Sang-Wook Kwon

Enhanced power saving through increasing unavailability interval in the IEEE 802.16e systems

The power saving mechanisms of the current IEEE 802.16e system are designed to take no consideration of the harmonization between power saving classes (PSCs) I and II. Using the IEEE 802.16e standard as a basis, we propose a dynamic power saving mechanism that increases unavailability interval when a mobile station (MS) uses PSCs. The proposed mechanism adjusts the timing of the sleep window of PSC I to maximize the unavailability interval of the MSs. As a result, the proposed scheme achieves power saving of the MSs. Through numerical analysis and simulations, we show that the proposed mechanism can reduce the power consumption of the MSs considerably compared with conventional mechanisms.

Adaptive beacon listening protocol for a TCP connection in slow-start phase in WLAN

In this letter, a new energy-efficient medium access control (MAC) protocol applicable to IEEE 802.11 is suggested. The proposed adaptive beacon listening (ABL) protocol dynamically determines the beacon listening interval (BLI) of mobile station based on the pdf of the estimated round-trip time (RTT). Theoretical and simulation results for power efficiency and average delay are derived. In general, there is a trade-off between delay and power conservation, in that a small number of beacon listening save power, while a large number of beacon listening reduce delay. However, the proposed scheme shows that we can achieve better performance with respect to average delay and power efficiency.

CDMA Code-Based Bandwidth Request Mechanism in IEEE 802.16j Mobile Multi-Hop Relay (MMR)Systems

In the IEEE 802.16 system, a relay station (RS) is required for the purpose of coverage extension and throughput improvement. However, if we use the RS, original bandwidth request mechanism is not applied to subscriber station (SS) which is connected to RS since the bandwidth request mechanism is optimized for single-hop environment. Therefore, we propose an efficient contention based CDMA bandwidth request mechanism for SS located in RS region in the IEEE 802.16 MMR system. In the proposed scheme, an SS can receive the uplink resource very well wherever an SS is located. Through the analysis, we show that the proposed bandwidth request mechanism reduces the signaling cost and delay of system.

Performance comparison of 802.16d OFDMA, TD-CDMA, cdma2000 1xEV-D0 and 802.11a WLAN on voice over IP service

We analyzed four systems designed for high-data rate transmission such as IEEE 802.16d OFDMA5 3GPP TD-CDMA, 3GPP2 cdma2000 1xEV-DO, and IEEE 802.11a WLAN, and compared their efficiency, the number of VoIP user, and the normalized number of VoIP user per 1 MHz. It is shown that the 802.16 system serves the most number of VoIP user, and the normalized number of user per 1 MHz is also the most. Even though 802.11a system is operated over the widest band, it supports the less number of user compared to the 802.16 system with smaller bandwidth, due to the inefficiency of CSMA/CA scheme. TD-CDMA and 1xEV-DO serve the same number of VoIP user per 1 MHz bandwidth, and TD-CDMA performs with the best efficiency among four systems. Comparing with TD-CDMA and 1xEV-DO, we concluded that 802.16d OFDMA system is the most flexible to assign its resource to users due to its finest granularity among three systems.

A new beacon management method in case of congestion in wireless LANs

A new beacon management method for stations (STAs) in power saving mode (PSM) in case of congestion is suggested in this paper. When the downlink network load reaches a certain level, an access point (AP) cannot transfer its whole pending packets to the STAs during one beacon transmission interval because the length of beacon transmission interval is not so long but short and fixed. This results in unnecessary power consumption of STAs which are in idle mode compared with that of STAs in sleep mode. So, our proposed scheme restricts the number of STAs to be marked in traffic indication map (TIM) field of beacon within appropriate range according to the length of the beacon transmission interval when congestion occurs. Performance regarding power consumption is evaluated and its application to delay reduction of packets with high priority is proposed.

Modeling and analysis for the coexistence of PSC I and PSC II in the IEEE 802.16e system

In wireless communication system, power saving mechanism is a key issue since a mobile station operates depending on limited power. Hence, the IEEE 802.16e system provides three types of power saving classes (PSC I, PSC II and PSC III) for the mobile station (MS) to reduce power consumption. Many models have been made to analyze the performance of power saving mechanism (PSM) of the IEEE 802.16e system. Although many researches have been studied about the PSC I and PSC II, no work has conducted the performance of PSM considering the coexistence of the PSC I and PSC II. Hence, in this paper, when the PSC I and PSC II are used simultaneously, we model the power saving mechanism (PSM) using a discrete-time Markov chain (DTMC) technique. We develop an analytical model considering the characteristics of the PSC I and PSC II. Using the model, we analyze the performance of the PSM by using several metrics such as power consumption and response delay. Then, by comparing numerical analysis with simulation results, we validate a proposed model.

Efficient Power Management Scheme Considering Inter-User QoS in Wireless LAN

In wireless LAN, power saving is the essential issue to the node since the node has the limited battery. Hence, the nodes can use the Power Saving (PS) mode unless transmitting or receiving packet exists for the certain period. For the PS node to receive the buffered packet in Access Point (AP), the PS nodes periodically check the Traffic Indication Map (TIM) field in the beacon frame that contains the information about buffered packet. If the buffered packet exists, they must transmit the PS. POLL to the AP. The AP transmits the buffered packet to the node that succeeds to transmit the PS_POLL. However, when the node transmits the PS-POLL, the transmission order is determined without any priority. Therefore, we propose the efficient power management scheme to support inter-user QoS and reduce the power consumption in wireless LAN. In the proposed scheme, the node with high priority transmits PS_ POLL earlier than that with low priority, so the node with high priority receives the buffered packet faster than that with low priority, and reduces the power consumption by converting the mode from Active Mode (AM) to Power Saving (PS) for remaining beacon interval (BI). Through the analysis and simulation, we show that the proposed scheme reduces power consumption and guarantees inter-user QoS compared to conventional scheme.

Power management scheme considering priority in wireless LAN

In wireless LAN, power saving is very important because the power of wireless LAN node is limited. Therefore, in IEEE 802.11 wireless LAN, the node can use the Power Saving(PS) mode to save the power consumption. When the nodes are in the PS mode, they awake periodically to check receiving packet through the beacon frame. If the receiving packet exists, they transmit PS POLL to the AP. After the AP receives the PS POLL, the AP transmits the buffered packet. However, in conventional scheme, when PS POLL is transmitted, the transmission order is determined without considering remaining power. Therefore, in this paper, we propose a priority based power management scheme that PS nodes transmit the PS POLL according to remaining power.

Asynchronous power management scheme for wireless ad-hoc networks

In wireless ad-hoc networks, power-saving by the terminals is a very important issue since their operation depends on limited battery-power. To reduce their power consumption the terminals are allowed to enter a low-power mode (LPM) in many wireless networks. However, as there is no clock synchronization of information transmission in ad-hoc networks, the problem occurs that terminals do not know when a neighboring terminal in LPM awakes. We propose a novel power management scheme using SLEEP _TABLE to solve this problem. Simulation results show that the proposed scheme outperforms 802.11 LPM and the conventional scheme in terms of power saving, and the power consumption of each terminal is distributed.

Dynamic Power Saving Mechanism for Mobile Station in the IEEE 802.16e Systems

In wireless communication system, power saving mechanism is a key issue since the mobile station operates depending on limited power. Hence, the IEEE 802.16e system provides three types of power saving classes (PSC I, PSC II and PSC III) for mobile station (MS) to reduce the power consumption. When the MS is using two or more power saving classes, the MS reduces the power consumption only during time interval that does not overlap with any listening window of active PSC called the unavailability interval. Therefore, in this paper, based on the IEEE 802.16e standard, we propose a dynamic power saving mechanism (DPSM) that increases unavailability interval when the MS is using two or more power saving classes (PSCs). The proposed mechanism adjusts sleep window of PSC I (III) to match the start point of listening window in PSC I (III) with that of listening window in PSC II. By doing so, the MS can reduce the listening time, and can increase the unavailability interval. Through analysis and simulation results, we show that the proposed DPSM can reduce the power consumption of MS with two or more PSCs considerably compared with conventional scheme. Index Terms—IEEE 802.16e, Wireless MAN, MAC, power saving, sleep mode.