Transmultiplexer as precoder

Transmultiplexer as Precodersin Modern Digital Communication

Presented By,

Nirnay Ranjan (1128731038)

Shashank Shukla (1128731058)

(ECE 3rd year)

Electronics & Communication

Engineering

Content

Summary

Introduction

Transmultiplexer System

Precoder

Controlling Bandwidth Efficiency

Optimizing for Noise

Blind Identification

Conclusion

Refrences

Naraina College Of Engg. & Technology , Electronics & Communication Engineering.Naraina College Of Engg. & Technology , Electronics & Communication Engineering.

Summary

This Seminar presents a system of modern communication which is

used to convert from time multiplexed components of a signal to a

frequency multiplexed version. In this Seminar we review the fundamental infrastructure behind these

methods. the transmultiplexer system is introduced and the

mathematical framework develope. we present the theory behind the

cancellation of multiuser interference and Amour system. We make

brief remarks on handling the effects of channel Noise.The

fundamentals behind blind identification of channels using

transmultiplexers is reviewed.

Naraina College Of Engg. & Technology , Electronics & Communication Engineering.

Introduction

Transmultiplexers have been known in digital communications

for many years.

Historically the transmultiplexer has been viewed as a system

that converts from time multiplexed components of a signal to

a frequency multiplexed version.

The role of transmultiplexers in digital communications has

gained new importance because of many recent results in filter

bank precoders.


Transmultiplexer System


A transmultiplexer is a structure that combines a collection of

signals into a single signal at a higher rate; i.e., it is the dual of

a filter bank.

Transmultiplexers were originally studied in the context of

converting time-domain-multiplexed (TDM) signals into

frequency domain multiplexed (FDM) signals with the goal of

converting back to time-domain-multiplexed signals at some

later point .

It includes discrete cosine transform processor used to receive

a linearly coded time division signal.

Block Diagram of Transmux System

In the given block diagram the symbol streams

are passed through the interpolation filters or

transmitter filters to produce the signals


In the above block diagram the received signal

are totally different from the input signal..

There are two reason behind this, the first is MUI

and second is ISI introduced by the Channel.

ISI is a form of distortion of a Signal in which

one symbol interferes with subsequent symbols


Generalization of M-userTransmux

In this the M-sampled signal are transmitted through M different

channels.

This generalization has become important in the context of

multiuser communication over wireless communication.


Zero-Padding

Zero-Padding is a simple concept, used to

adding an additional Zeroes at the ending of

any time domain symbol stream.

Zero-Padding is used to increase the length

of a time domain symbol stream.

It is used to counter the IBI (Inter Block

Interference).


TransMux with Zero-Padding


Zero-Jamming

Zero-Jamming is a simple concept, used to

adding an additional Zeroes at the Begining

of the successive received signal.

It is used to counter the IBI (Inter Block

Interference).


TransMux With Zero-Jamming


Precoding

Precoding is a generalization of beamforming to support multi-

stream (or multi-layer) transmission in multi-antenna wireless

communications.

In point-to-point systems, precoding means that multiple data

streams are emitted from the transmit antennas with

independent and appropriate weightings such that the link

throughput is maximized at the receiver output.


Controlling Bandwidth Efficiency

This is known precisely as AMOUR systemdeveloped by Giannakis et al.

AMOUR means A Mutually-Orthogonal Usercode-Receiver.

From the figure of transmux,it consists of Mindependent symbol stream. If these have to beseparated successfully later, then the spacingbetween the samples of sk (n) must be at least Mtimes larger than the spacing T between the symbolsentering the channels Ck (n).


The “Bandwidth expansion Factor” is given by,

Γ=P/M=M+L/M

It is price paid ,in terms of redundancy which allowsequalization of FIR channels of order n.

A slight variation of the redundant transmultiplexersystem is obtain when we make each user look likeK users.This can be done by blocking the mth user

K-fold.

Γ^= P^/MK=MK+L/MK


Optimizing For Noise

It is known that noise can never be eliminated

completely, but can only be reduced to optimum

value .

Consider a transmultiplexer. Assume that the filters

have order < P so E (z) and R (z) are constants.

All systems described in the preceding paragraphs

fall under the category of zero-forcing equalizers .


Block Diagram Of TRANSMUX In Polyphase Form


Consider a TransMux with Reciever and transmitter filters R(z) and

E(z) respectively.

The Transfer Function from Input to Output is the prouct of

E(z)Cb(z)R(z),where Cb(z) is the blocked version of channel.

The condition for perfect recovery in absence

of noise can be attained by

EAR=I

E is said to be the left inverse of AR which

used minimize the channel noise at the

reciever output.

Since P>M this same left inverse is not unique.


Blind Identification

In mobile communication, the channel transfer

functions are unknown and have to be estimated.

Such estimation can be done either with the help of

training signals or by blind identification methods.

It is well known that with non redundant systems

(P = M) blind identification is not possible unless we

use fourth order moments.


Consider again the single channel system of Fig. 10.Assume

as that the channel is FIR with order ≤ L, that the receiver filters

have order ≤ P −1, and that the transmitting filters have order ≤

M − 1.

Figure 11 shows the path from the transmitted symbols to the

channel output y(n).For convenience we consider the blocked

version y(n) as indicated. With the vector s(n) as defined in the

figure,we then have


Where A is defined as

This is a full-banded Toeplitz

matrix representing the FIR

channel of order ≤ L.


Conclusion

As all know that no system whether in

communication field or electronic field is perfect.

In this topic One problem which was not addressed

in this review is the minimization of redundancy in

the precoder.

Another important aspects was not defined is

resistance to channel nulls.


References:-

A tutorial review of “Transmultiplexer as precoder”.

Akansu, A. N., Duhamel, P., Lin, X., and Courville, M. de. “Orthogonaltransmultiplexers in communications: a review,” IEEE Trans. SP, April1998.

Giannakis, G. B. “Filter banks for blind channel identification and equalization,”IEEE Signal Processing Letters.

Giannakis, G. B., Wang, Z., Scaglione, A., and Barbarossa, S., “Amour—generalized multicarrier transceivers for blind CDMA regardless of multipath,”IEEE Trans. Comm., pp 2064–2076, Dec. 2000.

Precoding Techniques for Digital Communication Systems www.springer.com

Precoding - Wikipedia the free encyclopedia

www.en.wikipedia.org

Decimation (Digital Filter Design Toolkit) - LabVIEW 2013 Digital Filter DesignToolkit Help - National Instruments

www.zone.ni.com

www.google.com


http://www.springer.com/engineering/signals/book/978-0-387-71768-5

http://www.springer.com/

http://en.wikipedia.org/wiki/Precoding

http://www.en.wikipedia.org/

http://zone.ni.com/reference/en-XX/help/371988F-01/lvdfdtconcepts/dfd_decimation/

http://www.zone.ni.com/

http://www.google.com/

Transmultiplexer as precoder

Engineering

Transcript of Transmultiplexer as precoder