1 Introduction
- We introduce a general expression of the network’s energy efficiency when multi-connectivity is used, and estimate rough lower and upper bounds of its gains;
- We introduce a general framework for secondary cell selection;
- We design five algorithms for secondary cell association with a focus on improving the energy efficiency of the network;
- Finally, we evaluate our proposals using simulations.
2 Background and related work
2.1 Ultra-dense networks
2.2 Multi-connectivity
2.3 Power consumption model
3 Formulation of energy efficiency
3.1 Notations
3.2 Energy efficiency’s expression
3.2.1 Scenario 1: single connectivity
3.2.2 Scenario 2: multi-connectivity
3.3 Lower bound
3.4 Low performance bound
3.5 Upper bound
3.6 Ensuring energy efficient multi-connectivity
4 Secondary cell association
4.1 Framework for target selection and association
- Robustness this class regroups the most common metrics, such as Reference Signals Received Power (RSRP), Received Signal Strength Indicator (RSSI) or the Signal over Interference plus Noise Ratio (SINR), and are used to estimate the channel or signal quality. Optimizing these metrics allows to select more robust links.
- Performance Estimating the achievable bitrate can be used as a metric to increase the performance of the system.
- Energy the power consumption can be used as a metric when designing energy efficient algorithms. Realistic power models are however necessary.
- Cell utilization Metrics such as the cell load, the number of connected devices or the base station’s state can also be used as inputs.
4.2 Energy efficiency condition
5 Cell association algorithms
Parameters | Values |
---|---|
TTT (ms) | 50 |
\(\theta _\mathrm{add}\) | 0.8 |
\(\theta _\mathrm{rmv}\) | 0.5 |
\(\theta _{clst}\) | 0.8 |
\({\mathbf {w}}_\mathrm{AHP}\) | [0.5, 0, 0.5] |
Schemes | Performance | Robustness | Energy | Utilization |
---|---|---|---|---|
Max bitrate | x | |||
Max SINR | x | |||
Max bitrate-EE | x | x | ||
Max clustered-bitrate | x | x | x | |
Analytic hierarchy process | x | x | x | x |
5.1 Max bitrate
5.2 Max SINR
5.3 Max bitrate-EE
5.4 Max clustered-bitrate
5.5 Analytic hierarchy process
6 System models
6.1 Power consumption model
- After 10 ms in active mode and without any activity, the base station goes to the sleep level 1;
- The base station wakes up directly if it needs to transmit something, or a user connects. Without any activity, the base station stays in sleep level 1 for a maximum duration of 10 ms. After that time, it goes into sleep level 2.
- The base station stays in sleep level 2 until an activity is detected. When there is any activity, it goes directly into active mode.
6.2 Traffic model
6.3 Network model
Parameters | LTE | NR |
---|---|---|
\(N_S\) (number of sectors) | 3 | 1 |
\(N_C\) (number of carriers) | 4 | 4 |
\(P_0\) (W) | 130 | 56 |
\(\varDelta _P\) | 4.7 | 2.6 |
\(P_\mathrm{max}\) (W) | 20 | 6.3 |
\(P_\mathrm{sleep}\) (W) | 75 | 39 |
\(\delta _\mathrm{NR}\) | 0.29 |
Parameters | LTE | NR |
---|---|---|
Frequency (GHz) | 2 | 28 |
Carrier bandwidth (MHz) | 20 | 100 |
Antenna type | Tri-sector | Omni |
Antenna gain (dBi) | 15 | 0 |
Antenna height (m) | 30 | 10 |
Number of sites | 3 | 61 |
Inter-site distance | 400 | 100 |
7 Simulation results
7.1 Robustness and user throughput
7.2 Network-level metrics
7.2.1 Power consumption
7.2.2 System energy efficiency
7.2.3 Probability of multi-connectivity
Scheme | Probability (%) | Std |
---|---|---|
Max bitrate | 21.53 | 2.46 |
Max bitrate-EE | 18.71 | 2.27 |
Max clustered-bitrate | 13.16 | 4.93 |
AHP | 19.11 | 2.22 |