Constructive Multiuser Interference in Symbol Level Precoding for the MISO Downlink Channel

Abstract: This paper investigates the problem of interference among the simultaneous multiuser transmissions in the downlink of multiple antennas systems. Using symbol level precoding, a new approach towards the multiuser interference is discussed along this paper. The concept of exploiting the interference between the spatial multiuser transmissions by jointly utilizing the data information (DI) and channel state information (CSI), in order to design symbol-level precoders, is proposed. In this direction, the interference among the data streams is transformed under certain conditions to useful signal that can improve the signal to interference noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio transmission (MRT) based algorithm that jointly exploits DI and CSI to glean the benefits from constructive multiuser interference. Subsequently, a relation between the constructive interference downlink transmission and physical layer multicasting is established. In this context, novel constructive interference precoding techniques that tackle the transmit power minimization (min power) with individual SINR constraints at each user's receivers is proposed. Furthermore, fairness through maximizing the weighted minimum SINR (max min SINR) of the users is addressed by finding the link between the min power and max min SINR problems. Moreover, heuristic precoding techniques are proposed to tackle the weighted sum rate problem. Finally, extensive numerical results show that the proposed schemes outperform other state of the art techniques.

• The paper proposes viewing multiuser interference as a constructive force in MISO downlink symbol-level precoding, leveraging both data and channel information to design precoders that exploit it.
• The study develops the Constructive Interference Maximum Ratio Transmission (CIMRT) algorithm, which uses channel decomposition to align interfering streams constructively for improved signal-to-interference-plus-noise ratio.
• Numerical results demonstrate that the proposed constructive interference methods achieve superior performance compared to existing linear precoding techniques, with implications for spectrally dense environments and energy efficiency.

Analysis of Multiuser Interference Exploitation in Symbol Level Precoding for MISO Downlink Channels

The paper presents a focused investigation into the challenge of multiuser interference within the context of MISO downlink channels employing symbol-level precoding techniques. The novelty of the study lies in the proposition of viewing interference not just as a factor to be minimized, but as a potential asset to improve the performance metrics of the system, primarily SINR.

The approach leverages both Data Information (DI) and Channel State Information (CSI) to design precoders that can exploit the interference constructively, transforming it into a useful signal component under M-PSK modulated conditions. This novel concept counters the conventional scheme where interference is predominantly considered detrimental, needing avoidance at all costs.

Highlights from the study include the development of the Constructive Interference Maximum Ratio Transmission (CIMRT) algorithm, which integrates MRT principles to coalesce interfering streams constructively. This is achieved by harnessing the channel's singular value decomposition, ensuring rotational alignment of signals, thereby manifesting constructive interference potential.

Moreover, a dual problem formulation approach is employed to address transmit power minimization and fairness maximization through SINR convergence—compared and contrasted with established multicast frameworks. This relation points to where symbol-level strategies might provide performance gains beyond conventional user-level precoding models that divide codewords among users or groups, and instead precisely tune symbols directly.

The implications of this research are manifold, with practical ramifications for modern wireless transmissions especially in spectrally dense environments. Notably, the proposed strategies could revolutionize how downlink channels are visualized in system design, implying potential hardware and policy shifts to accommodate faster symbol-level precoding requirements.

Future developments anticipated from this investigation will likely explore the broader application of constructive interference-based frameworks in various multi-antenna broadcast settings. Such exploration could yield adaptability in cognitive radio systems, a solution to maintaining high SINR with reduced power consumption, all the while improving the intrinsic energy efficiency of wireless systems.

The numerical results underscore the efficacy of the proposed frameworks, evidencing superior performance over existing linear precoding techniques by effectively demonstrating the practical viability of these methods in benefitting from multiuser interference. Henceforth, the application scope of symbol-level precoding with constructive interference must be considered within both theoretical models and real-world wireless communication deployments.