We present our proposed designs of optical access architecture based on WDM technology toward new-generation networks for two types of topologies: Single-star (SS) and passive-double-star (PDS). We adopt the concept of WDM-direct which links multiple wavelengths to each optical network unit (ONU). Our proposed architecture based on WDM-direct can achieve more than 10Gbps access per ONU. Moreover, our architecture can provide not only conventional bandwidth-shared services but also bandwidth-guaranteed services requiring more than 10Gbps bandwidth by establishing end-to-end lightpaths directly to each ONU, and thus meet high requirements of QoS in new-generation networks. Firstly, we show our proposed designs of SS-type architecture, and experimentally demonstrate the system. We confirm that the optical line terminal (OLT) successfully switches between packet/lightpath data transmissions for each ONU. In addition, we measure and evaluate optical power loss in upstream/downstream transmissions between the OLT and ONUs. Secondly, we show our proposed designs of PDS-type architecture, and theoretically analyze and evaluate the bit-rate capacity of the system.

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We propose the network on demand concept to yield the optical access network system that well handles the diversity in user demands and support technologies such as module and devices configuration. In this proposal, the network accommodation equipment, such as OLT needed for each service, is installed ‘virtually’ using WDM, and the physical rate can adapt to the user-demanded service rate by using the WDM parallel transmission technique. It well handles the diversity in user demands/services and lowers system power consumption.

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This paper reviews the standardization work that has been done in question 2 of ITU-T study group 15, which is the lead group on optical access transport technology. The major topics covered are the progress in the G-PON series and the new point-to-point fiber access recommendation. Finally, a brief view of the future plan of XG-PON is presented.

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An Optical Line Terminal (OLT) needs to find and register newly connected Optical Network Units (ONUs) in the proposed Ethernet Optical Switched Access Network (E-OSAN) as well as the Ethernet Passive Optical Network (E-PON). In this discovery process, OLT measures round trip time (RTT) between OLT and each ONU and then assigns a Logical Link Identification (LLID) to each ONU. For E-OSAN, the conventional discovery method takes up to N discovery periods for OLT to register all ONUs, where N denotes the number of switch ports of the Optical Switching Module (OSM). This paper proposes an efficient method that completes discovery in just one period. This paper also evaluates the maximum ranging completion time of the proposed discovery method in a comparison with E-PON.

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We propose an optical switch control procedure for the Active Optical Access System (AOAS). Optical switches are used in AOAS instead of optical splitters in PON. In the proposed procedure, an OLT determines the switching schedules of optical switches on OSW (Optical Switching Unit) which is installed between OLT and ONU, and informs the OSW of them with a switch control frame preceding of data frame transmission. Then the switch controller on OSW controls the optical switches based on the switching schedules. We developed the prototype systems of OSW, OLT, and ONU. We implemented the optical switch control function with logic circuits on the prototype systems. We demonstrate the proposed procedure works effectively with logic circuits. We also evaluate the 10Gps optical signal transmission between OLT and ONU. We demonstrate the receiver sensibility on OLT and ONU achieves the distance of 40km for optical signals transmission with FEC (Forward Error Correction). These receivers are applicable for both AOAS and 10G-EPON.

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This paper proposes a power saving mechanism with variable sleep period to reduce the power consumed by optical network units (ONUs) in passive optical network (PON) systems. In the PON systems based on time division multiplexing (TDM), sleep and periodic wake-up (SPW) control is an effective ONU power saving technique. However, the effectiveness of SPW control is fully realized only if the sleep period changes in accordance with the traffic conditions. This paper proposes an SPW control mechanism with variable sleep period. The proposed mechanism sets the sleep period according to traffic conditions, which greatly improves the power saving effect. In addition, the protocols needed between an optical line terminal (OLT) and ONUs are described on the assumption that the proposed mechanism is applied to 10 Gigabit (10G) class PON systems, i.e. IEEE 802.3av 10G-EPON and FSAN/ITU-T 10G-PON systems. The validity of the proposed mechanism is confirmed by numerical simulations.

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We analyze the beat noise cancellation in two-dimensional optical code-division multiple-access (2-D OCDMA) systems using an optical hard-limiter (OHL) array. The Gaussian shape of optical pulse is assumed and the impact of pulse propagation is considered. We also take into account the receiver noise and multiple access interference (MAI) in the analysis. The numerical results show that, when OHL array is employed, the system performance is greatly improved compared with the cases without OHL array. Also, parameters needed for practical system design are comprehensively analyzed.

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We propose a new Internet group management protocol (IGMP) which can be used in passive optical network (PON) especially for IPTV services which dramatically reduces the channel change response time caused by traditional IGMP. In this paper, the newly proposed IGMP is introduced in detail and performance analysis is also included. Simulation results demonstrated the performance of the newly proposed IGMP, whereby, viewers can watch the shared IPTV channels without the channel change response time when channel request reaches a threshold.

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The scalability of three-stage Clos-network packet switches makes them an attractive approach in implementing large-size packet switches. However, the configuration time of Clos-network switches depends on both the buffering strategy used and the adopted configuration process. To reduce configuration time, this paper focuses on the so-called Memory-Space-Memory (MSM) Clos-network packet switch, where the switch modules in the first and third stages use memory to support resolution of output port contention. The configuration of these switches is then based on a process to dispatch cells from the first-stage modules to the third-stage modules. Therefore, the throughput of an MSM Clos-network switch depends on the dispatching scheme used. This paper introduces a cell dispatching scheme, called maximum weight matching dispatching (MWMD) scheme, for MSM Clos-network switches and a request queue structure in the first-stage modules. The MWMD scheme performs maximum weight matching, similar to that used for input-queued single-stage packet switches, that in combination with the request queues can achieve 100% throughput under independent and identical admissible traffic. This high throughput can be achieved without allocating buffers in the second stage and without expanding the second stage of this three-stage packet switch. A low-complexity dispatching scheme, the maximal oldest-cell-first matching dispatching (MOMD) scheme, is also introduced as an alternative to MWMD. The performance evaluation in this paper shows that MOMD achieves high throughput under unbalanced traffic through the execution of a finite number of iterations.

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Energy efficient routing is one of the key design issues to prolong the lifetime of wireless sensor networks (WSNs) since sensor nodes can not be easily re-charged once they are deployed. During routing process, the routes with only few hops or with too many hops are not energy efficient. Hop-based routing algorithms can largely improve the energy efficiency of multi-hop routing in WSNs because they can determine the optimal hop number as well as the corresponding intermediate nodes during multi-hop routing process under medium or high density network. In this paper, we not only focus on studying the relationship between energy consumption and hop number from theoretical point of view but also provide a practical selection criterion of the sub-optimal hop number under practical sensor network so as to minimize the energy consumption. We extend the theoretical deduction of optimal hop number and propose our Hop-based Energy Aware Routing (HEAR) algorithm which is totally distributed and localized. Simulation results show that our HEAR algorithm can reduce the average energy consumption about 10 times compared to the direct transmission algorithm and 2 to 10 times than other algorithms like LEACH and HEED under various network topologies.

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In the present paper, we propose an evolutionary P2P networking technique that dynamically and adaptively optimizes several P2P network topologies, in which all of the nodes are included at the same time, in an evolutionary manner according to given evaluation criteria. In addition, through simulations, we examine whether the proposed evolutionary P2P networking technique can provide reliable search capability in dynamic P2P environments. In simulations, we assume dynamic P2P environments in which each node leaves and joins the network with its own probability and in which search objects vary with time. The simulation results show that topology reconstruction by the evolutionary P2P networking technique is better than random topology reconstruction when only a few types of search objects are present in the network at any moment and these search objects are not replicated. Moreover, for the scenario in which the evolutionary P2P networking technique is more effective, we show through simulations that when each node makes several links with other nodes in a single network topology, the evolutionary P2P networking technique improves the reliable search capability. Finally, the number of links that yields more reliable search capability appears to depend on how often nodes leave and join the network.

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The number of threats on the Internet is rapidly increasing, and anomaly detection has become of increasing importance. High-speed backbone traffic is particularly degraded, but their analysis is a complicated task due to the amount of data, the lack of payload data, the asymmetric routing and the use of sampling techniques. Most anomaly detection schemes focus on the statistical properties of network traffic and highlight anomalous traffic through their singularities. In this paper, we concentrate on unusual traffic distributions, which are easily identifiable in temporal-spatial space (e.g., time/address or port). We present an anomaly detection method that uses a pattern recognition technique to identify anomalies in pictures representing traffic. The main advantage of this method is its ability to detect attacks involving mice flows. We evaluate the parameter set and the effectiveness of this approach by analyzing six years of Internet traffic collected from a trans-Pacific link. We show several examples of detected anomalies and compare our results with those of two other methods. The comparison indicates that the only anomalies detected by the pattern-recognition-based method are mainly malicious traffic with a few packets.

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Recently, the marginalized particle filter (MPF) has been applied to blind symbol detection problems over selective fading channels. The MPF can ease the computational burden of the standard particle filter (PF) while offering better estimates compared with the standard PF. In this paper, we investigate the application of the blind MPF detector to more realistic situations where the systems suffer from analog imperfections which are non-linear signal distortion due to the inaccurate analog circuits in wireless devices. By reformulating the system model using the widely linear representation and employing the auxiliary variable resampling (AVR) technique for estimation of the imperfections, the blind MPF detector is successfully modified to cope with the analog imperfections. The effectiveness of the proposed MPF detector is demonstrated via computer simulations.

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Multi-user multiple input multiple output (MU-MIMO) systems have attracted much attention as a technology that enhances the total system capacity by generating a virtual MIMO channel between a base station and multiple terminal stations. Extensive evaluations are still needed because there are many more system parameters in MU-MIMO than in single user (SU)-MIMO and the MU-MIMO performance in actual environments is still not well understood. This paper describes the features and effectiveness of a 16 × 16 MU-MIMO testbed in an actual indoor environment. Moreover, we propose a simple adaptive modulation scheme for MU-MIMO-OFDM transmission that employs a bit interleaver in the frequency and space domains. We evaluate the frequency efficiency by obtaining the bit error rate of this testbed in an actual indoor environment. We show that 16 × 4 × 4-user MU-MIMO transmission using the proposed modulation scheme achieves the frequency utilization of 870Mbps and 1Gbps (respective SNRs: 31 and 36dB) with a 20-MHz bandwidth.

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This paper analyzes the ergodic capacity of the MIMO multi-keyhole channel, assuming that the channel state information (CSI) is available only at the receiver. We first derive new closed-form expressions for marginal probability density function (pdf) of the single unordered eigenvalue as well as joint pdf of ordered eigenvalues of the channel matrix in a simple and general framework. With these statistical results, we then present an exact closed-form expression for the ergodic capacity. We analyze tight bounds on the exact capacity and propose a new tight lower bound. We also investigate the asymptotic capacity performances in low-signal-to-noise-ratio (SNR) and high-SNR regimes to gain further insights. All our results apply for arbitrary number of keyholes and antennas. Numerical simulations are presented to validate our theoretical analysis.

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In this paper, we propose a novel noncoherent maximum likelihood detection (NMLD) method for differential spatial multiplexing (SM) multiple-input multiple-output (MIMO) systems. Unlike the conventional maximum likelihood detection (MLD) method which needs the knowledge of channel state information (CSI) at the receiver, NMLD method has no need of CSI at either the transmitter orreceiver. After repartitioning the observation block of multiple-symbol differential detection (MSDD) and following a decision feedback process, the decision metric of NMLD is derived by reforming that of MSDD. Since the maximum Doppler frequency and noise power are included in the derived decision metric, estimations of both maximum Doppler frequency and noise power are needed at the receiver for NMLD. A fast calculation algorithm (FCA) is applied to reduce the computational complexity of NMLD. The feasibility of the proposed NMLD is demonstrated by computer simulations in both slow and fast fading environments. Simulation results show that the proposed NMLD has good bit error rate (BER) performance, approaching that of the conventional coherent MLD with the extension of reference symbols interval. It is also proved that the BER performance is not sensitive to the estimation errors in maximum Doppler frequency and noise power.

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The paper proposes and analyzes an adaptive p-persistent-based (APP) medium access control (MAC) scheme for IEEE 802.11 WLAN. The APP MAC scheme intends to support delay fairness for every station in each access, denoting small delay variance. It differentiates permission probabilities of transmission for stations which are incurred with various packet delays. This permission probability is designed as a function of the numbers of retransmissions and re-backoffs so that stations with larger packet delay are endowed with higher permission probability. Also, the scheme is analyzed by a Markov-chain analysis, where the collision probability, the system throughput, and the average delay are successfully obtained. Numerical results show that the proposed APP MAC scheme can attain lower mean delay and higher mean throughput. In the mean time, simulation results are given to justify the validity of the analysis, and also show that the APP MAC scheme can achieve more delay fairness than conventional algorithms.

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In this paper, the exact distribution of the channel capacity of MISO (multiple-input single-output) systems subject to co-channel interference is derived from an information theoretic viewpoint. It is found that the MISO channel capacity in the interference-limited channel follows the F-distribution. By using these capacity distributions, the outage capacity in Rayleigh fading channels can be accurately computed. We confirm the accuracy of our analysis by performing simulations. Our results exactly match those of the empirical simulations of interference-limited systems.

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It is well known that the performance of turbo codes can be improved by optimizing the energy allocation on coded symbols. Based on this fact, we propose an optimized 16-quadrature amplitude modulation (QAM) constellation for binary turbo codes. In the proposed scheme, the energy allocated on turbo coded symbols is optimized by modifying the constellation of QAM. The proposed 16-QAM constellation combined with a binary turbo code offers better coding gain compared to the conventional combination of binary turbo code and QAM.

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This paper proposes a new hybrid scheme based on a given set of channels for preventing channel interference and collision in mobile networks. The proposed scheme is designed for improving system performance, focusing on enhancement of performance related to path breakage and channel interference. The objective of this scheme is to improve the performance of inter-node communication. Simulation results from this paper show that the new hybrid scheme can reduce a more control message overhead than a conventional random scheme.

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A dynamic coding mechanism is presented to implement distributed signature based IDS (Intrusion Detection System) in IP-USN (IP-based Ubiquitous Sensor Networks). The proposed scheme allows the creation of a lightweight IDS in terms of storage, messaging and energy consumption, which make it appropriate for resource constrained sensor devices.

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Wireless sensor networks are subject to node and link failures for a variety of reasons. This paper proposes a k-disjoint-path routing algorithm that varies the number of disjoint paths (k) in order to meet a target-delivery ratio of critical events and to reduce energy consumption. The proposed algorithm sends packets to the base station through a single path without the occurrence of critical events, however, it sends packets to the base station through k disjoint paths (k > 1) under the occurrence of critical events, where k is computed from a well-defined fault model. The proposed algorithm detects the occurrence of critical events by monitoring collected data patterns. The simulation results reveal that the proposed algorithm is more resilient to random node failure and patterned failure than other routing algorithms, and it also decreases energy consumption much more than the multi-path and path-repair algorithms.

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This paper proposes a hardware-based parallel pattern matching engine using a memory-based bit-split string matcher architecture. The proposed bit-split string matcher separates the transition table from the state table, so that state transitions towards the initial state are not stored. Therefore, total memory requirements can be minimized.

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This letter investigates the space-time block codes from quasi-orthogonal design as a tradeoff between high transmission rate and low decoding complexity. By studying the role orthogonality plays in space-time block codes, upper bound of transmission rate and lower bound of decoding complexity for quasi-orthogonal design are claimed. From this point of view, novel algorithms are developed to construct specific quasi-orthogonal designs achieving these bounds.

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This paper proposes an optimized phase rotation sequence method for side lobe suppression by complementing and regulating the side lobe suppression sequence set. The sequence set is efficiently enhanced through the quadratically constrained least square model. The theoretical suppression performance of our method is discussed. Furthermore, our scheme is also suitable for cognitive radio, which is analyzed in the simulation part. The simulation results confirm the effectiveness of our schemes.

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Precoding techniques can be introduced into relay systems due to the similarity between relay systems and traditional multi-input-multi-output (MIMO) systems. A channel state information feedback scheme is firstly presented for the MIMO relay system in this letter, where the zero-forcing relaying protocol is proposed to be used so that the information of the equivalent channel and the relaying noise can be compressed into two coefficients. With the proposed feedback scheme, the distributed precoding is presented to be applied through two continuous transmitted vectors of the source node while the co-channel interference cancellation equalizer is used in the destination node. The system outage probability can be improved with the precoding in the source node. Furthermore, various spatial data rates can be conveniently supported by the proposed distributed spatial-temporal precoding method.

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In this letter, we analyze the error performance of a code combining based cooperative diversity protocol. For coded transmission schemes, code-combining can obtain a near optimal low rate code by combining repeated codewords. An analytical method for evaluating the performances of such scheme is presented. We develop a closed form expression for pairwise error probability and tight upper bounds for bit error rate (BER) and frame error rate (FER) under Rayleigh fading environment. The analytical upper bounds are verified with simulation results.

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We analyze the performance of an adaptive communication scheme in which by employing limited feedback, the source will decide to transmit signal to the destination either by the direct link or by the direct and relaying links. Specifically, by using the instantaneous SNR as the metric, if the S-D link is better, the source will transmit to destination directly. Otherwise, the two-phase transmission mode will be triggered in which source cooperates with the relay or transmits twice within two time slots based on the quality of the received signal at the relay. Initially, the spectral efficiency is derived by calculating the probabilities of direct transmission and two-phase transmission mode. Subsequently, the BER performance for the adaptive cooperation schemes is analyzed by considering the BER routines of two events: the source transmits the signal alone or cooperates with the relay. Also, the optimum power allocation is studied based on the BER result. Finally, Monte-Carlo simulation results are presented to confirm the performance enhancement offered by the proposed scheme.

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This paper investigates the performance of ARQ-aided downlink Time Switched Transmit Diversity (TSTD) in the WCDMA Low Chip Rate (LCR)-Time Division Duplex (TDD) system, when antenna switching and power ramping are applied. With the help of the ARQ signal, where the receiver sends the acknowledgement (ACK or NACK) to the transmitter, the proposed TSTD scheme switches the transmit antenna and ramps up the transmission power for the retransmitted data, when the transmitter receives a NACK signal. Simulation results demonstrate, that when the mobile speed is 3km/h and a frame error rate (FER) is set to 1%, the antenna switching scheme yields 2dB to 3dB performance gain in terms of average Eb/N0, and the power ramping gives 0.7dB to 1.6dB gain, compared with the conventional ARQ-aided TSTD. In addition, 6% of throughput gain is shown by amalgamating the antennas switching as well as the power ramping, when the average Eb/N0 is equal to 0dB.

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In this paper we investigate a low complexity channel estimation and data transmission scheme for bi-directional relaying networks. We also propose a semi-orthogonal pilot structure for channel estimation to increase the efficiency of data transmission between the Base Station (BS) and Mobile Station (MS) via a fixed Relay Node (RN).

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