7,860 research outputs found
Is the cyclic prefix necessary?
We show that one can do away with the cyclic prefix (CP) for SC-FDE and OFDM
at the cost of a moderate increase in the complexity of a DFT-based receiver.
Such an approach effectively deals with the decrease in the number of channel
uses due to the introduction of the CP. It is shown that the SINR for SC-FDE
remains the same asymptotically with the proposed receiver without CP as that
of the conventional receiver with CP. The results are shown for transmit
antennas and receive antennas where .Comment: 12 pages, 1 figure. Appeared in part in the Proceedings of
International Symposium on Information Theory (ISIT), Seattle, WA, USA, July
200
Autocorrelation Method for Cyclic Prefix OFDM Estimation
A radio system design providing various data service needs becomes one of the Software Defined Radio (SDR) system advantages. SDR technology applies software functions further to be run in hardware platforms. The need for services with greater data rates can be resolved by using multi-carrier transmission techniques, one of which is the Orthogonal Frequency Division Multiplexing (OFDM) technique. This paper discusses the detection of OFDM signals and their parameters. Multi-carrier transmission can prevent Inter-Symbol Interference (ISI) occurrence due to multi-path fading effect. The recognition can classify the correctly received signals, including the signal conditions mixed with AWGN noise. The autocorrelation method was used to estimate the OFDM parameters, namely the one symbol duration and the cyclic prefix duration. The detected cyclic prefix durations were 1/2, 1/4, 1/8, and 1/16. This method is very simple, because with the cyclic prefix presence, a different signal peak will be detected to further estimate the cyclic prefix duration. The results show the correlation method performance can detect one symbol duration with 100%, accuracy, starting at SNR 0 dB, whereas the cyclic prefix duration accuracy rate is getting more accurate by using a less cyclic prefix duration, which is 1/16 of the total symbol duration
Design of cyclic prefix characteristic-based OFDM system for WiMAX technology
Worldwide interoperability for microwave access (WiMAX) offers the wireless connectivity using orthogonal frequency division multiplexing (OFDM) modulation is a proficient wireless technology that capacities high-speed data transmission facilities. The existing WiMAX techniques have the problem of increase in inter-symbol interference (ISI) and bit error rate (BER) at reduced power spectrum that degrades the performance of WiMAX system due to high data rate transmission. The utilization of different adaptive modulation techniques seen as a potential solution to reduce the ISI and BER for high data rate transmission. In this paper, OFDM is adapted using advanced modulation technique for WiMAX system. The technique proposes the cyclic prefix (CP) is utilized that include supplementary bits at the stage of the transmitter. The proposed technique offers minimization of ISI and improvement in BER. It is defined that performance of the existing CP system is equated with the designed single cyclic prefix (SCP) and double cyclic prefix (DCP) and non-cyclic prefix (NCP). BER, probability of error, and power spectral density are utilized to analyse the performance of the designed system. The OFDM based SCP and DCP and NCP for WiMAX are demonstrated for modulation techniques such as; QPSK, BPSK, and QAM. It is determined that BPSK has the smallest BER when compared to QPSK, 16-QAM, and 64-QAM modulations. It is also demonstrated that QPSK is also very competent, however, it has a higher BER as compared to BPSK modulation. It is also observed that 16-QAM and 64-QAM are less efficient in terms of BER compared to QPSK and BPKS modulations. 64-QAM offers the high data rates, and due to high SNR ratio. The designed system is tested for under AWGN and Rayleigh fading channel, and effect power spectral density of signal to noise ratio on OFDM for rayleigh fading channel are demonstrated for SCP and DCP and NCP. It is determined that the OFDM transmitter with proposed DCP for random signals is efficiently reducing the BER and ISI for WiMAX system
Blind block synchronization algorithms in cyclic prefix systems
In orthogonal frequency division multiplexing
(OFDM) systems, symbol synchronization is a critical step for
successful data transmission. While this task is done in most
current systems by using training symbols, a few studies have
been dedicated to solving the problem blindly, that is, where
training symbols are not available. Blind symbol synchronization
problem is especially important in many blind channel estimation
algorithms in the literature which assume that OFDM symbol
synchronization is perfect. In this paper, a broader version of the
blind symbol synchronization problem is studied, namely, blind
block synchronization in cyclic-prefix (CP) systems. The proposed
algorithm for this broader problem covers the blind symbol
synchronization problem in OFDM systems. Unlike previously
reported algorithms which are based on obtaining sufficient
statistics of received samples, the proposed algorithm is capable
of identifying the correct block boundaries using much less
received data in absence of noise. Simulation results of the
proposed algorithm not only verify the declared property but also
demonstrate improvement in accuracy of symbol synchronization
over previously reported algorithms in presence of noise
OFDM Synthetic Aperture Radar Imaging with Sufficient Cyclic Prefix
The existing linear frequency modulated (LFM) (or step frequency) and random
noise synthetic aperture radar (SAR) systems may correspond to the frequency
hopping (FH) and direct sequence (DS) spread spectrum systems in the past
second and third generation wireless communications. Similar to the current and
future wireless communications generations, in this paper, we propose OFDM SAR
imaging, where a sufficient cyclic prefix (CP) is added to each OFDM pulse. The
sufficient CP insertion converts an inter-symbol interference (ISI) channel
from multipaths into multiple ISI-free subchannels as the key in a wireless
communications system, and analogously, it provides an inter-range-cell
interference (IRCI) free (high range resolution) SAR image in a SAR system. The
sufficient CP insertion along with our newly proposed SAR imaging algorithm
particularly for the OFDM signals also differentiates this paper from all the
existing studies in the literature on OFDM radar signal processing. Simulation
results are presented to illustrate the high range resolution performance of
our proposed CP based OFDM SAR imaging algorithm.Comment: This version has been accepted by IEEE Transactions on Geoscience and
Remote Sensing. IEEE Transactions on Geoscience and Remote Sensing 201
On the Persistency of Excitation for Blind Channel Estimation in Cyclic Prefix Systems
Recently, a new subspace-based blind channel estimation
algorithm in cyclic prefix (CP) system was reported.
A persistency of excitation (PE) property of the input signal is
required for the algorithm to work. In this paper, the probability
of fulfilling the PE property under different situations is studied.
Four factors in the algorithm affect the PE property of the input
signal: 1) signal constellation used; 2) precoder coefficients; 3)
number of consecutive blocks; 4) a number called the repetition
index. Theoretical derivations as well as numerical simulations
are given to demonstrate the main points of this paper. Important
conclusions are 1) that the probability of fulfilling the PE
property increases and converges to unity when the number
of received blocks increases but is always upper-bounded by
a value less than unity when the repetition index increases;
2) that the probability of fulfilling the PE property is smaller
when the algorithm is applied in orthogonal frequency division
multiplexing (OFDM) systems than in single-carrier-cyclic-prefix
(SC-CP) systems
Analysis of cyclic prefix length effect on ISI limitation in OFDM system over a Rayleigh-fading multipath
In this work, the influence of the cyclic prefix on the performance of the OFDM system is studied. We worked out an OFDM transceiver using a 16 QAM modulation scheme, a comparison of the BER for various lengths of the cyclic prefix has been achieved, and the influence of the noise introduced in the channel has been highlighted, for both a Gaussian and Rayleigh noise. The simulation was carried out on MATLAB where the curves of the BER for various lengths of the cyclic prefix are given and compared. We also adopted as a metric the QAM constellation to show the dispersion of the carriers as a consequence of the transmission channel, the mitigation of this effect by the CP is noticeable
Cyclic prefix-based universal filtered multicarrier system and performance analysis
Recently proposed universal filtered multicarrier (UFMC) system is not an orthogonal system in multipath channel environments and might cause significant performance loss. In this paper, the authors propose a cyclic prefix (CP) based UFMC system and first analyze the conditions for interference-free one-tap equalization in the absence of transceiver imperfections. Then the corresponding signal model and output signal-to-noise ratio expression are derived. In the presence of carrier frequency offset, timing offset, and insufficient CP length, the authors establish an analytical system model as a summation of desired signal, intersymbol interference, intercarrier interference, and noise. New channel equalization algorithms are proposed based on the derived analytical signal model. Numerical results show that the derived model matches the simulation results precisely, and the proposed equalization algorithms improve the UFMC system performance in terms of bit error rate
Performance Evaluation of OFDM and Modulation Techniques in Mobile WiMAX (IEEE 802.16e)
Mobile communication has developed very during the last few years. Due to this fast development in this field, subscribers of today are enjoying the use of many applications ranging from data, voice, audio to video irrespective of the place where they are stationed or moving about. WiMAX technology is fast capturing the market in the field of mobile broadband access. WiMAX uses Orthogonal Frequency Division Multiple Access (OFDMA)
at the physical layer. WiMAX uses an adaptive modulation technique to modulate the signal prior to transmitting it. Under adaptive modulation, BPSK, QPSK, 16-QAM and 64 QAM are used for modulating the data depending on the channel
conditions. Cyclic Prefix is used to improve the quality of the signal under hostile environments especially Rayleigh fading. Cyclic prefix adds bits to the start and end of data stream to spread the signal. The receiver removes the bits added prior to further processing of the signal. Cyclic prefixing improves the error performance of signals by minimizing Inter Symbol Interference (ISI). This study focused on the performance of the WiMAX system in terms of Bit Error Rate (BER), Signal to Noise Ratio (SNR), Power Spectral Density (PSD) and Probability of Error (Pe). Two models namely one without the Cyclic Prefix and the other with the Cyclic prefix were built to study these parameters. On analyzing the results, it was observed that adding cyclic prefix improved the error performance marginally especially when the signal is BPSK modulated. The
results of BER vs SNR and Pe vs SNR are different as Pe is the expected value of BER where BER approaches Pe when the simulation is run for a long period of time and the BER is very high. Other situations, Pe and BER show different
results under same conditions. Finally based on the evaluation and conclusion, recommendations were made for
further work
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