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WiFi Basics
Published in Mahbub Hassan, Wireless and Mobile Networking, 2022
Unlike wired LAN (Ethernet), Wireless LAN suffers from a specific collision detection problem called hidden node problem. Let’s consider the three wireless nodes, A, B, and C, as shown in Fig. 3. Let us assume that A can hear B, B can hear C, but C cannot hear A. Now, C may start transmitting to B while A is also transmitting to B. Clearly, collisions will be experienced at B, making it difficult for B to understand either of the communications. Unfortunately, the transmitters A and C cannot detect the collision. Only the receiver, B, can detect it. Therefore, unlike Ethernet, where transmitters can detect collision and back off, wireless LAN must implement some othertechniques that can avoid such collisions in the first place. Wireless LANs therefore use collision avoidance (CA) in contrast to collision detection (CD) used in Ethernet.
The Future of the Enterprise
Published in Marcus K. Weldon, The Future X Network, 2018
Fuad Siddiqui, Kevin Sparks, Furquan Ansari
Wireless LAN connectivity saves on in-building wiring installation and maintenance, and allows extension of the workspace and the work environment to many public and private locations. It can also make it easy for office visitors to connect to the enterprise LAN. From figure 4, it is clear that the shift of enterprise traffic to Wi-Fi and cellular is accelerating, and that the transformation of the enterprise from an all-wired system to an all-wireless one is underway — although, as argued in chapter 8, The future of the enterprise LAN, there is still a long way to go, with needed shifts in spectrum use, wireless architectures and service provider business models yet to happen. Mobile enterprise device adoption is expected to grow linearly, with corresponding use of wireless data to grow exponentially. By 2025, virtually all access will be via wireless — using Wi-Fi, Wi-Gig and 4G/5G — as discussed in depth in chapter 8.
Insights into CMOS Wireless Receivers toward a Universal Mobile Radio
Published in Krzysztof Iniewski, Wireless Technologies, 2017
Massimo Brandolini, Paolo Rossi, Danilo Manstretta, Francesco Svelto
The purpose of the IEEE 802.11 standard [69], formalized in 1999, was to allow high-rate wireless network connectivity between personal computers or workstations, avoiding the use of expensive and bulky wires. Today, WLANs are used worldwide in work environments, at home, and in “hot spots” at airports, hotels, and other public places for delivering high-speed Internet access. The original IEEE 802.11 standard provides a maximum data rate of 2 Mbps and allows radio implementations with frequency hopping (FH) or direct-sequence spread spectrum (DSSS), in the 2.4 GHz license-free ISM band. The need for more speed determined the definition of new standards, named IEEE 802.11a [70] (harmonized with ETSI HiperLAN2 [71]) and IEEE 802.11b [72]. The goal of the former was to standardize a high-rate (up to 54 Mbps) WLAN in the 5 GHz band, while the latter’s objective was to extend the throughput of the original 802.11 standard to data rates higher than 2 Mbps (reaching 11 Mbps). Finally, the IEEE 802.11g committee has recently drafted a high-speed wireless LAN standard [73] in the 2.4 GHz band that is backward-compatible with 802.11b and supports data rates up to 54 Mbps.
Joint CFO and channel estimation using pilot aided interpolation for high performance MIMO-OFDM
Published in International Journal of Electronics, 2023
S. Chitra, S. Ramesh, Ramya Vijay, G. Jegan, T. Samraj Lawrence
Orthogonal frequency division multiplexing (OFDM) has gained more attention in fourth and fifth generation (4 G and 5 G) wireless standards due to its high throughput, spectral efficiency, robustness to multipath fading and simple implementation with inverse fast Fourier transform (IFFT) and FFT algorithms. The principle of OFDM is dividing the total bandwidth into a number of orthogonal subcarriers, each with a narrow bandwidth. Since the subcarrier bandwidth is less than the coherence bandwidth of the channel, flat fading is possible in each subcarrier. As the frequency selective fading is converted to flat fading, OFDM system has reduced intersymbol interference (ISI), which simplifies the equaliser’s design. OFDM finds applications in digital video broadcasting, digital audio broadcasting, asymmetric digital subscriber line (ADSL) and IEEE 802.11 wireless LAN standards. The performance of 4 G and 5 G wireless services over multipath frequency selective fading channels can be improved by combining MIMO and OFDM algorithms.
Use of real time localization systems (RTLS) in the automotive production and the prospects of 5G – A literature review
Published in Production & Manufacturing Research, 2022
Christoph Küpper, Janina Rösch, Herwig Winkler
Wi-Fi is a Wireless Lan Area Network (WLAN) and common technology in broadband communications (Haotai Sun et al., 2020). It uses unlicensed frequencies in the range of 2.4 GHz and 5 GHz (Ning et al., 2013), and with the newest evolution of the standard IEEE 802.11ax also 6 GHz bands (Lee et al., 2019). A benefit of using Wi-Fi is its simple off-the-shelf availability and widespread usage with existing infrastructure (Bakri et al., 2020; Sosa-Sesma & Perez-Navarro, 2016). WLAN uses positioning as a secondary function next to the communication purpose (Hilty et al., 2012). Positioning methods include AOA (Cidronali et al., 2010), triangulation (Rusli et al., 2016; Wang Yuan et al., 2014), RSSI- based fingerprinting (Ren et al., 2019a, 2019b) and CSI-based fingerprinting (Hao Chen et al., 2017; Shi et al., 2018). From these methods, fingerprinting provides the best performance and allows for easy implementation and NLOS measurements without specialized hardware (Jaffe & Wax, 2014; Laoudias et al., 2018b). The accuracy is provided with about 2 ~ 3 m but can be heavily affected by barriers, multipaths of crowdedness, and the scanning time of 3 ~ 4 seconds by smartphones, resulting in low refreshment rates (Byunghun et al., 2015).
Improvement of heat storage performance and electricity consumption reduction of porous feldspar mixture
Published in Experimental Heat Transfer, 2022
Gichun Kang, Sung-Wook Kim, Dae Hong Go, Eun-Kyeong Choi, Seong-Kyu Yun
To investigate the temperature changes and electricity consumption, the heat storage layers had perforations in an 80 cm interval for thermometer installation. The temperature changes and electricity consumption were remotely observed in real-time during the two weeks of repetitive heating and cooling process. For the remote observation, temperature sensor was attached using the expansion GPIO (General Purpose IO) port of Raspberry Pi. The data were sent and saved in the cloud service through the wireless router [19]. The connection to the wireless internet of Raspberry Pi was enabled with a USB-type wireless LAN card. The electricity consumption during the heating and cooling process for the analysis of infrared thermal images were verified with the watt-hour meter. The total electricity consumption during maintenance was calculated with the meter images from CCTV (Figure 7). This study states the temperature changes and electricity consumption collected from the thermal images and fixed sense during the heating and cooling process of the heat storage layer.