314 research outputs found

    Comparison and Performance Analysis of DS-CDMA Systems by Genetic, Neural and GaNN (hybrid) Models

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    Direct Sequence-Code Division Multiple Access (DS-CDMA) technique is used in cellular systems where users in the cell are separated from each other with their unique spreading codes. DS-CDMA has been used extensively which suffers from multiple access interference (MAI) and inter symbol interference (ISI) due to multipath nature of channels in presence of additive white Gaussian noise (AWGN). Spreading codes play an important role in multiple access capacity of DS-CDMA system and Walsh sequences are used as spreading codes in DS-CDMA. DS CDMA receiver namely genetic algorithm neural network and GaNN (hybrid) based MUD receiver for DS-CDMA communication using Walsh sequences is designed. The performance of the same will be compared among themselves

    Spread Spectrum Is Good-But it Does Not Obsolete NBC v. U.S.!

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    The Authors criticize recent statements by leading legal commentators suggesting that the development of spread spectrum has eliminated radio interference and helped make the underlying legal foundations for regulating spectrum obsolete. The Authors provide a non-technical explanation of how spread spectrum works and why it does not have the effect of eliminating radio interference. The Authors conclude that new technologies are likely to increase the availability of usable spectrum, but they have not wiped out the problem of interference

    Interference Mitigation in WAIC Systems

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    Advancements in the field of wireless communications in the last few decades have made it an indispensable part of how human made entities, and by extension, humans interact with each other. The inherent lack of the need for significant physical infrastructure brings with it great advantages in terms of mobility, operational and maintenance costs, and overall reliability and flexibility. The characteristics of wireless techniques make for an attractive proposition for enabling operational communications in aircrafts. However, wireless networks bring with them their own set of challenges in terms of range, dependability or susceptibility to interference and security. The main objective of this thesis is to evaluate different wireless communications techniques for their feasibility to be employed as Wireless Avionics Intra-Communications (WAIC) systems. The major hindrance in ensuring reliable communications in this regard comes from the operation of the existing Radio Altimeter systems in the allotted frequency band of 4.2 - 4.4 GHz. WAIC systems based on wireless techniques such as Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) have been simulated in MATLAB for the analysis. The performance of the WAIC systems in the presence of interference from Altimeter signals and Additive White Gaussian Noise (AWGN) has been evaluated and studied

    Variable rate adaptive modulation for DS-CDMA

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    An adaptive coding scheme is introduced for a discrete sequence code-division multiple-access system. The system uses noncoherent M-ary orthogonal modulation with RAKE receiver and power control. Both a fast fading channel and a combined fast fading, shadowing and power control channel are considered. Analytical bounds and simulations are done to evaluate the performance of the system. It is found that there is significant improvement in the average throughput and the bit-error-rate performance in the adaptive coding scheme. The amount of improvement drops with the increase of diversity branches used. More importantly, it is found that adaptive coding scheme is relatively robust to shadowing, while fix-rate codes are ineffective in the shadowing environment. Finally, adaptive coding scheme is found to be robust to mobile speed, feedback delay, and finite interleaving depth.published_or_final_versio

    Spread Spectrum Is Good—But It Doesn’t Obsolete NBC v. US!

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    This short note addresses a popular misconception—that new technologies such as spread spectrum have eliminated the problem of radio interference. That is false. Spread spectrum is a great technology, but it does not eliminate the problem of interference. Similarly, although some have asserted otherwise, signals below the noise floor can create interference. We first show that a number of authors have embraced these misconceptions in works addressing public policy. Briefly, a basic argument of these papers is: (1) spread spectrum eliminates the problem of interference; (2) the Supreme Court’s decision in NBC v. US upholding the Communications Act of 1934 depended critically on the perception that radio interference is unavoidable; (3) given (1) the Court’s decision was wrong and must be revisited. We then provide a nonrigorous (no equations!) explanation of the nature of interference created by spread spectrum signals or by signals below the noise floor. We also offer a few pointers to the technical literature for those who wish to understand these issues in more depth

    Characterisation of MIMO radio propagation channels

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    Due to the incessant requirement for higher performance radio systems, wireless designers have been constantly seeking ways to improve spectrum efficiency, link reliability, service quality, and radio network coverage. During the past few years, space-time technology which employs multiple antennas along with suitable signalling schemes and receiver architectures has been seen as a powerful tool for the implementation of the aforementioned requirements. In particular, the concept of communications via Multiple-Input Multiple-Output (MIMO) links has emerged as one of the major contending ideas for next generation ad-hoc and cellular systems. This is inherently due to the capacities expected when multiple antennas are employed at both ends of the radio link. Such a mobile radio propagation channel constitutes a MIMO system. Multiple antenna technologies and in particular MIMO signalling are envisaged for a number of standards such as the next generation of Wireless Local Area Network (WLAN) technology known as 802.1 ln and the development of the Worldwide Interoperability for Microwave Access (WiMAX) project, such as the 802.16e. For the efficient design, performance evaluation and deployment of such multiple antenna (space-time) systems, it becomes increasingly important to understand the characteristics of the spatial radio channel. This criterion has led to the development of new sounding systems, which can measure both spatial and temporal channel information. In this thesis, a novel semi-sequential wideband MIMO sounder is presented, which is suitable for high-resolution radio channel measurements. The sounder produces a frequency modulated continuous wave (FMCW) or chirp signal with variable bandwidth, centre frequency and waveform repetition rate. It has programmable bandwidth up to 300 MHz and waveform repetition rates up to 300 Hz, and could be used to measure conventional high- resolution delay/Doppler information as well as spatial channel information such as Direction of Arrival (DOA) and Direction of Departure (DOD). Notably the knowledge of the angular information at the link ends could be used to properly design and develop systems such as smart antennas. This thesis examines the theory of multiple antenna propagation channels, the sounding architecture required for the measurement of such spatial channel information and the signal processing which is used to quantify and analyse such measurement data. Over 700 measurement files were collected corresponding to over 175,000 impulse responses with different sounder and antenna array configurations. These included measurements in the Universal Mobile Telecommunication Systems Frequency Division Duplex (UMTS-FDD) uplink band, the 2.25 GHz and 5.8 GHz bands allocated for studio broadcast MIMO video links, and the 2.4 GHz and 5.8 GHz ISM bands allocated for Wireless Local Area Network (WLAN) activity as well as for a wide range of future systems defined in the WiMAX project. The measurements were collected predominantly for indoor and some outdoor multiple antenna channels using sounding signals with 60 MHz, 96 MHz and 240 MHz bandwidth. A wide range of different MIMO antenna array configurations are examined in this thesis with varying space, time and frequency resolutions. Measurements can be generally subdivided into three main categories, namely measurements at different locations in the environment (static), measurements while moving at regular intervals step by step (spatial), and measurements while the receiver (or transmitter) is on the move (dynamic). High-scattering as well as time-varying MIMO channels are examined for different antenna array structures

    Turbo multiuser detection with integrated channel estimation for differentially coded CDMA systems.

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    Interference Mitigation in WAIC Systems

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    Advancements in the field of wireless communications in the last few decades have made it an indispensable part of how human made entities, and by extension, humans interact with each other. The inherent lack of the need for significant physical infrastructure brings with it great advantages in terms of mobility, operational and maintenance costs, and overall reliability and flexibility. The characteristics of wireless techniques make for an attractive proposition for enabling operational communications in aircrafts. However, wireless networks bring with them their own set of challenges in terms of range, dependability or susceptibility to interference and security. The main objective of this thesis is to evaluate different wireless communications techniques for their feasibility to be employed as Wireless Avionics Intra-Communications (WAIC) systems. The major hindrance in ensuring reliable communications in this regard comes from the operation of the existing Radio Altimeter systems in the allotted frequency band of 4.2 - 4.4 GHz. WAIC systems based on wireless techniques such as Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) have been simulated in MATLAB for the analysis. The performance of the WAIC systems in the presence of interference from Altimeter signals and Additive White Gaussian Noise (AWGN) has been evaluated and studied

    Parallel interference cancellation schemes based on adaptive MMSE detection for DS-CDMA systems

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    Master'sMASTER OF ENGINEERIN
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