On the Efficiency of Distributed Source Coding in Random Access Sensor Networks

在隨機存取感測網路中使用分散式訊號源編碼的效能分析

林志勳(Chih-Hsin Lin)

指導教授 ： 洪樂文

國立清華大學/電機資訊學院/通訊工程研究所/碩士(2009年)

摘要

在本論文中，我們分析斯里篇-沃夫分散式訊源編碼(Slepian-Wolf distributed source coding) 在隨機存取無線感測網路(random access sensor networks)中所能達到的系統吞吐量(throughput)、延遲(delay)和能量消耗(energy consumption)。利用這個分析結果，我們進一步研究媒體存取控制協定的設計對於系統效能的影響。在無線感測網路中，感測器(sensor)之間所觀測到的訊息往往具有高度的相關性，因此若將原始資料直接傳至中央處理器(sink node)將造成許多傳輸資源的浪費。為了提高傳輸效率，我們採用斯里篇-沃夫分散式訊源編碼來消除存在於感測器間重複的資訊。在此編碼方式之下，感測器間會以某種相依的次序執行資料壓縮；其解碼，也必需依此次序來執行。換言之，中央處理器要解出某一感測器的資料，必需先解出所有次序較前面的感測器的資料。若有其中一個感測器的資料遭到遺失，可能會造成許多其他感測器的訊息無法順利的解出。因此，媒體存取控制協定的設計，需要考量這樣的特性，對於每個感測器給予不同的傳送優先權。基於分散式訊號源編碼的特色，我們在單躍式(single hop)的網路架構中，利用時槽式ALOHA (slotted ALOHA)隨機存取之通訊協定系統，提出分析工具來研究吞吐量、延遲以及能量消耗。運用這些工具，我們比較各種不同傳輸機率分配方式所能達到的效能，並且研究媒體存取控制的系統設計對於效能的影響。最後，我們進一步將這些觀念延伸到多躍式的網路架構，並且利用蒙特卡摩(Monte Carlo)的數值模擬去分析系統的吞吐量、延遲和能量消耗。

關鍵字

分散式訊號源編碼 ； 無線感測網路

並列摘要

In this work, we analyze the throughput, delay, and energy e±ciency of random access
sensor networks that employ Slepian-Wolf distributed source coding (DSC) and study the
impact of MAC protocol design on these performances. Suppose that N sensors observe
correlated information from the environment and that their local data are sent to a sink
node through direct transmission links. To eliminate data redundancy, we allow sensors to
encode their local messages using the Slepian-Wolf DSC method. We assume that sensors
are ordered sequentially and that each sensor's message is compressed by exploiting the joint
data statistics between itself and the sensors earlier in the sequence. Due to properties of
DSC, a message can be decoded only if all messages transmitted by sensors earlier in the
sequence are successfully decoded. The loss of one message may cause failure in decoding
many other messages. Hence, the sensors' messages are not of equal importance and should
be given di®erent transmission priorities by the MAC. Based on the properties of DSC,
we provide analytical tools to study the throughput, delay, and energy e±ciency of slotted
ALOHA random access protocols in a single hop network. Utilizing these tools, we compare
between the performance of di®erent transmission probability assignments and study the
impact of MAC protocol design on the performance of these systems. Furthermore, an
adaptive MAC protocol is also proposed to improve upon the throughput and delay of the
original system. The concepts and ideas are then extended to the multihop scenario and
veri¯ed through numerical studies.

並列關鍵字

distributed source coding ； wireless sensor networks

參考文獻

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