Browsing by Author "Chen, Anderson"

Now showing 1 - 12 of 12

A cross-layer investigation for the throughput performance of CSMA/CA-Based WLANs with directional antennas and capture effect
(2007-09-01)
Wang, Li-Chun
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Chen, Anderson
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Huang, Shi-Yen
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we develop a physical/medium-access-control (PHY/MAC) cross-layer analytical model to investigate the throughput performance of the wireless local-area network (WLAN) in a lossy wireless environment. From the PHY-layer perspective, the developed model incorporates the effects of capture and directional antennas, while from the MAC-layer perspective, our approach takes into account the carrier-sense multiple access with collision-avoidance (CSMA/CA) MAC protocol and the effect of the backoff process in the IEEE 802.11 WLAN. We derive explicit analytical expressions for the frame outage and capture probabilities of a directional antenna system in the presence of shadowing and Rayleigh fading. Applying this analysis, we can model the interaction between the PHY and MAC layers more accurately for the infrastructure-based WLAN. The numerical results show that our analytical model can approach that attained by simulations. The proposed cross-layer analytical model not only provides insights into the PHY layer impacts on the throughput of the CSMA/CA MAC protocol but also indicates to how directional antennas can improve the CSMA/CA-based WLAN in terms of antenna beamwidth and the number of radio transceivers.
Cross-Layer Analysis of Joint Rate and Power Adaptation in Nakagami Fading Channels with Multiple-User Contention
(2009-11-01)
Wang, Li-Chun
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Huang, Jane-Hwa
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Chen, Anderson
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Chang, Chung-Ju
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電信工程研究所
Adaptively adjusting transmit rate and power concurrently to enhance goodput and save energy is a challenging issue in a wireless local area network (WLAN) because goodput enhancement and energy saving are usually two contradictory goals. In this paper, we propose channel-driven rate and power adaptation (CDRPA) schemes and develop a physical (PHY)/medium access control (MAC) cross-layer analytical method incorporating the impacts of Nakagami fading channel and the carrier sense multiple access (CSMA) MAC protocol. The CDRPA scheme has much lower computation complexity than the energy-optimal complete-search scheme. In a multiuser contention scenario, we analyze the energy efficiency and the goodput of the power-first and rate-first CDRPA schemes as well as the energy-optimal complete-search adaptation scheme. At the cost of lower goodput, the power-first scheme has better energy efficiency than the rate-first CDRPA scheme, whereas if the goodput is the main concern, the rate-first CDRPA scheme shall be chosen due to better goodput performance. More interestingly, we find that the power-first CDRPA scheme can achieve about the same goodput and energy efficiency as the energy-optimal complete-search link adaptation scheme.
Effects of Location Awareness on Concurrent Transmissions for Cognitive Ad Hoc Networks Overlaying Infrastructure-Based Systems
(2009-05-01)
Wang, Li-Chun
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Chen, Anderson
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電信工程研究所
;
Institute of Communications Engineering
Through wideband spectrum sensing, cognitive radio (CR) can identify the opportunity of reusing the frequency spectrum of other wireless systems. To save time and energy of wideband spectrum, we investigate to what extent a CR system incorporating the location awareness capability can establish a scanning-free region where a peer-to-peer ad hoc network can overlay on an infrastructure-based network. Based on the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol, the concurrent transmission probability of a peer-to-peer connection and an infrastructure-based connection is computed. It is shown that the frequency band of the legacy system can be reused up to 45 percent by the overlaying cognitive ad hoc network when CR users have the location information of the primary and secondary users.
Joint Rate and Power Adaptation for Wireless Local Area Networks in Generalized Nakagami Fading Channels
(2009-03-01)
Wang, Li-Chun
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Liu, Wei-Cheng
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Chen, Anderson
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Yen, Kuang-Nan
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電信工程研究所
In this paper, a channel-driven rate and power adaptation (CDRPA) algorithm is proposed for wireless local area networks (WLANs) in generalized Nakagami fading channels. Through the channel information of the first packet, the CDRPA algorithm can lower the complexity of comparing various rates and power levels. In the case of the IEEE 802.11 WLAN, the computation complexity of the CDRPA algorithms is reduced by more than 94% compared with the complete-search link adaptation. A physical and/or medium access control (MAC) cross-layer analytical model is also developed to evaluate the goodput and energy efficiency of the carrier sense multiple access with a collision avoidance MAC protocol in Nakagami fading channels. Our numerical results show that the CDRPA algorithm is not only more energy efficient in the Nakagami fading channel but can also achieve comparable and even higher throughput compared with the complete-search link adaptation approach.
Joint Rate and Power Adaptation for Wireless Local Area Networks in Nakagami Fading Channels
(2006)
Wang, Li-Chun
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Yen, Kuang-Nan
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Chen, Anderson
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交大名義發表
;
National Chiao Tung University
In this paper, we propose a fast channel-driven rate and power adaptation (CDRPA) algorithm for wireless local area networks (WLAN). The proposed algorithm jointly adjusts the rate and power for data frame transmission in a generalized Nakagami fading channel. Different from the previous works, the CDRPA algorithm bases on the channel quality observed from the previous ACK frames and makes the selection only from the limited combinations of rate and power, instead of exhausted searching. Thus, the CDRPA algorithm greatly reduces the complexity compared to the previous approaches. Furthermore, to meat the different performance requirements, we propose several alternatives based on the CDRPA algorithm. From the viewpoint of energy saving, the CDRPA algorithm determines the transmit power first to maximize energy efficiency; while achieving the maximum goodput performance, the CDRPA first selects the appropriate transmit rate to ensure the successful transmissions. The numerical results show that the CDRPA algorithm can approach to the optimum performance in terms of energy efficiency and goodput while keeping the low complexity.
Network selection with joint vertical and horizontal handoff in heterogeneous WLAN and mobile WiMax systems
(2007)
Wang, Li-Chun
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Chen, Anderson
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Chen, Hung-Hsi
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電信工程研究所
;
Institute of Communications Engineering
As the IEEE 802.11 wireless local area networks (WLANs) have become very popular and the emerging IEEE 802.16e wireless metropolitan area networks (WMANs) also attract a great deal of attentions, in the future we can expect the appearance of the hybrid IEEE 802.11 WLANs and IEEE 802.16e WMANs systems. Clearly, seamless handoffs in this hybrid network will become an increasingly important issue. However, the system which has shortest handoff latency may not always have the highest throughput. In this paper, we develop a dynamic network selection scheme to determine the connecting system in a new "WLAN to hybrid WLAN/WiMax" handoff scenario, in which we consider both the vertical and horizontal handoffs. The proposed scheme requests the station to wait an additional network selection time "t(w)" before the selection to maximize the amount of delivered bits during a dwelling time. We also formulate an optimization problem to find the optimal network selection time t(w)(*) and show that the proposed scheme can improve the delivered information bits during handoff.
On the coexistence of infrastructure-based and ad hoc connections for a cognitive radio system
(2006)
Wang, Li-Chun
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Chen, Anderson
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交大名義發表
;
National Chiao Tung University
Cognitive radio (CR) can sense the current spectrum usage of existing networks and make intelligent decisions on the opportunity of reusing the frequency spectrum. One fundamental issue for the CR system is how to rapidly establish a temporary communication link on the spectrum of the exiting users. In this paper we investigate the feasibility issue of establishing both an infrastructure-based link and an ad hoc link using the same spectrum simultaneously in an overlapped area. We also present a cross-layer performance analysis from both the physical (PHY) layer and medium access control (MAC) layer perspectives. The analytical results show that the probability that both an infrastructure-based connection and an ad hoc link coexist in an overlapping area can be as high as 45%. In addition, the normalized total throughput of the both links is more than 145% compared to the pure infrastructure-based link. However considering the shadowing effects, the transmission reliability varies from 30%similar to 90% depending on the locations of mobile stations.
On the performance of spectrum handoff for link maintenance in cognitive radio
(2008)
Wang, Li-Chun
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Chen, Anderson
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交大名義發表
;
National Chiao Tung University
Cognitive radio (CR) has the potential for resolving the spectrum scarcity issue in wireless communications. A CR device can establish unharmful links in the spectrum of the legacy system. Among many enabling functions for CR, spectrum handoff can restore CR's connection when the primary user appears in the occupied channel. In this paper, we study three types of spectrum handoff for the link maintenance: (1) non-spectrum handoff method, (2) the pre-determined channel list spectrum handoff, and (3) the spectrum handoff based on radio sensing scheme. We examine the performances of the three mechanisms in terms of the link maintenance probability and the effective data rate of the secondary user's transmission. Our numerical results show that erroneous channel selection probability, radio sensing time and the number of handoff trials are important for spectrum handoff schemes. We also provide the design guideline for these parameters.
Optimal Channel Search Time for Handoff in the IEEE 802.11 WLANs
(2006)
Wang, Li-Chun
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Chen, Hung-Hsi
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Chen, Anderson
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Chan, Chung-Ju
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交大名義發表
In recent years, the IEEE 802.11 wireless local area networks (WLANs) have become a very popular access network technique. However, due to the large handoff latency, most application scenarios are limited to hot spot areas without handoff across different access points (APs). As the advance of many real-time or highly interactive applications such as voice over IP (VoIP), one of burning issues for the WLAN is to reduce the handoff latency. Current studies in the literature have indicated that the latency in searching available APs dominates the handoff latency. Thus, we propose a simple analytical model to calculate the search latency and success probability for the handoff in the IEEE 802.11 WLAN. A new performance metric, namely the "effective search time (EST)", is introduced to evaluate the latency that is required for a station to successfully search a channel from neighboring APs. Based on the developed model, the optimum numbers of the probe request and response transmission for minimizing the EST can be obtained. Our results demonstrate that, in the environment of 100 contending stations, the EST with optimum number of transmissions can be reduced by 30% compared to that in the legacy IEEE 802.11 WLAN.
Optimal Radio Resource Partition for Joint Contention- and Connection-Oriented Multi-Channel Access in OFDMA Systems
(2008)
Wang, Li-Chun
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Chen, Anderson
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電信工程研究所
;
Institute of Communications Engineering
Orthogonal frequency division multiple access (OFDMA), adopted in the IEEE 802.16e WiMax system, possesses many advantages in the physical layer, but also poses many challenges from the aspect of radio resource allocation. In the IEEE 802.16e WiMax system, a truncated binary backoff algorithm is adopted for resolving the contention in random access, while the time-division OFDMA is used for the connection-oriented access. One interesting radio resource allocation issue in such an OFDMA system is to partition the overall radio resource (bandwidth and time duration) into two portions: one for random access and the other for connection-oriented access. The main contribution of this paper is to design an analytical approach to determine the optimal amount of reserved radio resource in both time and frequency domains for random access with the objective of maximizing the overall efficiency of radio resource while satisfying the delay requirements for supporting real-time services. Furthermore, an analytical model for calculating the access latency and the efficiency of the reserved radio resources is developed.
Optimal Radio Resource Partition for Joint Contention- and Connection-Oriented Multichannel Access in OFDMA Systems
(2009-02-01)
Wang, Li-Chun
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Chen, Anderson
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電信工程研究所
;
Institute of Communications Engineering
The IEEE 802.16e World Interoperability for Microwave Access (WiMax) system plays an important role in the future wireless metropolitan area network (WMAN). Orthogonal frequency division multiple access (OFDMA), adopted in the IEEE 802.16e WiMax system, has many advantages in the physical layer and also poses many challenges for radio resource allocation. One of interesting radio resource allocation issue in the OFDMA system is to partition the overall radio resource ( bandwidth and time duration) into two portions: one for random access and the other for connection-oriented access. In the IEEE 802.16e WiMax system, a truncated binary back-off algorithm is adopted to resolve the contention in random access, while the time-division OFDMA is used for the connection-oriented access. The main contribution of this paper is to design an analytical approach to determine the optimal amount of reserved radio resource in both time and frequency domains for random access, with the objective of maximizing the overall efficiency of radio resource while satisfying the delay requirements for supporting real-time services. Furthermore, an analytical model for calculating the access latency and the efficiency of the reserved radio resources is developed.
Optimal relay location in multi-hop cellular systems
(2008)
Wang, Li-Chun
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Su, Wen-Shan
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Huang, Jane-Hwa
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Chen, Anderson
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Chang, Chung-Ju
Relay stations (RSs) are usually used to enhance the signal strength for the users close to the cell boundary. However, transmission through a relay station needs two transmission phases, i.e., one is from the base station to the relay station and the other is from relay station to mobile stations. Thus, relay may also decrease system capacity if two phase transmission time is considered. As a result, whether or not data are transmitted by one hop or two hop transmission should be determined based on both signal strength and throughput. In this paper, we investigate the optimal relay location aiming to maximize system capacity. We consider two relay selection rules for determining whether a two hop transmission is necessary: signal strength oriented and throughput oriented. We find that the signal strength oriented two hop transmission may yield even lower system capacity than the one hop transmission. Based on the throughput oriented rule, we find that the throughput in the two hop transmission can be higher than that in the one hop transmission at some locations. We also identify the optimal relay location that can achieve the highest system capacity.