This letter proposes a new multicast traffic control policy in TDM-PON, which differentially classifies multicast flows which have relatively many associated receivers as high-class, and multicast flows which have relatively few associated receivers as low-class. Simulation results confirm that the proposed policy can effectively enhance multicast performance regarding delay and loss, specifically important to multimedia services, compared to the legacy policy.

In this paper, we demonstrate a 10.66 Gb/s bidirectional TDM over long-reach WDM hybrid PON supported by distributed Raman amplification, and the power budget margin is measured to be 15 dB for downstream transmission and 12 dB for upstream transmission, with dual Raman pump power of 300 mW.

Being different from other networks, the load and direction of data traffic for wireless sensor networks are rather predictable. The relationships between nodes are cooperative rather than competitive. These features allow the design approach of a protocol stack to be able to use the cross-layer interactive way instead of a hierarchical structure. The proposed cross-layer protocol CLWSN optimizes the channel allocation in the MAC layer using the information from the routing tables, reduces the conflicting set, and improves the throughput. Simulations revealed that it outperforms SMAC and MINA in terms of delay and energy consumption.

The use of frequency-domain interleaving on a frame-by-frame basis for orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) is presented. In conventional OFDM, FDE is not designed to exploit the channel frequency-selectivity and consequently, the frequency diversity gain cannot be obtained. To further improve the bit error rate (BER) performance of conventional OFDM an interleaving technique may be applied, but FDE cannot be fully exploited. In this letter, the OFDM/TDM signal (i.e., several concatenated OFDM signals) frequency components are interleaved at the transmitter and then, minimum mean square error frequency-domain equalization (MMSE-FDE) is applied at the receiver to obtain a larger frequency diversity gain. It is shown that frequency-domain interleaving on a frame-by-frame basis for OFDM/TDM using MMSE-FDE achieves improved BER performance in comparison with conventional OFDM due to enhanced frequency diversity gain.

Slotted wireless ad hoc networks are drawing more and more attention because of their advantage of QoS (Quality of Service) support for multimedia applications owing to their collision-free packet transmission. Time slot assignment is an unavoidable and important problem in such networks. The existing time slot assignment methods have in general a drawback of limited available bandwidth due to their local assignment optimization without the consideration of directions of the radio wave transmission of wireless links along the routes in such networks. A new time slot assignment is proposed in this paper in order to overcome this drawback. The proposed assignment is different from the existing methods in the following aspects: a) consideration of link directions during time slot assignment; b) largest bandwidth to be achieved; c) feasibility in resource limited ad hoc networks because of its fast assignment. Moreover, the effectiveness of the proposal is confirmed by some simulation results.

The medical body area network (MBAN) is an emerging technology to resolve the small area connection issues around human body, especially for the medical applications. This paper proposes a dynamic TDMA (DTDMA) protocol for MBAN with focus on the dependability and power efficiency. In DTDMA, the slots are allocated by the MBAN coordinator only to the devices which have buffered packets and released to other devices after the current allocation. Through the adaptive allocation of the slots in a DTDMA frame, the MBAN coordinator adjusts the duty cycle adaptively with the traffic load. Comparing with the IEEE 802.15.4 MAC protocol, the DTDMA provides more dependability in terms of lower packet dropping rate and less energy consumption especially for an end device of a MBAN.

This paper presents an efficient time slot assignment algorithm for a wireless sensor and actor network (WSAN), which consists of stationary sensors for detecting events and mobile actors for performing tasks. TDMA protocols are suitable for WSAN due to time-critical tasks, which are assigned to actors. In order to improve the performance of TDMA protocol, a time slot assignment algorithm should generate not only efficient TDMA scheduling but also reduce periodic run-time overhead. The proposed algorithm offers O(δ2) run-time in the worst case, where δ is the maximum number of one-hop and two-hop neighbors in the network. The average run-time in simulation results is far less than O(δ2), however, while the maximum number of assigned slots is bounded by O(δ). In order to reduce the run-time further, we introduce two fundamental processes in the distributed slot assignment and design the algorithm to optimize these processes. We also present an analysis and verify it using ns-2 simulations. Although the algorithm requires time synchronization and prior knowledge of two-hop neighbors, simulation results show that it reduces the run-time significantly and has good scalability in dense networks.

OFDM combined with TDM (OFDM/TDM) can be used to reduce a high peak-to-average power ratio (PAPR) of OFDM, but the PAPR reduction is not sufficient. To further reduce the PAPR, an amplitude clipping can be applied. In this letter, we investigate the effect of clipping on OFDM/TDM with and without channel coding. It is shown that amplitude clipped OFDM/TDM has an advantage over clipped OFDM with respect to the PAPR.

This paper addresses the issue of transmission scheduling in wireless ad hoc networks. We propose a Time Division Multiple Access (TDMA) scheduling scheme based on edge coloring and probabilistic assignment, called CP-TDMA. We categorize the conflicts suffered by wireless links into two types: explicit conflicts and implicit conflicts, and utilize two different strategies to deal with them. Explicit conflicts are avoided completely by a simple distributed edge-coloring algorithm µ-M, and implicit conflicts are minimized by applying probabilistic time slot assignments to links. We evaluate CP-TDMA analytically and numerically, and find that CP-TDMA, which requires only local information exhibits a better performance than previous work.

In one-cell-frequency-reuse Orthogonal Frequency Division Multiple Access based Time Division Multiple Access (OF/TDMA) systems, communication is blocked by interference from adjacent cells. The most promising solution would be an adaptive modulation and coding scheme that is controlled by estimating the signal-to-interference ratio (SIR). However, there has so far been no way to accurately estimate the SIR using the spreading codes for OF/TDMA systems, because of the asynchronous fast Fourier transform (FFT). In this paper, we propose a novel SIR estimation method that uses a spread pulse-wave symbol and carrier interferometry. Moreover, to introduce multi- input multi-output systems, we modify the proposed method by allocating a different spreading code to each cell. Computer simulation confirmed that the SIR is estimated accurately even if the FFT is asynchronous. On cell boundaries, the average estimation errors that are a ratio between accurate and estimated propagation characteristics are less than 2 dB.

In this paper, we propose an adaptive guard symbol insertion method for one-cell reuse TDMA cellular systems in which co-channel interference is reduced by adaptively selecting the best transmit-pulse waveform with different guard (null-) symbols according to the average error power (AEP) corresponding to signal-to-interference and noise power ratio (SINR), even though the same frequency channel is used at all base stations. Using the proposed system, current TDMA-based systems are readily extensible to one-cell reuse systems, which achieves higher spectrum efficiency. The system capacity is enhanced using the proposed method; moreover, the required qualities such as blocking probability and outage probability are retained.

In this paper, we propose a PON-based access network based on conventional TDM-PON architecture for the smooth, economical and effective transition to the future optical access network. We also propose a dynamic MAC protocol for wavelength channel and bandwidth allocation in the TDM-PON subscriber networks, which can provide enhanced network scalability and flexibility, and greater adaptability to the increasing number of subscribers in TDM-PON. In the proposed dynamic MAC protocol, several key functions are manifested, such as multiple wavelength channel utilization and dynamic allocation of multiple time-slots to a user depending on SLA between OLT and ONUs to meet QoS requirements. A dedicated control channel is used for delivering the request and status information between OLT and ONUs. We evaluate the performances of the proposed MAC protocol thru a statistical queuing analysis and numerical simulations. In addition, through simulations using various traffic models we verify the superior performance of the proposed approach by comparing it with conventional TDM-PONs.

In this letter, we propose PQ-MAC: a priority-based medium access control (MAC) protocol for providing quality of service (QoS) in wireless sensor networks (WSNs) which minimizes the energy consumption with traffic-based sleep-wakeup scheduling and supports QoS using differentiating channel access policy, packet scheduling, and queue management. The PQ-MAC utilizes the advantages of time division multiple access (TDMA) and slotted carrier-sense multiple access (CSMA). The proposed protocol is an energy-efficient, priority-based, and QoS compatible MAC protocol. It consists of multi-level queue management, sleep-wakeup scheduling, and an ordered contention period (CP) scheme. It also guarantees time-bounded delivery of QoS packets. Performance evaluation is conducted between PQ-MAC and S-MAC with respect to three performance metrics: energy consumption, throughput, and average latency. The simulation results show that the performance of PQ-MAC is better than that of S-MAC.

This paper proposes a channel estimation technique for the dynamic parameter controlled--orthogonal frequency and time division multiple access (DPC-OF/TDMA) systems studied as one of the candidates of the beyond third generation (B3G) systems. In the proposed scheme, the impulse response, which represents the channel state information (CSI) is estimated using carrier interferometry (CI) which is equivalent to impulse signal transmission. Moreover, because the minimum number of subcarriers allocated to terminals is 64, in order to estimate a CSI with its spreading factor of 64, we employ a code-multiplexed CI signal for a cell search process and a time-domain-multiplexed CI signal for transmit antenna identification. Furthermore, we also propose a flexible CSI estimation scheme that supports two cases: multiple subchannel block assignment and MIMO transmission cases. Computer simulation confirms that the proposed scheme can estimate the CSI with high accuracy.

During these years, we have been focusing on developing ultra high-data-rate wireless access systems for future wireless multimedia communications. One of such kind of systems is called DPC-OF/TDMA (dynamic parameter controlled orthogonal frequency and time division multiple access) which targets at beyond 100 Mbps data rate. In order to support higher data rates, e.g., several hundreds of Mbps or even Gbps for future wireless multimedia applications (e.g., streaming video and file transfer), it is necessary to enhance DPC-OF/TDMA system based on MIMO-OFDM (multiple-input multiple-output orthogonal frequency division multiplexing) platform. In this paper, we propose an enhanced DPC-OF/TDMA system based on Multi-Layer MIMO-OFDM scheme which combines both diversity and multiplexing in order to exploit potentials of both techniques. The performance investigation shows the proposed scheme has better performance than its counterpart based on full-multiplexing MIMO-OFDM scheme. In addition to the Exhaustive Detection (EXD) scheme which applies the same detection algorithm on each subcarrier independently, we propose the Reduced-Complexity Detection (RCD) scheme. The complexity reduction is achieved by exploiting the suboptimal Layer Detection Order and subcarrier correlation. The simulation results show that huge complexity can be reduced with very small performance loss, by using the proposed detection scheme. For example, 60.7% complexity can be cut off with only 1.1 dB performance loss for the 88 enhanced DPC-OF/TDMA system.

Downlink multiuser MIMO system has attracted considerable attention recently for its potential to increase the system capacity. However, due to the limitation on the number of transmit antennas, when there are more users than can be supported simultaneously in a cell, other multiple access schemes, such as TDMA, must be applied in combination with multiuser MIMO. In this paper, we aim to design practical user scheduling algorithms to maximize the system capacity. Because the brute-force search for optimal user allocation is computationally prohibitive, we propose three low complexity suboptimal scheduling algorithms that offer both low complexity and high performance.

During these years we have been focusing on developing ultra high-data-rate wireless access systems. One of such kind of systems is called DPC-OF/TDMA [2]-[4] (dynamic parameter controlled orthogonal frequency and time division multiple access) which targets at data rates beyond 100 Mbps. In order to support higher data rates, e.g., several hundreds of mega bps or even giga bps, it is necessary to evolve DPC-OF/TDMA on MIMO-OFDM (multiple-input multiple-output orthogonal frequency division multiplexing) platform. In this paper, we propose two MIMO-OFDM evolution schemes for DPC-OF/TDMA: M1 scheme and M2 scheme. M1 scheme is based on the combination of V-BLAST (vertical Bell laboratories layered space-time architecture) and OFDM. It invests all transmit antennas on multiplexing while exploits no diversity in the transmitter. M2 scheme is based on multi-layer space-time block coded OFDM (multi-layer STBC OFDM). This scheme achieves a good compromise between multiplexing and diversity in the transmitter. We conduct exhaustive simulations for 44, 46, 48, 66, 68, and 88 systems. We are assured that both evolution schemes are very promising in supporting several hundreds of mega bps data rates. Moreover, we find that each evolution scheme has its own prevailing area. When the receive diversity order is limited, M2 scheme has better performance since it embeds transmit diversity; as the receive diversity order increases, the performance gap between the two schemes shrinks and finally M1 scheme prevails in performance. Therefore, the proper choice depends on the system configuration, i.e., how many transmit and receive antennas are used.

A nonlinear optical fiber loop mirror (NOLM) adapted for all-optical 2R operation at ultrahigh bit-rates was experimentally and theoretically investigated. The proposed NOLM was created by adding inline/external fiber polarizers and also an inline optical phase-bias compensator (OPBC) to a standard NOLM. A theoretical investigation revealed that the operation of the standard NOLM became unstable due to residual polarization crosstalk of the polarization-maintaining optical components making up the NOLM, and that it could be dramatically improved with the inline/external polarizers. The NOLM with the polarizers ensured stable switching operation with high switching-dynamic-range (>30 dB) against the change of the wavelength of the input clock pulses, and the change of the environment temperature. We also experimentally verified that the OPBC played a dramatic role to ensure excellent dynamic switching performance of the NOLM, and to achieve signal-Q-recovery of the regenerated signals. All optical 2R experiments at 40 Gb/s and 160 Gb/s were performed with the modified NOLM. Signal regeneration with improved extinction ratio and signal Q value was successfully demonstrated. Q-recovery to the input of the control pulses degraded with ASE noise accumulation was also successfully achieved.

In this letter, we introduce frequency-domain space-time transmit diversity (STTD) encoding/decoding to orthogonal frequency division multiplexing combined with time division multiplexing (OFDM/TDM) on a frame-by-frame basis (i.e., over several concatenated OFDM signals in the frequency-domain) to achieve both spatial and frequency diversity gains and improve the bit error rate (BER) performance. The theoretical BER performance is evaluated by numerical computation using the derived conditional BER and confirmed by computer simulation.

We have been investigating an orthogonal frequency division multiple access (OFDMA) based cellular system that is called "dynamic parameter controlled orthogonal frequency and time division multiple access (DPC-OF/TDMA)" for the development of beyond third generation (B3G) mobile communication systems. Moreover, we have already proposed a time alignment control (TAC) to compensate propagation delays that induce a multiple-access interference (MAI) in the uplink OFDMA. However, that TAC includes a large amount of computations. This means that it is quite difficult for the OFDMA systems to implement TAC into volume-limited hardware devices such as field programmable gate array (FPGA). Thus, we propose a new complexity-reduced TAC (CRTAC) in this paper. CRTAC can be implemented into such devices easily. In this paper, we show some computer simulation results, and then evaluate the error rate performances of DPC-OF/TDMA employing CRTAC. Moreover, we also show the benefit of the reasonable level of the implementation complexity made by CRTAC.