# 5G Mobile Services and Scenarios: Challenges and Solutions
## 3 A Brief Review of Articles of this Special Issue
[23] discussed the challenges and the possible performance degradation of Transmission Control Protocol (TCP) due to path heterogeneity in highly integrated 5G systems [24]. The paper presents a performance analysis model for the TCP over multiple heterogeneous paths, with the consideration of link quality asymmetry (both delay and bandwidth). The accuracy of the proposed model is obtained by the comparison of simulation study with field experiment. The authors developed the interesting conclusion that the delay asymmetry between the multiple links is more dominant factor in the performance of TCP. The proposed model, no doubt, can provide guidance to the design of novel Concurrent Multipath Transfer (CMT) solutions for 5G mobile services. [PERSON] et al. [25] proposed a theoretical model for partitioning and allocating an arbitrarily divisible application, i.e., Optical Character Recognition (OCR), among a group of available resources, with the objective of reducing the completion time. The effectiveness of the proposed model for partitioning and allocating divisible applications in opportunistic computing environments is demonstrated through both the simulations and real experiments. The proposed work only focus on the benefit of offloading in terms of completion time, and the inclusion of the incurred energy consumption is suggested for the future work. [PERSON] and [PERSON] [26] evaluated the 5G based Cognitive Radio Networks (5G-CRN) [27] as one of the potential candidates for enhancing the spectrum utilization efficiency. The paper highlights the need of efficient handover management for the 5G-CRN as multi-tier network layout for 5G requires the Primary User (PU) to be more active. This paper focuses on the formulation and analysis of the sum utilization of spectrum policy for multi-channel scenarios under different PU and Secondary User (SU) co-existing network topologies, with the aid of sensing and handoff capabilities. The proposed work demonstrates that the different sets of channels, PU activities, and sensing outcomes have a significant impact on the sum utilization of spectrum associated with a specific network topology. [PERSON] et al. [28] investigated experimental performance analysis of Cooperative Communication (CC) [29] over Direct Communication (DC) in the lab environment to overcome channel fading and to improve channel capacity. The experimental setup is built using Universal Software Radio Peripheral (USRP) and Laboratory Virtual Instrument Engineering Workbench (LabVIEW). A text message is transmitted by using Phase Shift Keying (PSK) modulation schemes. The setup uses Amplify and Forward (AF) relaying mode and two time slot transmission protocols. The Maximum Ratio Combining (MRC) technique is used for combining Signal to Noise Ratio (SNR) at the receiver. The CC can significantly enhance the system performance in terms of reliability and channel capacity. Due to the high data rates and cost effective solutions, CC is considered as one of the most efficient technique, and it can be exploited for the 5G wireless networks as well. In this paper, extensive experiments are carried out for capacity gain of CC over DC in a lab environment. Experimental performance analysis shows that CC significantly improves the performance of the system than DC. Experimental analysis also shows that the increase in the transmit antenna gain results in improving the SNR at receiver. High SNR provides more channel capacity by using higher order PSK modulation. The performance of CC significantly increases the system reliability and the channel capacity of the system with and without obstacle environment. It is also analyzed that channel capacity increases by placing the relay at center between source and destination. To alleviate the spectrum scarcity problem in 5G networks, traditional mobile data offloading schemes from Long-Term Evolution (LTE) to WLANs have been revised by the third-Generation Partnership Project (3 GPP) in release 13, which is known as LTE-WLAN Aggregation (LWA) [30]. [PERSON] et al.