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Adaptive Techniques in Wireless Networks
Published in Mohamed Ibnkahla, Adaptation and Cross Layer Design in Wireless Networks, 2018
With the success of 802.11a/b/g WLANs, new applications are emerging for these wireless networks, such as video streaming, online gaming, and network-attached storage. Some of these new applications require extensive throughput support from the WLAN. The 802.11n proposal [30] aims to significantly improve the physical link data rate up to 600 Mbps by using multiple-input-multiple-output (MIMO) technology at the physical layer. Throughput performance at the MAC layer can be improved by aggregating several frames before transmission [43, 65]. Frame aggregation not only reduces the transmission time for preamble and frame headers, but also reduces the waiting time during the CSMA/CA random backoff period for successive frame transmissions. This section studies the frame aggregation techniques and introduces an optimal frame size adaptation algorithm.
Cognitive Radio with Spectrum Sensing for Future Networks
Published in Mahmoud Elkhodr, Qusay F. Hassan, Seyed Shahrestani, Networks of the Future, 2017
Nabil Giweli, Seyed Shahrestani, Hon Cheung
Instead of fragmenting a larger frame into smaller frames, a frame-aggregation mechanism is used to aggregate the upper layer frames to form larger frames at the MAC layer (e.g., Aggregated MAC Protocol Data Unit [A-MPDU] in IEEE 802.11n). This opposite approach to fragmentation is used when the transmission channel width is large enough for larger frames to be sent during a short time. The fragmentation approach is used for more reliability at the cost of more protocol overhead for legacy 802.11, whereas the aggregation approach is used to reduce the overhead for high-speed IEEE 802.11 networks (Sidelnikov et al., 2006). For Aggregated MAC Service Data Unit (A-MSDU), the aggregated frames belong to the same service category and are sent to the same destination. The maximum A-MSDU length that an 802.11n base station can receive is either 3839 bytes or 7935 bytes (Charfi et al., 2013). A-MPDU upper-layer frames being sent to the same destination are aggregated to form a frame with one of the following lengths: 8191, 16383, 32767, or 65535 bytes (Charfi et al., 2013). Several MSDUs can be aggregated in one larger MPDU and then one or more MPDUs are encapsulated into a single PHY protocol data unit (PPDU) to be sent to the PHY layer (Ginzburg and Kesselman, 2007). More studies are required to find the optimum size of the PPDU based on various factors, such as the sensing duration, the available channel width, and the desired PU protection.
Wireless Local Area Networks
Published in Stephan S. Jones, Ronald J. Kovac, Frank M. Groom, Introduction to COMMUNICATIONS TECHNOLOGIES, 2015
Stephan S. Jones, Ronald J. Kovac, Frank M. Groom
Frame aggregation: In earlier 802.11 standards (a/b/g), each frame that was transmitted had to be acknowledged by the receiver. While the frame was being acknowledged, no other frames could be transmitted. Frame aggregation attempts to decrease the time between sending and acknowledging of frames by combining frames that have the same physical source and destination end points and traffic class (quality of service [QoS]). The aggregated frame can be acknowledged by a single frame. In essence, multiple frames can be transmitted, and then a single frame can be sent back to acknowledge those multiple frames. This method is called Aggregated Mac Protocol Data Unit (A-MPDU). The second method, called Aggregated Mac Service Data Unit (A-MSDU), chains together frames that meet the same requirements above—the same physical end points and traffic class—but instead of combining the frames, A-MPDU chains the frames together. This creates slightly more overhead than the first method, but each frame retains its cyclical redundancy check (CRC). This means that an error in one frame only affects that single frame and does not corrupt the entire chain.
An automatic lane identification method for the roadside light detection and ranging sensor
Published in Journal of Intelligent Transportation Systems, 2020
Jianqing Wu, Hao Xu, Yuan Tian, Yongsheng Zhang, Junxuan Zhao, Bin Lv
The proposed method contains the following five major steps:Background filtering. The background filtering serves as the initial step for lane detection. The object of the background filtering is to exclude background points from the LiDAR sensor but keep the points of road users as much as possible.Point clustering. Point clustering means grouping the points belonging to one object based their internal relationships. There are two purposes for object clustering: (1) Distinguish different objects; (2) Exclude the noises left from the background filtering.Object classification. This step is used to distinguish vehicles and pedestrians based on their different features. Only vehicle points will be kept after object classification.Frame Aggregation. The purpose of this step is to increase the density of vehicle points in each lane.Traversal search. Traversal search is the key step of the lane identification.
Design of MAC Layer Resource Allocation Schemes for IEEE 802.11ax: Future Directions
Published in IETE Technical Review, 2018
Rashid Ali, Sung Won Kim, Byung-Seo Kim, Yongwan Park
The strategies like channel bonding, frame aggregation and block acknowledgment, reverse direction forwarding, etc. enhance the high throughput capabilities in 802.11 MAC protocol [3,4]. IEEE 802.11 standard-based WLANs often struggle to service diverse workloads and data types. Since the applications are categorized into different priorities by the access layer protocol, the method how to provide enhanced and efficient resource allocation has become an interesting and challenging topic. Recently, WLAN technologies and research work have introduced enhanced channel access mechanisms to increase network throughput. Although the researchers have spent plenty of time on 802.11 MAC protocol throughput enhancements using above mentioned techniques, efficient medium allocation in the MAC layer is still one of the important target areas for future WLAN researchers. Therefore, our study mainly focuses on the design of efficient MAC layer resources allocation (MAC-RA).