Hakyong Kim

Double-sided two-way ranging algorithm to reduce ranging time

In this letter we propose a novel ranging algorithm for the asynchronous location positioning system. The main idea of the proposed algorithm is to reply with multiple acknowledgement packets to a single ranging request. The ranging algorithm reduces the number of packets used in ranging process and improves the ranging accuracy at the same time.

Performance analysis of the multiple input-queued packet switch with the restricted rule

The multiple input-queued (MIQ) switch is the switch which manages multiple (m) queues in each input port, each of which is dedicated to a group of output ports. Since each input port can switch up to m cells in a time slot, one from each queue, it hardly suffers from the head-of-line (HOL) blocking which is known as the decisive factor limiting the throughput of the single input-queued (SIQ) switch. As the result, the MIQ switch guarantees enhanced performance characteristics as the number of queues m in an input increases. However, the service of multiple cells from an input could cause the internal speedup or expansion of the switch fabric, diluting the merit of high-speed operation in the conventional SIQ scheme. The restricted rule is contrived to circumvent this side effect by regulating the number of cells switched from an input port. In this paper, we analyze the performance of the MIQ switch employing the restricted rule. For the switch using the restricted rule, the closed formulas for the throughput bound, the mean cell delay and average queue length, and the cell loss bound of the switch are derived as the function of m, by generalizing the analysis for the SIQ switch by Hui et al., 1987.

Derivation of the mean cell delay and cell loss probability for multiple input-queued switches

The multiple input-queued (MIQ) asynchronous transfer mode (ATM) switch has drawn much interest as a promising candidate for a high-speed and high-performance packet switch. The most conspicuous feature of the switch is that each input port is equipped with m(1/spl les/m/spl les/N) distinct queues, each for a group of output ports. Since the MIQ switch has multiple queues, an input can serve up to m cells in a time slot, leading to an enhanced performance. We derive the average queue length, mean cell delay, and cell loss probability for the MIQ switch in terms of the number of queues in an input port (m) and input load. The results include a special case of the single input-queued (SIQ) switch (m=1), which is analyzed by Hui et al. (1987).

A ranging scheme for asynchronous location positioning systems

In a real-time locating system which does not require time synchronization among nodes, it takes a very long time to complete a ranging process for a single location estimation. Long ranging time makes mobile nodes consume a significant amount of battery power and limits the number of mobile nodes that a single fixed node can handle during a specific time interval. Therefore, it is crucial to shorten the ranging time in asynchronous locating systems without degradation in ranging or locating accuracy. In this paper, we propose an asynchronous two-way ranging scheme which reduces ranging time by replying with multiple packets to a single ranging request. The algorithm reduces ranging time by 17% or more, compared to that of existing methods.

Performance analysis of the SDS-TWR-MA algorithm

In this paper we evaluate the performance of the SDS-TWR-MA (Symmetric Double-Sided Two-Way Ranging with Multiple Acknowledgement) algorithm. The main idea of the ranging algorithm, which proposed in our previous work [5], is to reply with multiple acknowledgement packets to a single ranging request. The algorithm reduces the number of packets used for ranging process especially when we iterate it several times to yield a stabler ranging result. According to our analysis, the proposed ranging algorithm can reduce the ranging time by 30% or more, while keeping the locating accuracy high. Furthermore, the proposed algorithm allows us to use a coarse oscillator for precise location positioning by diminishing the influence of clock offset or clock drift.

A packet-based scheduling algorithm for high-speed switches

The bulk of the traffic passing through a data network is made up of variable-length packets like IP packets and, therefore, the efficient handling of variable-length packets is an essential and important issue in designing a high-speed and high-performance switch. Most high-speed switches or routers using virtual output queueing as their contention resolution scheme, switch variable-length packets in the form of small and fixed-size packets (or mini-packets), such as the ATM cell, enjoying benefits in the hardware implementation and the operating speed. That is, the scheduling algorithm used in those switches is based on cell-by-cell scheduling such as PIM and SLIP. These cell-based scheduling algorithms, however, can not fully guarantee the performance metrics of an application since performance measures relevant to the application are specified by the performance metrics of its data units (packets) rather than individual mini-packets. We present an efficient algorithm called packet-based SLIP (PBSLIP) for scheduling variable-length packets on high-speed packet switches. PBSLIP is a packet-based variation of SLIP proposed by N. McKeown (1993; 1995; 1999) and, therefore, most operations of PBSLIP are as simple as those of SLIP. A conspicuous dissimilarity is that PBSLIP consecutively switches a bunch of mini-packets belonging to a given packet while SLIP switches mini-packets irrespective of their correlation to adjoining mini-packets. Extensive simulation results demonstrate that PBSLIP could be a potential way to significantly improve the performance of conventional cell-based scheduling algorithms and reduce the control time.

A Speed-Adaptive Location Estimator for Wireless LAN-based RTLS Systems

In this paper, we propose a location estimation algorithm which improves the positioning accuracy in wireless LAN-based real-time locating systems (RTLS). For location estimation, the proposed algorithm makes use of the received signal strength (RSS) information and the speed information of mobile devices as well. We show that the proposed algorithm can provide better estimation accuracy than conventional ones through experiments, especially in positioning moving mobile devices

Throughput analysis of MIQ switches

The multiple input-queued (MIQ) switch is the switch which manages multiple (m) queues in each input port, each of which is dedicated to a group of output ports. Since each input port can attend m arbitration rounds, the switch suffers from a reduced HOL blocking which is known as the decisive factor limiting the throughput of the pure single input-queued (SIQ) packet switch. As a result, the MIQ switch guarantees satisfying performance characteristics as the number of queues m increases. However, the service of multiple cells from an input could cause the internal speedup or expansion of the switch fabric, diluting the merit of high-speed operation in the conventional SIQ scheme. The restricted rule is contrived to circumvent this side effect by regulating the number of cells switched from an input port to just one cell. In this paper we analyze the performance of the MIQ ATM switch employing the restricted rule. For the switch using the restricted rule, the closed formulae for the throughput bound of the switch are derived as the function of m, by generalizing the analysis for the SIQ switch by Hui et al. (1987).

Notice of Violation of IEEE Publication Principles An Approach to Reduce the Erlang B Probability in the M/M/2/2 System with Heterogeneous Servers

In this paper, we showed that the performance of the M/M/2/2 system can be improved by replacing its homogeneous servers with heterogeneous servers. Denoting by beta the ratio of the slow service rate to the fast service rate, we showed that there exists a range of beta within which the Erlang B probability is reduced. We also showed that there exists an optimal beta at which the Erlang B probability reaches its minimum

DSP: a MAC scheme with double-side scheduling for APON

MAC (medium access control) schemes for ATM-based passive optical network (APON) mostly adopt single-side scheduling in which only optical line termination (OLT) schedules the upstream access order for optical network units (ONUs). In this paper, we propose a MAC scheme called double-side scheduling protocol (DSP) in which both OLT and ONUs participate in the scheduling process. The proposed MAC scheme conforms to the ITU-T recommendation G.983.1. For the proposed MAC scheme, we present grant field format, minislot format, divided slot format, and scheduling algorithm. Through computer simulations, we find out that the cell delay variation (CDV) of real-time services can be improved remarkably using fewer overhead slots than that of MAC schemes adopting CDV control algorithm.