Nobuhiko Miki

Kagawa University, Takamatu, Kagawa, Japan

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Publications (61)6.06 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the performance of outer-loop control for selecting the best modulation and coding scheme (MCS) based on mutual information (MI) for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) spatial division multiplexing (SDM).We propose an outer-loop control scheme that updates the measured MI per information bit value for selecting the best MCS from a mapping table that associates the block error rate (BLER) and MI per bit instead of directly updating the MCS selection threshold so that the required BLER is satisfied. The proposed outer-loop control is applicable to continuous data transmission including intermittent transmission with a short blank period. Moreover, we compare the measured BLER and throughput performance for two types of outer-loop control methods: instantaneous block error detection and moving-average BLER detection. In the paper, we use maximum likelihood detection (MLD) for MIMO SDM. Computer simulation results optimize the step size for the respective outer-loop control schemes for selecting the best MCS that achieves the higher throughput and the target BLER simultaneously. Computer simulation results also show that by using the most appropriate step size, the outer-loop control method based on the instantaneous block error detection of each physical resource block is more appropriate than that based on the moving-average BLER detection from the viewpoints of achieving the target BLER more accurately and higher throughput. Copyright © 2015 The Institute of Electronics, Information and Communication Engineers.
    No preview · Article · Aug 2015 · IEICE Transactions on Communications
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    ABSTRACT: This paper presents the average block error rate (BLER) performance of star 16/64QAM schemes using iterative decision-directed channel estimation (IDDCE) associated with the turbo frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). We show that the turbo FDE with the IDDCE based on the a posteriori log-likelihood ratio (LLR) decreases the required average received signal-to-noise power ratio (SNR) compared to that based on the extrinsic LLR. We also show that the turbo FDE is effective in decreasing the required average received SNR considering the cubic metric (CM) compared to the linear minimum mean-square error based FF-FDE for star 16/64QAM schemes. Moreover, we show that the (8, 8) star 16QAM and (16, 16, 16, 16) star 64QAM schemes decrease the required average received SNR considering the CM at the average BLER of 10-2 by approximately 0.8 and 0.3 dB compared to the square 16QAM and 64QAM schemes, respectively, with a low turbo coding rate such as R = 1/3 when using the turbo FDE associated with IDDCE.
    No preview · Article · Jan 2014 · Journal of Communications
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    ABSTRACT: The interference rejection combining (IRC) receiver, which can strictly suppress intercell interference based on the minimum mean square error (MMSE) criteria, is effective in improving cell-edge user throughput. When assuming the Long Term Evolution (LTE) or LTE-Advanced downlink and open-loop transmit diversity employing the space–frequency block code (SFBC) using Alamouti coding, the IRC receiver must detect the Alamouti coded signals and suppress the interference signals using a couple of received signals in the frequency domain at the same time. To achieve this, the IRC receiver weight matrix, which consists of the channel matrix of the serving cell and the statistics of the covariance matrix, including the interference and thermal noise components, must be extended in the frequency domain, i.e., due to the effect of Alamouti coding, in addition to the spatial domain. These extended matrices can be estimated using the downlink reference signals (RSs) from the serving cell. However, some elements, including the effect of Alamouti coding in the extended covariance matrix, cannot be estimated using a practical estimation scheme that subtracts the replica symbols of the serving cell generated by the estimated channel matrix and the known RS sequence from the received RSs of the serving cell. This is because the RSs in LTE/LTE-Advanced are not transmitted using two adjacent subcarriers. This paper investigates the statistics of these unknown elements and proposes appropriate values, specifically inserting zero values, for these elements assuming the LTE/LTE-Advanced downlink. The results of simulations show that the IRC receiver using the proposed scheme, which has two receiver antenna branches, suppresses the intercell interference and improves the throughput by more than 10% compared with that for the conventional maximal ratio combining (MRC) receiver when a cell-edge environment is assumed.
    No preview · Article · Jan 2014 · IEEE Transactions on Vehicular Technology
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    ABSTRACT: This paper presents the average block error rate (BLER) performance for linear minimum mean-square error (LMMSE) based iterative decision-directed channel estimation (IDDCE) associated with the turbo frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the proposed IDDCE, estimated channel responses, which are used for weights of feed-forward and decision feedback FDEs, are iteratively updated using an accurate 2-dimensional LMMSE algorithm at each iteration of the turbo FDE. Through computer simulations, we clarify the best window size for the 2-dimensional LMMSE algorithm assuming the 9-path Extended Typical Urban (ETU) channel model and the maximum Doppler frequency of up to approximately 220 Hz. The computer simulations show that the 2-dimensional LMMSE based IDDCE is effective in decreasing the required average received signal-to-noise power ratio (SNR) satisfying the target average BLER for the turbo FDE in a frequency-selective Rayleigh fading channel with low-to-high maximum Doppler frequencies and with a wide range of root mean square delay spread values.
    No preview · Conference Paper · Oct 2013
  • Keita Miwa · Teruo Kawamura · Nobuhiko Miki · Mamoru Sawahashi
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    ABSTRACT: This paper presents the block error rate (BLER) performance of a posteriori log-likelihood ratio (LLR) computation methods at the output of a frequency domain equalizer (FDE) with antenna diversity reception using a low-rate turbo code for discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). In the paper, we propose an a posteriori LLR computation method based on the minimum squared Euclidean distance of the signal after coherently combining the FDE output of all receiver diversity branches. We compare the BLER performance level of the proposed LLR computation method to that for the conventional LLR computation method in which the a posteriori LLR is given as a summation of the minimum squared Euclidean distances of all receiver branches. In the BLER comparison, we consider the influences of noise correlation after frequency domain equalization and the channel estimation error. Computer simulation results show that the LLR computation using the signal after combining the receiver branches is more appropriate than the LLR computation with combining the squared minimum Euclidean distances in the probability domain with a low-to-high turbo coding rate as the a posteriori LLR at the FDE output associated with receiver diversity for DFT-precoded OFDMA.
    No preview · Conference Paper · Sep 2013
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    ABSTRACT: In Long-Term Evolution (LTE)-Advanced, heterogeneous networks where low power nodes such as picocells are overlaid onto macrocells were extensively investigated to improve further the system throughput per unit area. In heterogeneous networks, to achieve an offloading gain from macrocells to picocells, cell range expansion (CRE) is applied. Additionally, inter-cell interference coordination (ICIC) is applied to reduce the severe inter-cell interference transmitted from the macrocells to the sets of user equipment (UEs) connected to the picocells. In such cases, since the interference statistics are completely different from traditional well-planned macrocell deployments according to the parameters specified for CRE and ICIC, it is important to investigate using the interference rejection combining (IRC) receiver because it effectively improves the cell-edge user throughput by suppressing interference from the surrounding cells. To clarify the improvement in user throughput due to the IRC receiver, this paper investigates the interference statistics and evaluates the user throughput performance of the IRC receiver in heterogeneous networks employing CRE and ICIC. Simulation results show that the throughput gain from the IRC receiver becomes small due to a reduction in the severe inter-cell interference from ICIC. However, we clarify that a cell-edge user throughput gain from the IRC receiver exceeding 10% is achieved compared to the conventional minimum mean square error (MMSE) receiver in a heterogeneous network with four picocells within each macrocell. Furthermore, we show that the same parameters specified for CRE and ICIC can be set regardless of the IRC or conventional MMSE receiver.
    No preview · Conference Paper · Jun 2013
  • Akihito Morimoto · Nobuhiko Miki · Yukihiko Okumura
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    ABSTRACT: In Long-Term Evolution (LTE)-Advanced, heterogeneous networks are important to further improve the system throughput per unit area. In heterogeneous network deployment, low power nodes such as picocells are overlaid onto macrocells. In the downlink, the combined usage of inter-cell interference coordination (ICIC), which is a technique that reduces the severe interference from macrocells by reducing the transmission power or stopping the transmission from the macrocells, and cell range expansion (CRE), which is a technique that expands the cell radius of picocells by biasing the received signal power, is very effective in improving the system and cell-edge user throughput. In this paper, we consider two types of ICIC. The first one reduces the transmission power from the macrocells (referred to as reduced power ICIC) and the second one stops the transmission from the macrocells (referred to as zero power ICIC). This paper investigates the impact of the reduction in the transmission power when using reduced power ICIC and the restriction on the modulation scheme caused by the reduction in the transmission power when using reduced power ICIC on the user throughput performance with the CRE offset value as a parameter. In addition, the throughput performance when applying reduced power ICIC is compared to that when applying zero power ICIC. Simulation results show that the user throughput with reduced power ICIC is not sensitive to the protected subframe ratio compared to that with zero power ICIC even if the modulation scheme is restricted to only QPSK in the protected subframes. This indicates that reduced power ICIC is more robust than zero power ICIC for non-optimum protected subframe ratios.
    No preview · Article · Jun 2013 · IEICE Transactions on Communications
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    ABSTRACT: This paper proposes iterative decision-directed channel estimation (IDDCE) associated with the turbo frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). By using soft-symbol estimations based on the extrinsic log-likelihood ratio (LLR) at the Max-Log-MAP decoder output and for the reference signal (RS), the accuracy of the channel response is improved in the iterative inner loop employing the feed-forward (FF)-FDE at an iteration of the outer loop for the turbo FDE. Computer simulation results show that the improvement in the required average received signal-to-noise power ratio (SNR) that satisfies the target average block error rate (BLER) is saturated with two iterations for both inner and outer loops regardless of the modulation scheme. We also show that IDDCE using the FF-FDE based on the Minimum Mean-Square Error (MMSE) criterion at an iteration of the turbo FDE is effective in improving the average BLER of the turbo FDE.
    No preview · Conference Paper · Jan 2013
  • Akihito Morimoto · Nobuhiko Miki · Yukihiko Okumura
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    ABSTRACT: In Long-Term Evolution (LTE)-Advanced, heterogeneous networks are important to improve further the system throughput per unit area. In heterogeneous network deployment, low power nodes such as picocells are overlaid onto macrocells. In the downlink, the combined usage of inter-cell interference coordination (ICIC) that reduces the severe interference from macrocells and cell range expansion (CRE) that increases the offloading effect to picocells is very effective in improving the throughput performance. This paper investigates the impact of the reduction in the transmission power and the restrictions on the modulation scheme when using ICIC, which reduces the transmission power from the macrocell (referred to as reduced power (RP)-ICIC), on the user throughput performance. Simulation results show that the user throughput employing RP-ICIC is not sensitive to the protected subframe ratio compared to that employing ICIC, which stops the transmission from the macrocells (referred to as zero power (ZP)-ICIC), even if the modulation scheme is restricted to only QPSK in the protected subframes. This indicates that RP-ICIC is more robust than ZP-ICIC for a non-optimum protected subframe ratio. Keywords ?? LTE-Advanced, heterogeneous network, inter-cell interference coordination, cell range expansion
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: This paper investigates the dominant impact on the interference rejection combining (IRC) receiver due to the downlink reference signal (RS) based covariance matrix estimation scheme. When the transmission modes using the cell-specific RS (CRS) in LTE/LTE-Advanced are assumed, the property of the non-precoded GRS is different from that of the data signals. This difference poses two problems to the IRC receiver. First, it results in different levels of accuracy for the RS based covariance matrix estimation. Second, assuming the case where the CRS from the interfering cell collides with the desired data signals of the serving cell, the IRC receiver cannot perfectly suppress this CRS interference. The results of simulations assuming two transmitter and receiver antenna branches show that the impact of the CRS-to-CRS collision among cells is greater than that for the CRS interference on the desired data signals especially in closed-loop multiple-input multiple-output (MIMO) systems, from the viewpoint of the output signal-to-interference-plus-noise power ratio (SINR). However, the IRC receiver improves the user throughput by more than 20% compared to the conventional maximal ratio combining (MRC) receiver under the simulation assumptions made in this paper even when the CRS-to-CRS collision is assumed. Furthermore, the results verify the observations made in regard to the impact of inter-cell interference of the CRS for various average received signal-to-noise power ratio (SNR) and signal-to-interference power ratio (SIR) environments.
    No preview · Article · Dec 2012 · IEICE Transactions on Communications
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    ABSTRACT: This paper investigates an advanced receiver that employs two proposed interference rejection combining (IRC) modeling schemes, one for the covariance matrix and one for channel estimation errors. In a system performance evaluation, the link performance modeling of the IRC receiver, i.e., the output signal-to-interference-plus-noise power ratio (SINR) after IRC reception including the estimation errors, is very important in evaluating the actual performance of the IRC receiver in the system level simulation. This is because these errors affect the suppression of the interference signals for the IRC receiver. The results of simulations assuming the LTE-Advanced downlink with two transmitter and receiver antenna branches show that both proposed schemes accurately approximate the performance of the realistic IRC receiver, which estimates the covariance matrix and channel matrix of the serving cell based on the demodulation reference signal.
    No preview · Conference Paper · Dec 2012
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    ABSTRACT: This paper presents joint maximum likelihood detection (MLD) using channel coding information for orthogonal code division multiple access (CDMA) to decrease the required average received signal-to-noise power ratio (SNR) satisfying the target block error rate (BLER), and investigates the effect of joint MLD from the conventional coherent detection associated with channel coding. In the paper, we assume the physical uplink control channel (PUCCH) as specified in Release 8 Long-Term Evolution (LTE) by the 3rd Generation Partnership Project (3GPP) as the radio interface for the uplink control channel. First, we clarify the best scheme for combining correlation signals in two frequency-hopped slots and in two receiver diversity branches for joint MLD. Then, we show that the joint MLD without channel estimation, in which correlation signals are combined in squared form, decreases the required average received SNR compared to that for joint MLD with coherent combining of the correlation signals using channel estimation. Second, we show the effectiveness of joint MLD in terms of the decrease in the required average received SNR compared to the conventional coherent detection in various delay spread channels. Third, we present a comparison of the average BLER performance levels between cyclic shift (CS)-CDMA and block spread (BS)-CDMA using joint MLD. We show that when using joint MLD, BS-CDMA is superior to CS-CDMA due to a lower required received SNR in short delay spread environments and that in contrast, CS-CDMA provides a lower required received SNR compared to BS-CDMA in long delay spread environments.
    No preview · Article · Dec 2012 · IEICE Transactions on Communications
  • Keita Miwa · Teruo Kawamura · Nobuhiko Miki · Mamoru Sawahashi
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    ABSTRACT: This paper presented the average BLER performance using the combination of low-rate turbo code and codebook based transmit diversity associated with the IDDCE for DFT-precoded OFDMA. Computer simulation results showed that the average BLER of 10-2 for R = 1/15 (1/9) is achieved at the average received SNR of approximately -9.8 (- 8.2) and -11.8 (-10.4) dB for the NTx = 2- or 4-antenna codebook transmit diversity, respectively, with NRx = 4-antenna receiver diversity using the IDDCE. In conclusion, we confirmed the effectiveness of the combination of low-rate turbo code and codebook based transmit diversity using the IDDCE for achieving the very low required average received SNR satisfying the target average BLER.
    No preview · Conference Paper · Nov 2012
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    ABSTRACT: In orthogonal frequency division multiple access (OFDMA), time division multiplexing (TDM) based layer 1 (L1)/layer 2 (L2) control signals provide advantageous features such as a power saving effect using micro-sleep operation and a short round trip delay (RTD) for channel-dependent scheduling and adaptive modulation and coding (AMC) compared to a frequency division multiplexing (FDM) based structure. However, only a portion of the reference signal (RS) symbols is used for channel estimation assuming staggered RS multiplexing in order to obtain the merits of the TDM based control signals. Hence, this paper presents decision-feedback channel estimation (DFCE) methods using soft-symbol estimation for control signals for the TDM based control signals in the OFDMA downlink. In the proposed DFCE methods, channel estimation accuracy is improved by using soft-symbol estimation of the control signals based on the extrinsic log-likelihood ratio (LLR) at the soft output Viterbi algorithm (SOVA) for convolutional coding in addition to the RS symbols. Computer simulation results show that the required average received signal-to-noise power ratio (SNR) satisfying the average block error rate (BLER) of 10-2 using DFCE in the subframe of interest is decreased by approximately 0.6 dB compared to that for RS based channel estimation. Hence, we conclude that DFCE with soft-symbol estimation is very effective in improving the channel estimation accuracy using a limited number of RS symbols over the duration in which TDM based control signals are multiplexed, while maintaining the merits such as an efficient power saving effect using micro-sleep operation and a short processing delay.
    No preview · Conference Paper · Nov 2012
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    ABSTRACT: This paper presents the average block error rate (BLER) performance of the star 16QAM scheme using iterative decision-directed channel estimation (DDCE) for discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). The star 16QAM scheme achieves more efficient modulation compared to square 16QAM in that it decreases the actual required average received signal-to-noise power ratio (SNR) satisfying the target average BLER considering the peak-to-average power ratio (PAPR) of the transmitted signal for a low channel coding rate. Hence, the feature of the paper is that we apply iterative DDCE using soft-decision symbol estimation based on the log-likelihood ratio (LLR) of an extrinsic probability at the Max-Log-MAP (maximum a posteriori probability) decoder output to achieve an efficient modulation scheme with a low required average received SNR. Computer simulation results show that for the star 16QAM scheme, the average BLER using the iterative DDCE is very close to that with ideal channel estimation for a low channel coding rate such as an R = 1/3 turbo code. We also show that when iterative DDCE is employed, the (8, 8) star 16QAM scheme decreases the required average received SNR considering the cubic metric at the average BLER of 10-2 by approximately 0.7 dB compared to the square 16QAM scheme.
    No preview · Conference Paper · Oct 2012
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    ABSTRACT: This paper presents the performance of outer-loop control for adaptive modulation and coding (AMC) using mutual information (MI) based mapping between the block error rate (BLER) and received signal-to-interference plus noise power ratio (SINR) in the multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) downlink employing maximum likelihood detection (MLD). In AMC, we generate a mapping table between the BLER and MI per bit in advance, which is computed from the received SINR, assuming typical channel conditions including the path model and fading maximum Doppler frequency. Then, in the proposed outer-loop control, the measured MI per bit value for selecting the best modulation and coding scheme (MCS) is adjusted so that the measured BLER after turbo decoding satisfies the prescribed target value. Computer simulation results show that the outer-loop control achieves almost the same throughput as that with a mapping table assuming channel conditions identical to those for the actual measurement, while achieving nearly the identical target BLER. Moreover, we show that the best step size, which provides nearly the maximum throughput, differs according to the change in the maximum Doppler frequency in contrast to the relative feedback delay of the AMC loop. Nevertheless, it is insensitive to the target BLER value and frequency-selectivity of a channel model.
    No preview · Conference Paper · May 2012
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    ABSTRACT: The interference rejection combining (IRC) receiver, which can suppress inter-cell interference, is effective in improving the cell-edge user throughput. The IRC receiver is typically based on the minimum mean square error (MMSE) criteria, which requires highly accurate channel estimation and covariance matrix estimation that includes the inter-cell interference. To do this, the channel estimation and covariance matrix must be averaged within a subframe, i.e., 1 msec. However, the source of the inter-cell interference is changed within one subframe of the covariance matrix estimation due to the change in the user allocation at the interfering cells if asynchronous networks are employed. This affects the performance gain of the IRC receiver. This paper investigates the impact on asynchronous networks and the gain from the IRC receiver in terms of the downlink user throughput performance. Simulations results based on a 57-cell model environment, i.e., a cellular environment in the LTE-Advanced downlink, show that the IRC receiver which has two antenna branches effectively suppresses the inter-cell interference even when asynchronous networks are employed.
    No preview · Conference Paper · May 2012
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    ABSTRACT: This paper investigates the application of inter-cell interference coordination (ICIC) in heterogeneous networks for the LTE-Advanced downlink where picocells are overlaid onto macrocells. In LTE-Advanced, in order to perform ICIC, almost blank subframes (ABSs) are employed, where only the cell-specific reference signal (CRS) is transmitted to protect the subframes in the picocells from severe interference from the macrocells. Furthermore, multicast/broadcast over single-frequency network (MBSFN) subframes are employed to reduce the interference of the CRS on the data channel, although the control channel still suffers from interference from the CRS. When the cell range expansion (CRE), which offload the UEs from macrocells to picocells, is used to improve the system performance, the influence from the CRS increases. In order to assess the influence, the required CRE bias to improve the data channel is investigated based on a system-level simulation under various conditions such as the number of picocells, the protected subframe ratio, and the user distribution. The simulation results show that the cell-edge user throughput is improved with the CRE bias of more than 8dB, employing ABSs. Furthermore, simulation results show that one dominant source of interference is observed for the sets of user equipment (UEs) connected to the picocells via CRE with such a bias value. Based on observation, the influence that the CRS has on the control channel, i.e., physical control format indicator channel (PCFICH), and physical downlink control channel (PDCCH) is investigated based on a link-level simulation combined with a system-level simulation. The simulation results show that protecting the PCFICH is very important compared to protecting the PDCCH, since the block error rate (BLER) performance of the PCFICH becomes worse than the required BLER of 10-3 to support various conditions, although the BLER performance of the PDCCH can exceed the required BLER of 10-2 by spanning the PDCCH over three OFDM symbols.
    No preview · Article · Apr 2012 · IEICE Transactions on Communications
  • K. Miwa · T. Kawamura · N. Miki · M. Sawahashi
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    ABSTRACT: Single-carrier (SC)-Frequency Division Multiple Access (FDMA) using discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA) achieves flexible orthogonal multi-access in the frequency domain while retaining a low peak-to-average power ratio (PAPR). Although the two types of transmission schemes are evaluated including localized and distributed transmissions, only the localized transmission is adopted in the shared channel carrying user traffic data in the Release 8 Long-Term Evolution (LTE). This paper proposes distributed transmission with affinity to resource block (RB) based resource assignment in order to gain the frequency diversity effect for DFT-precoded OFDMA in a frequency-selective fading channel. We apply iterative decision-directed channel estimation (DDCE) to the RB based distributed transmission to decrease the channel estimation (CE) error, which is a major impairment to distributed transmission. We present a comparison based on the average block error rate (BLER) performance levels between the RB based distributed and localized transmission schemes without and with intra-subframe frequency hopping (FH). Through extensive simulation evaluations, we show the effectiveness of the RB based distributed transmission associated with the iterative DDCE in decreasing the required average received SNR satisfying the target average BLER compared to the localized transmission.
    No preview · Conference Paper · Jan 2012
  • Source
    Moo Ryong Jeong · Nobuhiko MIKI
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    ABSTRACT: Scheduling restriction is attracting much attention in LTE-Advanced as a technique to reduce power consumption and network overhead in interference coordinated heterogeneous networks (HetNets). Such a network with inter-cell interference coordination (ICIC) provides two radio resources with different channel quality statistics. One of the resources is protected (unprotected) from inter-cell interference (hence, called protected (non-protected) resource) and has higher (lower) average channel quality. Without scheduling restriction, the channel quality feedbacks would be doubled to reflect such quality difference of the two resources. We present a simple scheduling restriction scheme that addresses the problem without significant performance degradation. Users with relatively larger (smaller) average channel quality difference between the two resources are scheduled in the protected (non-protected) resource only, and a boundary user, determined by a proportional fair resource allocation (PFRA) under simplified static channels, is scheduled on either of the two resources or both depending on PFRA. Having most users scheduled in only one of the resources, power consumption and network overheads that would otherwise be required for the channel quality feedbacks on the other resource can be avoided. System level simulation of LTE-Advanced downlink shows that the performance degradation due to our scheduling restriction scheme is less than 2%, with the average feedback reduction of 40%.
    Preview · Conference Paper · Jan 2012

Publication Stats

247 Citations
6.06 Total Impact Points

Institutions

  • 2012-2015
    • Kagawa University
      Takamatu, Kagawa, Japan
  • 2000-2013
    • NTT DOCOMO
      Edo, Tōkyō, Japan
  • 2009-2012
    • Tokyo City University
      • Division of Information Engineering
      Edo, Tōkyō, Japan
  • 2006
    • Musashi Institute of Technology
      Edo, Tōkyō, Japan
  • 2004
    • NTT DATA Corporation
      Edo, Tōkyō, Japan