LTE與WLAN聚合技術無線資源管理之研究

A Study on Radio Resource Management for LTE-WLAN Aggregation

施盈如(Ying-Ju Shih)

指導教授 ： 林一平

國立交通大學/資訊學院/資訊科學與工程研究所/博士(2019年)

摘要

因應行動資料傳輸量的劇增，非授權頻譜已被用來提供LTE服務之額外容量。LTE與WLAN聚合技術（LWA）結合了LTE與WLAN的無線資源，無疑是滿足巨量需求之完美解決方案。在LWA系統中，無線資源管理（RRM）層掌控LTE與WLAN之無線資源，並且分配資源給用戶設備（UE）以進行數據傳輸。為了充分利用LWA容量，RRM亦於數據傳輸期間，根據通道品質動態調整傳輸速率。本研究探討LTE與WLAN聚合之無線資源管理。

當LTE基地台利用LWA傳送資料時，可分為LWA切換與LWA分流兩種政策。當使用LWA切換政策時，封包僅能使用LTE或是Wi-Fi一種無線資源傳輸。在此機制中，網路需要能聰明的切換資料無線承載（DRB）使用LTE或是WLAN傳輸資料。在本論文中，我們首先設計與實作具有LWA功能之無線資源管理層（RRM），並提出了兩種LWA切換政策：保證頻寬與均分頻寬政策。我們測量LWA程序之延遲時間以及評估LWA切換政策的性能。我們的研究顯示LWA切換政策，能以可忽略的時間成本在無線資源管理層運作，並能有效降低資料無線承載的阻斷機率。LWA切換政策優美之處在於資料無線承載的阻斷機率不受其服務時間分佈影響。與LWA切換政策相反，LWA分流政策可同時使用LTE與WLAN無線資源來傳輸資料封包。在此機制中，決定LTE與WLAN之傳輸比例，並用以調節傳輸速率是很重要的。為了提供適當的WLAN傳輸頻寬，用戶設備會週期性地量測WLAN訊號品質並將結果回報給基地台，基地台再根據回報結果決定是否該調整傳輸速率。我們研究週期回報的性能，然後提出改良式的事件觸發回報機制以提高WLAN傳輸速率調節的性能。我們亦建議如何選擇適當的回報頻率以最小化週期回報所產生的網絡流量。我們的研究指出，改良式的事件觸發回報優於週期回報。我們的解決方案使用標準的3GPP協議而不需修改手機軟體。

關鍵字

長期演進技術 ； LTE和WLAN聚合技術 ； 無線資源管理層 ； 無線區域網路 ； 量測報告 ； 速率調節 ； 資料無線承載 ； LWA切換政策 ； 非授權頻譜 ； 無線網路技術

並列摘要

Mobile data traffic has been dramatically increased and unlicensed spectrum is utilized to open up additional capacity to support LTE service. LTE-WLAN aggregation (LWA) combines the radio resources of LTE and WLAN, which is a perfect solution that satisfies this need. The radio resource management (RRM) administrates LTE and WLAN radio resources in the LWA system and allocates resources to a User Equipment (UE) for data transfer. To fully explore LWA capacity, the RRM also dynamically adapts the transmission rate based on the channel quality during data transfer. In this dissertation, we investigate the radio resource management for LTE-WLAN aggregation.

Two types of policies can be exercised at the eNB (LTE base station) to transfer packets: the switched LWA policy and the split LWA policy. In the switched LWA policy, the packets are delivered through either LTE or Wi-Fi. In this mechanism, it is essential that the network should intelligently switch a Data Radio Bearer (DRB) to utilize either LTE or Wi-Fi. In this dissertation, we first implement the RRM layer for LWA and then propose two types of the switched LWA policies: the guaranteed bandwidth and the equal sharing policies. We measure the delay times of the LWA procedures and evaluates the performance of the switched LWA policies. Our study indicates that switched LWA can be implemented at the RRM with negligible overhead and effectively reduce the blocking probability of the LWA’s DRBs. The beauty of the LWA policies is that the DRBs’ blocking probability is not affected by the DRB holding time distribution. Contrary to the switched LWA policy, packets can be delivered through both radio resources in the split LWA policy. In this mechanism, it is important to determine the ratio of packets delivered by LTE over WLAN for transmission rate adaption. To provide appropriate WLAN transmission bandwidth, the UE periodically measures the WLAN quality and reports the results to the eNB. The eNB then decides if the transmission rate should be adapted. We investigate the performance of periodical reporting and then propose the enhanced event-triggered reporting to improve the performance of WLAN transmission rate adaption. We suggest how to select appropriate frequency to minimize the network traffic of periodical reporting. We also show that enhanced event-triggered reporting outperforms periodical reporting. Our solution utilizes the standard 3GPP protocols and does not modify the mobile phone’s software.

並列關鍵字

Long-Term Evolution (LTE) ； LTE-WLAN Aggregation (LWA) ； Radio Resource Management (RRM) ； Wireless Local Area Network (WLAN) ； Measurement Report ； Rate Adaption ； Data Radio Bearer (DRB) ； Switched LWA ； Unlicensed Spectrum ； Wi-Fi

參考文獻

[3GPP2016a] 3GPP. “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); User Equipment (UE) radio transmission and reception (Release 14)”, 3GPP TS 36.101, V14.1.0, Sep. 2016.

[3GPP2016b] 3GPP. “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; stage 2 (Release 13)”, 3GPP TS 36.300, V13.4.0, Jun. 2016.

[3GPP2016c] 3GPP. “Evolved Universal Terrestrial Radio Access (E-UTRA) and Wireless LAN (WLAN); Xw layer 1 (Release 13)”, 3GPP TS 36.461, V13.0.0, Mar. 2016.

[3GPP2016d] 3GPP. “Evolved Universal Terrestrial Radio Access (E-UTRA) and Wireless LAN (WLAN); Xw signaling transport (Release 13)”, 3GPP TS 36.462, V13.0.0, Mar. 2016.

[3GPP2016e] 3GPP. “Evolved Universal Terrestrial Radio Access (E-UTRA) and Wireless LAN (WLAN); Xw application protocol (Release 13)”, 3GPP TS 36.463, V13.0.0, Mar. 2016.