Paola Bisaglia

Simplified soft-output demapper for binary interleaved COFDM with application to HIPERLAN/2

A comparison in the performance between hard- and soft-decision Viterbi decoding, with application to the HIPERLAN/2 standard, is presented. The results show that when channel state information (CSI) is included in the generation of the soft-decision information, the soft-decision method greatly outperforms the hard method. Moreover, a simplified algorithm for the soft-output demapper for the 16-QAM and 64-QAM constellations is developed, which allows the complexity of the demapper to be maintained at almost the same level for all the possible modes of HIPERLAN/2.

Receivers for MIMO-PLC channels: Throughput comparison

The demand for very high-quality connectivity for in-home distribution of data and multi-stream entertainment is increasingly motivating the development of high-speed power-line communication technologies offering more than hundreds of Mbit/s. In this paper, to achieve such data rates, power-line multiple-input multiple-output solutions are further investigated. The beamforming scheme, for an ideal Shannon code and continuous constellation sizes, achieves the capacity. However, using a turbo convolutional code and finite QAM constellations, it is shown that beamforming is not always the best solution; in fact, non linear equalization can be an equivalent or better scheme in terms of achievable rate, without the need of providing a feedback channel state information.

Characterization of in-home MIMO power line channels

In this paper a statistical description of in-home MIMO power line channels is derived, based on channel measurements in the 0 to 100 MHz range. In particular, it is shown that the power delay profile has a statistical distribution that could be well described by Weibull and Gaussian distributions. It is also confirmed that the channel attenuation has a linear behavior as a function of the frequency and that the average channel attenuation and the root mean square of the delay spread are inversely correlated. Furthermore, a statistical description of the MIMO power line channel coefficients is provided by using a suitable definition of the correlation among the channel coefficients. Based on the extracted statistical descriptions a new model for MIMO power line channels is proposed. Finally, the consistency between the measured and the generated power line channels is shown.

Performance of the turbo coded HomePlug AV system over power-line channels

The next generation technology of HomePlug, called HomePlug AV, aims at providing very high-quality connectivity for the in-home distribution of data and multi-stream entertainment using existing power-line wiring. To obtain very robust performance a powerful turbo convolutional code is adopted. In this paper, by means of simulations, the performance of the turbo coded HomePlug AV system is examined under a realistic power-line channel model. In particular, the effects of the interleavers length and of the number of iterations in an improved Max-Log-MAP turbo decoder are investigated. Results show that few iterations of the turbo decoding process give a massive gain in performance under the considered environment.

Parallel and successive interference cancellation for MC-CDMA and their near-far resistance

Recently, multi-carrier code division multiple access (MC-CDMA) systems have been considered as potential candidates for next generation (4G) technology. Within this context, due to their good compromise between complexity and performance, multi-user interference cancellation (IC) techniques have been proposed as an effective solution in the receiver design, both for downlink and uplink transmissions; nevertheless actual results are far from being exhaustive. In this paper, a performance comparison of parallel (PIC) and successive (SIC) IC techniques is presented, investigating also the influence of user power levels in a near-far environment, under dispersive channel conditions. The impact of the choice of the single-user detection (SUD) technique used in PIC and SIC receivers is also considered. Moreover, results are presented for convolutionally-coded systems, decoded by both hard and soft-input decoding methods.

Pre-equalization Techniques for Downlink and Uplink TDD MC-CDMA Systems

Time division duplex (TDD) multi carrier-code division multiple access (MC-CDMA) systems have recently been proposed as potential candidates for next generation (4G) technology. In order to mitigate multiple access interference, in this paper we investigate pre-equalization schemes for both downlink and uplink transmissions, the former also in a multiple transmit antenna scenario. In particular, new pre-equalizer techniques are introduced and complexity issues addressed. Numerical results are given to highlight the effectiveness of the proposed schemes with respect to other existing pre-equalizer solutions.

Bit-loading algorithms and SNR estimate for HomePlug AV

In this paper two different bit-loading algorithms with uniform power allocation are compared within the framework of the HomePlug AV system. Both algorithms try to maximize the overall throughput: the first one guarantees a target mean BER, while the second guarantees a target BER per sub-carrier. By means of simulations, we compare the performance of the two algorithms, in terms of throughput and BER versus average SNR under a realistic power-line channel model. Results show that, when ideal SNR knowledge is assumed, the first and more complex algorithm offers a greater throughput; however, when SNR estimate is included, the performance of the two algorithms gets closer.

Noise correlation and its effect on capacity of inhome MIMO power line channels

In this paper we study the characteristics of in-home multi-input multi-output (MIMO) power line channels in the 0 – 100 MHz frequency band. Channel measurements are obtained in several US homes by transmitting two independent signals over two wire pairs (line-neutral and line-protective earth) and receiving on all three wire pairs (line-neutral, line-protective earth and neutral-protective earth). Noise measurements on all three wire pairs are also performed and spectral properties of noise in MIMO power line channels are presented. In particular, noise is characterized in terms of correlation among the receive ports. We analyze the effect of noise correlation on the eigenspread of the channel matrix, and also its effect on MIMO channel capacity. It is shown that while noise correlation contributes to an increase in the eigen-spread and therefore correlation of a composite channel, it ultimately improves channel capacity. The capacity of MIMO power line channels is compared for 2×2 and 2×3 MIMO configurations, showing the gain of a third receive port. Finally, capacity gains of various MIMO configurations over the single-input single-output (SISO) power line systems are provided.

Performance comparison of single-user pre-equalization techniques for uplink MC-CDMA systems

In this paper the possibility of using pre-equalization on the uplink of a MC-CDMA system is investigated. Specifically, different single-user techniques are analyzed together with two approaches to limit the transmit power. Results of computer simulations show that pre-equalization is a very effective technique for the uplink and that several single-user techniques, with different degrees of complexity, can be applied.

Joint Optimum Linear Precoding and Power Control Strategies for Downlink MC-CDMA Systems

In this paper we derive two iterative joint precoding and power allocation methods for downlink MC-CDMA systems with multiple transmit antennas at the base station. The first method optimally solves the so called assigned target SINRs problem, i.e. determines the precoding coefficients and the minimum sum-power allocation under a constraint on the SINR of each user. The second method instead solves the maximum sum-rate problem, i.e. maximizes the system throughput under a constraint on the overall transmit power. The main result of this paper is that the proposed joint precoding and power control solutions provide an advantage with respect to suboptimal solutions for a fully loaded system, i.e. when the number of users is equal to the spreading factor times the number of transmit antennas. For lower loads, performance of the various schemes becomes closer.