STUDY ON SUBBAND ADAPTIVE ARRAY FOR SPACE-TIME CODES IN WIDEBAND CHANNEL

Recently, many works have been accomplished on transmit diversity for a high-speed data transmission through the wireless channel. A Multiple Input Multiple Output (MIMO) system which employs multiple antennas at transmitter and receiver has been shown to be able to improve transmission data rate and capacity of the system. When the channel state information (CSI) is unknown at the transmitter, an multiple input single output (MISO) system combined with the transmit diversity of space time coding modulation known as space-time block coding (STBC) has taken a great attention. However, the performance of STBC is deteriorated under frequency selective fading due to inter symbol interference (ISI). An STBC employing tapped delay line adaptive array (STBC-TDLAA) is known as a solution for this problem since it utilizes the delayed signals to enhance the desired signal instead of excluding them as interferences. However, this method requires a large computational load compared to the conventional adaptive array system. In this dissertation, assuming the CSI is unknown at the transmitter, and at the receiver the CSI is exploited from pilot signal, we propose an MIMO transmission scheme using STBC with adoptive subband adaptive array (SBAA) processing, where the received signal is converted into the frequency-domain and adaptive processing is done in each subband. A novel construction of SBAA is introduced to process received signal based on STBC. In addition, to improve the performance of STBC-SBAA, single carrier cyclic prefix (CP) is also introduced. Simulation results demonstrate that the proposed scheme has a better performance compare to the conventional STBC, and has a better performance and less computational load compare to STBC-TDLAA. Furthermore, we extend the proposed method to uplink multi-user space-time block coding (STBC) code division multiple access (CDMA) over a frequency selective fading channel. The proposed scheme utilizes CDMA with STBC and a receive array antenna with SBAA processing at the receiver. The received signal is converted into the frequency domain before de-spreading and adaptive processing is performed in each subband for each user. In order to reduce the effect of ISI and multiple access interference (MAI), a novel SBAA construction is introduced to process STBC CDMA signals. To improve the performance of the proposed scheme, we evaluate STBC-SBAA using spreading codes cyclic prefix (CP). Simulation results demonstrate an improved performance of the proposed system 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 presence of co-channel interferences (CCIs). This method based on the transversal filter adaptive array performing the joint interference suppression and equalization to overcome the problem of one symbol delay, namely codes synchronization error. The Modified STBC-STAA can maximize the transmission efficiency by incorporating the receive signal component for both non-conjugated and the complex conjugated version of desired signal in 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 the asynchronous multiuser signal to undergo the synchronous joint interference suppression and equalization. Simulation results show that both our proposed scheme has a better performance than the conventional STBC-STAA for frequency selective fading channel.