# IRS, LIS, and Radio Stripes-Aided Wireless Communications: A Tutorial
## 3 System and Signal Characterization  
mMIMO techniques in the mmWave frequency range can result in significant performance increases. However, massive antenna arrays allow the use of multiple antennas and spatial multiplexing techniques, providing an extra rise in data rates or improved dependability, with the potential of both advantages being realized concurrently by ensuring a connection among them. As a result, keeping receiver complexity low is critical, necessitating low-complexity frequency domain equalization (FDE) detectors, including the MRC and EGC, which do not necessitate inversion of the high-dimensional channel matrix for every frequency part, as needed for the ZF and MMSE receivers, while performing similarly. In order to avoid such matrix inversion, MRC and EGC can be used either as post-processing (at the receiver) or as pre-processing (precoding) components [33, 40]. In massive MIMO systems, there are numerous methods to design the receiver, which can make things more or less complicated. In this type of system, methods based on matrix inversions, such as ZF and MMSE, are plainly detrimental. Even if their error probability performances are good, the complexity rises exponentially as the transmitting and receiving antenna count increases [41]. \begin{table}
\begin{tabular}{c|c c c} \hline  & **IRS** & **LIS** & **Radio Stripes** \\ \hline
**Structure** & Massive-MIMO & Beyond Massive-MIMO & Cell-free Massive MIMO \\ \hline
**Antenna type** & Passive & Active & Active/Passive \\ \hline
**Deployment** & Easy & Easy & Easy \\ \hline
**Capacity/data rate** & High & High & High \\ \hline
**Energy efficiency** & Good & Slightly high & - \\ \hline
**Channel estimate** & Critical & Solved & - \\ \hline
**Propagation** & Near-field & Near-field & Near-field \\ \hline \end{tabular}
\end{table} 
Table 4: Comparison between IRS, LIS, and Radio Stripes. \begin{table}
\begin{tabular}{c c} \hline
**Reference** & **Main Contribution** \\ \hline
[9] & This research examines an uplink power allocation strategy aimed at improving network spectral efficiency (SE), which is described as an optimization-constrained issue explicitly considering the max-min fairness situation. \\ \hline
[14] & This paper present advantages of using radio stripes in mm waves. \\ \hline
[37] & This article demonstrates how inexpensive it is to implement and operate cell-free radio stripes. \\ \hline
[38] & This paper evaluates energy consumption of radio stripes with ideal CSI. \\ \hline
[39] & This approach suppresses interference in cell-free mMIMO while minimizing the cost and front-haul requirements. \\ \hline \end{tabular}
\end{table} 
Table 3: Representative Overview of Recent Studies on Radio Stripes. Accordingly, these receivers can be classified as:
* Linear feedforward, non-iterative FDE receivers (this type includes the ZF, MMSE, MRC, and EGC). * Iterative MRC and EGC, FDE receivers, known as iterative block-decision feedback equalization (IB-DFE) receivers. When used in conjunction with the necessary cyclic prefixes and FDE methods, block transmission methodologies have been shown to be suitable for high-data-rate transmission across extremely time-dispersive channels. The most widely used modulation based on this technology is orthogonal frequency division multiplexing (OFDM). An alternate approach based on this premise is single carrier (SC) modulation utilizing FDE (known as SC-FDE). The data blocks, as in OFDM, are preceded by a cyclic prefix that is large enough to account for the total channel length. SC-FDE techniques are especially appealing when simple and efficient power amplification is needed [12]. This is because the envelope variations of the broadcasted signals are smaller, resulting in a smaller peak-to-average power ratio. In [25; 42], the authors suggested a promising IB-DFE technique for SC-FDE that was later expanded to include additional diversity and spatial multiplexing [5] schemes.