某些時間靈敏的系統需要即時地將同一份資料送給所有的使用者。在此系統中，無線基地台首先會收到一個資料片段，隨後適當地將其分割為數個封包並以無線的方式傳送給覆蓋範圍內的使用者。所有使用者皆收齊該資料片段的時間稱為系統停止時間。本文即提出透過傳輸率排程及編碼的結合來減少此系統的停止時間，提升系統的效能。
具體來說，考慮一個單跳時間槽式的無線網路，並假設每個時間槽的間格皆相同且基地台有使用者頻道及封包的完整資訊。延續先前研究[14]本文提出三個方案，分別為Direct Selection (DS),、Last Set (LS)及Re-Weighting (RW)。DS將權重機率挑選封包的方式改為直接選取最大權重封包的方式；LS希望更進一步地考慮進度最慢的使用者去決定基地台的傳輸率；而RW則是簡單地修改了封包權重在[14]的計算。實驗結果顯示DS和RW兩個方案穩定地改善了系統的停止時間，而LS只適用於某些環境。當中效率最穩定的方案是DS_RW，其在mean SNR 6dB且group size 2048的環境中可改善SP在[14]的系統結束時間約10%。

關鍵字:編碼、傳輸率排程、群播。

Some time-sensitive system is required to timely send the same information to all users.In the system, a wireless base station first receives a segment of the information stream, divides the segment into packets suitable for wireless transmission, and then distributes them to all users under its coverage area.The period of transmitting packets from a given stream segment to all users is called stopping time.This thesis proposes joint rate scheduling and coding scheme, aimed to shorten the stopping time and thus effectively increase system throughput.
Specifically, consider a single-hop discrete-time wireless system where each time unit is a time slot of equal length. Also assume that the base station has full channel state information and all states of packets received by each user. Developed from earlier work [14], this thesis presents three schemes called Direct Selection (DS), Last Set (LS) and Re-Weighting (RW), respectively. DS is to deterministically select packets for coding and transmission from a sequence of packets, in the candidate set, ordered according to some weighting function rather than to select them probabilistically. LS decides transmission rate by further involving the rate and receiving status of users in the last set which consists of users receiving the number of packets below some given threshold less than the largest number of packets received. RW is proposed simply through modifying the definition of packet weight in [14]. Simulation results show that DS and RW do improve the performance of stopping time, while LS does only under some specific setting of simulation environment. DS_RW, the most effective one, is able to reduce 10% of mean stopping time for multicast group size 2048 and mean SNR 6dB,compared to that performed by SP[14].

keyword:Coding, Rate scheduling, Multicast.

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