The document discusses adaptive equalization techniques used in wireless communications. It introduces inter-symbol interference as a major challenge for high-speed data transmission over mobile radio channels. Adaptive equalization aims to track time-varying channel characteristics and counteract inter-symbol interference. The techniques include decision-directed and training modes. Common adaptive equalization algorithms are zero forcing, least mean squares, and recursive least squares.
the presentation consists of a brief description about ADAPTIVE LINEAR EQUALIZER , its classification and the associated attributes of ZERO FORCING EQUALIZER and MMSE EQUALIZER
the presentation consists of a brief description about ADAPTIVE LINEAR EQUALIZER , its classification and the associated attributes of ZERO FORCING EQUALIZER and MMSE EQUALIZER
Deterministic MIMO Channel Capacity
• CSI is Known to the Transmitter Side
• CSI is Not Available at the Transmitter Side
Channel Capacity of Random MIMO Channels
This topic will cover the listed topics below regarding linear equalization and its variations:
Fundamental of equalization
Equalizer
Categories of equalization
Depending on the time nature
Structure of adaptive equalization
Classification of equalizer
Linear equalizer
Transversal equalizer
Lattice equalizer
Advantage and disadvantages of lattice
Disadvantages of linear equalizer
Equalization, diversity, and channel coding are three techniques which can be used independently or in tandem to improve received signal quality.
Equalization compensates for intersymbol interference (ISI) created by multipath within time dispersive channels.
If the modulation bandwidth exceeds the coherence bandwidth of the radio channel, ISI occurs and modulation pulses are spread in time.
An equalizer within a receiver compensates for the average range of expected channel amplitude and delay characteristics.
Equalizers must be adaptive since the channel is generally unknown and time varying.
Deterministic MIMO Channel Capacity
• CSI is Known to the Transmitter Side
• CSI is Not Available at the Transmitter Side
Channel Capacity of Random MIMO Channels
This topic will cover the listed topics below regarding linear equalization and its variations:
Fundamental of equalization
Equalizer
Categories of equalization
Depending on the time nature
Structure of adaptive equalization
Classification of equalizer
Linear equalizer
Transversal equalizer
Lattice equalizer
Advantage and disadvantages of lattice
Disadvantages of linear equalizer
Equalization, diversity, and channel coding are three techniques which can be used independently or in tandem to improve received signal quality.
Equalization compensates for intersymbol interference (ISI) created by multipath within time dispersive channels.
If the modulation bandwidth exceeds the coherence bandwidth of the radio channel, ISI occurs and modulation pulses are spread in time.
An equalizer within a receiver compensates for the average range of expected channel amplitude and delay characteristics.
Equalizers must be adaptive since the channel is generally unknown and time varying.
introduction to pulse shaping and equalization in advanced digital communication, it's characterisation, signal design of band limited signal, design of bandlimited signal for no ISI and design of bandlimited signal with controlled ISI-partial response, linear equalization,
Echo Cancellation Algorithms using Adaptive Filters: A Comparative Studyidescitation
An adaptive filter is a filter that self-adjusts its transfer function according to an
optimization algorithm driven by an error signal. Adaptive filter finds its essence in
applications such as echo cancellation, noise cancellation, system identification and many
others. This paper briefly discusses LMS, NLMS and RLS adaptive filter algorithms for
echo cancellation. For the analysis, an acoustic echo canceller is built using LMS, NLMS
and RLS algorithms and the echo cancelled samples are studied using Spectrogram. The
analysis is further extended with its cross-correlation and ERLE (Echo Return Loss
Enhancement) results. Finally, this paper concludes with a better adaptive filter algorithm
for Echo cancellation. The implementation and analysis is done using MATLAB®,
SIMULINK® and SPECTROGRAM V5.0®.
P ERFORMANCE A NALYSIS O F A DAPTIVE N OISE C ANCELLER E MPLOYING N LMS A LG...ijwmn
n voice communication systems, noise cancellation
using adaptive digital filter is a renowned techniq
ue
for extracting desired speech signal through elimin
ating noise from the speech signal corrupted by noi
se.
In this paper, the performance of adaptive noise ca
nceller of Finite Impulse Response (FIR) type has b
een
analysed employing NLMS (Normalized Least Mean Squa
re) algorithm.
An extensive study has been made
to investigate the effects of different parameters,
such as number of filter coefficients, number of s
amples,
step size, and input noise level, on the performanc
e of the adaptive noise cancelling system. All the
results
have been obtained using computer simulations built
on MATLAB platform.
Comparison of different Sub-Band Adaptive Noise Canceller with LMS and RLSijsrd.com
Sub-band adaptive noise is employed in various fields like noise cancellation, echo cancellation and system identification etc. It reduces computational complexity and improve convergence rate. In this paper we perform different Sub-band noise cancellation method for simulation. The Comparison with different algorithm has been done to find out which one is best.
Enhancement of New Channel Equalizer Using Adaptive Neuro Fuzzy Inference SystemIOSR Journals
Abstract: The rapidly increasing need for information communication requires higher speed data transmission over the existing channels. The data rate over these channels is limited mainly by Inter Symbol Interference (ISI). Channel equalizers are used to reduce the effect of ISI. In this paper, a new equalizer based on Adaptive Neuro-Fuzzy Inference System is presented. The performance of the proposed equalizer is evaluated for both linear as well as non-linear channels in terms of bit-error rate for different noise powers. Simulation results show that the proposed equalizer has better Bit Error Rate (BER) performance compared to multi-layer perceptron and least mean square equalizers. However, its BER performance is slightly poorer than that of radial basis function network and optimal Bayesian equalizer but is better in terms of structural complexity. Keywords: Channel equalizer, Hybrid learning algorithm, Intersymbol interference, Membership function, optimal Bayesian equalizer.
Enhancement of New Channel Equalizer Using Adaptive Neuro Fuzzy Inference SystemIOSR Journals
The rapidly increasing need for information communication requires higher speed data transmission over the existing channels. The data rate over these channels is limited mainly by Inter Symbol Interference (ISI). Channel equalizers are used to reduce the effect of ISI. In this paper, a new equalizer based on Adaptive Neuro-Fuzzy Inference System is presented. The performance of the proposed equalizer is evaluated for both linear as well as non-linear channels in terms of bit-error rate for different noise powers. Simulation results show that the proposed equalizer has better Bit Error Rate (BER) performance compared to multi-layer perceptron and least mean square equalizers. However, its BER performance is slightly poorer than that of radial basis function network and optimal Bayesian equalizer but is better in terms of structural complexity.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
Simulation of Adaptive Noise Canceller for an ECG signal AnalysisIDES Editor
In numerous applications of signal processing,
communications and biomedical we are faced with the
necessity to remove noise and distortion from the signals.
Adaptive filtering is one of the most important areas in digital
signal processing to remove background noise and distortion.
In last few years various adaptive algorithms are developed
for noise cancellation. In this paper we have presented an
implementation of LMS (Least Mean Square), NLMS
(Normalized Least Mean Square) and RLS (Recursive Least
Square) algorithms on MATLAB platform with the intention
to compare their performance in noise cancellation application.
We simulate the adaptive filter in MATLAB with a noisy ECG
signal and analyze the performance of algorithms in terms of
MSE (Mean Squared Error), SNR Improvement,
computational complexity and stability. The obtained results
shows that, the RLS algorithm eliminates more noise from
noisy ECG signal and has the best performance but at the cost
of large computational complexity and higher memory
requirements.
Comparison of fx lms and n fxlms algorithms in matlab using active vibration ...IJARIIT
The paper presents simulation results of the performance of adaptive filtering algorithms such as Filtered –x Least
Mean Square (FxLMS) and the Normalized Filtered-x Least Mean Square (NFxLMS) algorithm using the concept of active
vibration control. The FxLMS and NFxLMS algorithms are most popular in adaptive filtering feed-forward control methods.
The FxLMS and the NFxLMS are used in order to overcome the disadvantages of conventional Least Mean Square (LMS)
algorithm. The MATLAB implementations for both the algorithms are carried out and the parameters such as convergence rate,
efficiency, and step size results are compared using the principle of Active Vibration Control.
AREA EFFICIENT & COST EFFECTIVE PULSE SHAPING FILTER FOR SOFTWARE RADIOS ijasuc
In this paper area efficient and cost effective techniques for design of pulse shaping filter have been
presented to improve the computational and implementation complexity. Pulse shaping filters have been
designed and implemented by using Raised cosine filter, Nyquist filter and optimized half band filters for
software defined radio (SDR) based wireless applications. The performance of different filters is compared
in terms of BER and hardware requirements. The results show that the BER performance of the optimized
designs is almost identical to the Raised cosine filter with significant reduction in hardware requirements.
The hardware saving of 60% to 90% can be achieved by replacing the Raised cosine filter with proposed
filters to provide cost effective solution for wireless communication applications.
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Adaptive Equalization
1. Page | 1
ADAPTIVE EQUALIZATION
Oladapo Kayode A.
Outline
Introduction
- Interference
- Inter-symbol interference
Equalization
Categories of equalization
Adaptive Equalization
Operating Modes of Adaptive Equalizer
Block diagram of Adaptive Equalization
Survey of Equalization Techniques
Algorithm for Adaptive Equalization
Introduction
Interference
Wireless transmissions need to counter interference from a large kind of sources. There are two
main type of interference namely:
- Co-channel
- Adjacent Channel
Co-channel is also known as narrow band interference which is due to alternative closely
systems using an equivalent transmission frequency.
Adjacent channel interference case is caused when signals in nearby frequencies have
components outside their allocated range, and these components may interfere with on-going
transmission in the adjacent frequencies.
Inter-symbol interference
In addition to these two types is another type called Inter-symbol interference, which is a form of
twist of a signal in which one symbol interferes with subsequent symbols. This is an unwanted
development because the previous symbols have similar result as noise, therefore creating less
reliable communication.
Figure 1: Inter Symbol Interference. Source: Chethan, Ravisimha & Kurian (2014)
2. Page | 2
Equalization
This is a commonly used strategy for resisting inter symbol Interference. Since Inter-symbol
interference has been recognized as the main blockage to high speed data transmission over
mobile radio channels. Equalization involves the gathering of the dispersed symbol energy into
its original time interval.
Categories of equalization
Equalizers are used in conquering the adverse effects of the channel and can be divided into two
broad categories:
1. Maximum Likelihood Sequence Estimation (MLSE): This consist the making of channel
impulse response measurement and then giving a means for receiver adjustment to the
transmission area.
2. Equalization with filters which make use of filters to reimburse the distorted pulses.
Depending on whether the timing is variant or invariant, equalizer can be categorize as
3. Preset equalizer assume that the channel is time invariant; try to find H(f) and then design
an equalizer depending on H(f).
4. Adaptive equalizer assume that the channel is time variant and also design an equalizer
filter with varying filter coefficients in time according to the change of channel which try
to eliminate ISS and additive noise at each time. This channel is assumed to be slow.
Adaptive Equalization
As a mobile channel fades randomly and varied in time, the equalizer must track that the time
varying characteristics of the mobile channel, and thus are called adaptive equalizers. It is
an equalizer that automatically adapts to time-varying properties of the mobile communication
channel.
The following are the working principles of adaptive equalizers:
1. Application of the received signal to receive filter. In this place, receive filter is not
linked filter. Because the channel impulse response is unknown. The receive filter in here
is just a low‐pass filter that refuse to accept all out of band noise.
2. The output of the receiver filter is pictured at the symbol rate.
3. Sampled signal is applied to adaptive transversal filter equalizer. Transversal filters are
actually FIR discrete time filters.
4. The object is to adapt the coefficients to minimize the noise and inter-symbol interference
(depending on the type of equalizer) at the output.
5. The adaptation of the equalizer is driven by an error signal.
Operating Modes of Adaptive Equalizer
Adaptive equalizer can operate in two modes:
a. Decision Directed Mode which indicates that the receiver decisions are used to generate
error signal.
b. Decision Directed Equalizer: This also indicates that adjustment is efficient in tracking
slow variations in the channel response.
Nevertheless, these approaches are not efficient during initial acquisition, which leads the
training and tracking mode.
c. Training Mode
- Initially a known fixed length training sequence is sent by the transmitter, so that the
receiver’s equalizer adapt to a proper setting for minimum bit error rate (BER) detection.
- Training sequence is pseudo-random sequence or a fixed prescribed bit pattern. The
training sequence is designed to permit an equalizer at the receiver to acquire the proper
3. Page | 3
filter coefficients in the worst possible channel conditions. Therefore when the training
sequence is finished, filter coefficients are near their optimal values for reception of user
data. An adaptive equalizer at the receiver uses a recursive algorithm to evaluate the
channel and estimate filter coefficients to compensate for the channel.
- User data is sent immediately following the training sequence.
- The adaptive equalizer utilizes algorithm to estimate the filer coefficients (maximum
delay, deepest fades, maximum ISI etc.) near the optimum value to compensate for the
distortion.
d. Tracking Mode
- When user data is received, the adaptive algorithm tracks the changes in the channel.
- As a result, adaptive equalizer continuously changes the filter characteristics over time
i.e., weight of the filter changes over time.
- When an equalizer is properly trained, it is said to be converged, equalizers are widely
used in TDMA system.
Block diagram of adaptive equalizer
An adaptive equalizer is a time varying filter which is constantly tuned i.e. the weights are
updated continuously by the adaptive algorithm either by sample basis or block by block basis.
The adaptive algorithm is controlled by error signal, e(t), derived by comparing the output of
equalizer, d(t), with some signal d^(t), which is either exact scaled replica of the transmitted
signal x(t) or which represents a known property of transmitted signal as shown in figure below:
Working Principle:
𝑦(𝑡) − 𝑥(𝑡) ∗ 𝑓(𝑡) + 𝑛𝑏 (𝑡)
𝑑(𝑡) = 𝑥(𝑡) ∗ 𝑓(𝑡) ∗ 𝑒𝑞 (𝑡) + 𝑛𝑏 (𝑡) ∗ 𝑒𝑞 (𝑡)
𝑑(𝑡) = 𝑥(𝑡) ∗ 𝑔(𝑡) + 𝑛𝑏 (𝑡) ∗ 𝑒𝑞 (𝑡)
If, nb(t)=0; d(t) = x(t), such that g(t) = f(t) * heq(t)= (t)
which implies that the equalizer is an inverse filter of the channel
Figure 2: Block diagram of adaptive equalizer Source: SriKisna (2016)
4. Page | 4
Survey of Equalization Techniques
Figure 3: Classification of equalization Source: SriKisna (2016)
The classification of equalizer is determined by the usage of adaptive equalizer output for
subsequent control of the equalizer. Mostly, the decision make determines the value of the digital
data bit being received and applies threshold activity.
This technique can be classified into two broad categories:
i. Linear equalizer which is generally the easiest to implement and have get the concept
involved though the techniques suffer from noise enhancement on frequency-
selective fading channels and are not applicable to wireless communications. In linear
equalization, the output signal d(t) is not used in feedback path to adapt the equalizer
and can be implemented as FIR filter.
ii. In Non-linear equalizer the most common is the decision-feedback equalization
because of its simplicity in implementing and does not suffer from noise
enhancement. But suffer from error propagation when binary digits (bits) are decoded
in error leading to poor performance on channels with low signal-to-noise ratio
(SNR). The best equalization technique to use is maximum likelihood sequence
estimation (MLSE).
Summary of Adaptive Equalization Algorithm
There are three adaptive equalization algorithms namely:
- Zero Forcing Algorithm (ZF): aims to eliminate the intersymbol interference (ISI) at
decision time instants (i.e. at the center of the bit/symbol interval).
5. Page | 5
- Least Mean Squares Algorithm (LMS): derived from “method of steepest descent” and it is
meant for convergence towards minimum mean square error (MMSE)
- Recursive Least Squares Algorithm (RLS): offers faster convergence, but is computationally
more complex than LMS (since matrix inversion is required).
Table 1: Comparison of various algorithms for adaptive equalization
Source: Deepa (n.d)
Bibliography
Chethan B, Ravisimha B & Kurian (2014). The effects of Inter Symbol Interference (ISI) and
FIR Pulse Shaping Filters: A survey. International Journal of Advanced Research in
Electrical, Electronics and Instrumentation Engineering. Vol. 3, Issue 5, May 2014. 9412 -
9416
Deepa T. (n.d). Adaptive Equalization. SRM University. Retrieved from
http://www.srmuniv.ac.in/sites/default/files/files/adaptive_equalizer.pdf.
Goldsmith A. (2004). Wireless Communication. Stanford University.
Ranjan B. (n.d.). Equalization and Diversity Techniques for Wireless Communications: Lecture
Note 30. Department of Electrical Engineering, Indian Institute of Technology, Delhi.
Retrieved from http://textofvideo.nptel.ac.in/117102062/lec29.pdf
SriKisna E. (2016). A Notebook on Wireless Communication System. Retrieved from
https://www.researchgate.net/profile/Shree_Krishna_Khadka2/publication/306035050.