Showing papers on "Cyclic delay diversity published in 2012"

Sum Rate Analysis of a Reduced Feedback OFDMA Downlink System Employing Joint Scheduling and Diversity

Abstract: We consider joint scheduling and diversity to enhance the benefits of multiuser diversity in an orthogonal frequency-division multiple access (OFDMA) downlink system. The OFDMA spectrum is assumed to consist of NRB resource blocks and the reduced feedback scheme consists of each user feeding back channel quality information (CQI) for only the best-NFB resource blocks. Assuming largest normalized CQI scheduling and a general value for NFB, we develop a unified framework to analyze the sum rate of the system for both the quantized and nonquantized CQI feed- back schemes. Based on this framework, we provide closed-form expressions for the sum rate for three different multiantenna transmitter schemes; transmit antenna selection (TAS), orthogonal space time block codes (OSTBC) and cyclic delay diversity (CDD). Furthermore, we approximate the sum rate expression and determine the feedback ratio (NFB/NRB) required to achieve a sum rate comparable to the sum rate obtained by a full feedback scheme.

Open loop spatial processing

Abstract: Methods and apparatus for multiple-input multiple-output (MIMO) transmissions are disclosed. A base station may precode wireless transmit/receive unit (WTRU)-specific reference signals and data that are transmitted to a WTRU using a randomly selected precoder. The precoder may be selected based on a predefined precoder selection sequence or by the base station. A different precoder may be applied to different resource blocks (RBs). In addition, a large delay cyclic delay diversity (CDD) or discrete Fourier transform (DFT) spreading may be applied on the WTRU-specific reference signals and the data. For heterogeneous deployed antennas, spatial diversity gain is achieved by dynamically scheduling resources between transmission points. A hopping scheme may be applied across the transmission points as the resources are dynamically partitioned between the transmission points. A different randomly selected precoder may be applied to each RB transmitted from a different transmission point.

ICI mitigation by Doppler frequency shift estimation and pre-compensation in LTE-R systems

Abstract: Inter-carrier interference (ICI) caused by high Doppler frequency shift has severe impact on link performance and capacity for High-Speed Railway (HSR) communications. In this paper we investigate the ICI mitigation scheme by utilizing the estimation and pre-compensation of high Doppler shifts in Long Term Evolution for Railway (LTE-R) systems with distributed remote radio units (RRU). We propose several schemes to estimate and mitigate ICI caused by Doppler frequency shifts. In addition, we propose to use cellular cyclic delay diversity (C-CDD) technique for mobile relay station (MRS) on the roof of HSR. Additional frequency diversity gain can be obtained when MRS lies within coverage area of two RRUs so that the communication quality is improved. The simulation results show that our proposed schemes can achieve the trade-off between complexity and performance.

Communication station and method for transmitting ofdm symbols with cyclic-delay diversity (cdd)

Abstract: A communication station uses a plurality of antennas for transmission of orthogonal frequency division multiplexed (OFDM) symbols. The communication station includes an interleaver to interleave a block of encoded bits of an associated input bit stream for use in generating an output bit stream having a desired code rate. The communication station also includes circuitry to modulate the bits of the output bit stream to generate complex-valued modulation symbols, circuitry to map the modulation symbols for transmit diversity to layers for each of the antennas based on a number of antennas used and to further map the modulation symbols for each antenna onto resource elements, circuitry to cyclically shift the mapped modulation elements, circuitry to provide the cyclically-shifted modulation symbols for transmission by an associated one of the antennas, and circuitry to add a cyclic prefix to the modulation symbols prior to transmission.

Uneven comb pilots based channel estimation for CDD-OFDM system

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for high speed data transmission over multipath fading channels. In an MIMO-OFDM system, cyclic delay diversity (CDD) serves as a simple and elegant solution to exploit transmit diversity. This paper investigates the uneven comb pilots based channel estimation for CDD-OFDM system with periodical frequency selective channel. Our study reveals that uneven comb pilots outperform their even counterpart in complicated channel conditions, such as adaptive CDD, where cyclic delay parameters may change from time to time. Furthermore, we identify the interpolation as a key problem in uneven-pilot based OFDM system and study several scattered data interpolation algorithms. Simulation results show that radial basis function (RBF) interpolation has the best tradeoff in terms of accuracy and computational complexity.

Cyclic delay transmission achieves full diversity without (Pre)coding

Abstract: Cyclic Delay Diversity (CDD) is a simple method that converts transmit antenna diversity into frequency selectivity, thus allowing simple operation and use of conventional receivers to capture the diversity. This paper shows that single-carrier CDD methods are capable of producing diversity without channel coding or linear precoding, and that this is made possible via the appropriate design and use of linear equalizers. At the heart of our result is the establishment of a functional equivalence between effective channels seen by the CDD MISO system and the cyclic-prefix SISO ISI system. Specifically, we show that in an M×1 CDD MSIO system, the MMSE receiver achieves maximum diversity for rate values R ≤ log L/M(ν+1)−1, where L is the data block length, R the spectral efficiency in b/s/Hz, and ν is the channel memory. The equivalence between the delay diversity (DD) system and a zero-padding single-carrier system can be also established (as long as the DD delay taps are carefully chosen) for which linear equalizers can achieve maximum diversity with no constraint on rate.

A study on performance enhancement of cyclic delay diversity OFDM system using frequency diversity

Abstract: This paper proposes a technology for performance enhancement of cyclic delay diversity OFDM system using frequency diversity. The frequency diversity in an OFDM system can be done as repetitive transmission of the same symbol on uncorrelated subcarrier, this makes modulation level larger according to the number of repetitive transmission for the comparison with the traditional transmission system. This technique, like cyclic delay diversity, has a benefit which it does not need any special subsidiary hardware irrespective of the increase of the number of transmitter. For the performance comparison, we simulate the proposed algorithm in multiple input single out channel environment, it shows a better performance enhancement in low dense modulation level in comparison with the traditional cyclic delay diversity OFDM system.

Integer frequency offset estimation by pilot subset selection for OFDM system with CDD

Abstract: Cyclic delay diversity (CDD) is a simple transmit diversity technique for an OFDM system using multiple transmit antennas. However, the performance of post-FFT estimation, i.e. integer frequency offset (IFO) is deteriorated by high frequency selectivity introduced by CDD. Proposed is an IFO estimation scheme for an OFDM system with CDD. Based on the pilot subset partitioning, the proposed IFO estimation scheme reduces the effect of frequency selective fading by adopting the CDD.

The Study on Cooperative Relay Coding in Multicarrier System

Abstract: Cooperative relay systems represent a promising solution overcoming the drawbacks of non-line-of-sight (NLOS) propagation in future wireless communications. In this paper, we propose a cooperative relay coding which uses adaptive hierarchical modulation based on cyclic redundancy check (CRC) and cyclic delay diversity (CDD). In the proposed scheme, the system consists of multiple single-antenna terminals acting as relays and cooperating to provide spatial diversity. Also, cyclic shift is introduced at the relays to increase the frequency selectivity in the relay channels. To exploit a highly selective channel, convolutional code is employed together with orthogonal frequency division multiplexing (OFDM). The proposed scheme is evaluated in terms of the bit error rate (BER).

Multicarrier modulation system having cyclic delay diversity

Abstract: Techniques to transmit data with cyclic delay diversity and pilot staggering are described. For cyclic delay diversity, OFDM symbols having different cyclic delay durations are generated. The cyclic delay durations for the OFDM symbols may be selected to be time varying with respect to the cyclic delay durations for OFDM symbols transmitted by a neighboring base station. An FDM pilot is generatedand multiplexed on multiple sets of subbands in different symbol periods. Waveforms for a second radio technology (e.g., W-CDMA) may be generated for data to be transmitted with this radio technology. The OFDM symbols are multiplexed onto time slots used for OFDM, and the waveforms for the second radio technology are multiplexed onto time slots used for this radio technology. One or multiple modulated signals may be generated based on the multiplexed OFDM symbols and waveforms. Each modulated signal is transmitted from a respective antenna.

Spectrum usage efficiency of coordinated multi-point transmission in mobile satellite communications

Abstract: In a mobile satellite system based on orthogonal frequency division multiplexing technique, the beam planning with frequency reuse factor 1 may induce severe inter-beam interference due to the usage of the same subcarrier between user equipments of adjacent beams. In order to solve this problem, this paper shows a coordinated multi-point transmission scheme combined with cyclic delay diversity. The proposed scheme improves frequency usage efficiency in a beam boundary region and minimizes interference inter-beam interference in mobile satellite communications based on orthogonal frequency division multiplexing technique. In addition, simulation results show that it makes total system capacity increased due to the significant improved signal to interference and noise power ratio in beam edge users.

A GA-based optimization for frequency-selective scheduling in downlink OFDMA systems with cyclic-delay diversity

Abstract: CDD (cyclic-delay diversity) aided frequency-selective scheduling has been known as an effective technique to increase system capacity of the OFDMA (orthogonal frequency-division multiple access) systems. By increasing the channels' frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. In this paper, we aim to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. A genetic algorithm (GA)-based optimization is devised to obtain the cyclic-delay values which provides a higher system sum-rate than the multi-degree adaptive cyclic-delay diversity method and has a lower computational complexity than the exhaustive method with only a slight degradation in system sum-rate. The effectiveness of the proposed method is verified by extensive computer simulations.

Hybrid relay diversity scheme for OFDM-based system

Abstract: A relay diversity scheme is proposed to provide diversity gain and better system performance in wireless fading environment. The hybrid relay diversity (HRD) scheme combines the concept of distributed space-time block coding (DSTBC) and relay cyclic delay diversity (RCDD) for OFDM-based relay communication network with more than one relay nodes. The scheme addresses the issue of achieving maximum spatial and multipath diversity without increasing the complexity of source and destination nodes. The bit error rate (BER) performance of HRD is compared to DSTBC and RCDD where better performance is obtained.

A Cooperative Spectrum Sensing Information Transmission Scheme Based on Cyclic Delay Diversity

Abstract: To improve the reliability of spectrum sensing, a cooperative spectrum sensing information transmission scheme is discussed in this paper. Pre-coding and cyclic delay diversity (CDD) techniques are fully considered and properly combined to obtain diversity gains. Simulation results show that the proposed scheme can reduce error rate and further improve the cooperative spectrum sensing performance in the multipath fading channel. Keywords-Cooperative spectrum; Cyclic delay diversity; Spacefrequency coding

Asymptotically Optimal Likelihood detector for cyclostationary signature induced by Cyclic Delay Diversity

Abstract: The Cyclic Delay Diversity (CDD)-induced cyclostationary signature is considered to be a robust and cost-efficient scheme for self-coordination of Cognitive Radio Network (CRN). However, the performance of network coordination relies on the reliable detection of such cyclostationary signatures. In this paper, we deduce an exact covariance matrix to characterize the statistics of cyclostationary signature. Based on the covariance matrix, we propose an Asymptotically Optimal Likelihood (AOL) detector for the test of the CDD-induced cyclostationary signature. In addition, an Asymptotically Maximum Likelihood Probability (AMLP) criterion is provided to solve the multiple signatures identification issue. Comprehensive simulations verify that the proposed detector provides superior performance in detection probability and observation duration, compared with the existing Constant False Alarm Rate (CFAR) detector.

Averaged BER Performance Analysis of CDD-DSF-Relay schemes for MC-CDMA Systems over Multipath Rayleigh Fading Channles

Abstract: In this paper, CDD(Cyclic Delay Diversity)-DSF(decode-and-selectively forward) relay schemes are proposed for MC-CDMA(multicarrier-code division multiple access) systems over multipath Rayleigh fading channels On the contrary to general DSF schemes, each relay equipped a CDD method can transmit on single channel Therefore, all link channels between destination and relays can be considered as a single channel which is widely delay spread The cooperative diversity of relay networks can be obtained as the frequency diversity for MC-CDMA systems with proposed CDD schemes Furthermore, a semi-analytical approach for the averaged bit error rare(BER) performance evaluation is proposed for the proposed CDD-DSF-Relay schemes By simulation and numerical results, it is confirmed that the proposed one can be a possible solution to achieve cooperative diversity gain without a reduction of spectral efficiency

A Robust Frequency Offset Estimation Scheme for OFDM System with Cyclic Delay Diversity

Abstract: Cyclic delay diversity (CDD) is a simple technique to intentionally increase frequency selectivity of channels for orthogonal frequency division multiplexing (OFDM).This paper proposes a residual carrier frequency offset (RFO) estimation scheme for OFDMbased broadcasting system using CDD. In order to improve the RFO estimation, this paper addresses a decision scheme of the amount of cyclic delay and pilot pattern used to estimate the RFO. By computer simulation, the proposed estimator is shown to benefit form propoerly chosen delay parameter and perform robustly. Keywords—OFDM, cyclic delay diversity, FM system, synchronization

A method of detecting signals

Abstract: A method of detecting signals transmitted using differential cyclic delay diversity is provided, the method including the steps of: computing a plurality of matrices using received sequences of observation symbols; determining possible transmitted symbol based on the set of possible information symbols; and computing transmitted symbol using maximum likelihood detection.

Transmission device for orthogonal frequency division multiplexing system and method for improving cyclic delay diversity performance

Abstract: This invention, belonging to a wireless communication technology filed, discloses a transmission device of an Orthogonal Frequency Division Multiplexing (OFDM) system and a method for improving cyclic delay diversity performance. The transmission device includes multiple antennas, and also includes: a sub-carrier generation module (31), which is set to generate sub-carrier signals to which a cyclic delay is applied with a cluster as a unit; an information generation module (32), which is set to generate information corresponding to the sub-carrier signals; a modulation module (33), which is set to modulate the information corresponding to the sub-carrier signals with corresponding sub-carrier; and a sub-carrier sum module (34), which is set to sum all the sub-carriers modulated by one antenna to obtain transmission signals of the antenna, wherein the transmission signals of the antenna are used to be transmitted to a terminal from the antenna. The transmission device and the corresponding method of this invention, generating the sub-carrier signals to which the cyclic delay is applied with a cluster as a unit at a transmission end, enable the terminal to obtain accurate channel estimation on the basis of no change of original algorithm after the terminal receives the transmission signals.

On Cyclic Delay Diversity OFDM Based Channels

Abstract: Orthogonal Frequency Division Multiplexing, so called OFDM, has found a prominent place in various wireless systems and networks as a method of encoding data over multiple carrier frequencies. OFDM-based communication systems, however, lacking inherent diversity, are capable of benefiting from different spatial diversity schemes. One such scheme, Cyclic Delay Diversity (CDD) is a method to provide spatial diversity which can be also interpreted as a Space-Time Block Coding (STBC) step. The main idea is to add more transmit antennas at the transmitter side sending the same streams of data, though with differing time delays. In [1], the capacity of a point-to-point OFDM-based channel with CDD is derived for inputs with Gaussian and discrete constellations. In this dissertation, we use the same approach for an OFDM-based single-input single-output (SISO) two-user interference channel (IC). In our model, at the receiver side, the interference is treated as noise. Moreover, since the channel is time-varying (slow-fading), the Shannon capacity in the strict sense is not well-defined, so the expected value of the instantaneous capacity is calculated instead. Furthermore, the channel coefficients are unknown to the transmitters. Thus, in this setting, the probability of outage emerges as a reasonable performance measure. Adding an extra antenna in the transmitters, the SISO IC turns into an MISO IC, which results in increasing the diversity. Both the continuous and discrete inputs are studied and it turns out that decoding interference is helpful in some cases. The results of the simulations for discrete inputs indicate that there