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Multiplexing
Kinds of Multiplexing Selected AbstractsNonlinear signal processing schemes for OFDM modulations within conventional or LINC transmitter structuresEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2008Rui Dinis This paper considers two classes of digital signal processing schemes, recently proposed by the authors, both combining a nonlinear operation in the time domain with a linear operation in the frequency domain, so as to reduce the envelope fluctuations and allow good power/bandwidth tradeoffs with Orthogonal Frequency Division Multiplexing (OFDM) transmission. These classes can be adopted within both conventional and two-branch, LInear amplification with Nonlinear Components (LINC) transmitter structures . The paper addresses the statistical characterisation of the transmitted frequency-domain blocks, so as to evaluate performances by analytical means, in a unified manner. A set of numerical results, which have been obtained with the help of this analytical method, is presented and discussed. These results allow a comparison between the two classes of signal processing schemes, namely for nonlinear operations of the ,clipping' type, when a conventional transmitter structure is employed. They also allow an accurate evaluation of the phase and gain imbalance effects in the two-branch power amplification case. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimum adaptive OFDM systemsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2003Lorenzo Piazzo When Orthogonal Frequency Division Multiplexing (OFDM) is used to transmit information over a frequency selective channel, it is convenient to vary the power and the number of bits allocated to each subcarrier in order to optimize the system performance. In this paper, the three classical problems of transmission power minimization, error rate minimization and throughput maximization are investigated in a unified manner. The relations existing among these three problems are clarified and a precise definition of optimum system is given. A general and rigorous way to extend the solution of any of the three problems in order to obtain the solution of the other two is presented. This result is used to devise an efficient algorithm for the error rate minimization. Copyright © 2003 AEI. [source] An efficient traffic control scheme for store-and-forward video-on-demand servicesINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2001Xue-Ming Yuan Abstract According to the MPEG-1/2 standard, full motion video can be compressed and stored in an information warehouse. Multiplexing with normal voice calls, it is retrieved and delivered to the customer's local BISDN central office via 155 Mb/s trunks. These voice calls have higher priority than video-on-demand (VOD) so that normal voice services will not be influenced by VOD transmission. The number of voice calls always fluctuates in real-time. Thus, an efficient traffic control scheme is highly desired to guarantee a given level of performance and achieve as great as possible use of available bandwidth. Based on the fact that the number of real-time voice calls is variable, and the use of available capacity is less than 100 per cent, this paper will present an efficient traffic control scheme for store-and-forward VOD services, and demonstrate the scheme by various simulation results. Copyright © 2001 John Wiley & Sons, Ltd. [source] Minimizing the cost of placing and sizing wavelength division multiplexing and optical crossconnect equipment in a telecommunications networkNETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2005Belén Melián Abstract Cost reduction is a major concern when designing optical fiber networks. Multiwavelength optical devices are new technology for increasing the capacity of fiber networks while reducing costs, when compared to installing traditional (e.g., SONET) equipment and new fiber. In this article we discuss the development of a metaheuristic method that seeks to optimize the location of Wavelength Division Multiplexing (WDM) and Optical Crossconnect (OXC) equipment in fiber networks. The procedure combines ideas from the scatter search, tabu search, and multistart methodologies. Computational experiments with both real-world and artificial data show the effectiveness of the proposed procedure. The experiments include a comparison with a permutation-based approach and with lower bounds generated with CPLEX. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 199,209 2005 [source] Resource allocation algorithms for minimum rates scheduling in MIMO-OFDM systems,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2010Johannes Georg Klotz In this paper, we consider a multiple-input-multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) downlink scenario, where each receiving mobile station has quality of service requirements, namely minimum rate requirements. For this problem we propose three heuristic resource allocation algorithms, which have a much lower complexity than the existing optimal solution (opt). We compare and evaluate these algorithms according to sum rate performance and complexity. The first strategy is based on a heuristic sum rate maximisation algorithm using the so-called eigenvalue updates. In our second algorithm, we make use of the duality of uplink and downlink, which allows us to do the allocation in the dual uplink. Finally, our third algorithm is based on the well-known zero-forcing dirty paper coding (ZF-DPC) principles, which use the Gram--Schmidt process to orthogonalise the transmissions towards the different users. Copyright © 2010 John Wiley & Sons, Ltd. [source] Performance analysis of optical code switching routerEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2010F. R. Durand In this work we study and evaluate the performance of an optical code switching router (OCSR), intended to be utilised in hybrid wavelength-division multiplexing/optical code-division multiplexing (WDM/OCDM) networks. This OCSR can transport and route efficiently user data over optical code paths without departing from the optical domain. Limitations of the proposed OCSR are investigated and its superior performance demonstrated based on non-coherent prime codes. Our results indicate that our solution is useful in showing the effects of the optimum threshold level on the OCSR performance. We propose a continuous adjustment of the optimum threshold level based on the measurement of the mean optical power before the decoder. The influence of various parameters of the optical codes on the OCSR performance are also considered and evaluated. Copyright © 2009 John Wiley & Sons, Ltd. [source] Assessment of the access selection gain in multi-radio access networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2009Joachim Sachs In this paper, we investigate the capacity gain of access selection in a multi-radio access network with heterogeneous radio access technologies (RATs). We classify the kinds of gain that can be achieved by access selection: statistical multiplexing in the multi-access system leads to a trunking gain, spatial transmission diversity results from the geographic capacity distribution of the cell layout, stochastic transmission diversity exploits the multi-path fading characteristics. We show how these different properties are affected by the cell layout of the different RATs, the characteristics of each RAT and the traffic load distribution in the network. In a simulation environment the system capacity for the combination of two wide-area access technologies, as well as, for the combination of a wide-area and a local-area access technology is investigated. For this, we compare two different access selection algorithms. One uses the radio link quality as an input parameter, while the other also considers the cell load. We derive quantitative figures for the capacity gain in a large number of scenarios and show that load-based access selection can significantly increase the capacity. We show that the gain of an overlay of local-area access cells provides little capacity gain for uniform geographic load distribution, whereas significant gain can be achieved when most users are located at hotspots. Copyright © 2007 John Wiley & Sons, Ltd. [source] Analysis of the effects of Nyquist pulse-shaping on the performance of OFDM systems with carrier frequency offsetEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2009Peng Tan An exact method for calculating the bit error rate (BER) of an uncoded orthogonal frequency-division multiplexing (OFDM) system with transmitter Nyquist pulse-shaping over AWGN channels in the presence of frequency offset is derived. This method represents a unified way to calculate the BER of this system with different one- and two-dimensional subcarrier modulation formats. The precise BER expressions are obtained using a characteristic function method. The effects of several widely referenced Nyquist pulse-shapings, including the Franks pulse, the raised-cosine pulse, the ,better than' raised-cosine (BTRC) pulse, the second-order continuous window (SOCW), the double-jump pulse and the polynomial pulse on intercarrier interference (ICI) reduction and BER improvement of the system with carrier frequency offset are examined in the AWGN channel. The dependence of the BER on the roll-off factor of the pulse employed for a specific system in the presence of frequency offset is investigated. Analysis and numerical results show that the Franks pulse exhibits the best performance among the Nyquist pulses considered in most cases. Copyright © 2008 John Wiley & Sons, Ltd. [source] Survivable wavelength-routed optical network design using genetic algorithmsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2008Y. S. Kavian The provision of acceptable service in the presence of failures and attacks is a major issue in the design of next generation dense wavelength division multiplexing (DWDM) networks. Survivability is provided by the establishment of spare lightpaths for each connection request to protect the working lightpaths. This paper presents a genetic algorithm (GA) solver for the routing and wavelength assignment problem with working and spare lightpaths to design survivable optical networks in the presence of a single link failure. Lightpaths are encoded into chromosomes made up of a fixed number of genes equal to the number of entries in the traffic demand matrix. Each gene represents one valid path and is thus coded as a variable length binary string. After crossover and mutation, each member of the population represents a set of valid but possibly incompatible paths and those that do not satisfy the problem constraints are discarded. The best paths are then found by use of a fitness function and these are assigned the minimum number of wavelengths according to the problem constraints. The proposed approach has been evaluated on dedicated path protection and shared path protection. Simulation results show that the GA method is efficient and able to design DWDM survivable real-world optical mesh networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Frequency domain equalisation in CDMA detectionEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2008Ihan Martoyo The present paper introduces frequency domain equalisation (FDE) as an efficient means for single-user detection (SUD) in universal mobile telecommunication systems (UMTS) handhelds. Such an SUD is, at least partially, able to remove multiple access interference (MAI) like a multi-user detector (MUD), however with several important advantages the operation principle of an FDE-SUD is simple and easy to understand, the FDE-SUD shows low numerical complexity and therefore, it is not power hungry like an MUD. The problem of applying FDE without zero-padding or cyclic-prefix insertion is solved by using the overlap-cut method. In this paper we also prove that the performance of the FDE-SUD is practically identical to that of linear MUD for a fully loaded UMTS cell. Furthermore, armed with the idea of FDE for code division multiple access (CDMA), we can construct a common receiver structure for CDMA, time division multiple access (TDMA), orthogonal frequency division multiplexing (OFDM) and multi-carrier CDMA (MC-CDMA) systems. This is an extremely useful idea in enabling a software-defined radio (SDR) which can operate seamlessly in several environments such as UMTS, the IEEE 802.11a and WiMaX. FDE based receivers could be one important building-block for the next generation mobile communications. Copyright © 2008 John Wiley & Sons, Ltd. [source] Resource allocation with minimum rates for OFDM broadcast channels,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2007Carolin Huppert Downlink transmissions with minimum rate requirements over orthogonal frequency division multiplexing (OFDM) channels are commonly done by means of scheduling algorithms. However, regarding it from an information theoretical point of view, this is not optimal since broadcast techniques can achieve higher rates. The drawbacks of the optimum broadcast algorithm are that the signalling overhead is larger than for scheduling and also the computational complexity is much higher. In this paper we propose an algorithm which overcomes these points. This algorithm is a hybrid algorithm combining scheduling and broadcast approaches. Thus, it combines advantages of both methods. Furthermore, we present modifications to this algorithm to avoid irresolvable decoding dependencies. We show by means of simulation results that the proposed algorithm operates close to the optimum performance and that it outperforms a pure scheduling approach. Copyright © 2007 John Wiley & Sons, Ltd. [source] Experiments on space diversity effect in MIMO channel transmission with maximum data rate of 1,Gbps in downlink OFDM radio accessEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2006Hidekazu Taoka This paper presents experimental results on the space diversity effect in MIMO multiplexing/diversity with the target data rate up to 1,Gbps using OFDM radio access based on laboratory and field experiments including realistic impairments using the implemented MIMO transceivers with the maximum of four transmitter/receiver branches. The experimental results using multipath fading simulators show that at the frequency efficiency of less than approximately 2,bits/second/Hz, MIMO diversity using the space-time block code (STBC) increases the measured throughput compared to MIMO multiplexing owing to the high transmission space diversity effect. At a higher frequency efficiency than approximately 2--3,bits/second/Hz, however, MIMO multiplexing exhibits performance superior to that of MIMO diversity since the impairments using higher data modulation and a higher channel coding rate in MIMO diversity overcomes the space diversity effect. The results also show that the receiver space diversity effect is very effective in MIMO multiplexing for maximum likelihood detection employing QR-decomposition and the M-algorithm (QRM-MLD) signal detection. Finally, we show that the real-time throughput of 500,Mbps and 1,Gbps in a 100-MHz transmission bandwidth is achieved at the average received Eb/N0 per receiver antenna of approximately 8.0 and 14.0,dB using 16QAM modulation and Turbo coding with the coding rate of 1/2 and 8/9 respectively in 4-by-4 MIMO multiplexing in a real propagation environment. Copyright © 2006 AEIT. [source] Suppression of sidelobes in OFDM systems by multiple-choice sequences,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2006Ivan Cosovic In this paper, we consider the problem of out-of-band radiation in orthogonal frequency-division multiplexing (OFDM) systems caused by high sidelobes of the OFDM transmission signal. Suppression of high sidelobes in OFDM systems enables higher spectral efficiency and/or co-existence with legacy systems in the case of OFDM spectrum sharing systems. To reduce sidelobes, we propose a method termed multiple-choice sequences (MCS). It is based on the idea that transforming the original transmit sequence into a set of sequences and choosing that sequence out of the set with the lowest power in the sidelobes allows to reduce the out-of-band radiation. We describe the general principle of MCS and out of it we derive and compare several practical MCS algorithms. In addition, we shortly consider the combination of MCS sidelobe suppression method with existing sidelobe suppression methods. Numerical results show that with MCS approach OFDM sidelobes can be reduced significantly while requiring only a small amount of signalling information to be sent from transmitter to receiver. For example, in an OFDM overlay scenario sidelobes power is reduced by around 10,dB with a signalling overhead of only 14%. Copyright © 2006 AEIT. [source] Broadband wireless access based on VSF-OFCDM and VSCRF-CDMA and its experimentsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2004Hiroyuki Atarashi This paper presents broadband packet wireless access schemes based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the downlink and variable spreading and chip repetition factors (VSCRF)-CDMA in the uplink for the systems beyond IMT-2000. In our design concept for wireless access in both links, radio parameters such as the spreading factor (SF) are optimally controlled so that the system capacity is maximized according to the cell configuration, channel load and radio channel conditions, based on the tradeoff between efficient suppression of other-cell interference and the capacity increase in the target cell by exploiting orthogonality in the time and frequency domains. We demonstrate that the peak throughput of greater than 100,Mbps and 20,Mbps is achieved by the implemented base station and mobile station transceivers using the 100-MHz and 40-MHz bandwidths in the downlink and uplink respectively. Moreover, the simulation results show the possibility of the peak throughput of approximately 1,Gbps for short-range area applications using the 100-MHz bandwidth OFCDM downlink by applying four-branch multiple input multiple output (MIMO) multiplexing with 16,QAM data modulation and punctured turbo coding. Copyright © 2004 AEI [source] Multi-user detection in OFDM systems using CDMA and multiple antennasEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2003Christoph Degen This paper deals with linear multi-user detection in orthogonal frequency division multiplexing (OFDM) systems. The separation of concurrently transmitted signals is based on space division and code division multiple access (SD/CDMA). The examined OFDM schemes are compared against frequency domain equalization for single-carrier transmission schemes (SC/FDE). Both show strong similarities. Therefore in this paper, we focus on a unified treatment of multi-user detection systems based on OFDM or SC/FDE. The trade-off between exploitation of diversity and user separation is analyzed for different spreading techniques and a varying number of receive antennas. The performance is evaluated in terms of both uncoded and coded bit error ratio (BER). Furthermore, a novel time domain spreading technique for OFDM systems is proposed for which the peak-to-average transmitter power ratio (PAPR) is independent of the applied spreading code. Copyright © 2004 AEI [source] Array antenna assisted doppler spread compensator for OFDMEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2002Minoru Okada This paper proposes a novel array-antenna-assisted Doppler spread compensator for orthogonal frequency division multiplexing (OFDM), which is sensitive to fast time-variation of the radio propagation channel. In the proposed compensator, a linear array antenna is installed on top of the vehicle. The compensator estimates the received signal at a certain point on the linear array antenna by using space domain interpolation. Because the relative position of the estimated receiving point with respect to the ground does not change during the effective symbol duration of an OFDM signal, the time variation due to the movement of the vehicle can be compensated for. Computer simulation shows that the compensator can compensate for the bit error rate performance degradation due to time-variation of the channel when the velocity of the vehicle is up to 180km/h and a two-element array antenna is used at the carrier frequency of 600 MHz. The bit error rate performance can be further improved by using a four-element array antenna. [source] Signal Dependence of Cross-Phase Modulation in WDM SystemsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2000Lutz Rapp In intensity modulated direct detection wavelength division multiplexing (WDM) systems, the effect of cross-phase modulation (XPM) combined with groupvelocity dispersion causes signal distortion, which depends on the transmitted signals. The influence of the mutual dependence of these signals on the resulting degradation of the system performance is investigated theoretically and by means of simulations. Considering the propagation of two digital signals, the eye-closure penalty is determined for different bit patterns and consequences for system design are pointed out. An approximation method is described in order to provide a better understanding of the signal dependence of XPM. Finally, a technique reducing the impact of XPM on data transmission in WDM systems is proposed. [source] Theoretical analysis of iterative signal reconstruction for impulsive noise mitigation in OFDM systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2010Nikola Rozic Abstract In this paper a theoretical analysis of the iterative signal reconstruction algorithm for impulsive noise mitigation in orthogonal frequency-division multiplexing (OFDM) systems is developed. The following main results are developed: first, analytical model for the total noise in the frequency domain, and second the model for the total noise probability density function (pdf) in the frequency domain, both defined for each step of the iterative reconstruction process. Finally, based on the pdf of the total noise, explicit expressions for BER in kth iteration are defined as well. The main intention of the paper is to present the approach to theoretical analysis of the iterative impulsive noise mitigation algorithm that has not yet been appeared in the literature, because the theoretical analysis of the noise pdf during iterations has been considered as too complex a problem. Analyses and analytical results presented in the paper are given for scenario with a fixed number of noise impulses per frame. However, this is not a handicap of the proposed approach, since all presented models can be used as building blocks for scenarios with other impulsive noise distributions including Bernoulli,Gaussian and Middleton's Class A. Copyright © 2009 John Wiley & Sons, Ltd. [source] Joint queue control and user scheduling in MIMO broadcast channel under zero-forcing multiplexingINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2009Feng She Abstract This paper studies the problem of queue control and user scheduling in multi-antenna broadcast (downlink) systems under zero forcing beamforming transmit strategy. In the system, we assume that the data packet arrives randomly to the buffered transmitter. By taking the broadcast channel as a controlled queueing system, we deduce the property of queue control function that maximizes the weighted system throughput while guarantees the delay fairness among users. We also present a low-complexity user selection algorithm with the consideration of queue state and channel state together. Simulation results show that the joint queue control and user selection policy can achieve considerable fairness and stability among users. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance of robust symbol-timing and carrier-frequency estimation for OFDM systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2009Nan-Yang YenArticle first published online: 7 NOV 200 Abstract In recent years, many maximum likelihood (ML) blind estimators have been proposed to estimate timing and frequency offsets for orthogonal frequency division multiplexing (OFDM) systems. However, the previously proposed ML blind estimators utilizing cyclic prefix do not fully characterize the random observation vector over the entire range of the timing offset and will significantly degrade the estimation performance. In this paper, we present a global ML blind estimator to compensate the estimation error. Moreover, we extend the global ML blind estimator by accumulating the ML function of the estimation parameters to achieve a better accuracy without increasing the hardware or computational complexity. The simulation results show that the proposed algorithm can significantly improve the estimation performance in both additional white Gaussian noise and ITU-R M.1225 multipath channels. Copyright © 2008 John Wiley & Sons, Ltd. [source] Low complexity bit allocation algorithm for OFDM systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 11 2008Changwook Lee Abstract A bit allocation algorithm is presented for orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic,geometric means inequality. Consequently, this algorithm has a simple procedure and low computational complexity. Copyright © 2008 John Wiley & Sons, Ltd. [source] Kalman filter-based channel estimation and ICI suppression for high-mobility OFDM systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2008Prerana Gupta Abstract The use of orthogonal frequency division multiplexing (OFDM) in frequency-selective fading environments has been well explored. However, OFDM is more prone to time-selective fading compared with single-carrier systems. Rapid time variations destroy the subcarrier orthogonality and introduce inter-carrier interference (ICI). Besides this, obtaining reliable channel estimates for receiver equalization is a non-trivial task in rapidly fading systems. Our work addresses the problem of channel estimation and ICI suppression by viewing the system as a state-space model. The Kalman filter is employed to estimate the channel; this is followed by a time-domain ICI mitigation filter that maximizes the signal-to-interference plus noise ratio (SINR) at the receiver. This method is seen to provide good estimation performance apart from significant SINR gain with low training overhead. Suitable bounds on the performance of the system are described; bit error rate (BER) performance over a time-invariant Rayleigh fading channel serves as the lower bound, whereas BER performance over a doubly selective system with ICI as the dominant impairment provides the upper bound. Copyright © 2008 John Wiley & Sons, Ltd. [source] Clustering-based scheduling: A new class of scheduling algorithms for single-hop lightwave networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2008Sophia G. Petridou Abstract In wavelength division multiplexing (WDM) star networks, the construction of the transmission schedule is a key issue, which essentially affects the network performance. Up to now, classic scheduling techniques consider the nodes' requests in a sequential service order. However, these approaches are static and do not take into account the individual traffic pattern of each node. Owing to this major drawback, they suffer from low performance, especially when operating under asymmetric traffic. In this paper, a new class of scheduling algorithms for WDM star networks, which is based on the use of clustering techniques, is introduced. According to the proposed Clustering-Based Scheduling Algorithm (CBSA), the network's nodes are organized into clusters, based on the number of their requests per channel. Then, their transmission priority is defined beginning from the nodes belonging to clusters with higher demands and ending to the nodes of clusters with fewer requests. The main objective of the proposed scheme is to minimize the length of the schedule by rearranging the nodes' service order. Furthermore, the proposed CBSA scheme adopts a prediction mechanism to minimize the computational complexity of the scheduling algorithm. Extensive simulation results are presented, which clearly indicate that the proposed approach leads to a significantly higher throughput-delay performance when compared with conventional scheduling algorithms. We believe that the proposed clustering-based approach can be the base of a new generation of high-performance scheduling algorithms for WDM star networks. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of a clock-recovery technique for circuit emulation services over packet networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2008James Aweya Abstract One important requirement of circuit emulation services (CES) over packet networks is clock synchronization and timing distribution among the nodes. CES depends on reliable and high-quality timing for operations. In the time division multiplexing (TDM) world, whether plesiochronous digital hierarchy (PDH), synchronous digital hierarchy (SDH) or synchronous optical network (SONET) based, timing and synchronization is inherent in the design of the network. However, when timing critical services such PDH and SDH/SONET are carried over packet network (e.g. IP, Ethernet, etc.), the timing element is lost and has to be carried across the packet network by other means. A well-known and widely implemented technique for clock recovery in CES is one that is based on packet inter-arrival time (sometimes called time difference of arrival) averaging. The technique is very simple to implement but provides good performance only when packet losses and packet delay variation (PDV) are very low and well controlled. This technique has been extensively analysed through simulations but has not been fully characterized analytically with correlated traffic in the literature. In this paper, we provide a full analytical examination of this well-known clock recovery technique. We analyse the effects of correlation of the delay variation in the traffic stream on the quality of the clock recovered by a receiver. We prove analytically that, for a general input process, high correlation of the delay variation produces a large variance of the recovered clock. Copyright © 2007 John Wiley & Sons, Ltd. [source] Clock synchronization for packet networks using a weighted least-squares error filtering technique and enabling circuit emulation serviceINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2007James Aweya Abstract Circuit emulation service (CES) allows time-division multiplexing (TDM) services (T1/E1 and T3/E3 circuits) to be transparently extended across a packet network. With circuit emulation over IP, for instance, TDM data received from an external device at the edge of an IP network is converted to IP packets, sent through the IP network, passed out of the IP network to its destination, and reassembled into TDM bit stream. Clock synchronization is very important for CES. This paper presents a clock synchronization scheme based on a double exponential filtering technique and a linear process model. The linear process model is used to describe the behaviour of clock synchronization errors between a transmitter and a receiver. In the clock synchronization scheme, the transmitter periodically sends explicit time indications or timestamps to a receiver to enable the receiver to synchronize its local clock to the transmitter's clock. A phase-locked loop (PLL) at the receiver processes the transmitted timestamps to generate timing signal for the receiver. The PLL has a simple implementation and provides both fast responsiveness (i.e. fast acquisition of transmitter frequency at a receiver) and significant jitter reduction in the locked state. Copyright © 2006 John Wiley & Sons, Ltd. [source] A novel search method to reduce PAPR of an OFDM signal using partial transmit sequencesINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2007Hao-Chung Tu Abstract One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub-blocks. In this paper, we propose a novel PTS technique with reduced complexity that each level inverts twice of phase factor bits from previous level. Then we also use initial random phase sequence to find the better search way of PAPR reduction. Numerical results show that the proposed method can achieve significant reduction in search complexity with little performance degradation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communicationsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2004P. L. Katsis Abstract Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency-selective fading environment with additive coloured Gaussian noise which is used to model the actual in-home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC-CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single-user and multi-user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal-to-noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd. [source] Burst scheduling for differentiated services in optical burst switching WDM networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2004David Q. Liu Abstract Optical burst switching (OBS) is one of the most important switching technologies for future optical wavelength division multiplexing (WDM) networks and the Internet. The model of differentiated services has been proposed to support quality of service (QoS) in the IP-based Internet. It is also very important to have differentiated service support in OBS networks. When the burst scheduling in an OBS network is set up appropriately, network can support differentiated services. In this paper, we proposed a new burst scheduling scheme, called differentiated scheduling with identical priority offset time (DSIPO). In DSIPO, the same priority offset time is used for all the bursts destined to the same edge node regardless of their priorities. Differentiated services in terms of burst loss probability are achieved by processing the control packets of higher priority class bursts, thus reserving resources for their data bursts, more promptly upon their arrival than those of lower priority class bursts. Each intermediate (core) node can adjust the burst loss probabilities of various burst classes by choosing its own differentiated processing delay value for each priority class or its own differentiated processing delay difference value between any pair of adjacent priority classes. We model and analyse DSIPO in terms of the burst loss probability for each priority class with simulation validation. The performance of DISPO is evaluated by simulation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Adaptive predistortion of COFDM signals for a mobile satellite channelINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2003Nibaldo Rodriguez Abstract In this paper, we consider the optimization of the performance of QPSK and 16-QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non-linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non-linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non-linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10,3 when compared to QPSK COFDM without the predistortion scheme and 16-QAM COFDM provides a gain of 0.5 dB output back-off and 1.2 dB signal to noise ratio at a BER of 3×10,5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10,4 for QPSK and 16-QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd. [source] Development of mobile broadband interactive satellite access system for Ku/Ka bandINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2006Yun-Jeong Song Abstract It is difficult to implement the broadband satellite Internet and broadcasting service for mobile environment. The paper presents the design and implementation of a mobile broadband satellite access system. In case of the system design, mobile terminal service is considered a critical factor than fixed terminal services, such as resource management, antenna tracking, weak signal recovery. In the paper, mobile broadband interactive satellite access technology system (MoBISAT) is presented. The system network, which is composed of a star network, consists of time division multiplexing-based forward link and multi-frequency time division multiple access-based return link. The MoBISAT provides both Ku-band satellite TV and Ka-band high-speed Internet base on DVB-S/DVB-RCS standards to the passengers and crews for land, maritime and air vehicles. The key factors of hub and mobile terminal are addressed for the design and implementation of the MoBISAT. Especially, the design and implementation of the return link demodulation method, resource management scheme and mobile terminal structure including mobile antenna are described. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||||||||