Shinsuke Ibi

EXIT Chart-Aided Adaptive Coding for Multilevel BICM With Turbo Equalization in Frequency-Selective MIMO Channels

This paper proposes an adaptive coding (AC) scheme for multilevel bit-interleaved coded modulation (ML-BICM) with minimum mean-square error (MMSE) turbo equalization in frequency-selective multiple-input-multiple-output (MIMO) channels. The aim of this paper is to minimize the information rate loss due to the mismatch between channel realization and channel coding. With the aid of the knowledge about extrinsic information transfer characteristics at the receiver, code parameters such as code rates and/or generator polynomials are adaptively selected independently for each ML-BICM layer. Model-based simulation results show that an achievable average throughput can be significantly improved with the proposed AC technique over automatic repeat request with fixed coding rate. Furthermore, the advantageous points of the proposed scheme are verified through field-measurement-data-based simulations.

Flexible Spectrum Control and Receiver Performance Improvement Technologies for B3G Wireless Systems

This paper will discuss trend and our views on the flexible spectrum control and receiver performance improvement technologies as a part of capacity maximization technologies for beyond third generation (B3G) systems. First of all, we will discuss dynamic spectrum control techniques that can minimize intra- and inter-system interference for both multi-carrier (MC) and single-carrier (SC) systems, thereby maximizing upper-limit of channel capacity. We will also discuss receiver performance improvement strategies as a part of capacity maximization technologies for MC and SC systems, especially joint operation of the adaptive equalizer and decoder using EXIT chart analysis for MC and SC systems

Adaptive Transmission With Single-Carrier Multilevel BICM

In this paper, we introduce adaptive link control techniques for multiple-input multiple-output (MIMO) systems with broadband single-carrier signaling. Soft cancellation and minimum mean squared error turbo equalization is assumed, where matching between coding and equalization plays crucial roles to achieve high throughput. This paper uses multilevel coded bit-interleaved coded modulation (ML-BICM) with linear mapping as a core part of the transmission, on top of which this paper applies automatic repeat request (ARQ) with adaptive coding (AC) for link control. The reason behind the use of the linear mapping ML-BICM is the separability between the layers in the modulation format: This should bring us a significant benefit in designing the link control strategies because each layer has its own reliability, and the adaptive link control should be optimized based on the each layers reliabilities. For ARQ with ML-BICM, we introduce layer-by-layer retransmission control, where turbo equalization and retransmission control can be performed independently over the layers because of the layer-separability. The layer-by-layer concept is then applied to AC with ML-BICM, where the code parameters such as code rate and generator polynomials are chosen so that after several iterations the mutual information between the transmitted and the soft-input soft-output decoder output information can reach a value very close to one while minimizing the rate loss due to the mismatch between the equalization and decoder. Extrinsic information transfer analysis is performed for the MIMO channel realization being given. The transmitter is notified of the selected codes for the each layer via the feedback channel, and uses the selected codes for the following transmission, assuming that the channel state information (CSI) stays the same at least over two consecutive frames. Finally, this paper evaluates the throughput performances of the ML-BICM ARQ and AC techniques using multidimensional field measurement data. The performance tendencies are correlated with propagation properties, obtained as results of the high-resolution channel analysis, such as spatial spreads at the transmitter and receiver sides.

A spectrum-overlapped resource management in dynamic spectrum control technique

This paper proposes a spectrum-overlapped resource management (SORM) technique using a dynamic spectrum control (DSC) and turbo equalizer for flexible frequency domain resource management under multiuser conditions. In the proposed technique, discrete spectrum of the transmitted signal is mapped onto spectrum components having the highest channel gain in the system band while accepting partial spectrum overlapping between users, and a frequency domain soft-canceller with minimum mean square error (FD-SC/MMSE) turbo equalizer is applied as the signal detection scheme for multiuser detection (MUD) in order to cancel not only inter-symbol interference (ISI) but also inter-user interference (IUI). Computer simulation including extrinsic information transfer (EXIT) analysis confirms that the proposed scheme can achieve high frequency selection diversity and realize flexible frequency domain resource management.

EXIT chart-aided adaptive coding for MMSE turbo equalization with multilevel BICM

This letter proposes adaptive coding (AC) for multilevel bit interleaved coded modulation (ML-BICM) with MMSE turbo equalization, of which aim is to minimize the information rate loss due to the mismatch between the channel realization and channel coding. With the aid of the knowledge about extrinsic information transfer (EXIT) characteristics at the receiver, the code parameters such as code rates and/or generator polynomials are adaptively selected independently in each the ML-BICM layer. Numerical results show that throughput efficiency can be significantly improved with the proposed AC technique over the automatic repeat request (ARQ) technique with fixed code rate

Spectrum Loading Type Dynamic Spectrum Allocation Technique for Cognitive Radio Systems

This paper proposes a spectrum loading type dynamic spectrum control technique for broadband cognitive radio systems. In the proposed scheme, based on the detection of available spot-wise spectra, discrete spectrum components of a framed symbol sequence are mapped onto the spot-wise spectra. Two spectrum mapping schemes are proposed; single-RF scheme in which available spot-wise spectra are located so close that the entire spot-wise spectra can be covered by an FFT/IFFT with a reasonable number of FFT points, and multi-RF scheme in which the spot-wise spectra are located far away so that the entire spectra cannot be covered by an FFT/IFFT processor. Computer simulation confirms that the proposed scheme is effective in utilizing spot-wise spectra. Moreover, the proposed scheme is confirmed to be effective in enhancement of co-channel and inter-symbol interference immunity when the number of opportunistically available spot-wise spectra is increased.

Joint channel-and-network coding using EXIT chart aided relay activation

This paper presents a relay activation scheme designed for joint channel-and-network (JCN) coded systems relying on an iterative decoding. A primary focus is on proposing criteria of the relay activation to find the best user combination for cooperative relaying, which exploits extrinsic information transfer (EXIT) chart analysis. We will demonstrate that the EXIT chart aided relay activation scheme is capable of reducing the probability of outages, despite increasing the effective throughput of network.

Implementation of OFDM baseband transceiver with dynamic spectrum access for cognitive radio systems

VLSI architecture for OFDM baseband transceiver is developed, which is dedicated to cognitive radio systems. To facilitate dynamic spectrum access, this transceiver architecture employs a specialized FFT/IFFT module and a mapping/demapping module. Efficient mechanisms to omit input/ output of unused subcarriers are introduced. Also, calculation of spectrum intensity for subcarrier level carrier sensing is successfully integrated to the FFT module. Whole transmitter/ receiver modules are implemented by keeping compatibility with IEEE 802.11g. A prototype system is constructed by using Xilinx Virtex-II FPGA, which can transmit video sequence in real time.

A Frequency Domain Scheduling for Uplink Single Carrier Non-Orthogonal Multiple Access with Iterative Interference Cancellation

This paper proposes a frequency-domain (FD) scheduling for an uplink single carrier non-orthogonal multiple access (SC-NOMA) with the assistance of iterative interference cancellation (IC). In the SC-NOMA, an evolved Node B (eNB) with an iterative IC receiver is capable of allocating overlapped spectra to plural intra-cell user equipments (UEs) exceeding the number of receive antennas. As a result, the SC-NOMA can enhance the spectral efficiency owing to the non-orthogonal multiplexing. However, when the subband (SB) criterion scheduling, that assigns an SB to a UE on the basis of the metric only on an SB, is applied, this scheduling is not suitable in the SC-NOMA. This is because the throughput in single carrier transmission depends on all the allocated SBs. Therefore, we propose a novel FD scheduling based on the expected value of cell throughput which is calculated by both the SB selected by the metric as a candidate and the previously allocated SBs. The eNB assigns the candidate SB if the expected cell throughput increases after allocating the candidate SB. Computer simulations confirm that the proposal can improve throughput performances compared to the SB criterion scheduling in the SC-NOMA.

VLSI design of OFDM baseband transceiver with dynamic spectrum access

The VLSI design of OFDM baseband transceiver is described, which is dedicated to cognitive radio systems. To facilitate dynamic spectrum accessing, this receiver architecture employs a specialized FFT module and a mapping/demapping module. Efficient mechanisms to omit input/output of unused subrcarriers are introduced. Also, calculation of spectrum intensity for subcarrier level carrier sensing is successfully integrated to the FFT module. Whole transmitter/receiver modules are implemented by maintaining compatibility with IEEE 802.11g. Implementation results show that the proposed architecture can process OFDM symbols in 60 MHz operation.