A packet scheduling scheme for broadband wireless networks with heterogeneous services
A frame-based packet scheduling scheme, the pinwheel scheduling (PWS) scheme, is proposed and investigated at the medium access control (MAC) layer in broadband wireless networks. The objective of the proposed scheduling scheme is to provide, respectively, low delay and low jitter for real-time traffic and short queue length for nonreal-time traffic. We have demonstrated in this paper that the proposed PWS scheme not only satisfies the packet-level QoS requirements but also has low implementation cost. As the number of constant bit rate (CBR) connections increases, variable bit rate (VBR) traffic would suffer a larger jitter, the PWS with modular strategy (PWS/MS) scheme is proposed to further enhance the PWS scheme. We also introduce two different slot-reuse strategies named real-time traffic first (RTF) and longest queue first (LQF), respectively, to improve the resource utilization. In order to demonstrate the performance of the PWS and PWS/MS schemes, comparisons are made with existing schemes such as the round-robin (RR) and weighted-round-robin (WRR) by using the OPNET software. Simulation results show that the proposed schemes are capable of maintaining the lowest delay and jitter for VBR and CBR traffic while not sacrificing the available bit rate (ABR) traffic.

title: The study of dynamic multi-channel scheme with channel de-allocation in wireless networks
abstract: This paper proposes an analytical model to demonstrate the benefit of data service in wireless networks using dynamic multi-channel scheme with channel de-allocation (DMC-w-DA). Buffers are provided for voice calls to reduce the voice blocking probability caused by data packets contention. All free channels are allocated to data users dynamically. For those data users using more than one channel, channels would be de-allocated for new requests, voice or data. Handoff calls are given priority to be queued in the front of the buffer instead of providing guard channels to reduce their dropping probability To compensate the data packet loss probability in data, guard channels are provided for data traffic. Based on a given handoff dwell time, we analyze the dropping probability of handoff call. The probability distribution of receiving service within the handoff dwell time is obtained for each buffered handoff call and based on this result, an appropriate amount of handoff call allowed in buffer is obtained. Numerical results show that the dynamic multi-channel scheme with possible de-allocation, compared with the dynamic channel scheme without channel de-allocation, fixed channel allocation and single channel allocation scheme, can enhance data traffic performance significantly in terms of the mean service time and the packet loss probability. A system providing buffer to voice traffic and giving priority to queued handoff calls can indeed decrease new call blocking probability and handoff call dropping probability.

title: The study of quick download mechanism in an infrastructural wireless environment
abstract: Frequent handoff consumes a lot of system capability and signalling resources in a mobile system. In this paper, we present download mechanisms in mobile systems or broadcast systems to support data users to receive the whole packet in time before moving out of the coverage area. Three download strategies: Quick Download using Multi-channel (QDM) scheme, Prior Download using Single channel (PDS) scheme and the Quit Download (QUD) scheme are proposed in this study where the efficiencies of the three strategies are compared with the one without particular treatment. Some significant estimations such as the percentage of handoff data users having completed service before leaving the cell, the mean waiting time of non-handoff data users, and the blocking probability of data users are analysed and compared. The numerical results show that, the QDM strategy is most efficient in reducing the handoff rate, the QUD strategy can assure the waiting time of non-handoff data users and the PDS strategy can keep the handoff rate constant at light and heavy voice load. Furthermore, various number of guard channels for data users are evaluated in terms of data and voice performance based on various download strategies.

title: New Disk Scheduling Algorithms for Reduced Rotational Latency
abstract: Disk arm scheduling algorithms have been studied for many years to increase disk I/O performance. Most of the disks by the early 1980’s are characterized as a linear seek time and their seek time is responsible for the most time of disk access. So, the existing disk scheduling algorithms have focused on the reduction of the average seek distance. Seek time has improved greatly and today’s disks usually have nonlinear seek time characteristics, whereas the rotation speed has been steady at the 3600 RPM. So, it is of value to reduce average rotational latency. In this paper we propose two disk scheduling algorithms, i.e. Shortest Rotational Latency First(SRLF) and Shortest Access Tie Fist(SATF) for reduced rotational latency. SRLF services first a request with the shortest expected rotational latency and SATF services first a request with the shortest expected access time. We analyze the expected access time of the request serviced first by each of SSTF and SRLF under the uniform cylinder access. We evaluated the response time of SSTF, SRLF, and SATF through the simulations under the uniform and localized cylinder access. The results of the analysis and simulations show that the algorithms proposed in this paper are more efficient than SSTF which is known for the fastest response time.

title: Automated ordering of fingerprinted clones
abstract: A considerable amount of human intervention is currently required to produce high-quality fingerprint-based physical maps for genomic studies.



An algorithm has been developed and implemented to automatically order fingerprinted clones within contigs. The resulting software, named CORAL (Clone ORdering ALgorithm), has been tested on maps that have previously been manually edited and on maps derived from in silico simulations. The fingerprint map and DNA sequence of the human genome has provided an additional test to CORAL. Measurements suggest that CORAL performs significantly better than the software currently used by most laboratories to order fingerprinted clones at throughputs far exceeding those that can be achieved manually.

title: An Accurate Worst Case Timing Analysis for RISC Processors
abstract: An accurate and safe estimation of a task's worst case execution time (WCET) is crucial for reasoning about the timing properties of real-time systems. In RISC processors, the execution time of a program construct (e.g., a statement) is affected by various factors such as cache hits/misses and pipeline hazards, and these factors impose serious problems in analyzing the WCETs of tasks. To analyze the timing effects of RISC's pipelined execution and cache memory, we propose extensions to the original timing schema where the timing information associated with each program construct is a simple time-bound. In our approach, associated with each program construct is worst case timing abstraction, (WCTA), which contains detailed timing information of every execution path that might be the worst case execution path of the program construct. This extension leads to a revised timing schema that is similar to the original timing schema except that concatenation and pruning operations on WCTAs are newly defined to replace the add and max operations on time-bounds in the original timing schema. Our revised timing schema accurately accounts for the timing effects of pipelined execution and cache memory not only within but also across program constructs. This paper also reports on preliminary results of WCET analysis for a RISC processor. Our results show that tight WCET bounds (within a maximum of about 30% overestimation) can be obtained by using the revised timing schema approach.

title: Fast Pattern Selection for Support Vector Classifiers
abstract: SVMs tend to take a very long time to train with a large data set. If "redundant" patterns are identified and deleted in pre-processing, the training time could be reduced significantly. We propose a k-nearest neighbors(k-NN) based pattern selection method. The method tries to select the patterns that are near the decision boundary and that are correctly labeled. The simulations over synthetic data sets showed promising results: (1) By converting a non-separable problem to a separable one, the search for an optimal error tolerance parameter became unnecessary. (2) SVM training time decreased by two orders of magnitude without any loss of accuracy. (3) The redundant SVs were substantially reduced.

title: Capacity statistics and scheduling gain for MIMO systems in correlated Rayleigh fading
abstract: Taking into account realistic propagation environments, in the presence of spatial fading correlation at both the transmitter and the receiver, we derive closed-form analytical expressions for the exact characteristic function and statistical moments (mean, variance, skewness, and kurtosis) of instantaneous capacity for multiple-input multiple-output (MIMO) wireless channels. These results enable us to analytically evaluate two relevant information-theoretic capacity measures - ergodic and outage capacity - and other higher-order statistics of the capacity. We also analyze the multi-user scheduling gain in rate-feedback systems using the Gaussian approximation to the capacity distribution.