臺灣博碩士論文加值系統

以正交分頻多工為基礎的無線區域網路系統原本是使用在幾乎靜態的環境下。但在如今講求使用者方便為導向下，如果我們想要支援移動性，最重要的話題就是由物體速度引起的都普勒效應。我們以修正過後的無線區域網路 802.11a規格當模擬環境，探討都普勒效應、訊號雜訊和不準確的估測對於系統中位元錯誤率的影響。對此，我們提出一些模擬結果和結論。
當通道脈衝響應和最大都普勒頻移都已知時，在相同的多重路徑數目下，我們可以發現到幾個現象。第一、主要是可加式白色高斯雜訊影響位元錯誤率。第二、在相同的通道延遲擴展下，物體速度越高，位元錯誤率越高。第三、在相同的物體速度下，通道延遲擴展越長，位元錯誤率越高。當通道脈衝響應已知但最大都普勒頻移未知時，在相同的最大都普勒頻移率和相同的多重路徑數目下，物
體速度越低，位元錯誤率相對變動的少。當通道脈衝響應未知但最大都普勒頻移已知時，在和相同的多重路徑數目下，通道延遲擴展越長，位元錯誤率越高。

OFDM-based WLAN systems are originally used for nearly static environment. But in the trend of user-convenience, if we want to support mobility, the most important issue is the Doppler effect caused by the object velocity. We investigate how the Doppler effect, signal-to-noise ratio (SNR) and imperfect estimation of channel impulse response (CIR) and the maximum Doppler shift fd influence the final bit error rate (BER) under the simulation environment, modified WLAN 802.11a specification. For these effects, we give some simulation results and conclusions.
If CIR and df are known with the same number of multipath, we can see some phenomenon. First, the BER is dominated by AWGN noise. Second, under the same channel delay spread, the higher the object velocity is, the more serious the BER is. Third, under the same the object velocity, the more serious the BER is. If CIR is known instead of fd, under the same error percentage of fd and the same number of multipath, the lesser the velocity is the lesser the BER curve changes. If fd is known instead of CIR with the same number of multipath, the longer the channel delay
spread is, the more serious the BER is.

List of Tables
Table 1. Parameters of simulation................................................................................22
List of Figures
Fig. 2.1 (a) Spectra of non-overlapped multicarrier channel
(b) Spectra of overlapped multicarrier channel ............................................. 3
Fig. 2.2 Traditional OFDM (a) transmitter (b) receiver .............................................. 6
Fig. 2.3 OFDM overall system block diagram ............................................................ 8
Fig. 2.4 OFDM system TX .......................................................................................... 8
Fig. 2.5 OFDM system RX ......................................................................................... 9
Fig. 2.6 Spectra relationships between transmitted signals .........................................10
Fig. 2.7 OFDM symbols with CP ................................................................................11
Fig. 4.1 BPSK, QPSK, 16QAM and 64QAM constellation .......................................20
Fig. 5.1 Velocity = 3 km/hr, fd is known, channel delay spread = 200ns ..................23
Fig. 5.2 Velocity = 60 km/hr, fd is known, channel delay spread = 200ns ................23
Fig. 5.3 Velocity = 100 km/hr, fd is known, channel delay spread = 200ns ..............24
Fig. 5.4 Velocity = 200 km/hr, fd is known, channel delay spread = 200ns ..............24
Fig. 5.5 Velocity = 3 km/hr, fd is known, channel delay spread = 400ns ..................25
Fig. 5.6 Velocity = 60 km/hr, fd is known, channel delay spread = 400ns ................26
Fig. 5.7 Velocity = 100 km/hr, fd is known, channel delay spread = 400ns ..............26
Fig. 5.8 Velocity = 200 km/hr, fd is known, channel delay spread = 400ns ..............28
Fig. 5.9 Velocity = 3 km/hr, fd is inaccurate, channel delay spread = 200ns ............28
Fig. 5.10 Velocity = 60 km/hr, fd is inaccurate, channel delay spread = 200ns ........28
Fig. 5.11 Velocity = 100 km/hr, fd is inaccurate,, channel delay spread = 200ns ......29
Fig. 5.12 Velocity = 200 km/hr, fd is inaccurate, channel delay spread = 200ns ......29
Fig. 5.13 Velocity = 3 km/hr, fd is inaccurate, channel delay spread = 400ns ..........30
Fig. 5.14 Velocity = 60 km/hr, fd is inaccurate, channel delay spread = 400ns ........30
Fig. 5.15 Velocity = 100 km/hr, fd is inaccurate, channel delay spread = 400ns ......31
Fig. 5.16 Velocity = 200 km/hr, fd is inaccurate, channel delay spread = 400ns ......31
Fig. 5.17 CIR is inaccurately, fd is known, channel delay spread = 200ns ...............32
Fig. 5.18 CIR is inaccurately, fd is known, channel delay spread = 300ns ...............33

[1] Ove Edfors ; Magnus Sabdell ; Jan-Jaap van de Beek ; Daniel Landstrom Frank
Soberg, “An introduction to orthogonal frequency-dividion multiplexing,”
September, 1996
[2] RayerLee, “Overview of OFDM system”
[3] Richard van Nee; Ramjee Prasad, “OFDM Wireless Multimedia Communication,”
Artech House Boston London
[4] Ahmad R.S.Bahai ; Burton R. Saltzberg, ”Multi-carrier Digital Communications
Theory and Applications of OFDM,“ Kluwer Academic/Plenum Publishers
[5] Leonard J. ; Cimini,JR ; YE(GEOFFREY)LI, “Orthogonal Frequency Division
Multiplexing For wireless Channel,” AT&T LABS-Research Dissertation
[6] Ramjee Prasad, “OFDM Based Wireless Broadband Multimedia Communication,”
ISCOM’99 Nov 7-10 1999
[7] Nakamura, M.; Seki, T.; Itami, M.; Itoh, K.; Hamid Aghvami, A., “New estimation
and equalization approach for OFDM under Doppler-spread channel,” Personal,
Indoor and Mobile Radio Communications, 2002. The 13th IEEE International
Symposium on Volume 2, 15-18 Sept. 2002, Page(s):555 - 560 vol.2
[8] Xiaodong Cai; Giannakis, G.B., “Error probability minimizing pilots for OFDM
with M-PSK modulation over Rayleigh-fading channels,” Vehicular Technology,
IEEE Transactions on Volume 53, Issue 1, Jan. 2004 Page(s):146 - 155
[9] Coleri, S.; Ergen, M.; Puri, A.; Bahai, A., “Channel estimation techniques based
on pilot arrangement in OFDM systems,” Broadcasting, IEEE Transactions on
Volume 48, Issue 3, Sept. 2002 Page(s):223 - 229
[10] Heejung Yu; Myung-Soon Kim; Taehyun Jeori; Sok-kyu Lee, “Equalization
scheme for OFDM systems in long delay spread channels,” Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International
Symposium on Volume 2, 5-8 Sept. 2004, Page(s):1297 - 1301 Vol.2
[11] Kunaruttanapruk, S.; Jitapunkul, S., “The novel decision feedback equalizer for
OFDM system with insufficient cyclic prefix,” Communication Networks and
Services Research, 2004. Proceedings. Second Annual Conference on 19-21
May 2004, Page(s):19 - 24
[12] Sagae, Y.; Suyama, S.; Suzuki, H.; Fukawa, K., “An OFDM turbo equalizer for
scattered pilot signals in multipath environments with delay difference greater
than guard interval,” Vehicular Technology Conference, 2004. VTC 2004-Spring.
2004 IEEE 59th Volume 1, 17-19 May 2004, Page(s):425 - 429 Vol.1
[13] Pladdy, C.; Ozen, S.; Fimoff, M.J.; Nerayanuru, S.M.; Zoltowsko, M.D., “Best
linear unbiased channel estimation for frequency selective multipath channels
with long delay spreads,” Vehicular Technology Conference, 2003. IEEE 58th
Volume 2, 6-9 Oct. 2003, Page(s):1238 - 1242 Vol.2
[14] IEEE Std 802.11a-1999 [Adopted by ISO/IEC and redesignated as ISO/IEC
8802-11:1999] Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications, High-speed Physical Layer in the 5GHz Band