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Comparison of OFDM and OFDMA.

Comparison of OFDM and OFDMA.

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Article
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Secret key generation exploits the unique random features of wireless channels, hence it is eminently suitable for the resource constrained Internet of Things applications. However, it has only been involved for single links between a pair of users, whilst there is a paucity of literature on group and multi-user key generation. This paper proposes...

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Context 1
... shown in Fig. 2(a), OFDM allocates all the available subcarriers to a single user, which can then achieve a high data rate within the given bandwidth. Duplexing is handled in a TDD mode. Therefore, OFDM has been employed for improving the key generation rate by exploiting the randomness both in the time-and in the frequency-domains [27]- ...
Context 2
... the other hand, OFDMA allows multiple users to simultaneously access the spectrum by transmitting in orthogonal non-overlapping bands, as illustrated in Fig. 2(b). Since the OFDM subcarriers are orthogonal, there is no interference amongst them. This allows the AP to simultaneously obtain channel measurements of multiple users. Surprisingly, however, this feature has never been exploited for key generation, mainly because OFDMA has never been adopted in Wi-Fi standardization until the recent ...

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... A useful key generation protocol was presented forth by Hershey [41] in 1995 and was based on the three properties of wireless channels-reciprocity, uniqueness, and randomness. Since then, many researchers have further studied the PKG in various scenarios from different angles [28,[42][43][44][45], which will be introduced later. ...
... In recent years, there are many practical protocols have been proposed to optimize the performance of PKG and meet the constraints of different scenarios, such as maximizing the sum key generation rate (KGR) and reducing the pilot overhead. However, they are generally composed of four steps: channel probing, quantization, information reconciliation, and privacy amplification [25,29,42,47,48], which are portrayed in Figure 3. As depicted in Figure 3, there are two legitimate users, namely Alice and Bob, and their PKG process can be summarized as follows: Alice and Bob perform channel probing firstly to obtain channel information, such as obtaining Y A and Y B by sending pilot signals S A and S B to the other party respectively and performing channel estimation based on the received signals, and often a preprocessing method is used to eliminate interference from non-reciprocal factors. ...
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... These studies target relatively small networks and require impractical communication times in dense networks. In the second category [9]- [13], the methods are purely based on broadcasting and are suitable for dense networks. In [9], the authors consider a new metric where, instead of raw RSSI values, difference of two received signal strength indicator (RSSI) values from two different channels is used. ...
... As main drawbacks, these algorithms either assume a noiseless channel or apply channel coding to provide a noiseless channel between the nodes for information exchange. In [13], an orthogonal frequency-division multiple access (OFDMA)-based key generation model is proposed. The method aims to reduce the duration of channel estimation phase by exploiting OFDMA. ...
... Zhang et al. [13] Reduces the load of channel estimation process for OFDMA networks. ...
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... Alice and Bob keep probing until they collect sufficient measurements, and , respectively. [72,135,154,159]. ...
... Since then, numerous studies have been conducted to investigate CSI-based key generation systems from different application scenarios and perspectives [135,154,159,162,164]. ...
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