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In an underwater environment signal propagation for the acoustic channel is subject to major multipath effect. Therefore, most underwater communication schemes require that the position of the transmitter or receiver is fixed while using directional antennas in order to ensure high signal-to-noise ratio. However, such a requirement hinders node discovery and ad-hoc formation of underwater networks...
In this paper we study joint transmitter adaptation and power control in multiuser wireless systems with multipath channels and target values imposed on the users' signal-to-interference+noise-ratio (SINR) at the receiver. We use a general framework that is applicable to a wide range of wireless systems and scenarios to cast this as a distributed constrained optimization problem, and study necessary...
In many wireless communication systems, the phase of the received signal can not be tracked accurately due to the random time-varying nature of the channel. Apart from the degradations caused by multipath fading and additive white Gaussian noise (AWGN), the imperfect phase estimation results in additional bit errors at receiver. In this paper, a simple semi-analytical method is presented for evaluating...
Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square...
Multipath propagation events are observed on the 50 km long fixed terrestrial link operating in 10 GHz band. Several receivers are located in different heights. Two year statistics of attenuation and enhancement due to multipath are obtained from measured signal fluctuations in different heights. The results are compared with cumulative distributions predicted by the two methods - the ITU-R method...
The two-curve MIMO performance model provides network planners with an intuitive model for MIMO system performance that not only incorporates the site-specific effects of multipath correlation, but also improves prediction accuracy compared to a single-curve lookup table. Most notably, the 2CMPM improved the standard deviation of the prediction by 8 Mbps in the 5.2 GHz band. Further, analysis of the...
This paper presents a practical low-density parity-check (LDPC) coded OFDM system designed for the underwater acoustic channel with its attendant multipath channel and large Doppler shift. The Doppler shift and channel state information (CSI) are assumed unavailable to both to the transmitter and the receiver. Due to the slow speed of sound in water, even small platform motions can affect the performance...
Training-based channel estimation involves probing of the channel in time, frequency, and space by the transmitter with known signals, and estimation of channel parameters from the output signals at the receiver. Traditional training-based methods, often comprising of maximum likelihood estimators, are known to be optimal under the assumption of rich multipath channels. Numerous measurement campaigns...
Coherent data communication over doubly-selective channels requires that the channel response be known at the receiver. Training-based schemes, which involve probing of the channel with known signaling waveforms and processing of the corresponding channel output to estimate the channel parameters, are commonly employed to learn the channel response in practice. Conventional training-based methods,...
Time-varying multi path channels lead to the loss of orthogonality among sub-carriers, resulting in inter carrier interference (ICI) in OFDM systems. Different from many schemes which only focus on equalizer design, our paper consider the entire receiver, and propose the semi-blind channel estimation and detection for OFDM systems in time-varying multi path channel. Theoretical analysis and simulation...
Novel Hopfield neural network (HNN) technique is proposed as an effective multiuser detection method of the uplink multiuser CDMA communication system. By the appropriate choice of the channel state information for the HNN parameters, the HNN collectively resolves the effects of both the inter-symbol interference due to the multipath fading channel and the multiple access interference in the receiver...
In this work, symbol error rate (SER) performance of quasi synchronous (QS) CDMA system over frequency selective time non-selective multipath Nakagami-m fading channels is obtained for M-ary phase shift keying (MPSK) signaling, deterministic spreading sequences and different chip waveforms with a maximal ratio combiner (MRC) at the receiver. We show that the performance of QS-CDMA will be as good...
This paper investigates the performance of a downlink space-time block code (STBC) multi-carrier code division multiple access (MC-CDMA) system employing a receiver with iterative channel estimation (ICE) and iterative equalization (IE). ICE based on the Kalman filter whereas IE based on the minimum mean square error (MMSE) equalizer. The performance of this system is investigated under time-varying...
Adaptive modulation can approach the channel capacity by adapting the number of bits per transmission symbol to channel quality variations. This paper proposes a fixed threshold adaptive modulation scheme for orthogonal frequency division multiplexing (OFDM) used in power line communications. This adaptive OFDM is combined with an adaptive power control scheme in order to combat with multipath fading...
Antenna systems for broadband polarization diversity reception rank among the emerging key technologies in next generation wireless communication systems. In order to suppress multipath conditioned polarization fading in typical applications of portable radios, antenna modules with dual-polarized transmission behavior are to be used. Self-complementary, logarithmically-periodic antennas serve as suitable...
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