Daehyoung Hong

Comments on "Teletraffic model and performance analysis for cellular mobile radio telephone systems with prioritized and nonprioritized handoff procedures"

A traffic model and analysis for cellular mobile radio telephone systems with handoff are described. Three schemes for call traffic handling are considered. One is nonprioritized and two are priority oriented. Fixed channel assignment is considered. In the nonprioritized scheme the base stations make no distinction between new call attempts and handoff attempts. Attempts which find all channels occupied are cleared. In the first priority scheme considered, a fixed number of channels in each cell are reserved exclusively for handoff calls. The second priority scheme employs a similar channel assignment strategy, but, additionally, the queueing of handoff attempts is allowed. Appropriate analytical models and criteria are developed and used to derive performance characteristics. These show, for example, blocking probability, forced termination probability, and fraction of new calls not completed, as functions of pertinent system parameters. General formulas are given and specific numerical results for nominal system parameters are presented.

Speech quality improvement for voice coders and synthesizers

A harmonic signal is created from a limited spectral representation of a voice signal. The harmonic signal is combined with the at least a portion of the limited delayed spectral signal to provide a reconstructed speech signal having perceptually improved audio quality.

Effects of time-to-trigger parameter on handover performance in SON-based LTE systems

In this paper, we evaluate handover (HO) performance when we apply various time-to-trigger (TTT) methods in self-organizing network (SON)-based long term evolution (LTE) systems. Although TTT can mitigate the wasteful ping-pong HO effect, it also can cause undesirable radio link failure (RLF) due to delayed HO. The optimal HO timings that produce the lowest ping-pong rate within allowable RLF rate vary depending on user equipment (UE) speeds and neighboring cell configurations. To achieve efficient HO timings, we propose and investigate two methods: “adaptive” and “grouping.” In the “adaptive method,” we select the adaptive TTT value for each UE speed based on RLF rate of 2%. The “grouping method” classifies UE speeds into three ranges and assigns the proper TTT value to each range. To apply the LTE specification more effectively, we suggest the criteria of grouping, and propose the proper TTT value for each range. We consider HO in two neighboring cell configurations: from a macro cell to either a macro cell or a pico cell. Simulation results show that the HO performance of the “adaptive method” is greatly improved compared to that of applying fixed TTT values. The results also show that the performance of the “grouping method”, using proposed criteria and proper TTT values, is comparable to that of the “adaptive method.”

Cost Reference Particle Filtering Approach to High-Bandwidth Tilt Estimation

In this paper, cost reference particle filter (CRPF) approach in estimating 1-D “tilt” of a vehicle attitude is proposed. CRPF has a couple of advantageous features compared to standard particle filtering; particularly, it does not require noise statistics in its application. H_ filter (HF) has common features as that of CRPF. The extended HF (EHF) is employed, which uses the approximate linearization of the nonlinear measurement function as the extended Kalman filter is extended. The performance of both approaches is investigated and compared in this paper. Low-cost “accelerometer” and “gyroscope” sensors are cooperatively employed instead of inclinometer in measuring the tilt. Simulation results show that CRPF outperforms EHF in estimating the tilt due to its robustness against the nonlinearity of the measurement equation, whereas EHF outperforms CRPF in estimating the tilt rate whose measurement equation is linear. Notably, an efficient CRPF outperforms EHF in tracking the tilt with just ten particles.

Inter-Carrier Interference Estimation in OFDM Systems With Unknown Noise Distributions

There are a number of approaches to estimating carrier frequency offset (CFO) that causes inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems: self-cancelation method, the extended Kalman filter (EKF), particle filter, Hinfin filter (HF), etc. In particular, the HF is of interest because prior statistical noise information is not necessarily required in its application. Cost reference particle filter (CRPF), newly developed in the particle filtering framework, has the same feature as HF; it also does not require the prior noise information of the state and the measurement equation. In this letter, we compare and analyze the performances of two similar methods. The simulation results show that CRPF outperforms HF, particularly when the bit energy to noise ratio of the measurement is low. Therefore, CRPF is very effective and robust, especially when the noise statistics are unknown with a low bit energy to noise ratio.

Statistical model of downlink interference for the performance evaluation of CDMA systems

A statistical model of the downlink interference for the analytical performance evaluation of code-division multiple-access (CDMA) systems is proposed. Based on Wilkinsons approximation, the statistical model of the relative other cell interference is developed in closed form. The best base station (BS) selection in the shadowed environment with a correlation is taken into consideration. We show that interference statistics obtained by the proposed analytical model agree with simulation results. It is also shown that the proposed analytical model can replace Monte Carlo simulation in outage analysis.

Gaussian Particle Filtering Approach for Carrier Frequency Offset Estimation in OFDM Systems

We propose Gaussian particle filtering (PF) approach for estimating carrier frequency offset (CFO) in OFDM systems. PF is more powerful especially for nonlinear problems where classical approaches (e.g., maximum likelihood estimators) may not show optimal performance. Standard PF undergoes the particle impoverishment (PI) problem resulting from resampling process for this static parameter (i.e., CFO) estimation. Gaussian PF (GPF) avoids the PI problem because resampling process is not needed in the algorithm. We show that GPF outperforms current approaches in this nonlinear estimation problem.

Management of neighbor cell lists and physical cell identifiers in self-organizing heterogeneous networks

In this paper, we propose self-organizing schemes for the initial configuration of the neighbor cell list (NCL), maintenance of the NCL, and physical cell identifier (PCI) allocation in heterogeneous networks such as long term evolution systems where lower transmission power nodes are additionally deployed in macrocell networks. Accurate NCL maintenance is required for efficient PCI allocation and for avoiding handover delay and redundantly in creased system overhead. Proposed self-organizing schemes for the initial NCL configuration and PCI allocation are based on evolved universal terrestrial radio access network NodeB (eNB) scanning that measures reference signal to interference and noise ratio and reference symbol received power, respectively, transmitted from adjacent eNBs. On the other hand, the maintenance of the NCL is managed by adding or removing cells based on periodic user equipment measurements. We provide performance analysis of the proposed schemes under various scenarios in the respects of NCL detection probability, NCL false alarm rate, handover delay area ratio, PCI conflict ratio, etc.

Downlink throughput and fairness analysis in multi-rate CDMA systems

This paper presents an analytical model and a method for the evaluation of the downlink throughput and fairness performance in multi-rate CDMA systems. We propose and use a model that can show the impact of self-interference to the received E/sub b//N/sub t/. The analytical method reflects the effect of lognormal shadowing, the best BS connection procedure, the bit rate granularity and the peak available bit rate limitation, and the limited number of spreading codes. A scheduling scheme for the fairness control is also developed and applied. The performance of packet channels for delay-tolerant service is evaluated in a 3GPP WCDMA system model. The system performance measures include asymptotic throughput, fairness performance factor, outage probability, and code shortage probability. From the analysis results, we can draw the downlink packet transmission control policy that can improve the system performance.

Coverage and capacity analysis for the multi-layer CDMA macro/indoor-picocells

This paper presents an analysis of coverage and capacity for the multi-layer CDMA cellular system. The multilayer CDMA system, that shares a common frequency band, consists of macrocells for outdoor users and picocells for indoor users. Though macrocells and picocells interfere with each other, the capacity of the whole system can be increased. We have analyzed the effect of mutual interference upon cell coverage, soft handover areas, and capacities. The parameters involved in the engineering of the system are discussed. The study results show that we can control the service coverage of indoor picocells with the system parameters set properly. It is also shown that the capacity of the whole system can be enhanced smoothly by deploying the indoor picocells within existing macrocells.