In typical home power-line communication (PLC) networks using contention-based access methods, providing quality-of-service (QoS) to high-priority users often comes at the expense of reducing the throughput of low-priority users. This paper proposes a cross-layer protocol which involves interaction between the physical (PHY) and the medium-access-control (MAC) layers, for ensuring politeness of the high-priority users toward the low-priority users for uplink transmission in home PLC networks. This protocol modifies the contention-based CSMA protocol of the MAC layer to exploit the cyclostationarity of the noise in home PLC networks. The PLC noise spectrum has been shown in literature to be periodic with the period of AC line cycle. Using this periodicity, the proposed protocol allows longer medium-access times for low-priority users in every AC line cycle, while meeting the high throughput requirements of the high-priority users. The proposed cross-layer protocol, termed opportunistic CSMA, improves the throughput of the low-priority users by as much as 300% compared to the current CSMA protocols in home PLC networks.

This paper investigates orthogonal frequency-division multiple-access (OFDMA) resource-allocation schemes for two-hop relays in a home powerline communication (PLC) network. Unlike wireless channels, which can have noticeable path loss and shadow effects to bring a substantial relay gain, the powerline channel usually observes a quality of the relay channel on par with the direct link so that simple fixed relay configurations often lose performance instead of gaining any. Besides, the quasi-cyclostationary powerline channel benefits little from diversity combining, a scheme often found in cooperative wireless relay protocols to obtain performance improvements on fast fading channels. To address these special and challenging features of the powerline channel, home-PLC relay protocols that jointly allocate subchannels and power to the source and relay nodes are proposed. Simulation results show that significant improvements of data rates can be achieved by jointly optimizing the subchannel and power allocation of home-PLC relay networks.

This paper presents the use of the common-mode signal in digital-subscriber-line (DSL) transmission. The DSL binder's metallic sheath is used as a common reference to obtain reliable channels for the common-mode signals. The direct and crosstalk channels for the common-mode signal are obtained using multi-conductor transmission line theory, and the data-rate improvement by exploiting these extra dimensions is presented. The lines in the binder are coordinated to cancel differential-mode crosstalk and also to avoid interference caused by radiation from the common-mode within the binder. The high level of common-mode noise is countered by exploiting the correlation between the differential- and common-mode noises. Numerical results based on the derived models show data-rate improvements of up to 100% compared to using only differential-mode transmission.

Power-saving benefits of Dynamic Spectrum Management (DSM) result from its increased robustness to channel and noise changes, as in this paper. A proposed intermittent noise model enables evaluation of the performance of DSM algorithms. Polite Level-1 DSM algorithm consumes much less power than non-polite DSL management algorithms in the presence of intermittent noise. Secondly, a proposed robust level- 2 DSM algorithm compares favorably with methods that change the PSDMASK only upon modem initialization or retraining. The proposed robust level-2 DSM algorithm significantly reduces power consumption. This DSM reduction of DSL transmit power can be even more significant when considering the additional loss of robustness and stability of non-DSM methods.

This paper reformulates the multi-user OFDMA resource allocation problems in broadcast and multiple-access channels by defining an equivalent interference channel. The resulting problems are then solved by employing low-complexity algorithms for spectrum optimization in the interference channel. The re-formulation averts the high-complexity integer programming problem that otherwise results from an OFDMA system that allocates each user to separate subchannels. Simulation results indicate that the proposed algorithm achieves near-optimal performance and is suitable for PLC resource allocation applications.

This paper investigates the unequal allocation of margin across tones in a multicarrier communication system. Using empirical statistics of the channel signal-to-noise-ratio variation, an algorithm is developed for modems to optimally distribute the available margin across tones instead of allocating equal per-tone margins. Such unequal per-tone margin allocation results in better stability of the line in terms of the outage probability especially when bit and energy adaptation mechanisms are not available or respond slowly to changes in the channel or noise spectrum.

This paper presents a discrete bit-loading algorithm for multi-user multicarrier systems with application to spectrum balancing in digital-subscriber-lines. The algorithm can be implemented in a distributed manner using limited information that is sent to modems by a spectrum management center (SMC). The SMC first classifies users as strong and weak. Strong users then form a rate-penalty table that is used along with the Levin-Campello bit-loading algorithm to limit the interference to weak users. Simulation results show that the proposed algorithm can achieve near-optimal performance. Moreover, the structure of the algorithm enables easy implementation of polite bit and gain adaptation procedures without the need for executing the entire bit-loading algorithm again.

This paper investigates the optimization of margins in digital subscriber lines employing level-2 dynamic spectrum management, where lines are jointly optimized with an emphasis on their stability, throughput-guarantee, and politeness. A new definition of noise margin and the concept of probability of outage are introduced, which allow for an easier formulation of the problems of joint margin and spectra optimization of the lines taking into account their stabilities. The solutions to the highly-coupled optimization problems are simplified using noise margins instead of signal-to-interference-and-noise-ratio margins. The presented algorithms provide up to 100% improvements in the data-rates or a reduction in the probability of outage by an order of magnitude, thus improving the stability of the lines at high data rates.

This paper investigates the optimization of margins in a digital-subscriber-line (DSL) system employing level-1 dynamic spectrum management. A central spectrum management center determines the empirical statistics of the noise variance of each DSL line using long-term observations and optimizes the margin allocation using the statistics. Compared to current systems that allocate ad-hoc margin values, the presented algorithms improve the line's stability, throughput-guarantee, and politeness to other lines in the binder.

This paper applies multiple-input multiple-output (MIMO) transmission methods to multiwire communication systems. Using channel matrices generated from a binder MIMO channel model, a performance assessment of digital subscriber line (DSL) technology based on MIMO transmission methods finds that symmetric data rates of more than 1 Gbps are achievable over four twisted pairs (category 3) for a 300 m range. Similar results are also obtained for a ldquoquadrdquo cable. To achieve this data rate, this paper proposes that the source and load be excited using common mode.

This paper introduces a multiple-input multiple-output channel model for the characterization of a binder of telephone lines. This model is based on multiconductor transmission line theory, and uses parameters that can be obtained from electromagnetic theory or measured data. The model generates frequency-dependent channel/binder transfer function matrices as a function of cable type, geometric line-spacing and twist-length parameters, and source--load configurations. The model allows the extraction of the magnitude and the phase of individual near end crosstalk, far end crosstalk, split-pair, and phantom transfer functions from the transfer function matrix of the binder. These individual crosstalk transfer functions are often found to be very sensitive to small imperfections in the binder. Examples of category 3 twisted pair American telephone lines and ldquoquadrdquo telephone cables are also presented.

This paper investigates the effect of non-zero SNR margin and coding gap on the maximum sum rate and achievable rate region of the Gaussian multiple-access channel (MAC). Frequency-division multiple-access (FDMA) is shown to be the only sum-rate-maximizing scheme for a scalar Gaussian MAC when the margin/gap is not zero. Furthermore, successive decoding is shown to be strictly sub-optimal from a sum rate perspective. With fixed probability-of-error, single-user codes with finite gap are sufficient to achieve the maximum sum rate. The achievable rate region of the scalar Gaussian MAC with non-zero margin/gap is also characterized. Unlike the capacity region of a scalar MAC, the optimal achievable rate region with non-zero margin/gap is not a pentagon. Finally it is shown that when there is non-zero margin/gap, the optimality of the FDMA scheme can be generalized to a Gaussian MAC with inter-symbol interference (ISI).

Transmit maximum-ratio combining (transmit MRC) is a popular antenna diversity technique that provides both spatial diversity and array gain in downlink multiple-input single-output (MISO) links. These gains, however, critically depend on the availability of the downlink channel state information (CSI). In time-division duplexing systems, channel reciprocity has been commonly put forth to justify the convenient use of the CSI already acquired from the uplink, in the calculation of the transmit-MRC weights. Recent work has questioned this practice, based on the non-reciprocity of multi-antenna RF transceivers, due to significant amplitude and phase mismatches across the antennas. Furthermore, expensive digital calibration solutions have been proposed to enforce the reciprocity of the multi-antenna RF transceivers. Both the impact of multi-antenna amplitude and phase mismatches and the performance of the proposed calibration approaches have only been assessed via simulations. In this contribution, we propose an alternative statistical analysis of the impact of these mismatches on transmit MRC. This analysis allows a faster and more reliable characterization as well as provides insight into the relative importance of these mismatches. Consequently, sufficient matching requirements can be extracted for the multi-antenna RF transceivers, for which simpler and cheaper calibration solutions can be devised.