A new approach based on “soft statistics” to thenonlinear blind-deconvolution of unknown data channels

In this paper, we present a new nonlinear receiver for the blind deconvolution of intersymbol interference (ISI) impaired data. The proposed receiver achieves fast identification of an unknown transmission channel using only one channel estimator and requiring the computation of only the second-order conditional statistics of the baud-rate sampled received signal and the knowledge of the transmitted constellation. The main novelty of the proposed approach is that the receiver accomplishes fast channel-identification by using soft-statistics. In particular, the receiver consists of a symbol-by-symbol maximum a posteriori (SbS-MAP) detector that feeds a nonlinear Kalman-like channel estimator with the soft statistics constituted by the a posteriori probabilities (APPs) of the state sequence of the ISI channel. Several numerical results confirm that the proposed blind detector achieves the identification of nonminimum phase channels with deep spectral notches within 300 symbols, even at low signal-to-noise ratios (SNRs). Furthermore, an attractive feature of the proposed blind channel estimator is that it directly estimates the discrete-time impulse response of the unknown channel so that, in principle, any equalization technique for known channels may be performed after channel identification has been achieved     

Some simple bounds on the symmetric capacity and outage probabilityfor QAM wireless channels with Rice and Nakagami fadings

In this article, quickly computable upper and lower bounds are presented on the symmetric capacity of flat-faded Rice and Nakagami channels with side information (SI) for data-transmissions via finite-size quadrature amplitude modulation (QAM) constellations. The proposed bounds exhibit the appealing feature to be tight and asymptotically exact both for high and low signal-to-noise ratios (SNRs). Furthermore, exponentially tight Chernoff-like formulas are also presented for an analytical evaluation of the resulting system outage probabilities when interleaved packet transmissions are carried out     

Optimal Energy Scheduling for Rate-Guaranteed Download Over Faded Multichannel Networks

In this contribution, we consider emerging wireless content delivery networks (CDNs), where multiple (possibly nomadic) clients download large-size files from battery-powered proxy servers via faded links that are composed of multiple slotted orthogonal bearers (e.g., logical subchannels). Since the considered transmit proxy servers are battery-powered mobile routers, a still open basic question deals with searching for optimal energy-allocation (e.g., energy scheduling) policies that efficiently split the available energy over the (faded) bearers. The target is to minimize the resulting (average) download time when constraints on the average available energy per information unit (IU), peak-energy per slot, and minimum energy per bearer (e.g., rate-induced constraints) are simultaneously active. The performance and the robustness of the resulting optimal energy scheduler are tested on the last hop of Rayleigh-faded mesh networks that adopt the so-called ldquodirty paper strategyrdquo for broadcasting multiple traffic flows that are generated by proxy servers equipped with multiple antennas .     

Approximate analytical evaluation of the continuous spectrum in a substrate-superstrate dielectric waveguide

In this paper, an original closed-form approximate evaluation is performed for the continuous-spectrum field excited by an infinite line source in a dielectric substrate-superstrate configuration, optimized for leaky-wave radiation. By means of a suitable approximate asymptotic representation obtained via Watson's lemma, the continuous-spectrum field has been expressed as the sum of the contributions of two leaky-pole singularities, each weighted by a transition function that depends on both the frequency and observation distance. The validity of these results is shown in the near and far fields at different frequencies, including the frequency range in which the leaky wave is physical and the entire transition region through the spectral gap. This new closed-form result explicitly shows the nature of the continuous-spectrum field in the transition region, and provides insight into the nature of the fields on more complicated structures in microwave integrated circuits.     

A novel tunable-complexity turbo-soft detector for high-throughputHDSL applications over ISI channels with crosstalk

We present a novel iterative (turbo) receiver with tunable complexity for reliable detection of (uncoded) payload data transmitted over long intersymbol interference (ISI) channels affected by crosstalk, as those typically encountered in emerging HDSL2 services standardized by ANSI T1.418 recommendation. The proposed receiver combines in an original way "minimum mean square error (MMSE) estimation principle," "turbo-processing principle" and "crosstalk-prediction principle" for achieving both suboptimal maximum a posteriori probability channel equalization and reliable soft-mitigation of ISI tail plus crosstalk. More in detail, according to the turbo-processing principle, at each iteration suitable extrinsic information is extracted from the equalizing and interference-canceling modules and used as "a priori information" for the next iteration. Several simulation results on typical HDSL-like test-loops confirm the superiority of the proposed turbo-detector (TD) over current solutions based on conventional MMSE decision-feedback equalizers and precoders (such as the Tomlinson-Harashima precoder). The numerical tests also point out that performance of the presented TD on typical high bit-rate digital subscriber lines (HDSL) is not limited by error-floor phenomena, even at error-probabilities below 10^-7     

Uniform analytical representation of the continuous spectrum excited by dipole sources in a multilayer dielectric structure through weighted cylindrical leaky waves

In this work, an original closed-form evaluation is performed for the continuous-spectrum field excited by a dipole source in substrate-superstrate configurations, which have been employed in microwave planar antennas. In particular, we derive an analytical representation of the continuous-spectrum field in the form of angular-dependent cylindrical leaky waves of TE or TM type, weighted by an appropriate transition function. The proposed formulation is uniformly valid as frequency is varied, i.e., also in the neighborhood of the transition region between leaky-wave and bound-wave ranges. In this way it is possible to describe in a simple and efficient way the behavioral features of guided and radiated fields excited by practical sources in open planar structures. Numerical results which show the accuracy of this approach are provided in different operating conditions.     

A Distributed Power-Allocation and Signal-Shaping Game for the Competitively Optimal Throughput-Maximization of Multiple-Antenna “ad hoc” Networks

This paper focuses on the competitively optimal power control and signal shaping for "ad hoc" networks composed by multiple-antenna noncooperative transmit/receive terminals affected by spatially colored multiple-access interference (MAI). The target is the competitive maximization of the information throughput sustained by each link that is active over the network. For this purpose, the MAI-impaired network is modeled as a noncooperative strategic game, and sufficient conditions for the existence and uniqueness of the Nash equilibrium (NE) are provided. Furthermore, iterative power-control and signal-shaping algorithms are presented to efficiently achieve the NE under both best-effort and "contracted QoS" policies. The presented algorithms also account for the effect of (possibly) imperfect channel estimates available at the transmit/receive units active over the network, they are fully scalable, and they may be implemented in a fully distributed and asynchronous way. The presented numerical results support the conclusion that the proposed distributed algorithms may be able to outperform the conventional centralized orthogonal MAC strategies (as time division multiple access, frequency division multiple access, and code division multiple access) in terms of a sustained network throughput, especially in operating scenarios affected by a strong MAI     

On the performance limits of TCM in fast-fading multipath channelswith combined equalization/decoding

We present some analytical performance bounds that point out the key parameters dominating the performance of symbol-by-symbol combined-type maximum a posteriori equalizers/decoders for trellis-coded modulation (TCM) transmissions over fast-faded intersymbol-interference-impaired Rayleigh-channels with diversity reception. Guidelines are also provided for the design of good TCM codes matched to the statistical features of the multipath transmission links and application examples are developed that support the actual effectiveness of the presented results     

A novel self-pilot-based transmit-receive architecture for multipath-impaired UWB systems

In the last few years, ultra-wideband (UWB) systems became an appealing technology for wireless communication applications. Unfortunately, when the transmission channel is affected by intersymbol interference (ISI), system performance of UWB systems equipped with receivers based on conventional matched filters presents error-floor phenomena. Aimed by these considerations, in this letter, we present a novel transmit-receive scheme allowing blind channel estimation and minimum mean-square error linear channel equalization. Essentially, the proposed scheme exploits a very short duration of the UWB pulse for achieving reliable blind deconvolution of the received signal. A nice feature of the resulting system is that blind deconvolution of the received signal is achieved without power and throughput losses. Simulation results support the effectiveness of the proposed scheme, and show that it is able to gain about 8 dB over current UWB receivers based on matched filtering on several test channels impaired by ISI.     

A new family of optimized orthogonal Space-Times codes for PPM-based MIMO systems with imperfect channel estimates

In this contribution, we develop a single Multiple-Input Multiple Output (MIMO) transceiver for Orthogonal PPM (OPPM) data transmitted over (baseband) faded MIMO channels with a priori unknown path-gains. The signaling-scheme we adopt allows to equip the Maximum-Likelihood receiver with reliable estimates of the (possibly time-varying) MIMO channel, without reducing the conveyed information throughput. Hence, after evaluating the performance of the proposed transceiver via a suitable version of the Union-Chernoff Bound, we introduce a novel family of unitary orthogonal Space-Times Block Codes (e.g., the Space-Time OPPM codes), that are able to attain both maximum diversity and coding gains. Afterwards, we present closed-form formulas for evaluating the SNR loss induced by mistiming effects possibly impairing the received signals. Lastly, we report several numerical results supporting both the medium/long coverage ranges attained by the proposed transceiver in outdoor applications and its performance robustness against correlated channel fading, mistiming effects and degradation induced by dense-multipath fading. This work is partially supported by Italian National Project Women 2005093248