This paper investigates the cancellation of the interfereences among Destination Users (DU's) and the improvement of system rate in the non- regenerative Multiuser Multiple-Input Multiple- Output (MU-MIMO) relay downlink system. A novel design method of transmit weights is proposed to successively eliminate the interference among DU's, each of which is equipped with multiple receive antennas. We firstly study the transmit weights design for the conventional Amplify-and-Forward (AF) relay system where the Relay Station (RS) just retransmits the received signals, then we extend it to the joint design of transmit weights both at the Base Station (BS) and the RS. In the joint design, Singular Value Decomposition (SVD) is used for the first channel link (link between BS and RS), then a user selection algorithm is adopted at the RS to generate the transmit weight of each DU. The channel matrix of system is transformed into a triangular matrix, where the Dirty Paper Coding (DPC) technique is employed to remove the interference among DU's and maintain the achievable rate of system. Simulation results verify the effectiveness of the proposed scheme.

In this paper, we propose a new channel model of optical satellite-to-ground link by analyzing the results of optical transmission experiments between ground station and the Optical Inter-orbit Communications Engineering Test Satellite (OICETS). This will be a practical model on high-capacity optical satellite-to-ground links. In addition, we propose an efficient channel coding scheme using low-density generator matrix (LDGM) codes as a long erasure code over the proposed channel model. Simulation results clarify the required coding rate and the interleaver size for this channel on bare 1 Mbps transmission. The basic idea of the proposed model and the coding system are suitable for higher-speed optical links.

In this paper, we have proposed the signal separation and equalization schemes for MFSK signals using FDE (Frequency Domain equalization) with CP (Cyclic Prefix) and the MLD (Maximum Likelihood Detection) with ZP (Zero Padding) on quasi-static MIMO frequency selective channels. Through computer simulations, we have verified that the MLD with ZP exhibits the better BER characteristics than the conventional FDE with CP. Moreover, we have decreased the computational complexity of MLD using M algorithm.

Maximum Likelihood Detection (MLD) featuring Log-likelihood (LLR) combining technique has been introduced in earlier works to achieve diversity gains in block fading channels for one relay node. In this paper, we extend this strategy to multiple relay systems (MRS) and introduce a new method such that the computational complexity of MLD is further reduced. This method approximates bit LLR values from the symbol LLR, thereby reducing the computational burden at the destination. A cooperative relay scheme of a source node (S), multiple relay nodes (R) and a common destination node (D) is considered. This scheme utilizes a simple relaying protocol which detects the signals (i.e. hard-decision) and forwards (DAF) to the destination node. While LDPC codes do not achieve significant performance gain in Single Input Single Output (SISO) scheme over block fading channel, we suggest that with the proposed scheme, the gain is essentially significant under MRS platform. This improvement is achieved by using a cheap DAF relaying protocol which is well-suited for resource limited conditions, for instance, in wireless sensor networks (WSN). The results are validated through a simulation work and compared with maximum ratio combiner (MRC) and cooperative-MRC (C-MRC).

In recent years, high speed, high-capacity and reliable transmissions are demanding in wireless communications. To achieve those requests, it is necessary to solve both time and frequency selective fadings caused by multi-path propagation on wireless channels. But up to now, the OFDM technique as the frequency domain equalization has been considered mainly for the frequency selective fading. In this paper, we have proposed some of time domain equalization schemes using block processing on SISO (single input single output) frequency selective channels, i.e., block linear equalizer (BLE), block equalization by QRD and M algorithm (QRD-M) and block equalization by SVD with adaptive modulation (SVD with adapt. mod.). They all have low complexities and excellent performances brought by the effects of path-diversity and zero padding for IBI (inter-block interference) cancellation.

Recently, a chaotic modulation has been proposed and attracts many researchers' attention because of some properties such as noise-like signal, nonlinearity, and pseudo-periodicity. The chaotic modulation is usually treated as a secure transmission scheme rather than an efficient scheme in terms of channel noise. In this paper, to achieve a secure and high-performance transmission, we propose a trellis-based chaotic modulation scheme (called as chaotic-coded modulation: CCM). The coding gain is obtained by the combination of trellis and chaotic convolutions and an adaptive decoding algorithm is used for this coded modulation. Simulation results show that the decoding scheme has a tradeoff between the performance and the decoding complexity.

Energy detection of frequency-shift keying (FSK) signals is the optimum noncoherent detection technique yielding a minimum bit-error rate (BER) on the additive white Gaussian noise channel. It is usually used when carrier phase estimation is difficult. When FSK signals are passed through a frequency-selective multipath fading channel, the multipath delay in the channel results in a multitone waveform being received during each signaling interval. An effective practical sequence estimation receiver for this situation is proposed. It makes use of energy detectors followed by a Viterbi (1979) or sequence estimator that uses an energy difference metric. Statistical properties of the detection variable are derived. Analytical upper and lower bounds on the BER are derived and the results compared with computer simulations to show the effectiveness of the technique.

We propose a turbo equalization scheme for GFSK signals with frequency detection. Although the channel is AWGN, there exists severe ISI in the received signal due to the premodulation Gaussian baseband filter in the transmitter as well as the narrowband IF filter in the receiver. We regard them as a real number inner convolutional encoder. At the same time, a recursive systematic convolutional (RSC) encoder can be used as an outer encoder. At the receiver side, the inner ISI equalizer and the outer RSC decoder are serially concatenated with an interleaver, to be iteratively decoded using a MAP (maximum a posteriori) algorithm or SOVA (soft-output Viterbi algorithm) with SISO (soft input/soft output). Through computer simulations, the proposed system shows BER=10/sup -5/ at E/sub b//N/sub 0/=7.3 dB, when we take BT=0.6 (IF filter bandwidth multiplied by symbol duration time) with the RSC code having the coding rate of R=1/2 and the constraint length of K=7, and the iteration number of 3. This means 2.9 dB improvement compared with the conventional concatenation scheme of an ISI equalizer with a hard decision Viterbi decoder.

The energy detection of continuous phase frequency shift keying (CP-FSK) signals is the optimum noncoherent detection technique yielding a minimum bit error rate (BER) on the additive white Gaussian noise (AWGN) channel. This scheme is usually used when carrier phase estimation is difficult. When a CP-FSK signal is passed through a frequency selective multipath fading channel, inter-symbol interference (ISI) is introduced which distorts the received signal waveform. However, this ISI can be compensated and the BER improved by use of sequence estimation at the output of the energy detectors. In this paper, we derive an analytical upper bound as well as a lower bound on the BER for this scheme on the multipath fading channels and compare the results with the computer simulation to show the effectiveness of the technique.

A communication scheme using binary FM with noncoherent limiter-discriminator detection has been well known. Up to now, the improvement of bit error rate at the receiver side has been carried out through the bandwidth optimization of the IF filter, the decision feedback equalization (DFE), or simple two-state maximum likelihood sequence estimator (MLSE). This channel is inherently the intersymbol interference (ISI) channel due to the premodulation baseband filtering as well as the narrowband IF filtering. So the sequence estimation scheme using the Viterbi algorithm can be applied successfully, although the channel is not additive white Gaussian and maximum likelihood in the strict sense. In this paper, through computer simulations, we examine the actual BER improvement of the sequence estimation scheme with multiple-state trellis especially for MSK and GMSK signals. We mainly consider static AWGN and frequency nonselective Rician fading channels. Consequently, by adjusting the IF filter bandwidth, very large estimation gains are obtained compared to the conventional DFE or MLSE detector for AWGN and Rician fading channels. This scheme does not produce large demodulation delay and is implemented only by adding the signal processing part to the final stage of the receiver. This scheme seems to be very useful for any applications including satellite mobile channels.>

A phase locked loop (PLL) is well known as an FM demodulator with threshold extension capability. This property can also be useful for low BER detection. A PLL also has frequency tracking ability for input center frequency variation. The author proposes a detection scheme for an MSK signal, using a digital signal processing type digital PLL (DSP DPLL) demodulator. The author also adopts a sequence estimation scheme to mitigate the inter-symbol interference (ISI) caused by the finite bandwidth of the DSP DPLL. Through computer simulations, the author shows that the proposed DSP DPLL demodulator with the sequence estimator exhibits very low BER characteristics in the presence of time-varying Doppler shift on frequency non-selective Rician fading channels. This scheme will be useful for detecting an MSK signal with large Doppler shift from, for example, LEO satellites.

As yet there exists no analytical method of obtaining the exact output distortion of BPF's for an angle-modulated signal input. In this paper, we have introduced a numerical method in which a filtering problem is described by the state space method and then is converted to a time domain difference equation. As a result, evaluation can be carried out quickly and easily.