# A Novel Self-Forming Virtual Sub-Nets Based Cross-Layer MAC Protocol for Multihop Tactical Network
## 4 Working of Algorithm
Therefore, it can be analyzed that the total number of control frames \(L\) depends on maximum hop transmissions, the complexity of the network, and the set of control parameters. #### 6.1.2 Control Overhead

In VSCL-MAC, the control overhead is much less than conventional TDMA-based MAC design because control packets contain only transmission information, and nodes take an autonomous decision on frequency selection and time slots scheduling by using TRANS_table. When \(L\) is small, the control overhead is low. For example, in a tactical network of 30 radios, the control overhead adds up to 38.57% in VSCL-MAC and 83.08% in TDMA-based design. This control overhead, including call setup time, is low when the network is small, and most of the radios are intending to communicate on lower hops. #### 6.1.3 Network Throughput of VSCL-MAC Protocol

The network throughput \(TH_{network}\) of the proposed design is calculated using Equation (1), which describes the number of bits \(b_{m}\) of message \(m\) transmitted by a node \(n_{i}\) on data channel \(h\) of data rate \(R_{t}\) kbps. The data is transmitted in a data slot \(d\) of TDMA frame of duration \(T\). \[TH_{network}=\sum_{h=1}^{F}\left(\frac{\sum_{i=1}^{N}\left(n_{ih}\times b_{m} /R_{t}\right)}{T_{d}}\right) \tag{1}\]

For network throughput analysis, we consider the channels of capacity 200 kbps to 1000 kbps based on the M-ary modulation scheme selected by the authors of [32]. Different data sizes are considered according to the requirement of application with the adjustment of conflicting design parameters such as data rate, bandwidth, delay concerning the number of hops \(k\), and radio transmit power by the model presented in [32]. The size of data slot \(S_{d}\) is double the size of control slot \(S_{c}\), e.g., for 30 nodes, \(S_{d}\) is 28.6 ms. We assume three different messages according to the data type and its size, specified in Table 11 and the number of data slots is equal to number of messages \(M\). #### 6.1.4 Network Throughput Concerning \(R_{t}\)

In consideration of above settings, the slot size \(S_{d}\) of 28.6 ms is not enough to send 1250 bytes (10 Kb) of data over \(R_{t}\) of 200 kbps and 300 kbps. However, with \(R_{t}\) of 400 kbps to 1000 kbps, each TX node of sub-nets can transmit all 10 Kb of text message, keeping the data slot size \(S_{d}\) unchanged, as shown in Figure 20. For visuals and voice messages, \(TH_{network}\) increases with \(R_{t}\), as more data bits can be transmitted. It is also due to the allocation of two and three data slots to each TX for respective message types and has a diverse impact on channel utilization and network throughput. Nevertheless, the increase in \(R_{t}\) only favors the prosperous transmission of all bits under a slot; it does not ensures utilization of all data slots. Henceforth, the channel capacity goes subverting and critically affects \(TH_{network}\). Under low \(R_{t}\) such as 200 kbps and 300 kbps, 57.2% and 86.67% bits are transmitted from 10 Kb, respectively. For visual messages, nodes can send 11.4% to 57.2% bits of the message over \(R_{t}\) of 200 kbps to 1000 kbps, and for voice messages, the bit transmission percentage goes from 1.72% to 8.58% for respective data rates. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Message** & **Bit** & **No. of** & **Data Slot** & **Data** \\
**Type** & **Identification** & **Slots Allocated** & **Time (ms)** & **Size** \\ \hline text & 00 & 1 & 28.6 & 10 Kb \\ Image/visuals & 01 & 2 & 57.2 & 100 Kb \\ voice/video & 10 & 3 & 85.8 & 1 Mb \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Particulars of data messages with reference to slot and data size for \(N=30\). #### 6.1.5 Impact of Increase in Slot Size and Number of Slots on \(TH_{network}\)

The proposed VSCL-MAC design improves results for large data sizes if we increase the data slot size, i.e., \(S_{d}=57.2\) ms for text and other types accordingly. The nodes can send more bits in a single slot and have a marginal impact on \(TH_{network}\).