Nobuhiko Miki

NTT DOCOMO, Edo, Tōkyō, Japan

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Publications (49)2.06 Total impact

  • [Show abstract] [Hide abstract]
    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.
    IEEE Transactions on Vehicular Technology 01/2014; 63(1):191-203. · 2.06 Impact Factor
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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.
    Wireless Communications & Signal Processing (WCSP), 2013 International Conference on; 01/2013
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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.
    Wireless Personal Multimedia Communications (WPMC), 2013 16th International Symposium on; 01/2013
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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.
    Vehicular Technology Conference (VTC Fall), 2013 IEEE 78th; 01/2013
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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
    Wireless Conference (EW), Proceedings of the 2013 19th European; 01/2013
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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.
    Signal Processing Advances in Wireless Communications (SPAWC), 2013 IEEE 14th Workshop on; 01/2013
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    ABSTRACT: This paper presents the average block error rate (BLER) performance of star 32/64QAM schemes employing a frequency domain equalizer (FDE) with the BLER performance of the cross 32QAM or square 64QAM scheme as a reference in discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). The star QAM scheme has an advantageous feature in that the fluctuation in the amplitude component is smaller than that for the cross or square QAM scheme. The feature of the paper is that we focus on the actual received signal-to-noise power ratio (SNR) taking into account a realistic peak-to-average power ratio (PAPR) measure called the cubic metric (CM) considering the non-linearity of the power amplifier. Link-level computer simulation results show that the star QAM constellation with independent bit mapping for the phase and amplitude modulations achieves a lower required average received SNR considering the CM compared to that with the minimum Euclidian distance but with composite mapping of the phase and amplitude modulations. Through extensive link-level simulations, we show the potential benefit of the star 32/64QAM schemes in terms of reducing the required average received SNR considering the CM that satisfies the target average BLER compared to the cross 32QAM or square 64QAM scheme.
    Wireless Personal Multimedia Communications (WPMC), 2012 15th International Symposium on; 01/2012
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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.
    Wireless Communication Systems (ISWCS), 2012 International Symposium on; 01/2012
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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.
    IEICE Transactions on Communications. 01/2012; E95.B(4):1208-1217.
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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.
    Vehicular Technology Conference (VTC Spring), 2012 IEEE 75th; 01/2012
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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.
    Wireless Information Technology and Systems (ICWITS), 2012 IEEE International Conference on; 01/2012
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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.
    Wireless Personal Multimedia Communications (WPMC), 2012 15th International Symposium on; 01/2012
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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.
    Vehicular Technology Conference (VTC Spring), 2012 IEEE 75th; 01/2012
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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.
    Wireless Communications & Signal Processing (WCSP), 2012 International Conference on; 01/2012
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    ABSTRACT: In Long-Term Evolution (LTE)-Advanced, heterogeneous networks where femtocells and picocells are overlaid onto macrocells are extensively discussed in addition to traditional well-planned macrocell deployments to improve further the system throughput. In heterogeneous networks, cell range expansion (CRE), which is a technique for expanding the cell radius of picocells by biasing the handover criteria, is applied so that the UEs will more frequently select the picocells. This paper investigates the transmission power control (TPC) method in the heterogeneous networks that employ CRE and evaluates the cell-edge user throughput and cell throughput performance. Simulation results (4 picocells and 25 UEs are located within 1 macrocell and the difference in transmission power between the macrocell and picocells is 16 dB) show that almost the same cell-edge user throughput is obtained by setting the appropriate difference in the target received signal power between the macrocell and picocells according to the CRE offset value.
    European Wireless, 2012. EW. 18th European Wireless Conference; 01/2012
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    ABSTRACT: In order to support efficiently Voice over IP (VoIP) traffic using semi-persistent scheduling in the Long-Term Evolution (LTE) uplink, frequency hopping (FH) should be applied to obtain a frequency diversity gain. In addition, subframe bundling (SFB) is also effective for improving the received signal quality of users in the vicinity of the cell edge. However, since a resource block (RB) allocation for the SFB with FH becomes widely dispersed, it might be difficult to utilize fully and densely whole RBs in a system bandwidth when simultaneously allocating the RBs to both users with and without employing SFB. Therefore, in this paper, two methods that enable dense RB allocation are proposed, which are referred to as SFB priority allocation and interlaced allocation. These two methods are evaluated in a system level simulation in a mixed traffic scenario of VoIP and non real-time traffic, taking into account the constraint of signaling overhead. Simulation results show that the two methods can increase the VoIP capacity by about 10% compared to a straightforward manner that simply allocates RBs based on the frequency index of RBs regardless of whether or not SFB is applied. In addition, it is shown that the Interlaced allocation can further increase the VoIP capacity compared to SFB priority allocation.
    14th International Symposium on Wireless Personal Multimedia Communications, WPMC 2011, Brest, France, October 3-7, 2011; 01/2011
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    ABSTRACT: With considerable interest being garnered in recent years, femto-cells are seen as a major contender to significantly increase capacity and fill coverage holes in rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) cellular networks. User- deployed femto-cells, each exclusively serving a set of registered users and sharing the same frequency spectrum as the overlay macro-cells are already defined in 3GPP specifications. Such a co- channel and random deployment of femto-cells can cause heavy downlink (DL) interference to a user equipment (UE) in the vicinity of one or more femto-cells and not belonging to their closed subscriber groups (CSGs). In this paperwe focus on protection of the most important LTE DL control channel, known as the physical control format indicator channel (PCFICH). Failure to decode this channel correctly results in the loss of the subsequent subframe. A technique which mitigates femto-to-macro PCFICH interference by carefully manipulating the physical cell identity (PCI) of the aggressor femto-cell is presented. It is shown that employing this technique results in a significant improvement of PCFICH effective signal- to- interference-plus-noise ratio (SINR) without the need for any additional network signaling.
    Proceedings of the 74th IEEE Vehicular Technology Conference, VTC Fall 2011, 5-8 September 2011, San Francisco, CA, USA; 01/2011
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    ABSTRACT: In Long-Term Evolution-Advanced (LTE-A), which is currently in the process of standardization in the rd generation partnership project (3GPP), carrier aggregation (CA) was introduced as a main feature for bandwidth extension while maintaining backward compatibility with LTE Release 8 (Rel. 8). In the CA mode of operation, since two or more component carriers (CCs), each of which is compatible with LTE Rel. 8, are aggregated, mobility management for CCs such as inter/intra-frequency handover, CC addition, and CC removal is needed to provide sufficient coverage and better overall signal quality. Therefore, the signaling overhead for Radio Resource Control (RRC) reconfiguration for the mobility management of CCs in LTE-A is expected to be larger than that in LTE Rel. 8. In addition, CA allows aggregation of cells with different types of coverage, and therefore, the signaling overhead might be dependent on the coverage of each CC assumed in a CA deployment scenario. This paper presents evaluation results on the CC control overhead with several CC management policies in some CA deployment scenarios, and shows that the increase in the control overhead is not significant even in a CA deployment scenario with overlaid picocells.
    Proceedings of the 74th IEEE Vehicular Technology Conference, VTC Fall 2011, 5-8 September 2011, San Francisco, CA, USA; 01/2011
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    ABSTRACT: This paper proposes a hybrid reference signal (RS) multiplexing scheme that employs a block spread (BS) and cyclic shift (CS) combination for the physical uplink control channel (PUCCH) in the Long-Term Evolution (LTE) uplink. In the proposed scheme, we give higher priority to BS multiplexing over the FFT blocks assigned to a RS within a slot than CS multiplexing. Hence, accurate channel estimation for coherent detection is achieved by shortening the despread interval in the frequency domain compared to the original multiplexing scheme using only CS to extract the channel estimate of each code channel. Computer simulation results show that, assuming the use of channel quality indicator (CQI) bits, the average received signal-to-noise power ratio (SNR) satisfying the required average block error rate when employing the proposed hybrid RS multiplexing is decreased compared to that for conventional RS multiplexing using only CS when the root mean square delay spread is longer than approximately 0.5 μsec particularly for a large number of multiplexed PUCCHs such as 12.
    01/2011;
  • Keita Miwa, Nobuhiko Miki, Mamoru Sawahashi
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    ABSTRACT: A low-rate turbo code can reduce the required average received signal-to-noise power ratio (SNR) that satisfies the target block error rate (BLER) due to its high coding gain. When a low-rate turbo code is used however, channel estimation (CE) error becomes a bottleneck in bringing out the potential coding gain. Therefore, this paper presents the average BLER performance using decision-directed channel estimation (DDCE) for a low-rate turbo code in orthogonal frequency division multiplexing (OFDM). In the proposed DDCE, we employ 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 in addition to reference signals (RSs). The DDCE works synergistically with the low-rate turbo code, since the extrinsic LLR at the Max-Log-MAP decoder becomes more reliable due to the increasing coding gain. Computer simulation results show that when the turbo code with R = 1/15 (1/9) and the constraint length of K = 4 bits is used, the required average received SNR at the average BLER of 10−2 using the DDCE is decreased by approximately 1.2 (1.2) dB compared to that for the RS based CE. As a result, the required average received SNR using the DDCE for R = 1/15 and 1/9 is decreased by approximately 6.0 and 4.4 dB, respectively, compared to that for R = 1/3.
    01/2011;