You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Multimedia Internet of Things: A Comprehensive Survey 
Chapter Title:  D. NARROW-BAND IoT 
1. Abstract of Cited Paper (BIB001):  Narrowband Internet of Things (NB-IoT) is a new narrow-band radio technology introduced in the Third Generation Partnership Project release 13 to the 5th generation evolution for providing low-power wide-area IoT. In NB-IoT systems, repeating transmission data or control signals has been considered as a promising approach for enhancing coverage. Considering the new feature of repetition, link adaptation for NB-IoT systems needs to be performed in 2-D, i.e., the modulation and coding scheme (MCS) and the repetition number. Therefore, existing link adaptation schemes without consideration of the repetition number are no longer applicable. In this paper, a novel uplink link adaptation scheme with the repetition number determination is proposed, which is composed of the inner loop link adaptation and the outer loop link adaptation, to guarantee transmission reliability and improve throughput of NB-IoT systems. In particular, the inner loop link adaptation is designed to cope with block error ratio variation by periodically adjusting the repetition number. The outer loop link adaptation coordinates the MCS level selection and the repetition number determination. Besides, key technologies of uplink scheduling, such as power control and transmission gap, are analyzed, and a simple single-tone scheduling scheme is proposed. Link-level simulations are performed to validate the performance of the proposed uplink link adaptation scheme. The results show that our proposed uplink link adaptation scheme for NB-IoT systems outperforms the repetition-dominated method and the straightforward method, particularly for good channel conditions and larger packet sizes. Specifically, it can save more than 14% of the active time and resource consumption compared with the repetition-dominated method and save more than 46% of the active time and resource consumption compared with the straightforward method. 
2. Abstract of Cited Paper (BIB002):  Narrowband-Internet of Things (NB-IoT) has been released by 3GPP to provide extended coverage and low energy consumption for low-cost machine-type devices. Requiring only a reasonably low-cost hardware update to the already deployed long term evolution base stations and being compatible with current core network and enhanced core solutions that aim to reduce the battery consumption and minimize the signaling, NB-IoT deployments are quickly increasing, making NB-IoT a dominating technology for low-power wide area networks. To this aim, in this paper, we focus on group communications (i.e., multicast) in NB-IoT to efficiently support the transmission of firmware, software, task updates, or commands toward a large set of devices. We discuss the architectural and procedural enhancements needed to support the unique features of group communications in machine-type environments, such as customer-driven group formation. We also extend the NB-IoT frame to include a channel for multicast transmissions. Finally, we propose two transmission strategies for multicast content delivery and evaluate their performance considering the impact on the downlink background traffic and the channel occupancy. 
3. Abstract of Cited Paper (BIB003):  Narrowband Internet of Things (NB-IoT) is a new cellular technology introduced by the third generation partnership (3GPP) providing low-power and wide-area coverage for IoT. In this paper, we consider the scenario that NB-IoT is deployed in an heterogeneous network and the quality of the direct link from the NB-IoT user equipment (UE) to the serving base station (BS) cannot satisfy the quality of service requirement for transmission of vital sensing data. Thereupon, device-to-device (D2D) communication is adopted as a routing extension to NB-IoT systems, and thus, enables two-hop routes between NB-IoT UE and the serving BS via a set of D2D relays. As the candidate UE relays work in duty cycle to save energy, we derive a model to select a set of UE relays and perform opportunistic D2D communication according to a working schedule. Two optimization problems are formulated aiming at achieving optimal expected delivery ratio (EDR) and expected two-hop delay, respectively. Dynamic programming-based algorithms are proposed to solve the optimization problems and obtain the optimal working schedule of the relays. Simulation results demonstrate that our proposed maxEDR and minEED algorithms improves the system performance compared with other state-of-the-art algorithms.

Literature Review:
NB-IoT is one of the Low Power Wide Area (LPWA) technologies released by the 3 rd Generation Partnership (3GPP). It is designed for heterogeneous IoT devices to achieve improved spectrum efficiency, extended, and in-depth coverage. The key feature of NB-IoT is that it can be directly deployed in the Global System for Mobile communication (GSM) or LTE spectrum BIB001 . However, the NB-IoT device has to continuously monitor the data transmission channel for service announcements and updates that waste energy resources. Tsoukaneri et al. BIB003 present an NB-IoT communication approach that dynamically creates a group of devices that are subscribed to receive multimedia services in a multicast transmission. To enhance the coverage area, the repetition of control and data transmission signals has been considered. The Adaptive Coding and Modulation (ACM) scheme and repetition numbers are in need of link adaption for NB-IoT systems. However, traditional link adaption techniques without repetition numbers are not applicable to NB-IoT systems. Yu et al. BIB002 proposed an inner loop and outer loop link adaption that copes with block error ratio and coordination between ACM and repetition numbers. The direct communication link between user and BS usually does not satisfy QoS for transmitting vital data. Li et al. BIB004 exploit D2D communication as an opportunistic communication with improved link quality to upload critical data to BS. The proposed optimization aims to improve end-to-end delay and packet delivery ratio. NB-IoT is an emerging technology that yet needs to be explored in-depth for deployment.