# Energy-Efficient BWP Configuration for Multi-Slice Users
## 1 Introduction  
Fifth Generation (5G) mobile networks support multiple heterogeneous services including the enhanced Mobile Broadband (eMBB) service requiring high throughput demand and the Ultra-Reliable Low-Latency Communications (URLLC) service requiring low latency and high reliability [1]. Owing to the concept of slicing, the physical network is partitioned into multiple logical networks (coined slices) where each slice is dedicated to a service and has a dedicated number of radio resources. User Equipment (UE) can be connected with up to 8 slices simultaneously [2].  
Moreover, the concept of a Bandwidth Part (BWP) was introduced in 5G to reduce UE power consumption where the UE can scan a limited part of the carrier band, termed BWP, instead of scanning the whole band. Additionally, this concept also supports flexible SubCarrier Spacing (SCS) designated by numerologies, where higher numerologies ensure lower latency and can be dedicated to more delay stringent services [3]. As such, a BWP is a set of contiguous Physical Resource Blocks (PRBs) linked to a specific numerology.  
In this work, UEs connected to two slices (eMBB and URLLC) are considered where each service requires a different numerology. Hence, for these users, two options are envisaged. The first consists of attributing different BWPs with different numerologies for each service (or slice) adequately. In such a case, BWP switching is required to retrieve the service-related data of each BWP. Hence, although this option endows each service with the most appropriate Quality of Service (QoS), it increases the UE power consumption due toscanning a wider bandwidth, and it inflicts an additional latency due to the BWP switching delay and signaling messages exchanged to perform BWP switching [4; 5]. The second option is to use a single BWP for all slices. Such an option corresponds to the legacy scheme and is applied currently in 5G networks. It has the merit to reduce complex signaling messages, costly BWP scanning and UE energy consumption but at the cost of reduced QoS. In fact, resorting to a single numerology (single BWP) fails to ensure satisfactory QoS for demanding services. Furthermore, using a single BWP with a single numerology may increase the UE's sojourn time in the network, which in turn increases its energy consumption. Hence, we devise a sagacious and flexible scheme that selects the most appropriate BWP configuration for each UE among the two previously mentioned solutions: either the multi-numerology BWPs per UE slice or a single-numerology BWP for all the UE slices, depending on the UE battery level and QoS strictness. To reach that aim, two approaches are adopted: a distributed approach using non-cooperative game theory where every UE autonomously selects the BWP configuration (multi-numerology or single numerology) that strikes a good balance between improving its QoS and reducing its battery consumption and a centralized approach where UEs are assigned optimally to the most adequate BWP configuration. In both approaches, a cost function is carefully defined and takes into account the BWP size, the BWP level of congestion, the UE sojourn time in the network and the UE battery level. The performances of both approaches are assessed through extensive simulations where they are compared against each other and against the legacy scheme which they largely surpassed. The rest of the paper is organized as follows. Section 2 gives the state of the art. Section 3 discusses our system model. Sections 4 and 5 tackle the proposed distributed and centralized approaches. Section 6 provides simulation results of the proposed solutions. Finally, Section 7 concludes the paper.