Kyun Hyon Tchah

An efficient and QoS-aware scheduling policy for Bluetooth

We propose an efficient and QoS (quality of service)-aware MAC (medium access control) scheduling algorithm for Bluetooth, which considers both throughput and delay performance on each master-slave pair in scheduling decisions, and thus, attempts to maximize overall performance. Since Bluetooth is basically operated with the round-robin scheduling policy, many slots may be wasted due to poll or null packets when there is no data waiting for transmission in queues. To overcome this link wastage problem, several algorithms have been proposed. Among them, queue state-based priority policy and low power mode-based algorithm can perform with high throughput and reasonable fairness. However, their performances may depend on traffic characteristics, and they require additional computational and signaling overheads. We propose a simple priority based scheduling algorithm providing service differentiation as well as high throughput and fairness. The performance of our proposed algorithm is evaluated with respect to throughput and fairness. Simulation results show that overall performance can be improved by selecting suitable parameters. Our results can serve as a guideline to the design of QoS-aware MAC scheduling policy in Bluetooth.

Multi-carrier CDMA system with parallel interference cancellation for multipath fading channels

The multi-carrier CDMA technique is attractive in a wireless communication system. It can support a high rate data transmission with a high spectral efficiency. The MC-CDMA (multi-carrier code division multiple access) receiver which employs a multiple access interference (MAI) canceller is proposed and analyzed. The receiver first demodulates the received signal to produce the initial data and the channel estimates. Based on these channel estimations, the cancellation scheme essentially creates the replicas of the MAI and removes them for the second improved data decision. Using theoretical analysis and simulation, the performance of MC-CDMA with parallel interference cancellation (PIC) is investigated according to the mean square error (MSE) of the channel estimation. The result shows the considerably large improvement in performance, which is attained by the interference cancellation technique. But if channel estimation is not performed accurately, then the effect of interference cancellation may be significantly decreased.

TCP performance enhancement by implicit priority forwarding (IPF) packet buffering scheme for mobile IP based networks

The smooth handoff supported by the route optimization extension to the mobile IP standard protocol should support a packet buffering mechanism at the base station (BS), in order to reduce the degradation in TCP performance caused by packet losses within mobile network environments. The purpose of packet buffering at the BS is to recover the packets dropped during inter-subnetwork handoff by forwarding the packets buffered at the previous BS to the new BS. However, when the mobile host moves to a congested BS within a new foreign subnetwork, the buffered packets forwarded by the previous BS are likely to be dropped. This subsequently causes global synchronization to occur, resulting in the degradation of the wireless link in the congested BS, due to the increased congestion caused by the forwarded burst packets. Thus, in this paper, we propose an implicit priority forwarding (IPF) packet buffering scheme as a solution to this problem within mobile IP based networks. In the proposed IPF method, the previous BS implicitly marks the priority packets being used for inter-subnetwork handoff. Moreover, the proposed modified random early detection (M-RED) buffer at the new congested BS guarantees some degree of reliability to the priority packets. The simulation results show that the proposed IPF packet buffering scheme increases the wireless link utilization and, thus, it enhances the TCP throughput performance in the context of various inter-subnetwork handoff cases.

Power-efficient and QoS-aware scheduling in Bluetooth scatternet for wireless PANs

In this paper, we propose a power-efficient and QoS (quality of service)-aware MAC (medium access control) scheduling algorithm for Bluetooth scatternet. If the inter-piconet scheduler in a bridge node between piconets operates simply by the round robin (RR) policy, a number of time slots may be wasted due to the guard time for piconet switching and the exchange of POLL-NULL packets. To overcome the link wastage problem in Bluetooth scatternet scheduling, several algorithms have been proposed. Although they can provide all of the links of a bridge node with fair service opportunities, they may cause waste of wireless resources since different Bluetooth devices may have various traffic characteristics. In addition, since Bluetooth devices are often required to operate under limited battery capacity, the number of unnecessary piconet switching has to be minimized for the power-efficient operation of a Bluetooth scatternet. Therefore, we propose a mechanism to support the power-efficient operation of a Bluetooth scatternet while guaranteeing various QoS requirements of Bluetooth devices. The proposed algorithm is compliant with the current Bluetooth specification, and we demonstrate its improved performance via simulations.

Handoff provisioning in Bluetooth wireless personal area networks

In this paper, we propose an efficient packet buffering in layer 2 to improve the handoff performance in wireless personal area networks (WPAN) using Bluetooth technology. By packet buffering in layer 2, the handoff performance can be significantly improved with minimum system overhead and thus better QoS (quality of service) can be given to the mobile WPAN users. The proposed packet buffering method, i.e., HQL2B (handoff QoS layer 2 buffering) is especially useful to the WPAN users who utilize TCP connections. Recently, some methods have been proposed especially for improving handoff performance in Bluetooth WPAN but unlike other works our method can improve handoff performance without any modification of TCP and Bluetooth specification. Through the simulations we show that the proposed method can greatly improve handoff performance in Bluetooth WPAN environment compared to other works.

Performance analysis of adaptive equalizer design for CCK-OFDM wireless LAN

An adaptive equalizer scheme is presented in OFDM system for IEEE 802.11a, g wireless LAN. Conventional OFDM system employs a guard interval and a 1-tap frequency-domain equalizer (FEQ) to prevent delay spread distortions. This scheme is simple to implement, but provides low spectral efficiency due to the use of the guard interval. Moreover its performance is poor because of the lack of multipath diversity and the energy loss contained within the guard Interval. In the case where the channel impulse response (CIR) is larger than the guard interval, the system performance is limited by the intersymbol and intercarrier interference. The proposed equalizer scheme consists of an adaptive time-domain equalizer (TEQ) and a 1-tap FEQ using long training OFDM symbols in the preambles. Its performance is better than that of the conventional OFDM system under severe delay spread and noise power conditions, especially in the case where the CIR is larger than the guard interval. This enables a reduction in the size of the guard interval and thus the spectral efficiency of the OFDM system can be improved.

Differentiated fairness guaranteeing scheduling policies for Bluetooth

This paper considers efficient and differentiated scheduling policies for Bluetooth MAC. The conventional queue state-based packet scheduling algorithms have some limitations such as unfair polling or traffic dependent performance. We propose two efficient MAC scheduling algorithms, which guarantee improved throughput and reasonable fairness, and can lead to Differentiated Services. The proposed policies are separate KFP (K-Fairness Policy) and Diff-KFP (Differentiated K-Fairness Policy). To reflect individual traffic characteristics of each master-slave pair, the proposed policy determines if current scheduling turns of master-slave pairs are sacrificed or not by the counter values of the pairs, and changes step size of the counter on each pair differently, and thereby, each pairs QoS can be incorporated. The proposed algorithms are compared with the conventional queue state-based algorithm. Simulation results show that our algorithms demonstrate better performance, and can be extended to satisfy QoS requirements of various applications.

Fabrication of silicon membrane using fusion bonding and two-step electrochemical etch-stopping

A new type of silicon membrane structure was fabricated using wafer fusion bonding and two-step electrochemical etch-stopping methods. An “active wafer” of p-type epi/n-type epi/p-type substrate was first elctrochemically etched to form a shallow cavity on the p-type epitaxial layer. Then, the cavity-formed side was fusionally bonded with p-type silicon “working wafer” and, afterwards, the p-type substrate of the active wafer part was removed by a second electrochemical etch-stopping leaving only the n-type membrane on the shallow cavity. Using the new membrane structure in mechanical sensors, more precise control of cavity depth and membrane thickness was achievable and the influence of crystalline imperfections on the sensing circuits located near the bonding seam was avoidable.

Realization of power line modem using a direct sequence spread spectrum technique

A power line modem (PLM) which transfers data safely through power lines in houses or small offices is realized in the form of a wall-socket plug. In order to cope with the noisy environment created by uncontrolled AC power lines, a direct sequence (DS) technique is employed. Most of the circuits required for the DS technique are implemented via software programmed inside the system controller, and the complicated synchronized circuit is replaced by a simple circuit using a 60 Hz power signal. The data rate is 60 bps and the PN (pseudonoise) chip rate is 2 kcps. Thus, the process gain of the PLM is about 15 dB. >

Differentiated Scheduling for Bluetooth QoS with Parameter Optimization

This paper considers an efficient scheduling policy for Bluetooth Medium Access Control (MAC) and its parameter optimization method. The proposed algorithm improves performance as well as supports Quality of Service (QoS) simultaneously. Since Bluetooth is basically operated with a Round Robin (RR) scheduling policy, many slots may be wasted by POLL or NULL packets when there is no data waiting for transmission in the queues of the polled pair. To overcome this link wastage problem, several algorithms have been proposed. However, they have some limitations such as a heavy signaling overhead or no consideration of QoS. Therefore, we have proposed an efficient Bluetooth MAC scheduling algorithm, Differentiated K-Fairness Policy (Diff-KFP), which guarantees improved throughput and delay performance, and it can also lead to differentiated services. That is, if the parameter of the proposed algorithm is optimized, we can satisfy the QoS requirement of each master-slave pair and thereby keep communications in progress from interruption, which is a source of throughput degradation. Simulation results show that our algorithm has remarkably improved the performance and gratifies the QoS requirements of various applications.