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 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 (STS) 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 BER 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 de-spreading, multipath combining and receiver diversity combining, while simultaneously suppressing the multiuser interfering signals

Broadband MC DS-CDMA Using Space-Time and Frequency-Domain Spreading

In this contribution multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) using space-time spreading (STS) assisted transmit diversity and frequency-domain (F-domain) spreading is investigated in the context of broadband communications over frequency-selective Rayleigh fading channels. We consider the attainable capacity extension of broadband MC DS-CDMA with the advent of using Time-Frequency-domain (TF-domain) spreading. The BER performance of STS assisted broadband MC DS-CDMA using Binary Phase Shit Keying (BPSK) modulation and TF-domain spreading is investigated by simulation for a range of parameter values. Both the correlation based single-user detector and the decorrelating multiuser detector are considered. Our study shows that the number of users supported by the broadband MC DS-CDMA system is determined by the product of the T-domain spreading factor and the F-domain spreading factor, while it is independent of the frequency diversity order. Furthermore, when multiuser detection assisted F-domain spreading is considered, the broadband MC DS-CDMA system is capable of supporting a substantially increased number of users, while maintaining a similar bit error ratio (BER) performance to that of the broadband MC DS-CDMA system using no F-domain spreading

Blind Joint Soft-Detection Assisted Slow Frequency-Hopping Multicarrier DS-CDMA

A novel multiple-access scheme based on slow frequency-hopping multicarrier direct-sequence, code-division multiple access (SFH/MC DS-CDMA) is proposed and investigated, which can be rendered compatible with the existing second-generation narrow-band CDMA and third-generation wide-band CDMA systems. Blind joint soft-detection of the SFH/MC DS-CDMA signals is investigated, assuming that the receiver has no knowledge of the associated frequency-hopping (FH) patterns invoked. The system’s performance is evaluated over the range of Nakagami multipath fading channels. The results show that blind joint soft-detection achieves the required bit-error rate performance, while blindly acquiring the FH patterns employed. This is advantageous during the commencement of communications or during soft handover. Index Terms—Blind detection, code-division multiple access, constant-weight codes, frequency-hopping, orthogonal frequency-division multiplexing

Slow Frequency-Hopping Multicarrier DS-CDMA for Transmission over Nakagami Multipath Fading Channels

A novel multiple access scheme based on slow frequency hopping multicarrier direct-sequence code division multiple access (SFH/MC DS-CDMA) is proposed and investigated, which can be rendered compatible with the existing second-generation narrowband CDMA and third-generation wideband CDMA systems. The frequency hopping patterns are controlled by a set of constant-weight codes. Consequently, multirate communications can be implemented by selecting the corresponding sets of constant-weight codes having the required weights controlling the SFH patterns invoked. Two FH schemes, namely random and uniform FH, are considered and their advantages as well as disadvantages are investigated. We assume that the system operates in a multipath fading environment and a RAKE receiver structure with maximum ratio combining (MRC) is used for demodulation. The system’s performance is evaluated over the range of multipath Nakagami fading channels, under the assumption that the receiver has an explicit knowledge of the associated frequency-hopping (FH) patterns invoked. Furthermore, the performance of the SFH/MC DS-CDMA system is compared to that of the conventional single-carrier (SC) DS-CDMA system and that of the conventional MC DS-CDMA system, under the assumptions of constant system bandwidth and of constant transmitted signal power. Index Terms—Code division multiple access, constant-weight code, frequency hopping, Nakagami fading, orthogonal frequency division multiplexing

Overlapping M-ary Frequency Shift Keying Spread-Spectrum Multiple-Access Systems using Random Signature Sequences

In this paper, a multiple-access spread-spectrum communication system using binary frequency shift keying (BFSK) or M-ary frequency shift keying (MFSK) and noncoherent demodulation is considered. In contrast to previous work typically assuming that the frequency shift keying (FSK) tones are nonoverlapping after direct-sequence (DS) spreading, here we consider a spread-spectrum multiple-access (SSMA) system under the assumption that the DS spread signals of different FSK tones are only orthogonal over the information symbol duration. Consequently, the frequency band of a spread FSK tone may be fully or partially overlapping with the other spread signals. An estimate of the variance of the multiple-access interference is obtained by assuming that the phase angles and time delays of the received signals are mutually independent random variables, provided that random signature sequences are employed for spreading. On the basis of the above assumptions, the bit error rate (BER) of our DS spread-spectrum multiple-access (DS-SSMA) and that of our hybrid DS slow frequency-hopping spread-spectrum multiple-access (DS-SFHSSMA) systems using FSK modulation is analyzed, when the channel impairments are constituted by a combination of additive white Gaussian noise (AWGN) and multiple-access interference. From our analysis and the numerical results, we concluded that, for a given system bandwidth and for a certain value of M, the system’s BER performance can be optimized by controlling the amount of overlapping and that the systems with optimized overlapping outperformed the systems using no overlapping. Index Terms—Frequency shift keying (FSK), slow frequency hopping, spread-spectrum multiple access

Mechanism conversion process and timeliness of N2-ECBM

Purpose. Based on the technology by which methane drainage is strengthened under gas injection, to examine the process of gas injection and the mechanism of action. Methods. Physical simulation experiment method, using the self-built coal seam and gas injection displacement experimental device, the experiment of layered pre-compression forming coal samples under vertical stress loading conditions and under the conditions of different gas injection pressures. Findings. The experiment on N2-ECBM is a dynamic process and has time effects. In the overall process, the rate of replacement was more than 60%, and the rate of displacement was less than 40%. Originality. According to the behavior of nitrogen injection in the coalbed, an assessment of displacement effects under gas injection and a quantitative evaluation of the replacement effect were presented. In every stage of the process, the replacement effect is dominant, while the role of displacement is of secondary importance. Practical implications. The experimental results have great guiding significance for optimization of gas parameters and gas source selection for gas injection flooding in underground coal seams.Мета. Вивчити процес вприскування газу у вугільний пласт й механізм його впливу на основі технології, яка дозволяє забезпечити дренаж метану, інтенсифікований за рахунок нагнітання газу. Методика. Використано експериментальний метод фізичного моделювання: була змонтована установка з моделлю вугленосного пласта для дослідження вприскування газу з метою витіснення метану. В експерименті попередньо стиснені зразки шаруватого вугілля піддавалися вертикальному навантаженню при тисках 200 кН, аналогічних тиску вприснутого газу. Газ для ін’єкцій вимірювався контролером масової витрати з максимальною швидкістю 5 л/хв, і через монітор контролювалися миттєвий і загальний потоки. В експерименті використано антрацит вугільної шахти Хуатай. Результати. Експериментальними дослідженнями встановлено, що концентрація і об’єм метану призводять до змін тиску, витрати і часу вприскування азоту, що свідчить про те, що процес заміщення метану вугільного пласта шляхом закачування азоту залежить від часу. Доведено, що експеримент з використанням технології N2-ECBM (інтенсивного вилучення вугільного метану) – це динамічний процес, в якому фактор часу відіграє вирішальну роль. Об’єм азоту, який залишається у вугіллі й витісняє метан, можна розглядати як кількісний вклад ефекту зміщення. Виявлено, що в результаті використання даної технології, рівень заміщення метану зріс більш, ніж на 60%; а рівень його витіснення – на 40%. Наукова новизна. Вивчено ефект витіснення метану при нагнітанні азоту у вугільний пласт з урахуванням поведінки газу у вугленосній товщі, а також дана кількісна оцінка ефекту заміщення, що чинить ключовий вплив на всіх стадіях процесу, в той час як роль витіснення – другорядна. Практична значимість. Результати експериментів мають принципове значення для оптимізації параметрів газу та для вибору джерела вприскування газу у вугільні пласти.Цель. Изучить процесс впрыскивания газа в угольный пласт и механизм его воздействия на основе технологии, которая позволяет обеспечить дренаж метана, интенсифицированный за счет нагнетания газа. Методика. Использован экспериментальный метод физического моделирования: была смонтирована установка с моделью угленосного пласта для исследования впрыскивания газа с целью вытеснения метана. В эксперименте предварительно сжатые образцы слоистого угля подвергались вертикальной нагрузке при давлениях 200 кН, аналогичных давлению впрыскиваемого газа. Газ для инъекций измерялся контроллером массового расхода с максимальной скоростью 5 л/мин, и через монитор контролировались мгновенный и общий потоки. В эксперименте использован антрацит угольной шахты Хуатай. Результаты. Экспериментальными исследованиями установлено, что концентрация и объем метана приводят к изменениям давления, расхода и времени впрыска азота, что свидетельствует о том, что процесс замещения метана угольного пласта путем закачки азота зависит от времени. Доказано, что эксперимент с использованием технологии N2-ECBM (интенсивного извлечения угольного метана) – это динамический процесс, в котором фактор времени играет решающую роль. Объем азота, который остается в угле и вытесняет метан, можно рассматривать как количественный вклад эффекта смещения. Выявлено, что в результате использования данной технологии, уровень замещения метана возрос более, чем на 60%; а уровень его вытеснения – на 40%. Научная новизна. Изучен эффект вытеснения метана при нагнетании азота в угольный пласт с точки зрения поведения газа в угленосной толще, а также дана количественная оценка эффекту замещения, оказывающему ключевое влияние на всех стадиях процесса, в то время как роль вытеснения – вторична. Практическая значимость. Результаты экспериментов имеют принципиальное значение для оптимизации параметров газа и для выбора источника впрыскивания газа в угольные пласты.The authors are grateful for the financial support from the Natural Science Foundation for the Youth of China (No. 51404091) and the PhD Foundation of Henan Polytechnic University (B2015-08)

Performance of Fractionally Spread Multicarrier CDMA in AWGN as Well as Slow and Fast Nakagami-m Fading Channels

Abstract—In multicarrier code-division multiple-access (MCCDMA), the total system bandwidth is divided into a number of subbands, where each subband may use direct-sequence (DS) spreading and each subband signal is transmitted using a subcarrier frequency. In this paper, we divide the symbol duration into a number of fractional subsymbol durations also referred to here as fractions, in a manner analogous to subbands in MC-CDMA systems. In the proposed MC-CDMA scheme, the data streams are spread at both the symbol-fraction level and at the chip level by the transmitter, and hence the proposed scheme is referred to as the fractionally spread MC-CDMA arrangement, or FS MCCDMA. Furthermore, the FS MC-CDMA signal is additionally spread in the frequency (F)-domain using a spreading code with the aid of a number of subcarriers. In comparison to conventional MC-CDMA schemes, which are suitable for communications over frequency-selective fading channels, our study demonstrates that the proposed FS MC-CDMA is capable of efficiently exploiting both the frequency-selective and the time-selective characteristics of wireless channels. Index Terms—Broadband communications, code-division multiple access (CDMA), fractionally spreading, frequency-domain spreading, multicarrier modulation, Nakagami fading, timedomain spreading

Performance Analysis of Coded MM-ary Orthogonal Signaling Using Errors-and Erasures Decoding Over Frequency-Selective Fading Channels

The performance of $M$-ary orthogonal signaling schemes employing Reed–Solomon (RS) codes and redundant residue number system (RRNS) codes is investigated over frequency-selective Rayleigh fading channels. “Errors-and-erasures” decoding is considered, where erasures are judged based on two low-complexity, low-delay erasure insertion schemes—Viterbi’s ratio threshold test (RTT) and the proposed output threshold test (OTT). The probability density functions (PDF) of the ratio associated with the RTT and that of the demodulation output in the OTT conditioned on both the correct detection and erroneous detection of $M$-ary signals are derived, and the characteristics of the RTT and OTT are investigated. Furthermore, expressions are derived for computing the codeword decoding error probability of RS codes or RRNS codes based on the above PDFs. The OTT technique is compared to Viterbi’s RTT, and both of these are compared to receivers using “error-correction only” decoding over frequency-selective Rayleigh-fading channels. The numerical results show that by using “errors-and-erasures” decoding, RS or RRNS codes of a given code rate can achieve higher coding gain than that without erasure information, and that the OTT technique outperforms the RTT, provided that both schemes are operated at the optimum decision thresholds. Index Terms—“Errors-and-erasures” decoding, $M$-ary orthogonal signaling, Rayleigh fading, redundant residue number system codes, Reed–Solomon codes

Adaptive Space-Time-Spreading-Assisted Wideband CDMA Systems Communicating over Dispersive Nakagami-m Fading Channels

In this contribution, the performance of wideband code-division multiple-access (W-CDMA) systems using space-timespreading-(STS-) based transmit diversity is investigated, when frequency-selective Nakagami-m fading channels, multiuser interference, and background noise are considered. The analysis and numerical results suggest that the achievable diversity order is the product of the frequency-selective diversity order and the transmit diversity order. Furthermore, both the transmit diversity and the frequency-selective diversity have the same order of importance. Since W-CDMA signals are subjected to frequency-selective fading, the number of resolvable paths at the receiver may vary over a wide range depending on the transmission environment encountered. It can be shown that, for wireless channels where the frequency selectivity is sufficiently high, transmit diversity may be not necessitated. Under this case, multiple transmission antennas can be leveraged into an increased bitrate. Therefore, an adaptive STS-based transmission scheme is then proposed for improving the throughput ofW-CDMA systems. Our numerical results demonstrate that this adaptive STS-based transmission scheme is capable of significantly improving the effective throughput of W-CDMA systems. Specifically, the studied W-CDMA system’s bitrate can be increased by a factor of three at the modest cost of requiring an extra 0.4 dB or 1.2 dB transmitted power in the context of the investigated urban or suburban areas, respectively

Apparatus and method for destructive removal of particles contained in flowing fluid

An apparatus and method for destructively removing particles from a flowing gas containing the particles is described. In the specific embodiments disclosed the apparatus is adapted to remove carbon particles from diesel engine exhaust products. The exhaust products are directed to a predetermined location where they are rapidly vaporized and combine with oxygen in the exhaust products to form carbon dioxide. Vaporization in one embodiment is effected by a discharge grid located within an exhaust conduit, the grid being chosen so that alternate conductors defining the grid are spaced apart a distance approximately 125 times the mean diameter of the particles to be removed. A voltage differential of approximately 690 volts is applied across adjacent conductors