147 research outputs found
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Improving NOMA Multi-Carrier Systems with Intentional Frequency Offsets
In this letter, we investigate the possible benefits of asynchrony in the frequency domain for the non-orthogonal multiple access (NOMA) schemes. Despite the common perspective that asynchrony in transmission or reception of multi-stream signals is harmful, we demonstrate the advantages of adding intentional frequency offset to the conventional power domain-NOMA (P-NOMA). We introduce two methods which add artificial frequency offsets between different sets of sub-carriers destined for different users. The first one uses the same successive interference cancellation (SIC) method as the conventional P-NOMA except that it enjoys reduced inter-user interference (IUI) between interfering sub-carriers. The second scheme adopts a precoding at the base station and a linear preprocessing scheme at the receiving user. It decomposes the broadcast channel into parallel channels circumventing the need for SIC. As a result, it fully exploits the advantages provided by the frequency asynchrony and enables the interference-free transmission to the users. The numerical results show that both methods can outperform the conventional P-NOMA
Trellis-Coded Non-Orthogonal Multiple Access
In this letter, we propose a trellis-coded non-orthogonal multiple access (NOMA) scheme. The signals for different users are produced by trellis coded modulation (TCM) and then superimposed on different power levels. By interpreting the encoding process via the tensor product of trellises, we introduce a joint detection method based on the Viterbi algorithm. Then, we determine the optimal power allocation between the two users by maximizing the free distance of the tensor product trellis. Finally, we manifest that the trellis-coded NOMA outperforms the uncoded NOMA at high signal-to-noise ratio (SNR)
Space-time code diversity by phase rotation in multi-carrier multi-user systems
Code diversity using space-time block codes was developed for single-carrier and single-receiver systems. In this paper, the extension of code diversity by phase rotation to multi-user and multi-carrier systems is proposed and analyzed. We show that code diversity with reduced feedback is possible in this new scenario and the coding gain has a mild logarithmic decrease with the number of users and the number of sub-carriers. In addition, we develop an analytical upper bound for the average error probability whose accuracy is verified by simulation
Differential spatial modulation for high-rate transmission systems
This paper introduces a new differential spatial modulation (DSM) scheme which subsumes both the previously introduced DSM and high-rate spatial modulation (HR-SM) for wireless multiple input multiple output (MIMO) transmission. By combining the codeword design method of the HR-SM scheme with the encoding method of the DSM scheme, we develop a high-rate differential spatial modulation (HR-DSM) scheme equipped with an arbitrary number of transmit antennas that requires channel state information (CSI) neither at the transmitter nor at the receiver. The proposed approach can be applied to any equal energy signal constellations. The bit error rate (BER) performance of the proposed HR-DSM schemes is evaluated by using both theoretical upper bound and computer simulations. It is shown that for the same spectral efficiency and antenna configuration, the proposed HR-DSM outperforms the DSM in terms of bit error rate (BER) performance
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