Soon Up Hwang

Low Complexity Iterative ICI Cancellation and Equalization for OFDM Systems Over Doubly Selective Channels

In this paper, a low complexity iterative intercarrier interference (ICI) cancellation and equalization technique is proposed for use in OFDM systems over doubly selective channels. In the iterative parallel interference cancellation/minimum mean square error (PIC/MMSE) detector has a high complexity and a restriction on the structure which can not remove the ICI in the initial stage. Therefore, an error propagation occurs due to the ICI regenerated by the incorrect output of soft-input soft-output (SISO) decoder. In order to reduce the error propagation, an MMSE detector based on the successive interference cancellation (SIC) is used in the initial stage. The low complexity MMSE detector is also derived to minimize the error propagation by quantifying the decision error before SISO decoding. In the first iteration, simulation results show that the proposed scheme outperforms the conventional PIC/MMSE scheme by about 3 dB at bit error rate (BER)=1 times 10-3 while maintaining the equivalent computational complexity. In the subsequent iteration, it is possible to cancel the ICI out in the received signals by the aid of soft log-likelihood ratio (LLR) fed from the SISO decoder. Converting the LLR to the decision error probability, the error covariance matrix is obtained more accurately. As a result, the error propagation can be effectively reduced by dealing with only the dominant components, when considering decision errors. Finally, simulation results show that the proposed scheme outperforms the conventional PIC/MMSE scheme.

Soft-output ML detector for spatial modulation OFDM systems

The spatial modulation (SM) divides input data into antenna indexes and data symbols, and transmits data symbols via the specific antenna chosen by the antenna index. Soft decision technology for the SM system has not been developed, and there is room for improving the receive performance. In this paper, soft-output maximum likelihood (ML) detector for antenna index and data bit is derived to recover the desired signals by soft decision. Simulation results show that the conventional SM system with hard decision has a limitation in its performance as compared to SIMO (single-input multiple-output) system. On the other hand, the proposed SM with soft decision outperforms the SM with ML detector based on hard decision.

Performance evaluation of MIMO-OFDM with signal space diversity over frequency selective channels

Vertical Bell labs layered space-time (V-BLAST) is known to provide a good tradeoff between performance and complexity for multiple antenna systems. In this paper, an improved scheme which utilizes signal space diversity is proposed for multiple-input multiple-output (MIMO) bit interleaved coded modulation (BICM). The signal space diversity (SSD) has the advantage to increase the diversity order without the expansion of extra bandwidth and power by means of rotating the modulated symbols and interleaving the in-phase and quadrature components separately. BICM combined with the SSD would further enhance the diversity gains. Simulation results show that the proposed scheme is superior to V-BLAST, regardless of the number of antennas and modulation order.

Interleaved Spatial Diversity Transmission with Coordinate Interleaver for MIMO-OFDM Systems

Multiple input multiple output (MIMO) system provides a promising means to increase the spectral efficiency. Orthogonal frequency division multiplexing (OFDM) allows broadband transmission over frequency selective fading channels. Recently, a coordinate interleaver (CI) is considered in order to maximize the diversity gain for MIMO system. In this paper, a new concept of coordinate interleaver for MIMO-OFDM system and an optimum receiver structure are suggested. Using the CI, the real and imaginary components of signals experience different fading channels and it provides additional diversity gains. Simulation results show that the system employing the proposed CI outperforms the conventional V-BLAST architecture.

Spatial diversity technique combined with rotated constellation for MIMO-OFDM systems

MIMO-OFDM system significantly improves the data rates over wireless channels. V-BLAST is well known effective technique which enhances the system performance while allowing low implementation complexity. However, the performance of V-BLAST technique would be degraded by the error propagation due to the nulling and canceling process. In order to improve the performance of V-BLAST, this paper proposes spatial diversity technique combined with rotated constellation for MIMO-OFDM systems. It is demonstrated in the simulation evaluation that the proposed technique can offer excellent performance with spatial diversity gain in time-varying typical urban channel.

Coordinate Interleaved Hybrid Transmission For MIMO-OFDM Systems

MIMO-OFDM systems would provide both multiplexing gain and diversity gain in order to improve the system capacity and the receive performance. This paper introduces the coordinate interleaved hybrid transmission for use in MIMO- OFDM systems to meet such requirements. The proposed CID- SFBC-OFDM and CID-STBC-OFDM combine the coordinate interleaver with Double SFBC-OFDM and Double STBC-OFDM to achieve additional diversity gain whilst retaining their spatial multiplexing gain. Our simulation results show that CID-SFBC- OFDM and CID-STBC-OFDM outperform the conventional schemes in typical urban (TU) channel.

On the Distribution of MISO Channel Capacity in the Noise and Interference-Limited Systems

In this paper, an exact distribution of channel capacity for MISO (Multiple-Input Single-Output) system with co-channel interference is derived from the information theo- retical viewpoint. It is found that the MISO channel capacity in the noise-limited channel follows the chi-square distribution, and capacity in the interference-limited channel follows the F - distribution. Using these distributions of capacity, the outage capacity in Rayleigh fading channels can be accurately computed. From simulations, we have confirmed the accuracy of our analysis which exactly coincides with the empirical simulations in the noise-limited and in the interference-limited systems.

A Layered Space-Time-Frequency Coded Transmission for MIMO-OFDM Systems

In this paper, we propose a layered space-time-frequency (STF) coded Orthogonal Frequency Division Multiplexing (OFDM) for next generation mobile multimedia systems. In [9], the architecture of a layered space-time-frequency coded transmission scheme is devised as a combination of orthogonal precoding and hybrid space-time block code (STBC). By doing so, it is possible to obtain higher spectral and power efficiencies than other conventional schemes [3][5]. However, this approach has performance degradation due to the loss of the orthogonality of STBC codes in high mobility environments. Therefore, we applied a time domain spreading method to [9], which individually distributes the data symbols over several OFDM symbols in a time domain. The proposed scheme provides both maximum transmit diversity and spatial multiplexing gains with a moderate complexity over multipath fading channels. Simulation results show that it is possible to obtain an additional transmit diversity gain by means of spreading in a time domain.

A Layered Space-Time-Frequency Coded OFDM for Next Generation Mobile Multimedia Systems

We consider the architecture of layered space-time-frequency (STF) coding as a combination of orthogonal precoding and hybrid space-time block coding (STBC) for multiple-input multiple-output (MIMO) wireless multimedia systems. This approach provides both maximum transmit diversity and spatial multiplexing with moderate complexity. The proposed layered STF coded transmission scheme is practical and efficient over multipath fading channels. In addition, it is possible to obtain maximum frequency diversity gain by means of the orthogonal precoding that enhances the system performance.

A layered spatial modulation technique for MIMO-OFDM systems

The spatial modulation (SM) divides input data into antenna indices and data symbols, and transmits data symbols via the specific antenna chosen by an antenna index. The performance of SM is affected by the worse one between the detection performances of antenna index and data symbol. In this paper, power efficient SM based transmitter and receiver architectures are proposed in order to provide different protection levels according to the important level of data, and also to improve the receive performance as compared with the conventional SM. To provide unequal error protection (UEP) at the transmitter, the antenna index and data symbol are separately encoded by two FEC codes. At the receiver, the two-stage detection and decoding based on a novel criteria is applied in order to enhance the bit error rate (BER) performance. Simulation results show that the proposed scheme outperforms the conventional SM over frequency selective channels.