In this paper, the overlay cognitive two-way relaying is considered, and the adaptive network coding (AdNC) protocol is proposed for improving the outage performance. The AdNC protocol switches between the digital and analog network coding schemes according to the decoding probability. The outage probabilities of the primary and secondary users are derived over Nakagami-m frequency-selective fading channels. Monte Carlo simulations are provided for verifying the accuracy of the derivations. Simulation and analytical results demonstrate that the proposed AdNC protocol possesses advantages of the digital and analog network coding schemes for the considered system.

In this study, a cooperative non-orthogonal multiple access (NOMA) transmission is investigated, and a pairing rule based on the geographic location and state of the users is proposed. Specifically, the users are located within non-adjacent geographic zones at the steady state could be paired and served via the NOMA. The stochastic geometric model is studied in which all users are distributed as an independent homogeneous Poisson point process. In addition, the operation probability of the NOMA for the proposed rule is analyzed by using the Markov chain model. To evaluate the performance of the proposed scheme, the outage probability in terms of geolocation for the paired users is derived over Nakagami-m frequency-selective fading channels.

In this paper, we investigate and analyze modulation-based detect-and-forward (MDeF) relaying for the noncoherent ultra-wideband cooperative system under Nakagami- m fading environments, which can cover a wide range of fading conditions. The MDeF relaying is performed based on the codeword modulation and detects symbols through the codeword mapping process and signal waveform aggregation scheme with good noise/interference mitigation. The proposed MDeF relaying is shown that the upper bound of the average bit error probability matches well to numerical counterpart as signal-to-noise ratio becomes larger and outperforms the conventional DeF relaying.

In this paper, an energy harvesting cognitive network with two-way overlay relaying is discussed, whose secondary users harvest the radio frequency energy from ambient primary information-bearing signals while obtain the spectrum sharing opportunities by relaying those signals. In addition, an adaptive power and time usage (APTUS) energy harvesting relay protocol is proposed as a flexible method that absorbs the essence and discards the dross of the existing schemes for the comprehensive applications. The outage probabilities of primary and secondary users with the APTUS protocol are also derived, and then verified by computer simulations under Nakagami-m frequency-selective fading channels.

In this paper, exact performance analyses of the noncoherent ultra-wideband differential transmitted reference systems are evaluated in the correlated Nakagami-m fading channels via applying the characteristic function (CF) method, where the correlated channel model is derived from the bivariate Nakagami-m distribution. Moreover, the independent Nakagami-m fading channel is considered as a special case by contrast. Numerical results show that the CF method can be demonstrated a better prediction in comparison with the Gaussian approximation scheme, and the system performance can be improved by increasing the number of frames appropriately.

A dynamic multiple-input-multiple-output (MIMO) system with carrier selection (CS) at the transmitter side and single-carrier frequency domain equalization (SCFDE) at the receiver side over dispersive Nakagami-m fading channels is examined. The estimation algorithm of the single-carrier spatially multiplexed data streams is proposed. Estimate the number of transmit diversity as the input information of the SCFDE, and then process the received data adaptively. Operationally, a unique word embedded with pseudo-noise codes has been used not only for stopping error propagation but also for identifying how many transmit antennae at the receiver side at the expense of little complexity. Simulation results reveal our proposed scheme is quite robust and very close to the perfect diversity estimation in dynamic MIMO systems.

The long term evolution (LTE) system employs orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) for the downlink and uplink transmission, respectively. However, in most existing literatures regarding the two-way OFDMA resource allocation, all terminals are assumed under an OFDMA operation, and the allocation scheme is always considered solely under the frequency domain for subcarrier assignment. In this letter, a joint time and frequency resource allocation algorithm for the LTE two-way relaying is proposed, in which the permutation of the subframe and the resource block is discussed for augmenting the system capacity.

In this paper, taking the multipath spread of the channel into account, the performance of two-way amplify-and-forward relaying over Nakagami-m frequency-selective fading channels is analyzed. Based on the channel state information (CSI), the exact probability density functions of the received signal-to-noise power ratio (SNR) for semi-blind and channel state information assisted AF relaying are derived first, respectively. Their corresponding moment generating functions for both relay schemes are also presented. According to these statistics, the average symbol error rate can be found, and then verified by computer simulations under Nakagami-m frequency-selective fading channels.

The expectation-maximization-based (EM-based) receiver provides a decent solution for conquering the delay problem of estimating the channel side information (CSI) via detecting data sequence iteratively at the expense of increasing the processing time. To accelerate the processing time, an α-expectation-conditional-maximization (ECM) design for direct-sequence (DS) code-division multiple access (CDMA) systems over frequency-selective fading channels is studied. Simulation results reveal that the adaptive α-ECM receiver can speed up the convergence speed of joint estimation and detection under severe Doppler shifts when the value of α is increasing. Furthermore, the BER performance of the adaptive α-ECM-based DS-CDMA receiver for joint channel estimation and symbol detection under single-user and multiuser systems is also scrutinized.

Taking the multipath spread of the channel into account, the performance of amplify-and-forward (AF) relaying over Nakagami-m frequency-selective fading channels is analyzed in this paper. The exact probability density functions of the received signal-to-noise ratio for the fixed and variable gain AF relaying are derived, respectively. Furthermore, the moment generating functions for both relay schemes are also presented. Based on these statistical characteristics, the average symbol error rate can be found, then verified by computer simulations under identical and non-identical Nakagami-m fading channels.

To overcome the limitation of the transmit power spectral density, the cooperative communication in the ultra wideband (UWB) differential transmitted reference system is studied. The amplify-and-forward is used as a relay protocol to re-transmit signals from multi-source terminals to one destination terminal. An adaptive amplification factor based on the channel information between relay and destination nodes is considered. Simulation results reveal that not only its capacity but also the associated bit error probability with adaptive amplification outperforms those with constant amplification.

The conventional amplify-and-forward relaying protocol has less complex but worse performance than the decode-and-forward type. In the orthogonal frequency division multiplexing (OFDM) multihop relay systems, the system capacity can be enhanced via using the subcarrier permutation scheme at the relay terminals. However, under the multiuser scenario, one subcarrier may possess the best condition for several users, but only one user can choose it to transmit the data. This competitive relation among users will influence the system performance. In this paper, the system capacity and outage probability with a direct link are studied for the multiuser OFDM dual-hop relay system in Rayleigh fading channels. Simulation and numerical results show that the system performance has a large impact under a multiuser scenario.

Under the impact of multiuser interference, the exact bit error probability of the time-hopping ultra-wideband differential transmitted reference system over the Nakagami-m fading channels is evaluated via applying the characteristic function (CF) method. The CF method does not introduce any unrealistic assumptions, therefore our numerical results from the CF method demonstrate a better match in comparison with those from the Gaussian approximation, which fail to match the simulation results for medium and large signal-to-noise ratio values.

Noncoherent and coherent multicode direct-sequence code-division multiple access (DS-CDMA) systems with successive interference cancellation (SIC) for multimedia reverse links over frequency-selective fading channels are studied. Followed by a RAKE receiver, the SIC scheme is applied for combating the multiple access interference. The bit error rate (BER) using the SIC technique over Nakagami-mfading channels is derived. Simulation results show that the multicode DS-CDMA system with SIC has demonstrated better performance than that without SIC under the multipath fading environment, while their corresponding numerical results from performance analyses are also provided for verifications. Furthermore, the coherent receiver could achieve a more satisfactory BER than the noncoherent counterpart at the expense of synchronization.

We have investigated the maximum-likelihood (ML) receivers for the fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) spread-spectrum communications system with a worst case multitone jamming (MTJ) and additive white Gaussian noise (AWGN) over frequency-selective Rayleigh fading channels. Owing to the fact that the analysis of the natural logarithm of the modified Bessel function is intractable, two ML diversity-combining receivers, that are named as ML-A and ML-B receivers according to the different conditions of the approximation, have been analyzed theoretically based upon a correlated two-path frequency-selective channel model. The performance of these two receivers compared with that of other diversity-combining receivers in terms of the bit error rate(BER) has been scrutinized. Computer simulations confirm that our numerical analyses are valid. Furthermore, the ML-B receiver outperforms other receivers, while the ML-A receiver is only as good as the ML-B counterpart when the signal-to-jamming ratio (SJR) is greater than 24 dB.

The performance of a noncoherent digital delay-lock loop (DDLL) with a RAKE scheme for direct-sequence spread-spectrum code division multiple access (DS/SS-CDMA) signals over frequency-selective Rayleigh fading channels is discussed. Closed-form expressions for the transition timing error probability density function (PDF) of the Chapman-Kolmogorov (C-K) equations of the first- and second-order loops are derived for driving analytical expressions of the steady-state timing error PDF. Furthermore, the statistics of the tracking error are scrutinized and verified via computer simulations, such as the mean square tracking error (MSTE) and Cramer-Rao lower bound (CRLB).

In this paper, we present a double-ring mobile-to-mobile channel model based upon a three-dimensional (3D) space-time-frequency correlation function via combining the antenna pattern, Doppler shift, and delay profile. This 3-D correlation function results in the probability density distribution (PDF) of an extra elevation angle (EA) being taken into the antenna pattern and the Doppler shift consideration. Four types of the EA PDF, Aulin, Parsons, Qu-Yeap, and uniform models, have been discussed. It is revealed through computer simulations that the 3-D scattering scenario outperforms the two-dimensional environment in terms of the cross-correlation for all four types of the EA PDFs. Furthermore, we find that the performance of the uniform model is better than the others when the radius of the circular antenna array is more than 0.5 times of the propagation wavelength, or 7.5 cm for a 2 GHz carrier frequency.

The EM (expectation-maximization) algorithm is used to solve the decision delay problem existed in maximum- likelihood sequence estimation (MLSE) receivers, while the a- EM-MLSE receivers provide an alternative controllable convex divergence scheme for accelerating the overall convergence speed at the expense of more complicated mathematical structures. Instead of the conventional symbol-spaced (SS) MLSE structure, a new design based upon T/2-spaced samples for a-EM MLSE receivers has been scrutinized. Simulation results reveal that the number of branch metric computations and the accuracy of received sampling data dominate the overall convergence speed. That is, fractionally-spaced (FS) adaptive a -EM MLSE receivers have not only demonstrated a better BER performance, but they also could further speed up the convergence speed for a ges - 0.5 under SNR20 dB and a ges - 0.5.

The Nakagami-m fading signals in wireless channels are getting more popular owing to their good fit for empirical data. In this paper, correlated and uncorrelated wide-sense stationary (WSS) Nakagami-m fading simulators based upon the sum-of-low-frequency-oscillators method are proposed. It has been confirmed via computer simulations that the proposed models not only outperform the existing Zhang's Nakagami-m simulator in terms of their statistics, but they also guarantee convergence, which Zhang's does not promise.

Statistical analyses of a non-coherent digital delay- lock loop (DDLL) for direct-sequence spread-spectrum signals over Nakagami-m fading channels are discussed. Analytical expressions to the characteristics, such as Cramer-Rao lower bound (CRLB), of the timing tracking errors have been proposed based upon the timing error probability density function (PDF) of the Chapman-Kolmogorov (C-K) equation of the first- and second-order loops. Furthermore, mean square tracking errors (MSTEs) against distinct parameters are also simulated, while their corresponding numerical results with CRLBs are confirmed by time-domain computer calculations.

In this paper, the performance of a noncoherent all-digital delay-lock loop (all-DDLL) for direct-sequence spread-spectrum signals over Nakagami-m. fading channels is analyzed. A closed-form expression for the timing error transition probability density function (PDF) of the Chapman-Kolmogorov (C-K) equation is evaluated. The transition PDF is employed to derive the analytical expression for the steady-state timing error PDF and the mean time to lose lock (MTLL) under the Nakagami-m fading environments, while the numerical results are confirmed by time-domain computer simulations.