• Journal of Korean Institute of Industrial Engineers
• /
• v.37 no.2
• /
• pp.89-95
• /
• 2011

The distributed coordination function (DCF) and point coordination function (PCF) protocols are the basic MAC protocols for legacy IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g and IEEE 802.11n wireless LANs. When the DCF protocol is used for the various versions of IEEE 802.11 wireless LANs, the MAC performance seriously degrades due to the collisions among the stations (STAs) as more and more STAs attempt to transmit their data frames. On the other hand, the PCF MAC performance becomes poor when many STAs exist in IEEE 802.11 wireless LANs, however, only small number of STAs actually attempt to transmit their data frames. In this paper, we propose the algorithm for improving the MAC performance by selectively using the DCF and PCF protocols according to the state of IEEE 802.11 wireless LANs. Numerical examples are presented to show the MAC performance improvement by the selective use of the DCF and PCF protocols according to the network state.

• The KIPS Transactions:PartC
• /
• v.12C no.3 s.99
• /
• pp.387-394
• /
• 2005

Every MAC (Medium Access Control) sub-layers of IEEE 802.11x, including IEEE 802.11e, defines Connection-based and CF (Contention Free)-based service functions in common. In this paper, a New-CF method is proposed. In the proposed method, conventional Round Robin method, which is used as a polling method by IEEE 802.11x PCF (Point Coordination Function) or IEE 802.11e HCCA, is modified to give weights to channels with heavier traffic load and to provide those weighted channels with more services. Based on NS-2 simulations, it is verified the proposed method shows better throughput in general, particularly under unbalanced traffic load conditions.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.11
• /
• pp.2062-2068
• /
• 2006

In his paper, embedded system implementation for IEEE802.l1p based OFDM-DSRC is presented. After the IEEE802.11p physical layer specification is introduced and BER performance of the modem is evaluated by simulation, implementation aspects of the system such as system architecture, design method and implementation results are addressed. Implemented embedded system for the OFDM-DSRC communication consists of FPGA, flash memory, ARM9 CPU Core, peripherals, etc. from the results, it is shown that the implemented system operates well according to IEEE802.11p specification. It is expected that implemented embedded system shall be used for wireless communication system such as ITS application by enhancing system optimizing.

• 한국ITS학회:학술대회논문집
• /
• 2010.05a
• /
• pp.22-25
• /
• 2010

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.11 no.3
• /
• pp.161-168
• /
• 2011

This paper provides the performance measurement and analysis of Wireless LAN IEEE 802.11 in a mobile environment. The performances of IEEE802.11b/g and IEEE802.11p designed for Vehicle-to-Vehicle(V2V) communication are measured and analyzed. Diameter of communication and link access time are compared under variation of speed of the vehicle.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.46 no.6
• /
• pp.39-47
• /
• 2009

This paper presents implementation of two types of the 802.11 MAC engine for the next generation WLAN, 802.11n. The first version of MAC engine consists of hardwired logic and embedded firmware. Hardwired logic includes Tx block, Rx block, Backoff block, and ChannelManage block. Embedded firmware contains Protocol Control block, MLME block, and MSDU processing block. The first version has a time-critical fault during the atomic transmission caused by software overhead, so it can not be applied to 802.11n MAC. For that reason, the second version has additional blocks with hardwired logic modules to reduce software overhead of the first version. This enhanced version has 73Mbps throughput and it is expected to be further improved up to 129 Mbps with frame aggregation which is one of the key additional features of 802.11n. As a result, the second version of MAC engine can be applied to 802.11n MAC.

• Journal of KIISE:Information Networking
• /
• v.36 no.5
• /
• pp.456-469
• /
• 2009

We develop a new wireless link quality metric, ECOT(Estimated Channel Occupancy Time) that enables a high throughput route setup in wireless mesh networks. The key feature of ECOT is to be applicable to diverse mesh network environments where IEEE 802.11 MAC (Medium Access Control) variants are used. We take into account the exact operational features of 802.11 MAC protocols, such as 802.11 DCF(Distributed Coordination Function), 802.11e EDCA(Enhanced Distributed Channel Access) with BACK (Block Acknowledgement), and 802.11n A-MPDU(Aggregate MAC Protocol Data Unit), and derive the integrated link metric based on which a high throughput end-to-end path is established. Through extensive simulation in random-topology settings, we evaluate the performance of proposed link metric and present that ECOT shows 8.5 to 354.4% throughput gain over existing link metrics.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.10A
• /
• pp.1003-1013
• /
• 2006

There is a serious problem in an 802.11g VoWLAN (Voice over Wireless LAN) terminal that talk time is less than 30% compared with an 802.11b terminal. It is almost impossible to achieve talk time level of the 802.11b MAC transmission method because IEEE 802.11g uses OFDM modulation, which is a kind of multi-carrier method and OFDM transmission speed is 54 Mbps faster than normal modulation. In this paper, a new concept of a Holdover time as a power saving method during a call with 802.11g terminal is suggested for the first time. Increase in the number of engaged terminals as a result of holdover time causes to QoS problem because of the increase in the number of back-off and then contention window. In this paper, to solve the QoS problem, a new approach is suggested such that when in down lint the sequence number of 802.11 G.711 is analyzed in the MAC of the terminal and then the Hold over time depending on loss rate is changed. Also, consumption of an electric current of 802.11b/g and MAC parameter's performance due to busy traffic caused by increase in the number of terminal are analyzed and then real data using VQT and Airopeek are analyzed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2010.10a
• /
• pp.456-458
• /
• 2010

VoIP services are growing fast and WLAN VoIP phones are being used in widespread. Emergency services are very critical in WLAN VoIP as in other traditional networks. This paper summarize recent standards of IEEE 802.11 supporting emergency services in WLANs. Two standards are discussed. The 11u deals with the aspect of access in WLAN emergency services, and the 11v deals with the location services.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.11A
• /
• pp.870-877
• /
• 2011

IEEE 802.11 devices are widely used, and terminals can be equipped with multiple IEEE 802.11 interfaces as low-cost IEEE 802.11 devices are deployed. The off-the-shelf IEEE 802.11 devices provide multiple channels and multiple data rates. In practical multi-channel networks, since there is channel heterogeneity which indicates that channels have different signal characteristics for the same node, channels should be efficiently assigned to improve network capacity. In addition, in multi-rate networks, low-rate links severely degrade the performance of high-rate links on the same channel, which is known as performance anomaly. Therefore, in this paper, we propose a heterogeneity aware channel assignment (HACA) algorithm that improves network performance by reflecting channel heterogeneity and performance anomaly. Through NS-2 simulations, we validate that the HACA algorithm shows improved performance compared with existing channel assignment algorithms that do not reflect channel heterogeneity.