Deni Torres

Self-Similarity, Packet Loss, Jitter, and Packet Size: Empirical Relationships for VoIP

In this paper, as result of a thorough self-similar analysis we found self-similar characteristics in different sets of VoIP Jitter traces, with short range and long range statistical dependence (i.e. LRD and SRD). We used the E-models R factor for estimating the QoS perceived by the end user, and we established the following empirical relationships: when the values of the estimated Hurst parameter were lower than 0.5 (SRD) the analyzed performance metrics, i.e. average packet loss rate and average Jitter, maintained stable values and acceptable QoS levels. While the values of the estimated Hurst parameter were greater than 0.5 (LRD) the variability of the analyzed performance metrics were increased and the QoS levels diminished. The other empirical relationship shown in this article refers to the payload size for each CODEC type used, the larger the payload size was, the higher the average Jitter became.

An Efficient Detector for Non-Orthogonal Space-Time Block Codes with Receiver Antenna Selection

A new architecture for detection of layered quasi-orthogonal space-time block codes (LQOSTBC) with receiver antenna selection over Rayleigh fading channels is presented. The LQOSTBC transmitter consists of a full-rate quasi-orthogonal space-time block code unit, plus one antenna operating as V-BLAST. The LQOSTBC receiver selects nR out of a total of NR available antennas using a low-complexity, nearly optimal algorithm. The proposed receiver is based on successive interference cancellation (SIC) and the QR decomposition, suggesting a simple hardware implementation. It is designed for zero-forcing (ZF) criterion and a spatially uncorrelated channel. Reduced complexity is achieved by means of a convenient rearrangement of the channel matrix elements. The detection scheme proposed is compared to similar, recently reported techniques.

Generalized ABBA-V-BLAST hybrid space-time code for wireless communications

Hybrid MIMO communication systems combine spatial multiplexing with diversity gain to achieve both high spectral efficiency and link reliability. We present a novel generalized hybrid scheme that allows the use of any number of spatial multiplexing layers (V-BLAST) and any number of quasi-orthogonal layers (ABBA).We also present a low-complexity, ordered, successive interference cancellation receiver based on sorted QR decomposition. The receiver detects each symbol in the same manner, regardless of whether it was spatially or diversity coded, simplifying the receiverpsilas formulation. We show that this novel scheme outperforms other recent hybrid schemes in terms of bit error rate, even when there is precoding at the transmitter. We also show our proposal has lower complexity, achieved by exploiting the structure of the linear dispersion matrices.

Detection Algorithm for Hybrid Space-Time and Spatial Multiplexing Wireless Communications Systems

In this paper we propose a new architecture for detection of hybrid layered space-time block codes (LSTBC). The proposed receiver is based on a successive interference cancellation (SIC) scheme and the QR decomposition, which leads to a suitable hardware implementation. It was designed for zero-forcing (ZF) criterion; reduced complexity is achieved by means of an adequate rearrangement of the channel matrix elements. Simulation results show that this new architecture outperforms similar, recently reported detectors in terms of bit error rate under spatially correlated channels.

Analysis of IP network path capacity estimation using a variable packet size method

Capacity estimation effective in an IP network path is a key enabling technology for proactive and reactive resource management as well as intelligent planning in next generation IP networks. We analyze capacity measurements at different Internet destinations. Particularly, we use the variable packet size (VPS) method to measure the per-hop capacity in some network paths. This method is based on round trip time (RTT) measurements as well as on the Internet control message protocol, ICMP. The RTT delay is approximated by a gamma distribution. We observe how the measurement accuracy of this active probing is affected by factors such as layer 2 device latencies, limited clock resolution at the probing host, or queuing delay. These factors cause non linearity on the RTT curves obtained and, consequently, inaccuracies on the estimation of path capacities. The use of robust regression to improve linear approximation in the VPS method is proposed. As a result, we obtain better qualitative and quantitative results.

An Efficient Scheduling Architecture for QR Decomposition Using Fixed-Point Arithmetic for Detection of STBC-VBLAST Codes

In this work we propose a low complexity detector for hybrid MIMO space-time codes based on linear dispersion coding. This detector is designed for systems with fewer receiver than transmitter antennas. We also present a fast, scalable hardware architecture (suitable for FPGA implementation) that performs the matrix inversion required by the detector. This architecture is based on the QR matrix decomposition, implemented with a low-complexity, parallel and pipelined CORDIC with fixed-point arithmetic. This results in a 60% reduction in complexity, compared with other reported algorithms. We show that the proposed detector achieves better bit-error rates than comparable double-space-time transmit diversity (DSTTD) fixed-point detectors.

The role of entropic index for detection of anomalous behaviors in a VoIP system

In this paper the use of Bandt and Pompe method and entropy are analyzed in order to detect the anomalous behaviors in a voice over IP (VoIP) system. Also, it is shown how the use of generalized entropies improves the anomalous behaviors detection by means of the entropic index. We use the entropic index in order to increase the variation between the entropy measure of normal and anomalous behavior, allowing us make a better discrimination and detection of anomalous behaviors.

Hurst Parameter Estimator Based on a Decomposition by Aggregated Series

In this work, a comparison of three estimators of the Hurst parameter is presented: the classical variance-based method and two new estimators based on an orthogonal decomposition (that can be achieved by aggregated series or by using Haar filters) and that use, respectively, a weighted and a non-weighted linear regression. These three estimators were applied to a set of synthetic fGN traces. The analyses showed that the variance method and the estimator that uses non-weighted linear regression underestimate the theoretical value of H, while the third estimator, decomposition-based, that uses a weighted linear regression, shows an excellent behavior. This estimator presented a bias nearer to zero and the lowest standard error when applied to fGN traces for lengths from 1024 to 1048576 samples. The presented decomposition can be extended to study the frequency information of the time series, by obtaining what we call Hurst spectrum, and to generate time series that comply the definitions of self-similar time series.

ABBA-VBLAST hybrid space-time code for MIMO wireless communications

Hybrid MIMO communication systems combine spatial multiplexing with diversity gain to achieve both high spectral efficiency and link reliability. We present a novel hybrid scheme that allows the use of any number of spatial multiplexing layers, plus one quasi-orthogonal layer (ABBA) of either 3 or 4 antennas. We transform the system equations in terms of linear dispersion codes, from which we derive a low-complexity, ordered, successive interference cancellation receiver based on sorted QR decomposition. Symbol detection is carried out in a unified manner, both for spatial and space-time coded symbols. We show that this novel scheme outperforms other recent proposals in terms of bit error rate, even those using CSI at the transmitter to precode. We also show our proposal has lower complexity, achieved by exploiting the structure of the linear dispersion matrices.