# Multi-Tier Cellular Handover with Multi-Access Edge Computing and Deep Learning
## 5 Proposed Algorithm
### Proposed DL LSTM Algorithm  
In this work, we propose a DL LSTM handover decision algorithm. To develop a DL LSTM, an understanding of what the inputs and outputs must be realized. First, the desired outputs are decided. These are based on what is desirable and what challenges that this proposal is trying to address. The metrics are:  
1. _User CQI_: This is chosen to be an output to ensure that data connections are never lost, and a good QoS is maintained;
2. _User data rate requirements_: This is required to ensure that the user's data rate (DR) requirements are met for as long as possible;
3. _User velocity_: This ensures that the algorithm is dependent on user mobility when connection requirements become more important. \begin{table}
\begin{tabular}{c c} \hline \hline
**A3 Event** & **A1 Event** \\ \hline target gNB RSS \(>\) source gNB RSS \(+\) A3 & source gNB RSS \(>\) A1 threshold \\ offset (3 dB) & (minimum RSS for a CQI of 1) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: A1 and A3 handover conditions. The parameters above were chosen because it provides the algorithm the best opportunity to meet the UEs' QoS and QoE requirements. Therefore, from these desired output metrics, the key input dimensions were chosen. This LSTM consists of four dimensions. The UE's velocity is split into direction and speed for a smoother and faster learning process for the DL LSTM. _First Dimension: User CQI_  
This is the UE's CQI rating for the potential BS, and only BSs that have a CQI \(\geq\) 1 are considered. This eliminates any BSs which are not within the range. This method, if implemented correctly, can reduce signaling overheads and UE costs. This is because there is no longer a need for the capability to monitor and report on a minimum of eight (four Inter-RAT and four Intra-RAT) BSs, as stated in [27]. _Second Dimension: User data rate ratio_  
The UE's data rate ratio (DRR) is derived as _DRR = minimum DR that BS can support/maximum user DR requirements_. The maximum data rate is the maximum of the uplink and downlink requirements. The minimum data rate that BS can support is given by: _minimum BS DR for a CQI of 3/number of UEs attached_ (if attached UEs > 0); or _minimum DR that BS can support for a CQI of 3_ (if there is no attached UE). A CQI of 3 was chosen as this is the average CQI that a UE will have when connecting to a BS at a distance equivalent to approximately 70% (\(\pm\)10-20%) of the BS's coverage. This distance was chosen as, in most cases, the CQIs of potential BSs that can be handed over to will not be higher than 50-70% of the BS coverage. Thus, a value of 20% of the maximum CQI value of 15 was taken. The variation takes into consideration of small-scale fading and shadow fading effects, which can cause a \(\pm\)10-20% variation in the channel quality. _Third and Fourth Dimensions: User direction and speed_  
Both dimensions are measured using RSS values in dBm. Firstly, the UE's direction is measured from the variation in RSS between two successive measurement reports (MRs) of the potential BS. A negative value denotes a user is moving away, while a positive value denotes the user is moving closer to the potential BS. Additionally, the variation in speed is calculated as an absolute value of RSS variation. All the following values are with respect to RSS variations:  
\[\text{UE direction}=\left\{ \begin{array}{ll}\text{Closer to potential BS}&\text{ARS}\ \geq 0\\ \text{Away from potential BS}&\text{ARS}<0\\ \text{UE speed}\ =|\Delta\ \text{RSS}|&\end{array} \right. \tag{1}\]  
where \(\Delta\ \text{RSS}=\text{RSS}_{\text{t}}-\text{RSS}_{\text{t}-1}\)  
A variation of 5 dBm or more was chosen to be the value of a fast-moving user, as a 1 m variation in 100 ms (equivalent to a vehicle traveling at approximately 36 km/h) accounts for an RSS change of 10-15% in free space. In addition, due to further pathloss factors such as wall losses and user noise interferences, a 3 dBm offset is added to avoid potential misrepresentations.