## 1 Introduction  
The development and deployment of the 4 th generation (4G) cellular system was undertaken by the International Telecommunication Union because user data demands have continued to grow at a rapid rate, thus necessitating further enhancement of cellular network capacities. Indeed, the advancement of cellular technologies towards 5 th generation (5G) systems is already underway in order to accommodate still further increases in user needs. In order to be effective, 4G and 5G systems must be capable of supporting data requirements within multi-user environments in a way that meets both economic and service demands. Additionally, the two key aims of 5G systems are spectral efficiency and energy efficiency. However, the challenge of how to couple and integrate these disparate objective performance metrics efficiently has yet to be resolved. Previously, complete overviews for 4G systems were published by [PERSON] and [PERSON] [1] and [PERSON] et al. [2], while articles by [PERSON] et al. [3], [PERSON] et al. [4], [PERSON] and [PERSON] [5], [PERSON] and [PERSON] [6], and [PERSON] et al. [7] surveyed recent advances in key 5G system technologies in detail. Among those advances, the ability of base stations (BSs) to make use of multiple component carriers (CCs) simultaneously during data transmissions is among the key characteristics of 4G/5G systems that makes them more powerful than less advanced networks, allowing them to achieve substantially higher capacities. In other words, the aggregation of multiple CCs in a single BS allows 4G/5G systems to support much broader transmission bandwidths than the more basic networks are capable of supporting. One of the key technical challenges of 4G/5G systems is the design of ideal packet schedulers, since any effective packet scheduler design must meet the following requirements: (1) It must effectively provide packet scheduling in environments with multiple CCs; (2) It must support the necessary quality-of-service (QoS) requirements even while handling various kinds of traffic, such as real-time (RT) traffic (i.e., QoS-sensitive traffic) and non-RT (NRT) traffic (i.e., QoS-non-sensitive traffic); (3) It must achieve high overall system throughput; and (4) it must maintain the necessary level of fairness among users. There have already been considerable research efforts dedicated to resource management designs for use in cellular systems, with much of those efforts focused on systems that make use of multi-user single-CC BSs [8; 9; 10; 11; 12; 13; 14]. For example, a scheme consisting of enhanced efficiency cross-layer packet scheduling and resource management was proposed by [PERSON] et al. [8], while various fast algorithms designed to provide optimal resource allocation that would, in turn, maximize overall system utility were proposed by [PERSON] et al. [9]. In 2012, a study by [PERSON] et al. [10] focused on the question of how resources should be allocated in order to ensure energy-efficient communication in single-cell environments with a high number of transmitting antennas. In a subsequent study, the same authors went further by also addressing that question with regard to multi-cell environments with cooperative BSs [11]. In a 2013 study, [PERSON] et al. investigated the use of a type of BS that engages in hybrid energy harvesting for data transmissions; in the BS in question, an energy harvester was used in combination with a constant energy source provided from a non-renewable resource in order to supply the system with the energy necessary for its operation [12]. Taking on the issue of energy efficiency from another perspective, the development of heterogeneous network deployments involving both small cells and macrocells was investigated by both [PERSON] et al. [13] and [PERSON] [14] as a means of enhancing energy efficiency. Unfortunately, while all these studies (i.e., [8; 9; 10; 11; 12; 13; 14]) contributed some important insights, the issue of using multiple-CC BSs for packet scheduler designs was not specifically considered by any of them.