# Study of 5G-NR-MIMO Links in the Presence of an Interferer
## 1 Introduction
This is needed for independent decoding and to increase the capacity of the channel. The benefits of this agenda are far-reaching. In a situation without any jammer or any interference signals between the transmitter and the receiver, we can achieve improvements over spatial multiplexing (SM) [27], or eigenvalue beamforming [27; 28]. The above trade-off is expressed especially under the assumption of dynamic and random channel response or very high mobility of the transmitter relative to the receiver, or vice versa. Assuming a scattering-rich propagation channel or a two-ring model scatter environment [5] also creates a challenge. Improvements in channel estimation or estimation of the random Direction Of Arrival (DOA) of the receive paths [29] are also considered to produce improvement in this agenda. Here, we present the significant effects of a smart jammer and interference on a wireless mobile network's physical (PHY) layer and in an unlicensed wireless communication environment. An understanding of these effects, without a doubt, will contribute to the modern techniques that we have mentioned. The common base of these phenomena is the destruction of the principle orthogonality region, which we expand in this paper (Appendix A). Orthogonality between the various receive paths in the surrounding multi-path channels is particularly significant in the MIMO array with multiple receive and transmit antennas [27]; however, it allows for high vulnerability in MIMO techniques. By creating orthogonality between the paths, we achieve maximum capacity in the channel [27]. The ability to receive multiple independent data streams fixes the internecine effects on the channel matrix, achieves a full rank in this matrix, and finds the optimum eigenvalue distribution that leads to a maximum capacity [27]. The maximum capacity is obtained when the ratio of the maximum eigenvalue to the minimum eigenvalue converges to 1 [27]. A system with only CSI at the Receiver (CSIR), every channel path has a power gain equal to the eigenvalue of the channel matrix. This is in addition to the fact that the effective transmit power is \(\frac{1}{N_{t}}\) times the total transmit power, when \(N_{t}\) is the number of transmit antennas. The orthogonality between the paths also leads to significant Success Interference Cancellation (SIC) implemented in many decoder techniques, especially in MRRC. In a multi-interfering environment there is damage to the orthogonal spectrum (Appendix A), and as a result, the performance of the receiver decreases significantly. Another significant effect that we present in this paper adds to the orthogonality region's hit: replicating the interference and information symbols in the MRRC combiner after the interferer is received. This phenomenon is reflected in the constellation receiver, dependent on the Signal Interference Ratio (SIR), and the constellation order. Without a feedback system that fixes those duplicate symbols, this phenomenon will be complicated for advanced decoder capabilities such as Sphere Decoder (SD), Zero Forcings (ZF), and Best Linear Estimation (BLE). These effects intensify under the assumptions we make in this paper. A clear example of our assumption can be found in the HetNet scenario [30; 31]. In this case, we assume that we have several small cells and pieces of User Equipment (UE), both equipped with multi-transmission and multi-receiver antennas and communicated with a single macro-cell in the same network environment without sharing the same scheduler. In this case, we assume a full-duplex (FD) mode and Time Division Duplex (TDD) access through a slow-fading channel, and a random DOA receives angle, in addition to Uniform Linear Array (ULA) antennas. This situation [31] is complicated because the UE, the small cells, and the base-station can play the role of the transmitter, receiver, and interferer at the same time.