A rate adaptive bit-loading algorithm for in-building power-line communications based on DMT-modulated systems

This paper deals with a variable rate discrete multitone modulation system for broadband power-line communications, based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable least mean square channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The system performance, expressed in terms of bit rate and bit-error rate, is derived by simulation with and without estimation errors. The propagation environment has been assumed as a frequency-selective multipath fading channel with additive colored Gaussian noise, according to the in-building networks model.     

A Low-Complexity Multiuser Detector for Asynchronous CDMA QPSK Adaptive Antenna Array Systems

This paper proposes a low complexity joint space-time multiuser detection algorithm for asynchronous DS/CDMA antenna array systems. The proposed multiuser detector is composed of an adaptive antenna array, used as a linear beamformer, and a sliding window decorrelator. A QPSK modulation scheme is used in order to increase bandwidth efficiency. Numerical results are given in terms of Bit Error Rate (BER) under the assumption of a frequency-selective Rayleigh slow fading channel. In particular, the proposed receiver is shown to be near-far resistant, even in worst fading cases, and to exploit completely array introduction while maintaining acceptable computational complexity. The proposed architecture avoids linear filter realization of the decorrelator, which is impractical in the case of a large number of users, and operates with relatively short data frames instead of the complete information sequence. Finally, this receiver is very flexible to changes in timing configuration.     

Ornament and function

The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect - thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading.     

A low‐complexity multiuser detector for up‐link CDMA QPSK mobile radio communications

This paper deals with a multiuser detector based on a new decorrelating approach for asynchronous uplink DS/CDMA communications in which the QPSK modulation scheme is used in transmission. It is shown here that the receiver proposed is near–far resistant and exhibits a low complexity which allows realtime operation. Performance is expressed in terms of bit error rate (BER) which has been derived by simulations under the assumption of a slowly frequencyselective Rayleigh fading channel.     

Frequency recovery techniques for TM/TC satellite modem in critical scenarios

Reliability and effectiveness are essential features of satellite transceivers for telemetry and telecommand applications. Modem performance has a strong impact on the success of a satellite mission, in particular, during critical scenarios as the early operation phase, the disposal of a satellite at the end of its life, or the deep‐space missions. In these specific mission critical scenarios, fast and correct data reception is even more important than high channel capacity. An unknown and fast variable channel condition, which can be caused by uncertain spacecraft attitude and large Doppler shift with respect to the data rate, requires efficient and innovative receiver architecture. This paper introduces a complete digital implementation of a transceiver for TM/TC application in low Earth orbit mission that is perfectly compliant with aforementioned requirements. Particular attention is dedicated to the definition and selection of the most appropriate frequency recovery technique; 2 open‐loop techniques that are derived from ML optimal estimator are presented and compared. Additionally, the performance of the proposed receiver is extensively studied and compared with an incoherent technique that is based on the double differential PSK modulation and is known to be suitable for sat‐com in critical scenarios.     

Ornament and function

The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect ‐ thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading.     

Cooperative strategies in satellite assisted emergency services

This paper deals with the cooperative strategies, which can be adopted in emergency scenarios by integrating space and terrestrial segments, and communication and localization services. First, the cooperative solutions for integrated Navigation and Communication systems are reviewed and an effective software‐defined radio implementation is described. Then, cooperative systems for broadcast and multicast communications in Incident Area Network are proposed and evaluated: in the broadcast scenario, low‐complexity relaying techniques are adopted to overcome the propagation impairments and the performance degradation; in the multicast system, radio resources management techniques for group communications are designed to allow the efficient use of scarce resources and improve connectivity and reliability of the overall system. The technical solutions have been studied and tested in the framework of the Italian National Research Project SAtellite‐assisted LocalIzation and Communication system for Emergency services [1]. Copyright © 2013 John Wiley & Sons, Ltd.     

Perspectives for present and future CDMA-based communications systems

In this article the main boosters of future CDMA communication systems are presented and described in order to highlight the ways to cope with the more challenging requirements of future systems and services. Particular attention is devoted to the inherent weak points of CDMA systems and detection techniques that can be used to overcome their impairments. Moreover, high-data-rate transmissions in wireless channels require proper link adaptation techniques; these are thoroughly described as well. Finally, the last part of this article focuses on the design of suitable protocol strategies for new heterogeneous multimedia packet services characterized by strict QoS requirements     

Design of Turbo-MUD Receivers for Overloaded CDMA Systems by Density Evolution Technique

This paper deals with a turbo multiuser detector suitable for applications in overloaded coded DS-CDMA systems. The turbo-MUD receiver is based on the use of a linear MMSE detector in the first iteration and a parallel interference cancellation scheme in the successive ones. The inputs of the interference cancellator are both the detector outputs and the soft information from a bank of turbo decoders. The performance of the proposed receiver has been derived by means of computer simulations and applications of the density evolution theory: in particular, this technique permits to properly evaluate the number of MMSE iterations, simplifying the overall receiver design.     

Reconfigurable Antenna for Future Wireless Communication Systems

This paper deals with the processing techniques which are known as reconfigurable antennas: these methods are foreseen to be a booster for the future high rate wireless communications, both for the benefits in terms of performance and for the capacity gains. In particular, adaptive digital signal processing can provide improved performance for the desired signal in terms of error probability or signal-to-noise ratio while the bandwidth efficiency can be increased linearly with the number of transmitting and receiving antennas. In this article, the main antenna processing techniques are reviewed and described, aiming at highlighting performance/complexity trade-offs and how they could be implemented in the future systems. The coexistence of all these different technologies in a wireless environment requires high efficiency and flexibility of the transceiver. Future transceiver implementations which are based on the Software Defined Radio technology are also reviewed and described.