Performance Evaluation of Serial/Parallel Block Coded CDMA System with Complex Spreading in Near/Far Multiple-Access Interference and Multi-path Nakagami Fading Channel

The channel capacity of multiple-input multiple-output (MIMO) wideband CDMA system with coherent RAKE receiver is considered. General multi-path intensity Nakagami fading and multiple-access near/far interference channel are assumed. The analysis for system performance shows that the error of channel estimation significantly degrades BER performance and can be effectively suppressed by RAKE receiver and MIMO schemes. Also, an attempt for comparing the channel capacity on different performance improvement schemes has been made. In particular, the channel capacity of MIMO system is compared with single-input single-output (SISO) system. The MIMO complex spreading CDMA system with path correlation yields better performance with respect to channel capacity than a SISO system with i.i.d. input and output. And a discussion on the multiple-access near/far interference is also included, which illustrates that it can be effectively limited by power control and channel estimation schemes.KeywordsChannel EstimationChannel CapacityPilot SymbolInterference ModelCDMA SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

It is well known that power control is critical in CDMA mobile systems and the power control error (PCE) exists in spite of power control methods being used. In this paper, the closed-form expressions of signal-to-interference-plus-noise ratio (SINR) and the average bit error rate (BER) are derived for a two-dimensional (2-D)-RAKE receiver with imperfect power control in a frequency-selective Nakagami fading channel.. The combined impact of PCE, multipath Nakagami fading, spatial and temporal diversity order, and multiple-access interference on the system performance has been analyzed for all kinds of fading environments. The simulation results indicate that the BER performance degrade due to PCE. But increasing spatial and temporal diversity order can possibly compensate for the performance loss when PCE is not very serious. The exact performance improvement due to space-time processing varies with the PCE and the fading environment.

This paper investigates the performance of ultra-wideband (UWB) correlator receivers for Gaussian monocycles under the condition of equal mean power and provides constructive reference to the selection of pulses. Several channel situations are examined including ideal single user AWGN channel, non-ideal synchronous, multipath fading and multiple access interference. Both numerical and analytical techniques show that the shapes of pulses have notable impact on the performance of correlator receivers, especially on the interference resistance ability and signal-to-noise ratio (SNR) of the output. he results are also extended to the field of fractional bandwidth to better understand the possible relationship between fractional bandwidth and correlator receivers.

Two major factors that limit the performance of DS-CDMA systems are multiple-access interference (MAI) and multipath channel distortion. In this paper, we propose a joint iterative channel estimation scheme for mitigating their effect on the space-time multiuser detector. The joint iterative channel estimation requires a careful design of training sequences, since the channel estimator are based on the cross-correlation matrix. Moreover, the detected decisions are then interleaved back to the channel estimator, which begins the next iteration. The channel estimator for space-time multiuser detection can use both data and training bits and re-estimate channel impulse response. The presented scheme can avoid heavy computations and improve the performance of systems effectively.

FBMC is a pivotal system in 5G, serving as a cornerstone for efficient use of available bandwidth while simultaneously meeting stringent requirements for high spectral efficiency. Notably, FBMC harnesses the power of multicarrier modulation (MC), a good alternative to orthogonal frequency division multiplexing (OFDM) technology that supports fourth-generation (4G) systems. The wireless communications field is full of challenges, the most important of which are channel estimation and interference cancellation, both of which deserve comprehensive study to increase the efficiency of data transmission. In this paper, our investigation takes a deliberate step towards the convergence of two prominent modulation models: OFDM and FBMC. We specifically contrast these modulation techniques with the intricate field of joint channel estimation and interference cancellation (JCEIC). In this research study, we take advantage of recurrent neural networks' (RNNs') efficiency as a vehicular channel to perform precise channel estimation and recovery of uncorrupted transmitted signals, thereby lowering the bit error rate (BER). Our channel estimation for a dual selective channel is based on the thoughtful placement of pilots scattered over the temporal and frequency dimensions, and is further improved by the interference cancellation method of low complexity that was selected. Our JCEIC proposal aims to integrate RNNs carefully, using the output sequences of JCEIC algorithms as useful inputs to this neural architecture. By clearly demonstrating a decrease in BER as compared to traditional approaches, it is evident that the performance of the novel approach is near to that of a perfect channel. Additionally, a comparison of the performance of FBMC and OFDM systems at various signal-to-noise ratios reveals a clear performance divide that favors the former in terms of system efficiency. The BER is restricted by FBMC to a commendable threshold of less than 0.1 at a modest 5 dB, continuing the higher trend started by its improved RNN-based channel estimate. The accuracy of channel estimation is clearly improved by this paradigm shift, and the computing complexity typical of 5G networks is also clearly reduced.

We consider a combined space-time (ST) block coding and direct-sequence code division multiple access (DS/CDMA) scheme for downlink transmissions over multipath fading channels, in which ST block coding is performed at the chip level, i.e. after code spreading. For this scheme, we develop low complexity and low decoding delay linear ST single-user detection algorithms. In addition, we demonstrate that by exploiting the signal structure imposed by the chip-level ST block coding, blind channel multipath estimation (with only a scalar ambiguity) is feasible, even with the assignment of a single code vector to each user.

Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next generation wireless systems use long spreading codes whose period is much larger than the symbol duration. In this paper, we derive the maximum likelihood channel estimate for long code CDMA systems over multipath channels using training sequences and approximate it using an iterative algorithm to reduce the computational complexity in each processing window. The asymptotic convergence of the mean of the iterative estimate to the actual channel is also shown. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. Finally, the proposed iterative channel estimation technique is extended to track slowly varying multipath fading channels using decision feedback. Thus, an MAI resistant multiuser channel estimate with reasonable computational complexity is derived for long code CDMA systems over multipath fading channels.

To improve communication network efficiency, researchers must look at all aspects of transmission and the mechanisms that regulate their evolution as a whole. These features include solutions for dealing with the channel's noise and interference. To decrease interference and increase spectrum efficiency, orthogonal frequency division multiple access (OFDMA) systems employ orthogonal signals. While transmitting and receiving signals, noise and numerous feeds can be done in diverse ways. It has become increasingly common to use 256 quadratic modulation (QAM), which is more vulnerable to noise and has a higher bit error rate (BER). BERs in OFDM systems were high when multiple feeds and noise were present, as demonstrated in this article. Starting with the transmission and reception of Gaussian subband signals, an improved system has been designed that includes numerous stages of development. Thus, the need for “orthogonally” of transmitted signals to increase spectrum efficiency has been eliminated, as has the effect of surrounding channels. We have created a header for every frame that has been transmitted. Several transmitters and numerous receivers send these frames in parallel so that the channel state information (CSI) attributes may be evaluated using parallel processing. Using the identical transmission conditions for both OFDM systems and the proposed system, the simulation results reveal a significant reduction in BER values. This results in BER values of fewer than 10 −1 when there are two tabs and 10 −1 when there are three tabs for multiple feeding in the OFDM system. This corresponds to BER values of 10 −11 in a suggested system when there are three tabs. Some improvements have been made to the proposed design to make it distinctive and qualified to be regarded as a multiaccess system in today's contemporary communication infrastructures.

In the context of interference channels with multiple transmitters and receivers, we propose a novel decoding scheme called anywhere decoding that does not pre-assign the receiver at which each message should be decoded, but rather requires that each message must be decoded at some receiver. This paper illustrates how system performance can improve if we allow for this flexibility. After developing a system model based upon the classical two-user, discrete-memoryless interference channel, we present two decoding schemes based upon the anywhere decoding concept, each requiring extremely low overhead to enable cooperation among the receivers. Both of these schemes offer the same achievable rate region, for which we outline the proof in the discrete-memoryless case and state the result for the Gaussian case with independent and identically distributed Gaussian inputs. When cast into a cellular setting with two cooperating basestations experiencing path-loss and multipath fading, we assess performance in terms of two system metrics: the common outage probability and the symmetric throughput. Asymptotic analysis of the outage probability of the anywhere decoding schemes demonstrates that they achieve full spatial diversity through multiple decoding opportunities, and they are no more than 1.5 decibels (dB) from full basestation cooperation at high signal-to-noise ratio (SNR).

We study interference channels (IFCs) where the interaction among sources and destinations is enabled, e.g., both sources and destinations can talk to each other using full-duplex radios. The interaction can come in two ways. First is through in-band interaction where sources and destinations can transmit and listen in the same channel simultaneously, enabling interaction. Second is through out-of-band interaction where destinations talk back to the sources on an out-of-band channel, which is possible from white-space channels. The flexibility afforded by the interaction among sources and destinations allows for the derivation of interference alignment (IA) strategies that have desirable “engineering properties,” i.e., insensitivity to the rationality or irrationality of channel parameters, small block lengths, and finite SNR operations. We show that, for several classes of IFCs, the interactive IA scheme can achieve the optimal degrees of freedom. In particular, we show a simple scheme (having a finite block length for channels having no diversity) for three-user and four-user IFCs with full-duplex radios to achieve the optimal degrees of freedom even after accounting for the cost of interaction. On the technical side, we show using a Gröbner basis argument that, in a general network potentially utilizing cooperation and feedback, the optimal degrees of freedom under linear schemes of a fixed block length is the same for channel coefficients with a probability of 1. Furthermore, a numerical method to estimate this value is also presented. These tools have potentially wider utility in studying other wireless networks as well.

The probability of packet error for Multi-Carrier CDMA system with maximum ratio combining diversity is evaluated and compared in the slow and fast correlated Nakagami fading plus multiple access interference channel. From the results, the probability of packet error in fast fading is higher than that in slow fading, and the difference of packet error probability between the fast fading and slow fading diminishes with Nakagami fading parameter approaching infinity. When the error correction coding technique is used, it is observed that coding technique for Multi-Carrier CDMA system is more effective in the fast fading case than that in the slow fading case.KeywordsFading ChannelDiversity BranchNakagami Fading ChannelFading CaseCorrelate FadingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. The paper presents space-time coded minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. For the above structure, we have presented the estimation of BER for a MMSE DFE using computer simulation experiments. The simulation includes the effects of additive white Gaussian noise, multipath fading and multiple access interference (MAI). Furthermore, the performance is compared with standard linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard linear equalizer (LE) and RAKE receiver.

A channel estimation scheme, based on both pilot and traffic channels, is proposed for next generation DS/CDMA systems. This scheme has no channel estimation delay, and is found to perform significantly better than a scheme based on only the pilot channel.

Space-time block coding (STBC) is a signaling algorithm utilizing multiple transmit and receive antennas in order to improve the system performance and increase the channel capacity in the presence of fading and interference. This paper introduces Prerake space-time block codes (PRK-STBC) for multiuser direct-sequence code-division multiple-access (DS-CDMA) systems operating in time-division-duplex (TDD) mode. PRK-STBC combines both antenna diversity and temporal precoding. In a DS-CDMA system, the transmit antennas are available to all users at all the time. In a multipath channel, the prerake coding of the transmitted signals results in multipath diversity, without the need of rake receivers at the mobile stations. Hence, only simplified mobile receivers are needed and most of the signal processing is done at the base station. The performance of PRK-STBC is examined in multipath fading. The performance is also investigated against the used number of transmit and receive antennas (up to four transmit antennas and one receive antenna are considered in the simulation).

Orthogonal frequency-division multiplexing (OFDM) is widely used to mitigate inter-symbol interference (ISI) from multipath fading. However, the open nature of wireless OFDM systems makes them vulnerable to jamming attacks. In this context, pilot jamming is critical as it focuses on corrupting the symbols used for channel estimation and equalization, degrading the system performance. Although neural networks (NNs) can improve channel estimation and mitigate pilot jamming penalty, they are also themselves susceptible to malicious perturbations known as adversarial examples. If the jamming attack is crafted in order to fool the NN, it represents an adversarial example that impairs the proper behavior of OFDM systems. In this work, we explore two machine learning (ML)-based jamming strategies that are especially intended to degrade the performance of ML-based channel estimators, in addition to a traditional Additive White Gaussian Noise (AWGN) jamming attack. These ML-based attacks create noise patterns designed to reduce the precision of the channel estimation process, thereby compromising the reliability and robustness of the communication system. We highlight the vulnerabilities of wireless communication systems to ML-based pilot jamming attacks that corrupts symbols used for channel estimation, leading to system performance degradation. To mitigate these threats, this paper proposes an adversarial training defense mechanism desined to counter jamming attacks. The effectiveness of this defense is validated through simulation results, demonstrating improved channel estimation performance in the presence of jamming attacks. The proposed defense methods aim to enhance the resilience of OFDM systems against pilot jamming attacks, ensuring more robust communication in wireless environments.