Cellular Mobile Systems Research Articles

An Analysis of Interference Mitigation Capability of Low Duty-Cycle UWB Communications in the Presence of Wideband OFDM System

Low duty-cycle (LDC) algorithm is interference mitigation technique, which can reduce the average interference to the existing radio systems by lowering pulse repetition interval or pulse occupation time. In this paper, the coexistence environment between low data rate ultra wideband (UWB) communication system such as wireless sensor network and the existing wideband system using orthogonal frequency division multiplexing (OFDM) such as 4th generation mobile cellular system (4G), worldwide interoperability for microwave access (WiMAX), and field pickup unit (FPU) is considered. In order to analyze the interference mitigation capability of LDC algorithm with impulse based UWB (LDC-UWB) system, the frame error rate (FER) of wideband OFDM system is examined for two types of LDC-UWB system: the signal with random polarity such as binary pole signals and without random polarity such as mono pole signals. We present that LDC algorithm is an efficient interference mitigation technique for low data rate UWB communication via computer simulations regardless of definitions of transmitted energy of UWB communication system, and also that the signal with random polarity is suitable for LDC-UWB system to mitigate interference to the other radio systems. We further investigate the adequate duty-cycle of LDC-UWB system for each definition of transmitted power of UWB communication.

Seguimiento de dispositivos móviles en un sistema de comunicaciones móviles celulares

Este artículo trata sobre el uso de algoritmos estadísticos en la estimación de señales de una red celular y su aplicación al posicionamiento y seguimiento de dispositivos móvil, con la finalidad de conseguir que la red esté en capacidad de proporcionar servicios basados en localización que podrían ser explotados conforme a las necesidades de los usuarios del sistema.Se introducen brevemente dos técnicas de posicionamiento homogéneas: la primera basada en la estimación de los instantes de llegada de la señal (TOA), y la otra en la observación de la diferencia de instantes de llegada (TDOA); y se utilizan ciertos estadísticos desarrollados para estimar la varianza del error de posicionamiento al aplicar estas metodologías, para simular un entorno realista en el cual se disponen de mediciones de posición de suscriptores móviles. Estas mediciones contienen errores asociados a las limitaciones inherentes de la aplicación de estas metodologías sobre canales móviles, en este caso especialmente a sesgos introducidos por la presencia de propagación multitrayecto. A partir de estas medidas y de las ecuaciones de estado que definen el movimiento del dispositivo, y mediante la aplicación del Filtro de Kalman, se refina la estimación de posición. En efecto, el Filtro de Kalman minimiza el ruido de medida, a partir de su estadística y del comportamiento de los datos; es un filtro adaptativo cuyo uso permite conseguir una mejor aproximación de los resultados, y por consiguiente una mayor flexibilidad en los servicios basados en localización (LBS) que potencialmente podrían derivarse de su incorporación al esquema de localización.El esquema desarrollado en esta propuesta se ha integrado para su visualización en un programa de mapas en tiempo real, GoogleEarth, que ocupa el puesto de servidor geográfico en este proyecto. En este artículo, se realiza la evaluación de las dos técnicas de posicionamiento ya mencionadas: TOA y TDOA, y del seguimiento de suscriptor móvil a través del uso del filtro de Kalman, en operación integrada, y no incluye los procesos de gestión y cálculo requeridos en una red celular para llevar a cabo la localización.

Quality-Based OVSF Code Assignment and Reassignment Strategies for WCDMA Systems

In third-generation code division multiple access (3G CDMA) mobile cellular systems, orthogonal variable spreading factor (OVSF) codes are applied in downlink to maintain the orthogonality between different channels. Since the number of available codes is limited, efficiently utilizing OVSF codes becomes an important issue. The code assignment and reassignment problem focuses on the subject of minimizing the number of code relocations. Previous works were based on some assumptions, including fixed service data rates and a code-limited system capacity. In this paper, we investigate this issue from a different perspective, by applying variable service data rates and an interference-limited system capacity. We have proposed three OVSF code assignment and reassignment strategies for this scenario, including sparse-first, sparse-first/rightmost, and modified sparse-first/rightmost, with a view to achieving the best service quality. The proposed strategies are well evaluated and compared with other strategies, based on the number of code reassignments, service quality, and throughput, via simulation. It is found that our proposed strategies outperform others under the scenario with variable service data rates and an interference-limited system capacity.

Temporal Dispersion Characterization of Over-Building Propagation Applied to Iso-Frequency Repeaters

This letter presents the results of a measurements campaign carried out at 2050 MHz with the aim of characterizing the time dispersion of multipath propagation when the transmit and receive antennas are placed near and situated on rooftops or mounted on masts. The measurements were taken in four separate locations within the urban area of Madrid, Spain. From the measured data, the root mean square (RMS) value of the delay spread and the delay interval that characterize the time dispersion propagation of the environment under study are analyzed. An average power delay profile (PDP), representative of the time dispersion, is proposed so as to extrapolate these results to other similar environments. The results can be useful for the designer to develop, analyze, and choose the best echo canceller technique and evaluate its performance in terms of the radio channel time dispersion when iso-frequency repeaters are used to enhance the coverage area and capacity of mobile cellular systems, as it is the case of the evolving third-generation UMTS networks.

Implementation and Performance Evaluation of Two Fuzzy-Based Handover Systems for Wireless Cellular Networks

Wireless mobile networks and devices are becoming increasingly popular to provide users the access anytime and anywhere. We are witnessing now an unprecedented demand for wireless networks to support both data and real-time multimedia traffic. The wireless mobile systems are based on cellular approach and the area is covered by cells that overlap each other. In mobile cellular systems the handover is a very important process. Many handover algorithms are proposed in the literature. However, to make a better handover and keep the QoS in wireless networks is very difficult task. For this reason, new intelligent algorithms should be implemented to deal with this problem. In this paper, we carried out a comparison study of two handover systems based on fuzzy logic. We implement two Fuzzy-Based Handover Systems (FBHS) called FBHS1 and FBHS2. The performance evaluation via simulations shows that FBHS2 has better behavior than FBHS1 and can avoid ping-pong effect in all simulation cases.

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space---time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.

Traffic Model and Performance Analysis of Cellular Mobile Systems for General Distributed Handoff Traffic and Dynamic Channel Allocation

An analytical model for channelized cellular mobile circuit-switched systems that support general arbitrary distributed handoff traffic has been proposed. The model is applicable for a dynamic channel allocation scheme. A 2-D Markov chain is developed, which can be used to compute congestion for all kinds of traffic streams. The proposed model is not restricted by a limited range of user mobility and can be reduced to predict congestion for Poisson-distributed handoff traffic and fixed channel allocation scheme.

Balancing Uplink and Downlink under Asymmetric Traffic Environments Using Distributed Receive Antennas

Recently, multimedia services are increasing with the widespread use of various wireless applications such as web browsers, real-time video, and interactive games, which results in traffic asymmetry between the uplink and downlink. Hence, time division duplex (TDD) systems which provide advantages in efficient bandwidth utilization under asymmetric traffic environments have become one of the most important issues in future mobile cellular systems. It is known that two types of intercell interference, referred to as crossed-slot interference, additionally arise in TDD systems; the performances of the uplink and downlink transmissions are degraded by BS-to-BS crossed-slot interference and MS-to-MS crossed-slot interference, respectively. The resulting performance unbalance between the uplink and downlink makes network deployment severely inefficient. Previous works have proposed intelligent time slot allocation algorithms to mitigate the crossed-slot interference problem. However, they require centralized control, which causes large signaling overhead in the network. In this paper, we propose to change the shape of the cellular structure itself. The conventional cellular structure is easily transformed into the proposed cellular structure with distributed receive antennas (DRAs). We set up statistical Markov chain traffic model and analyze the bit error performances of the conventional cellular structure and proposed cellular structure under asymmetric traffic environments. Numerical results show that the uplink and downlink performances of the proposed cellular structure become balanced with the proper number of DRAs and thus the proposed cellular structure is notably cost-effective in network deployment compared to the conventional cellular structure. As a result, extending the conventional cellular structure into the proposed cellular structure with DRAs is a remarkably cost-effective solution to support asymmetric traffic environments in future mobile cellular systems.

On Next Generation CDMA Technologies: The REAL Approach for Perfect Orthogonal Code Generation

All currently available code-division multiple-access (CDMA) technologies used in second-generation and third-generation mobile cellular systems are interference limited and can be appropriately called first-generation CDMA, whereas next-generation CDMA should provide a nearly interference-free performance. This paper addresses the issues on spreading code generation that is suitable for next-generation CDMA systems. The real environment adaptation linearization (REAL) approach is proposed to generate perfectly orthogonal complementary (POC) codes characterized by multiple access interference (MAI)-free and multipath interference (MI)-free operation. The REAL approach takes into account almost all major impairing factors in real applications, such as multipath propagation, asynchronous transmission, random data signs, and burst traffic, such that a CDMA system using them can offer an interference-resist operation. Two important conclusions are drawn in this paper: First, implementation of an interference-free CDMA will not be possible unless using complementary codes, such as the POC codes. Second, to enable interference-free CDMA, the flock size of the signature codes should preferably be equal to the set size of the codes. A fast algorithm to generate supercomplementary codes (a subset of POC codes) is also presented, and their ideal orthogonality is explicitly proven.

Physical relationships

There is continuing effort to increase the data transmission rate in evolving wireless systems. These evolving wireless systems include cellular mobile systems and wireless local area networks (WLANs). However, because of the complexity of these systems, it appears that fundamental physical relationships between transmission rate and the range over which transmission is possible are frequently overlooked. This can result in overly optimistic expectations for new wireless data systems or comparisons between systems that are not on an equal basis. This article reviews fundamental relationships between wireless system transmission rate (bit rate) and transmission range and includes the effects of some other system parameters on these relationships.

Superposition of Broadcast and Unicast in Wireless Cellular Systems

Practical application of superposition coding in multiplexing broadcast and unicast for OFDM-based mobile cellular systems is discussed. Superposition coding, whose gain is increased as the superposed signals have larger difference in signal-to interference-plus-noise ratio, is well matched for unicast and broadcast in a single-frequency network configuration. Combined with interference cancellation technique, broadcast signals from multiple base stations can be cancelled in a single step, minimizing the interference from broadcast to unicast. Issues related with scheduling and strategy for time, frequency and power resource sharing between broadcast and unicast are discussed. The application of superposed broadcast and unicast is then extended to MIMO systems. Simulation results in a practical mobile cellular environment are also provided, showing significant throughput gain of superposed broadcast and unicast.

An analysis of three multiple access techniques for the uplink of future cellular mobile systems

AbstractOrthogonal frequency division multiple access (OFDMA) is today a part of many standard specifications. Despite its attractive features, it has two main drawbacks when employed in the uplink: the high peak‐to‐average power ratio (PAPR) inherited from orthogonal frequency division multiplexing (OFDM) and the inherent frequency diversity loss. The loss of frequency diversity can be alleviated by precoding. Variants of precoded OFDMA include spread spectrum multi‐carrier multiple access (SS‐MC‐MA) and the frequency‐domain implementation of single‐carrier (SC) FDMA. The latter transforms OFDMA into a SC transmission system, avoiding the PAPR problem. This paper analyses OFDMA, several variants of precoded OFDMA and SC‐FDMA in its frequency‐domain implementations and compares them for uplink transmission. Copyright © 2008 John Wiley & Sons, Ltd.

Policy-based Network Management Reference Architecture for an Integrated Environment WLAN-3G

Strong demands for public wireless broadband services will require more capacity than even that can be supplied by advanced mobile cellular systems. For this reason, there is currently a strong need for interworking mechanisms between WLANs and cellular data networks. But one of the problems which the operators of this new architecture face is its process of management. Policy-based networking (PBN) is a novel technology that facilitates the management and operation of networks. In this article policy-based network management reference architecture for integrated environment WLAN-3G is proposed.

A New Approach to Synthesing Radio Frequency Channel Characteristics Models for TestinG of WCDMA Cellular Communication System

Channel modeling for mobile cellular communication systems is a rapidly changing area, and the models are becoming increasingly accurate and more comprehensive to allow radio channel simulators to be implemented either by software or hardware to simulate diversity systems with many users. However, the challenge is to develop models that exhaustively reproduce the propagation scenarios accounted in reality.The paper introduces a new method of synthesizing RF channels of cellular communication systems for computer simulation and for controlled laboratory testing that is based on extensive observations of real signals in the field. Channel parameters are utilized as time histories of deterministic estimates derived from the field measurements. The stored channel data then be used to reconstruct the field channel conditions for laboratory testing.An iterative gradient search is performed to refine the state estimate (measurements are compared to the modeled output). The processing is performed using a WCDMA acquire search (Primary Synchronization Code Acquisition) to estimate the CPICH power and PN position of detectable primary scrambling. Full description of this deterministic stored channel impulse response model is presented. Using this methodology, an accurate channel model is possible, because it provides actual information from the channel. This was done to show how some physical link aspects such as power control and data rate can be tested for quality performance of these systems under real field conditions due to the ability of constructing controlled laboratory testing, though this type of controlled testing is extremely difficult to accomplish in the field due to the practical constraints.

A Cellular Phone Type Mobile System with Speech-Driven Embodied Entrainment Characters by Speech and Key Inputs

A Cellular Phone Type Mobile System with Speech-Driven Embodied Entrainment Characters by Speech and Key Inputs

A Speed‐Aware Handover System for Wireless Cellular Networks Based on Fuzzy Logic

Presently, the wireless mobile networks and devices are becoming increasingly popular to provide users the access anytime and anywhere. The mobile systems are based on cellular approach and the area is covered by cells that overlap each other. In mobile cellular systems the handover is a very important process, which refers to a mechanism that transfers an ongoing call from one Base Station (BS) to another. The performance of the handover mechanism is very important to maintain the desired Quality of Service (QoS). Many handover algorithms are proposed in the literature. However, to make a better handover and keep the QoS in wireless networks is very difficult. In this paper, we propose a speed‐aware handover system based on fuzzy logic. The proposed system has 3 subsystems. The performance evaluation via simulations shows that proposed system has a good handover decision.

Simulation of Handoff Techniques in Mobile Cellular Networks

Mobility is the distinct feature of wireless mobile cellular system. Usually, continuous services is achieved by supporting handoff which is the transfer of an ongoing call from the current cell to the next adjacent cell as the mobile moves through the coverage area. usually handoff calls are given higher priority than new calls since it has a significant impact on the network performance. Simulation study of the relative signal strength with hysteresis and threshold (RSS-HT) algorithm for varying hysteresis and threshold are studies to evaluate the mean number of cell handoffs, mean number of wrong cell handoffs and expected average signal strength.

Detection of Fraudulent Usage in Wireless Networks

The complexity of cellular mobile systems renders prevention-based techniques not adequate to guard against all potential attacks. An intrusion detection system has become an indispensable component to provide defense-in-depth security mechanisms for wireless networks. In this paper, by exploiting regularities demonstrated in users' behaviors, we present a suite of detection techniques to identify fraudulent usage of mobile telecommunication services. Specifically, we explore users' behaviors in terms of calling and mobility activities because they are two of the most important components of mobile users' profiles. To utilize users' calling activities, we formulate the intrusion detection problem as a multifeature two-class pattern-classification problem. Parameters including call-duration time, call inactivity period, and call destination are extracted to form a feature vector to reflect users' calling activities. A nonparametric technique known as the Parzen window with a Gaussian kernel, is used to estimate a class-conditional probability density function. A Bayesian decision rule is applied in order to achieve a desirable error rate. To effectively exploit movement patterns demonstrated by mobile users, we first propose a realistic network model integrating geographic road-level granularities. Based on this model, an instance-based learning technique is presented to construct mobile users' movement patterns. A user's movement history is stored and compared against newly observed movement instances. We then define a novel similarity threshold to classify users' current movement activities. We simulate users' various behaviors and provide simulation results.

Adaptive Genetic Algorithms for Dynamic Channel Assignment in Mobile Cellular Communication Systems

Two adaptive genetic algorithms (GAs), namely GA for locking channel (GALC) and GA for switching channel (GASC), are proposed for a dynamic channel assignment in mobile cellular communication systems. The algorithms aim to minimize the blocking probability of new calls and the dropping probability of handoff calls in channelized systems, simultaneously considering three types of electromagnetic compatibility (EMC) constraints: 1) the cochannel; 2) the adjacent channel; and 3) the cosite. The proposed algorithms add a number of mechanisms to the canonical GA in order to increase their efficiency and velocity of convergence. Such mechanisms are adaptive parameters, random immigrants, a greedy policy, a reservoir to assist the initial population, a truncation selection scheme, and a three-point crossover. The GASC allows call switching between channels during the call holding time, whereas the GALC does not allow it. Computer simulations evaluated the performance of the proposed models considering a benchmark cellular environment formed by 49 cells with 70 channels and nonuniform traffic load characteristics. The impact of EMC constraints on the blocking probability of new calls and on the dropping probability of handoff calls was assessed, and the proposed models reached suitable performance. Equipment failure tests showed robust performance of the two adaptive GA schemes during the fault occurrence and recovery capability after the fault ends. The results suggest that the GASC has lower overall blocking probability of new calls than the GALC; however, the GALC may do better than the GASC in a number of combinations of handoff requests and EMC restrictions.

An improved handover algorithm based on signal strength plus distance for interoperability in mobile cellular networks

In future generation mobile cellular systems, position location of mobile terminal is expected to be available. In this paper, we propose an initiation algorithm for intersystem handover based on the combination of position location of mobile terminal and the absolute signal strength thresholds. Global System for Mobile communication (GSM) and Universal Mobile Telecommunication Systems (UMTS) networks are considered for interworking. The proposed algorithm reduces the handover rate by around 50% and thus improves the network resource efficiency as compared to that based on signal strength thresholds only.