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Relay-Assisted FSO Communications
Published in Z. Ghassemlooy, W. Popoola, S. Rajbhandari, Optical Wireless Communications, 2019
Z. Ghassemlooy, W. Popoola, S. Rajbhandari
Cooperative diversity is a paradigm shift in wireless communications technologies, which address a number of shortcomings in conventional point-to-point communication systems, mainly to combat fading and extend the transmission coverage area. This technique has been introduced as an alternative approach for implementing spatial diversity without using physical antenna arrays [36]–[39]. It is based on the broadcast nature of the RF wireless medium and enables single antenna–based users to take advantage of space diversity by sharing the physical resources through a virtual transmit and/or receive antenna array. This technique has been proposed in FSO systems and is known as the relay-assisted or multi-hop transmission, which offers an efficient and low-cost solution compared to MIMO with no requirement for additional Tx and Rx apertures.
Wireless Control Networks with Real-Time Constraints
Published in V. Çağri Güngör, Gerhard P. Hancke, Industrial Wireless Sensor Networks, 2017
Alphan Ulusoy, Ozgur Gurbuz, Ahmet Onat
Multi-path fading can cause significant degradation in the received signal strength over wireless channels, hence the capacity and quality of wireless communication networks are seriously degraded. Diversity techniques try to alleviate the effects of fading by generating and/or combining independently fading copies of the transmitted signal at the receiver [11], and cooperative diversity is one of the recent techniques to provide antenna diversity across cooperating nodes of a wireless network. In cooperative communications, the wireless broadcast advantage is exploited to disseminate the data to the cooperating nodes and via the cooperative transmissions, the receiver is provided with multiple copies of the original signal emanating from geographically separated transmitters (cooperating nodes); thus creating diversity at the receiver. At the receivers of cooperating nodes, Maximal Ratio Combining (MRC) is implemented, so that signals received from different nodes (branches) are combined in such a way that output Signal to Noise Ratio (SNR) is maximum, equal to the sum of SNRs of individual branches. This results in improved SNR at the receiver, higher link reliability, hence reduced number of retransmissions.
Cooperative Communication Technologies
Published in Jerry D. Gibson, Mobile Communications Handbook, 2017
To overcome the size, cost, and hardware limitations on wireless terminals, spatial diversity via multinode cooperation introduces a practical alternative to multiantenna terminals [1–6]. The basic idea behind cooperative diversity stems from the observation that, in a wireless environment, signals transmitted by the source node are overheard by other nodes, which can be recruited as “relays.” The source and other cooperative nodes can jointly process and transmit their information, creating a virtual antenna array even if these nodes are equipped with only one antenna, as shown in the example of Figure 33.1a. Similar to physical antenna arrays, these virtual antenna arrays combat wireless channel fading by letting receivers receive signals transmitted over independent diversity channels.
Network polar coded cooperative GSM scheme based on Plotkin’s construction
Published in International Journal of Electronics, 2023
Chunli Zhao, Fengfan Yang, Daniel Kariuki Waweru, Rahim Umar
Coded-cooperative diversity, which is an integration of channel codes and cooperative schemes like compress-and-forward (CF), decode-and-forward (DF) and amplify-and-forward (AF), has been considered as an effective technique to combat the channel fading. To attain the coded-cooperative diversity, various channel codes like polar code (Umar et al., 2018), LDPC code (Ejaz et al., 2015a) and turbo code (Zhao et al., 2020) have been proposed. In Arikan, 2009, Arikan proposed the capacity-achieving polar codes on the basis of the phenomenon of channel polarisation. In Andersson et al., 2010, the polar coded cooperative scheme via wiretap and relay channels was presented. The polar coded scheme for half-duplex cooperative communication was introduced in Zhan et al., 2014. In Ejaz et al., 2015b, the authors presented a Plotkin’s construction of polar codes for coded cooperative communications. However, the current coded cooperative schemes mostly focus on binary phase shift keying (BPSK) modulation, which results in poor spectral efficiency. In order to solve the problem, the GSM technique with high-order modulation is utilized in coded cooperative communications.