The introduction of Narrowband Internet of Things (NB-IoT) as a cellular (NB-IoT) technology aims to support massive Machine-Type Communications applications. These applications are characterized by massive connections from a large number of low-complexity and low-power devices. One of the goals of NB-IoT is to improve coverage extension beyond existing cellular technologies. In order to do that, NB-IoT introduces transmission repetitions and different bandwidth allocation configurations in uplink. These new transmission approaches yield many transmission options in uplink. In this paper, we propose analytical expressions that describe the influence of these new approaches in the transmission. Our analysis is based on the Shannon theorem. The transmission is studied in terms of the required Signal to Noise Ratio, bandwidth utilization, and energy per transmitted bit. Additionally, we propose an uplink link adaptation algorithm that contemplates these new transmission approaches. The conducted evaluation summarizes the influence of these approaches. Furthermore, we present the resulting uplink link adaptation from our proposed algorithm sweeping the device's coverage.
As a newly-developing technology, NB-IoT has still several issues to investigate. On the one hand, regarding NB-IoT performance, the authors of @cite_0 evaluate the coverage performance of NB-IoT. In @cite_8 , the authors also included results of capacity for a small rural area with real operator-deployed base stations. Nevertheless, these works and other similar provide final results for specific configurations that hinder the comparison of the results. Particularly, the authors of @cite_6 derive and simulate an analytical bound for the SNR gain from repetitions. On the other hand, the extensive use of repetitions in NB-IoT adds a new dimension for link adaptation that traditional LTE mechanisms do not consider. The works @cite_7 and @cite_4 examine this topic. The former proposed a downlink link adaptation algorithm. The latter investigated dynamic uplink link adaptation. However, neither of them examine analytically the impact of the repetitions. Additionally, the uplink link adaptation proposed in @cite_4 do not contemplate the bandwidth reduction as a new dimension in uplink link adaptation.
@cite_4 @cite_7 @cite_8 @cite_6 @cite_0
2586903650 2461492330 2007221528 2963793432
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. Coverage enhancement and low complexity are quite important aspects to support and broaden the application of machine type communication (MTC) in long term evolution (LTE). Repeating the same data across multiple subframes is widely considered as basic solution to improve the coverage. Low complexity target is mainly achieved by reducing the supported bandwidth and restricting the data processing size. Repetitions can be regarded as a new dimension of link adaptation besides the modulation and coding scheme (MCS) selection and the low complexity features are new factors impacting the link adaption as well. However, existing link adaptation mechanism in LTE system is unable to support such two-dimension link adaptation. Straightforward method suffers serious spectral efficiency loss and more power consumption and there is little other research on this issue, either. To save power and improve the spectral efficiency when performing the link adaptation for MTC, a smart method of coordinating the MCS selection and the repetition level determination with the consideration of new low complexity features is proposed in this paper. Extensive link level simulations are carried out to verify the effectiveness of proposed method. Simulation results show that proposed method could improve the spectral efficiency by around 42.1 and reduce the power consumption by around 36.8 Dynamic downlink and uplink resource adaptation in TDD (Time Domain Duplex) systems by flexibly changing the ratio of time slots for downlink and uplink transmissions is studied under Heterogonous Network (HetNet) scenarios. The time-scale of the resource adaptation and the interference management between downlink and uplink transmissions from different cells are important factors in determining the achievable level of resource efficiency, user experience and energy saving in TDD systems. In this paper, we apply the dynamic downlink and uplink resource adaptation in multi-cell macro-pico scenarios with co-channel interference. The performance is evaluated in system level for LTE-Advanced TDD configurations. Reconfiguration rates of 10 msec and 640 msec are considered as the time-scale of the dynamic resource adaptation. In addition, the time domain inter-cell interference coordination between the macro cells and the pico cells is applied for handling the high level of interference from macro cells to pico cells in the downlink multi-cell dynamic simulations. Using stochastic geometry, we develop a tractable uplink modeling paradigm for outage probability and spectral efficiency in both single and multi-tier cellular wireless networks. The analysis accounts for per user equipment (UE) power control as well as the maximum power limitations for UEs. More specifically, for interference mitigation and robust uplink communication, each UE is required to control its transmit power such that the average received signal power at its serving base station (BS) is equal to a certain threshold ρ o . Due to the limited transmit power, the UEs employ a truncated channel inversion power control policy with a cutoff threshold of ρ o . We show that there exists a transfer point in the uplink system performance that depends on the following tuple: BS intensity λ, maximum transmit power of UEs P u , and ρ o . That is, when P u is a tight operational constraint with respect to (w.r.t.) λ and ρ o , the uplink outage probability and spectral efficiency highly depend on the values of λ and ρ o . In this case, there exists an optimal cutoff threshold ρ o *, which depends on the system parameters, that minimizes the outage probability. On the other hand, when P u is not a binding operational constraint w.r.t. λ and ρ o , the uplink outage probability and spectral efficiency become independent of λ and ρ o . We obtain approximate yet accurate simple expressions for outage probability and spectral efficiency, which reduce to closed forms in some special cases.