Performance of Convolutionally Coded Multicarrier DS-CDMA System

A new convolutionally coded direct sequence （DS） CDMA system is proposed. The outputs of a convolutional encoder modulate multiple band-limited DS-CDMA waveforms. The receiver detects and combines signals for the desired user and feeds a soft-decision Viterbi decoder. The performance of this system is compared to that of a convolutionally coded single carrier DS CDMA system with a Rake receiver. At roughly equivalent receiver complexity, results will demonstrate superior performance of the coded multicarrier system.     

阵列天线多载波DS-CDMA系统基于子空间的信道估计

阵列天线多载波DS-CDMA系统在未来移动通信中具有重要的应用前景。本文研究了阵列天线多载波DS-CD MA系统基于子空间的信道盲估计方法。通过在阵列天线多载波DS-CDMA系统下构造统一的信号模型,实现了基于子空间的信道盲估计。仿真结果表明所提出的方法可有效地对阵列天线多载波DS-CDMA系统的信道参数进行估计,并可抵抗适度的远近效应。     

Comparison of advanced coding and modulation schemes for multicarrier satellite communication systems

Digital satellite communication systems use coherent quaternary PSK (QPSK) as the preferred modulation scheme. In recent years, however, the search for bandwidth and power-efficient digital modulation methods has become an active research area. In this paper the performances of combined coding and modulation schemes employing multilevel signal alphabets are considered, in the framework of a system model which reasonably approximates the INTELSAT SCPC system. The main goal of the research was to investigate whether the efficiency of coded modulation schemes and their savings in transmitted power could be maintained in a system environment dominated by interference more than by the additive white Gaussian noise. A second goal was to compare the performance of signals with constant envelope, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel QAM. In the paper, we propose a channel model which is reasonably close to the real system, and a method for performance evaluation leading to an estimate of the asymptotic power gain of the modulation systems. The channel model and the method are applied to the analysis of coded 16- and 32- PSK and QAM.     

THE PHASE—OFSET OVERLAPPED WAVE TECHNIQUE

A new digital communication technology based on the Phase-Offset Overlapped Waves (POOW) has been introduced in this letter.The waves can be considered as a special multicarrier different from traditional ones.The sud-waves in a coded word‘s period of the POOW are sine waves and have the same frequencies,but different starting phases.The most important characteristic is that these sub-waves are the piecewise functions and not orthogonal in a code word period.The decoding can be implemented by solving a linear equation group.This code has very high efficiency and thus the data transmissin rate is increased greatly.     

Performance studies for high-speed indoor wireless communications

A major difficulty in achieving high-bit-rate wireless transmission is the large delay spread which severely limits the maximum data rate. In this paper, techniques are presented for overcoming these transmissionrate limits. Specifically, the performances of multicarrier modems and a single-carrier modem with equalization are characterized in terms of the efficiency (or achievable bit rate) versus outage, under a wide range of conditions and parameters.For the multicarrier approach, the extensive set of performance results indicate the following: for QPSK, in a typical office-building environment (rms delay spreads of 50–100 ns), if the subchannel symbol rate is limited to 1 Mbaud,and provided there is sufficient power, an efficiency of 1–1.2 b/s/Hz can be achieved with 99% availability (1% outage) with either the multitone or the Orthogonal Frequency Division Multiplexing realizations. With 16 subchannels this corresponds to at least 16 Mb/s. To achieve higher data rates (for example, 155 Mb/s), or where there are larger delay spreads (for example, in outdoor microcells), more subchannels can be used, if practical. Otherwise, equalization can be combined with wider subchannels and/or sophisticated antenna techniques.Link-budget calculations, also presented here, show how transmitted power can be a limiting factor in transmission bit rate. In particular, for 20 MHz of bandwidth and a frequency of 5 GHz or less, a transmitted power of 100 mW to 1 W should be sufficient to accommodate 30–50 m cells with good performance (for example, bit error probability of 10^–8 and 1% outage). However, for larger bandwidths (for example, 100–200 MHz), the frequency must be higher (for example, 20 GHz) and the distance will be severely limited, possibly to a single room.     

Experimental study and empirical evaluation of carrier compression and third order intermodulation products of unequal carriers in a communication satellite transponder

Carrier compression and third order intermodulation products of two and three unequal carriers have been studied experimentally using a 36 MHz wide C-band transponder of INSAT-1B satellite. From the experimental data, empirical relations for carrier compression for two unequal carriers have been derived, which agree with the measured data within ±0.5 dB. The empirical relations for carrier compression derived for two unequal carriers have been extended to three unequal carriers and good correlations with measured data have been obtained. Empirical relations for third order intermodulation products of two and three (f₁+f₂-f₃ type) unequal carriers have also been derived.     

SPATIAL-FREQUENCY CHANNEL ANDDOA JOINT BLIND ESTIMATOR FORMC-CDMA SYSTEMS

The MC-CDMA (Multicarrier Code Division Multiple Access) technique is known to be appropriate for high-data-rate wireless communications due to its robustness to multipath fading and its capability of handling high data rates with a simple one-tap equalizer. This paper investigates a uniform linear antenna array at the base station for macroceH MC-CDMA systems in a frequency-selective fading channel environment, and develops a blind joint estimator for the spatial-frequency channel and the DOA (Direction-Of-Arrival). By constructing the matrix including both spatial-frequency channel and DOA information, and performing eigen decomposition on it, the closed-form solution of spatial-frequency channels and DOAs for all active users within the macrocell can be obtained. The overall performance using this novel scheme is demonstrated by extensive computer simulations.     

Bandwidth efficient MT-DS-SS via reduced subcarrier frequency spacing

We investigate modifications to conventional multitone direct-sequence spread spectrum (MT-DS-SS) signaling to improve spectral efficiency, for high-data-rate systems with small processing gain. Reduction in subcarrier frequency spacing to half the symbol rate improves bandwidth efficiency at no cost in complexity or performance. Via both analysis and simulations, we provide example results that illustrate the attractive performance and throughputs attainable with reduced frequency spacing. We extend study to synchronous multiuser transmission, and show that our best spectrally efficient MT-DS-SS scheme outperforms the conventional MT-DS-SS in a dispersive multiuser environment.     

多载波时分多址及其快速卷积实现

为了解决正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统峰均功率比(Peak Ave-rage Power Ratio,PAPR)过高 以及对频率偏移敏感的问题,提出了多载波时分多址(Multicarrier Time Division Multiple Access,MC-TDMA),其采用交织映射和改进离散傅里叶变换(Modified Discrete Fourier Transform,MDFT)滤波器组技术,可以有效地降低系统的峰均功率比,增强系统的抗频率偏移的性能,并且可以同时用于上行和下行通信中。文中分别从交织映射和MDFT滤波器组两个方面研究了MC-TDMA系统的实现。为了增强系统的灵活性,采用快速卷积方案实现MC-TDMA,使其能够更好地应对5G复杂的应用场景。分别从系统结构、频域采样滤波器等方面对系统进行设计,并且对快速卷积MC-TDMA系统的性能进行仿真,并与MC-TDMA进行比较。研究表明,使用快速卷积方案实现的MC-TDMA系统,通过灵活地调整重叠因子、抽取因子和滚降因子等参数,可以使其性能优于MC-TDMA。     

CAPACITY IMPROVEMENT OF MULTICARRIER DS-CDMA SYSTEM WITH ANTENNA ARRAY

An antenna array based base station receiver for multicarrier Direct Sequence Code Division Multiple Access （DS-CDMA） system is proposed. The main advantage of the receiver is that the spatial diversity is achieved by combining signals of array elements. Based on the detailed analysis of multiuser interference and noise characteristics, the performance of the proposed receiver is analyzed. Theoretical analysis shows significant performance improvement in terms of system capacity due to the use of antenna arrays compared with the conventional single antenna multicarrier DS-CDMA approach. Simulation results confirm the theoretical analysis.