The promising growth of Electric Vehicles (EVs) places a mandate for a continuous increment in the power demand on the grid. To prepare for this directive, charging infrastructure plays a vibrant role. The future evolving technology for implementing charging infrastructure with the concept of no wait time to charge the battery is workable with a dynamic wireless charging system (DWCS). In this paper, the comprehensive assessment and performance analysis of solar PV-powered and the dc grid-powered DWCS is investigated. Further, the simulation is carried out through MATLAB software of version 2020a to examine and analyze the performance of the DWCS. Finally, it is observed that the solar PV-powered DWCS needs power help during the poor weather conditions which can be effectively executed by switching to the dc grid.

This paper focuses on the use of satellite communication systems for the support of Internet of Things (IoT). We refer to the IoT paradigm as the means to collect data from sensors or RFID and to send control messages to actuators. In many application scenarios, sensors and actuators are distributed over a very wide area; in some cases, they are located in remote areas where they are not served by terrestrial access networks and, as a consequence, the use of satellite communication systems becomes of paramount importance for the Internet of Remote Things (IoRT). The enabling factors of IoRT through satellite are: 1) the interoperability between satellite systems and sensors/actuators and 2) the support of IPv6 over satellite. Furthermore, radio resource management algorithms are required to enhance the efficiency of IoT over satellite. In this work, we provide an integrated view of satellite-based IoT, handling this topic as a jigsaw puzzle where the pieces to be assembled are represented by the following topics: MAC protocols for satellite routed sensor networks, efficient IPv6 support, heterogeneous networks interoperability, quality of service (QoS) management, and group-based communications.

Independent living of senior citizens is one of the main challenges linked to the ageing population, due to the impact on: (1) the life of the elderly people, (2) the national health systems, (3) the insurance companies, (4) the relatives and (5) the care-givers. Senior citizens may suffer from a number of diseases, including the decline in cardiopulmonary conditions, weaker muscle functions and a declined neuromuscular control of the movements, which result in a higher risk of fall and a higher vulnerability for cardiovascular and pulmonary diseases. With respect to cognitive functions, senior citizens may suffer from a decline of memory function, less ability to orientate and a declined ability to cope with complex situations. This paper describes work in progress and proposes a novel architecture design for eHealth services in support of independent living and compensating for prevailing age- or disease-related physical and cognitive impairments for a significant prolongation of the primary end-user's functional capacity, a delay in institutionalization, increased autonomy and, prolonged participation in the society.

Each user in the uplink of an Division Multiple Access (OFDMA) system may experience a different carrier frequency offset (CFO). These uncorrected CFOs destroy the orthogonality among subcarriers, causing inter-carrier interference and multi-user interference, which degrade the system performance severely. In this paper, novel time-domain multi-user interference cancellation schemes for OFDMA uplink are proposed. They employ an architecture with multiple OFDMA-demodulators to compensate for the impacts of multi-user CFOs at the base station's side. Analytical and numerical evaluations show that the proposed schemes achieve a significant performance gain compared to the conventional receiver and a reference frequency-domain multi-user interference cancellation scheme. In a particular scenario, a maximum CFO of up to 40% of the subcarrier spacing can be tolerated, and the CFO-free performance is maintained in the OFDMA uplink.

A distributed M2M local cloud platform which consists of distributed M2M gateways, needs to be equipped with an Intrusion Detection System (IDS) to monitor its resources against security attacks, especially from the insider, e.g. another gateway within the local cloud. In this paper, the interaction between rational attacker and defender in the context of an M2M local cloud platform as a multi-stage Bayesian game is studied. In this game formulation, a defender is able to update its belief upon the maliciousness of the attacker. The feasible Nash equilibrium of the game is reviewed and an analytical framework for the rational attacker and defender is provided for a given set of resources with different security values under some constraints on the attack and monitor resources. In the numerical analysis, it can be shown that by having multiple resources to be attacked and/or monitored simultaneously provides a kind of diversity which helps to improve the belief update of the defender.

Various methods and models have recently been proposed and applied for evaluating IP Multimedia Subsystem (IMS) in terms of reliability, availability and performance. End-to-end availability is one of the key factors that can improve the quality of service (QoS) and increase the reliability of Next Generation Networks (NGNs). In this paper, an end-to-end availability model is proposed and evaluated using a combination of Reliability Block Diagrams (RBD) and a proposed five-state Markov model. The overall availability for intra and inter domain communication in IMS is analyzed, and the state-of-the-art models are compared with the proposed novel Markov-based reliability modeling for both simplex and redundant systems. The proposed model is proved to efficiently represent the system behaviors. The effect of the end-to-end availability model when applying redundancy in the IMS core system is investigated and numerical results are included.

The last few years have seen the promising growth in the application of wireless sensor networks (WSNs). The contribution of this paper is on a cluster-based time division multiple access (TDMA) scheduling algorithm to improve the performance of WSN applications in terms of energy efficiency, delay, throughput and scalability. Cluster-based scheduling improves the scalability by stabilizing the topology and it also improves the delay by increasing the reuse of slots. The paper proposes the Green Conflict Free (GCF) algorithm for finding a conflict free schedule across three-hop neighbours for inter- and intra-cluster communication. The algorithm is applied to a multi-hop cluster and uses a conflict graph to find the conflict free schedule. It helps to reduce the number of conflicts. Compared to state-of-the-art solutions, the algorithm shows better energy efficiency, average delay, scalability and better slot sharing through a reduced number of conflicts.

This paper proposes a novel efficient admission control (AC) algorithm, which guarantees quality of service (QoS) for new users while maintaining QoS for existing users and also increases the number of users admitted in to the system. To guarantee the QoS, a Markov based modeling of the queue in the MAC layer is done by considering the effects of adaptive modulation and coding (AMC) in the physical layer. Using the Markov model, the number of resources required by the new user is predicted by taking the QoS requirements of the user application and channel parameters into consideration. The proposed AC algorithm is based on mean resource calculation, where the mean number of resources used by the existing users is calculated taking in to account the buffer conditions of users. The efficiency of AC algorithm is measured w.r.t number of users admitted in the system. The AC algorithm is verified on a Long Term Evolution (LTE) system and simulations show a 10% increase in the number of users and a decrease in the dropping probability.

Spectrum sensing is a key component for enabling the cognitive radio paradigm. In this paper, we propose a novel totally-blind spectrum sensing technique for cognitive radio device equipped with multiple antennas, namely the Space Frequency Cross Product Sensing (SFCPS) algorithm. Existing correlation-based spectrum sensing techniques rely on the assumption that the received signals are correlated and their performance becomes poor when the signal correlation is low. By appropriately combining the received signals from multiple antennas, the proposed method creates new signals that are fully correlated and on which a sensing method is developed. SFCPS performs better than existing correlation-based techniques and with a lower computational complexity for small number of observed samples.

Space-time coded cooperative transmission has been proposed as a means to prolong the battery lifetime of conventional single-antenna energy-constrained wireless sensor nodes. However, newly proposed smart-antenna sensor prototypes enable the existence of more than one antenna within a single-radio transceiver architecture. Exploiting such capability, this paper proposes simple non-cooperative space-time techniques for single-RF switched-antenna systems that reduce significantly both the transmission and the circuit energy consumption. The energy savings of the suggested schemes are shown not only against conventional SISO systems, but also against cooperative diversity schemes in Rayleigh and log-normal shadowed Rayleigh fading channels with distance-based path loss.

In wireless sensor networks, one of the key challenge is to achieve minimum energy consumption in order to maximize network lifetime. In fact, lifetime depends on many parameters: the topology of the sensor network, the data aggregation regime in the network, the channel access schemes, the routing protocols, and the energy model for transmission. In this paper, we tackle the routing challenge for maximum lifetime of the sensor network. We introduce a novel linear programming approach to the maximum lifetime routing problem. To the best of our knowledge, this is the first mathematical programming of the maximum lifetime routing problem that considers the operation modes of the node. Solution of the linear programming gives the upper analytical bound for the network lifetime. In order to illustrate the application of the optimization model, we solved the problem for different parameter settings for an example network.

The International Telecommunication Union (ITU) established new requirements for the next generation of wireless communications. To meet those requirements, the concept of femtocells emerged as a solution, aiming at increasing capacity and offloading the macrocell network. In a co-channel deployment between macrocells and femtocells, the interference is a serious problem and that needs to be addressed. Since the femtocells are deployed by the end-user, the operator does not have a pre-planned solution to avoid interference, thus a self-organizing solution between femtocells located in the same area is required to manage the interference. In this paper we propose a flexible spectrum usage algorithm which runs at the femtocells, while the macrocells use a fixed reuse scheme in order to manage the interference in the network. In this study we verify that by assigning a fixed reuse scheme 1/3 for the macrocells, the performance achieved by the users is higher, when comparing the same scenario with reuse 1. We also propose a flexible spectrum usage algorithm for the femto cell, which is able to achieve higher user throughput in the femto layer and minimize the interference in the macro layer, when compared to a non-channel aware algorithm, which allocates the PRBs randomly.

This paper proposes a robust voice activity detector (VAD) based on the observation that the distribution of speech captured with far-field microphones is highly varying, depending on the noise and reverberation conditions. The proposed VAD employs a convex combination scheme comprising three statistical distributions - a Gaussian, a Laplacian, and a two-sided Gamma - to effectively model captured speech. This scheme shows increased ability to adapt to dynamic acoustic environments. The contribution of each distribution to this convex combination is automatically adjusted based on the statistical characteristics of the instantaneous audio input. To further improve the performance of the system, an adaptive threshold is introduced, while a decision-smoothing scheme caters to the intra-frame correlation of speech signals. Extensive experiments under realistic scenarios support the proposed approach of combining several models for increased adaptation and performance.

In this paper an analysis on the use of Adaptive Coding and Modulation (ACM) techniques for EHF satellite communications is presented. In particular, our analysis is focused on W-band channels and includes the main channel impairments in this frequency band, i.e. rain fading and HPA non-linearity. The aim of the analysis is to identify modifications to the ACM mode switching algorithm to optimize their use at those high frequency bands.

A novel orthogonal space time block code (OSTBC) that is capable of extracting a diversity order of two via a single RF frontend is proposed in this paper. The scheme is implemented using a practical antenna system of two transmit antennas connected to a common ground. An orthogonal block of two real (non-complex) signals is transmitted over a duration of two symbol periods by exciting one antenna every symbol period while exciting the other parasitically by the field of the active one. A switched-antenna system similar to the one reported in [10] can be used for simultaneously driving and switching the antenna elements. Besides the orthogonality of the signals, the array far-field is a linear mixture of two eigenpatterns onto which the BPSK signals are mapped, hence independent fading among the signals is almost always guaranteed.

Disaster relief networks have to be highly adaptable and resilient. Cognitive radio enhanced ad-hoc architecture have been put forward as a candidate to enable such networks. Spectrum sensing is the cornerstone of the cognitive radio paradigm, and it has been the target of intensive research. The main common conclusion was that the achievable spectrum sensing accuracy can be greatly enhanced through the use of cooperative sensing schemes. When considering applying Cognitive Radio to ad-hoc disaster relief networks, spectrum sensing cooperative schemes are paramount. A centralized cluster-based orchestration cooperative sensing scheme is proposed, where the cluster head controls and adapts the distribution of the cluster sensing's nodes according to the monitored spectrum state. The proposed scheme performance is evaluated through a framework, which allows gauging the accuracy of wideband multi-channel spectrum sensing cooperative schemes, showing that the proposed scheme performance reaches the theoretical maximum achievable accuracy while outperforming the round robin scheme.

The downlink performance of systems exploiting multiuser diversity has been shown to improve by using multiple antenna receivers and diversity combining techniques. However, the cost and power restrictions of the user mobile terminals prohibit the use of multiple antennas whereas the size limitations can result in correlated and coupled receive antenna elements downgrading the effectiveness of the applied schemes. In this paper, we propose a simple beam selection combining (SC) technique using a miniaturized single radio receive antenna system assisted by low cost parasitic antennas. The system is optimized for both antenna efficiency and diversity thus made capable of forming four practically uncorrelated beam-patterns. The computer simulations show that the proposed beam SC technique outperforms classical antenna SC as well as a previously reported beam combining approach in terms of the average throughput especially for small user populations.

Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square error (MMSE) principle. The paper shows that the proposed receiver is able to work also in highly time-variant channels where a traditional frequency domain equalizer gets very bad performance. Moreover, it is shown that this joint time-frequency equalization is able to exploit time diversity without coding. The performance of the proposed equalizer are shown both in case of perfect channel estimation and in presence of a MMSE linear channel estimator.

Disaster relief networks need to be highly adaptable and resilient in order to encompass the emergency service demands. Cognitive Radio enhanced ad-hoc architecture have been put forward as candidate to enable such networks. Spectrum sensing, the cornerstone of the Cognitive Radio paradigm, has been the target of intensive research, of which the main common conclusion was that the achievable spectrum sensing accuracy can be greatly enhanced through the use of cooperative sensing schemes. When considering applying Cognitive Radio to ad-hoc disaster relief networks, the use of spectrum sensing cooperative schemes becomes essential. A cluster based decentralized orchestration cooperative sensing scheme is proposed, where each node in the cluster decides which spectrum it should monitor, according to the past sensing decisions of all the cluster nodes. The proposed scheme performance is evaluated through a framework, which allows gauging the accuracy of multi narrow-band spectrum sensing cooperative schemes as well as to gauge the error in the estimation of each of the channels un-occupancy. Through that evaluation it is shown that the proposed decentralized scheme performance reaches the performance of the correspondent centralized scheme while outperforming the Round Robin scheme.

Wireless Personal Area Networks (WPANs) are short-range ad-hoc networks centered around a person that make use of unlicensed bands for data transmission. Two complementary types of standards have been proposed by IEEE working groups for both High Data Rate (HDR) and Low Data Rate (LDR) WPANs. However, because of the unlicensed nature of WPANs, interference issues exist between uncoordinated WPANs. These interference issues are particularly severe when two or more nodes are closely located (e.g. in a multimode LDR/HDR device). This paper proposes a novel collaborative coexistence mechanism named Alternating Wireless Activity (AWA, patent pending) between a HDR WPAN based on the standard IEEE 802.15.3 and a LDR WPAN based on the standard IEEE 802.15.4. The AWA coexistence mechanism does not require any modification to the mentioned standards because it exploits their already available features.

The trend on the proliferation of handheld devices triggered an increase on the development of pervasive and personalized mobile applications that exploit and support peer-to-peer/ad-hoc networks. This creates the conditions and motivation for a mobile electronic ID system, preferably one which provides a friendly privacy solution. The existing mobile identification solutions place the interviewer in a more authoritative position than the interviewee, while little or no privacy control is applied by the interviewee. With the mobile ID system (MobIS), this paper proposes a universal mobile ID system which is suitable for various scenarios (e.g. for professional, medical, or official uses) in a heterogeneous network environment. Such systems are highly prone to security and privacy threats, so a context aware privacy mechanism is developed in the proposed framework. The security and privacy frameworks are elaborated, and a demonstration of the prototype is presented in this paper.

A universal scheme for encoding multiple symbol streams using a single driven element (and consequently a single radio frequency (RF) frontend) surrounded by parasitic elements (PE) loaded with variable reactive loads, is proposed in this paper. The proposed scheme is based on creating a MIMO system by expanding the far-field of a compact parasitic array into an orthogonal set of angular functions (basis). Independent information streams are encoded by means of angular variations of the far-field in the wavevector domain, rather than spatial variations as usually happens in conventional MIMO systems. The array can spatially multiplex the input streams by creating all the desired linear combinations (for a given modulation scheme) of the basis functions. The desired combinations are obtained by projecting the ratio of the symbols to be spatially multiplexed on the ratio of the basis functions' weights (complex coefficients), which is a function of the currents induced on the PE within the antenna domain, and controlled by the independent reactive loadings.

This letter addresses the application of Linear Dispersion Codes (LDC) in space and frequency domains in Single Carrier-Frequency Domain Equalization (SCFDE) systems. Space-frequency (SF)-LDCs are more suitable than space-time (ST) LDC in high mobility environments. However, the application of LDCs in space and frequency domains in SCFDE systems is not straightforward as in orthogonal frequency division multiplexing (OFDM) systems because in this case there is no direct access to subcarriers at the transmitter. This letter shows that it is possible to induce a target SF symbol dispersion in SCFDE by using a simple linear pre-coder and a conventional LDC that spreads the symbols in time and space domains according to specific ST dispersion matrices. The letter shows how to derive the ST dispersion matrices to be used at the transmitter as a function of the dispersion matrices describing the target SF dispersion. The presented procedure can be applied to both pure transmit diversity and pure multiplexing schemes, which are special cases of LDCs. Therefore, the proposed scheme provides a low complexity implementation of any dispersion in space and frequency over SCFDE systems, which alternatively would require the use of FFT/IFFT also at the transmitter side. The letter also shows a performance comparison of SF-LDCs and ST-LDCs in a typical propagation environment for future radio systems. The comparison confirms the suitability of using the dispersion in frequency rather than time for a wide range of coherence bandwidths.

This paper proposes a novel interference cancellation technique using the concept of a distributed array, for the secondary use of the frequency resources in frequency division duplexing (FDD)-based cellular systems. In order to achieve efficient distributed interference cancellation, the secondary system exploit intervals for periodic training signals transmitted by FDD-time division multiple access (TDMA)-based cellular systems. We show that an efficient interference cancellation can be achieved by introducing helpers that decode the interference and transfer it to the secondary nodes. We take advantage of the high-speed links within the secondary system and devise a data compressing scheme that reduces time for transferring the decoded interference. We clarify the effectiveness of the proposed scheme by using computer simulation. As a parameter, the transmission quality between the helper and secondary nodes is varied. The results indicate that the proposed distributed interference cancellation is effective compared to a conventional adaptive array using a zero forcing algorithm, when the signal to noise ratio between the helper and the target secondary node is greater than 20 dB.

In wireless communication systems, the signal strength/quality generally varies with the distances between transmitters and receivers. As a consequence, the throughput in the MAC layer (or the transmission data rate in the PHY layer) also varies accordingly. In this paper, we call this phenomenon as the rate-distance nature of the wireless communications. Inspired by our success in the study of the random distances between nodes in the wireless ad hoc networks, we pioneer employing the distance-related concept to study the rate-distance nature of the multiple access protocols. By selecting slotted Aloha as a pilot multiple access protocol, we successfully analyze and demonstrate the rate-distance adaptability of slotted Aloha with finite and infinite populations. We also demonstrate how the rate- distance concept can be applied to the rate adaptation of the MAC protocol in the cognitive radio.

Recently, Personal Networks (PNs) have been focused in supporting the userpsilas business and private activities without jeopardizing privacy and security of the users and their data. The support in business and private activities will take place through the userpsilas own personal network consisting of a core Personal Area Network (PAN) extended with clusters of remote devices which could be private, shared, or public and able to adapt to the quality of the network accessed. The extended PAN with its cluster communication with another PN forms a Federation of Personal Networks (PN-F). PN-F is a secure cooperation between different PNs, making services and resources available for the purpose of achieving a common goal, increasing the security requirements and challenges. The communication in this scenario can happen in various places (home, work, public places), involving various types of network infrastructure, between various types of hardware, and exchanging any kind of service. Context aware security manager (CASM) has been proposed to solve the PN security issue, putting all the security decision in the gateway between PAN and cluster or PN and another PN. CASM relies on providing security policy based on the context being given by user. So far, algorithm regarding how to input the context has not yet been defined. Furthermore, how CASM react upon the context in deciding what security action should be performed has also not yet been elaborated. This paper will analyze the impact of context to security. The paper will work as a continuation of CASM by elaborating further a proposed algorithm on defining the context parameters, quantifying context parameter so that CASM can make decision upon it, and optimizing the matrix of context information.

The evolution of air interfaces for 4G wireless systems often appears as an OFDM-CDMA battle which OFDM is going to win. This paper reviews this point of view and highlights some other features of this evolution. The paper presents a novel multicode DS-CDMA scheme which has the same advantages as OFDMA over frequency selective channels: good performance with low complexity one-tap receiver. Actually, OFDMA can be seen as a special case of the proposed scheme. The analysis of this scheme will help identifying the main features of the evolution of the air interfaces towards 4G.

The future broadband wireless cellular systems Evolved UTRAN (E-UTRAN) and WiMAX are receiving a lot of interest in recent years. Both systems deploy Orthogonal Frequency Division Multiplex (OFDM) physical layer consisting of large number of mutually orthogonal sub-carriers. This physical layer provides high robustness against multi-path effects, high flexibility in allocation of the physical resources, high bandwidth scalability and relatively easy combination with Multiple-Input-Multiple-Output (MIMO) transmission and reception. In this study we investigate several algorithms for allocation of the downlink resources for E-UTRAN and WiMAX cellular systems. The goal of the study is to see the differences in downlink sector and user throughput, and user throughput versus distance from the reference base station for the resource allocation algorithms: Reuse-one, Reuse-three, Soft re-use, Reuse partitioning, Proportional Fair and Maximum C/I. Additionally, we observe the difference in performance between E-UTRAN and WiMAX under the conditions selected in this study. The evaluations are done via MATLAB simulations of a cellular system with one central three-sectored site surrounded with two tiers of interfering three-sector sites.

This paper proposes a generalized carrier frequency offset (CFO) estimator for the uplink of orthogonal frequency division multiple access (OFDMA) wireless systems. Using the maximum likelihood criterion, the estimator estimates CFOs using the phase shift between two observation windows at distance less than the length of OFDMA symbol. The scheme offers the possibility to shorten the OFDMA preamble used in synchronization, and thus reduce overhead in packet-based wireless communications.

In wireless communication systems, the signal strength/quality generally varies with the distances between transmitters and receivers. As a consequence, the throughput in the MAC layer (or the transmission data rate in the PHY layer) also varies accordingly. In this paper, we call this phenomenon as the rate-distance nature of the wireless communications. Inspired by our success in the study of the random distances between nodes in the wireless ad hoc networks, we pioneer employing the distance-related concept to study the rate-distance nature of the multiple access protocols. By selecting slotted Aloha as a pilot multiple access protocol, we successfully analyze and demonstrate the rate-distance adaptability of slotted Aloha. We also demonstrate how the rate-distance concept can be applied to the rate adaptation of the MAC protocol in the cognitive radio.

Orthogonal frequency division multiplexing based wireless systems are spectrally efficient, but they are vulnerable to inter-carrier interference (ICI). In a wide area scenario, users will experience varying signal strength due to different individual path loss and also varying amount of Doppler spread because of their independent velocities. Therefore, the ICI among users will vary over a wide range. It is proposed in this work to use dynamically adaptive sub carrier bandwidth (ASB) along with adaptive bit loading to mitigate ICI in such conditions, which will keep receivers simple while maintaining maximum throughput in each situation. Results show that ASB can provide higher throughput than its fixed sub carrier bandwidth counterpart when both may use adaptive bit loading per sub carrier.

We propose generic relay and subcarrier allocation schemes for multicarrier (MC) system with amplify-and-forward (AF) relays. The outage probability bounds are derived analytically for each scheme. Simulation results show that these bounds are very tight and better than the bounds obtained straightforwardly from the analysis in the Single-Carrier (SC) case. This is because in our analysis we reckon with the increased degree of freedom brought by the parallel channels. One of the proposed schemes, the Average Best Relay Selection scheme, is best suited for practical implementation since it approaches the best performance while minimizing the required amount of signaling.

In this paper, a low complexity transmit diversity scheme for single carrier-frequency domain equalization (SCFDE) is proposed, which is robust in high time-selective channels, (i.e. in high mobility environments), when the channel cannot be assumed constant over two consecutive processed symbols. The proposed scheme is equivalent to space-frequency block code (SFBC) for orthogonal frequency division multiplexing (OFDM) systems. However, the extension of SFBC to SCFDE systems is not straightforward since in SCFDE systems there is no direct access to subcarriers at the transmitter. The proposed scheme outperforms SCFDE-space-time block code (STBC) over fast fading channels also in high frequency selective channels, with a slight decrease in the overall complexity (in terms of complex multiplications).

Orthogonal Frequency Division Multiplex (OFDM) based wireless communication is becoming a standard for providing broadband wireless services. OFDM is already deployed in various WLAN systems such as 802.11 a/g/e and in the mobile WiMAX systems (802.16e). The OFDM physical layer is also considered by 3GPP for the Long Term Evolution (LTE) of UMTS. The OFDM based physical layer enables a so-called Orthogonal Frequency Division Multiple Access (OFDMA) where the total number of sub-carriers is divided in distinctive sets and consequently allocated to different users. This study evaluates several algorithms for allocation of the sub-carrier sets for the downlink direction. The performance comparison is based on the sector throughput, user throughput and the average user throughput versus the distance from the reference sector. We have performed the evaluations based on simulations of a UMTS-LTE system.

This paper presents a general framework for applying the Linear Dispersion Codes (LDC) in the space and frequency domains to Single Carrier - Frequency Domain Equalization (SCFDE) systems. Space-Frequency (SF)-LDC are more suitable than Space-Time (ST)-LDC in high mobility environment. However, the application of LDC in space- frequency domain in SCFDE systems is not straightforward as in Orthogonal Frequency Division Multiplexing (OFDM), since there is no direct access to the subcarriers at the transmitter. This paper describes how to build the space-time dispersion matrices to be used at the transmitter as a function of the desired dispersion matrices in the space and frequency domains. The performance comparison of SF-LDC and ST-LDC in a typical propagation environment for future radio systems confirms the suitability of using the dispersion in frequency instead of in time. The sensitivity of SF-LDC with respect to different levels of time and frequency selectivity is also shown.

In a real cellular system, existence of a number of multi-antenna schemes in neighboring cells means that different multi-antenna schemes will experience co-channel interference (CCI) from the same or other multi-antenna schemes. In this work, we have summarized our analysis and simulations related to cellular interference of some specific multiple input multiple output (MIMO) schemes on the same and other MIMO schemes. The goal is to study the impact of interference from MIMO schemes at a user located in the cell edge. Semi-Analytical evaluations of signal to interference and noise ratio (SINR) is done to find out the SINR statistics of different combinations of desired and interfering links. We have studied linear combining receivers for all the link combinations. Based on the current analysis, it is found that space-time block code (STBC) is a severe interferer compared to others, and specific attention is needed to counter the interference introduced by STBC interfering link.

In order to fully exploit wireless radio resource and then increase spectrum efficiency, cognitive radios shall sense and cognize environments so that the secondary system(s) may coexist with primary communication systems. In this paper, we acquire an effective set of cognitive information under a proposed spectrum sensing cycle for orthogonal frequency division multiple access (OFDMA) systems. To avoid interfering with primary systems, detecting existence of the primary system by tracking fundamental symbol rate of the primary system and measuring RSSI is the first step in coexistence. Furthermore, using cyclic property of OFDMA signal, we can precisely determine existence of a specific OFDMA system and its frequency band, via Neyman-Pearson criterion. Simulation results show that near perfection detection is achieved even at low SINR. With a priori knowledge of frame structure in potential primary systems, communication parameters, such as data transmission rate and resource allocation, are extracted by decoding frame header. Finally, we can determine available radio resource with respect to cognitive radios using rate-distance relationship, while guarantee interference to primary systems. Moreover, by parametric adjustment, our sensing procedure can be applied to any state-of-the-art OFDMA systems nowadays.

Orthogonal frequency division multiplexing (OFDM) is widely used in wireless systems because of its high spectral efficiency, though it is known that it is highly vulnerable to frequency synchronization errors, which severely impede its performance. Such errors arise due to carrier frequency offset and Doppler frequency spread. They destroy the orthogonality among sub carriers and introduce inter carrier interference (ICI). The interference power is proportional to the received signal strength and amount of frequency offset. Several proposal to reduce the impact of ICI in OFDM use very complex signal processing and some have associated bandwidth efficiency loss. Since ICI is inversely proportional to the sub carrier bandwidth, it is interesting to investigate the gains in a system with adaptable sub carrier bandwidth. A system which can support variable sub carrier bandwidths simultaneously meeting the needs of different ICI conditions is compared against a normal OFDM system which uses fixed carrier bandwidth (FSB). Results show that the VSB schemes can be preferred over FSB OFDM system when users with different receive signal strength and Doppler condition have to be served simultaneously.

The impact of high power amplifier (HPA) on the performance of orthogonal frequency division multiplexing (OFDM) based wireless systems using link adaptation (LA) is analyzed in this work. LA maximizes throughput while maintaining a target bit error rate (BER) at the receiver. The non linear behaviour of the HPA introduces distortion in the OFDM signal which has high peak to average power ratio (PAPR). It is found in this work that this causes LA schemes to fail to meet the target BER. It is shown in this work that to make the LA system satisfy the BER constraint, the signal to noise ratio thresholds for changing the adaptive modulation needs to be updated.

In orthogonal frequency division multiplexing (OFDM) systems, there are several degrees of freedom in time and frequency domain, such as, sub-band size, forward error control coding (FEC) rate, modulation order, power level, modulation adaptation interval, coding rate adaptation interval and power adaptation interval, which can be exploited for link adaptation to achieve high spectral efficiency. The variable channel parameters such as delay spread, Doppler frequency spread, average signal to noise ratio and instantaneous channel gains influence the link adaptation parameters. Optimal adaptation of the link parameters based on the channel conditions would lead to highly complex systems with high overhead. Hybrid strategies to vary the adaptation rates to tradeoff achievable efficiency and complexity are presented in this work.

In this paper, the possibility for a short-range cognitive radio (secondary communication system) to be located within the service area of the primary system is discussed. Although the secondary system interferes with the primary system, there can be certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without disturbing it or being disturbed by the primary system. We say that in those locations there is a spatial opportunity for communication in the secondary system. The primary and secondary systems have different features and usage scenarios, which result in different deployment conditions. This gives rise to differences between the path loss for a link in the primary system and the path loss for the interference from the primary to secondary systems. This paper investigates the impact of the heterogeneous path loss conditions on the spatial opportunity for the secondary system. Our approach can be applied as a general way to investigate the coexistence among multiple systems. We clarify that the change of the path loss coefficient due to the different antenna heights of the primary and secondary systems can largely affect the spatial opportunity for frequency reuse by the cognitive radios.

Co-Channel Interference (CCI) caused by different Multiple Input Multiple Output (MIMO) signalling schemes impact the same or other MIMO schemes in different ways. Due to the symbol-by- symbol processing in a desired Single Input Multiple Output (SIMO) link, an interfering Space-Time Block Code (STBC) link may become equivalent to an interfering Spatial Multiplexing (SM) link. Using this knowledge and understanding, we propose an interference cancellation receiver robust to different types of MIMO interferers at cell edge for the Downlink (DL) of cellular systems. The receiver systematically performs a multiple symbol processing: this is the appropriate processing when the signal of interest or the signal of interferer is correlated across symbols, which is the case for STBC transmission. We evaluated different link combinations in terms of Signal to Interference and Noise Ratio (SINR) statistics and Bit Error Rate (BER) performance in cellular Orthogonal Frequency Division Multiple Access (OFDMA) . We have found that the proposed multiple-symbol linear interference cancellation receiver performs satisfactorily when any kind of single 'logical' stream MIMO scheme is present as interferer.

Cyclic delay diversity can be used to increase the frequency selectivity of the wireless channel seen from the receiver. In this work, we have used this simple technique on top of a spatial multiplexing based orthogonal frequency division multiplexing system. In our analysis, it is found that nearly 2 b/s/Hz of 10% outage capacity improvement can be achieved on a basic 2times2 system. This is achieved with little changes at any standard spatial multiplexing system. Also, the number of transmit antennas can be increased to increase the link capacity without making any changes to the receiver. Thus, the proposed technique can be used with any existing MIMO-OFDM system. We have shown significant improvement in FER by using this scheme compared to a simple spatial multiplexing scheme.

In this work, we have studied bit and power allocation strategies for multi-antenna assisted Orthogonal Frequency Division Multiplexing (OFDM) systems and investigated the impact of different rates of bit and power allocations on various multi-antenna diversity schemes. It is observed that, if we cannot find the exact Signal to Noise Ratio (SNR) thresholds due to different reasons, such as reduced Link Adaptation (LA) rate, Channel State Information (CSI) error, feedback delay etc., it is better to fix the transmit power across all sub-channels to guarantee the target Frame Error Rate (FER). Otherwise, it is possible to use adaptive power distribution to save power, which can be used for other purposes, or to increase the throughput of the system by transmitting higher number of bits. We also observed that in some scenarios and in some system conditions, some form of simultaneous bit and power allocations across OFDM sub-channels are required together for efficient exploitation of wireless channel.

In this article the performance of orthogonal frequency division multiplexing (OFDM) systems with dynamically adaptable sub carrier bandwidth to mitigate inter carrier interference (ICI) is compared against standard OFDM systems with fixed sub carrier bandwidth. In current OFDM system, the sub carrier bandwidth or sub carrier spacing is a fixed design parameter. This is not efficient since the optimum sub carrier bandwidth depends on ICI, which is a function of several parameters such as residual frequency offset, Doppler frequency spread, received signal strength and carrier frequency. Existing algorithms to combat ICI are very complex and sometimes reduce bandwidth efficiency. As an alternative approach, it is worth verifying the benefits of using adaptive bandwidth for sub carrier (ABS). A method for implementing the above scheme is given. Results show that this type of adaptive OFDM scheme has the potential to provide a significant improvement in performance over OFDM systems which use fixed sub carrier bandwidth.

Frequency Hopping (FH) technology has been widely used for short-range networks operating in unlicensed band. As the short-range FH networks gain momentum in ubiquitous usage, the interference that collocated FH networks cause to each other, termed self-interference, becomes one of the major sources that degrade the communication performance. This paper proposes the Adaptive Frequency Rolling (AFR), a particular adaptive instance of FH that enables FH networks to cooperate and effectively avoid the self-interference. The AFR uses as input solely the observed packet error rate (PER) and it does not require any exchange of information among the collocated networks. The effect of the AFR over a longer time interval is that the networks use the complete set of disposable channels in an implicit time-division and cooperative manner. The parameter choice is such that a network which uses AFR never occupies the channels in the unlicensed spectrum more than what is permitted by the current regulation. AFR is designed to be robust towards the noise-induced channel errors. We also design AFR with probing (AFR-P), a modified version of AFR, which can also overcome frequency-static interference from collocated non-FH network by introducing channel removal strategy with probing. Our simulation results show that AFR and AFR-P have superior goodput performance to pseudorandom frequency hopping (PFH), and also standard adaptive frequency hopping (AFH), where the latter is designed to exclusively combat frequency-static interference. All these features promote the great potential of AFR as a coexistence mechanism for unlicensed operation

Along with a vision that foresees the fourth generation (4G) as based on a cellular system that will also support short-range communications among its terminals, in this paper we propose an innovative geolocation scheme that exploits such an architecture and combines long- and short-range location information in a novel location algorithm. The simulation results presented in the paper show that our proposed scheme permits to enhance the location estimation accuracy with respect to the actual stand-alone hybrid cellular solutions.

An algorithm for implementing variable guard interval (VGI) in Orthogonal Frequency Division Multiplexing (OFDM) based wireless networks is presented in this article. The required guard interval is derived as a function of the root mean square (rms) delay spread of the channel, time duration of discrete fourier transform used in OFDM and the required signal to noise ration (SNR). In this work the algorithm has been verified in a highly dynamic channel condition and results show that the algorithm can reduce guard interval significantly and is also found to be robust against time variation of rms delay spread and mean excess delay of the channel.

The design of spectrally efficient and robust schemes is vital to overcome the harsh wireless environment when delivering high data rate services. In the present paper, the performance of a constant power and discrete rate adaptation scheme is evaluated in a multiple antenna scenario. Such a technique has low complexity, and needs a low rate feedback channel to adapt the transmission rate. However, the feedback can become outdated when the channel is rapidly changing. In the light of the feedback delay, the authors propose to analyze the effect of outdated channel information. Closed form expressions are obtained for the bit-error-rate (BER) performance for MIMO diversity, and spatial multiplexing (SM) schemes. Through simulation results, we analyze the impact of feedback delay on the BER. The feedback delay proves to have different impact on each of the MIMO scheme when coupled to a rate adaptive system. We demonstrate that antenna selection suffers more from feedback delay than other diversity schemes. The results can be used to assess the performance of different MIMO techniques, and may be applied to a switching mechanism, where, at each instant, the channel behavior is analyzed and the best fit MIMO mode is selected

We consider the uplink of an orthogonal frequency division multiple access (OFDMA)-based system, where each mobile station (MS) experiences a different carrier frequency offset (CFO). Unconnected CFOs destroy the orthogonality among subcarriers, which could cause severe inter-carrier interference (ICI) and degrade the system performance considerably. In this paper, we propose a novel multi-user interference (MUI) cancellation scheme for uplink OFDMA, which utilizes multiple orthogonal frequency division multiplexing (OFDM)-demodulators architecture to correct and then compensate the negative effects of multiple CFOs at the receiver's side. Numerical evaluation has shown a considerable performance gain compared to the conventional receiver

Several multi-carrier spread spectrum (MC SS) access techniques which are based on Orthogonal Frequency Division Multiplexing (OFDM) have been developed till date. Different schemes are expected to perform optimally in different channel conditions. Their performance is also influenced by receiver impairments, such as synchronization error and channel estimation errors. This work is targeted towards unified verification of performance of the schemes for different spreading gains, load conditions and sub carrier grouping schemes in quasi static realistic indoor channel environment in the presence of carrier frequency offset and channel estimation error for sub carrier hopping and non hopping systems. The results presented in this article will prove very important in deciding on a robust access scheme and its relevant parameters for down link indoor wireless local area networks.

In this work, we have combined quasi-orthogonal space-frequency block code (QSFBC) and spatial multiplexing (SM) in one joint diversity and multiplexing (JDM) structure. Minimum mean square error (MMSE) and zero forcing (ZF) nulling based ordered successive interference cancellation (OSIC) receivers are derived for above mentioned JDM scheme. Performance comparison is done in realistic wireless scenario. It is observed through simulations that our JDM scheme performs very well in presence of spatial correlation caused by antenna separation and by line of sight (LOS) situation. The gains in frame error rate (FER) and outage spectral efficiency for JDM schemes with studied receivers are very high compared to corresponding SM only schemes.

Network mobility introduces far more complexity than host mobility. Therefore, host mobility protocols such as Mobile IPv6 (MIPv6) need to be extended to support this new type of mobility. To address the extensions needed for network mobility, the IETF NEMO working group has recently standardized the network mobility basic support protocol in RFC 3963. However, in this RFC, it is not mentioned how authentication authorization and accounting (AAA) issues are handled in NEMO environment. Also, the use of IPsec to secure NEMO procedures does not provide robustness against leakage of stored secrets. To address this security issue and to achieve AAA with mobility, we propose new handover procedures to be performed by mobile routers and by visiting mobile nodes. This new handover procedure is based on leakage resilient-authenticated key establishment (LR-AKE) protocol. Using analytical models, we evaluate the proposed handover procedure in terms of handover delay which affects the session continuity. Our performance evaluation is based on transmission, queueing and encryption delays over wireless links

Wireless networks beyond 2G aim at supporting real-time applications such as VoIP. Before a user can start a VoIP session, the end-user terminal has to establish the session using signaling protocols such as H.323 and session initiation protocol (SIP) in order to negotiate media parameters. The time interval to perform the session setup is called the session setup time. It can be affected by the quality of the wireless link, measured in terms of frame error rate (FER), which can result in retransmissions of packets lost and can lengthen the session setup time. Therefore, such protocols should have a session setup time optimized against loss. One way to do so is by choosing the appropriate retransmission timer and the underlying protocols. In this paper, we focus on SIP session setup delay and propose optimizing it using an adaptive retransmission timer. We also evaluate SIP session setup performances with various underlying protocols (transport control protocol (TCP), user datagram protocol (UDP), radio link protocols (RLPs)) as a function of the FER. For 19.2 Kbps channel, the SIP session setup time can be up to 6.12 s with UDP and 7 s with TCP when the FER is up to 10 percent. The use of RLP (1, 2, 3) and RLP (1, 1, 1, 1, 1, 1) puts the session setup time down to 3.4 s under UDP and 4 s under TCP for the same FER and the same channel bandwidth. We also compare SIP and H.323 performances using an adaptive retransmission timer: SIP outperforms H.323, especially for a FER higher than 2 percent

As the wireless personal area network (WPAN) gets utilized by more individuals, the interference that collocated WPANs cause to each other, termed self-interference, will be one of the major sources that degrade WPAN's communication performance. The conventional adaptive frequency hopping (AFH) strategies avoid frequency-static interference by reducing the hopset, but this deteriorates the performance if there is also self-interference. In this paper, we propose dynamic AFH (DAFH) mechanisms that are concurrently employed by collocated WPANs in order to avoid the self-interference. With DAFH, WPAN adaptively self-allocates a subset of frequency channels to be hopped, such as to minimize the experienced interference. The packet error rate is the only input to the proposed mechanisms, which enables DAFH to also avoid interference from frequency-static interferer. The optimization of the throughput should not be the sole target of the DAFH because WPAN operates in unlicensed spectrum and arbitrary adaptation of the FH pattern may be harmful to proximate non-WPAN devices. Therefore, we define and adopt an etiquette rule to characterize the behavior of the collocated WPANs with DAFH as a single collective entity that produces interference. The operation of DAFH is robust and adaptive to the dynamic changes in the environment and to the noise errors in the channel. Simulation results show that DAFH significantly increases the throughput of the WPANs in presence of both self-interference and frequency-static interference, while the WPANs employ best effort to minimize changes in the overall interference pattern

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA systems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to a pure SNIR-based strategy (i.e., only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20 - 30% is observed in presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should not neglect this component of the power control.

With the growth in the number of devices with an integrated Bluetooth module, the range of applications based on the Bluetooth technology becomes larger, going beyond peer-to-peer use-cases. This paper considers a hybrid network, consisting both of infrastructure and ad hoc parts, referred to as scatternet with infrastructure support. The introduction of the scatternet structure allows to extend the coverage and to enable access of a larger number of users. The formation algorithms are discussed and the importance of synchronization of the formation process for creation of a height- and width-balanced tree topology is illustrated. Simulation results presenting the impact of the link establishment policies on the resulting topology are given.

The goal of this paper is to highlight the benefits of using variable guard interval (VGI) in orthogonal frequency division multiplexing (OFDM) based wireless local area network (WLAN) systems. An algorithm is derived and its performance merit for implementing VGI in the presence of carrier frequency offset is provided. OFDM system needs to maintain orthogonality among sub carriers, which may be lost due insufficient guard interval and carrier frequency offset (due to local oscillator mismatch and Doppler effects). Static guard interval is usually kept large enough to tolerate worst case channel delay spread conditions, which in turn causes loss in efficiency of the system. The use of variable guard interval is expected to improve the system throughput. Since insufficient guard interval and carrier offset together cause orthogonality loss among sub carriers, the dynamic selection of guard interval in the presence of carrier frequency offset is considered in this work. Results are presented to analyze achievable gains. It has been shown that significant improvement in throughput is achievable by this scheme.

In wireless networks, security is an essential feature that can be provided using a variety of protocols. On the other hand, the security protocols can affect applications to varying degrees depending on the network conditions. In this paper, we propose to evaluate the overhead introduced by the security mechanisms in WLAN such as authentication. To do so, we develop an analytical model based on random errors to evaluate the authentication delay for various error rates taking into account the reliability mechanisms involved. We also measure the authentication delay for WLAN 802.11b using CISCO access point and client cards. We generate the average, minimum and maximum delay for the different authentication configuration available in the CISCO security suite. The analytical and the experimental results are compliant. The major contributor of the authentication delay is the probing time needed to detect the surrounding access point.

The support of IP-based real-time services in the next-generation mobile systems requires the coupling of mobility with quality of service. The mobile node can experience disruptions or even intermittent disconnections of an ongoing real-time session due to handovers. The duration of such interruptions is called disruption time or handover delay and can heavily affect user satisfaction. Therefore, this delay needs to be minimized to provide good quality VoIP services. In this paper, we focus on the network-layer mobility, specifically on mobile Internet protocols (MIP) since they are natural candidates for providing network layer mobility. Using analytical models, we evaluate MIPv4 and MIPv6 and compare their performances in terms of handover delay for VoIP services. To optimize the handover delay, we propose to use the adaptive retransmission timer described in this paper. The results obtained using the adaptive timer technique show that for 3% frame error rate and a 9.6 Kbps channel, the handoff delay is about 0.67 s for MIPv6 and 0.32 s for MIPv4. MIPv4 gives an appropriate support to VoIP services in terms of handover delay but the end-to-end delay may be affected by the triangular routing avoided in MIPv6.

In this paper we introduce a novel header compression technique for parallel channels as they are found in meshed networks. The approach introduced advocates the cooperative behavior of parallel channels to maintain the compression state on sender and receiver side. The general concept as well as one particular implementation are shown. Our approach is characterized by no need of a feedback channel and a low complexity of a compression strategy. By means of analytical study combined with our testbed results we show the performance of the introduced approach. The designing goals were to have a low complex, highly efficient and also robust header compression dealing with the characteristics of the wireless channel. As a first result we can show that for independent error pattern a number of three cooperative channels achieves both robustness and efficiency for a wide range of errors.

In this paper we advocate the use of multiple base stations for providing wireless link to an OFDM-based terminal and thus obtain macro diversity, in particular site diversity. The wireless link to a terminal is defined through a subset of sub-carriers that is optimized in a greedy manner over the union of base stations. The wireless terminal is unaware of how many and which base stations are providing its allocated set of sub-carrier, which simplifies the terminal design. We give an analytical comparison of our approach to the conventional solutions. The results show that the proposed schemes with multiple base stations can outperform the single base station case, while keeping the complexity of the wireless terminal unchanged. We further evaluate our schemes by considering minimize signalling over the air interface.

4G wireless communication networks are characterized by the need to support heterogenous terminals differing in size, display, battery, computational power, etc. For efficient usage of the wireless spectrum all devices should be served by the same spectrum instead of allocating spectra dedicated to the different terminal classes. This feature is naturally supported when the source coding of the traffic is done as a multiple description coding. The restoration quality of the information source is proportional to the quantity of the descriptors used in the restoration process. Hence, terminals with less capabilities may simply discard or not receive some of the descriptors, while high class terminals try to receive all information. In the case of partial reception of descriptors the performance can be improved by selection strategies for the descriptors. We advocate the usage of new descriptor selection schemes for multiple description coded services. The proposed schemes differ with respect to the availability of a feedback channel. All solutions are terminal oriented and are beneficial in the design of terminals that have robust and high quality services. Furthermore, our approaches inherently achieve fairness among different terminals. As an example of our results for video communication, we can show gains of 4 dB when the proposed approach is utilized in the system.

The dynamic selection of guard interval in orthogonal frequency division multiplexing (OFDM) based wireless local area network (WLAN) systems is described in this work. It derives an algorithm and provides its performance merit for implementing variable guard interval (VGI). The proposed system improves mean, outage and maximum throughput significantly as compared to standard OFDM system using fixed guard interval without sacrificing bit error rate performance.

In this paper, the session setup delay of the session initiation protocol (SIP) is studied. The session setup delay is a relevant metric for evaluating real-time services signaling: it has a direct impact on the user satisfaction as the user expects to wait the same time as in GSM or PSTN. The transmissions on both forward and reverse channel are assumed to experience Markovian errors. The session setup delay is evaluated for different transport protocols and with the use of the radio link protocol (RLP). An adaptive retransmission timer is proposed to optimize SIP performances. Using numerical results, we find that SIP over UDP instead of TCP can make the session setup up to 30% shorter. Also RLP reduces drastically the session setup delay down to 8s even in environment with high frame error rate (10%) and significant correlation in the fading process (f/sub D/T=0.02).

The coupling of mobility and quality-of-service with security is a challenge that should be addressed in future wireless overlay systems. The mobility of a node can disrupt or even intermittently disconnect an ongoing real-time session because a secure handover must be performed to ensure continuous connectivity. The duration of the such interruptions is called disruption time or handover delay and can heavily affect the user satisfaction. The handover procedure needs to protect its integrity and confidentiality-otherwise, the packets may be rerouted to a malicious node and the legitimate handover may not be performed. The security procedure to ensure this should not lengthen significantly the handover delay to provide good quality real-time services. In this paper, we focus on the network-layer mobility, specifically, on Mobile Internet protocol version 6 (MIPv6) since it is the natural candidate for providing such mobility in future systems. To solve the problem of on-path attackers and prevent leakage of secrets, we propose a security architecture for MIPv6 based on leakage resilient-authenticated key establishment (LR-AKE) protocol and its cooperation with public key infrastructure. The proposed architecture prevents against on-path attackers which was not addressed in the specifications of MIPv6, and also provides robustness against leakage of secret values. Using analytical models, we evaluate MIPv6 handover delay for real-time services. We identify the crucial factors affecting the handover delay among transmission delays of MIPv6, security and LR-AKE messages, queueing delays and en/decryption delays.

The issue of the performance degradation of transmission control protocol/Internet Protocol (TCP/IP) over wireless links due to the presence of noncongestion-related packet losses has been addressed with a physical layer approach. The effectiveness of automatic repeat request techniques in enhancing TCP/IP performance depends on the tradeoff between frame transmission delay and residual errors after retransmissions. The paper shows how a truncated power control can be effectively applied to improve that tradeoff so that a higher transmission reliability is provided without increasing the frame transmission delay through the radio link layer and without increasing the energy consumption. An analytical framework has been developed to show the feasibility and effectiveness of the proposed power control. The analytical results, which are carried out assuming a constant multiuser interference level, show that the proposed algorithm turns out to be very effective when the time variability of the channel is high, which-in case of constant interference level-means that the Doppler frequency is high. Simulations carried out in a variable interference scenario show that the proposed strategy is very effective in improving the end-to-end throughput of a TCP connection. Moreover, these improvements are higher when the traffic is more bursty, like in typical Internet data applications such as e-mail and web surfing.

Wireless networks beyond 2G aim at supporting real-time applications such as VoIP. Signalling protocols such as the session initiation protocol (SIP) are used to set up VoIP calls. The session setup time can be affected by the quality of the wireless link, measured in terms of frame error rate (FER), which can result in retransmission of lost packets and can lengthen the session setup time. Therefore, such protocols should have a session setup time optimized against loss. One way to do so is by choosing the appropriate retransmission timer and the underlying protocols. In this paper, we focus on the SIP protocol and evaluate its session setup delay with various underlying protocols (transport control protocol (TCP), user datagram protocol (UDP), radio link protocol (RLP)) as a function of the FER. For a 9.6 Kbps channel, the SIP session setup time can be up to 84.5 s with UDP and 105 s with TCP when the FER is up to 10%. The use of RLP(1,2,3) puts the session setup time down to 2.4 s under UDP and 3.5 s under TCP for the same FER and the same channel bandwidth.

Ad-hoc networks are usually constructed with a lot of nodes managed by unknown users and have a vague reliability level. In order to establish a reliable connection with the target node, users somehow need to evaluate the nodes and connection paths as correctly as possible. One of the solutions to this problem is to employ the trust-metrics to the node-and-path evaluation of the ad-hoc network. The trust-metrics are mainly used to evaluate the reliability (validity) of the public-keys of unknown users, e.g. in PGP. We, however, point out that there are some drawbacks when applying the ever known metrics to the node-and-path evaluation of the ad-hoc networks. We show that they are either low privacy - high utility or high privacy - low utility. To overcome these disadvantages, we propose the realization of high privacy high utility trust metrics and its application for evaluating the node's performances in ad-hoc networks (electronic power consumption, transmission speed, etc).

A main issue in wireless communications is to improve the transmission quality of service (QoS), which may be represented by the bit error rate (BER). In [H. Che, et al., 2002] we studied the combining effect of channel situation and OFDM modulation on BER performance and defined a factor P/sub FR/ based on both OFDM parameter and channel parameter that influences BER performance. But this parameter doesn't influence BER in all the situations. In this paper we find out by simulation results that the factor PFR is effective on BER within a certain range of signal to noise ratio (SNR). And our simulation results indicate that this SNR range is different for different Rician K factor and for different modulation levels. This paper demonstrates that for each modulation level there is a relationship between the effective SNR range and Rician K factor and gives out the formula to describe the relationship. The result is quite useful to build up an optimum criteria for adaptive OFDM systems.

The issue of the performance degradation of TCP protocols over wireless links due to the presence of non-congestion related packet losses has been addressed at the physical layer. The feasibility and effectiveness of a proper power management strategy that allows the performance to be improved without increasing the transmission delay and/or increasing the energy consumption has been analyzed. In particular, the dependence of the key parameters of the proposed solution with respect to the correlation of the fading channel has been evaluated. Furthermore, it is shown that the proposed strategy can be effectively exploited to remove local retransmissions at the link layer.

The Wireless Networking Group (WING) at the Center for PersonKommunikation (Aalborg University, Denmark) has been developing an IP simulator framework (see Kock, B.A. et al., Proc. VTC 2001 Fall, 2001). The WING-IP simulator has been extended with an improved mobility structure. Now it is possible to add the Bluetooth protocols to the simulator and investigate the performance in various configurations. The paper gives the general structure of the framework of the WING-IP simulator and explains the implementation of the Bluetooth protocols in this framework. Simulation results are analysed and used to verify the implementation of the Bluetooth protocols.

The paper proposes a novel multiple access scheme, which is a combination of inhibit sense multiple access (ISMA) and frequency division multiple access (FDMA). Two types of the proposed protocol are considered. They are based on FDD and TDD modes. The performance of each hybrid protocol is evaluated in terms of throughput; the comparison of the proposed schemes with the pure ISMA scheme is discussed. Two examples are constructed to show the main property of the ISMA/FDMA scheme.

The paper considers the application of forward error correction (FEC) and automatic repeat request (ARQ) schemes over correlated wireless channels. In particular, the depth of the interleaver and its influence on the frame-error-rate and transmission delay in the presence of correlated fading and delay constraints is investigated. It is found that an increased interleaver depth in a correlated channel, although improving the bit-error-rate, does not always improve the frame-error-rate (FER). Further, it is shown that, in the case of bursty channels, a large interleaver depth is required to improve the FER, thus negatively influencing the delay. In this case, the use of a retransmission scheme can improve delay performance.

The next generation of wireless mobile networks will apply IP to offer a mixed set of services, varying from real time voice-over-IP and videoconferencing, to best effort transmission of E-mail messages. This paper investigates the coupling between the queuing mechanism on the IP and data link layer to be able to offer end users a guaranteed QoS. Priority scheduling is investigated as a means to directly map the QoS levels from the network layer and the MAC layer. A novel scheduling strategy, which introduces a control unit, and synchronises QoS requirements on the IP network layer and the radio layer, is presented as well. The combination of information from different layers in the protocol stack allows for a more optimised and accurate control of the traffic flows with different QoS requirements.

This paper investigates the possibility of using pre-equalization on the up-link of a time division duplex (TDD) OFDM system. The application of this principle is suggested to enhance the spectral efficiency by omitting the usage of training sequences on the up-link. This is desired in order to enable the efficient transmission of very short data packets, like single ATM cells. The principle proposed also keeps the complexity of synchronization low at the base station, which is accessed by many users. We describe a simple scheme to limit the transmission power on the up-link. The power is kept constant by deleting subcarriers that are severely attenuated due to fading. Parameter estimation steps for retrieving the data at the base-station are explained and evaluated. Those include the estimation of the timing-offset, the carrier phase offset, and the received magnitude. Coherent demodulation is considered.

Abstract The concept of adaptivity is of paramount importance in the design of future communication systems, in which a careful exploitation of the limited available resources (bandwidth, power, etc.) is required. The potential of channel‐adaptive transmission has been already recognized 30 years ago, but it did not receive much interest at that time. In the last decade, the advent of feasible software radio systems, and hence, the availability of fast flexible and reconfigurable transceivers has renewed interest in adaptive techniques, which include adaptive modulation and coding, adaptive antennas and adaptive equalization techniques. This paper focuses on adaptive modulation and adaptive error control mechanisms. Basic concepts are highlighted and an overview on the achieved results and new trends in this research area are presented. Some results from information theory are also presented, which show the limitations of these techniques and motivate further research on the practical and design issues that have to be addressed to enable performance to reach close to the theoretical limit. Copyright © 2002 John Wiley & Sons, Ltd.

This paper describes a network simulator for IPv6 networks. Such a network can consist of both fixed and wireless components, like routers, nodeBs, computers, mobile nodes, etc. The simulator can be used to analyse the performance of the TCP/IP protocol suite in wireless and wired networks.

This paper investigates a wireless IPv6-based network architecture to provide access to various multimedia applications with support of voice services, in terms of end-to-end quality of service (QoS) and mobility support in order to ensure global mobility in a converged wired/wireless, voice/data network. The objective is how to jointly use already proposed by the International Engineering Task Force (IETF) protocols for the provision of an end-to-end service with some QoS guarantees. Our work studies transmissions for real-time traffic based on formats for voice over IP (VoIP) and differs from others in that it has been based on the development of a detail simulator instead of a real testbed. QoS is addressed at a packet-level in terms of packet delivery delay and error performance (packet loss). To enforce QoS in the backbone network, data packets entering the backbone network are classified to differentiated service (DiffServ) aggregates. resource reservations protocol (RSVP) is used as the end-to-end signaling protocol. To provide for hierarchical mobility support it has been enhanced by several extensions.

This paper describes a method of deriving channel parameters for a time-dispersive (=frequency-selective) radio channel from simple wide-band power measurements. A novel relationship is found allowing the estimation of the root-mean-square (RMS) delay spread from such data. Furthermore, we describe a set of equations that can be used for fitting the (measured) channel parameters to a mathematical model, the so-called frequency-domain (FD) model. We also show a simulation procedure, which directly implements the mathematical description of the channel. The output of this procedure-realizations of frequency-selective channel transfer functions-may be used for instance in the investigation of OFDM systems. The study is restricted to the small-scale modeling; Rayleigh and Ricean fading channels are considered. The estimation of the RMS delay spread is based on the frequency-domain level crossing rate (LCR/sub f/), which is derived from the FD-channel model. It is shown that the RMS delay spread is proportional to the LCR/sub f/. Because of the simple hardware required for finding the LCR/sub f/, the suggested measurement method is particularly interesting for the millimeter-wave frequency band (>30 GHz). However, it can be used at other frequencies as well, where standard laboratory equipment is sufficient for conducting the measurements. The accuracy of this technique depends on the bandwidth observed and can be increased further by combining multiple measurements performed within a small local area.

With non-GEO constellations the primary means of counteracting the shadowing and the blockage effects is through the use of the satellite diversity, i.e. multiple satellites in the constellation are simultaneously visible to user. The probability system availability is improved by increasing the probability at least one satellite is in clear line of sight. In the selection diversity (SD) scheme the user is served by one satellite selected on the basis of the better signal to noise ratio. In CDMA systems the spatial diversity provided by the satellite diversity can be more effectively exploited by combining signal replica coming from satellites in view with the aim at increasing the system capacity. Actually, the performance of signal combining/selection diversity schemes depend on the specific propagation scenario and it is not always effective to combine signal replica. In this paper hybrid selection/combining diversity schemes are proposed and a performance comparison in terms of system availability and capacity enhancement is carried out. Furthermore, an analytical methodology of the downlink of DS-CDMA systems which takes into account the power constraints of a satellite environment is described and applied for the capacity assessment of the proposed satellite diversity schemes.

This paper proposes a novel signal scheme called "hybrid OFDM/CDMA/SFH approach" which combines OFDM with CDMA and SFH to generate a system functionally superior to MC-CDMA systems. The paper describes the merits and demerits of the proposed system and publishes simulation results in AWGN and fading channels.

This paper presents a hardware platform that enables the realistic emulation of wide-band air interfaces at low cost. Real-time base-band algorithms for the modulator and demodulator are implemented on separate-and thus independent-DSP evaluation boards. A channel simulation sub-system is suggested, consisting of another DSP board for multipath channel simulation and of analog I/Q-modulators and -demodulators for emulating carrier frequency offsets. The latter allows assessment of frequency synchronization techniques. Reduced speed (bandwidth -40 kHz) tremendously reduces implementation difficulties. The advantages and limitations compared to full-speed hardware and pure computer simulation are elaborated on. The system is used by the authors to assess real-time algorithms for OFDM air-interfaces, but it can be used for other modulation schemes as well. Another possible application is in the education of electrical engineers.

This paper proposes a scheme based on an algorithm for synchronising OFDM systems. Different types of synchronisation techniques are discussed. It is found that every existing synchronisation scheme has certain advantages and disadvantages. An alternative scheme based on an algorithm is proposed. In the proposed scheme, the best features of each existing synchronisation scheme are integrated into a whole, yielding an optimum approach to OFDM synchronisation. The implementation retains the inherent simplicity of OFDM systems, without any circuit complications and is therefore, suitable for hardware realisation.

A concept for broadband wide-area networking based on the use of the Internet Protocol (IP) over asynchronous transfer mode (ATM) broadcast over extremely high-frequency (EHF) 30/20 GHz Ka-band satellite communication (SATCOM) is presented. It is primarily intended to support applications such as broadcast of data and video, fast Internet access, and teleconsultation with interactive white board. Operation from midsize terminals located at a corporate headquarters to small highly transportable terminals at remote facilities is envisioned.

We analyse three different possibilities to reduce multi-user interference in a MC-CDMA system. First a quasi-synchronous uplink channel has been proposed with a relative synchronisation algorithm; secondly different diversity combining techniques have been simulated and evaluated in an uplink and downlink channel; finally comparing the performances of single and multi-user detection strategies a successive interference cancellation method has been used.

This paper proposes and investigates a medium access control (MAC) layer for the FRAMES Multiple Access (FMA) platform mode 1 without spreading. It has been constructed bottom-up using circuit reservation multiple access (CRMA) as a basis. Real time (RT) terminals are served in a CRMA mode manner and receive a reservation for a certain slot (or number of slots) for the entire duration of their conversation. Non-real time (NRT) terminals are served in a packet switched like mode manner and receive a reservation for the duration of a single frame.

A multi-carrier code division multiple access (MC-CDMA) scheme is used in a multi-cellular environment in order to reduce the interference present in typical mobile systems. The conventional approach to limit the interference of the users in adjacent cells is frequency reuse (FR). In this paper, a new scheme-code reuse (CR)-is proposed in order to achieve a higher order of diversity. In this method, all the cells in the cluster use the total number of available carriers to transmit the users data signal. The distinction of the data signal of different users is made by using orthogonal Walsh-Hadamard codes for each user. A comparison between the frequency reuse and code reuse schemes is done as a function of the environment path loss, number of carriers, frequency gap between adjacent carriers, number of users and cluster size. The results obtained for a cluster size equal to four show that, increasing the number of carriers and the frequency gap between adjacent channels the performance of both schemes improve. When the number of carriers is increased, the best improvement is achieved for the CR scheme, while for the frequency gap increase it is the FR scheme that improves the most. When a cluster size equal to seven is considered, CR achieves a better performance than FR, since in this case, the co-channel interference is clearly reduced due to the larger distance between cells using the same codes.

This study assesses the performance of the decorrelating detector for DS-CDMA systems over multipath Rayleigh fading channels with AWGN. The decorrelating detector applies the inverse of the correlation matrix to decorrelate the matched filter outputs. The drawback of the decorrelating detector is that it enhances noise and that the inverse of the correlation matrix not always exists. The theoretical performance of the decorrelating detector is presented and the problem of inversion of the correlation matrix is discussed. This article also considers the case when the inverse of a smaller correlation matrix can be used for decorrelating the received data. The performance of the decorrelating detector is compared with other multi-user detectors proposed for DS-CDMA.

In this paper, a novel frequency-domain model (FD-model) for the frequency selective Ricean fading radio channel is presented. Frequency domain filtering and the Hilbert transform are used to generate samples of the channel's transfer function with appropriate frequency correlation properties (WSSUS model). One of the main advantages of this approach is the availability of analytical expressions relating channel parameters to model parameters. This can be used to conveniently fit the proposed channel model to any of the (measured) channel parameters. Based on this new model, level crossing statistics of the channel's transfer function were investigated. Results have shown that the level crossing rate (LCR/sub f/) is proportional to the RMS delay spread (RDS) of the channel. This implies that from the LCR/sub f/, which can be derived from wide-band power measurements, an accurate estimation of the RDS is possible. Previously, expensive and cumbersome equipment like network analyzers was required to measure this parameter. Computational results have been evaluated with measurements and a time-domain model for the 60 GHz frequency band.

In this paper we propose and analyze a novel multiple access scheme based on the combination of the TDMA and CDMA protocols. This hybrid protocol is capable of integrating different types of traffic and complies with the requirements of next-generation systems, such as the Universal Mobile Telecommunication System (UMTS). The performance of both the CDMA and the hybrid TDMA/CDMA protocol is evaluated in terms of throughput, delay and spectrum efficiency using a Markovian model of the protocol and computer simulation.

The paper presents the performance analysis in terms of outage probability of a cellular hybrid DS/SFH CDMA system for the analytical channel model. The mobile-to-base link is modelled as a Rayleigh fading channel with all users experiencing independent fading. The standard receiver for CDMA systems is susceptible to the near-far effect problem. Power control techniques attempt to overcome near-far effect by varying transmitted power levels to ensure that all signals are received with equal power levels. We evaluated the performance for given a bit rate in a situation with and without power control and selection diversity. Since the power control algorithms cannot perfectly compensate for power fluctuations in a mobile communications channel, the performance of the system is reduced for a given BER. This paper examines the effect of imperfect power control on the number of users by extending analytical techniques that account for multiple access and adjacent cell interference.

This paper proposes an OFDM-based wireless ATM transmission system. In the proposed system, the guard bits, which are cyclically extended by repeating information bits, are inserted before and after serial-parallel converted wireless ATM data bits for OFDM transmission, and these bits are applied for the wireless ATM frame synchronization and the decision of the DFT (discrete Fourier transform) start point at the receiver. In addition, the cyclically extended PN sequence is inserted in some of the proposed OFDM transmission subchannels with the fixed interval to estimate phase rotation, frequency offset and delay characteristics. This proposed system does not need to equip the "bit by bit " guard interval insertion and removal circuits which are needed in a conventional OFDM system. It is easy to estimate phase rotation, frequency offset and delay characteristics, and the synchronization of wireless ATM cell is also easy. In this paper, moreover, the bit error rate (BER) and the ATM cell error rate (CER) of this wireless ATM transmission scheme are evaluated by computer simulations.

The performance of cellular digital mobile radio systems is investigated using quadrature amplitude modulation (4-QAM) and differential phase shift keying (DPSK) in a frequency nonselective Rayleigh fading environment with lognormal shadowing, including the effects of (white) Gaussian noise, narrow-band impulsive noise/interference (Middleton's Class A model), and cochannel interference. The performance is analyzed in terms of probability of bit error. The UHF groundwave propagation law is introduced by considering the local mean power to be inversely proportional to the fourth power of propagation distance. To investigate the improvement in performance the influence of selection diversity and maximal ratio combining on the bit error probability is analyzed. It has been found that shadowing significantly affects the bit error performance. Application of selection diversity or maximal ratio combining results in important improvement of system performance. Selection diversity gives better results than maximal ratio combining for low signal-to-noise ratios. Results of our analysis show maximal ratio combining is not that sensitive to unequal branch signal-to-noise-plus-interference ratio.

Overlay of existing narrowband mobile communication systems with future wideband systems may improve spectrum efficiency and create the possibility for high-rate data services. This paper presents a generic capacity analysis applied to a GSM-CDMA overlay. The effects of shadowing and imperfect implementation of sectorization, power control and notch filtering are modeled for both uplink and downlink. Based on maximum allowable levels of mutual interference, the total system capacity is modeled and evaluated. Under moderate shadowing and perfect implementation of sectorization, power control and notch filtering, the results match those obtained in previous analyses by other authors, i.e., a capacity gain factor between 3 and 4. However, for low GSM margins in addition to imperfect sectorization, power control and notch filtering, the capacity gain is shown to reduce significantly. Particularly under heavy shadowing conditions, the overlay does not lead to capacity gain. The propagation loss factor and notch filtering are shown to have a large influence on the results. Provided almost perfect notch filtering and power control, the downlink performs slightly better than the uplink.

The performance of a single-code type I hybrid ARQ error-control technique is analysed for a spread slotted ALOHA uplink. The low Earth-orbiting (LEO) satellite channel under study is prone not only to multipath propagation and multiple in-band transmission interference but also heavy shadowing. The results indicate that coded spread slotted ALOHA is robust against heavy shadowing.

The sensitivity of multicarrier (MC) transmission over a multipath channel, to the phase impairment is addressed. The degradation of the performance of the system with the BPSK and QPSK signaling due to the variance of phase error, carrier frequency offset, delay spread of the multipath channel as well as the number of carriers is investigated. The results can be used in the design and evaluation of realistic nonideal multicarrier systems for high speed communications over multipath mobile/indoor radio channels.

Evaluation results of a time division multiple access (TDMA) slow frequency hopping (SFH) system, using a dual signal receiver (DSR), are presented for the Rayleigh fading channel. With the DSR two narrow band binary phase shift keying (BPSK) co-channel signals can be received simultaneously. The DSR is used in the uplink to allow two users simultaneously in a frequency band, and is shown to enhance the system capacity significantly compared to a conventional receiver. In addition, antenna diversity is used in the uplink, and convolutional coding is used for the uplink and downlink. Both, single and multiple-cellular systems are investigated. The performance is evaluated using simulation results in terms of the average BER, capacity and spectral efficiency, using the COST 207 channel model for the macro-cellular channel.

This paper presents the throughput and delay analysis of a packet-switched code division multiple access (CDMA) network based on the hybrid direct sequence (DS)/slow frequency hopping (SFH) spread-spectrum multiple access (SS MA) technique with Q-, B-, and D-PSK modulation using analytical and measured pico cellular channels. The performance of the hybrid DS/SFH, DS, and SFH multiple access techniques have been compared in a pico cellular personal communications network (PCN) environment. Multipath and multiple access interference are considered. The performance is evaluated for a given delay spread and a fixed bandwidth. The effects of forward error correction (FEC) coding and diversity techniques, such as selection diversity and maximal ratio combining on the performance, are also investigated.

The influence of code synchronization errors on the performance of direct-sequence spread-spectrum (DS/SS) communication systems is investigated. Insight is gained in the degradation of some basic performance parameters due to the tracking bias of a noncoherent delay lock loop (DLL). The performance parameters investigated are the bit-error probability, throughput and delay. Numerical results show that for receivers with an early-late spacing of d=1, using a noncoherent DLL, the results of a system performance analysis in a fast fading environment can be much too optimistic if the tracking errors are ignored.

Results from propagation measurements, conducted in an indoor office environment at 2.4, 4.75, and 11.5 GHz, are presented. The data were obtained in small clusters of six measurements, using a coherent wideband measurement system. The channel characteristics for the three frequencies are compared by evaluating path loss, rms delay spread, and coherence bandwidth. An analytical model for evaluation of the bit-error rate (BER) of the stationary frequency selective indoor channel is developed for a coherent binary phase shift keying (BPSK) receiver, based on the complex impulse response of the channel. Computational BER results are obtained for data rates up to 50 Mb/s, using the measured multipath channel impulse responses. The BER results for a number of clusters are presented and compared for the maximum reliable data rate as inferred by the measured rms delay spread of the channel.

This paper presents a method to apply progressive transmission to line drawings using the wavelet transform. Experiments have been conducted and showed that the wavelet transform, combined with a quantization step, performs progressive transmission using a data rate comparable to standard chain coding at the expense of almost no visually perceptible distortion.

High-speed communications suffer from intersymbol interference (ISI) introduced by the channel. In order to combat ISI one commonly uses equalizers that need a training sequence to adjust the equalizer tap weights. When sending a training sequence is not appropriate, blind equalization has to be used. A new blind linear equalizer is proposed. The equalizer has a recursive structure. To avoid stability problems, a soft limiter is used in the feedback loop. The weights are controlled by means of the decorrelation algorithm. For channels without precursors, the equalizer converges to the desired weights in around 500 iterations, depending on the amount of distortion. The novel blind equalization technique is globally convergent for minimum and non-minimum phase channels.

The multi-carrier (MC) technique is attractive in indoor radio communication systems. It combats frequency selectivity of the channel as well as providing spectral efficiency. In this paper performance of the multi-carrier system with BPSK modulation is evaluated over the empirical data base of 12000 impulse response estimates of indoor radio propagation channels at two dissimilar office buildings. These indoor channels have lognormal amplitude fading and modified Poisson distribution of arrival time of multipath components. Performance is evaluated in terms of the average probability of bit error as a function of signal-to-noise ratio. The influence of changing the number of tones as well as the guard interval on the average bit error rate is investigated. Degradation of the performance caused by carrier phase error is studied. Results can be used in the design and assessment of indoor wireless communication systems.

The effect of multipath characteristics on the performance of a wireless DS CDMA system has been analysed by considering a specific wireless indoor system for multimedia applications in the 2.4 GHz band. The downlink performance of the system is evaluated in terms of the bit error rate and user capacity. The results are compared for two analytical channel models and one empirical model based on measured profiles. One analytical model assumes independent identically distributed path gains, the other one assumes independent exponentially distributed path gains. The results obtained with the analytical channel models show more pessimistic results than with the measured channels.

Currently a lot of research is done on a future Universal Mobile Communication System (UMTS), which is a third generation system. An important research topic is to determine a suitable and flexible multiple access technique. The performance of a multi-user receiver in combination with a groupwise successive interference cancellation (CSIC) scheme for a DS/CDMA system is investigated. An analysis of the GSIC scheme is presented for BPSK modulation under Rayleigh fading in an asynchronous channel. The GSIC scheme results in a considerable reduction of the hardware complexity. A performance comparison with a SIC scheme without grouping is done. Numerical results show that the system performance of the GSIC scheme approaches the performance of the SIC scheme, when the group size is not too large.

The throughput and delay characteristics of a land-mobile satellite channel are analyzed for both slotted ALOHA. And slotted direct-sequence CDMA (code division multiple access), using binary phase shift keying (BPSK) modulation and forward error correction coding (FEC). In the case of CDMA, the application of path diversity techniques-maximal ratio combining and selection diversity-is also taken into account. Packet success probabilities are derived for both slow and fast fading, in order to evaluate the throughput and delay. Numerical results are presented for arbitrary code lengths and for specific values of the number of resolvable paths. It is shown that CDMA can offer a substantial improvement over slotted ALOHA, especially when the chip time is less than the delay spread.>

The bit error probability in a Rician fading channel is evaluated for indoor wireless communications considering direct-sequence spread spectrum multiple access (DS/SSMA) with differential phase shift keying (DPSK) modulation and two types of diversity: selection diversity and maximal ratio combining. The performance of the indoor radio system is also obtained in terms of outage probability and bandwidth efficiency. The analysis is done for a star-connected multiple access radio network. Furthermore the influence of three types of forward error correcting (FEC) codes namely, the (15,7) BCH code, the (7,4) Hamming code and the (23,12) Golay code, on the performance is studied. Computational results are presented for suitable values of Rician parameters in an indoor environment and using Gold codes as spread spectrum codes.>

The paper presents the throughput and delay characteristics of a CDMA network using hybrid DS/SFH, DS and SFH, all with B- and Q-PSK modulation. The performance of these three spread spectrum multiple access (SS MA) techniques is compared. The network is considered to be operating in a slow Rician fading environment, where multipath and multiple access interference are the major causes for errors. The effect of selection diversity as well as the effect of FEC coding on the performance are investigated. The performance is evaluated for a given bit rate, bandwidth and delay spread.

The maximum user capacity and the spectrum efficiency of the downlink of an indoor wireless DS CDMA system operating in the 2.4 GHz ISM band with system bandwidth 64 MHz is investigated using measured delay profiles. BPSK modulation is considered and the receiver is equipped with selection diversity and matched filter detection. It is shown that the user capacity can be enhanced by using a lower bit rate and a larger code length. Furthermore it is expected that the performance results obtained with measured profiles are less pessimistic than the results obtained using analytical channel models.

The paper analyses the performance of quasi-coherent combining of signals from a small circular antenna array in a Rician fading indoor multipath channel at microwave or millimetre wave frequencies. Instead of maximum ratio combining, where the complex weighting of signals results in an optimum for a single frequency, the proposed concept is based on quasi-coherent combining of the dominant component of the multipath signal of each antenna. The resulting channel impulse response, shows less delay spread and a higher signal to noise ratio. A scheme for this combining technique is given for a coherent binary phase shift keying receiver and evaluated by simulation. Cumulative BER results for the Rician channel and normalised bit rates are presented for circular arrays of 1, 2 and 4 antennae with a diameter of one wavelength. It is shown that this combining technique results in a significant improvement of the BER or application of higher bit rates,.

Performance of direct sequence code division multiple access (DS-CDMA) technique with binary phase shift keying (BPSK) modulation is evaluated over measured data base of 12000 impulse response estimates of indoor channels obtained at two dissimilar office buildings. These indoor channels have lognormal amplitude fading characteristic as well as modified Poison time of arrival of multipath components. Matched filler receiver and average power control are considered. Gold codes are used as spread spectrum codes. Performance is evaluated in terms of average probability of bit error as a function of signal-to-noise ratio. Results can be used in design and assessment of wireless indoor communication systems.

The impact of buffering and the use of a multichannel base station on the performance of a hybrid CDMA/ISMA protocol is investigated by simulation. Buffering moves the performance bottleneck from the terminal receiver link to the base station. The protocol performs best when both buffering and multiple return channels are used. The throughput and delay have been evaluated for the proposed hybrid CDMA/ISMA protocol considering packet buffering, multiple return channels, spread spectrum CDMA and p-persistent ISMA with DPSK modulation scheme for computer communications in Rayleigh fading indoor environments.

This paper investigates the performance of the packet reservation multiple access protocol in terms of the packet dropping probability of speech packets. Capture is considered where the desired (test) packet is a BPSK modulated signal suffering from Rician fading and the near-far effect. The test packet is transmitted on an additive white Gaussian noise channel where it receives interference from other BPSK modulated packets which are assumed to suffer from Rayleigh fading and the near-far effect.>

The performance of the stack algorithm in mobile radio channels with Rayleigh fading, shadowing and near-far effect is analysed. Three versions of the stack algorithm are taken into consideration, each with a different ability to distinguish between channel events in a previous time slot. The stack algorithm is described as a regenerative process. Throughput and delay characteristics are determined up to a critical traffic generation rate, where the mean packet delay and mean basic session length grow to infinity.>

Mathematical models are developed to analyze the performance of a sectorized microcellular mobile radio system considering binary phase shift keying (BPSK) modulation. The performance is evaluated in terms of co-channel interference probability, bit error probability and spectrum efficiency. The influence of directional angle, turning point, reuse distance, traffic intensity and signal-to-noise ratio on the performance parameters is investigated.>

An improved performance assessment for a slotted CDMA system in the outdoor mobile radio environment is presented. The performance is obtained in terms of throughput and delay of the system in both macro- and micro-cellular systems. Shadowing, fading and near-far effect are incorporated in the channel model. The influence of Forward Error Correction (FEC) coding on the performance parameters is studied.>

The feasibility of line-drawing (handwritten text and graphics) transmission is investigated in the indoor and outdoor radio environment. The indoor and outdoor radio channel is modelled by Rician and Rayleigh fading, respectively. The effect of error sensitivity on the line-drawing quality degradation in the hostile indoor and outdoor mobile radio channel is presented by a typical example. Efficient encoding of handwriting is realised using differential chain coding (DCC). Performance is evaluated in terms of bit error rate and packet success probability.>

A combination of direct sequence code division multiple access (DS-CDMA) and p-persistent inhibit sense multiple access (ISMA) protocols is proposed for indoor wireless communications (IWC). The combination of these two protocols is called the hybrid CDMA/ISMA protocol. The performance of the hybrid CDMA/ISMA protocol is analyzed with a Markov model considering differential phase shift keying (DPSK) modulation. The performance is measured in terms of throughput and delay. The performance is also evaluated using computer simulation of which the results are in close agreement with the Markov model results. The study of indoor wireless communications using a hybrid CDMA/ISMA protocol can be useful for various applications in research and design offices, medical data communication in hospitals, etc.>

Hidden Markov models are used to model the generation of handwritten, isolated characters. Models are trained on examples using the Baum-Welch optimization routine. Then, given the models for the alphabet, unknown characters can be classified using maximum-likelihood classification. Experiments have been conducted, and an average error rate of 6.9% was achieved over the alphabet consisting of the lowercase English alphabet.

An analytical model is developed for the performance of a microcellular radio network in the presence of cochannel interference and additive white Gaussian noise. The modulation schemes considered are binary phase-shift keyed (BPSK), binary frequency-shift keyed (BFSK), and quadrature phase-shift keyed (QPSK). The multiple-access channel is statistically modeled by one Rician-distributed desired signal and several uncorrelated Rayleigh plus log-normally shadowed interfering signals, propagating according to dual path loss law with a turning point. The performance is determined in terms of bit error rate (BER), outage probability, block error probability, crosstalk probability, and spectrum efficiency, considering both fast and slow multipath fading. The effect of error correction codes, consisting of blocks with equal number of bits, on the performance parameters is also studied. The computational results show that the propagation loss exponents, Rician factor, turning point, and cell size all plays a major role in the design of an efficient microcellular system.>

The performance of a slotted ALOHA-network in a slow Rayleigh-fading channel for mobile data communications is investigated considering error correction and detection coding with binary phase shift keying (BPSK) modulation. The performance is measured in terms of receiver error probability and throughput. An enhanced performance is obtained by using error correction coding. In spite of the use of error correction coding, a packet can be in error, i.e. the receiver erroneously detects a codeword that none of the terminals transmitted. Bounded distance decoding can be used effectively to reduce the packet error probability. A comparison of the performance is presented for a specific code with equal Hamming distance d/sub min/, exchanging between the error correcting and error detecting capability of that code. Also, the effects of signal carrier detection on receiver error probability and throughput are investigated.>

The performance in terms of the throughput of a slotted CDMA personal communication system is evaluated considering a hybrid slow frequency hopping/direct sequence (SFH/DS) spread spectrum transmission technique with differential phase shift keying (DPSK) modulation and selection diversity. The effects of multi-user interference and multiple resolvable paths on the performance for slow Rician fading channel are investigated. The performance results for macro-, micro- and pico-cellular CDMA systems are compared.>

The performance of a direct-sequence spread-spectrum land-mobile satellite transmission system, using binary phase-shift keying (BPSK) modulation, is analysed. The satellite channel is modeled as having Rician fading characteristics. The bit-error probability is evaluated, considering both the envelope and the phase variation. Assuming a Gaussian approximation for the interference, numerical results are obtained for both spread-spectrum and narrowband land-mobile satellite communication systems with BPSK modulation. A comparison of the two systems is made for light, average, and heavy shadowing.>