Communicating in the Mediumband:What it is and Why it Matters

TL;DR

The opportunities and challenges posed by an emerging area of study known as “medium-band wireless communication,” which refers to digital radio-frequency wireless communication through mediumband channels, are articulated.

Abstract

This paper, based on recent research, articulates the opportunities and challenges posed by an emerging area of study known as ``mediumband wireless communication'', which refers to digital radio-frequency (RF) wireless communication through mediumband channels. This class of channels that falls in the transitional region between the narrowband and broadband channels, in many ways, is unique and shows significant potential. For instance, the effect of a highly unfavourable non-line-of-sight (NLoS) propagation environment can be transformed into a significantly favourable condition without making any intervention on the original propagation environment, but by simply communicating in the mediumband. The more unfavourable a propagation environment for wireless communication, the higher the potential gain by communicating in the mediumband. In this paper, using lay language as much as possible, we elaborate the unique properties of mediumband channels and implications of communicating in the mediumband for wider wireless communication along with some future research directions.

Figures (12)

• Figure 1: Main regions on the $T_mT_s$--plane representing three classes of wireless channels. BasJ23.
• Figure 2: a) A depiction of a typical transmit signal $s(t)$. In digital wireless communication, not all parts of $s(t)$, but only the points regularly separated in time (i.e. RED dots), carry information. This separation time is the symbol period or $T_s$. b) A depiction of a multipath profile as an impulse train, where the $x$--coordinate and the height of the impulses represent the excess delay and the strength of the corresponding MPC respectively. $T_m$ is a suitable measure of the time spread of MPCs. A wireless communication system, whose $T_m$ and $T_s$ approximately satisfy the condition: $0.1T_s \leq T_m \leq T_s$, which is represented by the GREEN region in Fig. \ref{['fig:fig0']}, is said to be operating in the mediumband.
• Figure 3: a) A graphical depiction of the PDF of $h$ in a typical NLoS propagation environment as described in (3). Typically, $h$ is complex, but here only the PDF of the real part of $h$ denoted by $h^i$, that is $f_{h^i}(x)$, is shown for brevity. Note that $\sigma_O$ is a parameter to capture the width of the PDF, but does not measure the distance as shown. b) A depiction of $f_{h}(x,y)=f_{h^i}(x)f_{h^q}(y)$, which is the complex PDF of $h$. Note the peak at (0,0) signifying the fact that the probability of either Re$\{h\}$ or Im$\{h\}$ being very small is very high, which is the single most problematic dampening force in modern wireless communication.
• Figure 4: a) Typical trend of average SIR with PDS. When PDS is less than 10%, the narrowband model (i.e. \ref{['eq1']}) is deemed to be satisfied, and the larger region, where PDS is greater than 10%, is the mediumband region. The RED circle (i.e. $\text{PDS}=5\%$ ) represents a narrowband system, while the GREEN square (i.e. $\text{PDS}=20\%$ ) represents a mediumband system BasJ23. b) Scatter plots showing the real and imaginary parts of $h$ in \ref{['eq1']} and $g$ in \ref{['eq2']} in NLoS propagation, where $\beta=0.22$ and $N=10$ (see Table \ref{['table:1']} for variable definitions). The low correlation between the real and the imaginary dimensions and, due to the "four leaf clover" shape on the right, the effect of deep fading avoidance in $g$ are clearly visible.
• Figure 5: On the right is a typical PDF of $g$ (only the real part) in a typical NLoS propagation environment BasJ23Bas22. Importantly, it is the same NLoS environment, which gives rise to the Gaussian PDF (in RED dotted line) for $h$ for narrowband systems, that gives rise to the bimodal PDF (in BLUE solid line) for $g$ for mediumband systems. It is the different operating points on the $T_mT_s$–plane that create this difference, but not different propagation environments.