A Novel Design of Time Varying Analysis of Channel Estimation Methods in OFDM (original) (raw)

Channel estimation in MIMO-OFDM spatial multiplexing using Least Square method

2011 International Symposium on Intelligent Signal Processing and Communications Systems (ISPACS), 2011

In this paper, channel estimation for Spatial Multiplexing (SM) is investigated for MIMO-OFDM system. Due to the channel characteristic of the transmission system is always changed by the time and its importance in wireless transmission to reconstruct the transmitted signals, the channel needs to be known as well as possible. Pilot symbols are used to gather knowledge about the channel and try to estimate it. The channel estimation based on the pilot symbol is called pilot aided channel estimation. In this research, Least Square (LS) method was chosen for initial channel estimation. By using applicable proposed system design, channel state information is estimated through the use of channel information before in subcarriers with no pilot symbols. Zero forcing (ZF) algorithm is used to detect and separate the received signal. The result shows that channel estimation would be better by increasing SNR. Normalized Mean Square Errror (NMSE) value of the channel reached 5x10 -5 for SNR 25 dB. The value of BER reached 3x10 -4 for SNR 25 dB. The estimated channel capacity has the values that closed to the known channel capacity.

AN EXTENSIVE REVIEW OF SIGNIFICANT RESEARCHES ON CHANNEL ESTIMATION IN MIMO-OFDM 1

In communication systems, Multiple-Input Multiple-Output (MIMO) plays a major role because of its high performance. In MIMO systems, multiple antennas are used in both transmitter and receiver to improve the communication performance, whereas the orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation method. MIMO-OFDM is commonly used for communication systems due to its high transmission rates and robustness against multipath fading. In MIMO-OFDM, channel estimation plays a major role and channel estimation is the estimation of the transmitted signal bits using the corresponding received signal bits. While designing the channel estimator for wireless OFDM systems, two main problems will occur. The first problem is the arrangement of pilot information, in which pilot is the reference signal employed by both transmitters and receivers, whereas the second problem is the design of an estimator with both less intricacy and excellent channel tracking ability. In this paper an extensive review on different channel estimation methods used in MIMO-OFDM like pilot based, least square (LS) & minimum mean square error method (MMSE), least mean square (LMS) & recursive least squares (RLS) methods and also other channel estimation methods used in MIMO-OFDM was discussed with their achieved results.

Comparison And Analysis Of Channel Estimation Algorithms In OFDM Systems

International Journal of Scientific & Technology Research, 2013

: - The channel estimation can be performed for analyzing effect of channel on signal by either inserting pilot tones into all of the subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. The block type pilot channel estimation has been developed under the assumption of slow fading channel. When the data is transmitted at high bit rates, the channel impulse response can extend over many symbol periods, it leads to inter symbol interference. Orthogonal Frequency Division Multiplexing is one of the promising candidate to mitigate the ISI. This work improved various channel performance measures based on the comparison of various channel estimation algorithms and suggest a new technique which provides better performance. Keywords: - OFDM, Block Pilot symbols, Channel estimation, Linear minimum mean square error (LMMSE), Mean square error (MSE), Bit error rate (BER) ———————————————————— I. I NTRODUCTION Orthogonal Frequency Division Multiplex...

Channel Estimation in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) provides an effective and low complexity means of eliminating intersymbol interference for transmission over frequency selective fading channels. This technique has received a lot of interest in mobile communication research as the radio channel is usually frequency selective and time variant. In OFDM system, modulation may be coherent or differential. Channel state information (CSI) is required for the OFDM receiver to perform coherent detection or diversity combining, if multiple transmit and receive antennas are deployed. In practice, CSI can be reliably estimated at the receiver by transmitting pilots along with data symbols. Pilot symbol assisted channel estimation is especially attractive for wireless links, where the channel is time-varying. When using differential modulation there is no need for a channel estimate but its performance is inferior to coherent system. In this thesis we investigate and compare various efficient pilot based channel estimati on schemes for OFDM systems. The channel estimation can be performed by either inserting pilot tones into all subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. In this present study, two major types of pilot arrangement such as block-type and comb-type pilot have been focused employing Least Square Error (LSE) and Minimum Mean Square Error (MMSE) channel estimators. Block type pilot sub-carriers is especially suitable for slow-fading radio channels whereas comb type pilots provide better resistance to fast fading channels. Also comb type pilot arrangement is sensitive to frequency selectivity when comparing to block type arrangement. The channel estimation algorithm based on comb type pilots is divided into pilot signal estimation and channel interpolation. The pilot signal estimation is based on LSE and MMSE criteria, together with channel interpolation using linear interpolation and spline cubic interpolation. The symbol error rate (SER) performances of OFDM system for both block type and comb type pilot subcarriers are presented in the work.

Channel Estimation for MIMO-OFDM Systems

2012

Multiple-input multiple (MIMO) communication system combined with the orthogonal frequency division multiplexing (OFDM) modulation technique can achieve reliable high data rate transmission over broadband wireless channels. In this paper performance analysis of channel estimation through different algorithms for estimating channel using different modulation scheme are investigated. The estimation of channel at pilot frequencies is based on Least Square, Minimum mean square, Least Mean Square and Recursive Least Square channel estimation algorithm. We have compared the performances of channel estimation algorithm by measuring bit error rate vs. SNR with BPSK, QPSK 16-PSK and 256-PSK modulation schemes. Recursive Least Square estimation has been shown to perform much better than LS, MMSE and LMS but is more complex than other channel estimation algorithm.

Channel Estimation in MIMO-OFDM System using LS, LMMSE and STBC Technique

International Journal of Engineering Research and, 2017

In this paper, various channel estimation method has been investigated for MIMO-OFDM based system. Multiple input, multiple output (MIMO) is a suitable technique which can gives a high transmission data rate without dominating the transmission power for wireless communication system. The combination of multiple input, multiple output (MIMO) with orthogonal frequency division multiplexing (OFDM) provides excellent data rate transmission beyond the broadband wireless channel. In multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system, the channel state information is very convenient. So channel state information sometime censorious the efficacy of the system and the correct signal cannot received properly at the receiver side. The system performance has been amended by examine the channel at the receiver side properly. The training symbol sends along the data symbol to estimate the channel in the system. In OFDM the cyclic prefix is used at the starting of every transmitted OFDM symbol to reduces the inter carrier interference (ICI) and inter symbol interference (ISI). There is another improved pilot pattern algorithm is used to aid the channel estimation and provide good performance of the system. Space time block code (STBC) is a method though which the channel estimation can be done more effectively in MIMO-OFDM system. In space time code data is encoded and then data is discarding into n-number of spurt and then this data is send by a number of transmitted antennas. In STBC n-number of transmitted and receiving antenna can be used and it provides a good performance in multipath fading channels.

Channel Estimation Schemes for OFDM-MIMO Systems and their Performance Evaluation

2011

High data rates techniques in communication systems have gained considerable attraction in recent years. Orthogonal Frequency Division Multiplexing (OFDM) is a strong candidate for these systems, which is a multi-carrier modulation technique. In OFDM systems, channel estimation is usually performed by sending pilot symbols on sub carriers known at the receiver. The quality of the estimation depends on the pilot arrangement. In this paper we compared the different channel estimation schemes by inserting pilot tones into all of the subcarriers of OFDM symbols with a specific period (Block-type) and (Comb-type). In this paper we also illustrate the minimum requirement of the number of pilots for channel estimation based on Sampling Theorem and other by the use of OFDM linear system.

Channel Estimation in MIMO-OFDM System

Nepal Journal of Science and Technology, 2014

There are no limit of human desire, so day by day we need much higher data speed to facilitate our need but every physical resource like frequency band, transmit signal strength are finite. Within the given limited resource, higher data speed is accomplished by new proficiency called Multiple Input Multiple Output (MIMO), Orthogonal Frequency Division Multiplexing (OFDM) system. MIMO-OFDM fulfills the high data rate requirement through spatial multiplexing gain and improved link reliability due to antenna diversity gain. With this technique, both interference reduction and maximum diversity gain are achieved by increasing number of antennae on either side. Received signal in MIMO-OFDM system is usually distorted by multipath fading. In order to recover the transmitted signal correctly, channel effect must be estimated and repaired at receiver. In this paper the performance evaluating parameter mean square error and symbol error rate of least square error, minimum mean square error a...

A study of channel estimation in OFDM systems

2002

The channel estimation techniques for OFDM systems based on pilot arrangement are investigated. The channel estimation based on comb type pilot arrangement is studied through different algorithms for both estimating channel at pilot frequencies and interpolating the channel. The estimation of channel at pilot frequencies is based on LS and LMS while the channel interpolation is done using linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Furthermore, the channel estimation based on block type pilot arrangement is performed by sending pilots at every sub-channel and using this estimation for a specific number of following symbols. We have also implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots. We have compared the performances of all schemes by measuring bit error rate with 16QAM, QPSK and DQPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.

Channel Estimation for MIMO-OFDM Systems Based on Data Nulling Superimposed Pilots

2017

This paper proposes a new channel estimation algorithm based on data nulling superimposed pilots for the spatial multiplexing multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. In the proposed method each OFDM data symbol of each transmit antenna is spread over all subcarriers by using a spreading matrix then nulls are introduced at certain subcarriers to cancel the mutual interference between data symbols and superimposed pilots. At receiver accurate channel estimation can be easily acquired based on the superimposed pilots. Then the superimposed pilots are removed from the received signal and simple iterative data detection scheme is used to compensate the distortion which occurred in the data symbols. The simulation results of the proposed algorithm show improvement in the estimation accuracy, bit error rate (BER) and computational complexity compared to that of the conventional superimposed pilot technique. The simulation results also show that the performance of the proposed technique approaches that of the frequency division multiplexed pilots technique while having higher data rate and some excess in the receiver complexity.