Maria C. Yuang

Opportunistic media access control and rate adaptation for wireless ad hoc networks

Many rate adaptation schemes at the medium access control (MAC) layer have been proposed to utilize the multirate capability offered by the IEEE 802.11 wireless MAC protocol through automatically adjusting the transmission rate to best match the channel conditions. In this paper, we present the Opportunistic packet Scheduling and Auto Rate (OSAR) protocol to exploit the channel variations. The basic idea of OSAR is as follows: rather than just matching the channel condition for a node pair in communications, our protocol takes advantage of the multiuser diversity as much as possible and adapt the rate accordingly, i.e., based on the channel conditions to its neighboring nodes, the sender chooses the neighboring node with channel quality better than certain level to schedule the transmissions of packets in its queue, then the overall system throughput may be increased. The key mechanisms of OSAR are channel aware media access, rate adaptation and packet bursting. We carry out several sets of ns-2 simulations and evaluate the impact of various factors such as channel condition, network topology and traffic load on the throughput of OSAR. Simulation results show that our proposed protocol can achieve much better performance than other auto rate schemes.

Multiple access control with intelligent bandwidth allocation for wireless ATM networks

Two major challenges pertaining to wireless asynchronous transfer mode (ATM) networks are the design of multiple access control (MAC), and dynamic bandwidth allocation. While the former draws more attention, the latter has been considered nontrivial and remains mostly unresolved. We propose a new intelligent multiple access control system (IMACS) which includes a versatile MAC scheme augmented with dynamic bandwidth allocation, for wireless ATM networks. IMACS supports four types of traffic-CBR, VBR, ABR, and signaling control (SCR). It aims to efficiently satisfy their diverse quality-of-service (QoS) requirements while retaining maximal network throughput. IMACS is composed of three components: multiple access controller (MACER), traffic estimator/predictor (TEP), and intelligent bandwidth allocator (IBA). MACER employs a hybrid-mode TDMA scheme, in which its contention access is based on a new dynamic-tree-splitting (DTS) collision resolution algorithm parameterized by an optimal splitting depth (SD). TEP performs periodic estimation and on-line prediction of ABR self-similar traffic characteristics based on wavelet analysis and a neural-fuzzy technique. IBA is responsible for static bandwidth allocation for CBR/VBR traffic following a closed-form formula. In cooperation with TEP, IBA governs dynamic bandwidth allocation for ABR/SCR traffic through determining the optimal SD. The optimal SDs under various traffic conditions are postulated via experimental results, and then off-line constructed using a back propagation neural network (BPNN), being used on-line by IBA. Consequently, with dynamic bandwidth allocation, IMACS offers various QoS guarantees and maximizes network throughput irrelevant to traffic variation.

A Lagrangean relaxation approach to routing and wavelength assignment for multi-granularity optical WDM networks

In this paper, we propose an efficient approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve routing and wavelength assignment (RWA) for multi-granularity WDM networks facilitating fiber, waveband, and lambda switching capabilities. The task is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. The LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. With lower and upper bounds, we delineate the performance of LRH with respect to accuracy and convergence speed under different parameter settings. We further draw comparisons between LRH and a typical linear programming (LP) approach via experiments over the widely-used NSFNET and three randomly generated networks. Numerical results demonstrate that LRH outperforms the LP approach in both accuracy and computational time complexity particularly for larger sized networks.

HOPSMAN: An Experimental Testbed System for a 10-Gb/s Optical Packet-Switched WDM Metro Ring Network

For future WDM MANs, optical packet-switching has been considered to be a promising paradigm that efficiently supports a wide range of Internet-based applications having time-varying and high bandwidth demands and stringent delay requirements. This article presents the design of an experimental testbed system for a high-performance optical packet-switched WDM metro ring network, HOPSMAN. HOPSMAN boasts three crucial features. First, it has a scalable architecture in which the number of nodes is unconstrained by the number of wavelengths. Second, HOPSMAN nodes are equipped with high-speed photonic hardware components, including fast tunable receivers and optical slot erasers, capable of performing speedy optical packet-switching operations. Third, HOPSMAN incorporates a MAC scheme that embodies efficient and dynamic bandwidth allocation, resulting in exceptional delay-throughput performance. The article presents the key hardware components by highlighting the challenging issues we faced and the solutions we proposed for the testbed implementation. Finally, to demonstrate the feasibility of HOPSMAN, the article describes the experimental setup and presents the results obtained from running a commercially available remote media player application on the system.

21 Gb/s after 100 km OFDM long-reach PON transmission using a cost-effective electro-absorption modulator.

We experimentally demonstrate a superior performance of 2.1-Tb/s·km OFDM signal transmission over 100-km long-reach PONs. While the bandwidth of a 100-km SMF transmission system is limited to 4.3 GHz due to positive chirp, we successfully achieve spectrally-efficient 21-Gb/s signaling by using a cost-effective and low-chirp EAM, and adopting the 128-QAM format and adaptive subcarrier pre-emphasis.

Using Superimposed ASK label in a 10-Gb/s multihop all-optical label swapping system

A novel optical-label-swapping technique is proposed, experimentally verified, and theoretically analyzed in this paper. The technique superimposes a low-speed amplitude-shift-keying (ASK) label on top of a high-speed dc-balanced-line-coded ASK payload. A multihop long-distance transmission experiment using a recirculating loop has been successfully demonstrated, and an experimental record is set when compared with other optical-label-swapping techniques.

High-efficiency wide-band SOA-based wavelength converters by using dual-pumped four-wave mixing and an assist beam

Wavelength conversion with a high efficiency and wide conversion range can easily be realized by applying an assist beam of short wavelength to a dual-pumped semiconductor optical amplifier (SOA). Experimental results reveal that an assist beam can improve the conversion efficiency and signal-to-background ratio by up to 8.5 and 4.1 dB, respectively, when the SOA is biased at the current that makes the SOA transparent to the assist beam. The efficiency can exceed -10 dB over an 80-nm wavelength conversion range using a 23-dB gain SOA. The assist beam increases the system power budget because it simultaneously improves the conversion efficiency and reduces the receiver power penalty. The power penalties for up-converting and down-converting 10-Gb/s signals to 25 nm of wavelength range are less than 0.5 and 2.5 dB, respectively.

A High-Performance OFDMA PON System Architecture and Medium Access Control

Orthogonal frequency-division multiplexing (OFDM) passive optical network (PON) has been considered to be a promising next-generation broadband wired access solution. However, based on the current tree-based architecture, existing OFDM PON systems face severe challenges when increasing the scalability and data-rate performance. In this paper, we propose a high-performance virtual-tree orthogonal frequency-division multiple access PON system (VTOPS). With the virtual-tree architecture and coupled with the use of inexpensive direct modulation, VTOPS features high reliability, scalability, spectrum efficiency, and cost effectiveness all at once. For governing the flexible/fair access and dynamic allocation of bandwidth, VTOPS incorporates a rate-based medium access control (MAC) scheme. The MAC scheme performs dynamic rate adjustment using a neural-fuzzy system. By adjusting the system parameters, the MAC scheme can achieve a wide range of delay and fairness performance under a variety of traffic patterns. Finally, we show both theoretical and experimental results to demonstrate that, by applying the power pre-emphasis algorithm and adaptive subchannel modulation, VTOPS achieves 40 Gb/s downlink and 40 Gb/s uplink transmissions, using low-cost 10 GHz directly modulated lasers.

Bandwidth assignment paradigms for broadband integrated voice/data networks

Broadband Integrated Services Digital Networks (BISDNS)/Asynchronous Transfer Mode (ATM) are expected to support diverse applications demanding different bandwidth and Quality of Services (QoSs). Particularly for integrated voice and data networks, voice traffic results in call losses and data traffic suffers from longer delays should networks have insufficient bandwidth. The main goal of the paper is to analytically determine optimal bandwidth allocated to voice and data by means of a queueing model with heterogeneous arrivals and multiple designated channels. The accuracy of analytical results is confirmed by simulation results. On the basis of the analysis, the paper proposes a bandwidth assignment paradigm for the assignment of network bandwidth to voice and data in an effort to guarantee minimal data delay and voice call blocking probability. The run time complexity of the bandwidth assignment computation and paradigm construction is shown to be polynomial bounded. Consequently, the resulting bandwidth assignment assures QoSs in terms of data delay and voice call blocking probability under various network loads.

QoS burstification for optical burst switched WDM networks

In this paper, we propose a QoS burstification (QBT) mechanism on the basis of a new notion window. The QBT mechanism efficiently emulates the burst behavior by exerting simple FIFO service within the window and weight-proportional service at the window boundary. As will be shown, QBT achieves fairness and mean-burstification-delay guarantees among various traffic classes.