In the context of ultra-low end applications such as smart homes, smart vehicles and Industrial Internet of Things (IIoT), the use of Plastic Optical Fibers (POFs) as communications backbone to enable the convergence of wireless and optical systems has emerged as a cost-effective and ruggedized solution. The transmission of standalone Narrowband IoT (NB-IoT) signals through large-core Step-Index POF (SI-POF) can be achieved by directly modulating a laser diode at the cost of introducing non-linear effects. In this work, the performance of a Radio-over-POF (RoPOF) link is enhanced by Digital Predistortion (DPD) using a memoryless polynomial approach whose complexity is reduced by scaling down the number of samples using a novel technique that preserves the data statistics by organizing the data into a number of clusters.

This paper analyzes and evaluates the use of Machine Learning (ML) techniques as an alternative to heuristic methods to identify UEs in Licensed-Assisted Access (LAA) networks that are being affected by collisions from hidden nodes sources. The paper analyzes different models based on supervised ML methods to classify UEs into two possible classes: UEs affected by collisions and UEs free of collisions. To implement them, we employ a set of typical parameters of the LTE standard, e.g., Channel Quality Indicator (CQI), Reference Signal Received Quality (RSRQ) and number of Physical Resource Blocks (PRB). These parameters are fed into different supervised ML models which, once optimized, obtain the best models to predict when an UE is facing interference from hidden nodes in a dynamic channel environment. Results show that classification methods based on ML techniques are capable of predicting with a high level of accuracy when a UE is affected by collisions and, consequently, if this node is located in a hidden area. Nevertheless, and despite the growing interest in applying ML techniques in an increasing number of fields, we can conclude that, in this case, the performance of the ML approach is not necessarily better than heuristic methods. For instance, it does not outperform the Dynamic Collision Detection (DCD) previously presented by the authors. In addition, the ML algorithms exhibit a higher prediction time and computational complexity, with respect to those obtained with DCD algorithm. This should be considered a drawback in some LTE-Advanced and 5G wireless network scenarios that prioritize lower latencies.

The Bluetooth Low Energy (BLE) mesh profile, standardized by the Bluetooth Special Interest Group (SIG), has an increasing interest in IoT solutions. However, the standard assumes that relay and friend nodes should be continuously scanning the channel awaiting any incoming transmissions. This could be very inefficient in terms of energy consumption, particularly in application scenarios where the backbone of the mesh network cannot be powered and traffic is infrequent. Hence, we present a novel strategy, named PSM-DMO, that minimizes the scan periods and thus, significantly reduces the overall energy consumption of the mesh network. PSM-DMO is defined as a new and optional feature for the currently published BLE mesh specifications, coexists with the standard operation, and is implemented without modifying the core of the specification. The proposal, that ensures the reliability of the mesh operation, can be used in BLE sensor networks that can tolerate a certain transmission delay. PSM-DMO replaces the continuous scan by a periodic but asynchronous polling process whereby the relay and sink nodes interrogate their neighbors about the existence of data to receive or to retransmit through the network. Nodes only go into scan mode during the period of time the mesh network will be involved in the transmission and dissemination. This period is estimated by the node which is the source of data, it is announced to its neighbors and it is propagated consecutively by all the relay nodes until the destination. PSM-DMO allows a theoretical reduction in the energy consumption of relay nodes up to 99.24 %.

The Bluetooth low-energy (BLE) mesh profile, currently standardized by the Bluetooth Special Interest Group (SIG), assumes that friend and relay nodes should be continuously scanning the channel ready to receive any incoming transmissions (TXs). This is very inefficient in terms of energy consumption. Hence, we present BMADS, an asynchronous dynamic scanning mechanism designed to reduce the overall energy consumption of the mesh network. BMADS is implemented as a new feature for the currently published BLE mesh specifications without modifying its core. This feature reduces the scanning cycles of the nodes, but still ensuring the reliability. To make this possible, BMADS sends a new control message sequence before transmitting the data. This sequence puts the nodes into continuous scan mode, preparing the network for data TX. The proposal can be used in BLE sensor networks that can tolerate a certain TX delay and require especially low-energy consumption. BMADS allows a theoretical reduction in the energy consumption of the relay nodes up to 98%.

LTE operation in the unlicensed spectrum based on Licensed-Assisted Access (LAA) is being considered as an option to increase the capacity of 4G/5G wireless networks. This solution allows the eNodeB to contend with other nodes by accessing the shared medium and, through carrier aggregation (CA), to use both licensed and unlicensed bands to deliver best effort services. Nevertheless, the hidden node problem over shared medium access networks is an obstacle that must be addressed in order to reduce or avoid performance degradation problems. The metrics associated to LAA reflect the behavior of a node facing collisions. A better understanding of these metrics can help to identify nodes affected by hidden terminals, making it possible to take smart decisions about the continuity of a node on the unlicensed band, resulting in an improved network performance. In this paper, we first study the Channel Quality Indicator (CQI), Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) metrics on the context of LAA for a User Equipment (UE) that is facing different levels of interference. Then, a combination of the above metrics is used in order to develop an algorithm for collision detection. Finally, the performance of the algorithm is evaluated using a simulation tool under realistic channel conditions. The results show that is feasible to detect, with an adequate accuracy level, if a node is affected by collisions and subsequently if this node is located in hidden area. This is demonstrated with different levels of interference, realistic channel conditions and users in movement inside the hidden area.

LTE operation in the unlicensed spectrum emerges as an alternative to increase the capacity of 4G wireless networks. 3GPP has finished the standardization of Licensed Assisted Access (LAA) for LTE operation in 5 GHz unlicensed spectrum, this solution makes use of Listen Before Talk (LBT) algorithm which is pretty similar to Wi-Fi medium access control (MAC) protocol. In this context, the hidden node problem in heterogeneous networks (LAA/Wi-Fi) is a topic that must be addressed in order to avoid or reduce the degradation of the network. Finding out hidden nodes and understanding the main metrics that reveals how the network performance gets affected by its presence inside LAA networks is an issue that, if managed correctly, can make possible to take intelligent decisions for the sake of the efficiency of LAA and Wi-Fi network. In order to understand how these metrics evolve, we have proceeded to analyze LAA/Wi-Fi networks with the presence of hidden node(s) through a simulation tool. The results demonstrate that using the distribution of Channel Quality Indicator (CQI) metric makes possible to detect nodes in hidden areas, likewise that there are a set of metrics associated to hidden nodes that describes how much a network`s performance get reduced.

LTE operation in unlicensed spectrum bands, based on Licensed-Assisted Access (LAA-LTE), is nowadays considered as an option to increase the capacity of 4G wireless networks. These solutions use a Listen Before Talk (LBT) protocol that enables the eNodeB (eNB) to opportunistically access the medium avoiding collisions from/to other eNBs or Wi-Fi stations. However, the hidden node problem in the context of LAA-LTE networks is a challenge that must be addressed in order to reduce or avoid the degradation of the network. Identifying hidden nodes and understanding the main metrics concerning their behavior will make it possible to take intelligent decisions and to improve the efficiency of LAA. In this work, different LAA-LTE scenarios with hidden nodes are analyzed. The results show that it is possible to detect the presence of hidden nodes by only using CQI (Channel Quality Indicator) metrics, and also that there is a set of metrics associated to hidden nodes that make it feasible to understand why and how much a hidden node degrades the network performance.

An efficiency-optimized transmitter architecture for multi-band and OFDM (Orthogonal Frequency Division Multiplexing)-based standards operation is proposed and evaluated. It utilizes a power amplifier (PA) stood on a VDMOS transistor and two reconfigurable matching networks (RMNs). By means of frequency-independent both source and load mismatch correction, the reconfigurability provided by the RMNs allow the architecture to improve power-added efficiency (PAE) at several frequency bands for different OFDM-based standards. In order to obtain the optimum parameters (RMNs state), a meticulous optimization process is completed. Refer to a fixed design approach, PAE is improved for both continuous and OFDM-modulated signals. For the OFDM-modulated wave approach, PAE is improved 52.03% at 410 MHz and 5.86% at 700 MHz, referred to the fixed design. Thus, significant PAE enhancement is achieved, specially at the low frequency band.

An optimized process for linearity and efficiency performance using a reconfigurable matching network (RMN) for power amplifiers (PAs) is presented. Long-term evolution (LTE) waveforms modeled as multisine excitations are used to simulate a general purpose PA, assuming that the antenna is perfectly matched. Selecting RMN state for linearity the adjacent channel power ratio (ACPR) is improved while obtaining efficiency enhancement. Moreover, it is shown that power added efficiency (PAE) is highly increased selecting properly RMN state while linearity also improves. With this architecture both linearity and efficiency are improved simultaneously.

In this paper, we propose several frequency reuse coordination schemes for interference management in orthogonal frequency division multiple access. The aim of these schemes, working together with time and frequency domain packet scheduling, is to achieve reuse of 1 at sector level in a tri-sectorized base station scenario. Inter-sector interference is strong at the frontier between sectors, and a tight coordination scheme needs be applied. To support this coordination scheme, the users' location information is then essential to determine if a user is prone to suffer strong inter-sector interference. The performance of these resource allocation algorithms is compared with schemes based on fractional frequency reuse, where reuse of 1 at cell level is assumed. Copyright © 2012 John Wiley & Sons, Ltd.

The performance of an SC-FDMA cellular system highly depends on the proper selection of the parameters involved in the Fractional Power Control (FPC) algorithm. When a real cellular system is deployed, a power control algorithm must be combined with a resource allocation strategy under some interference coordination scheme, such as the well known Fractional Frequency Reuse (FFR). However, in order to set a suitable operation point for FPC, previous studies have not considered enough the joint behavior of all those factors. In this paper, we analyze how the system performance is affected when different FPC operation points are combined with different Inter-Cell or Inter-Sector Interference Coordination (ICIC/ISIC) schemes derived from FFR. Our study reveals that different power control parameters must be set depending on the per-cell or per-sector basis of the frequency reuse strategy considered in the interference coordination scheme.

ABSTRACT In this paper, we analyze the problem of efficient paging for group call searches under realistic mobility patterns. Taking as a basis a location update scheme, based on the definition of an adaptive macro‐location area, adapted to the mobility pattern of the terminals, we characterize the residence probabilities in each location area of a generic macro‐area. With this information, we propose and evaluate different sequential group paging strategies, also taking into account their computational cost. Results show the suitability of some of the proposals (semiadaptive and hybrid schemes) and its applicability to new packet‐based broadband cellular systems. Copyright © 2010 John Wiley & Sons, Ltd.

With the popularity of navigation applications and the integration of GPS in user devices, location-awareness is becoming an essential feature demanded by users. Nevertheless, location-awareness in indoor environments is still limited by the inability of GPS to operate indoors. With a centimeter-level ranging resolution, Ultra-Wideband (UWB) is one of the most promising technologies to provide indoor location. Several location & tracking algorithms have been proposed in the literature to compute user's position according to the estimated distances to some reference nodes, each one providing the best performance in certain conditions. Nevertheless, most of these proposals are evaluated under too specific or simplistic conditions that do not account realistically for the specific implications of the UWB-based distance estimation and the indoor environment. This paper aims to evaluate the performance of different location and tracking algorithms on a realistic indoor scenario and with a specific UWB indoor ranging model, analyzing their advantages and drawbacks in relation to different conditions and system design parameters.

In this paper we study the performance of a SC-FDMA cellular system when a complete Inter-Cell Interference (ICI) management strategy is implemented. We also introduce a novel sector-and-zone frequency ICI coordination scheme, derived from Fractional Frequency Reuse (FFR), which succeeds on increasing the capacity of an SC-FDMA cellular system. Working together with open-loop Fractional Power Control (PFC), time-dependent scheduling (to maintain fairness constraints to all users), opportunistic scheduling in frequency domain (FD, intended to improve the overall throughput) and adaptive modulation and coding schemes (AMCS), our simulations show that our novel scheme outperforms other typical resource allocation schemes by reducing the dropping probability and increasing the supported traffic load, while guaranteeing the required level of Quality of Service (QoS) for real-time traffic.

Tailbiting convolutional codes are used in several new cellular mobile radio systems such as WiMAX or LTE. This encoding method does not reset the encoder memory at the end of each data block, avoiding the overhead of the zero tail and improving the efficiency. Nevertheless, the absence of a known tail increases the complexity of the decoding process. Since the computational burden of maximum likelihood (ML) decoding is very high, several suboptimal algorithms have been proposed attaining good performance in terms of computational load and error correction capabilities. In this work we propose a decoding algorithm of low complexity which achieves error rates close to those of ML decoding. The proposed algorithm is based on the Circular Viterbi algorithm (CVA) and performs several iterations of the Viterbi algorithm until a tailbiting pattern is found within the path with the highest metric of the extended trellis. Simulations results obtained in an OFDM system under gaussian and wireless channels are near to the performance of the maximum-likelihood decoding and other suboptimal algorithms.

Digital predistortion (DPD) is a well-known method to reduce non-linear distortion in RF power amplifiers (PAs). In this paper, we present a study on the sensitivity of this linearization technique under large mismatch conditions, and how this sensitivity can be improved using a tunable matching network (TMN). Under different load conditions, PA behavior may change significantly making more complicated the DPD solution convergence, reducing its performance or even disabling its correct operation. Using a TMN the load impedance variation effect can be reduced, observing improvements in adjacent channel power ratio (ACPR) and regions of DPD convergence in the Smith chart.

It is commonly assumed that the antenna input impedance remains static during the transmission and reception process. However, in a real scenery the impedance value is a dynamic parameter, affected by the user and the environment, that can be very different compared to the static situation. With a statistical approach, the impedance variation can be characterized in the matching domain. This information can be very useful for the design of efficient adaptive matching circuits. In this paper, we propose the design and optimization of a varactor-based tunable matching network (VMN) to improve the antenna matching, using the previous knowledge of the antenna input impedance variations. Improvements in power transmission greater than 3 dB for the originally unmatched region, and reduced power losses (under -0.5 dB) in the originally matched area can be achieved using this circuit.

With the popularity of navigation applications and the integration of GPS in user devices, location-awareness is becoming an essential feature demanded by users. Nevertheless, location-awareness in indoor environments is still limited by the inability of GPS to operate indoors. With a centimeter-level ranging resolution, Ultra-Wideband (UWB) is one of the most promising technologies to provide indoor positioning, allowing the development of combined data transmission and location networks. Existing studies mainly focus on different distance estimation methods and position computation algorithms, but usually the implications of a real system such as transmission delay and resource constraints are not taken into account. Specifically, latency due to distance estimation and transmission has a negative impact on positioning accuracy, and limited availability of resources limits the amount of mobile nodes that can be tracked and the frequency of position updates. In this paper, the impact of an 802.15.4-based MAC layer is assessed, and different tracking system architectures, as well as different strategies for the acquisition and distribution of location information are proposed and evaluated in order to optimize the latency of position updates and the amount of resources needed.

In this paper we propose three different frequency resource management strategies that, working together with FFR and open-loop Fractional Power Control (PFC), succeed on mitigating both uplink inter-cell interference (ICI) and ICI fluctuations, that usually reduce the performance of SC-FDMA cell-based systems. Simulations are carried out with real-time traffic patterns at different loading scenarios, showing that our strategies outperform a typical FFR scheme suggested to coordinate frequency assignments among neighboring cells.

In this paper, we analyze the problem of efficient paging for group call searches under realistic mobility patterns. Taking as a basis a location update scheme, based on the definition of an adaptive macro-location area, adapted to the mobility pattern of the terminals, we characterize the residence probabilities in each location area of a generic macro-area. With this information, we propose and evaluate different sequential group paging strategies, also taking into account their computational cost. Results show the suitability of some of the proposals (semiadaptive and hybrid schemes) and its applicability to new packet-based broadband cellular systems.

Tailbiting convolutional codes will be used for several applications in new cellular mobile radio systems. This encoding method does not reset the encoder memory at the end of each data block, avoiding the overhead of the zero tail and improving the efficiency. Nevertheless, the absence of a known tail highly increases the complexity of the decoding process. Recently, the use of the A* algorithm has highly decreased the computational complexity of Maximum Likelihood (ML) decoding of tailbiting convolutional codes. The decoding process in this case requires two steps. In the first step, a typical Viterbi decoding is employed to collect information regarding the trellis. The A* algorithm is then applied in the second step, using the information obtained in the first step to calculate the heuristic function. The improvements proposed in this work decrease the computational complexity of the A* algorithm using further information from the first step of the algorithm. This information is used for finding early terminating conditions for the A* algorithm. Simulation results show that the proposed modification decreases the complexity of ML decoding with the A* algorithm in terms of the performed number of operations.

This paper presents the application of a reconfigurable matching network (RMN) to improve the efficiency and linearity of an RF power amplifier under load impedance variations. Unlike dynamic load modulation technique, in this paper we consider the state of the RMN remains the same with the input power, but changes depending on the load impedance, a changing parameter in mobile environments. Simulations show relevant improvements in adjacent channel power ratio (ACPR) and efficiency for arbitrary load impedances.

In this paper, we analyze the performance gain achieved when a channel-aware deferring (CaD) strategy is applied to defer the allocation of users with transitory bad channel state in a mobile OFDMA system. Users with good channel conditions receive more resources and the radio resource utilization improves. To reduce the impact of the CaD strategy on the quality of service (QoS) provisioning for the deferred users, a delay-dependent criterion is also applied. We show that the CaD significantly reduces both the dropping rate and the mean delay for the most restrictive traffic in a multi-service scenario, under a certain power and subcarrier allocation (PSA) algorithm that efficiently controls the inter-cell interference (ICI).

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper a digital correction method, which corrects these gain and phase imbalances, is implemented and verified. Commercial analog devices and a digital platform for signal processing purposes are used. The experimental results applied in an OFDM transmitter show a linearity improvement close to 20 dB without reducing the output power and without increasing the in-band distortion.

Abstract This paper focuses on the inter‐cell interference (ICI) management problem in the downlink channel for mobile broadband wireless OFDMA‐based systems. This subject is addressed from the standpoint of different interrelated resource allocation mechanisms operating in multi‐cell scenarios in order to exploit frequency and multi‐user diversity: ICI coordination/avoidance and adaptive subcarrier and power allocation. Even though these methods can be applied in a stand‐alone way, a significant performance improvement is achieved if they are jointly designed and operate in a combined basis. Several alternatives for mixed frequency and power ICI coordination schemes are proposed in this paper. Connected with a proper power mask‐based design, the potential gain of a flexible frequency sectorization solution, halfway between fractional/soft frequency reuse and pure frequency sectorization, is explored. The main objective is to outperform fractional/soft frequency reuse offering an attractive trade‐off between cell‐edge user data rates and average cell throughput. Proposals concerning ICI coordination/avoidance have been evaluated in combination with several heuristic adaptive subcarrier and power allocation algorithms. Copyright © 2009 John Wiley & Sons, Ltd.

In this paper, a comparative analysis of the performance of the non-synchronized initial random access channel in mobile WiMAX and E-UTRA systems under different conditions (fast fading, multiuser interference) is carried out. The analysis is focused on the correlation properties of the code sequences used in each case. We evaluate their ability to provide low values for false alarm and erroneous detection probabilities (detecting a sequence that has not been transmitted) at the same time as guaranteeing low non detection probabilities of the effectively transmitted sequences.

This work addresses the problem of inter-cell interference (ICI) management in the context of single frequency broadband OFDMA-based networks. Five proposals, based on a combination of ICI coordination/avoidance techniques along with a set of heuristic adaptive power and subcarrier allocation algorithms, have been considered in order to achieve better interference performance and resource utilization in a multi-cellular environment. Connected with a proper power mask based design, the potential gain of a flexible frequency sectorization solution, halfway between fractional/soft frequency reuse and pure frequency sectorization, is explored.

In this work we analyse the performance of a joint coding-precoding scheme for OFDM systems over fading channels. The design of the precoder is based on the information redistribution of the input modulated symbols amongst all the output precoded symbols. The proposed precoder decreases the variance of the instantaneous noise power at the receiver produced by the channel variability. In this sense, the noise at the output of the receiver deprecoding block can be considered as gaussian causing an improvement in the performance of the channel coding scheme employed in the system. The proposed system is evaluated under realistic radio channels which present multipath frequency-selective fadings and are affected by Doppler spread.

This paper presents the application of a reconfigurable impedance tuning network for a mobile DVB-H terminal. These kind of networks are becoming widely used in wireless communication systems to improve its efficiency. On the other hand, antenna design in DVB-H terminals is challenging due to the size limitation and as a result, the antenna presents large mismatches. To address this issue, we propose the use of a reconfigurable tuning network to reduce the mismatch (or the antenna size for a given mismatch) between the antenna and the RF front-end in a DVB-H terminal. This technique offers some advantages over other proposed alternatives and improves the antenna realized gain, as well as the efficiency of the DVB-H receiver.

This paper presents a new design of an automatic impedance synthesizer based on RF switches and its performance. A study about the implementation has been carried out and two prototypes of 50 Omega and 75 Omega of characteristic impedance have been successfully constructed. As switching elements in the tuning network we employ GaAs MMIC RF switches. An evaluation of impedance matching zones in the Smith chart has been carried out using simulations, taking into account both the return losses and the dissipative losses due to the physical implementation of the prototypes. Finally two prototypes of 50 Omega and 75 Omega have been constructed, verifying its correct operation.

Power amplifiers (PAs) are the most extended and widely used nonlinear devices in communications. Their non- linearities generate distortion both in amplitude and phase of the PA's output signal. The use of wideband efficient modulations in the last generation systems, such as wideband code-division multiple access (WCDMA) or orthogonal frequency-division multiplexing (OFDM), adds new problems to the use of PAs, due to the memory effects associated with the bandwidth and the increase of distortion by the non-constant envelope. In this paper it is shown the need of taking into account the memory effects in order to get a more accurate model of PA operation. We compare the performance of the memoryless model with some well-known memory models based on memory polynomials and Volterra series using a novel calibration signal.

Predistortion techniques are a well known power amplifier linearization method in order to reduce out-of band interferences in a non-constant envelope modulation system. A new adaptive digital predistorter based on the use of PSO (particle swarm optimization) algorithm is developed and applied in an orthogonal frequency-division multiplexing (OFDM) transmission scheme, such as a digital video broadcasting system. OFDM transmission is an efficient way to deal with multipath, being its implementation less complex than traditional equalizers, however, it is also very sensitive to nonlinear distortions due to its greatly variable envelope. The performance of this method has been verified by means of simulation using an amplifier characterized by a level-dependent complex gain using a memoryless model for different input power levels. In addition, the influence of some PSO parameters (the number of particles) on convergence is studied.

This paper proposes an automatically-adjusted linearization method based on the well-known linearization technique LINC (Linear amplification using Nonlinear Components) applied to the base station transmitter. A correction method of the gain and phase imbalances between both amplifying branches in a LINC transmitter is proposed to reduce the adjacent channel interference. A simple architecture is designed to compensate the unmatching between both branches being the adjusting coefficients calculated by means of a genetic algorithm. Several nonidealities are included in the analysis to deal with a realistic model, such as quadrature modulator imbalances, reconstruction filters and quantization error.

The high development that mobile networks and the provided services have experienced in the last few years has involved a great scientific and technical effort in order to support quality of service mechanisms for mobile users. In the case of mobile ad hoc networks (MANETs) this effort is even more noticeable due to the complexity of the dynamic environment of these networks. An appropriate resource allocation capable of integrating multimedia services with different requirements implies the design of efficient call admission control (CAC) techniques that in this ad hoc scenario require a distributed operation. This operation can be performed through a QoS routing process based on a cross-layer design. The interlayer cooperation allows to define new QoS metrics that reflect the network resource utilization and a bandwidth reservation carried out according to the different service demands during the path discovery guarantees the quality of the admitted connections

Wireless ad hoc networks require a complex resource management to efficiently exploit the networks resources due to the shared nature of the medium. The spatial reuse highly determines the network capacity, which can be increased through power control techniques. In this paper we propose and evaluate through simulation a MAC structure based on the adhoc MAC protocol. The actual interference produced by all the transmitting terminals is taken into account. In this scenario, we propose a solution to guarantee the reliability of the protocol. Moreover, we take advantage of the signaling information distributed by the adhoc MAC protocol to carry out an interference-aware power control scheme for the point-to-point data communications

The Feedforward linearization technique is a well-known power amplifier linearization method to reduce out-of-band distortion that can approach wideband signals with high efficiency. The Feedforward structure consists of two loops, where an accurate adjustment between them is necessary to ensure a correct behaviour. This adjustment must remain along the time to compensate for temperature, environmental and operating changes. Amplitude and phase imbalances of the circuit elements in both loops produce mismatched effects that lead to degrade the performance of the Feedforward technique. A method is proposed to compensate for these mismatches, introducing two complex gain coefficients calculated by means of a genetic algorithm. The method is applied to broadband systems based on OFDM modulation schemes. The OFDM transmission is an efficient way to deal with multipath, being its implementation less complex than traditional equalizers. This together with an efficient implementation, using the Fast Fourier Transform algorithm, has made it ideal for new technology. However, it is also very sensitive to nonlinear distortions due to its greatly variable envelope and high peak to mean envelope power ratio values. Therefore, Feedforward is a good linearization method for OFDM systems because simultaneously offers wide bandwidth and good nonlinear distortion suppression. The method functionality has been verified by means of simulation.

In this paper, a third-generation universal mobile telecommunications system (UMTS) solution for the delivery of biomedical information from an ambulance to a hospital is presented. The joint transmission of voice, real-time video, electrocardiogram signals, and medical scans in a realistic cellular multiuser simulation environment is considered, taking into account the advantages and particularities of UMTS technology for such transmission. The accomplishment of quality of service constraints for different services is investigated and quantitative results are provided in order to demonstrate the feasibility of using UMTS technology for emergency care services on high-speed moving ambulance vehicles.

In this paper, a multiservice transmission scheme is evaluated for the dedicated channel of the Universal Mobile Telecommunications System. The transmission rate for each service is determined according to its QoS requirements by means of an adaptive transport format selection. The proposed selection is based on buffer occupation, delay requirements and target bit rate, keeping power constraints. This power restriction depends on the estimated residual capacity and the contribution of this particular mobile user to the system load. Service multiplexing in upper layers (logical channels) sharing a common transmission rate (transport channel) has been evaluated by means of two different dequeueing strategies.

The linear amplification using nonlinear components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system, such as the OFDM modulation. The major drawback of LINC transmitters is the inherited sensitivity to gain and phase imbalances between the two amplifier branches. In this paper a novel adaptive full-digital base band method, which corrects any gain and phase imbalances in LINC transmitters mainly due to the un-matching between two branches, is described. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator impairments. A computer simulation has been carried out to verify method functionality.

Packet transmission combined with WCDMA (wideband code division multiple access) access technique defined in the Universal Mobile Telecommunication System (UMTS) provides high flexibility in resource allocation in order to integrate multimedia services with different requirements. However, this flexibility requires designing an efficient call admission control (CAC) able to control the number of active users in a system where capacity varies according with the level of interference. Taking into account the stochastic nature of multimedia traffic and the changes in the available capacity in the CDMA system, an effective capacity request is derived and used to characterize the resources required by each mobile user in order to meet its respective quality of service requirements. These requirements are expressed in terms of rate and delay constraints in addition to the signal to interference ratio. After setting an effective capacity threshold for the system, a linear approximation is used to find the total amount of resource required by all the mobile users already admitted in the system and the new connection request. Packet transmission is considered for both real time and non real time services while a centralized demand assignment algorithm has been implemented in order to provide QoS in the packet level. Performance in a multicell scenario and in time variant wireless channel conditions has been evaluated considering channel-stated scheduling algorithms. Computer simulation results are given to demonstrate the performance of the proposed method.

This paper analyses the effect of the propagation environment on the theoretical performance of the downlink transmit diversity techniques specified in the standard of the UTRA FDD mode. These techniques are classified as open loop and closed loop modes. Simulation results, obtained via a C simulator of the physical layer of UMTS, show the negative effect of mobility. The diversity gain obtained with the closed loop techniques, which are the best ones, drops drastically when the Doppler frequency rises. In that case, the open loop mode of diversity performs well. Nevertheless, it is highly dependent on the correlation of the antennas, which reduces the theoretical improvement.

The study of a digital Cartesian loop transmitter as power amplifier linearization technique is presented. It is based on the Cartesian loop architecture but introducing the advantages and possibilities of using digital solutions. Stability is assured by including some adjustment elements in the loop and the digital implementation avoids modulator and demodulator impairments and provides an accurate control and compensation of loop delay.

Fast power control is perhaps the most important aspect in a WCDMA system like UTRA-FDD. In this paper, closed loop power control procedures in UTRA-FDD are studied. A physical layer simulator, which has been implemented in the C language from the standard of the UTRA-FDD mode, has been the tool to get the results included in this research. Simulations have been made for different mobile speeds (3, 30, 50 and 120 Km/h) getting very different results. Power control gets worse quickly as the mobile speed grows. The implementation of an adaptive algorithm to predict the received power to try to improve the power control has been studied, but large improvements have not been obtained. The probability distribution of the power control error and influence of SIR estimation error have also been studied.

We present a computer-tool to simulate traffic over a mobile communications network based on TETRA (trans European trunked radio) technology. This tool is specifically orientated to estimate network performances, prior to network development, in order to make an optimum network design.

In this paper, we present a capacity analysis in order to set an effective threshold for connection admission control associated to the reverse link of a multimedia wireless communication system using CDMA. The analysis has been associated to the WCDMA concept defined in UMTS, where packet transmission has been considered for both real time and non real time services. A centralized demand assignment algorithm has been considered in the packet level in order to provide QoS, in terms of lost packet and delay constraints.

The paper presents a new design for an antenna input impedance automatic matching system. In order to achieve this main objective, it is necessary to accomplish several intermediate tasks. On the one hand, a study of the implementation of a generic electronically tunable impedance synthesizer is carried out. Then, a prototype based on the research is constructed, and its characteristics and improvements are evaluated. On the other hand, a fully automatic system is developed. The device is integrated inside a commercial mobile radio communications handset, in order to evaluate the improvements achieved with the automatic system. Experimental results about the influence of the human body on the input impedance of helical and monopole antennas are presented for the 380-400 MHz frequency band. Several control methods are studied.

This paper presents the performance analysis of different scheduling strategies suitable for transmission of real time and nonreal-time services in packetized form in the FDD mode of UMTS. A centralized demand assignment protocol is implemented to transmit over the dedicated physical channel. Given that in CDMA the capacity is not fixed and varies with the interference, the arrangement of transmissions is combined with a distributed power control that allows one to maximize the throughput by adjusting the transmitted power of terminals in order to minimize the interference. The scheduling strategies analyzed are based on the establishment of static priorities between classes of traffic combined with the assignment of dynamic priorities, associated with time stamps, to the individual packets belonging to a connection. Although scheduling based in time stamps offers differentiated quality of service to multimedia users, we have shown that the maintenance of the control channel (DPCCH) associated with data channel (DPDDH), when mobile stations MS are waiting their permit to transmit, is an important factor in the reduction of the capacity of system. So, this paper also considers that DPCCH are only present if mobiles are transmitting on DPDCH. In this case, the impact of imperfections in the power control mechanism is evaluated. Although results improve, simulations show that the mean and variance of the ratio between intercell and intracell interference grows, decreasing the global capacity. A new scheduling mechanism is proposed in order to improve the performance. The main idea is to limit the number of changes in the assignment of permits to transmit maintaining the permits to the same users as long as the delay tolerance of the waiting users allows it. A complementary priority is associated to the packets.

This paper presents an analysis of soft-output equalization and coding techniques applied to 4 and 16-QAM TDMA radio systems for frequency selective fading channels. In particular, typical urban and hilly terrain environments have been considered. The use of the soft information provided by the equalizer enhances the system performance considerably. Specifically, an improvement of more than 4 dB can be achieved in relation to hard decoding techniques. The necessity of introducing some interleaving in order to destroy the channel memory has also been stated. The actual investigated equalizers have been a soft-output decision-feedback equalizer (SODFE) and a soft-decision M-algorithm (SDMA) jointly with convolutional coding and both ideal and finite interleaving.

Presents an investigation of diversity and/or equalization techniques applied to 4 and 16-QAM TDMA radio systems for rapid fading dispersive channels. In particular, typical urban (TU) environments have been considered. A least sum of squared errors (LSSE) channel estimator has been introduced in order to allow the analytic calculation of the equalizer coefficients. By means of simulation methods the authors have found that a degradation of 4 dB can be expected in relation to ideal estimation. Furthermore, the degrading effects of non-linear power amplifiers have been analyzed and a degradation of 2 dB has been found.>