Multicarrier-Division Duplex: A Duplexing Technique for the Shift to 6G Wireless Communications

Abstract

In-band full-duplex (IBFD) has the potential to not only double the spectral efficiency (SE) but also greatly reduce the transmission latency. However, the less maturity of existing self-interference cancellation (SIC) techniques renders IBFD impractical for future wireless applications. To inherit the merits of full-duplex (FD) but with practical SIC requirements, multicarrier-division duplex (MDD) was proposed and studied recently. In this article, we demonstrate the advantages of MDD over the IBFD mode and the conventional half-duplex (HD) modes of frequency-division duplex (FDD) and time-division duplex (TDD) from several essential aspects, including SIC capability, resource integration and the support for high-mobility communications. Several numerical results are included to show that MDD outperforms IBFD in terms of energy efficiency and SIC. Compared with the HD modes, MDD is capable of efficiently integrating the DL/UL resources to achieve higher SE and significantly outperforms TDD, when communicating over fast time-varying channels. Lastly, some implementation challenges of MDD systems are discussed.

Heterogeneous graph neural network for power allocation in multicarrier-division duplex cell-free massive MIMO systems

“…In the system under study, the subcarriers of one band are divided into two mutually exclusive subsets, namely, a DL and a UL subcarrier subset to support DL and UL transmissions, respectively. Despite the fact that MDD-CF systems suffer from the similar problems of SI and CLI in analog domain as IBFD-CF systems, it can be free from digital-domain SI and CLI with the aid of the FFT operation at the receiver, since interference and desired signal are transmitted over orthogonal subcarriers [10]. In this case, leveraging the existing methods in analog domain, such as power allocation and antenna polarization [4,12], and the FFT operation in the digital domain, the CLI and SI can be individually mitigated at each AP and MS node, which makes it possible to enable FD-style distributed systems.…”

“…The SI refers to the interference that a transmitting access point (AP) causes to itself, which can be mitigated by propagation-, analog-and digitaldomain SI cancellation (SIC) methods [5][6][7][8][9]. But the SIC implementation imposes large complexity and resource burden on small-scale APs of CF networks [10], and none of the existing methods can fully suppress the SI, leading to the performance degradation of desired transmission caused by residual SI. Furthermore, CLI, known as inter-AP interference (IAI) and inter-mobile station (MS) interference (IMI), have shown to be the most serious problem in multi-cell IBFD and dynamic TDD (DTDD) systems [11], and the situation is exacerbated in CF networks due to the dense distribution of APs, as the IAI received at each AP may come from various directions.…”

Multicarrier-Division Duplex for Solving the Channel Aging Problem in Massive MIMO Systems

“…Secondly, the large-scale fading of MT-MT link and the MT's relatively lower transmit power allow the received signal of an MT to efficiently pass the ADC. Consequently, the IMI can be readily removed by the FFT operation in the digital-domain, when all MTs and the BS are assumed to be synchronized within an allowable time window [14].…”

“…By contrast, in the MDD-assisted systems, this amount of SIC can be attained at nearly no extra cost of system resources, owing to the embedded fast Fourier transform (FFT) operation [9], which allows to ideally separate UL signals from DL signals in the digital-domain. For more detailed comparison between MDD and the existing duplex modes, e.g., TDD, FDD and IBFD, in terms of system architecture, initial access of physical layer and resourceallocation, the readers are referred to our previous works [9,[12][13][14].…”

“…This means IBFD costs more computation effort and system complexity than MDD for SIC, and hence achieves lower energy efficient[14] 7. Note that 100 dB of SI is often assumed in IBFD systems, which is regarded as the bottleneck value based on the existing SIC approaches[30,31].…”