臺灣博碩士論文加值系統

本文係討論數位訊號在緩慢時變頻率選擇性多重路徑瑞雷(Rayleigh)衰
落通道下之序列檢測. 將考慮最大可能序列檢測配合為維特比演算法(
MLSE-VA)與時序序列檢測配合單一堆疊演算法. 研究結果顯示結合等化器
與多重接收(diversity)的系統架構較僅使用等化器的接收價架構的 效能
有顯著的優點存在.除了使用多重接收架構外,亦可藉由犧牲系統複雜度
且/或通道頻寬, 以獲致系統效能的改善.此外,效能改善的程度端視系統
複雜度,頻寬及訊雜比(SNR)來決定. 本文的主要目的在於研究如何在系統
效能,複雜度與頻寬利用上作取捨,茲將所獲致的結果摘 要如下: .以增加
系統頻寬的方式,可獲致較佳的系統效能且系統具有較低的複雜度.此外,
與未使用多 重接收架構的系統效能比較,使用多重接收架構的情形下,增
加頻寬所獲致效能上的改善則變 得較不明顯. .以幾乎相同的頻寬及複雜
度,可經由正確選擇波形因子濾波器,以獲致效能上的改善.一般而 言,較
小的波形因子可獲致較的佳的系統效能,然而改善卻相當有限.此外,較小
的波形因子常 造成較多的系統狀態,這使得最大可能序列檢測(MLSE)及時
序序列檢測(SSE)的接收機變得非 常複雜.不過有某些情形,在不增加系統
複雜度的前題下,亦可能獲致較佳的效能. .對於在頻率選擇性多重路徑瑞
雷衰落通道下之最大可能序列檢測,就效能改善而言,多重接 收的系統架
構是一種相當有效的技術. .天線多重接收架構常造成較佳的效能,但卻需
要兩套以上的微波(RF)設備.由於成本過高,並 不適用在實際的狀況;然而
對於某些無法使用天線多重接收架構的情況下,利用增加系統頻寬 ,可以
對改善系統效能產生互補的功效. .就系統效能而言,時序序列檢測配合單
一堆疊演算法(SSE-SSA)較最大可能序列檢測配合維 特比演算法(MLSE-
VA)有一些的衰減,模擬結果顯示僅存在小於1 dB的見衰減.

Sequence detection of digital signaling on the slowly time-
varying frequency-selective multipath fading channels is
investigated here. Two methods for sequence detection, namely,
maximum likelihood sequence estimation via Viterbi algorithm
(MLSE-VA) and sequential sequence estimation via single stack
algorithm(SSE-SSA) have been considered in this thesis. Joint
equalization and diversity reception technique is shown to have
significant advantage over employing equalization alone. In
addition to using diversity reception technique, the improvement
in perform-ance can be achieved at the sacrifica of increasing
the channel occupied bandwidth and/or the system complexity.
Furthermore, the amount of performance improvementis generally
associated with the imposed complexity, occupied bandwidth, and
the oper-ating signal to noise ratio (SNR). It is our main aim
to investigate the trade-offsbetween system performance, system
complexity, and bandwidth utilization. The obtainedresults of
this study are summarized as follows..With an increasing system
bandwidth, a better performance with lower system complexityis
obtained. In addition, for cases with diversity reception, the
performance improve-ment is less significant than ones without
diversity reception..With almost the same bandwidth and
complexity, the performance can be improved by properselection
of the shaping filter. In general, with a smaller roll-off
factor beta, a bettersystem performance is obtained. However,
the improvement is quite limited. In addition, a smaller roll-
off factor often results in a larger number of system states,
and then the MLSE and SSE receivers become much more
complicated. Nevertheless, in some cases, it ispossible to
obtain a better performance without increasing the system
complexity..Diversity reception is a pretty effective technique
for the performance improvement of maximum likelihood sequence
detection on frequency-selective multipath Rayleigh
fadingchannels..Antenna diversity reception often results in a
better performance, but requires twoor more sets of RF
equipments. Since it costs too much, it is unsuitable for the
practicalsituations. Instead, for the cases which can't apply
the antenna diversity reception, withan increasing occupied
bandwidth, there exists a complementary function to improve
thesystem performance..As far as system performacne is
concerned, SSE-SSA suffers a little degradation withrespect to
MLSE-VA. As shown, only less than 1 dB degradation for SSE-SSA.