Abstract: In this paper, a dual-hop relay based on channel state is studied. In the conventional relay scheme, a relay uses the same modulation method without reference to channel state. But, a relay uses an adaptive modulation method with reference to channel state. If the channel state is poor, a relay eliminates latter 2 bits and uses Quadrature Phase Shift Keying (QPSK) modulation. If channel state is good, a relay modulates the received symbols with 16-QAM symbols by using 4 bits. The performance of the proposed scheme for Symbol Error Rate (SER) and throughput is analyzed.
Abstract: Because current wireless communication requires high
reliability in a limited bandwidth environment, this paper proposes
the variable modulation scheme based on the codebook. The variable
modulation scheme adjusts transmission power using the codebook in
accordance with channel state. Also, if the codebook is composed of
many bits, the reliability is more improved by the proposed scheme.
The simulation results show that the performance of proposed scheme
has better reliability than the the performance of conventional scheme.
Abstract: In the cooperative transmission scheme, both the
cellular system and broadcasting system are composed. Two cellular
base stations (CBSs) communicating with a user in the cell edge use
cooperative transmission scheme in the conventional scheme. In the
case that the distance between two CBSs and the user is distant, the
conventional scheme does not guarantee the quality of the
communication because the channel condition is bad. Therefore, if the
distance between CBSs and a user is distant, the performance of the
conventional scheme is decreased. Also, the bad channel condition has
bad effects on the performance. The proposed scheme uses two relays
to communicate well with CBSs when the channel condition between
CBSs and the user is poor. Using the relay in the high attenuation
environment can obtain both advantages of the high bit error rate
(BER) and throughput performance.
Abstract: The conventional Wi-Fi backscatter system can only
process one-to-one communication between the Wi-Fi reader and the
Wi-Fi tag. For improvement of throughput of the conventional system,
this paper proposes the multi-to-multi communication system. In the
proposed system, the interference by the multi-to-multi
communication is effectively cancelled by the orthogonal multiple
access based on the identification code of the tag. Although the
overhead is generated by the procedure for the multi-to-multi
communication, because the procedure is processed by the Wi-Fi
protocol, the overhead is insignificant for the entire communication
procedure. From the numerical results, it is confirmed that the
proposed system has nearly proportional increased throughput in
according to the number of the tag that simultaneously participates in
communication.