臺灣博碩士論文加值系統

摘 要


本文係以系統模擬方式探討一類似GSM的蜂巢網TDMA系統在無線電通
道下之效能，其中特別針對GSM系統中之跳頻(Frequency Hopping)、功率
調控(Power control)、語音偵測(Voice Activity Detection)、不連續
發射(Discontinuous Transmission)、細胞分割(Sectorization)等技術，以及不完美之功率調控與細胞分割對系統效能的影響。模擬時，我們以平均訊號干擾比(Signal to Interference Ratio, SIR)和斷話率(Outagerate)評估系統效能及其運作的最小細胞群集。
當以斷話率<2%為評估標準時，傳統TDMA系統只有在細胞群集大於7時
才能符合要求標準。當TDMA系統應用了跳頻、功率調控、語音偵測及不連
續發射等技術後，因系統效能的改善，使得系統能夠在較小的細胞群集運
作。在完美功率調控下，系統在語音活動率為3/8時，符合要求標準的最
小細胞群集為4。在不完美功率調控下，若調控誤差的標準差小於1dB，系
統效能無明顯降低；而當標準差大於2dB，則最小細胞群集提高為7。

當TDMA系統再配合3等份細胞分割後，在完美功率調控下，系統在語
音活動率為3/8時，符合要求標準的最小細胞群集可降低為3；當調控誤差
的標準差為2dB，最小細胞群集提高為4；而當標準差為3dB，則最小細胞
群集提高為7。當系統再配合6等份細胞分割後，則既使在調控誤差的標準
差大於2dB的狀況下，最小細胞群集亦可達到3。對於不完美的細胞分割，
由模擬結果發現，其分割效率比完美細胞分割時至多減少8%，這結果對
TDMA系統效能的影響不大。

當以GSM之最小要求平均SIR=9dB做為評估標準時，則系統比以斷話率
<2%容易達到所要求之標準。根據模擬的結果顯示，當調控誤差=0及其標
準差為1、2及3dB時，系統要符合斷話率<2%的最小平均SIR值分別為13.8
、14.3、14.9及16.3dB。因此，GSM所訂定之9dB平均SIR要求略嫌過低。
同時我們也發現，功率調控誤差的標準差最好控制在2dB以內，否則應用
功率調控反而會造成負面的影響。

ABSTRACT


The performance of the GSM-like time division multiple access
(TDMA) systems is simulated over a radio channel, where the
performance improvement due to the application of frequency
hopping, power control, voice activity detection (VAD),
discontinuous transmission (DTX), and sectorization techniques
is investigated. Both outage rate and average signal-to-
interference ratio (SIR) are used to evaluate system performance
in our simulation. Imperfect sectorization due to the
overlapping of two adjacent base station (BS) antenna patterns
and imperfect power control are also considered.

When the system performance is required to have an outage rate
<2%, a conventional TDMA system without those GSM techniques can
only operate at a cluster size above 7. By incorporating
frequency hopping, power control, VAD and DTX into TDMA systems,
the operable cluster size is reduced due to the improvement in
system performance. When power control is perfect, the minimal
operable cluster size for a VAF of 3/8 is 4. When power control
is imperfect and the power control error has a standard
deviation less than 1 dB, the degradation in system performance
is not significant; while for a standard deviation greater than
2dB, the minimal operable cluster size becomes 7 .

When 3-sectors cells are introduced, and if power control is
perfect, the minimal operable cluster size for a VAF of 3/8 is
reduced to 3. For a 2dB standard deviation of the power control
error, the minimal operable cluster size becomes 4, while the
minimal operable cluster size increases to 7 for a standard
deviation of 3 dB. When 6-sector cells are introduced, the
minimal operable cluster size can be reduced to 3, even for a
standard deviation above 2 dB. Due to imperfect sectorization,
The performance degradation is less than 8%, which has no
significant effect on system performance.

Compared to the requirement of an outage rate less than 2%,
the requirement of a minimal average SIR of 9dB is easier to be
achieved. From our simulations, we find that the average SIR
required to ensure a system outage rate<2% is 13.8dB for
perfect power control situation, while for power control errors
having standard deviation of 1, 2 and 3dB, the average SIR is
14.3, 14.9 and 16.3 dB, respectively. In addition, we also
observe that the standard deviation of power control errors
should be maintained to be within 2 dB, so that the application
of power control is able to provide positive effect on system
performance.

目 錄


誌謝………………………………………………………………......ii
摘要…………………………………….……………..………………….iii
ABSTRACT…………………………………………..…………..………v
目錄……………………………………………………………………..vii
表錄………………………………………………………..….………….ix
圖錄……………………………………………………………...………..x
1. 緒論…………………………………………………………………....1
1.1.研究動機與目的………………………………………………….1
1.2.文獻回顧…………………………………………………………2
1.3.研究方法…………………………………………………………3
1.4.內容大綱…………………………………………………………4
2. 蜂巢網行動無線通訊的概說…………………………………………5
2.1.蜂巢網的概念…………………………………………………….5
2.2.蜂巢網無線通訊系統之組織架構……………………………….9
2.3.無線通道……………………………..…………………………11
2.4.多重接取的方法…………………………………………..……15
2.5.TDMA系統組成……..…………………………………………19
3. 現代TDMA系統之效能分析……………………………………….21
3.1.傳統的TDMA系統………………………..……………………21
3.2.跳頻配合功率調控對TDMA之效能影響……………………..24
3.3.語音偵測與不連續發射對TDMA之效能影響………………..27
3.4.細胞分割對TDMA之效能影響……………………………….29
4. 系統模擬與結果討論………………………………..………………36
4.1.傳統TDMA……………………………………………………..38
4.2.跳頻配合功率調控對TDMA之效能模擬……………..………47
4.3.語音偵測和不連續發射對TDMA之效能模擬………..………50
4.4.細胞分割對TDMA之效能模擬………………………………..53
4.5.完美功率調控下的綜合效能…………………………………..58
4.6.不完美功率調控下的綜合效能…...…………………………..61
4.7.整體效能評估………………………………..………………….64
4.7.1.傳統TDMA之效能評估………………………………….64
4.7.2.系統在完美與不完美功率調控下之效能評估…………..64
5. 結論……………………………………………..……………………70
參考文獻…………………………………………………..…………….72
自傳……………………………………………………..……………….75

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