Maintaining phase coherence in large phased arrays is challenging in all-RF implementations, while alternatives based on optical signal conditioning require expensive phase-locked lasers. We present a novel transmit architecture for an optically-fed large phased array where high coherence is ensured by using two inexpensive phase-locked lasers operating at different wavelengths, representing the signal carrier and its local oscillator reference signal. Heterodyne detection via photomixing of the optical signals ensures the generation of high quality RF signals by canceling out most contributions to phase noise. We also impose the co-propagation along the same fiber of the modulated carrier and the local oscillator so that, differently from other implementations, random phase variations induced by acoustic, mechanical, and thermal perturbations along the fiber are easily cancelled out at photomixing. This technique requires the design of a novel optical Vector Modulator that operates on the phase-locked laser pair and enables control of the complex state of a transmitted wave by controlling its amplitude and phase rather than its I/Q components. Mathematical modeling of the system confirms that the proposed architecture can ensure highly coherent fully digital opto-electronic beamforming with multi-beam and multi-band support for large phased arrays.

We study an old but unconventional waveguiding technique based on the use of overhead bare metal Medium Voltage (MV) power lines as open waveguides and not as transmission lines. This technique can be used in support of 5G applications such as backhauling and broadband access in the mmW frequency range or above. Although the analysis of open waveguides dates back a century or more, very few communications oriented papers are available in the literature and there is today no commonly agreed upon channel model. This paper offers a first step in covering this gap by first solving numerically the characteristic equation derived from Maxwell equations, then deriving an analytical expression for the transfer function, and finally reporting for the first time capacity values for bare metal open waveguides. A channel capacity of 1 Tbps over 100 m can be achieved using a single overhead Medium Voltage power line, 1 W of total transmitted power, and the 1-100 GHz band.

We analyze the resiliency of Massive Multiple-Input Multiple-Output (M-MIMO) systems to Inter-Symbol Interference (ISI) when diversity combining techniques are used at the Base Station (BS). We show that Maximum Ratio Combining (MRC) alone can equalize an ISI channel as the number of antennas grows unbounded. Additional constraints on the nature of the channel must be postulated depending on whether the information of the Angle-of-Arrival (AoA) is exploited at the receiver or not. Interestingly, the simpler Equal Gain Combiner (EGC) receiver is also able to equalize the channel as the number of antennas grows but, in this case, at least one channel path must be Ricean faded. These findings are confirmed via simulation on WSSUS channels and channels generated with a ray tracing engine simulating a real BS deployment in downtown Hong Kong and Shanghai. Finally, the observed scaling law indicates that normalized ISI power decreases N-fold for every N-fold increase in the number of antennas at the BS.

Newly available standards for broadband access using digital subscriber lines (DSLs) have a high degree of spectrum overlap with home networking technologies using broadband power line communications (BB-PLCs) and this overlap leads to electromagnetic compatibility issues that may cause performance degradation in DSL systems. This paper studies the characteristics of measured PLC-to-DSL interference and presents the novel results on its statistical characterization and impact on the performance of various DSL technologies. The electromagnetic coupling between power line cables and twisted pairs is estimated in the frequency domain from measurements, and a statistical model based on a mixture of two truncated Gaussian distributions is set forth. The proposed statistical model allows the accurate evaluation of the impact of BB-PLC on various DSL technologies in terms of both average and worst case impact on data rate. This paper further provides an extensive assessment of the impact of PLC-to-DSL interference at various loop lengths and for multiple profiles of very-high-speed DSL 2 (VDSL2), vectored VDSL2, and G.fast. The results of this paper confirm that the impact of PLC-to-DSL interference varies with loop length and whether vectoring is used or not. Furthermore, the average impact is found to be generally small but large couplings can lead to substantial degradation of DSL.

Are Power Line Communications (PLC) a good candidate for Smart Grid applications? The objective of this paper is to address this important question. To do so, we provide an overview of what PLC can deliver today by surveying its history and describing the most recent technological advances in the area. We then address Smart Grid applications as instances of sensor networking and network control problems and discuss the main conclusions one can draw from the literature on these subjects. The application scenario of PLC within the Smart Grid is then analyzed in detail. Because a necessary ingredient of network planning is modeling, we also discuss two aspects of engineering modeling that relate to our question. The first aspect is modeling the PLC channel through fading models. The second aspect we review is the Smart Grid control and traffic modeling problem which allows us to achieve a better understanding of the communications requirements. Finally, this paper reports recent studies on the electrical and topological properties of a sample power distribution network. Power grid topological studies are very important for PLC networking as the power grid is not only the information source but also the information delivery system-a unique feature when PLC is used for the Smart Grid.

We report here that channel power gain and Root-Mean-Square Delay Spread (RMS-DS) in Low/Medium Voltage power line channels are negatively correlated lognormal random variables. Further analysis of other wireline channels allows us to report a strong similarity between some properties observed in power line channels and the ones observed in other wireline channels, e.g. coaxial cables and phone lines. For example, it is here reported that channel power gain and logarithm of the RMS-DS in DSL links are linearly correlated random variables. Exploiting these results, we here propose a statistical wireline channel model where tap amplitudes and delays are generated in order to reflect these physical properties. Although wireline channels are considered deterministic as their impulse response can be readily calculated once the link topology is known, a statistical wireline channel model is useful because the variability of link topologies and wiring practices give rise to a stochastic aspect of wireline communications that has not been well characterized in the literature. Finally, we also point out that alternative channel models that normalize impulse responses to a common (often unitary) power gain may be misleading when assessing the performance of equalization schemes since this normalization artificially removes the correlation between channel power gain and RMS-DS and, thus, Inter-Symbol Interference (ISI).

Two new metrics for the high-level comparison of Forward Error Correction (FEC) schemes are proposed and applied to the study of Turbo and LDPC codes. These new metrics retain simplicity and allow us to compare FEC schemes by factoring in their relative complexity. Furthermore, for the case of Turbo and LDPC codes, we determine the number I of LDPC iterations that correspond to an iteration performed by a Turbo decoder under the constraint that an equal number of elementary operations is performed at the receiver. As a practical example, we apply these metrics to the comparison of the FEC schemes debated in the ITU-T G.hn Working Group (WG) confirming the technical validity of the selection of the LDPC-based proposal over the Turbo Code one.

Given K simultaneously active users, an Optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always C Gt K at any given time for any truly asynchronous OCDMA system that employs quasi-orthogonal codes, there is always a set of unused codes. We here propose to exploit these unused codes to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log2(M)-tuple of bits so that each user effectively uses a multi-dimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system and find in closed form an upper bound on the average probability of error. Moreover, we report for the first time that, under lightly loaded, non interference-limited conditions, the multi-dimensional OCDMA scheme here proposed allows us to obtain both higher spectral efficiency and lower bit- error probability (BEP) than a conventional OCDMA system, which employs one code only per user. The analysis here presented allow us to formulate a useful system design criterion that yields truly asynchronous OCDMA systems with very high spectral efficiency.

Digital Subscriber Lines (DSL) transmit over twisted-pair telephone loops, and knowledge of the loop make-up is vital for determining what types of DSLs may be deployed and what bit rates they may transmit. Single-ended automatic loop identification (LID) is essential for achieving low-cost deployment of DSL, since it allows loops to be qualified in bulk and does not involve any human intervention at the customer's location. This paper describes strategies to enhance previous algorithms for loop make-up identification via single-ended measurements based on Time Domain Reflectometry. In particular, we show that clustering techniques can be effectively used to partition the set of possible loop topologies so as to reduce overall identification time. Furthermore, statistical data is used to improve overall LID accuracy by accounting for the likelihoods of different cable gauges at different distances from a central office (CO).

We propose a novel optical networking concept enabling the routing of groups of spectrally phase encoded (SPE) optical code division multiple access (OCDMA) signals. This code grouping is based on particular properties of the Hadamard sequences, i.e. the existence of a multiplicative basis based on Walsh sequences. We describe here how this code grouping concept permits groups of SPE codes to be passively "labeled" and routed as groups on the basis of those labels and provide simulation results demonstrating the process. The ability to deal with groups of codes has important implications for routing and for the overall signal obscurity provided by OCDMA.

The characterization of the transfer function of the power line (PL) channel is a nontrivial task that requires a truly interdisciplinary approach. Until recently, a common attribute and limitation of existing models for the PL channel transfer function lay in the phenomenological or statistical approach usually followed. This approach allows one to describe the channel only partially, e.g., as dominated by multipath-like effects, and prevents one from unveiling special properties of it. Multiconductor transmission line (MTL) theory was recently found by the authors to be a useful and accurate tool in modeling the PL transfer function while, at the same time, taking into account the wiring and grounding practices mandated by several regulatory bodies for commercial and residential premises. Crossing several layers of abstraction and following a bottom-up approach, complex circuit-level models originating from MTL theory can be manipulated and represented in terms of cascaded two-port networks (2PNs), thus allowing one to compute a priori and in a deterministic fashion the transfer function of any PL link. In the present contribution, we present additional analysis and data that validate the accuracy of the MTL approach and further justify its use in the PL channel context. Moreover, we also describe in detail the methodology to follow for modeling both grounded and ungrounded PL links in a unified framework. A consequence of the validity of the proposed modeling is that it can facilitate the process of standardization of the PL transfer function, an important step toward the availability of a commonly agreed upon (set of) channel transfer functions.

Given K users simultaneously active, an optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always CGtK at any given time for an asynchronous OCDMA system employing quasi-orthogonal codes, there is always a set of unused codes and these codes can be exploited to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log2(M)-tuple of bits so that each user effectively uses a multidimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system, and find that an upper bound on the probability of error can be expressed in terms of the performances of the conventional case where one code only per user is employed. Moreover, we also find that, under certain conditions, the multidimensional modulation here proposed allows us to obtain higher spectral efficiency, higher power efficiency, and lower bit-error rate (BER) than conventional OCDMA, which employs one code per user

To build ad-hoc networks with hundreds or even thousands of nodes, the network must be split into relatively independent layer 3 clusters. There are currently no general approaches or methodologies for the creation of domains that take into account the following important engineering constraints: balanced domains, minimal inter-domain traffic, robust network design. Moreover, there is also no contribution that specifically addresses the problem of area formation for OSPF-based ad hoc networks. By assuming that the creation of layer 3 clusters is done after layer 2 topology management has set local radio parameters, we have re-formulated the problem at hand in a graph theoretic framework and found a strong connection between the problem of area design and a classical problem in graph theory, the graph partitioning (GP) problem. The limitation of GP algorithms (GPAs) is that they are OSPF-agnostic and, therefore, are not capable of solving the problem of robust backbone network (Area 0) design. We here propose a two-step approach for OSPF area design: the first step consists of an efficient GPA that will create areas (including a rough Area 0 design), and the second step consists of ad-hoc heuristics that are able to ameliorate the Area 0 design as well as factoring in OSPF specific metrics.

We propose and experimentally validate a novel method for transmitting several OCDMA channels in the unused bandwidth of a single WDM channel, thus allowing the OCDMA and SONET signals to share the same WDM channel. The theoretical justification of this new modulation scheme is based on a powerful property of spectrally phase-encoded OCDMA signals which is reported and proved for the first time: the operation of spectral phase encoding allows us to convey broadband signals over a disjoint (non-contiguous) frequency support. Remarkably, this property' does not impair signal orthogonality' so that it can be exploited both in synchronous and asynchronous OCDMA.

The loop plant can be optimized to provide significantly higher bit rates than currently provided, offering higher speeds that in some cases will even support digital entertainment video, without installing new remote terminals or repeaters. Algorithms for using measured crosstalk data to jointly optimize DSL performance have been recently published, and are based on finding the optimal transmit PSD in an iterative fashion. However, these algorithms can ensure joint optimization of homogenous DSL services only. In this paper, we present an iterative algorithm for jointly optimizing single-carrier and multi-carrier DSL services. In particular, we address the case of joint optimization of ADSL and G.shdsl. Simulations are run with many different crosstalk couplings for several scenarios of loop length and numbers of crosstalkers. Simulation results show that average bit rate increases of several hundred percent are commonly achieved on relatively long loops with these dynamic spectrum management (DSM) techniques.

Considerable effort has recently been devoted to the determination of accurate channel models for the power line (PL) environment, for both the indoor and outdoor cases. The common denominator (and limitation) of the known and previously published models is the particular type of approach followed. In fact, until now, the PL channel (PLC) has been treated from a mere phenomenological or statistical point of view. This allows us to describe the channel only partially, e.g., as dominated by multipath-like effects, and prevents us from unveiling any of its particular properties. We report results about a new approach to the modeling of the PLC based on multiconductor transmission line (MTL) theory. The need for an MTL approach arises from the fact that indoor power cables consist of three conductors, and not just two as for classical twisted-pair and coaxial cable cases. This approach allows us to include wiring and grounding practices dictated by the United States National Electric Code (NEC). On the basis of this modeling, we reveal that the PLC is a more deterministic medium than commonly believed. Moreover, it is also possible to prove an interesting symmetry property of the PLC that was previously unknown: the PLC, regardless of its topology, exhibits the same transfer function when driven from either side, provided that the source and load impedances are the same.

We present initial results on a WDM compatible spectrally phase encoded optical CDMA (OCDMA) system that uses 16 phase-locked laser lines within an 80-GHz tunable window and an ultrahigh frequency resolution encoder/decoder. The described system differs from conventional OCDMA systems by independently phase encoding individual spectral line of a mode locked laser (MLL). We report here novel properties of phase codes and we also demonstrate compatibility of the proposed OCDMA system with conventional WDM networking by simultaneous transmission of two 2.5 Gb/s OCDMA users in one DWDM window along with six DWDM channels in other DWDM windows through a transparent reconfigurable network having 25 km node spacing.

Although there are a plethora of mobility management solutions proposed in the literature, there is no method for analytical comparison that helps identify optimal solutions in a specific scenario. Since simulations and implementations can provide only limited information, we propose an analytical approach for the comparative analysis of mobility protocols. By decomposing existing protocols into their building blocks, we obtain general cost functions for different mobility mechanisms. Our analysis allows us to identify network and topology conditions under which a certain protocol performs better than another, according to specific criteria. We present results for the signaling and overhead case, whereas the handoff delay case is addressed in S. Galli et al. (2004).

An important case of multiuser channel estimation is considered here, the problem of identifying the crosstalk that disturbs a DSL signal. Crosstalk originates from signals transmitted on nearby pairs in a telephone cable, and couples over unknown pair-to-pair crosstalk coupling channels into the pair carrying the signal. While crosstalk is generally the dominant impairment for current DSL systems, only recently have papers appeared addressing the problem of multiuser crosstalk channel estimation. In Galli et al. (2001), it was proposed to identify crosstalk sources by finding the maximum correlation with a "basis set" (dictionary) of representative measured coupling functions. It is shown here that this can be considered equivalent to finding an optimal sparse representation of a vector from an overcomplete set of vectors. A well-known algorithm that solves this problem is the matching pursuit (MP) algorithm (Mallat et al. (1993)), a greedy algorithm for choosing a subset of vectors from an overcomplete dictionary and finding a linear combination of that subset which approximates a given signal vector. A method based on singular value decomposition (SVD) for reducing the size of the dictionary is also discussed.

Digital subscriber lines (DSLs) offer carriers the possibility of exploiting the existing loop plant to deliver high-speed data and voice services. However, before deploying DSL, local loops must be tested in order to see whether they can support service, and at what level. In fact, there are many impairments that could disqualify a loop for supporting DSL services: load coils, excessive loop length, bridged taps, and wideband noise. Single-ended automatic qualification is essential for achieving low-cost deployment of DSL, since it allows loops to be qualified in bulk and does not involve any human intervention at the customer's location. An even more ambitious challenge is to fully characterize a loop, i.e., to identify its loop makeup. If it is feasible to perform loop makeup identification via single-ended measurements with sufficient accuracy, then operators will benefit substantially because, besides qualifying a loop for DSL service, this capability will allow the updating of telephone company loop-records. These records can in turn be accessed to support engineering, provisioning and maintenance operations. Despite its potential importance, the possibility of achieving loop makeup identification via single-ended measurements is not widely addressed in the current literature. In the present contribution the feasibility of loop makeup identification via single-ended measurements is presented.

Decision-directed adaptive receivers suffer performance degradation on time varying and intersymbol interference-impaired links because of two major problems: the use of predicted channel estimates due to the unavoidable decision delay of any detector, and the unreliability of hard decisions used for channel estimation and tracking. It is shown here that combining a recursive nonlinear symbol estimator with a channel estimator with a low prediction order may alleviate this performance degradation. In particular, it is here proposed to employ the nonlinear minimum mean-square error (NL-MMSE) filtered and fixed-lag smoothed estimates of the transmitted symbols in place of the usual hard decisions for channel estimation and tracking. It is also shown that these NL-MMSE estimates can be recursively computed on the basis of a linear transformation of the vector of the a posteriori probabilities (APPs) of the states of the channel. This approach allows the prediction order of the channel estimates to be limited and, at the same time, limits the performance degradation due to erroneous hard decisions. Another result presented here is that the use of NL-MMSE estimates in place of hard decisions is not based on mere intuition only, but is a straightforward consequence of the statement of the problem of MMSE channel estimation when the overly optimistic assumption of correct decisions is dropped. On the basis of this novel approach, a new family of soft-output adaptive receivers is presented for time-division multiple-access-based radio communications. The proposed family of adaptive receivers is based on an APP-computer and exploits the APPs for both channel estimation and detection. The versatility of the APPs ensures that the architecture of the proposed receiver is flexible, so that several estimators and detectors can be embedded in it.

Digital subscriber lines (DSLs) are fundamentally limited by crosstalk. The case where all crosstalk is from the same type of DSL has been studied over the years and accurate models have been standardized. However, crosstalk from multiple different types of DSLs is a relatively new area of study and models of summing mixed crosstalk have only recently been postulated. As more and more types of DSLs are deployed by multiple service providers, it is imperative to gain confidence in the method of modeling worst-case mixed crosstalk and to understand its limitations in order to enable efficient spectrum management of the loop plant. All known crosstalk summation methods are described here in detail and their properties are compared. This paper also presents a new methodology for deriving sound crosstalk summation methods. This new methodology consists of deriving lower bounds to the worst-case method, which is intrinsically too pessimistic. In particular, it has been ascertained that the Minkowski inequality and, to a lesser extent, the Holder inequality, yield new crosstalk summation methods that exhibit appealing properties. It is also shown here that the standardized full service access network (FSAN) method is a particular case of the more general Minkowski-bound method.

For pt.I see ibid., vol.50, p.453-61, (Mar. 2002). In a companion paper, the problem of summing crosstalk from mixed sources has been deeply analyzed. The problem of determining a good model for the summation of mixed crosstalk is becoming more important now that many digital subscriber line (DSL) services are being deployed in the field. The straightforward application of the usual 1% worst-case model for only one kind of disturber to all the individual worst-case contributions is overly pessimistic. The most well-known methods of summing mixed crosstalk, the FSAN and the Mean PSD methods, are less pessimistic. Also, the two new summation methods presented previously, the Minkowski-bound and the Holder-bound methods, are less pessimistic and offer the appealing feature of choosing the level of pessimism or optimism through a parameter. However, the accuracy of these methods has never been quantified in the past. As more and more types of DSLs are deployed by multiple service providers, it is imperative to gain confidence in the methods of modeling worst-case mixed crosstalk and to understand their limitations. In this paper, the problem of defining an accurate statistical modeling of the pair-to-pair crosstalk power coupling losses is addressed first. This has been accomplished by exploiting a large measurement campaign performed on real cables. The results of a large simulation campaign that compares the accuracy of known and newly proposed methods of summing mixed crosstalk are then presented. In addition, it is proposed here to use the signal-to-noise ratio (SNR) as the metric for determining the actual system performance in the presence of mixed crosstalk. A Monte Carlo simulation is run that assigns randomly each disturber to a pair-to-pair NEXT coupling which matches the statistics of measured cables. The Monte Carlo method accurately determines the I % worst-case impact on the SNR of DSL systems affected by mixed crosstalk. ISDN, HDSL, HDSL2, T1 and ADSL are each simulated with many different numbers and types of mixed crosstalk.

Non-linear minimum mean square error (NL-MMSE) estimators have seldom been used in practice because of the intrinsic analytic difficulties that arise in their development. However, it has been shown by Galli (2000) that the a posteriori probabilities (APPs) of the states of the ISI channel can be efficiently used to generate NL-MMSE filtered and fixed-lag smoothed estimates of the transmitted symbols. On the basis of this new result, a novel soft-output adaptive receiver is presented for TDMA-based cellular land-mobile radio communications. The proposed receiver uses NL-MMSE fixed-lag smoothed estimates of the transmitted symbols for channel estimation and tracking and exploits the APPs for the computation of the branch metrics of the Viterbi algorithm (VA). Simulations have shown that, in some situations, gains of at least 14 dB over the conventional hard-decision driven receivers are obtainable.

Digital subscriber lines (DSL) are fundamentally limited by crosstalk. The case where all crosstalk is from the same type of DSL has been studied over the years and accurate models have been standardized. However, crosstalk from multiple different types of DSL is a relatively new area of study and models of summing mixed crosstalk have only recently been postulated. In this contribution, a new method of summing crosstalk due to mixed sources is proposed. This new method consists of deriving lower bounds to the worst-case method, which is intrinsically too pessimistic. It has been ascertained that the exploitation of the Minkowski inequality yields a new model that exhibits appealing properties. Moreover, it is shown here for the first time that the full service access network (FSAN) method is a particular case of the Minkowski-bound method and not, as previously believed, a method with no "physical justification or mathematical soundness." Finally, simulation results that confirm the effectiveness of this new method are presented.

Crosstalk between multiple services transmitting through the same telephone cable is the primary limitation to digital subscriber line services. From a spectrum management point of view, it is important to have an accurate map of all the services that generate crosstalk into a given pair. If crosstalk is measured via modem-based methods, i.e., while a digital subscriber line (DSL) system is running, what is measured is the crosstalk in the bandwidth of the considered DSL system. For this reason, DSL services running on adjacent pairs may not be detected if their bandwidth is not significantly overlapping with the bandwidth of the disturbed system. This is a major drawback of modem-based system identification techniques since, from a spectrum management point of view, it is important to be able to identify all crosstalkers. We address the important problem of crosstalk identification when the pair under test does not bear DSL services, i.e., via a non-modem-based approach. Crosstalk sources are identified in the frequency domain by finding the maximum correlation with a "basis set" of representative measured crosstalk couplings. The effectiveness of the proposed technique is also verified on the basis of real crosstalk measurements performed on actual cables. Finally, new techniques based on multiple regression and best basis selection are also discussed.

The goal of this contribution is to give some insight into the cochannel interference (CCI) suppression capability of novel symbol-by-symbol-type maximum a posteriori probability single-user receivers for nonspread-spectrum multiuser narrow-band systems impaired by intersymbol interference and CCI. The presented multiuser receivers minimize the error probability in the detection of the desired user message on a per-symbol basis. Practical application environments for the developed detectors can be constituted by Ethernet-type LANs and DSL-based high-throughput links connecting central offices to subscribers.

In this contribution, novel symbol-by-symbol (SbS)-type maximum a posteriori probability (MAP) receivers are presented for non spread-spectrum (SS) multiple-access (MAC) narrowband systems impaired by ISI and co-channel interference (CCI). The proposed decentralized type receivers minimize the error probability in the detection of the desired user message on a per-symbol basis. A practical application environment for the presented receivers can be constituted by Ethernet-type local area networks (LANs) where central offices are linked to subscribers via multitapped buses.

We present a new blind equalizer that achieves identification of a channel by exploiting only second-order statistics of the observations. The novelty of the proposed approach is that the receiver accomplishes channel identification by using soft statistics; roughly speaking, it consists of an Abend-Fritchman (1970) type maximum a posteriori (MAP) equalizer that feeds a nonlinear Kalman-like channel-estimator with the soft statistics constituted by the a posteriori probabilities (APPs) of the channel-state sequence. So, since the receiver employs second-order statistics only, it achieves channel identification with fewer symbols than most techniques based on higher-order statistics.

The symmetric cut-off rate is derived for quadrature-amplitude-modulated (QAM) block-coded data-transmissions over noisy links impaired by time-correlated multipath-phenomena which give rise to Rayleigh-distributed randomly time-variant intersymbol Interference (ISI) effects. The presented formulas for the cut-off rate are new; they are derived from a random coding bound developed "ad hoc" for bounding the ensemble-averaged block-error probability of a maximum likelihood (ML) decoder supported by perfect channel-state-information (CSI). The assumption of time-correlated ISI phenomena introduces memory in the link and makes the underlying ISI-channel a continuous-state channel with memory.

The paper presents a novel fast-adaptive nonlinear receiver which exploits soft statistics for tracking the random fluctuations experienced by time division multiple access (TDMA) mobile radio links impaired by frequency-selective time-variant multipath phenomena. The detection task is accomplished by an Abend-Fritchman-like symbol-by-symbol maximum likelihood (SbS-ML) detector which delivers both hard decisions and soft statistics in form of a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel. In the proposed adaptive receiver, these APPs are employed in place of the conventional hard-detected data to feed an ad hoc developed nonlinear recursive Kalman-type channel estimator. Extensive computer simulations show that the exploitation of soft statistics enhances the tracking capability of the channel estimator so that the proposed receiver generally outperforms the usual ones based on adaptive maximum likelihood sequence estimators (MLSEs) for signal-to-noise ratio (SNR) values over 12-13 dB. Furthermore, the experienced performance gap with respect to more complex per-survivor processing (PSP)-based multi-estimator detectors appears generally small on slowly and moderately fast time-varying channels characterized by values of the product Doppler bandwidth /spl times/ signaling period B/sub D/T/sub S/ below 5/spl times/10/sup -3/.

New upper bounds for the performance of the optimum combined symbol-by-symbol (SbS) Abend-Fritchman-like equalizer and decoder are presented, and a related criterion for the actual design of good trellis-coded-modulated (TCM) schemes effectively matched to the distortion introduced by the intersymbol interference (ISI)-corrupted transmission channel is developed. The actual application of the proposed design criterion is also addressed.

The design of good TCM schemes matched to ISI channels requires that analytical performance bounds are also available. In this paper, starting from an application of the union-Bhattacharyya bound, upper-bounds for the performance of the theoretically optimum combined symbol-by-symbol (SbS) Abend-Fritchman like equalizer and decoder are presented for the first time in literature. The combined detector acts on the distorted version of the TCM signal received at the output of a channel impaired by (known) ISI and AWGN. On the basis of these bounds a novel simple criterion for the design of TCMs optimally matched to any assigned ISI-corrupted transmission channel is then derived and its application to some actual test-channels is illustrated.

GMSK is an efficient modulation technique for digital mobile communications. In this paper a simple solution to the modeling and simulation of GMSK systems impaired by fading channels and additive white Gaussian noise is given, and its effects on the channel characteristics are also considered. The modeling is based on the well-known linearized representation of phase-modulated signals. The analysis is not only useful for modeling and simulation purposes, but also gives a tool for the design of simple receivers.

New analytical upper bounds are derived for the performance of symbol-by-symbol maximum-likelihood (ML) Abend-Fritchman-type detectors for multi-amplitude/phase-modulated digital sequences transmitted over time-dispersive (generally) time-variant linear channels introducing finite intersymbol interference (ISI) and additive white Gaussian noise (AWGN). The proposed bounds are obtained starting from a novel form of the standard Bhattacharyya bound and take explicitly into account the allowed decoding delay. Both deterministic and random multipath slow-fading Rayleigh transmission ISI channels are considered. Simulation results obtained for some test channels of practical interest show the tightness of the derived analytical bounds.