| Summary: | 碩士 === 國立高雄第一科技大學 === 電腦與通訊工程系 === 89 === In communication system of modern times, modulater-demodulster and error-correcting codes for CODEC are two main parts. They pay key roles in transmission equipments to enchance communication system data transmission rate and lower bit error rate. To satisfy curreat getting strict bandwidth requirements, increase bandwidth efficiency and data transmission rate head for two direction to develop:
(1)R&D bandwidth which own higher utilization rate modulation;such as, high transmission data rate M-aryQAM, M-aryAM and M-aryPM. Especially to which has better spectrum characteristic CPM,TFM,MSK,MSK(GMSK),QPSK and XPSK. The main advantages of CPM are that the signals pccupy less narrowband and carry less radiation out. Therefor, the ISI (intersymbol interference) is also less.
(2)Enchence the original communication hardware; especially to the phone circuit transmission data rae. To develop high speed transmission data moduation which is adequate to these limited bandwidth(3KHz as usual), such as, QAM and M-aryQAM. Datas transmission’s efficacy and reliance are contradicatory in digital communication system. Generous to say, system bit error rate increases. It would be meaningful to study and solve that system bit error rate raises causing by increased atas transmission rate in communication system design and impementation.
In 1974, Massey based on Shannon message theory and proved that encoding and moculation as a design package could improve the system functions largly. Ungerbock and Imai and Hirakawa researched on this at the later stage of 70 decade. In 1982, they found to used rate n/(n+1) Trellis code as convolution code and gathered each mapping 2n+1 Modulation signal. After demodulater and decoding, It become to convolution code sequence at the receiver. Finally, put it into Viterbi decoding unit. So it was the way to combine of modulation and encoding. Under the conditions of not increasing bandwidth and same datas speed rate gained 3~6dB poer gain. Due to modilate signals and convolution code could be took for Trellis code, so we called that”Trellis Coded Modulation”, TCM is abbrevivation.
Moreover, we use FPGA as simulation to design CODEC in TCPTCM. We form rate 2/3 TCPTCM by using two same 1/2 rate RSC and the way of pipeline interleaving. By using pipeline and interleaving to the convolution encoder:pipeline increases coding gain; interleaving improves performance at the channel coding. On one hand, it strengthens errors correction ability; and the other hand, it increases bandwidth efficiency by using turbo code. We use 8PSK modulation because the average power lower less relatively after comparing the variable signals power spectrum and average power under the condition of transmission frequency unchanged. Meanwhile, we use 2 methods to decode. One, to use BAHL decoding at the beginning and Viterbi at the end; the other, BAHL decodingonly to increase decoding accurate. To sum up, TCPTCM develop wireless communication system in transmission and decoding speed, also enhance coding gains relatively by without increasing bandwidth.
In 1997, N.Seshardri, V.Tarokh and A.R.Calderbank found Space-Time coding and applied in the high speed data transmission in wireless communication. In 1999, Gerhard Bauch concatenated TTCM(turbo-TCM) and STBC(Space-Time Block Codes) to improve channel coding gerneration bits and error correction required decoding transmission speed: besides, it increased coding gain and performance by power without increasing transmitted bandwith and required power. Therefor, TTCM and STBC would be very helpful in high speed and massive datas transmission.
|
|---|
