大森 達也

Multi-user multi-input multi-output (MU-MIMO) can achieve more transmission speed and multi-user diversity. Furthermore, since frequency symbol spreading (FSS) can mitigate the effect of frequency selective fading, it is useful for improving the BER performance. However, FSS cannot be applied to MIMO system with adding forward error correction (FEC) due to interference of the transmit antennas. In this paper, we consider the difference of the transmitted power for each user and the difference of the distance from base station (BS) to each user in general mobile wireless communications, we propose that applying FSS and adaptive subcarrier block (ASB) method with considering the imbalanced transmitted power for MU-MIMO. From the simulation results, it is shown that the proposed scheme can achieve a superior BER and throughput performance.

Massive MIMO has been recognized as promising ways to provide high speed data transmission. However, since the number of pilot symbol is proportionally depending on the number of transmit antenna, the total transmission rate of massive MIMO would be degraded. To solve this problem, channel estimation by virtual pilot signal (VPS) with a few pilot signals has been proposed. However, since the conventional method iteratively identifies the channel state information (CSI), the complexity is considerable work. Then again, time-frequency interferometry (TFI)-OFDM has been proposed. This method can achieve a good BER performance with a few pilot symbols. In this paper, we propose a novel channel compensation based on VPS and TFI for massive MIMO without increasing the system complexity. The proposed scheme has a low complexity, with improving BER performance to compared with the conventional method using linear interpolation and FFT/IFFT after specific operations. From the simulation results, the proposed scheme can improve BER performance to compared with the conventional method in 4 × 4 and 8 × 8MIMO systems.

Recently, visible light communication(VLC) is widely researched due to the spreading of LED usage. It satisfies demands of ubiquity and high speed communication. However, it is impossible to transmit the phase information and frequency information due to limitation of LED. From this reason, the achievable transmission rate is worse than that of wireless communications. To solve this problem, color clustered MIMO(multiple-input multiple-output) system that takes advantage of independency of the three primary colors of the light has been proposed. However, color filters which use on this system are supposed ideal one that extracts only a desired signal. Realistic color filters have the incompleteness which extract signals except a desired signal. Therefore, in this paper, we evaluate and clarify the spatial performance of color clustered VLC-MIMO system with incompleteness of color filters.

At present, the theory and algorithm of wireless indoor positioning systems have been widely researched. Some applications of these systems have been successfully used such as inventory management. Nevertheless, positioning using radio signals indoor is subject to multipath propagation and other causes. Therefore, how to determine the location accurately has been recognized as a difficult task. This paper focuses on one of the positioning methods called received signal strength indication(RSSI) in a Wireless Local Area Network(WLAN). To improve the positioning accuracy, we proposed a scheme which to estimate the distance between access point(AP) and mobile station(MS) using the average of pilot signal strength in frequency domain. We then propose another scheme to estimate the position of the MS based on the estimated distances. At last, the simulations results show that the proposed schemes has a higher degree accuracy compared with the conventional methods.

Wireless visible light communication system uses LED illumination for data transmission. It is important for a performance index to evaluate a variation of communication quality with the number of users. Although CDMA (Code Division Multiple Access) is a representative of a conventional multiple access in a wireless communication, the maximum number of users is limited due to the length of the spread code, ISI (Inter-Symbol Interference) and MAI (Multiple Access Interference). To solve these problems, we propose the OFDM-IDMA (Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access), which has robustness for the above-mentioned problems. Moreover, we can improve the robustness by using multi carrier modulation. Therefore we apply the OFDM-IDMA system to visible light communication system. The simulation result shows that BER performance of an optical OFDM-IDMA with multiuser situation is the approximately same as that of single user.

A direct-conversion receiver (DCR) can reduce the power consumption and cost. However, a DCR with orthogonal frequency-division multiplex (OFDM) suffers from IQ imbalance. Until this time, many algorithms have been proposed to compensate IQ imbalance in OFDM systems. However, the calculation complexity is still a considerable work to achieve the implementation of a DCR. Moreover, an accurate channel identification is also necessary for a DCR. Recently, time-frequency interferometry-OFDM (TFI-OFDM) system has been proposed to achieve an accurate channel identification property with small number of pilot symbols, and it has a periodicity of pilot amplitude. In this paper, we focus on the feature of TFI and propose a novel IQ imbalance estimation and compensation schemes using TFI-OFDM system. In the proposed system, by using the feature of the TFI pilot symbols, we can identify an IQ imbalance without high calculation complexity. Furthermore, by using subcarrier selection, the influence of the noise power can be reduced. From the simulation results, the proposed scheme can achieve the low complexity for IQ imbalance estimation and compensation without a degradation of the bit error rate performance. A direct-conversion receiver (DCR) can reduce the power consumption and cost. However, a DCR with orthogonal frequency-division multiplex (OFDM) suffers from IQ imbalance. Until this time, many algorithms have been proposed to compensate IQ imbalance. However, the calculation complexity is still a considerable work to achieve the implementation of a DCR. Moreover, an accurate channel identification is also necessary for a DCR. Recently, time-frequency interferometry-OFDM (TFI-OFDM) system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we focus on the feature of TFI and propose a novel IQ imbalance estimation and compensation schemes using TFI-OFDM system. In the proposed system, by using the feature of the TFI pilot symbols, we can identify an IQ imbalance without high calculation complexity. Furthermore, by using subcarrier selection, the influence of the noise power can be reduced. From the simulation results, the proposed scheme can achieve the low complexity for IQ imbalance estimation and compensation without a degradation of the bit error rate performance.

Visible light communication has been attracted attention because of its ubiquitous and safety. However, faults of LED communication are that the value of optical power shows nonlinear characteristic to input current and the Peak to Average Power Ratio (PAPR) characteristic deteriorates. To reduce the PAPR, we propose a PAPR reduction method by applying adaptive clipping with adding a peak mitigate signal. We also propose a performance enhancement by applying Frequency Symbol Spreading (FSS) and Priority Power selection (PPS) to improve the BER performance. With the proposed method, we achieve a significant PAPR reduction as large as 8dB compared with the conventional VLC-OFDM.

近年、更なる高速・大容量の無線通信システムを実現するため、マルチユーザMIMO技術の研究開発が盛んに行っている。マルチユーザMIMOシステムのダウンリンク(基地局から各ユーザ端末への伝送)においては、通常、各ユーザ端末で他ユーザの干渉波を分離できないため、基地局ではマルチビームをウェイト制御することが重要である。先行研究として提案されているプリコーディング技術は、干渉成分が完全に除去できず、システムの性能が劣化する問題があった。また、ビーム・フォーミング技術として、重み係数を計算する手法としてSMI(sample matrix inversion)法が提案されているが、計算量が大きく、高速処理ができない問題がある。本研究ではマルチユーザMIMOのダウンリンクにおいてビーム・フォーミング技術として広く利用されているSMI法を改善し、低演算・高速処理が可能な新しいビーム・フォーミング法を提案する。提案法は、各ユーザの信号を分離し、共分散を計算することで、重み係数を決めず、各ユーザの信号分離の前に共分散を計算する共通共分散SMI法を提案する。提案共通共分散SMI法はSMI法と同じ演算量を持つが、重み係数をまとめて一回計算すればよいので、高速処理ができる。送信アンテナ4本の基地局から受信アレーアンテナ4本の移動端末4ユーザへ伝送することを想定し、シミュレーシュンを行い、従来手法と比較した結果、提案共通共分散SMI法は従来SMI法とくらべ優れたBER特性を実現することができ、その有効性を示すことができる。

The symbol timing synchronization inaccuracy can bring about phase offset (FO), inter-symbol interference (ISI) and inter-channel interference (ICI). To overcome these shortcomings as much as possible, in this paper, a novel symbol timing synchronizer is proposed for orthogonal frequency division multiplexing (OFDM) systems based on the properties of PN sequences. By utilizing four identical blocks with inverted signs of the latter two blocks and two different PN sequences with the same period as weighted factors to ensure that the metric function has impulse-like shape at correct timing position without any burst side-peaks. It is demonstrated by the computer simulations that the proposed scheme achieves accurate timing offset estimation with smaller error mean (EM) and standard deviation (SD) compared with the existing method under flat-fading channels. When it is subjected to frequency-selective fading channels, in spite of some unsatisfactory results when Fast Fourier Transform (FFT) window size is small, the performance is relatively better than others with the increases of FFT window size referring to 3GPP LTE specifications.

In this paper, we propose a polarization diversity scheme to enhance maritime VHF communications. Multiple antenna systems require an antenna separation of 5-10 wavelengths to keep the correlation coefficient below 0.7 to permit the realization of space diversity. However, this may be difficult to implement in a maritime VHF system, because the maritime VHF is working in the frequency range from 156 to 174 MHz, with wavelength of approximately 2 m. On the other hand, the polarization device technique allows two colocated antennas by using a micro-strip technique. For this reason, the polarization technique is a practical method of attaining diversity. However, the theoretical model of polarization is very difficult and complex. Therefore, we express the cross correlation of each polarization antenna and the cross polarization discrimination of multiple polarization antennas with a simple model. Simulations show that the polarization diversity of a maritime VHF system shows better BER performance than that of the conventional reception diversity on the basis of vertical antenna with the antenna separation of 10 wavelengths.

In recent, orthogonal frequency division multiple access (OFDMA) has been used for a multiuser wireless communication. In a wireless network, the transmitted signal of each user has independent channel fluctuation characteristic. By using this characteristic, OFDMA can achieve the multiuser diversity (MUDiv). Until this time, to achieve a low complexity and performance improvement, the adaptive subcarrier block (ASB) and frequency symbol spreading (FSS) methods have been proposed. However, the system performance in a low Eb/N0 is worse than that of maximal sum capacity (MSC) and peak to average power ratio (PAPR) does not decrease greatly. To solve these problems, in this paper, we propose the subcarrier allocation with the power priority selection (PSS) and the adaptive clipping (AC) with the peak reduction signal to improve the system and PAPR performance.

正帰還回路を用いた中心周波数及び帯域幅を任意に設定できる高周波再帰型高次フィルタが提案されている.本論文では再帰型高次フィルタの中心周波数と比帯域幅の自動設定手法について検討した.まず試作した高周波リコンフィギャラブルフィルタチップを用いて高次フィルタの合成実験を行った.2次の伝達関数を有する再帰型フィルタコアの周波数特性を合成することで4次バタワースバンドパスフィルタ特性を得ることに成功し,この特性が広範囲で連続的に可変であることがわかった.次に,再帰型フィルタコアの中心周波数及び比帯域幅の自動設定手法について提案した.提案した自動設定手法を試作再帰型高次フィルタに実装し動作実験を行い,その有効性を示した.最後に,再帰型4次フィルタの周波数特性の自動設定手法について提案した.提案した自動設定手法を実装し動作実験を行い,その有効性を示した.

A direct-conversion receiver (DCR) can reduce the power consumption and cost. However, a DCR in Orthogonal frequency division multiplexing (OFDM) systems suffer from IQ imbalance and Carrier Frequency Offset (CFO). Until this time, many algorithms are proposed to compensate IQ imbalance and CFO in OFDM. However, it is insufficient for the joint IQ imbalance and CFO estimation. On the other hand, timefrequency interferometry-OFDM (TFI-OFDM) system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we focus on the channel identification property of TFI-OFDM and propose the novel IQ imbalance and CFO estimation schemes. In the proposed system, by using the feature of the TFI pilot symbols, we can identify an IQ imbalance in the presence of CFO, and the influence of the noise power can be mitigated by subcarrier selection. Moreover, by using autocorrelation of the TFI pilot symbols, we can estimate CFO after IQ imbalance estimation. From the simulation results, the proposed scheme can estimate IQ imbalance and CFO and compensate without a significant degradation of the BER performance.

A direct- conversion receiver (DCR)reduces the power consumption and cost. However, DCR in Or-thogonal frequency division multiplex (OFDM)systems suffer from IQ imbalance. Until this time, many algorithms are proposed to compensate IQ imbalance in OFDM. However, the complexity is still considerable work. 0n the other hand, time- frequency interferometry-OFDM (TFI-OFDM)system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we propose a novel IQ imbalance estimation and compensation scheme using TFI-OFDM system. In the proposed system, by using the feature of the TFI pilot symbols, we can identify IQ imbalance without high calculation complexity. Furthermore, by using subcarrier selection, the influence of the noise power can be reduced. From the simulation results, the proposed scheme can achieve the low-complexity IQ imbalance estimation and compensation without a degradation of the BER performance.

Recently, the wireless communication technology is required to carry a large amount of digital infer- mation with spread of the mobile phone and wireless LAN. Space Division Multiplex (SDM)system has actively studied for increasing the channel capacity. However, SDM requires a signal identifying technique at the receiver in order to identify each transmission stream. Although Maximum Likelihood Detection (MLD)shows the best BER performance, it requires prohibitively large amount of computation to implement at the receiver. To mitigate the above mentioned problems, we have proposed the sequential decision algorithm for QRM-MLD in order to reduce the computation without performance deterioration. However, the number of computation of the proposed system is l by 10 as much as conventional MLD and still remained the BER degradation. Thus, for improving the performance of the proposed system, we propose the branch cutting method with channel ranking. Prom the simulation results, the number of the proposed method computation is aproximately an half as much ELS the conventional sequential decision algorithm.

STBC is a technique to achieve transmit diversity. QO-STBC is full rate STBC constructed from relaxing orthogonality, and requires a decoder to search symbol pairs with ML decoding. Motivated by this, we have proposed single symbol decodable QO-STBC with full diversity. This code achieves full transmit rate and 10w system complexity. However, the proposed QO-STBC can achieve a throughput performance like SISO. In order to exploit the advantages of single symbol decodable QO-STBC, the combination of the proposed QO-STBC and adaptive modulation has been considered. The system performances of non-adaptive QO-STBC, adaptive single symbol decodable QO-STBC are evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of non-adaptive QO-STBC system.

A direct- conversion receiver (DCR)reduces the power consumption and cost. However, DCR in Or-thogonal frequency division multiplex (OFDM)systems suffer from IQ imbalance. Until this time, many algorithms are proposed to compensate IQ imbalance in OFDM. However, the complexity is still considerable work. 0n the other hand, time- frequency interferometry-OFDM (TFI-OFDM)system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we propose a novel IQ imbalance estimation and compensation scheme using TFI-OFDM system. In the proposed system, by using the feature of the TFI pilot symbols, we can identify IQ imbalance without high calculation complexity. Furthermore, by using subcarrier selection, the influence of the noise power can be reduced. From the simulation results, the proposed scheme can achieve the low-complexity IQ imbalance estimation and compensation without a degradation of the BER performance.

STBC is a technique to achieve transmit diversity. QO-STBC is full rate STBC constructed from relaxing orthogonality, and requires a decoder to search symbol pairs with ML decoding. Motivated by this, we have proposed single symbol decodable QO-STBC with full diversity. This code achieves full transmit rate and 10w system complexity. However, the proposed QO-STBC can achieve a throughput performance like SISO. In order to exploit the advantages of single symbol decodable QO-STBC, the combination of the proposed QO-STBC and adaptive modulation has been considered. The system performances of non-adaptive QO-STBC, adaptive single symbol decodable QO-STBC are evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of non-adaptive QO-STBC system.

近年,直交周波数分割多重アクセス(OFDMA)が複数端末への無線通信で適用されている.無線通信では,ユーザー毎にチャネルは独立している.この特性を利用しシステム特性を向上させる方法をマルチユーザーダイバーシティ(MUDiv)と呼び,0FDMAと組み合わせたMUDiv/OFDMAが提案されている.これまでに,MUDiv/OFDMAに対して低演算量を実現するブロック選択法(ASB)と,システムの特性を向上させる周波数シンボル拡散法(FSS)が提案されている.しかしながら,これらの手法ではEb/No)が小さい場合,ブロックを用いない最良選択法(MSC)と比べBERは劣化し,ピーク対平均電力比(PAPR)も大きく改善されない.これらの問題を解決するために,本論文は電力優先配置(PPS)とピーク軽減信号による適応クリッピング(AC)を行い,BERとPAPRの両方を改善する方法を提案する.

MIMO-OFDMではガードインターバル(GI)を超える超遅延波が生じた場合にシステム特性が著しく劣化することが知られている.これは超遅延波により各シンボルにおいてシンボル間干渉(ISI)とキャリア間干渉(ICI)が生じるためである.スキャッタードパイロット(SP)を用いた場合にはパイロット信号にもISIとICIが生じるためにチャネル状態情報(CSI)を正しく推定できない.本研究では並列レプリカを用いた干渉一括補償法を提案する.受信信号と推定したチャネル応答から受信パケットのISI成分とICI成分の並列レプリカ信号を作成する.受信信号からレプリカ信号を差し引くことで干渉を補償する.SPを抜き出して再度チャネル推定を行う.最後に再度推定したCSIを用いて補償後の受信信号に等化処理を行い信号を検波する.

Recently, the wireless communication technology is required to carry a large amount of digital infer- mation with spread of the mobile phone and wireless LAN. Space Division Multiplex (SDM)system has actively studied for increasing the channel capacity. However, SDM requires a signal identifying technique at the receiver in order to identify each transmission stream. Although Maximum Likelihood Detection (MLD)shows the best BER performance, it requires prohibitively large amount of computation to implement at the receiver. To mitigate the above mentioned problems, we have proposed the sequential decision algorithm for QRM-MLD in order to reduce the computation without performance deterioration. However, the number of computation of the proposed system is l by 10 as much as conventional MLD and still remained the BER degradation. Thus, for improving the performance of the proposed system, we propose the branch cutting method with channel ranking. Prom the simulation results, the number of the proposed method computation is aproximately an half as much ELS the conventional sequential decision algorithm.

STBC is a technique to achieve transmit diversity. QO-STBC is full rate STBC constructed from relaxing orthogonality, and requires a decoder to search symbol pairs with ML decoding. Motivated by this, we have proposed single symbol decodable QO-STBC with full diversity. This code achieves full transmit rate and low system complexity. However, the proposed QO-STBC can achieve a throughput performance like SISO. In order to exploit the advantages of single symbol decodable QO-STBC, the combination of the proposed QO-STBC and an adaptive modulation has been considered. The system performances of non-adaptive QO-STBC, adaptive single symbol decodable QO-STBC are evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of non-adaptive QO-STBC system. © 2013 IEEE.

Orthogonal frequency division multiplexing (OFDM) based on scattered pilot (SP) can accurately estimate the channel state information (CSI) with small number of pilot signals under the fast fading channel. In fact, the channel response at a particular subcarrier frequency is not supposed to be totally different from its neighboring frequencies, and they must have correlation which depends on the coherence bandwidth of channel. Therefore, the frequency separation of SP should smaller than the coherence bandwidth. However, when the maximum delay spread exceed the length of GI, unacceptable degradation of error performance is caused by inter-symbol-interference (ISI) and inter-carrier-interference (ICI). Moreover, coherence bandwidth is also to be narrow. In this case, channel estimation of SP-OFDM based on the frequency interpolation is poorly operated due to narrow coherence bandwidth. To mitigate this problem, in this paper, we propose the novel time domain channel estimation scheme using a cyclic property of SP for OFDM. © 2013 GIRI.

In MIMO systems, maximum likelihood decoding (MLD) shows the best performance of all kinds of detections. However, the complexity of MLD exponentially increases with increasing the number of antenna branches and constellation size. Accordingly, it is impractical to use a full MLD without reducing its computational complexity, because it would be prohibitively large to implement. Recently, the use of QR decomposition with an M-algorithm (QRM-MLD) has been proposed to reduce the system complexity while maintaining the performance of the system. However, QRM-MLD performance depends on the surviving symbol replica candidates. To reduce this problem, in this paper, we propose the complexity reducing QRM-MLD with threshold method using the estimated noise variance. The proposed method shows the superior performance while maintaining the low complexity. From the simulation results, the proposed method achieves 1/10 complexity reduction compared with a full MLD for the threshold index kth = 3.3. © 2013 GIRI.

近年,無線通信では高速伝送の需要が増加している.しかしながら,セル端のように多地点の送信局から同時に信号を受信する環境下では,スループット特性が劣化する.この問題を解決するため,LTE-Advancedで提案されている多地点強調(CoMP: Coordinated Multipoint)送信を用いる.CoMP送信では,複数の送信局が協調して送信データを送ることによりシステム特性を向上させる.そこで本論文は, CoMP送信に準直交時空間ブロック符号(QO-STBC: Quasi-Orthogonal Space Time Block Code)を適用することによるセル端スループットの改善法を提案する.シミュレーション結果から,提案法は,時間的相関を無くす従来法よりもスループット特性が優れていることを示した.

In mobile communications, MIMO-OFDM transmission performance suffers severe degradation caused by the large delay spread channel greater than guard interval (GI). This is because the excess delay results in considerable inter-symbol interference (ISI) between adjacent symbols and inter-carrier-interference (ICI) among subcarrier in the same symbol. In the case of scattered pilot (SP), the interference of pilot signals causes the deterioration of channel estimation. In this paper, we propose the interference compensation scheme using the time domain replica signals.We make the time domain replica signals from detected signals and the excess channel impulse responses over GI. After compensation of the time domain replica signals and the received signals, we recalculate the channel state information (CSI) and the CSI is updated. Finally, we carry out the channel compensation with updated CSI for obtaining an accurate compensated signals. © 2013 IEEE.

In recent, orthogonal frequency division multiple access (OFDMA) has been used for a multiuser wireless communication. In a wireless network, the transmitted signal of each user has independent channel fluctuation characteristics. By using this characteristic, the multiuser diversity (MUDiv) can be obtained, and a MUDiv/OFDMA has been proposed. Until this time, to achieve a low complexity and performance improvement, the adaptive subcarrier block (ASB) and frequency symbol spreading (FSS) methods have been proposed. However, the system performance in a low Eb/N0 is worse than that of maximal sum capacity (MSC) and peak to average power ratio (PAPR) does not decrease greatly. To solve these problems, in this paper, we propose the subcarrier allocation with the power priority selection (PSS) and the adaptive clipping (AC) with the peak reduction signal to improve the system and PAPR performance. © 2013 IEEE.

弾性表面波(SAW)共振子を用いたRFフィルタは,小型,高性能であることから,移動体通信機器に広く用いられている.近年では,周波数資源を有効利用する観点から,ソフトウェア無線,コグニティブ無線の技術が注目されており,複数の周波数帯に適宜対応できるチューナブルRFフィルタへの要求が高まっている.SAW共振子を用いたチューナブルRFフィルタとして,様々なものが提案されているが,筆者らはラダー型SAWフィルタに可変容量を付加した構成を提案している.本報告では,さらに広く帯域を調整できるチューナブルRFフィルタを目指して,SAW共振子と可変容量を用いた新しい構成のフィルタについて検討した.

In a wireless network, the signals transmitted from one sender to different users have independent channel fluctuation characteristics. The diversity that exists between users is called multiuser diversity and can be exploited by the sender to enhance the capacity of wireless network. In multiuser diversity OFDMA system, exploiting channel fluctuation diversity is in essence done by selecting the user with the strong subcarrier channels. The individual subcarrier selection for each user can achieve the best system performance but high signaling overhead and high system complexity are required. On the other hand, the adaptive subcarrier block method achieves worse BER than that of individual subcarrier selection. This is because the selected block contains the poor channel subcarriers. To overcome this problem, in this paper, we propose an adaptive subcarrier block selection with frequency symbol spreading for an OFDMA system. © 2012 Elsevier Inc. All rights reserved.

スキャッタードパイロット(SP)-OFDMは少ないパイロット信号で正確にチャネル情報を推定できる.OFDMにおいてガードインターバル(GI)を超える超遅延波が存在する場合は遅延波によるシンボル間干渉(ISI)とキャリア間干渉(ICI)によりシステム特性が劣化する.さらにSPではパイロット信号間にデータ信号が存在するためISIとICIの影響を受けて正確なチャネル情報が得られない問題がある.本論文はパイロット信号の周期性を考慮したFFT補間法を用いたチャネル推定とレプリカ信号に基づくISIとICIの補償法を提案する.提案法はまず雑音分散を求めることにより閾値を決定し,最後に雑音を除去する.次にパイロット信号の周期性を考慮して時間領域で先行波と遅延波のパスのみを選ぶ.そしてFFTを用いてパイロット信号間を補間しCSIを推定する.最後に,受信信号からISIとICIを除去するために受信信号を検波したレプリカ信号を用いて干渉成分を除去する.シミュレーションから,超遅延環境において提案法は従来法と比較しBER特性が向上した.

MIMOシステムにおいて、最大尤度検波(MLD;Maximum Likelihood Detection)は最良のBER特性を示す検波手法であることが知られている.しかし、MLDはアンテナ本数や変調値の増加に対して演算量が指数的に増大してしまう問題がある.演算量の増大は処理遅延や消費電力の増加をもたらす.すでに提案されている低演算型QRM-MLDは演算量削減とBER特性がトレードオフの関係にあり、十分な演算量削減性能を得るためにはBER特性の劣化が避けられない,提案アルゴリズムは、まず最も生き残りシンボル候補が少ない形でのQRM-MLDを行い、その結果得られたシンボル候補に関して雑音分散値に基づくしきい値より判定を行う.判定の結果誤りとみなされた場合に、生き残りシンボル候補を新たに作り、判定を繰り返すことによってFull MLDと同等の特性を有するアルゴリズムである.提案システムにおいて、しきい値パラメータk_<th>=3.5で演算量1/10程度の削減を実現した.

近年,無線通信における多様なサービスを実現するためにETE-Advancedが規格化され,アップリンクではシングルキャリア周波数分割多重アクセス(SC-FDMA)が採用されている.無線通信では,送受信間のチャネルは変動し,チャネル歪みが大きい箇所では誤りが多くなる.この問題を解決するために,Waterfilling Power Allocation(WF/PA)が提案されている.無線通信における高品質化を実現するために,協調通信が近年幅広く研究されている.加えて,複数の中継局を利用した多重リレーはダイバーシティ効果をさらに向上させる.しかしながら,多重リレー環境の協調通信においてパケットを最適分割する方法は提案されていない。本論文は,WF/PA-SC-FDMAを用いた多重リレー協調通信におけるパケットの最適分割を提案し,性能向上を試みる.シミュレーション結果から,提案法はBER特性を向上させた.

Orthogonal space-time block code (OSTBC) can achieve full diversity with a simple MLD, but the rate of OSTBC only achieves 3/4 of the maximum rate when applying more than two transmit antennas. To solve this problem, a quasi-orthogonal STBC (QOSTBC) scheme has been proposed. Even though a QOSTBC scheme can achieve the full rate, there are interference terms resulting from neighboring signals during detection. The existing QOSTBC using the pairs of transmitted symbols can be detected with two parallel MLD. Therefore, MLD based QOSTBC has higher complexity than OSTBC. To reduce the detection complexity, in this paper, we propose the heterogeneous constellation based QOSTBC for improving the detection property of QRD-MLD with maintaining a simple decoding structure. © 2012 IEEE.