NPRACH-Aware Link Adaptation and Uplink Resource Allocation in NB-IoT Cellular Networks

Abstract : In narrowband Internet of Things (NB-IoT), a link adaptation technique can be performed, considering multiple resource unit types, repetition numbers, and modulation-coding schemes, to enhance transmission reliability. Then, a base station should allocate downlink and uplink resources for each device using the link adaptation decision to transmit data in NB-IoT frame structures. However, because narrowband physical random access channels (NPRACHs) will occupy the partial uplink radio resource, the uplink transmission of a device using the assigned uplink radio resource without considering NPRACHs will cause severe interference. To solve the above issue, this article investigates the joint link adaptation and uplink resource allocation problem with the consideration of NPRACHs. The objective is to minimize the consumption of radio resources while the uplink data requirement of each device can be satisfied. We prove our target problem is NP -hard and cannot be approximated with a ratio better than 3/2 . Then, we propose a dynamic-programming algorithm without considering NPRACHs for the link adaptation problem and finally propose an uplink resource allocation algorithm considering NPRACHs based on the dynamic-programming algorithm. We prove that the proposed dynamic-programming algorithm with pseudo-polynomial time can find an optimal solution for the link adaptation problem. Compared with two previous algorithms, the simulation results show the efficacy of the proposed algorithm.

 EXISTING SYSTEM :

 ? These design changes earn IoT requirements while ensuring best co-existence performance with the existing LTE system. ? It is expected that the time required for developing NB-IOT products will be positively reduced for existing LTE equipment and software vendors. ? NB-IOT design is based on existing LTE functionalities, it is possible to use existing infrastructure for sites with newer equipment, only with software upgrade. ? However, it is still challenging to incorporate the NB-IOT features such as repetition, low complexity (which affects channel estimation quality), and mobility in deploying the already existing LTE interference management techniques.

 DISADVANTAGE :

 ? The problem is combinatorial due to the binary variables which can be converted to a convex problem using the well-known time-sharing property. ? The rate maximization problems are well-known and they are non-convex due to the presence of a binary assignment variable and an interference term in the denominator. ? The scope of this article is further extended to provide a novel approach for some of the issues of RRM design (i.e., inter-cell interference and asymmetric traffic between downlink and uplink) using recently introduced solutions as cooperative interference prediction (CIP) and flexible duplexing techniques. ? In order to address this issue, in, the authors proposed a resource muting approach within the flexible duplexing framework.

 PROPOSED SYSTEM :

 • They proposed an enhanced OLLA (eOLLA) scheme to adaptively modify the step size and to update the offset according to the reception conditions. • Therefore, optimal resource use techniques must be proposed that incorporate repetition, mobility, tones allocation, etc. for efficient spectrum usage. • Most of the proposed algorithms are power hungry because most of the power is consumed during transmission and reception. • The purpose of inner loop link adaptation is to guarantee the transmission BLER to the target. • The Repetition is the key solution adopted by NB-IOT to achieve enhanced coverage with low complexity.

 ADVANTAGE :

 ? It is of utmost importance to evaluate the performance of NB-IoT in HetNets and to devise novel solutions for ICI mitigation, as traditional solutions might not be well suited to NB-IoT due to its limited bandwidth availability. ? However, this raises serious concerns about the performance of the technology due to severe interference from multi-tier 5G heterogeneous networks (HetNets). ? However, the performance evaluation is conducted in a single-cell scenario and the effect of ICI, retransmission, and control channel overhead have not been considered. ? Retransmissions improve undoubtedly the packet reception reliability but at the cost of increased latency, reduced spectrum efficiency and battery life, due to overhead and redundancy.