JooHyun Yi

MMSE-OSIC² Signal Detection for Spatially Multiplexed MIMO Systems

In spatially multiplexed MIMO systems that enable high-data-rate transmission over wireless communication channels, spatial demultiplexing at the receiver is a challenging task. Thus, various demultiplexing methods have been developed by many researchers. In this paper, a novel signal detection method that achieves near-ML performance in a computationally efficient manner is proposed. The proposed method is based on the well-known minimum mean squared error (MMSE) ordered successive interference cancellation (OSIC) method. However, unlike the conventional MMSE-OSIC, a number of candidates are selected at each layer, hence, it has been termed MMSE-OSIC with candidates (MMSE-OSIC2). In this study, it is demonstrated via a series of computer simulations that the MMSE-OSIC2 achieves near-ML performance while requiring a complexity comparable to that of the conventional MMSE- OSIC. Also shown here is that the log likelihood ratio (LLR) values are successfully generated via the proposed method.

RAKE receiver with adaptive interference cancellers for a DS-CDMA system in multipath fading channels

An adaptive RAKE receiver with diversity combining is proposed for a DS-CDMA system in multipath fading channels. The proposed adaptive RAKE receiver exploits antenna diversity and adaptive interference cancellation (AIC) to mitigate the effect of both multipath fading and multiple-access interference (MAI). The LMS algorithm with variable step-size is used to update the tap-weight vector of AICs. The performance of the proposed receiver is evaluated by computer simulation for the various numbers of antennas and RAKE fingers. It is shown that the proposed receiver achieves significant performance improvement over a conventional RAKE receiver.

Interference cancellation for a space-time coded DS-CDMA system in a Rayleigh fading channel with arrival time difference

An interference cancellation scheme is applied to the space-time coded DS-CDMA system in a Rayleigh fading channel having arrival time difference from multiple transmit antennas. Arrival time difference causes not only multiple-access interference but also intersymbol interference between the desired signals transmitted from different antennas. To mitigate the effect of the interferences, an adaptive interference canceller (AIC) and maximum likelihood (ML) joint decoding scheme is proposed for a space-time coded DS-CDMA system in which an adaptation process for the AIC is merged in the conventional ML decoding scheme. The performance of the proposed decoding scheme is evaluated for the space-time coded DS-CDMA system with two transmit antennas. It is shown that the proposed decoding scheme achieves significant performance improvement over the conventional ML decoding scheme.

Adaptive step-size algorithm for the interference canceller in the space-time coded DS-CDMA system

In this letter, we propose an adaptive step-size algorithm for the adaptive interference canceller (AIC) in the space-time coded DS-CDMA system. To improve the performance of the fixed step-size AIC (FS-AIC), the regular adaptive step-size algorithm is extended in complex domain and applied to the joint AIC and ML decoder scheme. Simulation results show that the joint adaptive step-size AIC (AS-AIC) and ML decoder scheme using the proposed algorithm has better performance than not only the conventional ML decoder but also the joint FS-AIC and ML decoder scheme without much increase of the decoding delay and complexity.

Joint interference cancellation and ML decoding scheme for a space-time coded DS-CDMA system in a multipath fading channel

A joint interference cancellation and maximum likelihood (ML) decoding scheme is proposed for a space-time coded DS-CDMA system in a multipath fading channel. Arrival time difference between multiple transmit antennas by multipaths causes not only inter-symbol interference but also multiple-access interference and inter-antenna interference between the desired signals transmitted from different antennas. To mitigate the effect of the interferences a joint algorithm for the proposed scheme is presented, in which an adaptation process for the AIC is merged in the conventional ML decoding algorithm. The performance of the proposed scheme is evaluated for the space-time coded DS-CDMA system with two transmit antennas. It is shown that the proposed scheme achieves significant performance improvement over the conventional ML decoding scheme.

Efficiency of Transmission Techniques in Multiple-Input Single-Output (MISO) Communication System

This paper examines methods of increasing the downlink channel capacity based on transmitting a signal through a multiple antenna system such as beamforming (BF), transmit diversity (TD) and the combined approach integrating BF and TD. A convenient criterion of efficiency of these techniques is proposed, which reflects the capacity improvement. It is shown that the efficiency of using the multiple transmit antenna system depends on two factors - improvement of the reception performance and mitigation of the intra-system interference. The paper provides the comparative assessment of the methods being researched in terms of their efficiency.

Per-survivor AIC based on group decoding for the space-time trellis coded DS-CDMA system

We propose a per-survivor adaptive interference canceller (PSAIC) based on group decoding for the uplink of the space-time trellis coded DS-CDMA system. The trellis-based group decoder (TBGD) obtains a trade-off between performance and complexity by decomposing the super-trellis for the entire decoder into group-trellises for subsets of users. As the TBGD uses tentative decisions in each state transition to reduce MAI, the tentative decision error causes the error propagation performance to degrade severely. To mitigate the performance degradation, we utilize an adaptive interference canceller using per-survivor processing, which reduces the negative effects of error propagation, instead of tentative decisions. Simulation results show that the proposed scheme has better performance over the conventional single user decoder scheme without much increase of decoding delay and complexity, and also achieves a performance near that of the optimum super-trellis decoder with significantly lower complexity.