Seo Weon Heo

The impact of application signaling traffic on public land mobile networks

As mobile Internet applications supporting real-time communications services are pervasively used, traffic patterns in mobile networks have changed significantly. New mobile Internet applications differ from traditional applications such as web browser and FTP in that they need always-on connectivity and generate a large amount of signaling traffic. The traffic patterns of these new mobile applications lead to frequent change of radio resource control states between connected and idle in the user equipment, consuming device battery power and causing excessive signaling overhead. The growth in signaling has resulted in a traffic surge that has attracted the attention of mobile network operators. In this article, we first explore traffic composition in a 3G network and show that chatty applications such as instant messenger and social network services contribute to the frequent change of radio states. We then describe the mechanism behind the surge in signaling traffic and describe the disastrous outcome when an application server failure and recovery occurs. Lastly, we discuss some remedies to reduce the application signaling traffic and network load in 3G and LTE networks. These remedies include development of network-aware smart applications that consider the mobile network characteristics and introduction of push notification services. We also present related future work and our research directions.

Non-systematic RS encoder design for a parity replacer of ATSC-M/H system

An efficient RS encoder for a parity replacer circuit of ATSC M/H mobile DTV receiver is presented. First, we derive the non-systematic RS encoder architecture which requires the well-known Forney algorithm to evaluate the parity symbol values located at arbitrary positions. We notice that only at most three information symbols corresponding to the trellis initialization symbol determine the RS parity symbols to be replaced in the parity replacer circuit. So we derive another form of the Forney algorithm to represent the parity symbol value as a linear combination of the input information symbols. With the new form, efficient architecture for implementing the RS encoder of a parity replacer is presented.

Time-domain calculation of spectral centroid from backscattered ultrasound signals

Spectral centroid estimation from backscattered ultrasound RF signals is the preliminary step for quantitative ultrasound analysis in many medical applications. The traditional approach of estimating the spectral centroid in the frequency domain takes a long time because discrete Fourier transform (DFT) processing for each RF segment is required. To avoid this, we propose time-domain methods to estimate the spectral centroid in this paper. First, we derive the continuous-time-domain equations for the spectral centroid estimation using Parsevals theorem and Hilbert transform theory. Then, we extend the method to the discrete-time domain to ease the implementation while maintaining the same accuracy as the calculation in the frequency domain. From the result, we observe that it is not practical to apply the discrete-time equations directly, because a high sampling rate is needed to approximate the time derivative in the discrete-time domain. Therefore, we also derive the feasible version of the discrete- time equations using a circular autocorrelation function, which has no constraints on the sampling rate for real RF signals acquired from pulse-echo ultrasound systems. Simulation results using numerical phantoms show that the time-domain calculation is approximately 4.4 times faster on average than the frequency-domain method when the softwares built-in functions were used. The average estimation error compared with that of the frequency-domain method using DFT is less than 0.2% for the entire propagation depths. The proposed time-domain approach to estimate the spectral centroid can be easily implemented in real-time ultrasound systems.

A Token-Bucket Based Rate Control Algorithm with Maximum and Minimum Rate Constraints

We propose a token-bucket based rate control algorithm that satisfies both maximum and minimum rate constraints with computational complexity of O(1). The proposed algorithm allocates the remaining bandwidth in a strict priority queuing manner to the flows with different priorities and in a weighted fair queuing manner to the flows within the same priority.

A novel power spectrum calculation method using phase-compensation and weighted averaging for the estimation of ultrasound attenuation

An estimation of ultrasound attenuation in soft tissues is critical in the quantitative ultrasound analysis since it is not only related to the estimations of other ultrasound parameters, such as speed of sound, integrated scatterers, or scatterer size, but also provides pathological information of the scanned tissue. However, estimation performances of ultrasound attenuation are intimately tied to the accurate extraction of spectral information from the backscattered radiofrequency (RF) signals. In this paper, we propose two novel techniques for calculating a block power spectrum from the backscattered ultrasound signals. These are based on the phase-compensation of each RF segment using the normalized cross-correlation to minimize estimation errors due to phase variations, and the weighted averaging technique to maximize the signal-to-noise ratio (SNR). The simulation results with uniform numerical phantoms demonstrate that the proposed method estimates local attenuation coefficients within 1.57% of the actual values while the conventional methods estimate those within 2.96%. The proposed method is especially effective when we deal with the signal reflected from the deeper depth where the SNR level is lower or when the gated window contains a small number of signal samples. Experimental results, performed at 5MHz, were obtained with a one-dimensional 128 elements array, using the tissue-mimicking phantoms also show that the proposed method provides better estimation results (within 3.04% of the actual value) with smaller estimation variances compared to the conventional methods (within 5.93%) for all cases considered.

Multi-channel DTV signal generator design using modified Farrow filter

This paper proposes a compact multi-channel DTV signal generator. To combine multi-channel signal sources in digital domain, the baseband signal is up-sampled and interpolated using the modified Farrow-type filter. We formulate the optimization problem and design the filter coefficients. The designed filter contains a small number of multipliers with more than 40dB sideband signal suppression capability.

Analytic Model of Four-switch Inverter-fed Driving System for Wye or Delta-connected Motor with Current Ripple Reduction Scheme

This paper proposes an analytic model for four-switch inverter (FSI)-driven wye (Y) or delta (Δ)-connected motors with a current ripple reduction algorithm. FSIs employ four switches in controlling three-phase load instead of using six switches. They have split dc-link stage, and due to this inherent structure there exists the voltage difference between upper and lower capacitors, which results in distortion of the inverter output voltage. To study characteristics of FSIs, this paper presents an advanced simulation models of FSI-driven control system for 3-phase motor that can has a wire connection either Y or Δ. In addition, this paper introduces a current ripple reduction scheme that mitigates degradation of control performance due to the voltage difference between the dc-link capacitors. The validity of the proposed method and the analytic model is verified by simulations and experiments carried out with 1-HP induction machine with Y or Δ-connection

OpenMP and GPU based software DVB-T receiver design

In this paper, We design the OpenMP and GPU based software DVB-T receiver. First, 1 symbol processing time measured in software DVB-T receiver will compared with the required time. Halfband LPF, FFT and Viterbi decoder blocks are designed to be processed by GPU. And some blocks are processed by OpenMP. As a result, it can be simulated in realtime.

Double edge trailing PWM based full digital audio amplifier design

This paper presents double edge trailing PWM (DEPWM) based full digital audio amplifier design method. Several works about the design method of trailing edge PWM (TEPWM) or leading edge PWM (LEPWM) are reported previously but little work are reported on the design of the DEPWM based full digital audio amplifier. In this paper we derive mathematical equations about the DEPWM procedure in terms of the quantization noise reduction using the well-known sigma-delta digital to digital converter (DDC) and show the simulation result.

Serial concatenated turbo TCM coding scheme for enhanced VSB system

A new coding scheme using serial concatenated turbo TCM (SCTTCM) for enhanced VSB reception system is proposed. The proposed coding scheme is backward compatible with the conventional VSB receivers and at the same time is able to receive the enhanced stream. The conventional schemes are based on the idea of directly combining an outer convolutional code with the standard 8-VSB trellis code, but our proposed method inserts a random interleaver between the two codes comprising the SCTTCM. The performance of the proposed scheme is evaluated and compared with the conventional method considering both the mixed and non-mixed mode stream. We also apply the extrinsic information transfer chart (EXIT chart) method for the performance analysis of the proposed scheme.