Performance Analysis of Uplink Scheduling Algorithms for VoIP Services in the IEEEE 802.16e OFDMA System

While the voice over Internet protocol (VoIP) services is expected to be widely supported in wireless mobile networks, the performance of VoIP services has not previously been evaluated in the IEEE 802.16e orthogonal frequency division multiple access (OFDMA) system taking the adaptive modulation and coding scheme into consideration. To support real-time uplink service flows, three different types of scheduling have been designed in the IEEE 802.16e standard: the unsolicited grant service (UGS), the real-time polling service (rtPS), and the extended rtPS (ertPS). In this paper, we compare the three real-time scheduling algorithms in terms of the performance of VoIP services by using the analytical and simulation models that we developed.

On the Performance of Broadband Mobile Internet Access System

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment.

A New Linear Group-Wise Parallel Interference Cancellation Detector

In this paper, a new linear group-wise parallel interference cancellation (LGPIC) detector is proposed. Four different group-detection schemes are derived, namely, the linear group matched filter PIC (LGMF-PIC) detector, the linear group decorrelator PIC (LGDEC-PIC) detector, the linear group minimum mean square error PIC (LGMMSE-PIC) detector and the linear group parallel interference cancellation weighted PIC (LGPIC-PIC) detector. The convergence behavior of the proposed detector is analyzed and conditions of convergence are derived. Finally, extensive simulations regarding the convergence behavior and the effect of the grouping on the convergence behavior of the proposed LGPIC detector are conducted.

Interference Suppression Consisting of Pre-distortion Filtering and Selective Transmit Diversity

In this paper we present and evaluate a pre-distortion (PD) scheme for the downlink of Wideband-code division multiple access (W-CDMA) systems considering a Rake in the receiver in order to exploit multipath diversity. Its performance is compared with schemes without the PD at the base station (BS), and combined with a transmit diversity (TD) scheme to improve the performance by exploiting spatial diversity. It is shown that the proposed PD scheme allows receivers (Mobile Stations) with very low complexity, contrarily to the case where a post-processing multi-user detector (MUD) approach is adopted to improve the performance. Therefore, the proposed PD scheme can be seen as an alternative to post-processing schemes.

Performance Verification of Successive Interference Cancellation for STBC MIMO-OFDM System with Channel Correlation

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) transmission can improve both the transmission capacity and performance due to diversity gain. However, when the antennas are close to each other in a MIMO-OFDM system, the diversity order will be decreased because of channel correlation. In the paper performance of various detection methods for space–time block code (STBC) MIMO-OFDM with channel correlation are evaluated, including the conventional Alamouti full matrix detection, the modified diagonal matrix detection, the least square-zero forcing (LS-ZF) detection, and the successive interference cancellation (SIC). The paper also verify that the SIC detection can still keep excellent detection performance under large channel correlation.

Queueing Delay Analysis for the Joint Scheduling Exploiting Multiuser Diversity over a Fading Channel

In this paper, we consider a joint packet scheduling algorithm for wireless networks and investigate its characteristics. The joint scheduling algorithm is a combination of the Knopp and Humblet (KH) scheduling, which fully exploits multiuser diversity, and the probabilistic weighted round-robin (WRR) scheduling, which does not use multiuser diversity at all. Under the assumption that the wireless channel process for each user is described by the Nakagami-m model, we develop a formula to estimate the tail distribution of the packet delay for an arbitrary user under the joint scheduling. Numerical results exhibit that under the joint scheduling, the ratio of the number of slots assigned for the WRR scheduling to that for the KH scheduling dominates the characteristics of the delay performance.

Interference Cancellation and Avoidance for Secondary Users Co-existing with TDD-based Primary Systems

This paper proposes a new interference cancellation/avoidance scheme for secondary spectrum usage, which takes advantage of the features of Time Division Duplex (TDD) based primary systems. We focus on the co-existence between the heterogeneous systems, where the primary and the secondary are using the same spectrum simultaneously. The secondary systems have to accurately find the possible interference from/to the primary systems for discreet and efficient secondary transmission. In order to judge the arrival of interference from/to the primary system, the secondary access point (AP) compares the difference in power between the up and downlink signals in TDD-based primary systems. This scheme enables the secondary AP to know the level of interference from the primary systems that arrives at the AP without employing complex signal detection. The proposed scheme also determines the level of interference induced to the primary system by measuring the difference in power. To cancel and avoid interference in the proposed scheme, we introduce an adaptive array at only the AP that creates a null toward the interference with a higher power level between the up and downlink signals. Moreover, new algorithms by using scheduling information of the multiple primary nodes are introduced in the proposed method, in order to enhance the transmission quality of a secondary mobile station (MS) while maintaining a simple control scheme for the MS. Finally, we verify the effectiveness of the proposed method based on computer simulations.

A Novel Adaptive Detection Scheme based on Parallel Interference Cancellation for V-BLAST System

In this paper, in order to reduce the computational complexity of the detector of vertical Bell Laboratories layered space-time (V-BLAST) system over time-varying channels, an adaptive detection scheme is proposed based on parallel interference cancellation (PIC). The presented scheme has three units, which are primary adaptive detector, detection ordering determiner, and adaptive PIC detector. The proposed scheme can employ many of known adaptive algorithms for detection of V-BLAST system. In this paper, we present computational complexity of the proposed scheme using LMS, RLS, APA and AMSER adaptive algorithms and evaluate its performance with numerical simulations.

Optimal Joint Diversity and Power Control for Wireless Networks

We propose in this paper an efficient method to derive the optimal feasible power and weight for joint diversity and power control. Instead of solving a constrained optimization problem where both the variables of power and the variables of weight are involved, this method simply solves a set of equations where only the variables of power are involved. It is proven that the power and weight obtained from the proposed method can minimize the power consumption. To reduce the computational complexity, we further propose another method where the number of equations can be reduced from the number of users to the number of base stations.

Improving Spectral Capacity and Wireless Network Coverage by Cognitive Radio Technology and Relay Nodes in Cellular Systems

Methods to enhance the use of the frequency spectrum by automatical spectrum sensing plus spectrum sharing in a cognitive radio technology context have been presented and discussed in this paper. Ideas to improve the wireless transmission by orthogonal OFDM-based communication and to increase the coverage of cellular systems by future wireless networks, relay channels, relay stations and collaborate radio have been presented as well. A revised hierarchical deployment of the future wireless and wired networks are shortly discussed.

Isolation of Failing Scan Cells through Convolutional Test Response Compaction

This paper describes a non-recursive fault diagnosis technique for scan-based designs with convolutional test response compaction. The proposed approach allows a time-efficient and accurate identification of failing scan cells using Gauss–Jordan elimination method.

Performances of the H-ARQ Adaptive-QAM Transmissions over Multipath Channels

This paper presents the evaluation of the average spectral efficiencies provided by the adaptive use of a set of LDPC-coded QAM modulations in an OFDMA downlink scheme over mobile radio channels, considering a joint modeling of the channel and user-access method. It discusses the selection of the set of coded modulations, briefly describes the joint modeling of the channel and access method employed, and derives the average spectral efficiency provided by this approach in non-ARQ or H-ARQ environments. Some comments about the effects of the system’s parameters upon its performances are also included.

Task scheduling accuracy analysis in optical grid environments

Currently optical networks have been employed to meet the ever-increasing data transfer demands of grid applications and thus give rise to the concept of an “optical grid”. Task scheduling is an important issue for an optical grid, for it optimally allocates both grid and optical network resources to accelerate application execution and increase the resource utilization ratio. However, most task scheduling algorithms based on theoretical models may generate accuracy deviations between the scheduled results and the actual finish time of the applications. Accuracy deviations may lead to inefficient resources utilization and unsatisfied Quality of Service (QoS). This paper aims to improve the accuracy of task scheduling algorithms in optical grid environments. We first propose the theoretical task scheduling algorithm and demonstrate that the scheduling result is deviated with actual finish time in the real optical grid environment. Then, we reveal several factors which are likely to influence scheduling accuracy and develop a realistic task scheduling algorithm. We evaluate the theoretical and realistic task scheduling algorithms in our optical grid testbed. The experimental result shows the scheduling accuracy can be improved significantly by the realistic task scheduling algorithm.

Policies for the reconfiguration of cognitive wireless infrastructures to 3G Radio Access Technologies

The ceaseless evolution of wireless communications is reflected nowadays on the introduction of Beyond-3G (B3G) systems, characterized by the coexistence and cooperation of various Radio Access Technologies (RATs), over a common infrastructure. Major facilitator of this convergence is the advent of cognitive networks, which deploy elements (base stations and mobile terminals) that are able to proactively adapt to environmental stimuli, so that to optimize their performance. Part of the adaptation action takes place in cognitive base stations that own several reconfigurable transceivers, which are controlled by appropriate management functionality and may dynamically change their operating parameters. Each reconfiguration set includes a specific RAT, carrier frequency, as well as demand volume to be allocated per transceiver. Accordingly, proper evaluation of the various candidate reconfiguration sets appears to be of high significance. To this effect, in this paper we consider a cognitive network segment with transceivers operating at 3G RAT/carrier and we solve the DAMC problem (Demand Allocation into Multiple Carriers problem), which aims at evaluating and selecting the optimum policy to allocate the demand into the available 3G carrier frequencies. Optimality is expressed in terms of minimizing the total transmitted/received power per base station, thus deciding for the reconfigurations with the least impact on network interference. Indicative simulation scenarios and results are also presented for the validation and verification of the proposed functionality.

Time-frequency hopping sequences with three no hit zones

Based on the idea of no hit zone (NHZ) in frequency hopping (FH) systems, new sequences with three no hit zones (T-NHZ) in time-frequency hopping (TFH) systems are presented. With the T-NHZ in the time- frequency (TF) correlation functions, the proposed T-NHZ sequences can be directly employed in time-frequency hopping code division multiple access (TFH-CDMA) communication systems to reduce or eliminate multipath interference. Simulation results show that T-NHZ sequences can achieve much better bit error performance than the NHZ sequences and the traditional FH sequences.

A Joint OFDM Channel Estimation and ICI Cancellation for Double Selective Channels

Orthogonal frequency division multiplexing (OFDM) systems suffer significantly from inter-carrier interference (ICI) caused by double selective channels. In this paper, we develop a two-stage hybrid channel estimation and ICI cancellation structure for OFDM. The double selective channels are approximated by an improved Basis Expansion Model (BEM), which is more accurate than the conventional BEM when the normalized Doppler frequency is smaller than one. Based on this improved model, a new ICI cancellation scheme is proposed to reduce ICI impact. Simulation results show that the framework performs well.

WCDMA Uplink Capacity of a Long Tunnel Cigar-shaped Microcells for Underground Train Service

In this paper, the capacity and the interference statistics of the sectors of the cigar-shaped WCDMA microcells are studied using the hybrid model of propagation. A model of nine microcells in a metro tunnel is used to analyze the uplink capacity and the interference statistics. The capacity and the interference statistics of the microcells in metro tunnels are studied in this work for different propagation parameters, antenna side lobe levels, sector ranges and bends losses.

Bounds on Inter-carrier Interference Power of OFDM in a Gaussian Scattering Channel

This letter derives the upper and lower bounds on inter-carrier interference power P _ICI of Orthogonal Frequency Division Multiplexing (OFDM) in a Gaussian scattering channel. The bounds are computed as functions of f _d T _s product of the maximum Doppler spread f _d and symbol duration T _s , ζ frequency tracking and ϵ mobile travelling direction. Insightful discussions on the characteristics of P _ICI are given. Future work is also outlined.

A Cell Based Dynamic Spectrum Management Scheme with Interference Mitigation for Cognitive Networks

Future wireless systems are expected to be characterized by the coexistence of different radio access technologies (RATs) resulting in complex heterogeneous wireless environments. In parallel with this, the tremendous demand for spectrum has inspired the requirement of dynamic spectrum management (DSM). This paper aims at designing a cell based dynamic spectrum management (CBDSM) scheme to enhance the spectrum utilization and maximize the profit of operators in wireless heterogeneous networks. The system architecture and the functional modules supporting the CBDSM scheme are designed. As a fundamental issue in spectrum management, the inter-system interference issue is solved in the proposed CBDSM scheme. Furthermore, game theory, which is a potential tool for studying the distributed autonomous resource optimization algorithms, is applied to design a spectrum trading algorithm enabling the heterogeneous wireless networks to dynamically trade spectrum and to share the profit. In the algorithm, we take into account the economic value of the spectrum of wireless systems in order to guarantee the rationality for the spectrum trading. The simulation results show that the proposed CBDSM scheme effectively improves the spectrum utilization and the profit of operators while it reduces the mutual interference between wireless networks to a tolerable level.