer outperforms or attains the DA synchronizer in terms of reliability, accuracy and acquisition range for carrier phase synchronization. It means that the idea of eliminating the preamble from the short packet seems practical. The only downward is that there is a packet size limitation for the effective functionality of turbo synchronizer. Simulations indicate that the number of transmitted symbols should be higher than 128 coded symbols

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Lo standard LTE

Per il sempre crescente traffico dati la rete mobile, attualmente basata sul sistema UMTS, sta cominciando a dimostrare i suoi limiti. Per questo il 3GPP (third Generation Partnership Project) ha avviato la standardizzazione di un nuovo sistema di telecomunicazioni mobile, chiamato LTE (Long Term Evolution), che migliora il precedente ponendo ambiziosi traguardi in quanto a prestazioni. Attualmente il sistema è ancora in fase sperimentale e le prime applicazioni commerciali si avranno solo tra il 2010-2011. Questa tesi ha lo scopo di studiare le principali caratteristiche del livello fisico dell'LTE e valutarne le prestazioni offert

Telecommunications for a deregulated power industry

Telecommunication plays a very important role in the effective monitoring and control of the power grid. Deregulation of the US power industry has enabled utilities to explore various communication options and advanced technologies. Utilities are increasingly investing in distributed resources, dynamic real-time monitoring, automated meter reading, and value added services like home energy management systems and broadband access for its customers. Telecommunication options like power line communications (PLC) and satellites are fast replacing legacy telephone and microwave systems in the US.;The objective of this thesis is to study the communication options that are available for utilities today. Phasor measurement units (PMUs) are analyzed in detail and communication delays due to the use of PMUs in wide area measurement systems (WAMS) are also studied. The highlight of this thesis is a close look at the characteristics of the power line channel by presenting a power line channel model and the use of digital modulation techniques like SS and OFDM, which help overcome the effects of such a hostile medium of communication. (Abstract shortened by UMI.)