Particle filter based Bayesian inference modulation recognition algorithm

A communication system model for mutual information performance analysis of multiple-symbol differential M-phase shift keying over time-correlated, time-varying flat-fading communication channels is developed. This model is a finite-state Markov (FSM) equivalent channel representing the cascade of the differential encoder, FSM channel model and differential decoder. A state-space approach is used to model channel phase time correlations. The equivalent model falls in a class that facilitates the use of the forward–backward algorithm, enabling the important information theoretic results to be evaluated. Using such a model, one is able to calculate mutual information for differential detection over time-varying fading channels with an essentially finite time set of correlations, including the Clarke fading channel. Using the equivalent channel, it is proved and corroborated by simulations that multiple-symbol differential detection preserves the channel information capacity when the observation interval approaches infinity.

In this paper, the performance of limited feedback precoded spatial multiplexing multiple-input multiple-output orthogonal frequency division multiplexing (MIMO - OFDM) systems is investigated in time varying fading channels. Most studies into limited feedback precoded (MIMO - OFDM) systems are based on the notion of time invariant channels throughout transmission. Therefore, the precoding matrix for each subcarrier can be designed at the receiver in terms of the current channel state, fed back to the transmitter, and used for the subsequent block of data symbols. However, in time varying channels, the feedback information becomes outdated, which results in significant system performance degradation. To mitigate this system performance degradation caused by outdated information due to a delay in the feedback channel, this paper considers a more practical system, where the channel varies from one block of symbols to another. A method is proposed based on modelling the channel as an autoregressive (AR) model and using a Kalman filter linear predictor at the receiver to predict the channels states, required to design the precoding matrices for the next OFDM symbol carriers whose indexes are fed back to the transmitter. The performance of this method is investigated using computer simulation, and the results obtained for the proposed channel prediction demonstrate improved bit error rate performance for time-varying Rayleigh fading channels, even in systems with high mobility.

For direct-sequence code-division multiple-access (DS-CDMA) time-varying channels with additive Gaussian noise, we propose a new receiver. Since channel tracking plays an essential role in practice in equalization of the receiver, a new and viable design approach, a modified interacting multiple-model (MIMM) algorithm, is proposed for tracking of multipath time-varying fading channels. We employ a set of second-order auto-regressive (AR2) multiple models associated with a Makov jump process to cover the range of channel dynamics. This setup leads to an AR2-based MIMM channel tracker which can automatically adjust channel model parameters to track time-varying fading channels for all times once some design parameters are initialized. We employ a Kalman filter as a symbol detector (KBSD). Simulation studies demonstrate that the performance of the AR2-MIMM channel tracker together with a conventional KBSD performs at least as well as that of the ideal AR2-based Kalman channel estimator having the exact knowledge of the Doppler rate of each channel in combination with the KBSD

In selective cooperative relaying only a single relay out of the set of available relays is activated, hence the available power and bandwidth resources are efficiently utilized. However, implementing selective cooperative relaying in time-varying channels may cause frequent relay switchings that deteriorate the overall performance. In this paper, we study the rate at which a relay switching occurs in selective cooperative relaying applications in time-varying fading channels. In particular, we derive closed-form expressions for the relay switching rate (measured in Hz) for opportunistic relaying (OR) and distributed switch and stay combining (DSSC). Additionally, expressions for the average relay activation time for both of the considered schemes are also provided, reflecting the average time that a selected relay remains active until a switching occurs. Numerical results manifest that DSSC yields considerably lower relay switching rates than OR, along with larger average relay activation times, rendering it a better candidate for implementation of relay selection in fast fading environments.

Instantaneous mutual information (IMI) is the amount of information that a time-varying channel can convey for the given time instant. In this paper, second-order statistics of IMI are studied in time-varying underwater acoustic particle velocity channels. First, the autocorrelation function, correlation coefficient, level crossing rate, and average outage duration of IMI are provided in a time-varying fading channel. Exact expressions are given in terms of the summation of special functions, which facilitate numerical calculations. Then, accurate approximations for the autocorrelation function and correlation coefficient are presented for low and high signal-to-noise ratios. Moreover, analytical and numerical results are provided for the correlation and level-crossing characteristics of IMI in underwater particle velocity channels. The results shed light on the dynamic behavior of mutual information in underwater acoustic particle velocity channels. [Work supported in part by the National Science Foundation (NSF), Grant CCF-0830190.]

In this paper, we study the achievable rate of the training-based multi-input multi-output (MIMO) systems over time-varying flat fading channels modeled with the $L$-th order autoregressive, AR($L$), process. Using the Bayesian Cram\'{e}r-Rao lower bound (BCRB) to characterize the mean squared error of channel estimation, the achievable rate of the MIMO systems is investigated from the information-theoretical perspective. The optimum lengths for the training and the data blocks are determined to maximize the achievable rate. Besides, by modeling the time-varying wireless fading channel with a proper AR($L$) model for the specific normalized Doppler frequency, $f_dT_s$, the aforementioned results can be extended to characterize the achievable rate in a more realistic time-varying wireless fading channel.

Channel interpolation for LTE uplink systems with high mobility using Slepian sequences

Particle filters for probability hypothesis density filter with the presence of unknown measurement noise covariance

It is well-known that space-time block coded transmit diversity system suffers from a diversity penalty in the time-varying channel. Lately, based on the Alamouti two-input single-output (2ISO) antenna diversity system, Vielmon et al. investigated the impact of a time-varying channel on the bit-error-rate (BER) performance and also recommended three detectors to increase the system robustness for rapid channel variation. In this paper, we generalize these detectors and their BER expressions to the two-input multiple-output (2IMO) antenna configuration. Moreover, the bit-error-outages (BEOs) are also derived to provide a more objective judgment on the transmission quality within a fading environment. These generalized results can be easily extended to the orthogonal frequency-division multiplexing (OFDM) and code-division multiple-access (CDMA) systems with the 2IMO antenna configuration.

In this paper, we proposed a frequency-hopped space-time coded orthogonal frequency-division multiplexing (FHST-OFDM) over time-varying multipath channels. Although OFDM is robust against frequency-selective fading channels, it is more vulnerable to the time-varying channels and has a higher peak-to-average power ratio (PAPR) than single-carrier systems. In space-time block coded OFDM (ST-OFDM), channel time variations cause not only the intertransmit-antenna interference (ITAI), but also the inter-carrier interference (ICI). In this paper, based on the analysis of the ITAI and ICI in ST-OFDM systems, the FHST-OFDM transmission scheme is proposed to reduce both ITAI, ICI, and PAPR simultaneously. By combining the Alamouti scheme and the frequency hopping, full data rate and frequency diversity can be achieved by the proposed FHST-OFDM over the time-varying multipath channels. Finally, simulation shows that the proposed FHST-OFDM scheme gets better performance over time varying channels.

This paper evaluates the performance of a pilot-assisted fine carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) in time-varying channels. An analytical closed-form expression of the mean square error (MSE), of the post-FFT based CFO synchronization scheme, is presented in terms of time-variant fading channels. To verify our analysis in this paper, simulations are carried out within the framework of mobile WiMAX systems.

Highmobility is an important scenario for the 5G wireless communications. However, the high mobility results in serious time-varying fading, bringing challenges to the reliabilities of wireless transmission. Diversity technique is an essential method to overcome the effect of fading. It is noted that an LDPC (low-density parity-check) code is a concatenation of single parity-check codes (SPC) and repetition codes (REP) by a random interleaver, and a REP can be viewed as a typical example for achieving time/frequency diversity. Thus, it is appealing to jointly consider LDPC codes and diversity techniques. This paper presents parity-check coding transmit diversity (PCTD) schemes based on half-rate invertible LDPC codes, which are capable of achieving both diversity and coding gains from the time-varying fading channels. Besides, we investigate two types of PCTD schemes, and take into consideration two transmission modes, which are single-carrier (SC) and orthogonal frequency division multiplexing (OFDM) transmission modes. A chase combining based message passing algorithm (CC-MPA) is proposed for the proposed schemes, which can take full advantages of signal processing and coding gains. Furthermore, the Shannon limits of time-varying fading channels with BPSK signaling are deduced. Simulation results show that the proposed PCTD with CC-MPA algorithm can provide better BER performances than the classical time-domain diversity scheme in time-varying fading channels, which is appealing for the high mobility communications.

Interference control is crucial in cognitive radio networks and the existing related works focus on quasi-static channels. The expansion of wireless services and applications in everyday life has necessitated support of higher mobility, as evident from the emerging wireless standards. This results in time-varying fading channels within a transmission frame for which the interference power control schemes and power allocation strategies have not been developed yet. This paper proposes several interference control and power allocation strategies with different criteria for underlay cognitive radios in time-varying frequency-selective fading channels and extend the transmission schemes to multiple secondary systems. The transmission schemes are evaluated in terms of interference statistics at the primary receiver and the ergodic capacity of the secondary user link. Simulation results over the wide Doppler range show how the proposed schemes with different criteria shape the interference at the primary receiver and the capacity of the secondary user. The results also illustrate better interference control capability of the proposed approaches over the existing scheme.

Multiple-input/multiple-output (MIMO) frequency selective fading channels introduce both the intersymbol interference (ISI) and the inter-(sub)channel interference (ICI) that are the major performance limiting factors for MIMO wireless data communications. This paper focuses on joint suppression of such two interferences in receiver design under the criterion of the minimum mean-squared error (MMSE). The well-known Kalman filtering arises as a natural design tool to achieve the optimum joint suppression of the ISI and ICI in the sense of MMSE that results in a two-stage design method that suppresses the ISI and ICI in series. Specifically, a state-space solution is derived for the optimum decision-feedback equalizer (DFE) based on temporal Kalman filtering, and is shown to be equivalent to a conventional finite length DFE for ISI suppression. A novel spatial Kalman filtering scheme is proposed as the second stage to successively cancel the ICI. It is shown that the proposed two-stage method yields the realizable and optimum joint ISI and ICI suppression, while it admits lower computational complexity than the conventional finite length DFE for ISI suppression and the MMSE V-BLAST receiver for ICI suppression. The results are applicable to any linear channels that admit state-space realizations, including MIMO frequency selective time-varying channels, and are thus the most general. Simulation results show the effectiveness of the proposed two-stage method and its robustness to channel estimation uncertainties that may arise in practical systems.

Channel estimation for single-input single-output (SISO) frequency-selective time-varying channels is considered using superimposed training. The time-varying channel is assumed to be described by an orthogonal polynomial basis expansion model (OP-BEM). A periodic (non-random) training sequence is arithmetically added (superimposed) at a low power to the information sequence at the transmitter before modulation and transmission. First we present a novel approach to channel estimation using only the first-order statistics of the data under a fixed power allocation to training. We then present a performance analysis of this approach for time-varying random channels to obtain a closed-form expression for the channel estimation variance. Finally, we address the issue of superimposed training power allocation. Illustrative computer simulation examples are presented where a frequency-selective channel is randomly generated with different Doppler spreads via Jakes' model