Differentially coherent code phase synchronization technique in a DS-SS mobile packet radio

A rapid acquisition scheme for direct-sequence (DS) spread-spectrum packet radio systems using PN matched filters is described. The system operates in burst mode, with limited permitted time for synchronization using a fixed length preamble at the beginning of each data burst. Multiple PN codes are available for acquisition at the first portion of the preamble. The second portion of the preamble consists of several PN codes which are modulated with a marker. The receiver may achieve code acquisition anywhere within the first portion of the preamble. Since it is not known a priori in which of the several code periods acquisition will occur, coincidence detection is done using the marker for frame synchronization. The analysis shows that the scheme yields better performance than some other previous schemes in packet radio systems. >

This paper investigate the properties of space-time bit-interleaved coded modulation (ST-BICM) systems in fast Rayleigh fading channels. We first show that ST-BICM with QPSK signaling in fast fading channels possesses the uniform distance property, which makes performance analysis tractable. We also derive the probability distribution of the squared Euclidean distance between space-time symbols assuming uniform bit-interleaving. Based on the distribution, we show that the diversity order for each codeword pair becomes maximized as the frame length becomes sufficiently long. We analyze the performance of ST-BICM in fast fading channels by deriving an FER upper bound. The derived bound turns out very accurate, requiring only the distance spectrum of the binary channel codes of ST-BICM. Numerical results demonstrate that the bound is tight enough to render an accurate estimate of performance of ST-BICM systems.

This paper aims at comparing the performance of numerous space-time trellis coded modulations (STTCM) over slow and fast Rayleigh fading channels in order to identify the most efficient ones. After a brief presentation of the STTCM concept, we propose to recall the criteria used to construct the codes studied herein, depending on the channel properties and the number of transmit and receive antennas. Then, we introduce our new representation of the STTCM as an extension of the one currently used to describe regular trellis codes, namely the polynomial representation. Simulation results and especially new performance relative to BER scale are then given in order to compare the behavior of Tarokh's, Baro's, Blum's, Chen's and Firmanto's codes over slow and fast Rayleigh fading channels. From these comparisons, it follows that the codes constructed with the trace criterion, namely Chen's codes, outperform all the other tested codes over both channels.

In this paper, we use the minimum mean square error (MMSE) criterion to design the scaled and offset belief propagation (BP)-based decoding algorithms for short low-density parity-check (LDPC) codes on the fast Rayleigh fading channel. Based on the MMSE criterion, the theoretical formulas and numerical calculations on the optimum factors for these two improved BP-based algorithms are provided. The simulation results for several short (Chen et al., 2005 and Gallager, 1962) regular LDPC codes on the fast Rayleigh fading channel demonstrate that the scaled and offset BP-based algorithms with our proposed factors can achieve the performance better than that of the BP algorithm.

An exact closed-form bit error rate expression is derived for an orthogonal frequency-division multiplexing system, each subcarrier modulated by /spl pi//4-shifted differentially encoded quadrature phase shift keying, in the presence of carrier frequency offset over frequency-selective fast Rayleigh fading channels. Both single channel reception and diversity reception with maximal ratio combining are considered. The closed-form expression allows us to investigate the effect of several channel parameters, including mean delay spread and maximum Doppler shift, on the system bit error rate performance. Particularly, the effect of carrier frequency offset on the system performance can be studied for a more realistic wireless channel environment model. Small carrier frequency offsets have slight influences on the system performance. Compared with the same amount of Doppler shift, carrier frequency offset usually leads to a greater degree of performance degradation. Systems with fewer subcarriers are more sensitive to the channel mean delay spread. By using the exact closed-form bit error rate expression, an optimum number of subcarriers can be found, and the allowable carrier frequency offset, Doppler shift, and mean delay spread for given operating conditions can be determined.

We investigate the detection of space time coded (STC) signals modulated using continuous phase modulation (CPM) in fast Rayleigh fading channels. A symbol-by-symbol iterative detector with an optimum front-end is derived, and its practical implementation using the concept of principal component analysis (PCA) is considered. To assess the performance, numerical examples for different STC-CPM schemes are presented. According to the simulation results, the proposed detector obtains very good power efficiencies. Moreover, the bit error rate (BER) performance of the proposed detector is in the range of 0.5-1 dB from the case without fading, highlighting its effectiveness to mitigate fading.

A modified pseudonoise (PN) code tracking loop is proposed for direct-sequence spread-spectrum communications in the fast fading channel and strong interference environment. First, to formulate the problem we analyze PN code autocorrelation character in the fast fading channel and strong interference. Then the modified PN code tracking model using limited-length curve fitting algorithm is developed to improve the tracking performance. Analytical expressions of the curve fitting algorithm are derived and then confirmed by means of extensive computer simulation results. In addition, utilizing a DS/BPSK experimental system, several simulation results for PN code tracking performance are also presented in this paper. Very attractive behaviors obtained using the proposed technique are verified.

In this work we examine the probability of error performance for a multiuser DS-CDMA system that exploits spatial and temporal diversities over fast-fading Rayleigh channels using a space-time block coding scheme. We commence the analysis by finding the probability density function (pdf) for the signal to interference ratio (SIR). Then, using this pdf, a closed form expression for the probability of error using the decorrelator multiuser detector is obtained. We verify the accuracy of this expression by comparison with simulations for different number of users. Both theoretical and simulation results show that the diversity order is maintained irrespective of the system load.

Wireless communication system plays an essential role in data transmission system. In wireless systems like satellite network, mobile communication, or any data transmitted network, a specified band is allotted. Such network has its own specified allotted spectrum for secure communication. Safe data transmission and reception are important and difficult tasks. Such data transmission needs some secure techniques to transmit data securely, and one such technique is hiding the transmission data or hiding the message signals. To provide security to message signal, random noise is added through pseudo-noise (PN) sequence generator. When PN sequence is added to a message signal, it resembles like a noise making it hard to decode and increases the signal bandwidth to utilize the whole spectrum. In this paper, the approach to generate PN sequence using Vedic multiplier has been proposed. In a Vedic multiplier, multiplication is done by using Urdhva Tiryagbhyam sutra, and basic multiplication method is used to design conventional multiplier. The PN sequence generator is implemented using Verilog HDL. The comparative analysis of Vedic multiplier over the conventional multiplier is implemented using Altera FPGA. Vedic multiplication gives an effective result when compared to conventional multipliers.

In this paper, the receiver performance of Alamouti coded orthogonal frequency division multiplexing (OFDM) systems is analyzed. When the channel is not constant during the period of Alamouti codeword transmission, the conventional linear maximum likelihood (ML) receiver suffers from performance degradation. We use three different receiver combining methods and study the error performance. The sensitivity of different receivers is investigated by varying the correlation coefficient. Our results can be easily extended to be applicable to other block coded OFDM schemes with different antenna configurations. The performance loss in linear ML receiver can be partially improved by employing a decision-feedback strategy. In the decision feedback steps preliminary decisions are used to subtract the intercodeword coupling. However this increases the computational complexity of the receiver.

Existing SCMA systems presented for multiuser detection has high computational complexity. The complexity is a prime concern considering its implementation in a machine-to-machine (M2M) communication involving limited capacity devices. Since these devices have low processing power, so practical implementation of SCMA needs to be optimised for better performance. This paper proposes an SCMA decoder with a soft demapping technique to reduce the computational complexity, providing better performance. To improve the stability of SCMA system for M2M communication, this paper proposes the use of noise variance threshold ψ, to handle the system’s stability. Results confirmed that the proposed soft demapper-based SCMA reduced the execution time to 33% and the iteration number to 63% compared to the conventional SCMA scheme deploying message passing algorithm (MPA)-based decoding. The proposed SCMA provides an improvement of 2.5 dB at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> under the block Rayleigh fading channels and an improvement of approximately 1.1 dB at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> dB under the fast Rayleigh fading channels. The improvements come from the fast convergence of iterative decoding using a soft demapper supported by a variance threshold ψ that avoids the duality decision at the border of the decision area.

We propose a method for blind multiuser detection (MUD) in synchronous systems over flat and fast Rayleigh fading channels. We adopt an autoregressive-moving-average (ARMA) process to model the temporal correlation of the channels. Based on the ARMA process, we propose a novel time-observation state-space model (TOSSM) that describes the dynamics of the addressed multiuser system. The TOSSM allows an MUD with natural blending of low-complexity particle filtering (PF) and mixture Kalman filtering (for channel estimation). We further propose to use a more efficient PF algorithm known as the stochastic M -algorithm (SMA), which, although having lower complexity than the generic PF implementation, maintains comparable performance.

This chapter contains sections titled: Introduction Performance Analysis of the Cooperation-Aided UL CUS for the Uplink Joint CPS and CUS for the Differential Cooperative Cellular UL Using APC Chapter Conclusions ]]>

We derive detection metrics for soft-output diversity combining for the case of imperfect channel state information at the receiver. We treat in particular the case when the noise variance at the receiver is unknown. We contrast conventional training-based methods to a detector based on the generalized likelihood-ratio (GLR) test paradigm. We study the performance of the detectors via EXIT chart analysis and via simulations of LDPC coded transmission over a fast Rayleigh fading channel. The results show that the GLR receivers can significantly outperform the conventional detectors.

In this paper, a data-aided (DA) synchronization method is developed to jointly recover symbol-timing, frequency offset, and carrier phase for MF-TDMA on-board processing (OBP) satellite system. The estimates, which are obtained from a block of symbols transmitted through an Additive White Gaussian Noise (AWGN) channel and a fast Rayleigh fading channel, can be obtained with reduced computational complexity and fast acquisition time. The estimation accuracy in terms of MSE is derived and illustrated. Its effect on the overall system BER performance is also discussed. Furthermore, the relationships between timing synchronization, frequency offset recovery, and carrier phase error compensation are also analyzed respectively. It is apparent that the proposed estimation method is not only accurate and efficient, but it makes the communication system robust to impairment parameters as well.