Furthermore, we got involved in link adaptation and especially the uplink link adaptation scheme for NB-IOT systems. We investigate the uplink adjustment scheme with the repetition number determination, which consists of the adjustment of the inner loop link to ensure transmission reliability and improve the throughput of NB-IOT systems.
Narrowband internet of things
- Introduction in NB-IOT
- NB-IOT transmission schemes
- Downlink transmission scheme
- Uplink transmission scheme
- Deployment
- Physical channels
- Downlink channels
- Uplink channels
- NB-IOT objectives
- Coverage
- Capacity
- Device complexity
- Throughputs
- Long range and long battery life
- IoT applications
- Smart cities
- Transport and logistics
- Localization
- Smart metering
- Farming and forestry
- Comparison with other IoT technologies
- Comparison between NB-IOT and LoRa
In the in-band operation, the allocation of resources between LTE and NB-IOT is not fixed. The following table describes the NB-IOT physical signals and channels and their relationship with LTE counterparts. NB-IOT also supports massive IoT capacity by using only one PRB in both uplink and downlink.
NB-IOT uses two primary RRC protocol modes: RRC_idle and RRC connected as LTE.
SCHEDULINK AND LINK ADAPTATION
Scheduling in LTE and NB-IOT
- Basics of Scheduling in LTE
- Factors that affects scheduling
- Scheduling characteristics
- Types of Schedulers
- LTE Services and Scheduling Mechanism
- Uplink scheduling
- Downlink scheduling
- Scheduling in NB-IOT
- NB-IOT scheduler
Rate control: It is responsible for allocating resources between the radio carriers of the same UE, which are available on the eNB for DL and on the UE for UL. Some or all of these characteristics determine what types of packet schedulers are required on the LTE MAC to adhere to the required QoS requirements of the respective applications. All services can be scheduled using dynamic scheduling, but at the expense of control signaling [using PDCCH - scarce resource].
Semi-Persistent Scheduling: It is a hybrid mode of scheduling which tries to overcome the drawbacks of Dynamic Scheduling and Persistent Scheduling. OFDMA is one of the key access technologies in 4G wireless systems due to its high degree of flexibility in resource allocation, scalability, simple equalization, and strong anti-frequency selective fading characteristics. The role of RRM is to ensure that radio resources are used efficiently, taking advantage of available adaptation techniques to serve users according to their QoS attributes.
One of the key elements of the network is the ability to control and prioritize bandwidth across UEs. NPDCCH is considered the core element of the downlink control channels as it carries DCI. The resource allocation must be in a specific format taking into account reserved signaling resources and capabilities of the UE.
Introduction to link adaptation
- Literature review of Link Adaptation
- Link adaptation in LTE
- Downlink transmission
- Uplink transmission
Link adaptation was first proposed in 1997 by Sampath, Sarath Kumar, Holtzman, in which an analytical model of outer loop power control was studied to handle signal-to-interference ratio (SIR) fluctuations. Xia (2009) proposed an Auto-Rate Fallback for High-Throughput (ARFHT) algorithm for emerging IEEE 802.11n high-throughput wireless networks, which extends the legacy link adaptation algorithms for single-input-single-output (SISO) wireless networks. v 802.11n wireless networks based on multiple input multiple output (MIMO). Cavalcante (2016) provided a system-level analysis of OLLA for IEEE 802.16e systems in the paper “On System-Level Analysis of Outer Loop Link Adaptation for IEEE 802.16e Systems”.
Link adaptation in LTE systems dynamically adjusts the data rate of transmitted information (modulation scheme and channel code rate) to equalize the existing radio channel capacity allocated for each user. Link adaptation is therefore closely related to the channel coding scheme project used for forward error (FEC). LTE specifications are designed to provide the necessary indicators of interoperability between the eNodeB and the UE, enabling the eNodeB to optimize link adaptation.
For LTE uplink transmission, the link adaptation process is similar to the downlink adaptation process, again with the eNodeB handling the selection of modulation and coding schemes (MCS). The main difference between uplink and downlink is that, instead of basing link adaptation on CQI feedback, the eNodeB can make its own estimate of the uplink data rate that the ringing channel can handle, e.g., using sound reference signals (SRS). A final important aspect of link adaptation is its use for multi-user time and frequency scheduling, which allows radio transmission resources to be efficiently shared between users (since the channel capacity for individual users changes).
SIMULATION IN UPLINK ADAPTATION
Uplink adaptation simulation
The uplink connection adjustment scheme includes the inner loop connection adjustment and the outer loop connection adjustment. In particular, the inner loop connection adjustment is designed to deal with variations in the block error ratio by periodically adjusting the iteration count. The outer loop connection adjustment coordinates the MCS level selection and repeat number determination.
Parameter Settings and Metrics
Simulation Results
When the frequency is 3.75kHz due to the problem of the toolbox in the demodulation system, we only do the simulation for NPUSCH encoding and decoding. The experimental procedure also showed that the power of each cell can transmit a symbol by utilizing the power of the NPUSCH channel, as reported in the paper. Finally, the results show that BLER disappears as the receive SNR increases (i.e., the channel condition is better).
Furthermore, from the results we can observe when we receive ACK/NACK for a specific MCS level, RU and repeat settings. In the following diagrams, (fiq1-fiq2) we use the parameters as they appear in the table below. The diagrams of T throughput are given in Figure 3 and Figure 4 for each of the two series of simulations.
Furthermore, the graph below (Figure 5) shows a number of simulations for all repetition numbers and for all SNR for each of the four desired network settings. The results show that when we use a larger number of repetitions, we can correctly decode the message with worse channel conditions. Moreover, it can be observed that a message with worse channel conditions can be successfully transmitted if we use a larger number of railway operators.
Code in matlab
Get the slot grid and number of slots per frame if strcpi(ue.NBULSubcarrierSpacing,'15kHz') slotGridSize = [12, 7];. Calculate the frame number and slot number within the frame ue.NFrame = fix(slotIdx/NSlotsPerFrame);. Set the RV used for the current transport block chs.RV = rvSeq(mod(blockIdx,size(rvSeq,2))+1);.
Open issues and further work
Open issues
- Performance analysis
- Scheduling issue
- Link adaptation
- Co-existence with other technologies
- Security
With a large number of UEs and a fixed number of available subcarriers to be allocated, resources are not guaranteed even with successful random access procedures. Link customization has several problems, for example, the resource allocation must be in a special format taking into account the reserved signaling resources and NB-IOT UE capabilities. Since the design of NB-IOT is based on existing LTE functionalities, it is possible to use the existing infrastructure for cities with newer equipment only by upgrading the software.
However, older equipment may not be able to support LTE and NBIOT at the same time and may require a hardware upgrade. Furthermore, regarding coexistence with other technologies in some sectors of smart grids, a significant research effort is still needed to make it feasible. Some protocols such as Wi-Fi, ZigBee or Bluetooth require the use of a gateway, and many LPWA technologies (Telesna, Sigfox) require a new network to connect to the Internet of Things, the market adoption of NB-IOT may be lower.
In addition, many devices in use in the Smart Grid need to be upgraded, which requires a tremendous amount of work. NB-IOT will generate data traffic with patterns that are expected to be significantly different from those observed in the current Internet. Security issues such as Authentication, data integrity and privacy supported by NB-IOT technology were not discussed in most cases.
Further work
- Resource allocation
- Interference Mitigation
- Mobility Management
- Latency
- Battery and range performance
- Timing Advance
Most simulation work has ignored the mobility impact of NB-IOT channel modeling. The increase in mobility of NB-IOT UEs causes the channel to suffer from rapidly varying channel conditions, which may require adaptive transmission schemes that include channel estimation, error correction, etc. Early data transmission schemes and the second NB-IOT HARQ process for devices that have good channel conditions are among the features that can be used to reduce transmission latency and improve transmission link performance.
However, only a handful of research articles have discussed the effectiveness of these processes when applied to NB-IOT. PSM and eDRx were introduced in NB-IOT Release 12 and 13 to extend the battery life of NB-IOT devices. When the base station responds to the NB-IOT UEs regarding the RRC connection request, it includes the TA command to be used for the NB-IOT UE terminal data connection transmission time (i.e., to synchronize time the UEs with the base station and to help compensate for propagation delays).
However, for the NB-IOT UE, the accuracy of the TA adjustment of the signaled time advance with respect to the previous uplink transmission can be greatly affected by the huge number of NB-IOT devices competing for access. This is because the base station may need to correct the UE for some time, while other NB-IOT UEs that have already sent NPRACH might receive a random access response that is not intended for them. Some works have considered receiver algorithms for NPRACH TA estimation as well as detection time pre-adjustment decoding schemes to improve the estimation, but the sensitivity of the NB-IOT receiver and the poor quality of the channel estimate still negatively affect the TA adjustment.
Conclusion
Eric Wang, Xingqin Lin, Ansuman Adhikary, Asbjorn Grovlen, Yutao Sui, Yufei Blankenship, Johan Bergman, Hazhir S. Uplink Scheduling and Link Adaptation for Narrowband Internet of Things Systems, Changsheng Yu, Li Yu, Yuan Wu, Yanfei He, Qun Lu , IEEE Access (Volume: 5), 2017. Evaluation, Modeling and Optimization of Coverage Enhancement Methods of NB-IOT, Sahithya Ravi, Pouria Zand, Mohieddine El Soussi and Majid Nabi Holst, Center / IMEC-NL, Eindhoven, The Netherlands, Electrical Engineering Department, Eindhoven University of Technology, February 2019.
Research on NB-IOT Downlink Scheduling: Issues and Possible Solutions, Rubbens Boisguene, Sheng-Chia Tseng, 13th International Conference on Wireless Communications and Mobile Computing (IWCMC), 2017. Uplink Resource Allocation for Narrowband Internet of Things (NB-IoT ) Cellular Networks, Ya-Ju Yu and Jhih-Kai Wang, APSIPA Annual Summit and Conference, 2018. Narrowband Internet of Things (NB-IOT): From a Physical (PHY) and Media Access Control (MAC) Layer Perspective, Collins Burton.