Browsing by Author "Hsieh, Jing-Rong"

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A Bandwidth Efficient Pairing Strategy for the MIMO-OFDM Based WLANs
(2009)
Lee, Tsern-Huei
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Hsieh, Jing-Rong
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Huang, Ming-Chih
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Huang, Yu-Wen
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電信工程研究所
The advanced MIMO (multiple-input multiple-output) system can provide higher capacity gain or higher diversity gain in modern wireless networks. The capacity gain is achieved by interference cancelation technique to fully utilize the spatial degree of freedom. In a multiuser wireless system, the increased degrees of freedom provide the chance to select multiple wireless stations (STAs) to maximize the throughput. In this paper, we consider a scenario where the access point (AP) equipped with two antennas to simultaneously communicate with two STAs, each with single antenna. After obtaining the statuses of the size of buffered traffic and the achievable transmission rate, the AP should pair compatible STAs to minimize the loss of spatial degree of freedom. Therefore, three pairing algorithms are proposed and are evaluated through computer simulations. The algorithms have much less implementation complexity than the brute force pairing algorithm and achieve satisfactory performance of throughput.
A Rearrangement Algorithm for Scheduled Automatic Power Save Delivery of Wireless LANs
(2010)
Lee, Tsern-Huei
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Hsieh, Jing-Rong
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Chen, Hsiao-Wei
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傳播研究所
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Institute of Communication Studies
One of the major challenges to integrate the wireless LAN technology into portable devices is the limited battery life. The IEEE 802.11e introduced an advanced architecture to improve 802.11 power saving mechanism, named Scheduled Automatic Power Save Delivery (S-APSD). In S-APSD, the access point negotiates periodical schedules with wireless Stations (STA) to deliver buffered traffic and thus prevents the need to poll for each frame by STAs. In S-APSD, in order to reduce wastage of energy, the AP has to avoid overlapping of Service Periods (SPs). Based on existing scheduled events (SEs), the OAS-APSD (Overlapping Aware S-APSD) and LCS-APSD (Low Complexity S-APSD) were proposed to incrementally select the Service Start Times (SSTs) for the new joining traffic streams (TSs) to minimize the chance of SP overlapping. However, in this scheduling fashion, the resulted power saving performance depends on the joining order of TSs and thus may be unsatisfactory. Therefore, our idea is to rearrange the relative offsets of existing SEs to enlarge the system minimum distance. From numerical results, we find that the proposed scheduling algorithms can provide better power saving.
An energy saving scheme with error recovery for multi-polling in wireless LANs
(2008)
Hsieh, Jing-Rong
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Lee, Tsern-Huei
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電信工程研究所
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Institute of Communications Engineering
Various multi-polling schemes have recently been proposed to reduce the overhead resides in legacy IEEE 802.11 WLAN protocols. In particular, the Two-Step Multi-Polling (TSMP) scheme utilizes the acquired buffer status and channel condition to derive exact required time of each wireless station. Consequently, it seems to he easy to incorporate an energy saving schedule to prolong the operating time of the portable devices. However, even though it adopted the concept of rate adaptation, the TSMP scheme did not take into account frame retransmissions caused by transmission errors due to, say, fading of the wireless channel. The uncertain time spent on retransmission of former stations in the schedule may introduce energy-consuming overhearing for later ones. In this paper, we propose wake-up time schedules and an adaptive updating algorithm to save more energy for the later stations under the error-prone wireless environment. The proposed scheme is simple and thus quite feasible. Besides, from extensive simulation results, we found that the proposed solution is effective.
Design and Evaluation of a High Throughput MAC with QoS Guarantee for Wireless LANs
(2009)
Kuo, Yaw-Wen
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Lee, Tsern-Huei
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Huang, Yu-Wen
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Hsieh, Jing-Rong
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電信工程研究所
The IEEE 802.11e and the IEEE 802.11n focus on quality of service (QoS) and enhancements for high throughput respectively. Modern wireless LAN (WLAN) products should integrate both features. This paper presents a design of a high throughput MAC with QoS guarantee which combines the Hybrid Coordination Function (HCF) of the 802.11e with the frame aggregation technique in the 802.11n. The basic idea of the design is to improve the throughput of best-effort traffic under the constraint that QoS is just met for real-time traffic. Simulation results show that the proposed MAC has high channel utilization and the delay of best-effort traffic is also reduced.
Energy-Efficient Multi-Polling Scheme for Wireless LANs
(2009-03-01)
Hsieh, Jing-Rong
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Lee, Tsern-Huei
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Kuo, Yaw-Wen
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電信工程研究所
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Institute of Communications Engineering
In the past few years, IEEE 802.11 wireless LANs (WLANs) has rapidly gained large popularity for broadband wireless access. With the growing of various applications, users are demanding features such as higher throughput white keeping respectable operation time for their devices. To provide higher system bandwidth utilization, multi-polling mechanisms are often employed to reduce protocol overhead. However, they require wireless stations (STAs) to spend much time in overhearing which tends to waste energy and reduce battery lifetime. In this paper, we propose an energy-efficient multi-polling mechanism which combines power management strategy with a low overhead Medium Access Control (MAC) protocol. The main idea is to put STAs into the Doze state and determine a suitable wake-up time schedule to statistically achieve desirable guarantee of bandwidth utilization. From both analysis and simulation results, we found that, compared with the original ordered-contention multi-polling scheme, our proposed mechanism saves up to 80% of energy for a network consisting of 20 polled STAs with 5% loss of system bandwidth utilization as tradeoff. The significant saving of energy is a consequence of alleviating the overhearing problem with well scheduled wake-up times for STAs.
Gaussian approximation based admission control for variable bit rate traffic in IEEE 802.11e WLANs
(2007)
Huang, Yu-Wen
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Lee, Tsern-Huei
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Hsieh, Jing-Rong
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電信工程研究所
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Institute of Communications Engineering
For QoS requirements of real-time traffic, IEEE 802.11 working group introduces a QoS-aware channel access mechanism, called Hybrid Coordination Function (HCF), which consists of contention-based Enhanced Distributed Channel Access (EDCA) and contention-free HCF Controlled Channel Access (HCCA). The TXOP allocation and the admission control units of the HCCA reference scheduler are only appropriate for constant bit rate (CBR) flows. It may result in serious packet loss for variable bit rate (VBR) flows. In this paper, we propose a simple admission control algorithm which adopts Gaussian distribution to approximate VBR traffic. Numerical results obtained from computer simulations show that our proposed algorithm can effectively and efficiently allocate Transmission Opportunity (TXOP) durations to QoS-enhanced stations (QSTAs) to guarantee a predefined packet loss probability. Moreover, our proposed scheme can easily handle multiple VBR flows of the same QSTA to get the advantage of multiplexing gain.
Low-Complexity Class-Based Scheduling Algorithm for Scheduled Automatic Power-Save Delivery for Wireless LANs
(2013-03-01)
Lee, Tsern-Huei
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Hsieh, Jing-Rong
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傳播研究所
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Institute of Communication Studies
Power saving is an important issue when integrating the wireless LAN technology into mobile devices. Besides Quality of Service (QoS) guarantee, the IEEE 802.11e introduces an architecture called Scheduled Automatic Power-Save Delivery (S-APSD) aiming at delivering buffered frames to power save stations. In S-APSD, the Access Point (AP) schedules the Service Period (SP) of stations. To increase power efficiency, SPs should be scheduled to minimize the chance of overlapping. In a recent paper, an algorithm named Overlapping Aware S-APSD (OAS-APSD) was proposed to find the wake-up time schedule for a new Traffic Stream (TS) to minimize the chance of SP overlapping. The combination of OAS-APSD and HCF Controlled Channel Access (HCCA) was proved to outperform 802.11 Power Save Mode (PSM) with Enhanced Distributed Channel Access (EDCA) in power saving efficiency and QoS support. However, the OAS-APSD algorithm requires high online computational complexity which could make it infeasible for real systems. Without harming the optimality, this paper presents an efficient algorithm with much less complexity by exploiting the periodicity of service schedule. Because of largely reduced online computational complexity, the proposed algorithm is much more feasible than OAS-APSD.
Power efficient multipolling mechanism for next generation wireless LANs
(2007)
Hsieh, Jing-Rong
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Lee, Tsern-Huei
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Kuo, Yaw-Wen
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電信工程研究所
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Institute of Communications Engineering
As the Wireless LAN (WLAN) becomes prevalent, users are demanding more and more features such as high throughput and low power consumption. To provide higher channel efficiency, contention-based multipolling mechanism was proposed to improve the single polling and contention-free multipolling mechanisms. However, when this medium access control (MAC) protocol is used, wireless stations would need to spend much time in overhearing which tends to waste energy and reduce battery lifetime. We propose a power efficient multipolling mechanism to arrange wireless stations into groups and put them into sleep mode when other stations are transmitting. From the simulation results, we find the proposed mechanism can address the issue of overhearing while also keeping the flexibility and high channel efficiency properties.