一种高速调制解调器，它通过电话线发送和接收一载频集的数字数据。 该调制解调器包括在载波之间可变地分配数据和功率，以便补偿等效噪声和使数据速率最大的系统。 此外，也介绍不需要一个均衡网络、可自适应地分配信道的控制和可跟踪线上参数变化的系统。

Ensemble modem structure for imperfect transmission media

A new multiresolution $M$ -ary differential chaos shift keying (DCSK) modulation scheme is proposed in this paper. It is a promising technique for providing a different quality of service for transmitted bits within a symbol according to their different bit error rate (BER) requirements based on the principle of nonuniformly spaced constellations. The new system not only is simple but also provides better antimultipath fading performance against various spreading factors, inheriting the advantages of the conventional DCSK system. Furthermore, the proposed scheme and its multicarrier version further increase spectral efficiency and use lower energy consumption at the same bandwidth as compared with the conventional DCSK and its multicarrier system. Explicit BER expressions of the new system are derived and analyzed over additive white Gaussian noise and multipath Rayleigh fading channels. All simulation results verify the prominent advantages of the new scheme and the accuracy of the new analytical approach.

Design and Performance Analysis of a New Multiresolution $M$ -Ary Differential Chaos Shift Keying Communication System

We consider chaotic digital communications in multiple-input-multiple-output (MIMO) wireless multipath fading channels. In particular, we focus on systems that employ M -ary differential chaos shift keying (M-DCSK). We consider two transceiver schemes, both of which require no channel state information at either the transmitter or the receiver. The first one employs a distinct chaotic sequence at each transmit antenna to spread the same data symbol and transmits omnidirectionally. At each receive antenna, the corresponding differential detection statistic is formed, and these statistics are then combined with equal gain for symbol detection. The second scheme employs a single chaotic spreading sequence and makes use of adaptive transmit and receive beamforming. The beamformers are updated by using a simple stochastic gradient method that is based on the received signal power and a finite-rate feedback strategy. Simulation results show that both schemes can effectively exploit the spatial diversity of the underlying MIMO system, and the adaptive beamforming scheme significantly outperforms the omnidirectional transmission.

$M$ -DCSK-Based Chaotic Communications in MIMO Multipath Channels With No Channel State Information

The cognitive radio (CR) technology will allow a group of potential users to identify and access available spectrum resources provided that the interference to the users for whom the band has been licensed is kept below a prescribed level. However, this research area is at a very immature stage because various research challenges have to be addressed and solved. In this paper our objective is to present an overview of some research issues for CR networks. Specifically, we present some research and development in CR networks with focus on i) information- theoretic aspects, ii) spectrum sensing, iii) link adaptation, iv) advanced transceiver design, and v) admission control. We also discuss some important research problems related to these specific topics that needs to be addressed before deployment of CR systems in practice.

Some research issues in cognitive radio networks

Fast communication: Performance analysis of STBC-CSK communication system over slow fading channel

It is shown that the use of chaos shift keying (CSK) with a transmit diversity technique such as beamforming and space-time coding can provide a secure communication link with improvement in the system error performance. Spreading sequences that are used to scramble data in spread spectrum (SS) systems can be generated using a single mathematical relationship of a chaotic generator. These chaotic sequences are very difficult to predict over long-term chaotic pattern unless the exact initial condition of the chaotic generator is known, providing security. On the other hand, beamforming and orthogonal space-time block coding (OSTBC) transmit diversity techniques are known to provide optimal transmitting structures for communication systems, especially if combined. Based on the signal angle-of- arrival (AoA) estimates, the channel correlation matrix can be constructed, and it is shown that signal transmission of OSTBC codes in the eigen-modes of this matrix gives an effective array weighting gain which improves system error performance without sacrificing any diversity and coding gain. A performance study of CSK with beamforming and space-time encoded is carried out in this paper.

/pdf/space-time-encoded-secure-chaos-communications-with-transmit-2hsiqvylia.pdf

Space-Time Encoded Secure Chaos Communications with Transmit Beamforming

We propose an optimum transmitting structure consisting of adaptive modulation, space-time block coding (STBC), and transmitter beamforming for orthogonal frequency division multiplexing (OFDM) systems to improve the data throughput and error performance. Using correlative properties of multi-input multi-output (MIMO) channels, we maximize the channel-to-noise ratio (CNR) based on a water-filling principle to optimally select the number of antenna beams and the power splitting ratio. The adaptive modulator employed is based on a lookup matrix adaptive bit and power allocation (LM-ABPA) scheme. As compared to non-adaptive systems, simulation results demonstrated that the proposed configuration achieves spectrally more efficient transmission under a constant error rate as well as better error rate performance under a constant data rate

Space-time block coded OFDM with adaptive modulation and transmitter beamforming

Recently an adaptive transmit eigenbeamforming with orthogonal space-time block coding (Eigen-OSTBC) has been proposed. This model was simulated over macrocell environment with a uniform linear array (ULA) at the base station (BS). In this paper we investigate the impact of various antenna geometries on the performance of this scheme as well as the performance over microcell and macrocell channel environments. The geometrical-based hyperbolically distributed scatterers (GB- HDS) channel models were simulated with angular spreads (AS) taken from experimental data. The ULA and the uniform circular array (UCA) are considered at the BS. In the simulation conducted, results have shown that the Eigen-OSTBC system has a higher performance gain than OSTBC systems in macrocell than microcell environment (where the AS gets larger). It is also observed that BS antenna array with different separation distances also affects the performance of both Eigen-OSTBC and OSTBC systems. However, the error-rate performance curves of ULA and UCA configurations are very similar.

/pdf/performance-of-adaptive-transmit-diversity-with-orthogonal-25a5ps4qmb.pdf

Performance of Adaptive Transmit Diversity with Orthogonal Space-Time Block Coding in Microcell and Macrocell Channel Environments

Over the recent years, advance multiantenna transmission schemes have attracted considerable interest due to their potential benefits in improving the system capacity and error-rate performance. As a result, space-time coding and transmit beamforming have emerged as the two most promising techniques. Because of limited space at the mobile station (MS) and the fact that download intensive services are to be introduced in the next generation of cellular systems, most of research efforts have been pouring on transmit diversity techniques. In this paper, we focus on adaptive uplink transmission and reception techniques for wireless communications and introduce a new frequency-time encoding scheme that can be used to exploit frequency diversity branches for broadband OFDM systems with only one antenna at the MS. By incorporating this with receive beamforming at the base station (BS), the instantaneous signal- to-noise ratio (SNR) is maximized and the system error-rate performance is then further improved. Numerical results showed that systems employed the proposed transceiver structure have a 4-dB improvement over the conventional space-time coding scheme when two receive antennas are used.

/pdf/adaptive-receiver-beamforming-for-diversity-coded-ofdm-ppg5q5in9h.pdf

K.H. Lin

Papers

Space-Time Encoded Secure Chaos Communications with Transmit Beamforming

Space-time block coded OFDM with adaptive modulation and transmitter beamforming

Performance of Adaptive Transmit Diversity with Orthogonal Space-Time Block Coding in Microcell and Macrocell Channel Environments

Adaptive Receiver Beamforming for Diversity Coded OFDM Systems: Maximum SNR Design