Application of Randomization Techniques to Space-Time Convolutional Codes

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.

Development of LTE is a milestone in the field of communication engineering. Compared to the performance of 2G the network involving LTE provides much higher data rates and support much more services. The evolution to LTE has provided the users to utilize many commercial activities to bring forward to the public and provide them the improved services compared to older versions of communication technologies. As the growth of LTE has provided much faster network still there are improvements going on the new technology. Various performance measures have been taken into considerations has the networks has performed very well on such test. One of the performance analyses has been presented in this paper comparing the performance of the LTE system over the Rayleigh and Rician fading channel. In the paper the performance of the MIMO LTE has been analyzed for the networks with various modulation schemes for Rayleigh and Rician fading channel with a 2x2 MIMO channel for EPA 0Hz, EVA 5Hz, EVA 70Hz. By varying Signal to Noise Ratio (SNR), Bit Error Rate (BER) of LTE is calculated for different Multi-Input Multi-Output (MIMO) schemes. The analysis is concluded in terms of speed of the data rate in Mbps.

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.

This paper introduces a new signal processing technique for designing transmit data to improve reliability of communications over wireless fading channels when there is a single transmit and multiple receive antennas using space-time convolutional codes. The original space-time convolutional code design was based on combining transmit diversity and coding to obtain reliability over fading channels when there are multiple transmit antennas. In this paper, we demonstrate that by appropriate transmit data design, we can implement space-time convolutional codes when there is only a single transmit and multiple receive antennas. We achieve this objective by transmitting multiple symbols during a symbol period from one transmit antenna. Multiple symbols are transmitted by multiplying each symbol with a random variable and superimposing them on top of each other. Inducing randomness into the channel is equivalent to creating additional paths, called virtual paths. Although these virtual paths are statistically dependent, by optimizing these induced random variables we can achieve block error rate performance improvement close to that of space-time convolutional codes on systems with multiple physical transmit antennas. Simulation results compare the performance of this technique and that of multiple transmit antenna systems with equal number of receive antennas for QPSK signal constellation when 4 and 16 state space-time convolutional code designs are applied.

This paper considers the channel capacity of 60GHz wireless communications systems over Rayleigh fading channels and Ricean fading channels. The SNR and therefore capacity varies according to the communication distance. The capacity is presented for line-of-sight (LOS) and non-line-of-sight (NLOS) channels given based on a 60GHz link budget model. Phase shift keying (PSK) modulation is considered under FCC power constraints for the unlicensed 59-64GHz radio spectrum. The channel capacity over Rayleigh fading channels is compared with the capacity in additive white Gaussian noise channels. The paper also investigates the channel capacity of 60GHz wireless communications systems over Ricean fading channels and gives the channel capacity compariasion with q-ary PSK modulation over Ricean fading channel, AWGN channel and Rayleigh channel when the SNR per symbol is given. The results show that a 60GHz wireless system is more suitable for short range communications less than 100 meters rather than long distances

This paper studies the feasibility of using chirp spread spectrum signals to combat multipath interference in binary digital communication systems over Rayleigh and Rician fading channels. The chirp system can be implemented using surface acoustic wave devices and can be made compact in size. Under also the influence of additive white Gaussian noise, the bit error probability has been successfully derived. Through numerical examples it is witnessed that chirp system can be used to greatly reduce the effect of multipath interference. The arrangement is quite attractive in deploying, for example, indoor wireless communications. >

A new channel model for binary additive noise communication channel with memory, called weighted queue-based channel (WQBC), is introduced. The proposed WQBC generalizes the conventional queue-based channel (QBC) such that each queue cell has a different contribution to the noise process, i.e. the queue cells are selected with different probabilities. Suitably selecting the modeling function, the generalization introduced by the WQBC does not increase the number of modelling parameters required compared to the QBC. The statistical and information-theoretical properties of the new model are derived. The WQBC and the QBC are compared in terms of capacity and the accuracy in modeling a family of hard decision frequency-shift keying demodulated correlated Rayleigh and Rician fading channels. It is observed that the WQBC requires a much smaller Markovian memory than the QBC to achieve the same capacity, and provides a very good approximation of the fading channels as the QBC for a wide range of channel conditions.

A new postdetection maximal ratio combining (MRC) and weighted maximal ratio combining (WMRC) diversity receivers for (N, M) differential amplitude phase shift keying (DAPSK) signal are proposed. In the MRC receiver, decision at each branch is made by the minimum distance criterion. The performance of the MRC receiver is analyzed in terms of the union bound for the bit error probability. The WMRC receiver assigns weighting factors to the decision variable at each diversity branch according to the relative distance from the optimum decision boundary. From the results, performance of the WMRC is found to be better than that of the MRC and equal gain combining (EGC) receiver on both the Rayleigh and Rician fading channel. It is also found that the performance improvement of the WMRC over the MRC increases as the number of the diversity branches increases.

This paper investigates the performances of multiuser downlink opportunistic beamforming (OBF) systems in both Rayleigh and Rician fading channels with the limited feedback information. The statistical characteristics of the equivalent channels show how OBF affects the channel gain. The optimal OBF weight is derived to achieve the maximum capacity. Moreover, the relationship between the capacity and feedback information is analyzed in details. In order to meet different quality of service requirements, we propose two transmission mechanisms that are, respectively, based on maximum-capacity and fairness criterions. Since the closed-form expression of the bit error ratio (BER) is hard to obtain, the upper and lower bounds of BER are derived to approximate the theoretical values. Finally, numerical results are presented to validate our analysis and provide further insights.

A new performance evaluation of switched antenna diversity, for the switch-and-examine strategy, is described. Expressions are derived for three-branch switched diversity with unequal branch statistics for independent Rayleigh and Rician fading channels. Comparisons are made using two and three-branch diversity with equal and unequal branch statistics. New expressions are also derived for an N-branch diversity system with equal branch statistics. The results of an analysis of various higher order diversity systems with equal statistics are compared to each other and to a no-diversity system. It is clearly demonstrated that, as the order of the diversity system increases, performance improves below and just above the switching threshold.

Hybrid code division multiple access (CDMA) scheme utilizes advantages of both direct sequence spread spectrum (DS/SS) and frequency hopped spread spectrum (FH/SS) systems, while overcoming some of their shortcomings. To enhance performance of this hybrid system, an efficient modulation scheme must be used that can perform favorably in a fading environment. We have compared the bit error rate (BER) performance of two spectrally efficient schemes namely, quadrature phase shift keying (QPSK) and minimum phase shift keying (MSK), when used in a hybrid system, over a Rayleigh fading channel. Simulation results show that hybrid MSK indeed is a better scheme in a multi-user (CDMA) environment in that, it achieves lower BER than hybrid QPSK. The comparison has been extended by including a predetection diversity reception scheme. >

Beamforming (BF) technique in cooperative multiple input multiple output (MIMO) antenna arrays improves signal to noise ratio (SNR) of the intended user. The challenge is to design transmit beamforming vectors for every user while limiting the co-channel interference (CCI) from other users. In this paper, we proposed cooperative beamforming based on Signal-to-Leakage Ratio (SLR) to exploit the leakage power as a useful power in the second time slot after user cooperation, for this purpose successive interference cancellation (SIC) is employed in each user to separate the leakage signal from the desired signal. Without increasing the complexity, Maximizing Signal-to-Leakage Ratio (SLR) subject to proposed power constraint instead of a unity norm is the way to achieve extra leakage power. To reduce the erroneous, Bose–Chaudhuri–Hocquenghem (BCH) codes employed in Beamforming of (SIC) cooperative scheme BF(CS-SIC-BCH). Maximum-likelihood (ML) estimator method is used at each user receiver. Simulation results show that the performance of the proposed scheme BF (CS-SIC-BCH) over Rayleigh and Rician fading channel is significantly better than the performance beamforming based on SLR in Non-cooperative system. More specifically to achieve a BER of about the required SNR for the proposed scheme is about 1 dB less than the Non-cooperative system.

The demand for wireless communication has grown in recent years due to increase use of mobile services. The wireless communication channel constitutes the basic physical link established in the transmitter and the receiver. It is the challenging situation to model any wireless channel for radio wave propagation over tough geographical terrain like hilly areas, sea surface, mountains, etc. Channel modeling is one of the most fundamental aspects for study of optimization and design of transmitter and receiver. The operating environment factors like fading, multipath propagation, types of geographical areas limit the performance of wireless communication system. In this paper, wireless channel is modeled by randomly time-variant linear systems. The behavioral analysis of the channel model is performed for both the Rayleigh and Rician fading channels in terms of error probability, and it is shown that in small-scale fading, the Rayleigh fading can be preferred over Rician fading due to high SNR.

In this paper, we analyze the Bit Error Rate (BER) performance of Golden coded Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over Rician multipath fading channel. We also compare the performance of the MIMO-OFDM system using Golden code in Rayleigh and Rician multipath fading channels. We discuss the effects of the presence of line-of-sight (LoS) component in the multipath fading environment which renders the improvement in the overall performance of the Golden coded MIMO-OFDM. This paper discusses the performance of Golden codes in a frequency selective Rician fading channel. To deal with the frequency selective fading channel, we use the OFDM (Orthogonal Frequency Division Multiplexing) modulation. The BER performance of the Golden coded MIMO-OFDM system under several propagation conditions has been evaluated. Keywords—MIMO, OFDM, Golden STBC, Rayleigh fading, Rician fading.

We propose a mathematical interference model of cognitive wireless networks based on two channels suffering different fading. The primary channel between primary transmitter and primary receiver is under Rayleigh fading. The secondary interference channel between secondary transmitter and primary receiver is under Rice fading. By employing various factors, such as the spectrum sensing scheme and the spatial distribution of the secondary users, the proposed model gives an accurate expression of interference probability compared to the statistical models that just approximate the probability model of the interference or bounds models that aim at finding the bounds of the interference. The proposed probability density function (PDF), cumulative distribution function (CDF), and the mean and variance of interference can be extended to a number of applications including power control, spectrum sensing evaluation, secondary users density analysis, and setting interference toleration threshold. Moreover, the framework developed in this paper can be applied to the interference analysis for the nodes of cognitive networks distributed in irregular geographical shapes like finite or infinite zone. The simulation result verifies our theory and is in agreement with the expectation.