Comparison And Analysis Of Channel Estimation Algorithms In OFDM Systems (original) (raw)

A Review of Channel Estimation Techniques for OFDM

IJSRD, 2014

During the past few years, the developments in digital communication are rapidly increasing to meet the ever increasing demand of higher data rates. Data rate is decreases due to multipath fading in multiuser environment. OFDM becomes promising technique for achieving higher data rate. Orthogonal Frequency Division Multiplexing (OFDM) has an edge over other frequency multiplexing techniques by using more densely packed carriers, thus achieving higher data rates using similar channels. The primary importance of channel estimation is that it allows the receiver to take into account the effect of channel on the transmitted signal, secondly channel estimation is essential for removing ISI, noise rejection techniques etc. In this report the channel estimation techniques for OFDM is examined and its implementation in MATLAB using pilot based block type channel estimation techniques.. In the end, results of different simulations are compared to conclude that LS algorithm gives less complexity but MMSE algorithm provides comparatively better results. The focus of this paper is non-blind channel estimation technique & compare with blind techniques.

An Improved Algorithm for Channel Estimations of OFDM system based Pilot Signal

2009

This paper presents a new algorithm for the channel estimation of the OFDM system based on a pilot signal for the new generation of high data rate communication systems. In orthogonal frequency division multiplexing (OFDM) systems over fast-varying fading channels, channel estimation and tracking is generally carried out by transmitting known pilot symbols in given positions of the frequency-time grid. In this paper, we propose to derive an improved algorithm based on the calculation of the mean and the variance of the adjacent pilot signals for a specific distribution of the pilot signals in the OFDM frequency-time grid then calculating of the entire unknown channel coefficients from the equation of the mean and the variance. Simulation results shows that the performance of the OFDM system increase as the length of the channel increase where the accuracy of the estimated channel will be increased using this low complexity algorithm, also the number of the pilot signal needed to be inserted in the OFDM signal will be reduced which lead to increase in the throughput of the signal over the OFDM system in compared with other type of the distribution such as Comb type and Block type channel estimation.

Channel Analysis in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) Technique has received a lot of interest in mobile communication research. For wideband mobile communication system, the radio channel is usually frequency selective and time variant. In OFDM system, the channel transfer function of radio channel appears in both frequency and time domains. Therefore, a estimation of channel is necessary for demodulation of OFDM signal. Channel estimation methods for OFDM system based on pilot aided. In this thesis we investigate and compare different pilot based channel estimation 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, major type of pilot arrangement such as 1. Block type 2. Comb type. Both type of pilot arrangement have been focused employing least square error (LSE) and Minimum mean square error (MMSE) channel estimators. Block type pilot subcarrier is suitable for slow fading radio channels. Comb type pilot subcarrier is suitable for fast fading radio channels. Also com type pilot arrangement is sensitive to frequency selective when compare to block type pilot arrangement. Channel estimation algorithm based on comb type pilot is dividing into pilot signal estimation and channel interpolation. Symbol error rate performance of OFDM systems for both type pilot subcarriers are presented in this thesis.

PILOT-AIDED CHANNEL ESTIMATION FOR WIRELESS OFDM SYSTEM IN FADING CHANNELS

Orthogonal frequency division multiplexing (OFDM) is a special case of multi-carrier transmission and it can accommodate high data rate requirement of multimedia based wireless systems. Since channel estimation is an integral part of OFDM systems, it is critical to understand the basis of channel estimation techniques for OFDM systems so that the most appropriate method can be applied. In this article, an extensive overview of channel estimation techniques employed in OFDM systems are presented.

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 Techniques Based on Pilot Arrangement In OFDM Systems

IEEE Transactions on Broadcasting, 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.

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 Algorithms in OFDM, A Review

2013

Main objectives of this paper is to review the work already done related to channel estimation in OFDM (Orthogonal Frequency Division Multiplexing) using QAM (Quadrature Amplitude multiplexing) & PSK (Phase Shift Keying) modulation techniques used in OFDM for wireless communications. To estimate the channels three algorithms are used i.e. LS, LMMSE & Modified MMSE. These three algorithms have basically played key role in channel estimation.

Analyzing block type channel estimation for OFDM based digital communication system

MATEC Web of Conferences, 2016

Orthogonal frequency division multiplexing (OFDM) is a promising technique in the current broadband wireless communication system due to the high data rate transmission capability and the ability to combat frequency selective fading of the channel. Channel estimation is mainly implemented by sending pilot symbols in the transmitted bit streams. In this paper, channel estimation based on block type pilot arrangements is analyzed using Least Square (LS) and Minimum Mean Square Error (MMSE) channel estimators. Performance is analyzed in terms of Bit Error Rate and Mean Square Error by varying pilot energy levels and by varying channel length. It is gathered that performance gets affected considerably with change in pilot energy levels implying there exist an optimum value for pilot energy for getting better performance.