Showing papers on "Cyclic delay diversity published in 2009"

Cyclostationary Signatures in OFDM-Based Cognitive Radios with Cyclic Delay Diversity

Abstract: The man-induced cyclostationary signatures can provide a robust mechanism for the self-coordination of cognitive radio networks. However, such artificial signatures incur signaling overhead and come at the bandwidth cost. In this paper, we show intrinsic cyclostaionary signatures in the Orthogonal Frequency Division Multilplexing (OFDM) system with Cyclic Delay Diversity (CDD). The standard conformable CDD technique is initially motivated by the objective for exploiting spatial diversity. Significantly, the underlying periodicity of CDD can simultaneously induce advantageous cyclostationary signatures without any signaling overhead. The lag-indices of the CDD-induced signatures are uniquely determined by the assigned amount of cyclic delay. Consequently each CDD-OFDM system can be identified by a pre-assigned cyclic delay. The signed system can be easily and robustly recognized through cyclostationary detection. Furthermore, the CDD-OFDM systems still preserve the cyclic-prefix induced cyclostationarity as primitive OFDM. By exploiting the overall cyclostationarity, we present a desirable cyclostionarity detector with asymptotical constant false alarm rate for spectrum sensing. Comprehensive simulations are also given to show the performance improvement.

Cyclic delay diversity with frequency domain turbo equalization for uplink fast fading channels

Abstract: Cyclic delay diversity (CDD) is an attractive diversity technique due to its low complexity and compatibility to existing wireless communication systems. This letter proposes a CDD with frequency domain turbo equalization (FDTE) for single carrier (SC) transmission, in order to achieve the full spatial diversity of frequency-selective multi-antenna channels. The frequency diversity inherent in SC is picked up from the increased channel selectivity of CDD. The noise or intersymbol interference enhanced by equalization for highly selective channels is then mitigated through applying FDTE at the receiver. Simulation results show that the performance of proposed system approaches the corresponding orthogonal spacetime block coding (STBC) system in slowly fading channels without any data rate loss, and considerably outperforms the STBC system in fast fading channels.

Maximizing Outage Capacity of OFDM Transmit Diversity Systems

Abstract: Performance analysis of open-loop transmit diversity schemes for orthogonal frequency-division-multiplexing (OFDM) systems is addressed by investigating the outage capacity limits in frequency-selective fading channels. It is shown that the variance of the mutual information provides details on the amount of available diversity, and it suggests guidelines on transmitter design. The optimal delays, in the outage capacity maximization sense, are found for linear and cyclic delay diversity (LDD and CDD) schemes. It is proved that the outage rates for subcarrier diversity (SD) systems are the same as for the optimized CDD case. The effect of spatial correlation on system performance for a uniform linear transmit array is discussed and numerically evaluated.

A novel CDD-OFDM scheme with pilot-aided channel estimation

Abstract: Cyclic delay diversity (CDD) is a low-complexity standard-conformable transmit diversity scheme for coded orthogonal frequency division multiplexing (OFDM) systems. However, it makes channel estimation more challenging due to the increased frequency-selectivity of the equivalent single-input single-output channel. In this paper, we propose a novel CDD-OFDM scheme with pilot-aided channel estimation for any number of transmit antennas. By alternating and optimizing the cyclic delay parameter over adjacent OFDM symbols, we design a simple yet efficient channel estimation scheme and illustrate its excellent performance for the DVB-T application.

On the Optimal Cyclic Delay Value in Cyclic Delay Diversity

Abstract: In this paper, we propose a method to determine the optimal cyclic delay value of cyclic delay diversity (CDD) in orthogonal frequency division multiplexing (OFDM) systems. As the cyclic delay value increases, we can get signal to interference and noise ratio (SINR) gain by the diversity effect, while SINR loss increases because of channel estimation errors. If the optimal cyclic delay value obtained by the proposed method is applied to a CDD scheme, we can minimize the required SINR for a given frame error rate (FER) under the above-mentioned trade-off.

Joint iterative channel estimation and soft-chip combining for a MIMO MC-CDMA anti-jam system

Abstract: Multicarrier code division multiple access (MCCDMA) systems using complex-quadratic spreading sequences and cyclic delay diversity (CDD) facilitate frequency or time domain chip combining to mitigate different types of jamming. In this paper, multiple-input multiple-output (MIMO) channel coefficients, jamming power, and jammer state information (JSI) are jointly estimated to suppress the adverse effects of partial-band noise jamming. We derive weighted least square error (LSE) and linear minimum mean square error (MMSE) channel estimators operating under jamming and investigate the constraints on the cyclic delays. The JSI for the pilot symbols is estimated to assist estimation of the time-varying frequency selective channel coefficients by updating the noise covariance matrix. We also derive the optimum (sufficient statistics) chip combining weights for the data symbols that require the JSI; hence, the JSI for the data symbols is iteratively estimated using the decoder output. Simulation results demonstrate that the proposed iterative despreading (includes JSI estimation and chip combining), demapping, and decoding receiver with soft- JSI-assisted channel estimation and chip combining is very robust against partial-band noise jamming.

Cyclic delay diversity based transmission with delay hopping

Abstract: A method of providing delay information in a multi-antenna transmission system is provided. A time delay value is selected from a set of time delay values. A mobile station is informed of information related to the selected time delay value. The same data is transmitted from a first antenna and from a second antenna. The data is transmitted from the second antenna after the data is transmitted from the first antenna according to the selected time delay value. The time delay value is selected based on a deterministic method or a random method.

Space-Time Cyclic Delay Diversity Encoded Cooperative Transmissions for Multiple Relays

Abstract: Among spatial diversity schemes, orthogonal space-time block code (OSTBC) and cyclic delay diversity (CDD) have been widely studied for the cooperative wireless relaying system. However, conventional OSTBC and CDD cannot cope with change in the number of relays owing to low throughput or error performance. In this letter, we propose the space-time cyclic delay diversity (STCDD) scheme which provides good error performance and full rate. Simulation results show that bit error rate (BER) performance of the proposed STCDD is superior to that of OSTBC and CDD when sufficient quality of source-relay channels are guaranteed.

On the Parameter Choice for Cyclic Delay Diversity Based Precoding with Spatial Multiplexing

Abstract: A method called open loop cyclic delay diversity (CDD) precoding has recently become part of the standard for 3GPP Long-Term Evolution (LTE) cellular communications systems. CDD had previously been proposed as single stream diversity method for OFDM systems. The proposal in LTE is an extension to spatial multiplexing using so called large delay CDD. The purpose of this paper is twofold: First, we give two different interpretations of the CDD precoding scheme in LTE as beam switching and transformation of spatial diversity to frequency diversity. We then discuss the impact of the delay parameter in CDD precoding on the achievable rates and BER performance. It turns out that while the choice of large delay causes a capacity degradation in single stream CDD, the achievable rates in CDD based spatial multiplexing are robust to variations of the delay parameter. This is even true in correlated scenarios and when only a resource block of a few subcarriers is allocated to a specific user. However, in case of separate encoding of the spatial streams, large delay CDD precoding shows a BER advantage over small delay CDD precoding since the spatial diversity is transformed into frequency diversity among adjacent subcarriers and, hence, is easily picked up by the decoder. Finally, we give a performance comparison of open loop CDD based precoding and closed loop precoding in LTE. It is shown that for 2 transmit antenna systems, only little gain is achieved by the additional effort of closed loop precoding. Closed loop precoding shows substantial benefits over CDD based precoding only for a higher number of transmit antennas.

Mimo transmitter and methods for transmitting ofdm symbols with cyclic-delay diversity

Abstract: A multiple-input multiple output (MIMO) transmitter and methods for transmitting orthogonal frequency division multiplexed (OFDM) symbols with cyclic-delay diversity (CDD) are generally described herein. In some embodiments, a base station uses a number of antennas for MIMO transmission of OFDM symbols. For the number of antennas, quadrature-amplitude modulated (QAM) symbols are distributed across a group of OFDM tones of a block comprising the group of tones and a group of OFDM symbols. An incremented cyclic delay is applied to the QAM symbols of the block associated with each subsequent of the antennas for CDD transmission. Each blocks is transmitted by an associated one of the antennas.

Method and apparatus for transmitting data in radio communication system

Abstract: The present invention provides a method and an apparatus for transmitting data in a radio communication system. The method for transmitting data in a radio communication system in which a radio resource for data transmission includes a plurality of data symbols in a time domain, wherein the method comprises the steps of transmitting first data using a space-time block coding (STBC) scheme via a portion of the data symbols from among the plurality of data symbols; and transmitting second data using a cyclic delay diversity (CDD) scheme via the residual data symbols excluding the portion of data symbols.

Cyclic space-frequency filtering for BICM-OFDM systems with multiple co-located or distributed transmit antennas

Abstract: In this paper, we introduce cyclic space-frequency (CSF) filtering for orthogonal frequency division multiplexing (OFDM) systems using bit-interleaved coded modulation (BICM) and multiple transmit antennas for fading mitigation, and discuss the extension to orthogonal frequency division multiple access (OFDMA) systems. CSF filtering is a simple form of space-frequency coding (SFC) and may be viewed as a generalization of cyclic delay diversity (CDD) where the cyclic delays are replaced by CSF filters. CSF is applicable to both traditional multiple-input multiple-output systems with co-located transmit antennas and cooperative diversity systems with decode-and-forward relaying and distributed transmit antennas. Similar to CDD and in contrast to other SFC schemes, CSF filtering does not require any changes to the receiver compared to single-antenna transmission. Based on the asymptotic pairwise error probability of the overall system we derive an optimization criterion for the CSF filters for co-located and distributed transmit antennas, respectively. We show that the optimum CSF filters are independent of the interleaver if they do not exceed a certain length. If this length is exceeded, the adopted interleaver has to be carefully taken into account in the CSF filter design. For several special cases we derive closed-form solutions for the optimum CSF filters and for the general case we provide various CSF filter design methods. Our simulation results show that CSF filtering can achieve significant performance gains over existing CDD schemes.

Why Downlink Cyclic Delay Diversity Helps Uplink Transmit Diversity

Abstract: In this paper, we show that the use of cyclic delay diversity (CDD) on the downlink (DL) can improve the performance of uplink (UL) diversity methods such as antenna selection in a time-division duplexing (TDD) system. An analytical framework for showing why CDD transmission on the DL improves UL diversity transmission in TDD system is provided. The analysis is used to quantify the gain in the UL received signal-to-noise ratio (SNR) when DL CDD is used. The analytical results show that for a 2times2 MIMO system that uses DL CDD, UL transmit diversity based on antenna selection improves the average UL SNR by 0.41 dB relative to the case when CDD is not being applied at the BS transmitter and improves the 1% CDF UL SNR by 1.58 dB. Measurement-based analysis validates the analytical results using measured frequency response of a MIMO system using a wideband channel sounder.

Antenna Selection and Ordering for EST-Based Modulation With Cyclic Delay Diversity

Abstract: In this paper, antenna selection and ordering for energy-spreading transform (EST)-based modulation employing multiple transmit antennas for cyclic delay diversity (CDD) is considered. First, we analyze the signal-to-interference-plus-noise ratio (SINR) of the iterative receiver based on a soft decision that has been designed for EST-based modulation. Then, an antenna-selection and ordering criterion that maximizes the SINR of the soft-decision receiver is proposed.

Method and device of processing data in multiple input multiple output system

Abstract: PROBLEM TO BE SOLVED: To provide a method of processing data capable of improving a signal quality in an MIMO system. SOLUTION: The method of processing data includes dividing user terminals into groups based on channel characteristics and QoS requirements of the user terminals, and further includes a step A of setting a corresponding precoding code word and cyclic delay for each of the groups and a step B of determining a group to which the user terminal corresponding to a processing object data belongs and subjecting the processing object data to the cyclic delay diversity (CDD) precoding processing applying the precoding code word and cyclic delay corresponding to the relevant group. In addition, the present invention discloses a device for processing data. The device includes a grouping module and a cyclic delay diversity (CDD) precoding processing module. COPYRIGHT: (C)2009,JPO&INPIT

Pilot-Aided Channel Estimation Schemes for OFDM Systems with Cyclic Delay Diversity

Abstract: Cyclic delay diversity (CDD) is a low-complexity transmit diversity technique for coded orthogonal frequency division multiplexing (OFDM), which transforms a mutiple-input channel into an equivalent single-input channel with increased frequency selectivity and provides additional frequency diversity. However, it makes channel estimation more difficulty due to the increased frequency selectivity. In this paper, we focus on the direct estimation of the equivalent single-input channel for CDD-OFDM systems. We first propose a cyclic cross-correlation channel estimation scheme based on the equispaced constant-modulus pilot structure. Using the statistical parameters of the channel and noise derived by the result of the cyclic cross-correlation channel estimation, we propose an improved channel estimation scheme based on the Wiener filter to reduce the estimation error further. Computation simulations are given to demonstrate the effectiveness of two proposed channel estimation schemes for CDD-OFDM systems.

Transmitter and signal transmission method

Abstract: The invention provides a signal transmission method and a transmitter thereof, which belong to the technical field of transmitter-side signal processing. The method comprises the following steps: performing space-time block coding of a bit stream; modulating the space-time block coding result by means of orthogonal frequency division multiplexing (OFDM), and treating the OFDM result by means of cyclic delay diversity. The signal transmission method achieves the effects of full diversity gain and coding gain at the same time.

Partial-Differential Distributed Cyclic Delay Diversity for Nonregenerative Two-Way Relaying System

Abstract: In wireless ad-hoc networks, network coding can take advantage of the bi-directional traffic flows to increase the achievable throughput. In this letter, on the one hand, cooperative diversity based on distributed cyclic delay diversity is integrated into the physical network coding scheme to combat fading in wireless channel. On the other hand, to reduce the system overhead for the coherent detection at each destination terminal, differential modulation based on linear constellation precoding is proposed. Theoretical analysis and numerical results both confirm that our two-way relaying scheme can achieve full spatial diversity. Furthermore, the proposed scheme can significantly improve the performance over traditional one-way wireless relay scheme and the existing two-way wireless relay schemes due to its enhanced spectral efficiency and lower implementation complexity.

Increasing reliability of an interactive mobile satellite telecommunication system using diversity and MIMO schemes

Abstract: Observation of the Mobile Satellite System industry shows a significant growth in the need for more demanding services and higher rates these last years; as an example, recent success of hybrid broadcasting system (XM, Sirius) and DVB-SH arrival are meeting commercial users expectations in terms of high rates mobile communications. In this context, the use of diversity and MIMO schemes (Cyclic Delay Diversity and Alamouti) is studied in this paper in the aim of increasing reliability of interactive systems which don't take benefit of very long interleaving time durations (as pure broadcasting systems). Simulations have been done on a DVB-SH physical layer adapted to support 1×1, 1×2, 2×1, 2×2 multiplexing schemes. Satellite mobile MIMO channels have been used. This paper presents combinations of diversity/MIMO architectures, interleaving durations, channels, and makes the trade off of the air interface adjustment regarding of the results.

A Scheme of Cyclic Delay Diversity Based Precoding for Downlink MIMO System

Abstract: The objective of this paper is to research and analyse the scheme of Cyclic Delay Diversity (CDD) based precoding with two and four transmit antenna on MIMO systems operating in flat and multi-path channel. MIMO precoding is an effective MIMO multiplex mode to improve throughput, and CDD is an efficient transmit diversity scheme suitable for OFDM radio access. In this contribution the principle and system structure of MIMO precoding based on CDD is introduced. The system throughput of the CDD-based precoding with codebook-based precoding according to delay sample, codebook size and RB size for PMI and CQI feedback is evaluated. By choosing a proper cyclic delay between a zero delay (e.g., τ=0) and a small delay(e.g., τ=2), we can efficiently adapt to the proper MIMO mode with a single unified precoding structure.

Bit-interleaved coded DPSK with cyclic delay diversity: design and analysis

Abstract: In this paper, the bit-interleaved convolutionally coded differential phase shift keying (DPSK) in combination with cyclic delay diversity (CDD) is theoretically analyzed in terms of pairwise error probability (PEP). We show that bit-interleaved coded DPSK with CDD can achieve full spatial and frequency diversity offered by the frequency selectivity of wireless channel conditioned that the minimum free distance dfree of the convolutional code is larger than the target diversity order. The design criterion of the considered system is presented based on the analysis of diversity and coding gains. Finally, the theoretical results obtained in this paper are confirmed by computer simulations.

Performance of relay cyclic delay diversity in multicarrier system

Abstract: In this paper, the performance of a cooperative relaying scheme with cyclic delay diversity (CDD) for an orthogonal frequency division multiplexing (OFDM) system is investigated. The system under consideration consists of multiple single-antenna terminals acting as relays and cooperating to provide spatial diversity. Cyclic shift is introduced at each relay and thus increase the frequency selectivity of relay channels. To exploit a highly selective channel, convolutional code is employed together with OFDM. Simulations demonstrate the bit error performance of the proposed scheme with different numbers of relays as well as performance in flat and frequency selective fading channels. The performance of the system is also compared to conventional multiple-input multiple-output (MIMO) with CDD and a conventional amplify-and-forward (AF) relay system. The results indicate that the proposed scheme provides enhanced performance under various considerations.

Coding method for improving transmit diversity in multi-antenna system

Abstract: The invention relates to a coding method for improving the transmit diversity in a multi-antenna system. The coding method comprises the following steps: transmitter units are divided back and forth by a plurality of antennae as adjacent units; a space-time group code is adopted among the transmitter units; and each transmitter unit internally adopts cyclic delay diversity (CDD). The invention effectively solves the problem of code rate reduction under the condition that the transmit antenna number of the orthogonal space-time group code is larger than 2, also utilizes the CDD theory and is particularly suitable for frequency selectivity channels. In addition, the scheme has a receiver scarcely increasing the complexity, thereby being a very transmit diversity scheme with compromise performance and complexity.

Cyclic delay diversity for single carrier FDMA with linear precoding technology

Abstract: Cyclic Delay Diversity (CDD) has been considered as an improving way to obtain frequency diversity. Single Carrier FDMA (SC-FDMA) combines the advantages of the OFDMA but with lower Peak to Average Power Ratio (PAPR). In this paper we propose SC-FDMA with CDD system which achieves full diversity without data rate loss. In addition we apply linear precoding to SC-FDMA-CDD system especially in Rayleigh fading channel to further improve the BER performance.

A Theoretical Treatment of PA Power Optimization in Clipped MIMO-OFDM Systems

Abstract: This work presents a theoretical framework for determining the optimal clipping level for a multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system. We start by modeling of the clipping noise, and propose a maximum likelihood (ML) receiver for the resulting signal. The bit error rate (BER) for this ML receiver is then derived for MIMO spatial multiplexing, space time coding, and cyclic delay diversity schemes. A search through the tradeoff space between the BER performance penalty and power amplifier (PA) power consumption advantage reveals optimum clipping levels of the system. Using an IEEE 802.11n like system, we show that the optimum clipping as predicted by this approach can improve PA power efficiency as much as 70%.

Performance Evaluations of MBMS Signals Using Transmit/Receiver Diversity with SFN in OFDM Based Evolved UTRA Downlink

Abstract: This paper investigates the best cell-common reference signal (RS) structure and transmit diversity scheme for Multimedia Broadcast Multicast Service (MBMS) signals considering frequency diversity in a single-frequency network (SFN) in the OFDM based Evolved UTRA downlink. Link-level simulation results show that cyclic delay diversity (CDD) is the most promising transmit diversity scheme for the MBMS signals considering the RS overhead. It is also elucidated that the required average received signal energy per symbol-to-noise power spectrum density ratio (Es/N0) using CDD is reduced by approximately 0.5dB even though the MBMS signal obtains a sufficient frequency diversity gain in SFN operation. Furthermore, we clarify the achievable data rate for the MBMS signal at the cell edge of the centered MBMS cell that satisfies the required block error rate (BLER) using two-antenna transmit CDD and diversity reception by system-level simulation. Then, the simulation results show that the offered data rates with the required BLER of less than 10-2 at 95% coverage are 0.211 (0.17), 0.243 (0.196), 1.168 (1.084), and 2.754 (2.754)bps/Hz with the number of cells providing MBMS, NMBMS = 1, 3, 21, and 57, respectively, employing transmit CDD with two antennas (single-antenna transmission) for ISD = 500m.

Relay Selection in Amplify-and-Forward Relay Network with Multiple Antennas at the Destination

Abstract: In this paper, we consider an amplify-and-forward (AF) relay network where a source node transmits information to a destination node through the cooperation of multiple relay nodes. It is shown in prior works that the outage behavior and average throughput of the selection AF (S-AF) scheme where only the best relay node is chosen to assist can outperform the conventional all-participate AF (AP-AF) scheme. Assuming multiple antennas at the destination node and single antennas at other nodes in this paper, we propose a relay selection scheme according to the criterion of maximizing receive signal to noise ratio (SNR), where a group of relays is chosen to assist in the transmission simultaneously in a manner similar to cyclic delay diversity (CDD). Compared with S-AF, the proposed scheme achieves better outage behavior and average throughput. It can be seen from simulation results that the performance improvement of symbol error rate (SER) is significant compared with S-AF.

Performance comparison of 802.11n system with WLAN channel model

Abstract: As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. In this paper, we propose a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with cyclic delay diversity and block diagonalization procoding method to improve bit error rate (BER) performance with wireless local area network (WLAN) channel model C and D for 802.11n WLAN system. The results of mathlab simulation show the improvement of BER performance in 802.11n wireless indoor channel environment.

Delay diversity for correlated MIMO channel

Abstract: Although uncorrelated channels are commonly assumed in cyclic delay diversity (CDD) based multiple input and multiple output (MIMO) orthogonal frequency division mutiplexing (OFDM) systems, correlated channels can evolve due to closeness of antennas or lack of scatterers in the environment. To mitigate the correlation effect, a random continuous phase offset is induced into the transmitting symbols. In a correlated channel the random phase offset scheme provides all the OFDM symbols the same average received power as offered by the uncorrelated channel. Our numerical results demonstrate that depending on the channel spatial correlation, the random phase offset scheme is capable of yielding a dramatic performance improvement of CDD based MIMO-OFDM systems. A modified scheme with random binary phase offset is also introduced that yields almost identical performance as the continuous phase offset scheme yet with a simpler implementation.