The Experts below are selected from a list of 2172 Experts worldwide ranked by ideXlab platform

K. Kikuchi - One of the best experts on this subject based on the ideXlab platform.

E Geraniotis - One of the best experts on this subject based on the ideXlab platform.

  • ber of ds cdma using symbol aided Coherent Demodulation over rician and rayleigh fading channels
    International Symposium on Spread Spectrum Techniques and Applications, 1998
    Co-Authors: M M Khairy, E Geraniotis
    Abstract:

    The BER of DS/CDMA systems that use symbol-aided Demodulation (SAD) over Rayleigh and Rician fading channels is evaluated. Known symbols are transmitted with a certain frequency together with the data symbols and are used by the receiver to extract a phase reference for Demodulation. Different schemes for filtering of the known symbols to obtain the phase reference needed for Demodulation are considered and BER comparisons are made. The BER of these SAD DS/CDMA schemes is also compared with that of fully Coherent and differentially Coherent DS/CDMA systems operating over Rician and Rayleigh fading channels. The important role of filtering in SAD for DS/CDMA networks is studied in detail and it is shown that under some channel and system conditions (such as terrestrial mobile with low data rates) optimum (Wiener) filtering is needed while for other channel and system conditions (such as GEO satellite with higher data rates) simpler low pass filters are sufficient.

  • the probability of multiple correct packet receptions in direct sequence spread spectrum networks
    IEEE Journal on Selected Areas in Communications, 1994
    Co-Authors: E Geraniotis
    Abstract:

    We provide methods to evaluate the probabilities P(l, m-l|K), l=0, 1, ..., m and m/spl les/K of exactly l correct packet receptions in a group of m receivers, given that K packets are transmitted simultaneously from users employing direct-sequence spread spectrum (DS/SS) signalling schemes. This quantity is useful for the design and performance evaluation of protocols for admission control and dynamic code allocation in multiple-access spread spectrum packet radio networks intended for terrestrial or satellite applications. The evaluations are carried out for DS/SS networks employing BPSK modulation with Coherent Demodulation and convolutional codes with Viterbi decoding. Systems with geographically dispersed receivers and systems with colocated receivers are considered. Approximations based on the independent receiver operation assumption (IROA) and the Gaussian multivariate distribution are developed, and their accuracy is checked against the exact expressions derived for synchronous systems. The joint first error event approximation (JFEEA) is also developed for coded systems and compared to the IROA. >

J M Shea - One of the best experts on this subject based on the ideXlab platform.

  • iterative channel estimation and partially Coherent Demodulation of cpfsk in time selective fading channels
    Military Communications Conference, 2011
    Co-Authors: Oluwatosin A Adeladan, J M Shea
    Abstract:

    When continuous-phase frequency-shift keying (CPFSK) is used over a fading channel, Coherent Demodulation can offer a significant performance gain over nonCoherent Demodulation. However, when the fading varies over a packet, pilot symbols must typically be inserted to help track the channel phase, thus reducing the data rate and energy efficiency. If the spacing between pilot symbols is greater than the channel coherence time, then the phase estimates for symbols that are far from the pilot symbols will be poor. In such scenarios, partially Coherent Demodulation can be utilized to properly demodulate symbols based on the quality of their phase estimates. In this paper, we apply iterative channel estimation, partially Coherent Demodulation in a system employing CPFSK modulation over a time-selective Rayleigh fading channel. We show that this approach can significantly improve the performance of CPFSK over schemes that use only nonCoherent or Coherent Demodulation.

  • interference mitigation with partially Coherent Demodulation in a slow frequency hopping spread spectrum system
    Military Communications Conference, 2009
    Co-Authors: Oluwatosin A Adeladan, J M Shea
    Abstract:

    Iterative signal processing has gained in popularity over the last decade as a way of reducing the effects of interference in a communication system. In previous work, the expectation maximization (EM) algorithm was used to estimate the parameters and data of colliding transmissions in a slow frequency-hopping spread-spectrum (FHSS) system using binary frequency-shift keying (BFSK). As in many FHSS systems, nonCoherent Demodulation was used. In this paper, we propose a refinement to the EM algorithm to allow the phase estimator in each iteration to be characterized as a Tikhonov random variable. We then use partially Coherent detection for the desired user's signal. The parameters of the Tikhonov distribution are refined at each iteration, which results in the demodulator transitioning from fully nonCoherent operation in the first iteration to nearly Coherent detection in later iterations for many dwell intervals. We show that this approach significantly improves the multiple-access capability of the system.

  • nonuniform phase shift key modulation for multimedia multicast transmission in mobile wireless networks
    IEEE Journal on Selected Areas in Communications, 1999
    Co-Authors: M B Pursley, J M Shea
    Abstract:

    It is a common requirement in a mobile wireless communication network that a radio must be capable of simultaneously transmitting a message to two or more neighbors in the network. Some of the intended recipients may be more capable than others in the sense that their communication links from the transmitter have less interference, fading, or attenuation. Because it is desirable that a multicast or broadcast transmission be received successfully by all radios for which it is intended, the usual approach is to limit the transmission rate to that which can be demodulated by the least capable among these radios. Nonuniform nonbinary phase-shift-key (PSK) signal constellations can be designed to increase the throughput of multicast transmissions by delivering additional information to more-capable receivers along with the multicast message. This additional throughput can be employed to transmit multimedia messages (e.g., voice and data) to the more-capable receivers. In this paper, we determine the error probabilities for Coherent Demodulation of nonuniform PSK signals and nonCoherent Demodulation of nonuniform differential PSK signals. Because the PSK constellations have a constant envelope, they are better for use in mobile wireless communication networks than the constellations based on quadrature-amplitude modulation that have been proposed in previous publications.

Hideo Kobayashi - One of the best experts on this subject based on the ideXlab platform.

  • a novel channel estimation method for ofdm transmission technique under fast time variant fading channel
    Vehicular Technology Conference, 2003
    Co-Authors: T Fukuhara, Hao Yuan, Y Takeuchi, Hideo Kobayashi
    Abstract:

    This paper proposes a novel estimation method of channel frequency response for orthogonal frequency division multiplexing (OFDM) systems operating in fast time-variant fading channels. The proposed method enables accurate Coherent Demodulation without using pilot signals, which are usually required to be inserted in the data symbols periodically to cope with fast time-variant fading. Computer simulation results show that the proposed method maintains better BER performance even when the vehicle speed reaches 180 km/h.

  • a novel Coherent Demodulation for m qam ofdm signal operating in the burst mode
    Vehicular Technology Conference, 2000
    Co-Authors: Hideo Kobayashi
    Abstract:

    This paper proposes a novel Coherent Demodulation method for orthogonal frequency division multiplexing (OFDM) systems with multi-level quadrature amplitude modulation (M-QAM) that are operating in a burst mode such as wireless LAN communications systems. The salient feature of the proposed method is that two training symbols placing at the start of every burst frame are used both for the synchronization of received burst signal and the estimation of channel frequency response under frequency selective fading environments. Furthermore, this paper proposes a simple phase tracking method for compensating the phase rotation of signal constellation points due to the residual frequency offset as the result of frequency offset estimation method of using two training symbols. The Coherent demodulator including the phase tracking method proposed in this paper offers excellent C/N performance even under severe frequency selective fading environments without any assistance of the pilot tones which is usually employed in the conventional Coherent Demodulation for the M-QAM OFDM signal.

Yuejiang Song - One of the best experts on this subject based on the ideXlab platform.

  • bit error rate analysis of ook modulation scheme under non Coherent Demodulation for space uplink optical communication systems
    International Conference on Communication Technology, 2015
    Co-Authors: Mi Li, Tingguang Li, Xuping Zhang, Yuejiang Song
    Abstract:

    With the development of communication technique, space microwave communication technique has shown its limitation in the transmission of high data rate. While space optical communication system introduces laser as the signal carrier and can solve this problem very well. At present, on-off keying (OOK) is one of the most important modulation scheme widely used in space optical communication systems, and the intensity modulation direct detection (IM-DD) non-Coherent Demodulation is the corresponding Demodulation scheme. However, researchers always pay attention to the Coherent Demodulation for OOK modulation scheme. That deviates from the practical systems. This paper focuses on the OOK communication systems with non-Coherent Demodulation and analyzes the relationship between BER and the key parameters of this systems, such as transmission power, ratio of beam radius and transmission power, ratio of receiver radius and transmission power, ratio of divergence angle and transmission power, and so on. We also compare the BER performance between non-Coherent Demodulation and Coherent Demodulation under the same low level of noise. The work will practically benefit the optimal design of the space optical communication systems.

  • ber performance of msk in ground to satellite uplink optical communication under the influence of atmospheric turbulence and detector noise
    Optics Letters, 2013
    Co-Authors: Jiachen Ding, Minghui Tang, Yuejiang Song
    Abstract:

    Minimum shift keying (MSK) has been widely used in fiber optical communication and free-space optical communication. In order to introduce MSK into satellite laser communication, the bit-error rate (BER) performance of the MSK scheme is investigated in uplink communications under the influence of atmospheric turbulence consisting of weak fluctuation and beam wander. Numerical results indicate that the BER performance of MSK is much better than the performance of on–off keying (OOK). With the laser power being 4 W, the improvement is 5 dB in Coherent Demodulation and 15 dB in delay Coherent Demodulation. Furthermore, compared with OOK, optimal values of the divergence angle, receiver diameter, and transmitter beam radius are easier and more practical to achieve in the MSK scheme. The work can benefit ground-to-satellite laser uplink communication system design.