Showing papers on "Cyclic delay diversity published in 2015"

Single-Carrier Frequency-Domain Equalizer with Multi-Antenna Transmit Diversity

Abstract: Single-carrier (SC) block transmission with cyclic prefix (CP) is a method with several advantages that has been incorporated into standards. This paper has analyzed the performance of multi-antenna SC-FDE under Alamouti signaling and cyclic-delay diversity (CDD). Our analysis shows that the characteristic of diversity it is depends on data block length and data transmission rate as well as on the channel memory and antenna configuration. At higher rates their diversity diminishes and full diversity is available to both CDD and Alamouti signalling below a certain rate threshold. From our investigation we say that at high rates Alamouti signalling provides twice the diversity of SISO SC-FDE, while the diversity of the SISO SC-FDE under the CDD diversity degenerates. In this paper, we analyze the performance of SC-FDE in conjunction with either cyclic delay diversity (CDD) or Alamouti signaling, fully characterizing the diversity as a function of transmission-block length, number of antennas data rate and channel memory. In the process, we obtain a threshold rate (as a function of data-block length, channel memory, and number of antennas) below which the full spatial-temporal diversity is achieved, while at higher rates the diversity of both schemes diminishes. Our analysis shows that at high rates Alamouti signaling provides twice the diversity of SISO SCFDE, while the CDD diversity degenerates to the diversity of the SISO SC-FDE.

Artificial frequency selective channel for covert cyclic delay diversity orthogonal frequency division multiplexing transmission

Abstract: Multiple-input multiple-output orthogonal frequency division multiplexing has become an attractive air-interface solution for the next generation wireless networks because of its high spectrum efficiency. This paper addresses the security concern and proposes to achieve covert orthogonal frequency division multiplexing transmission using cyclic delay diversity featured multiple-input multiple-output technology. Particularly, our physical layer security scheme takes the advantage of cyclic delay diversity formed periodical frequency selective channel and utilizes uneven comb pilots to confuse unauthorized receivers and benefit authorized receivers. We conduct simulation study to evaluate the impact of different cyclic delay, antenna number, and interpolation algorithms on our scheme. Numerical results show that our scheme can provide authorized users with significant advantage over eavesdroppers without complicated upper-layer encryption and decryption. Moreover, the scheme has flexible choice of parameters and thus can be easily deployed in a variety of wireless networks with different requirements. Copyright © 2014 John Wiley & Sons, Ltd.

A Cyclostationarity-Based Implicit Channel for Cognitive Radio Applications

Abstract: Cognitive Radio (CR) technology is believed to be a favorable complement to current and future wireless communication systems, due to its distinctive capability in promoting spectrum efficiency. However, as the number of CR applications increases, coexistence has become a vital issue for radio systems in CR networks. In this paper, a Cyclostationarity-based Implicit Channel (CIC) is proposed to assist conflict-avoidance coexistence for radio systems in the CR networks with Orthogonal Frequency Division Multiplexing (OFDM). First, an asymptotic maximum likelihood demodulation scheme is derived analytically based on a bijective-mapping based modulation. Subsequently, the performance of the proposed CIC is investigated via numerical simulations. It is demonstrated that the CIC can work effectively as an information sharing platform. Moreover, the CIC can work as an independent add-on module to the data bearing OFDM schemes, with minimum impact on the existing systems. Therefore, it is a highly attractive solution for delivering coexistence information in CR networks.

Better Performance of New Generation of Digital Video Broadcasting-terrestrial (DVB-T2) Using Alamouti scheme with Cyclic Delay Diversity

Abstract: The goal of the future terrestrial digital video broadcasting (DVB-T) standard is to employ diversity and spatial multiplexing in order to achieve the fully multiple-input multiple-output (MIMO) channel capacity. The DVB-T2 standard targets an improved system performance throughput by at least 30% over the DVB-T. The DVB-T2 enhances the performance using improved coding methods, modulation techniques and multiple antenna technologies. After a brief presentation of the antenna diversity technique and its properties, we introduce the fact of the well-known Alamouti decoding scheme cannot be simply used over the frequency selective channels. In other words, the Alamouti SpaceFrequency coding in DVB-T2 provides additional diversity. However, the performance degrades in highly frequencyselective channels, because the channel frequency response is not necessarily flat over the entire Alamouti block code. The objective of this work is to present an enhanced Alamouti space frequency block decoding scheme for MIMO and orthogonal frequency-division multiplexing (OFDM) systems using the delay diversity techniques over highly frequency selective channels. Also, we investigate the properties of the proposed scheme over different channels. Specifically, we show that the Alamouti scheme with using Cyclic Delay Diversity (CDD) over some particular channels has the better performance. Then, we exemplarity implement this scheme to the DVB-T2 system. Simulation results confirm that the proposed scheme has lower bit error rate (BER), especially for high SNRs, with respect to the standard Alamouti decoder over highly frequency-selective channels such as single frequency networks (SFN). Furthermore, the new scheme allows a high reliability and tolerability. The other advantages of the proposed method are its simplicity, flexibility and standard compatibility with respect to the conventional methods.

A low-power antenna selective synchronization method for IEEE 802.11ac WLAN systems

Abstract: This paper proposes an antenna selective timing synchronization method for multiple-input multiple-output orthogonal frequency division multiplexing-based IEEE 802.11ac wireless local area network systems. IEEE 802.11ac systems support up to eight antenna elements for adopting an MIMO technique. The increase in the number of antennas results in high power consumption due to the very high computational complexity involved. In addition, cyclic delay diversity applied for each antenna causes timing synchronization difficulties due to the pseudo-multipath problems. In order to solve these problems, a method to reduce the computational complexity of the synchronization is proposed by utilizing selective antennas with higher received signal power. The timing synchronization method with the adaptive accumulation window is also proposed to enhance synchronization performance. The simulation and power estimation results show that the proposed timing synchronization method not only improves the performance, but als...

Cyclic Delay Diversity With Discrete-Hartley-Fourier Transform in OFDM System

Abstract: Cyclic Delay Diversity (CDD) is a simple approach to provide spatial diversity for Orthogonal Frequency Division Multiplexing (OFDM) system. CDD provides not only the multipath diversity without channel coding but also a sample receiver structure. Discrete Hartley transform (DHT) as a linear precoding based OFDM outperforms the OFDM based on discrete Fourier transform (DFT) for it intrinsic frequency diversity. In this paper a simple scheme that DHFT-OFDM system with spatial multipath diversity by using CDD technique in the frequency selective fading channel is proposed. Simulation results are provided to validate the advantages of the proposed scheme that combining CDD with DHFT-OFDM system.

Enhancing the Performance of Multicarrier Delay Diversity Modulation Systems Using Alamouti Codes

Abstract: This paper investigates the performance of multicarrier delay diversity modulation (MDDM) systems with both cyclic delay diversity and Alamouti space time code techniques and compare its performance with conventional MDDM systems. Deploying Alamouti space time code can allow cost efficient and flexible system deployment compared to classical MDDM system with multiple cyclic delays. In this paper, we propose MDDM system with both cyclic delay and Alamouti codes. The performance of the proposed MDDM system is mathematically illustrated and modeled. The received signals at MDDM receiver are mathematically derived and analyzed. The minimum mean square error (MMSE) and QR decomposition M-algorithm maximum likelihood detection (QRM-MLD) techniques for signal detection is mathematically analyzed and applied to the proposed MDDM system. The performance of the proposed MDDM system is evaluated by simulating the BER for a certain range of SNRs. The BER is calculated for the proposed and classical MDDM systems to investigate the effect of cyclic delay with Alamouti codes in MDDM techniques. Finally, simulation results demonstrate that the proposed MDDM system with QRM-MLD technique enhances the performance of classical MDDM system and gives low values of BER compared with the classical case.

Self-adaptive open-loop CSD (cyclic delay diversity) method used for wireless communication system

Abstract: The invention discloses a self-adaptive open-loop CSD (cyclic delay diversity) method used for a wireless communication system. The self-adaptive open-loop CSD method includes performing channel estimation through a training sequence; calculating relevance of channels among different emitting antennas; applying a certain rule to judge whether CSD operation is performed or not; performing feedback and control of self-adaptive CSD operation on each frame through two reserved or newly-increased bits of a signaling field. According to the self-adaptive open-loop CSD method, each frame is estimated, and self-adaptive CSD operation is performed according to channel change conditions, so that system performance is improved; especially under the circumstance of low signal-to-noise ratio, gain brought by self-adaptive CSD is more obvious.

Low latency timing synchronization scheme for IEEE 802.11a/n/ac systems

Abstract: This paper addresses the problem of timing synchronization at the receiver of an IEEE 802.11a/n/ac communications system. In such systems, typically with multiple antennas at the transmitter, cyclic delay diversity (CDD) is implemented in the transmitted signal to provide diversity and hence, performance improvement in the error rates. However, the use of CDD creates pseudo-multipaths which degrade the performance of conventional timing synchronization algorithms, due to the increased delay spread of the channel. This paper proposes a method that achieves fine timing synchronization with low latency in two concurrent steps. The proposed scheme first achieves a coarse synchronization point so that important receiver operations can first take place. A fine timing synchronization algorithm operates concurrently to achieve a more accurate synchronization point and, to avoid incurring additional latency, post-processing is performed on the frequency domain samples of the preambles to compensate for the difference in synchronization points. The proposed scheme is shown to achieve excellent packet error rate performance with low latency requirements.

Dynamic selection for CoMP-JT over correlated MIMO channel with open loop precoding and IRC receiver for LTE-A

Abstract: This paper addresses the problem of Co-channel interference in the presence of fading correlation between transmit and receive antenna pairs. There are two ways for mitigating interference and improving the cell-edge user performance in Long Term Evolution-Advanced (LTE-A) system. First method is coordinated multi-point transmission and reception (CoMP) and second method is interference rejection combining (IRC) receiver. In this paper we propose a joint transmission (CoMP-JT) scheme for LTE-CoMP with open loop cyclic delay diversity (CDD). We enhance the performance of CoMP with dynamic cell selection and compare two schemes for open loop CDD. A cell-edge user selects the base stations that jointly transmit the desired signal from the available ones (we assumed 3). In addition, edge users are likely to be subject to severe Co-channel interference from eNBs outside the joint transmission set. In order to address this issue, IRC receiver is introduced. In this paper the performance of linear IRC receiver structures is investigated for interference suppression for CoMP-JT with open loop CDD. Simulation results show that the CoMP-JT using open loop MIMO with proposed precoding scheme, in case of cell selection, considerably improves the performance. In addition, using MMSE-IRC gives much better performance than the conventional minimum mean square error (MMSE) in the presence of co-channel interference.

Method and apparatus for implementing space time processing

Abstract: A method and apparatus for implementing spatial processing with unequal modulation and coding schemes (MCSs) or stream-dependent MCSs are disclosed. Input data may be parsed into a plurality of data streams, and spatial processing is performed on the data streams to generate a plurality of spatial streams. An MCS for each data stream is selected independently. The spatial streams are transmitted via multiple transmit antennas. At least one of the techniques of space time block coding (STBC), space frequency block coding (SFBC), quasi-orthogonal Alamouti coding, time reversed space time block coding, linear spatial processing and cyclic delay diversity (CDD) may be performed on the data/spatial streams. An antennal mapping matrix may then be applied to the spatial streams. The spatial streams are transmitted via multiple transmit antennas. The MCS for each data stream may be determined based on a signal-to-noise ratio of each spatial stream associated with the data stream.

A low detection complexity of multiple antenna two-way collaboration communication transmission scheme

Abstract: MIMO systems transmit signals by multiple antennas at the terminals, thus, to get spatial diversity gain and improve system capacity dramatically. Compared with single MIMO systems, the distributed MIMO system has higher coverage and larger capacity. MIMO systems using the joint coding technique through the full diversity of the space-time code can not only obtain the full diversity gain, but also improve spectrum efficiency effectively. But the detection complexity is high at the receiving terminal and information interference exists when transferring between antennas. Space-time coding can reduce the information interference between antennas and obtain diversity gain without sacrificing the bandwidth. The cyclic delay methods can effectively reduce the detection complexity. We present a high rate of distributed cooperative MIMO transmission scheme combining with space-time coding technique and cyclic delay technology. The transmitting terminal sends message to the relay nodes. Meanwhile, the source through the direct channel broadcasts information to all terminals. After the space-time coding, the received information at relay nodes is sent to the transmitters using cyclic delay method and amplifying forwarding (AF) method. This program applies to scene of both the communication source node and relay nodes all configured with multiple antennas. And the simulation results show that this two-way scheme we proposed can significantly improve the diversity gain and the total transmission rate, and enlarge the coverage of wireless network.

Reduced-Complexity synchronization technique for MIMO-OFDM WLAN systems

Abstract: In this paper, we study the application of a robust and Reduced-Complexity (RC) synchronization technique to the IEEE 802.11n Wireless Local Area Networks (WLAN). The studied technique exploits a preamble of two identical parts and splits the synchronization processing into two stages: a first auto-correlation based coarse stage and a second differential correlation based fine stage. The coarse synchronization aims to roughly localize the preamble position by auto-correlating the received signal using a correlation shift equal to the preamble sub-sequence length. The calculated metric exhibits a plateau that results in an uncertainty in the time detection accuracy. In the second stage and to mitigate the plateau effect, differential correlation is performed using a correlation shift different from the preamble sub-sequence length. The calculated metric provides high sharp peak that results in a very accurate detection. The fine stage is processed over a short interval centered on the coarse time estimate, which reduces the computational load of differential correlation operations. The repetitive structure of the preamble proposed in the IEEE 802.11n standard allows the application of the RC technique on it, using either the first legacy short preamble part or the second legacy long preamble part. Moreover, by choosing a correlation shift equal to the delay used to implement the Cyclic Delay Diversity (CDD) scheme, the RC technique allows to overcome the pseudo-path problem caused by the CDD. As a byproduct, the fractional part of the frequency offset is also estimated through the evaluation of the timing metric at the fine estimate. Simulation results show that, when applied to the IEEE 802.11n signal, the RC synchronization technique provides high detection accuracy that outperforms the considered benchmark.

Space-Time Block Coded Amplify-and-Forward Relay with Cyclic Delay Diversity

Abstract: Recently, we proposed space-time block coded (STBC) amplify-and-forward (AF) relay for wireless relay communication using unmanned aircrafts (UAs). In STBC-AF relay, UAs perform AF-STBC encoding consisting of conjugate operation and block exchange only. Then, the destination node performs frequency-domain equalization (FDE), diversity combining and linear STBC decoding by using an equivalent channel which is a concatenation of the channels of the source-UA link and the UA-destination link. Our previous study showed that STBC-AF relay can improve bit error rate (BER) performance by increasing the number of UAs. However, when the number of UAs is more than 3, the code rate of AF-STBC decreases, resulting in the throughput degradation. In this paper, we proposed STBC-AF relay with cyclic delay diversity (CDD). In STBC-CDD-AF relay, a number of UAs are divided into 2 groups, and then AF-STBC encoding for 2 UAs is performed by the group. And then, the each UA in each group adds different cyclic delay to each transmit signal. We evaluate, by the computer simulation, the average BER performance and throughput performance when using STBC-CDD-AF relay and showed that STBC-CDD-AF relay achieves higher throughput than STBC-AF relay when the number of UAs is 4. Keyword space-time block coding, cooperative amplify-and-forward relay, cyclic delay diversity 1. まえがき 先の日本を襲った東日本大震災のような大規模な 災害では通信ケーブルの切断や基地局の停電などによ りネットワークから孤立したエリアが発生してしまう. そのよう場合に迅速にネットワークを復旧する手段と して無人航空機(UA)を用いる無線中継システムが注 目されている [1].しかしながらこのシステムでは UA が上空を高速で旋回するため地上―UA 間リンクは周 波数選択性フェージング,伝搬損失およびシャドウイ ング損失などによって通信品質が変動する不安定なリ ンクとなる [2].そのため高品質・高安定な無線中継シ ステムを達成するための優れた信号検出技術が必要と なる.周波数選択性フェージングを克服するための手 段として,直交周波数分割多重(OFDM)伝送が広く 知られている [3].また複数の送受信アンテナを用いる 時空間ブロック符号化(STBC)ダイバーシチにより送 信機の構成を簡易に保ちながら空間ダイバーシチ効果 により伝送特性を改善させることができる [4-6]. 筆者らはこれまで STBC 符号化と非再生(AF)中継 伝送を組み合わせた STBC-AF 中継伝送を提案してき た [7-8].図 1 に UA2 機の STBC-AF 中継伝送の動作を 示す.STBC-AF 中継伝送では,第 1 タイムスロットに おいて,送信局が UA に向けて 2 個の信号ブロックを 送信する.その後 UA は,受信ブロックに AF-STBC 符 号化を施し,第 2 タイムスロットにおいて受信局に向 けて増幅・送信する.STBC-AF 中継伝送では,UA 毎 に複素共役の信号ブロックと複素共役でない信号ブロ ックが共に存在しない AF-STBC 符号化を用いること により,受信局における受信信号を送信局―UA 間チ ャネルと UA―受信局間チャネルの積で与えられる等 価チャネルと AF-STBC 符号化行列の積で表現できる. そのため,受信局では,周波数領域等化(FDE)とダ イバーシチ合成を行った後,簡易な四則演算のみで構 成される線形 STBC 復号を行うことで 2 個の受信信号 ブロックを得ることができる.これまでの検討により, STBC-AF 中継伝送は従来の AF 中継伝送 [9,10]より優 れた平均 BER 特性を達成できることおよび中継 UA 数 を増やすにしたがってさらに平均 BER 特性を改善で きることを明らかにした [7,8].しかしながら,中継 UA 数が 3 機以上の場合,AF-STBC 符号化の符号化率が低 下してしまい,それに伴ってスループットも低下して しまうという問題があった [8]. そこで本稿では中継局で STBC-AF 中継伝送と循環 遅 延 ダ イ バ ー シ チ ( CDD ) [11] を 組 み 合 わ せ た STBC-CDD-AF 中継伝送を提案する.STBC-CDD-AF 中 継伝送では,複数の UA を 2 つのグループに分け,符 号化率が低下しない中継 UA が 2 機の場合の AF-STBC 符号化をグループ単位で適用する.そして,それぞれ のグループ内で UA ごとに異なる循環遅延を与えて AF-STBC-CDD 符号化信号を生成し,受信局に増幅・ 中継する.これにより,STBC 符号化率を低下させる ことなく周波数ダイバーシチ効果を獲得でき,優れた スループット特性を達成できる.中継 UA 数が 4 機の 場合の STBC-CDD-AF 中継伝送の平均ビット誤り率 (BER)特性およびスループット特性を計算機シミュ レーションにより求め,中継 UA 数が 4 機の場合, STBC-CDD-AF 中継伝送は STBC-AF 中継伝送より高い スループット特性を達成できることを明らかにしてい る. 本稿の構成は以下のようになっている.第 2 章にて STBC-CDD-AF 中継伝送を提案する.第 3 章で計算機 シミュレーション結果を述べた後,第 4 章にてまとめ る. 図 1 STBC-AF 中継伝送

Cyclic delay diversity with phase shift in low rate SC-FDMA uplink

Abstract: This paper proposes a phase shift scheme in cyclic delay diversity (CDD) for single-carrier frequency division multiple access (SC-FDMA) in Internet of Things (IoT) applications. The proposed scheme is assumed to be applied to the uplink of Long Term Evolution (LTE) systems. Since the transmission rates of IoT applications are small, each uplink connection may occupy less than 12 subcarriers that corresponds to one resource block (RB) of the LTE. Since the length of the data sequence in time domain is short so that CDD may provide limited frequency diversity. The proposed scheme shifts the phases of the data symbols in time domain and spreads each subcarrier component over multiple subcarriers. Thus, more diversity gain can be realized with CDD. Numerical results obtained through computer simulation shows that the proposed scheme improves the performance by about 5 – 7 dB at the bit error rate (BER) of 104 for the data sequence length of 4.