Fast Fading Radio Channels Research Articles

Image super resolution based channel estimation for future wireless communication

In this paper, a novel image-based Deep Learning (DL) approach for channel estimation for future wireless communications is proposed. The time–frequency response of the fast-fading wireless channel is represented as a 2D image to estimate the unknown values of the channel response using known values at the pilot locations. With given images, both image Super-Resolution (SR) and image Denoising Network (DnN), termed as Super-Resolution and Denoising Network (SRDnN), are combined to estimate the wireless channel. To show the effectiveness, the proposed SRDnN is applied to Massive Multiple-Input Multiple-Output (mMIMO) with Non-Orthogonal Multiple Access (NOMA). The enhanced performances of SRDnN are quantified in terms of Mean Square Error (MSE) and Symbol Error Rate (SER). In addition, the influence of pilot numbers on SRDnN performance for next-generation mMIMO-NOMA networks is presented. The simulation results demonstrate that SRDnN is comparable to the level of Maximum Likelihood (ML) detection for both with and without complete Channel State Information (CSI) at the receiver with less number of pilots.

Characterization and performance evaluation of turbulent plasma sheath channel

Radio waves are highly attenuated and distorted by turbulent plasma sheath around hypersonic vehicles in near space, leading to communication blackout. The purpose of the paper is to investigate the plasma channel characteristics and the communication performances over the channel. We treat the turbulent plasma medium as a fast fading wireless channel. The coherence time and the spectrum spread of the plasma sheath channel are obtained in terms of root-mean-square (RMS). Baseband simulation scheme is proposed based on a stratified model of the plasma flow field. Results indicate that the coherence time is on the order of milliseconds and decreases rapidly with the increasing electron density turbulence. The spectrum spread due to plasma turbulence is also significant. Extensive simulations have been carried out to make communication performance evaluations. Quantitative results show that error floor takes place for PSK and QAM, while FSK with noncoherent detection is a promising method to mitigate the blackout problem.

Full time-division broadband communication system-based MIMO OFDM technology

In current broadband system schemes, such as VSF-OFCDM, TDD-MIMO-OFDM, TDD-CDM-OFDM and so on, CDMA or OFDMA was adopted as multi-access schemes. The channel estimation overhead and multiuser detection complexity, were the main factors that limited system performance in fast fading wireless channel access environments. So, the full time division cellular mobile communication system was given in this paper as a way out of the parlous issues in current broadband system design scheme. The most effective way out is to reduce channel estimation overhead as possible and avoid multi-access interferences. Moreover, dissymmetrical multimedia data service is the dominate service for next generation communication systems. The time slot structure of wireless frame and system parameters for the proposed system scheme, were also described in this paper. According to numerical analysis results for system capacities, better system diversity and capacity could be achieved by the presented future broadband system scheme.

Exploiting multipath and Doppler array gains in fast-fading wireless channel

This study deals with signal transmission and reception over a fast-fading wireless environment. Conventional methods usually consider the rapid change of channel to be harmful, which may decrease the performance of existing systems. There are also methods proposed to make use of the cause of degradation in existing systems – Doppler spread – to provide additional diversity, at the cost of folds increased complexity. In this study, the authors focus on exploiting the array gains provided by the fast-fading wireless channel multipath array gain (MAG) and Doppler array gain (DAG). The conceptions of MAG and DAG are straightforward extensions of the conception of array gain in multi-antenna systems. For methods which exploit multipath and Doppler diversities, complex signal processing is required at the receiver side, leading to a great increase in complexity. The MAG and DAG can be easily obtained using simple transmit waveform design. Therefore, no extra computational load is required. Both analytical and simulation results show that, with the same computational complexity, the proposed methods can significantly outperform the conventional ones.

On autoregressive model order for long-range prediction of fast fading wireless channel

Long-range prediction of fading wireless channel quality is considered to be one of the most important techniques for high speed wireless communication systems. For example, to enable an efficient adaptive transmission, channel state has to be predicted several symbols ahead to compensate for delay in the feedback loop and adaptation rate limitations. Autoregressive model based linear predictor is addressed in this paper, in particular an impact of predictor order on prediction accuracy for various fading scenarios is investigated. The results show that memory length is an important factor that affects channel state prediction accuracy especially for fast fading channels.

Cosine Modulated and Offset QAM Filter Bank Multicarrier Techniques: A Continuous-Time Prospect

Prior to the discovery of the celebrated orthogonal frequency division multiplexing (OFDM), multicarrier techniques that use analog filter banks were introduced in the 1960s. Moreover, advancements in the design of perfect reconstruction filter banks have led to a number developments in the design of prototype digital filters and polyphase structures for efficient implementations of the filter bank multicarrier (FBMC) systems. The main thrust of this paper is to present a tutorial review of the classical works on FBMC systems and show that some of the more recent developments are, in fact, reinventions of multicarrier techniques that have been developed prior of the era of OFDM. We also review the recent novel developments in the design of FBMC systems that are tuned to cope with fast fading wireless channels.

Jamming games in fast-fading wireless channels

In this article, we adopt outage probability (λ-capacity) in fast-fading channels as a pay-off function in a zero-sum game between a legitimate transceiver pair and an uncorrelated Gaussian jammer. The transmitter aims at minimising the outage probability, while the jammer attempts to maximise the outage probability. We consider both peak (over each codeword) and average (over all codewords) power constraints. For peak power constraints, a transmission rate is either supported by the system, or if too large, causes the whole transmission to fail. By imposing average power constraints, large rates can be supported at the cost of positive probability of codeword error. Maxmin (where the jammer is assumed to play first) and minimax (where the transmitter is assumed to play first) power control strategies are developed under each power constraint, which show that no Nash equilibrium of pure strategies exists under the average power constraint when the follower has perfect knowledge about the randomisation outcome of the first player.

A sequential Monte Carlo technique for blind synchronization and detection in frequency-flat Rayleigh fading wireless channels

This paper is aimed at the derivation of adaptive signal processing algorithms that jointly perform the tasks of blind data detection and generalized synchronization in a digital receiver. Optimal recovery of the synchronization parameters (timing, phase and frequency offsets) is analytically intractable and, as a consequence, most existing synchronization methods are either heuristic or based on approximate maximum likelihood (ML) arguments. We herein introduce an alternative approach derived within a Bayesian estimation framework and implemented via the sequential Monte Carlo (SMC) methodology. The algorithm is derived by considering an extended dynamic system where the reference parameters and the transmitted symbols are system-state random processes. The proposed model is well suited to represent frequency-flat fast-fading wireless channels. We also suggest two possible configurations for the receiver architecture that, combined with the proposed SMC technique, guarantee the achievement of asymptotically minimal symbol error rate (SER). The performance of the proposed technique is studied both analytically, by deriving the posterior Cramér–Rao bound (PCRB) for timing estimation, and through computer simulations that illustrate the accuracy of synchronization and the overall performance of the resulting blind receiver in terms of its SER.

Performance analysis of fractal modulation transmission over fast-fading wireless channels

Fractal modulation schemes have been under investigation for signal transmission over time-varying channels because of their advantages in data transmission at different frequency bands. This also allows efficient reception when channel conditions are varying by selecting the optimal frequency/time resolution based on the current channel condition. We present a performance analysis of fractal modulation transmission over Rician fast-fading channels in the presence of AWGN. A quadrature transmission scheme is simulated and compared, in terms of error robustness, to a QAM transmission system. Other papers analysing fractal modulation system performance do not consider time-varying channels, which are important as they represent the main configuration for communication systems based on this modulation technique. The novelty of our paper lies in the comparison of a fractal modulation system to a QAM one (core of the OFDM modulation technology, extensively used in broadcasting) using a testbed simulation environment where additive noise and fast fading are considered as typical error sources for transmission over wireless channels. Several wavelet families for a fractal modulation scheme have been considered and performance for each one measured; results reported show the effectiveness of the fractal modulation paradigm and confirm its effective utilization in data broadcasting.

Tracking of time-varying mobile radio channels. II. A case study

For pt.I see ibid., vol.49, p.2207-17 (2001). Low-complexity Wiener LMS (WLMS) adaptation algorithms, of use for channel estimation, have been derived in Lindbom et al. (2001). They are here evaluated on the fast fading radio channels encountered in IS-136 TDMA systems, with the aim of clarifying several issues: How much can channel estimation performance be improved with these tools, as compared to LMS adaptation? When can an improved tracking MSE be expected to result in a meaningful reduction of the bit error rate? Will optimal prediction of future channel estimates significantly improve the equalization? Can one single tracker with fixed gain be used for all encountered Doppler frequencies and SNRs, or must a more elaborate scheme be adopted? These questions are here investigated both analytically and by simulation. An exact analytical expression for the tracking MSE on two-tap FIR channels is presented and utilized. With this tool, the MSE performance and robustness of WLMS algorithms based on different statistical models can be investigated. A simulation study then compares the uncoded bit error rate of detectors, where channel trackers are used in decision directed mode in conjunction with Viterbi algorithms. A Viterbi detector combined with WLMS, based on second order autoregressive fading models possibly combined with integration, provides good performance and robustness at a reasonable complexity.

ALOHA with capture over slow and fast fading radio channels with coding and diversity

The effects of capture on the average system throughput and delay performance of slotted ALOHA were analyzed for slow and fast Rayleigh fading radio channels. A short-range multipoint-to-base station packet radio network is considered. It is shown that larger capture effects and thus improved network performance can be achieved with proper choice of modulation. It is also shown that the use of simple error-correcting codes improves capture. The use of selection diversity also improves the capture effect both for fast and slow fading. It is concluded that the inverse distance variability of the received signal is the main reason for the capture effect. The Rayleigh fading alone yields a very small contribution in terms of throughput; nonetheless, it helps to stabilize the system. Numerical results are presented for a slotted ALOHA system with 50 users. It is found that the maximum average throughput can be increased from about 36% to almost 60% by using channel coding and space diversity. >