在WiMAX網路上的快速交遞協定設計與分析

Abstract

本論文之目的是發展在WiMAX網路上無接縫快速交遞協定，以支援即時資料流及群播廣播(MBS)服務。IEEE 802.16e對即時資料流提供品質服務。然而在交遞過程中發生資料傳輸中斷仍是個待解決的重大課題，特別是在高速移動的行動裝置上所產生的頻繁交遞。因此，為提供即時資料流服務品質而設計一個可支援頻繁交遞及短暫服務中斷的交遞協定是必要的。在本論文中，我們提出一個符合IEEE 802.16e規範的新穎網路架構來支援無接縫的頻繁交遞，特別是支援高速移動的行動裝置。基於這個架構，我們提出一個在交遞過程中可以縮短服務中斷時間的網路輔助快速交遞 (NFHO)協定。透過解決連線識別碼(CIDs)分配及上傳鏈結(uplink - UL)時序調整問題，我們提出的NFHO協定可以在交遞進行到ranging前，即可重啟上傳(UL)和下載(DL)資料，此點為本協定獨特的特色。我們同時發展一個分析模型，來探討交遞過程中的緩衝封包數目期望值(expected number of buffered packets)，封包遺失率(packet loss probability)，及服務中斷時間(service disruption time)。效能評估結果顯示，相較於IEEE 802.16e的硬式交遞協定，NFHO協定可降低75% DL服務中斷時間。另相較於Jiao et al.及IEEE 802.16e硬式交遞協定(Choi et al. 亦同)，NFHO協定可分別降低55.6%及75%的UL服務中斷時間。 此外，為了提供群播廣播服務，WiMAX標準制定在WiMAX網路上的資料傳輸協調機制。然而在此協調機制裡的封包遺失回復程序會增加封包傳輸延遲(packet transmission latency)及增大封包緩衝池(packet buffer pool)需求。在本論文中，我們提出一個in-frame control (IFC)機制來降低封包錯誤率(packet error rate)及封包重傳數(packet retransmission count)，此等同於降低封包傳輸延遲及封包緩衝池需求。此外，為支援level-2 frame-offset協調機制，我們提出一個可對任兩相鄰群播廣播服務區(MBS zones)間提供資料連續性服務的動態群播廣播服務區架構。基於此架構，我們提出一個無接縫的動態跨兩個群播廣播服務區之間的交遞協定(DMZ HO)來解決交遞時資料不連續(封包遺失)的問題。針對所提出的IFC機制，我們發展一個分析模型來分析封包錯誤率及封包重傳數。另針對DMZ HO，我們透過分析通道占用時間(channel occupation time)來評估所需額外頻寬(bandwidth overhead)。效能評估結果顯示，相較於制定在WIMAX標準中的原始機制，IFC機制可分別降低49.8% (error clusters arrival rate, λ = 0.001 (/ms))及 49.73% (λ = 0.001 (/ms)) 的封包錯誤率及封包重傳數。除此之外，我們提出的DMZ HO機制，其效能勝過一個具有代表性的現有overlapping zone (OLZ)機制。相較於OLZ機制，當HO arrival rate為1 (/sec)時，DMZ HO機制可降低89.3%通道占用時間。 再則，我們提出的DMZ HO機制比OLZ機制消耗較少通道頻□。DMZ HO機制的通道閒置率(channel idle ratio)是89.3% (μ = 1, PDU-offset = 10) 遠大於同條件下的OLZ機制。

The goal of this dissertation is to develop seamless fast handover schemes for supporting real-time traffic and multicast broadcast service (MBS) in WiMAX networks. The IEEE 802.16e provides QoS for real-time traffic; however, packet transmission disrupted by the handover (HO) process is still a big concern, especially when frequent HO is performed by mobile stations (MSs) with high mobility. Therefore, an HO scheme that supports frequent HO and also provides short service disruption time is necessary for providing QoS to real-time traffic. In this dissertation, we present a novel network architecture, which complies with the IEEE 802.16e standard, to support seamless frequent HO, especially for MSs with high mobility. Based on this architecture, a network assisted fast handover (NFHO) scheme is proposed to shorten service disruption time during the HO process. By resolving CIDs (connection identifiers) assignment and uplink timing adjustment issues, the proposed NFHO scheme can restart both the uplink (UL) and downlink (DL) packet transmissions before the MS proceeds to the HO ranging, which is a unique feature of our scheme. An analytic model has been developed to investigate the expected number of buffered packets, packet loss probability, and service disruption time during HO. Performance evaluation results show that the NFHO scheme reduces the DL service disruption time by 75% compared to the IEEE 802.16e hard HO scheme, and it also reduces the UL service disruption time by 55.6% and 75% compared to Jiao et al. and the IEEE 802.16e hard HO scheme (Choi et al. as well), respectively. In addition, to support multicast broadcast service, the WiMAX standard defines a coordination mechanism to coordinate data transmission over the WiMAX network; however, the packet loss recovery procedures, which are parts of the coordination mechanism, enlarge the packet transmission latency and packet buffer pool requirement. In this dissertation, we propose an in-frame control (IFC) scheme to decrease the packet error rate and packet retransmission count, so as to reduce the packet transmission latency and packet buffer pool requirement. Furthermore, to support level-2 frame-offset coordination, we also propose a dynamic MBS zone (DMZ) framework that can provide data continuity between any two adjacent MBS zones. Based on the proposed DMZ framework, a seamless dynamic inter-MBS zone handover (called DMZ HO) scheme is proposed to resolve the data discontinuity (or packet loss) problem during inter-MBS zone HO. An analytic model has been developed to analyze the packet error rate and packet retransmission count for the proposed IFC scheme and the bandwidth overhead in terms of channel occupation time for the proposed DMZ HO. Performance evaluation results show that, compared to the original WiMAX scheme, defined in the WiMAX standard, the proposed IFC scheme reduces the packet error rate and packet retransmission count by 49.8% (error clusters arrival rate, λ = 0.001 (/ms)) and 49.73% (λ = 0.001 (/ms)), respectively. Moreover, the proposed DMZ HO scheme outperforms an existing overlapping zones (OLZ) scheme. It reduces channel occupation time by 89.3% compared to the OLZ scheme when the HO arrival rate, μ, is 1 (/sec). In addition, the proposed DMZ HO scheme consumes less channel bandwidth than the OLZ scheme. The channel idle ratio of the proposed DMZ HO scheme is 89.3% (μ = 1, PDU-offset = 10) larger than that of the OLZ scheme.