# Effective 5G Wireless Downlink Scheduling and Resource Allocation in Cyber-Physical Systems +
## 1 Introduction  
Cyber-Physical Systems (CPS) and the Internet of Things (IoT) support numerous important applications, such as connected cars, factory automation, intelligent surveillance, smart homes and smart agriculture. The total number of IoT devices has already exceeded seven billion in the second quarter of 2018 without including two billion smartphones in the world [1]. It is projected that there will be approximately 50 billion connected devices by the end of 2020 [2]. Further, 70% of IoT devices will use cellular technology with better connectivity and reliability [3]. Thus, massive cellular traffic and connectivity requirements should be handled gracefully, dramatically increasing the demand for higher wireless communication performance and enhanced connectivity. It is difficult to support the demand using today's wireless technology [3; 4]. To address these challenges, the International Telecommunication Union (ITU) and International Mobile Telecommunication (IMT) have envisioned the fifth generation of cellular communication technology, called 5G for brevity. A 5G base station needs to support efficient Scheduling and Resource Allocation (SRA) via Time Division Duplexing (TDD), as well as Frequency Division Duplexing (FDD) [5; 6; 7]. In 5G, user applications are classified into three broad categories: (1) enhanced Mobile Broadband (eMBB), (2) enhanced Machine Type Communication (eMTC) and (3) Ultra-Reliable LowLatency Communication (URLLC) [8]. To support different 5G use-cases, as illustrated in Figure 1, a base station needs to use different numbers of Resource Blocks (RBs) along the time axis for TDD and different sub-carrier bandwidth allocations on the frequency axis to support FDD. For eMBB, typically, a 100-MHz bandwidth in the frequency domain and at least 500 RBs in the time domain are needed. For URLLC, the latency and reliability are critical. It uses a modest bandwidth up to 5 MHz with an RB sequence of 25 symbols for FDD and TDD, respectively. In addition, eMTC uses 1.4 MHz bandwidth and six RBs in the frequency and time domain, respectively. These use-cases show that a 5G base station needs to handle diverse traffic at each transmission interval. It is challenging to schedule and allocate resources at each transmission interval for many devices with diverse use-cases. In addition, the first generation of 5G comes as a Non-Stand-Alone (NSA) architecture that requires backward compatibility with the previous generation Long-Term Evolution (LTE) technology [9; 10; 11; 12], making Scheduling and Resource Allocation (SRA) even more challenging. To address the challenges of 5G, [PERSON] et al. [13] have recently proposed a novel cross-layer SRA framework by extending their previous work [14]. In their work, the utility function is defined in terms of the weighted goodput for cross-layer SRA. It provides a greedy cross-layer optimization over the Physical (PHY) and Data Link Control (DLC) layers to support effective SRA for massive Multiple-Input-Multiple-Output (MIMO) systems by taking advantage of higher bandwidth [15] and adaptive Modulation and Coding Schemes (MCSs) [16]. However, their SRA algorithm is greedy, potentially producing sub-optimal results; hence, it may not perform well for broader 5G use-cases. To address this issue, we have designed a new SRA algorithm based on dynamic programming [17]. It formulates the utility function based on the available bandwidth and required RBs, while allocating resources to maximize the total utility. Although the knapsack-like problem of dynamic SRA is usually NP-hard, we show that the time complexity of our algorithm is polynomial in a practical sense. In this paper, we further extend our conference publication [17] as follows:  
Figure 1: International Mobile Telecommunication (IMT)-2020 use-cases from Frequency Division Duplexing (FDD)/Time Division Duplexing (TDD) perspectives. eMBB, enhanced Mobile Broadband; URLLC, Ultra-Reliable Low Latency Communication; eMTC, enhanced Machine Type Communication.