Choongchae Woo

Performance Analysis of Reuse-Partitioning-Based Subchannelized OFDMA Uplink Systems in Multicell Environments

This paper presents a performance analysis of reuse partitioning (RUP)-based subchannelized orthogonal frequency-division multiple-access (OFDMA) uplink systems in multicell environments. The cochannel interference (CCI) statistic is calculated for OFDMA uplink systems. The derived statistic is then used to analyze the performance of subchannelized OFDMA systems based on RUP. Analysis and simulation results show that the performance of a subchannelized OFDMA system in multicell environments is noticeably dependent on the CCI, and the effect of CCI can be reduced by the RUP scheme. Finally, the results of the analysis yield the optimum RUP area for achieving the maximum system throughput.

Call admission control strategy for system throughput maximization considering both call- and packet-level QoSs

This letter presents a call admission control (CAC) strategy for system throughput maximization in wireless uplink systems. This strategy considers not only the call-level quality of service (QoS) (i.e., blocking probability) but also the packet-level QoS (i.e., outage probability). Using the statistical co-channel interference (CCI) model and state diagram, the outage probability and the blocking probability are investigated as a function of the relative traffic load. We formulate the CAC strategy problem based on relative traffic load, and suggest a solution. The numerical results show that maximum system throughput can be achieved by controlling the relative traffic load. In addition, we illustrate the region where system throughput is constrained by call- and packet-level QoSs. This examination shows that the call and packet-level QoSs must be considered together to achieve maximum system throughput.

Performance Analysis of Dynamic Channel Allocation Based on Reuse Partitioning in Multi-Cell OFDMA Uplink Systems*This paper was presented on Poster 3: Communications (1) section at the ITC-CSCC 2005.

Our investigation is presented into analysis of the co-channel interference (CCI) statistic in orthogonal frequency-division multiple access (OFDMA) uplink systems. The derived statistic is then used to analyze the performance of reuse partitioning (RP)-based dynamic channel allocation (DCA). Analysis and simulation results show that the performance of DCA in multi-cell environments is noticeably dependent on the CCI. Finally, the results of the analysis yield the optimum RP area for achieving the maximum spectral efficiency.

Combining nonlinear equalization and simple detection for high-density optical recording channels

This paper discusses new systems for nonlinear optical recording channels. The systems combine neural network structure into simple detectors such as the multilevel decision-feedback equalizer (MDFE) and the discrete matched filter (DMF). The latter (denoted as DFNE/DMF) provides powerful nonlinear tolerance, while the former (denoted as NMDFE) shows poor tolerance because of conditional training property in the MDFE. When compared with a partial response neural equalizer with maximum-likelihood (PRNE/ML), the proposed DFNE/DMF proves to be very hardware-efficient and able to support high data rates. Simulation results show that the DFNE/DMF increases bloom tolerance up to roughly 30% at a density of S = 6.

Simple Dynamic Subcarrier Allocation With CQI Feedback Reduction for OFDMA Systems

The focus of this paper is a proposal for a computationally efficient dynamic subcarrier allocation (DSA) algorithm for orthogonal frequency-division multiple access (OFDMA) systems. The proposed DSA algorithm considerably reduces the computational complexity and the amount of channel quality information (CQI) compared to amplitude-craving greedy (ACG) algorithms, which use full CQI. At the same time, the performance of the proposed algorithm closely approaches that achieved by ACG algorithms. Moreover, the authors present a new bandwidth-assignment algorithm produced by modifying bandwidth assignment based on the signal-to-noise ratio (BABS). This modified BABS algorithm enables the proposed DSA algorithm to produce a strong outage performance gain over the conventional scheme.

Performance Analysis of Multistage Interference Cancellation for Asynchronous TH-UWB Systems in Multipath Fading Channels

In this paper, we present an accurate analytical method for an asynchronous time-hopping (TH) ultrawideband (UWB) system using multistage interference cancellation (MIC) in multipath fading channels. To model the asynchronous transmission, we first investigate the chip-asynchronous case and extend the results of chip-asynchronous transmission into completely asynchronous transmission as a more general environment. Specifically, the approximate closed-form expression is derived for numerically calculating the average bit-error probability (BEP) of the MIC receivers, which are based on the hard-decision (HD) and soft-decision (SD) detections, respectively. In performing the analysis, the effect of multiple-access interference (MAI) is modeled as a Gaussian process. The results of an interference cancellation (IC) receiver as a function of the ratio between the two types of processing gain-1) pulse combining gain N s and 2) pulse spreading gain N c-are analyzed and compared under the constraint that the total processing gain of the system is large and fixed. To build up intuitive knowledge, some remarks on the analytic results are presented to describe the design criterion for the interference suppression. In numerical results, the theoretical analysis is verified via comparison with simulation results in terms of the number of IC stages, the set of cancellation parameters, and the number of users.

UWB interference cancellation receiver in dense multipath fading channel

Interference cancellation (IC) scheme using partial RAKE combining is proposed in multiuser ultra-wideband (UWB) fading channels. The UWB system under consideration employs a time-hopping impulse radio multiple access (TH-IRMA) format. The proposed IC scheme includes a design for a modified impulse radio transmitter model, and uses a partial RAKE combining technique to estimate the tentative decisions for reconstructing multiple access interference (MAI). In addition, partial user interference cancellation is considered in order to reduce the complexity of the receiver. Unlike conventional UWB systems, the proposed IC scheme exhibits little degradation in BER performance as the number of users increases. Moreover, the partial user IC scheme achieves considerable improvement in performance with reduced IC receiver complexity.

Simplified signal space detector for optical recording

A signal space detector is a low-complexity approximation of fixed-delay tree search with decision feedback (FDTS/DF). This paper proposes the simplest version possible of a /spl tau/ = 2 FDTS/DF for a minimum run-length constraint of d = 2. The hardware needs only two multiplications and additions, facilitating high data-rate/low-complexity implementations. Simulation results show that the performance of the proposed detector equals that of the /spl tau/ = 2 FDTS/DF even when jitter noise is present. It is shown that for d = 2, a partial response maximum-likelihood detector with the target response /spl Sigma//sub k=0//sup 3/ D/sup k/ outperforms one with (1 + D)/sup 3/ because of good spectral matching at normalized density S /spl ges/ 4.6.

A dual noise-predictive partial response decision-feedback equalizer for RLL(1,x) coded perpendicular magnetic recording channels

Partial response maximum likelihood (PRML) is a powerful and indispensable detection scheme for perpendicular magnetic recording channels. The performance of PRML can be improved by incorporating a noise prediction scheme into branch metric computations of the Viterbi algorithm (VA). However, the systems constructed by VA have shortcomings in the form of high complexity and cost. In this connection, a new simple detection scheme is proposed by exploiting the minimum run-length parameter d=1 and is extended to dual-detection scheme for improving the bit-error rate (BER) performance. Simulation results show that the proposed scheme has a comparable performance to noise-predictive maximum likelihood detector with less complexity when the partial response (PR) target is (1,2,1).

A noise-predictive partial response decision-feedback equalizer for RLL(1,x) coded perpendicular magnetic recording channels

In this paper, a noise-predictive partial response decision-feedback equalizer for RLL(1,x) coded perpendicular magnetic recording channels has been investigated.