Study on subband adaptive array for space-time codes in wideband channel 広帯域無線通信における時空間符号化伝送のためのサブバンドアダプティブアレーに関する研究

博士論文

2007

Recently, many works have been accomplished on transmit diversity for a high-speed datatransmission through the wireless channel. A Multiple Input Multiple Output (MIMO)system which employs multiple antennas at transmitter and receiver has been shown to beable to improve transmission data rate and capacity of the system. When the channel stateinformation (CSI) is unknown at the transmitter, an multiple input single output (MISO)system combined with the transmit diversity of space time coding modulation known asspace-time block coding (STBC) has taken a great attention. However, the performanceof STBC is deteriorated under frequency selective fading due to inter symbol interference(ISI). An STBC employing tapped delay line adaptive array (STBC-TDLAA) is knownas a solution for this problem since it utilizes the delayed signals to enhance the desiredsignal instead of excluding them as interferences. However, this method requires a largecomputational load compared to the conventional adaptive array system.In this dissertation, assuming the CSI is unknown at the transmitter, and at thereceiver the CSI is exploited from pilot signal, we propose an MIMO transmission schemeusing STBC with adoptive subband adaptive array (SBAA) processing, where the receivedsignal is converted into the frequency-domain and adaptive processing is done in eachsubband. A novel construction of SBAA is introduced to process received signal based onSTBC. In addition, to improve the performance of STBC-SBAA, single carrier cyclic prefix(CP) is also introduced. Simulation results demonstrate that the proposed scheme hasa better performance compare to the conventional STBC, and has a better performanceand less computational load compare to STBC-TDLAA.Furthermore, we extend the proposed method to uplink multi-user space-time blockcoding (STBC) code division multiple access (CDMA) over a frequency selective fadingchannel. The proposed scheme utilizes CDMA with STBC and a receive array antennawith SBAA processing at the receiver. The received signal is converted into the frequencydomain before de-spreading and adaptive processing is performed in each subband for eachuser. In order to reduce the effect of ISI and multiple access interference (MAI), a novelSBAA construction is introduced to process STBC CDMA signals. To improve the performanceof the proposed scheme, we evaluate STBC-SBAA using spreading codes cyclicprefix (CP). Simulation results demonstrate an improved performance of the proposedsystem for single and multiuser environments compared to the conventional techniques.Moreover, we also evaluate the STBC-SBAA for the multi-code multi-rate CDMA system.Finally, we present a modified spatio-temporal adaptive array for multiuser STBC(Modified STBC-STAA) transmission in frequency selective fading channel with the presenceof co-channel interferences (CCIs). This method based on the transversal filteradaptive array performing the joint interference suppression and equalization to overcomethe problem of one symbol delay, namely codes synchronization error. The ModifiedSTBC-STAA can maximize the transmission efficiency by incorporating the receive signalcomponent for both non-conjugated and the complex conjugated version of desired signalin the receive signal, which is not only dispersed in space, but also in the time. Furthermore,Modified STBC-STAA overcomes the multiuser timing errors by re-aligning theasynchronous multiuser signal to undergo the synchronous joint interference suppressionand equalization. Simulation results show that both our proposed scheme has a betterperformance than the conventional STBC-STAA for frequency selective fading channel.