A theoretical analysis of the performance of code division multipleaccess communications over multimode optical fiber channels-part I:transmission and detection

This paper presents results of a theoretical investigation to evaluate the performance of code division multiple access communications over multimode optical fiber channels in an asynchronous, multiuser communication network environment. The system is evaluated using Gold sequences for spectral spreading of the baseband signal from each user employing direct-sequence biphase shift keying and intensity modulation techniques. The transmission channel model employed is a lossless linear system approximation of the field transfer function for the α-profile multimode optical fiber. Due to channel model complexity, a correlation receiver model employing a suboptimal receive filter was used in calculating the peak output signal at the ith receiver. The performance measures for the system, i.e., signal-to-noise ratio and bit error probability for the ith receiver, are derived as functions of channel characteristics, spectral spreading, number of active users, and the hit energy to noise (white) spectral density ratio     

Performance analysis of punctured convolutional codes andturbo-codes

Digital radio transmission techniques offer the prospect of improved reception compared with analogue signals and are being introduced for radio broadcasting in the short-wave bands. The coding scheme adopted plays an important part in achieving a high quality in the presence of noise and fading, which can be particularly severe for Digital Radio Mondiale (DRM) receivers. This paper compares the performance of turbo-codes and punctured convolutional codes over the radio broadcast transmission channels proposed in ITU-R Circular Letter 10/LCCE/39. The results show that the bit error ratio for binary communication over both additive white Gaussian noise (AWGN) and Rayleigh fading channels is low for turbo-codes in comparison with that for punctured convolutional codes having the same code rate. This result holds over a wide range of bit energy to noise power ratios. The results, which are evaluated in terms of the efficiency for Gaussian and Rayleigh fading channels, show that system efficiency increases with decreasing code rate     

Trellis coded MDPSK in correlated and shadowed Rician fadingchannels

The performance of trellis-coded multilevel differential phase-shift keying (TC-MDPSK) signals in correlated and shadowed Rician fading channels is evaluated. The pairwise error probabilities of the TC-MDPSK signals in the channels are calculated directly and approximated asymptotically. The asymptotic expression can be put into a product form and used in a transfer function approach to estimate the error performance of TC-MDPSK. The bit error rate of TC-MDPSK is estimated by using a truncated form of the union bound and by an asymptotic expression. In the two examples considered, these formulas show fairly good agreement in both correlated and shadowed Rician channels and are at least 2-dB tighter in signal-to-noise ratio than the Chernoff bound in the correlated Rician channels. Asymptotic expressions for the error probability of uncoded MDPSK in both correlated and shadowed Rician channels are also obtained     

Antenna selection and forwarding strategy in SWIPT relay channels

This letter proposes a low-complexity ‘harvest-and-forward’ relay strategy in simultaneous wireless information and power transfer (SWIPT) relay channels. In the first phase of relay transmission, the relay’s antennas are divided into two subsets. The signals received by the antennas in one subset are converted to energy, and the signals received by the antennas in the other subset are combined. In the second phase, the relay forwards the combined signal using all antennas with the harvested energy. A low complexity antenna selection (AS) algorithm is given to maximize the achievable rate over fading channels. The simulation results show that the achievable rate of this strategy is close to that of the two-stage strategy where a two-state procedure is proposed to determine the optimal ratio of received signal power split for energy harvesting, and the optimized antenna set engaged in information forwarding. The proposed strategy has better performance than the two-stage strategy when the relay is equipped with medium-scale antennas, and the performance gap between two strategies grows with the increase of the number of the relay’s antennas. The computational complexity of the proposed strategy is O(N2) (N is the number of relay antennas), which is obviously lower than that of the two-stage strategy (O(3N3)).     

Union Bounds on the Bit Error Probability of Coded MRC in Nakagami-m Fading

In this letter new union bounds are derived for coded maximal ratio combining (MRC) over Nakagami-m fading channels. The union bounds are expressed in the product form, which makes them easily, evaluated using the transfer function of the code. The bounds are general to any diversity order and coding scheme with a known transfer function. Results show that the new bounds are tight to simulation results for wide ranges of diversity orders and Nakagami parameters     

The multitone channel

The maximum bit rate of multitone QAM (quadrature amplitude modulation) over a general linear channel is found. First, the overall bit rate for an AWGN channel with a two-level transfer function is maximized, using a multitone QAM system. The power distribution between the tones and the number of bits/symbol per tone is optimized for a given symbol error rate. Extending these results to the general channel, it is shown that the optimum power division for multitone signals is similar to the water-pouring solution of information theory. Furthermore, multitone QAM performance is about 9 dB worse than the channel capacity, independent of the channel characteristics. The multitone results throughout are compared to those of an equivalent single-tone linearly equalized system. The comparison shows that the multitone system is useful for some channels, e.g. those with deep nulls in the transfer function. The maximum bit error rate over a twisted-pair channel which is performance dominated by near-end crosstalk (NEXT) is also found     

MIMO-assisted space-code-division multiple-access: linear detectors and performance over multipath fading channels

In this contribution, we propose and investigate a multiple-input-multiple-output space-division, code-division multiple-access (MIMO SCDMA) scheme. The main objective is to improve the capacity of the existing direct-sequence (DS)-CDMA systems, for example, for supporting an increased number of users, by deploying multiple transmit and receive antennas in the corresponding systems and by using some advanced transmission and detection algorithms. In the proposed MIMO SCDMA system, each user can be distinguished jointly by its spreading code signature and its unique channel impulse response (CIR) transfer function referred to as spatial signature. Hence, the number of users might be supported by the MIMO SCDMA system and the corresponding achievable performance are determined by the degrees of freedom provided by both the code signatures and the spatial signatures, as well as by how efficiently the degrees of freedom are exploited. Specifically, the number of users supported by the proposed MIMO SCDMA can be significantly higher than the number of chips per bit, owing to the employment of space-division. In this contribution, space-time spreading is employed for configuring the transmitted signals. Three types of low-complexity linear detectors, namely, correlation, decorrelating, and minimum mean-square error (MMSE) are considered for detecting the MIMO SCDMA signals. The bit-error rate performance of the MIMO SCDMA system associated with these linear detectors are evaluated by simulations, when assuming that the MIMO SCDMA signals are transmitted over multipath Rayleigh-fading channels. Our study and simulation results show that MIMO SCDMA assisted by multiuser detection is capable of facilitating joint space-time despreading, multipath combining, and receiver diversity combining, while simultaneously suppressing the multiuser interfering signals.     

Co-channel Interference Energy Harvesting for Decode-and-Forward Relaying

In this paper, co-channel interferences are exploited for energy harvesting in a Cooperative Network (CICN) in which a power constrained relay uses a power splitting architecture (CICN-PS) and a time switching architecture (CICN-TS) to harvest energy from the radio-frequency signals received from a source node and co-channel interferences. In the proposed CICN-PS and CICN-TS protocols, the relay applies decode-and-forward technology to decode the information of the source node, and then forwards the recoded information to a destination with the overall harvested energies. The system performance of the proposed protocols is discussed and evaluated using the exact throughput analyses and is then checked using Monte Carlo simulations over Rayleigh fading channels. The optimal power splitting ratio and energy harvesting time are derived by the Golden Section Search method, and throughput performance evaluations are performed. Our numerical and simulation results show distributions as follows. Firstly, the CICN-PS protocol outperforms the CICN-TS protocol. Secondly, the proposed protocols strictly depend on the location, amount and power of the co-channel interferences. Thirdly, when signal-to-noise ratio increases, the proposed CICN-PS protocol achieves the perfect throughputs where the cooperative relay applies the ideal receiver and co-channel interferences do not affect the destination. Finally, the numerical analyses agree well with the simulation results.     

A Unified Approach to Computing Error Probabilities of Diversity Combining Schemes over Correlated Fading Channels

The average bit-error rate performance of one-stage and two-stage diversity combining schemes operating over correlated fading channels is investigated. Two channel models that can significantly simplify the performance analysis are considered. In particular, a linear correlation channel model having equal branch variances can be decorrelated at the receiver, so that the branches become independent. It is shown that, in general, employing diversity combining schemes for decorrelated or orthogonalized branches can recover some of the diversity gain lost due to the branch correlations. This is observed, for example, for the case of hybrid selection/maximum ratio combining operating over decorrelated and orthogonalized non-zero mean Gaussian fading channels. Furthermore, a fading amplitude channel model is proposed assuming vector norm superposition of the impinging plane waves. This channel model is well-suited for the performance analysis of maximum ratio and equal gain combining schemes operating over correlated fading channels. Finally, the average bit error rates of several diversity combining schemes are evaluated analytically using the Prony approximation method as well as using computer simulation.     

Decision feedback differential detection for differential orthogonal space-time modulation with APSK signals over flat-fading channels

Differential orthogonal space-time modulation (DOSTM) with amplitude/phase shift keying (APSK) signals has been recently proposed to improve the data throughput of the DOSTM with PSK signals over quasi-static channels. In this letter, decision feedback differential detection (DF-DD) based on linear prediction is presented for the DOSTM with APSK Signals (DOSTM-APSK) over flat-fading channels. The proposed DF-DD offers better performance than the differential detection when the channel experiences fast fading. The coefficients of the linear prediction based DF-DD can be obtained by an adaptive recursive least-squares algorithm, where the channel statistics are not needed. The proposed DF-DD is also applicable to the general unitary differential space-time modulation.     

Real-time implementation of distributed beamforming for simultaneous wireless information and power transfer in interference channels

In this paper, we propose one-bit feedback-based distributed beamforming (DBF) techniques for simultaneous wireless information and power transfer in interference channels where the information transfer and power transfer networks coexist in the same frequency spectrum band. In a power transfer network, multiple distributed energy transmission nodes transmit their energy signals to a single energy receiving node capable of harvesting wireless radio frequency energy. Here, by considering the Internet-of-Things sensor network, the energy harvesting/information decoding receivers (ERx/IRx) can report their status (which may include the received signal strength, interference, and channel state information) through one-bit feedback channels. To maximize the amount of energy transferred to the ERx and simultaneously minimize the interference to the IRx, we developed a DBF technique based on one-bit feedback from the ERx/IRx without sharing the information among distributed transmit nodes. Finally, the proposed DBF algorithm in the interference channel is verified through the simulations and also implemented in real time by using GNU radio and universal software radio peripheral.     

Equalization and semi-blind channel estimation for space-time block coded signals over a frequency-selective fading channel

In this paper, we investigate the equalization and channel identification for space-time block coded signals over a frequency-selective multiple-input multiple-output (MIMO) channel. The equalization has been considered by taking into account the cyclostationarity of space-time block coded signals. The minimum mean square error (MMSE) solutions have been derived for the linear and decision feedback (DF) equalizers. The channel estimation is required for the equalization. With known symbols (as pilot symbols), MIMO channels can be estimated. In addition, due to the redundancy induced by space-time block code, it is possible to identify MIMO channels blindly using the subspace method. We consider both blind and semi-blind channel estimation for MIMO channels. It is shown that the semi-blind channel estimate has fewer estimation errors, and it results in less (bit error rate) performance degradation of the MMSE linear and DF equalizers.     

高速UWB-PPM信号传输的并行捕获与检测技术

高速(≥100 Mbit/s)超宽带一脉冲位置调制(UWB-PPM)信号传输是实现超宽带(UWB)室内通信的关键技术.文章结合UWB二元脉冲位置调制(PPM)的信号特征,采用多个并行积分器捕获簇脉冲能量取得快速同步,同时完成PPM的射频同步检测.系统传输试验与系统仿真表明,这种检测方式在室内多径信道下有良好的抗码间干扰能力.     

Some criteria for frequency domain design of signals imbedded in Gaussian noise

The design of time-limited binary signals imbedded in colored Gaussian noise resulting from passing white noise through a channel of known transfer function is investigated. It is shown that, for a class of channels whose magnitude characteristic is expressible as the ratio of polynomials with the numerator divisible by and of lower or the same degree as the denominator, the output noise kernel (correlation function) and its inverse will have Fourier transforms which are reciprocals of each other. The above assumption results in an expression for probability of error which is independent of the received waveform and depends solely on the transmitter signal-to-noise ratio. The additional freedom of design afforded by the above enables one to impose further restrictions in the form of energy concentration in the frequency domain on the received signal without deterioration of system performance. Some such bandwidth constraints and their associated optimum signal designs are considered in this paper.     

A high-performance reduced-complexity GMSK demodulator

A four-state adaptive maximum-likelihood sequence estimation (MLSE) Gaussian minimum-shift keying (GMSK) demodulator for modulation (BT=0.3) on AWGN channels is analyzed and simulated. This demodulator uses the linear representation of GMSK signals and achieves near-optimum BER performance. The channel-impulse response used in the MLSE demodulator is initialized to the highest energy component in the linear representation, and then adapted in a decision-directed mode to offset any performance losses incurred by initially ignoring other lower energy (and time-varying) components in the linear representation. The number of MLSE states is reduced to two, at about 0.1-dB performance loss, by implementing a whitening matched filter which concentrates most of the GMSK pulse energy in its two leading samples     

Sequence detection and channel state estimation over finite stateMarkov channels

A useful model for general time-varying channels is a finite state Markov chain. In this paper, maximum likelihood sequence estimation (MLSE) for signals over finite state Markov channels (FSMCs) is studied. Also studied is the maximum a posteriori (MAP) channel state estimation. When coded signals with interleaving are transmitted, the channel estimates can be used to make soft-decision decoding. The error performance of the proposed sequence and channel state estimation schemes are evaluated through computer simulations. The effect of channel modeling error is also discussed     

Signal design for efficient detection in dispersive channels

Signal design for maximizing the efficiency of the Neyman-Pearson detection procedure in randomly dispersive media is investigated. The medium is modeled as a randomly time-varying linear filter; by viewing the filter transfer function as a homogeneous random field on the time-frequency plane, a second-order theory results that relates various second-order measures of the time and frequency structures of input and output processes. A signal design strategy is developed that dictates transmitting signals that produce output processes with degrees of freedom possessing a signal-to-noise ratio (SNR) in the vicinity of 2. A distribution of signal energy in the output time-frequency plane that achieves the proper SNR for each degree of freedom is deduced and is used to infer constraints on input ambiguity functions that maximize detection efficiency. The general structure of efficient input signals for both high and low SNR is briefly discussed.     

Equalization algorithms in the frequency domain for continuous phase modulations

In this paper, novel equalization algorithms for continuous phase modulations (CPMs) are illustrated. Both conventional (linear and decision-feedback) and turbo equalization techniques are derived using the Laurent decomposition of CPM signals. All of them operate in the frequency domain and process two samples of the received signal per channel symbol. Numerical results show that on one hand, conventional equalization strategies offer good performance for binary partial response signaling over severely frequency-selective wireless channels at a moderate complexity. On the other hand, there is evidence that turbo techniques provide a small energy saving at the price of a substantial computational burden.     

Analysis of linear crosstalk in photonic crossbar switches based onon/off gates

This paper presents expressions for the linear crosstalk and the resulting error rate degradation in a photonic switch based on on/off gates, considering cyclostationary interference among digital signals. The periodically time-varying interference accounts for the dependencies of error probability both on the spectrum of transmitted signals and on random bit-skews between channels. This paper quantitatively verifies the intuitions that bit-aligned channels increase the crosstalk power penalty, and that a sharp modulating pulse improves error probability. These dependencies on spectrum and bit-skews become noticeable at high crosstalk levels caused by either a low contrast ratio or a large switch size     

A Reed-Solomon coded DS-CDMA system using noncoherent M-aryorthogonal modulation over multipath fading channels

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are invoked and the related performance is evaluated for both uncoded and coded DS-CDMA systems. “Errors-and-erasures” decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The probability density functions (PDF) of the ratio associated with the RTT conditioned on both the correct detection and erroneous detection of the M-ary signals are derived. These PDFs are then used for computing the codeword decoding error probability of the RS coded DS-CDMA system using “errors-and-erasures” decoding. Furthermore, the performance of the “errors-and-erasures” decoding technique employing the RTT is compared to that of “error-correction-only” decoding refraining from using side-information over multipath Rayleigh fading channels. As expected, the numerical results show that when using “errors-and-erasures” decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information