Ergodic Spectrum Management (ESM)'s basic features are introduced as a cloud-based management of wireless connectivity that targets improvement of internet-user's quality of experience. Ergodic Spectrum Management (or ESM) learns and exploits near-ergodicity, or time-consistency, to improve a communication-link connection's stable and efficient use in time, space, and frequency; while using consumer quality of experience as the target metric. ESM methods can also improve existing radio resource management, particularly advancing unlicensed spectrum-use efficiency to levels at or exceeding those associated with licensed spectra, as shown herein. ESM's use of learned probability distributions' dimensional (time, space, and frequency) consistencies enables latency-insensitive remote-cloud-based resource management to be applied to wireless multi-user transmission. ESM methods are developed for 3 increasingly more effective stages that correspondingly increasingly rely on data collection and functional-profile (policy) guidance of physical-layer design choices. ESM application to either and both of existing and future unlicensed- and licensed-spectra networks is suggested as a means to improve overall wireless performance. Examples and field data are provided to show the potential of very large improvements in wireless system connectivity, throughput, and quality of experience.

Wireless-wireline convergence and cellular wireless deployment can economically accelerate through partial transmission of wireless 4G, 5G (generally 3GPP-standards-compliant), and/or Wi-Fi 6 baseband signals on the billions of copper phone, Ethernet, coaxial cable, and other wireline connections. This article poses such a Cellular Subscriber Lines (CSL) re-use architecture and investigates large bandwidth-efficiency gains, as well as the consequent cost-efficiency improvement that accrues for CSL's deployment infrastructure. In-home wireless signals' seamless distribution partially over copper links can achieve good data-rate-versus-distance profile. Results here also expand to Wi-Fi (possibly with MIMO use) on Ethernet multi-pair cables, finding very large gains over existing enterprise mesh (ad-hoc or otherwise) approaches.

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.

In this paper, we optimize the use of existing DSL low-power sleeping modes (L2 and L3) in order to improve the energy efficiency of DSL access networks. Given that switching on a DSL line can cause instability by increasing the amount of time-varying crosstalk in the cable bundle, and that it takes energy and time to switch a DSL line on and off, we develop a method to optimally choose the appropriate sleeping state based on the line and traffic characteristics. We further develop and prove the structural properties of the optimal policy for switching to the appropriate sleeping state, allowing transitions between submodes with different power and transmit rate characteristics. We also present techniques that guarantee stable sleep mode operation. Using a realistic DSL simulator, we demonstrate the three-way tradeoff among energy consumption, delay performance, and stability. The increased flexibility of control introduced by our approach improves the energy-delay Pareto optimal tradeoff, and results in a more energy efficient and stable DSL operation compared to existing power saving policies.

Very-high rate Digital Subscriber Lines (VDSL) are beginning to be deployed by competitive network operators. Short lines can radiate high power crosstalk into long lines hence the power transmitted on the short lines should be controlled to limit the degradation they may cause to a competitor's long lines. This paper presents a new method of enhanced upstream power backoff (eUPBO). eUPBO limits the normalized ensemble of transmit power across lines, unlike previous techniques that operated independently per line. This new technique is effective because it limits the weighted sum crosstalk into any given line, and allows flexible optimizations. This paper shows new algorithms for eUPBO optimizing transmit power per band per user (Level 1), and for eUPBO optimizing transmit spectra per user (Level 2). Simulation results show that the flexibility of eUPBO can significantly increase select users' bit rates as chosen by the VDSL operator.

Switching off a DSL line to a low-power sleeping state is becoming an important method to enhance energy efficiency of DSL broadband access networks. Although a low-power (L2) state and an off (L3) state are already defined in DSL standards, they have not been fully exploited due to concern about the resulting time-varying crosstalk. In this paper, we develop a method to optimally choose the appropriate sleeping state based on the modem's switching cost characteristics and the power consumption incurred during each sleeping state. We further develop the optimal policy for switching to the appropriate sleeping state, allowing transitions between operating modes with different power and transmit rate. Numerical results on our realistic DSL simulator show that more flexibility in control, introduced by our approach, improves the energy-delay Pareto optimal tradeoff, and results in a more energy efficient and stable DSL system compared to the existing power saving policies.

This paper presents a new methodology for calculating the end-to-end (E2E) impact on video quality of multiple stages of degradation across a multihop network. Using this methodology, the individual degradations of each stage of compression and transmission loss need only be known in order to calculate the overall E2E impact on video quality. A theoretical derivation of the methodology is presented, and this is initially verified by 90 experiments. This methodology is a powerful new tool for evaluating the impact of complex network scenarios on new services such as mobile video and user-generated content.

Long-Term Evolution (LTE) networks comprising conventional cellular macrocells plus user-installed femtocells offer an economically viable solution to achieving high user capacity and upgrading to future fourth-generation systems. With the growing impetus for frequency reuse, the capacity of each user depends on not only the power spectral density of its own, but also on those of others in neighboring cells. Mitigating interference among macrocells and femtocells requires allocating physical resource dynamically in response to channel conditions. In this paper, we formulate the resource allocation problem as a utility optimization and develop a distributed algorithm for joint power control and user scheduling. The algorithm makes novel use of a class of fairness measures for determining user scheduling and is shown to be very efficient for realistic network parameters. Additionally, using a practical model for the LTE air interface that captures geographic distribution of users and buildings, we provide for a framework that allows comparison of different resource allocation algorithms. A variety of problem formulations, including femtocell density, resource tradeoff, and complexity-optimality tradeoff are derived and analyzed using a geometry-based stochastic LTE air interface model. Our analysis also offers useful guidelines for the planning and design of macrocells and femtocells.

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).

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.

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) 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.

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.

This paper presents a new type of fault-tolerant access network: an all-passive coaxial cable mesh network. The passive mesh network could have any topology, with cycles allowed. A technique for calculating the multipath response of the passive mesh network is presented. Both the delay and attenuation of a coaxial cable are represented by a single transform variable. The mesh network is modeled as a linear system with a state space that represents signal propagation. The channel responses of the individual sections of cable define the entries of a state-transition matrix. Using this theory, expressions are given for the overall mesh-network channel response. These expressions are manipulated to derive equalizer structures. The equalizers are zero-forcing and use decision feedback. It is shown that signals transmitted on any mesh network can be equalized. An example mesh topology, and equalizers for it, are presented. Signal and interference attenuation, and opposite-phase received carrier cancellation, are also discussed. The passive mesh network could be an inexpensive fault-tolerant architecture for residential access to telephony, cable TV, and future services.

This paper describes the error performance of the ISDN basic access digital subscriber line (DSL), the high bit rate digital subscriber line (HDSL), and the asymmetric digital subscriber line (ADSL) in the presence of impulse noise. Results are found by using data from the 1986 NYNEX impulse noise survey in simulations. It is shown that a simple uncoded ADSL would have an order of magnitude more errored seconds than DSL and HDSL.>

Asymmetric digital subscriber lines (ADSL) transmit high bit rate data in the forward direction to the subscriber, and lower bit rate data in the reverse direction to the central office, both on a single copper telephone loop. This paper provides a comprehensive description of the performance of ADSL's that use currently available technologies with optimized parameters. Passband ADSL's encounter no self-near-end crosstalk (NEXT) since the forward and reverse channels are separated in the frequency domain. The absence of NEXT allows reliable transmission at high bit rates on long loops. The passband ADSL is disturbed by background noise, self-far-end crosstalk (FEXT), and NEXT from other digital transmission systems that share its spectrum, such as Basic Access DSL, HDSL, and T1 lines. This paper determines the performance of DS1 rate passband ADSL's in the presence of each of these impairments. Although baseband ADSL's are disturbed by NEXT from the reverse channel, they are suitable for data rates at 3 Mb/s or above since they experience less high frequency loss than passband ADSL's. The range of reliable baseband ADSL transmission is determined for forward data rates between 1.5 and 9 Mb/s, and reverse data rates up to 1.5 Mb/s. An analysis and comparison of different codes that could be applied to an ADSL is also presented. The performance of forward error correction codes and trellis codes is found for ADSL's in the presence of crosstalk and impulse noise.>

Crosstalk from digital subscriber lines, high rate digital subscriber lines, and asymmetric digital subscriber lines is analyzed. The probability density of crosstalk is estimated. From this estimate the entropy power and chi-squared statistics of crosstalk are computed and compared with that of a Gaussian density.>

The case in which there are several channels available for transmission, and the additive noise on each channel may have different power, is treated. A signal constellation, called the coordinated code, for the signal space formed by the different channels is presented. The coordinated code has good performance when the noise powers are equal, while simultaneously providing diversity for good performance when the noise powers are unequal, and is relatively simple. The maximum-likelihood receiver is presented; it extracts information from the coded signal in inverse proportion to each channel's noise power. The minimum distance of the code is found, and the coding gain over a system that transmits independent bit streams on each channel is derived as a function of the noise statistics. The gain of the code is also found relative to symbol splitting diversity, which transmits a copy of the same message on each channel; this gain is as high as 9 dB. The code is considered in detail for use with a high rate digital subscriber line (HDSL) comprised of two pairs of a local loop, each pair having different amounts of near end crosstalk (NEXT).>

The authors present a study of run-length-limiting codes that have a null at zero frequency or DC. The class of codes or sequences considered is specified by three parameters: (d, k, c). The first two constraints, d and k, put lower and upper bounds on the run-lengths, while the charge constraint, c, is responsible for the spectral null. A description of the combined (d, k, c) constraints, in terms of a variable length graph, and its adjacency matrix, A(D), are presented. The maximum entropy description of the constraint described by a run-length graph is presented as well as the power spectral density. The results are used to study several examples of (d, k, c) constraints. The eigenvalues and eigenvectors of the classes of (d, k=2c-1, c) and (d, k=d+1, c) constraints for (c=1,2,. . .), are shown to satisfy certain second-order recursive equations. These equations are solved using the theory of Chebyshev polynomials.>

Using an ideal decision feedback equalizer (DFE), the SNR of quadrature amplitude modulation (QAM) and baseband pulse amplitude modulation (PAM) in the presence of self near-end crosstalk is computed for a large sample of loops within a carrier serving area (CSA). When baud-space feedforward filters are used, PAM has 1-2 dB more SNR than QAM, where the type of PAM is the 2B1Q line code. However, when using fractionally spaced feedforward equalizers (FSEs), the SNRs of 2B1Q and QAM are almost equal for loops at the extreme range of a CSA. Four- and 16-state trellis-coded modulation is applied to PAM and QAM. Coded and uncoded PAM and QAM are simulated with parallel decision feedback estimation. Viterbi receivers and coding gains are computed. QAM has up to 1 dB higher coding gains that PAM. However, the higher coding gains of QAM do not compensate for the lower SNR of uncoded QAM, and coded QAM has worse performance than coded PAM in the presence of self near-end crosstalk. The error rates of PAM and QAM with impulse noise are computed using a collection of measured impulse noise events. Results indicate that QAM has a lower error rate than PAM in the presence of impulse noise.>

A class of binary runlength codes, also known as (d,k) codes, is analyzed. These codes are developed by constructing a lossless source code that maps runlengths into unconstrained binary sequences. The source code is constructed for the maxentropic distribution on runlengths. The inverse of the source code, which outputs runlengths guided toward the ideal maxentropic distribution, is the (d,k) code. Four types of source codes are investigated for this purpose: Huffman, enumerative, variable-length-to-block, and Elias or arithmetic. The rates of the codes are each proven to converge to the capacity with increasing complexity. The codes are not state dependent and are variable rate except for the fixed-rate enumerative code. A combined source-(d,k) code is presented that is based on the arithmetic code.>

A limit on the absolute value of the running digital sum of a sequence is known as the charge constraint. Such a limit imposes a spectral null at DC. The maximum-entropy distribution of a charge-constrained sequence is presented. A closed-form expression for the power spectral density of maximum-entropy charge-constrained sequences is given and plotted.>

A binary symmetric source with binary side information is given. An encoder codes the source for data compression with no knowledge of the side information. It is then decoded, perhaps with and perhaps without the presence of side information. The rate-distortion function of this scheme is a function of two variables:D_{1}is the distortion when side information is present at the decoder, and D2 is the distortion when side information is absent at the decoder. The rate-distortion function is shown to reduce to previously solved problems in much of the(D_{1}, D_{2})-plane. Tight upper and lower bounds are found for the rate-distortion function in the rest of the(D_{1}, D_{2})-plane.