窄頻物聯網是由第三代合作夥伴(The Third Generation Partnership Project, 3GPP)於版本 13 中所訂定的一種基於長期演進技術標準(Long Term Evolution, LTE)的蜂巢式物聯網技術。窄頻物聯網通常應用於低吞吐量且低移動性的情況，例如偶爾傳送小數據封包的感測器網路。為了提高用戶設備端的性能，3GPP 在版本 15 中提出一機制稱作資料提前傳輸 (Early Data Transmission, EDT)。當上行數據大小小於或等於資料傳輸塊 (Transport Block Size, TBS)時，用戶設備可以啟用EDT機制，並在隨機存取過程中提前完成上行數據的傳輸。反之，當上行數據大小大於TBS時， 用戶設備會以原本的方式進行資料傳輸(non-EDT)。因此，在大量用戶設備連接的情況下，資料傳輸的延遲與連接時的碰撞會分別成為EDT 與non-EDT機制的代價。考慮到分別以EDT及non-EDT機制進行傳輸資料的用戶設備數量之間的權衡，我們根據不同的網路設置條件情況提出最佳化的TBS，網路設置條件包含最大封包長度、總用戶設備數量及隨機存取通道的子載波數量。本研究依據分析所估計出的效能指標，並使用窮舉法為每個給定的配置條件找到最佳化的TBS。且透過模擬結果驗證分析結果的正確性，由其數值結果所得的最佳化TBS可以最大化總成功傳輸數據的用戶設備數目及最小化平均資料傳輸延遲。

Narrowband Internet of Things (NB-IoT) is a cellular IoT technology based on Long Term Evolution (LTE), and introduced by 3GPP (The Third Generation Partnership Project) in Release 13. The use cases of NB-IoT are usually for the low throughput with low mobility, such as sensor network which have infrequent small data packet transmissions. To improve the performance of sensor-like user equipment (UE), 3GPP introduced a mechanism named Early Data Transmission (EDT) in Release 15. UE can enable the EDT procedure when the uplink data size less than or equal to Transport Block Size (TBS), and complete the data transmission during the random-access procedure without the transition to connected mode. Otherwise, UE would transmit the data by following the conventional (non-EDT) procedure when the uplink data size larger than TBS. Therefore, under the massive connections, the collision and data delay would be the price for the EDT and non-EDT procedure, respectively. Taking into account the tradeoff between the number of EDT UE and non-EDT UE, we propose the optimal TBS depending on the various network conditions, including the maximum packet length, number of contention UE and the number of subcarriers in random access channels. Based on the performance estimation of NB-IoT system supported EDT mechanism, we used the exhaustive search method to find the optimal TBS for each configuration setting. The accuracy of the analysis is verified by computer simulations and the numerical results show that the proposed optimal TBS is able to maximize the total number of successfully accessing UE or minimize the average total data delay.

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