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Wireless Mesh Networks
Published in K. R. Rao, Zoran S. Bojkovic, Bojan M. Bakmaz, Wireless Multimedia Communication Systems, 2017
K. R. Rao, Zoran S. Bojkovic, Bojan M. Bakmaz
Performance analysis and improvement of protocol stack, particularly the MAC protocol, is an important research topic for WMNs. IEEE 802.11x is one of the most influential WLAN standards, and its basic MAC protocol is called the distribution coordination function (DCF). DCF is based on carrier sense multiple access with collision avoidance (CSMA/CA), which is a typical contention-oriented protocol. CSMA/CA is widely used in test beds and simulations for WMN research [4]. The IEEE 802.16 standard allows for backhauling by providing an optional mesh connectivity mode in addition to the inherent point-to-multipoint (P2MP) connectivity. The key difference between P2MP and mesh is that communication in P2MP is based on direct connection between the base station (BS) and the subscriber stations (SSs), whereas in mesh mode, multihop communication is allowed and traffic can be routed through other SSs or occur directly between SSs [5].
Contemporary Wireless Technologies
Published in G. S. V. Radha Krishna Rao, G. Radhamani, WiMAX, 2007
G. S. V. Radha Krishna Rao, G. Radhamani
The basic access method, DCF, is drawn from the family of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocols. The collision detection (CD)mechanism, as used in the CSMA/CD protocol of Ethernet, cannot be used under 802.11 due to the near/far problem: to detect a collision, a station must be able to transmit and listen at the same time, but in radio systems the transmission drowns out the ability of the station to hear a collision. So, 802.11 uses CSMA/CA, under which collisions are avoided by using explicit packet acknowledgment (ACK) to confirm that the data packet arrived intact. The 802.11 standard supports three different types of frames: management, control, and data. The management frames are used for station association and disassociation with the access point, timing and synchronization, and authentication and deauthentication. Control frames are used for handshaking during a contention period (CP), for positive acknowledgment during the CP, and to end the contention-free period (CFP). Data frames are used for the transmission of data during the CP and CFP, and can be combined with polling and acknowledgments during the CFP. Figure 2.7 shows the standard 802.11 frame format, and Figure 2.8 shows the 802.11 standard and the ISO model. (See also Table 2.2.)
SC-MCHMP: Score-Based Cluster Level Hybrid Multi-Channel MAC Protocol for Wireless Sensor Network
Published in Noor Zaman Jhanjhi, Khalid Hussain, Azween Bin Abdullah, Mamoona Humayun, João Manuel R.S. Tavares, Information Security Handbook, 2022
Sowjanya Ramisetty, Divya Anand, Kavita, Sahil Verma, Abdulellah A. Alaboudi
A distributed coordination function (DCF) to share the access toward the medium, depending upon the CSMA/CA protocol, is defined by the IEEE 802.11 standard for WLAN. Because the channel, as well as the transmission data, is not detected by the node at the same time, the application of collision detection is not done. The node for the transmission is determined when a node listens to the channel. Two methods are used to perform the carrier sensing, wherein the activity upon the radio interference is detected by physical carrier sensing and the DCF RTS/CTS access mode is used to perform virtual carrier sensing.
Software architecture design, implementation, and evaluation of DCF-based MAC protocol on a low-power transceiver
Published in Journal of the Chinese Institute of Engineers, 2018
Yaw-Wen Kuo, Jane-Hwa Huang, Wei Lu
The carrier-sensing multiple access with collision avoidance (CSMA/CA) protocol is the most well-known multiple access technology, in which a station needs to sense the channel and defers a random time interval before transmitting to avoid collisions. There are two standards (IEEE 2006, 2007) based on the CSMA/CA technology. The wireless local network (WLAN), based on IEEE 802.11 standard (IEEE 2007), is the most widely deployed wireless network in the world. One can access the internet by WLANs at hot spots such as coffee shops, hospitals, airports, railroad stations. The primary MAC protocol of IEEE 802.11 (IEEE 2007) is called the distributed coordination function (DCF). In the DCF protocol, all stations contend for the wireless channel based on the CSMA/CA protocol with the contention window adapted by the slotted binary exponential backoff (BEB) scheme to avoid repeated collisions. The random backoff is only active when the channel is idle. Whenever the channel is busy, the backoff is paused. Another standard based on CSMA/CA is the IEEE 802.15.4 (IEEE 2006) MAC layer which is designed for low-rate wireless networks such as wireless sensor networks (WSN) or body area networks. In addition to low rate and low power, the computing power of an IEEE 802.15.4 node is typically very limited to reduce power consumption and prolong the battery life. Similarly, to avoid repeated collisions, the backoff exponent is increased by one after a collision to adjust the contention window.
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
To maintain a collision-free environment within the WLAN, DCF channel access is the integral and mandatory part of the 802.11 standard, which provides distributed contention-based resource allocation on the wireless medium to the STAs. As mentioned earlier, DCF channel access has two modes: basic and RTS/CTS. The introduction of RTS/CTS mode was to avoid the hidden terminal problem in WLANs. In both cases, each STA checks the medium status by CS before transmission. If the medium is sensed as idle for the DIFS period, a BEB procedure is invoked. While the medium is sensed as idle, the BEB decrements by one time slot for each backoff slot. The packet is transmitted when the timer reaches zero. In addition, if the medium is sensed as busy, the STA keeps sensing the channel until it senses the channel for the DIFS period. The key element for medium access is to select an optimal BEB value. We have shown the access modes used by DCF for resource allocation in Figure 2. The value of the backoff counter is uniformly chosen in the range [0, CW-1], where CW is the contention window size. On the first transmission attempt, CW is set to the minimum contention window, and is doubled whenever an unsuccessful transmission is detected. It stops incrementing when it reaches the maximum value. The CW is maintained at its maximum value for subsequent transmission attempts. This retry process also has a limit. When the number of retransmissions exceeds the limit, the frame is discarded and the CW is reset to the minimum value. This CW value returns to the minimum value after every successful frame transmission. If the medium becomes busy during BEB counting, the counter is frozen until the detected transmission is finished, and it resumes after sensing the medium for another idle DIFS. A STA transmits its frame once its BEB times out successfully.