Adaptive Modulation Technique to Improve OFDM

Zayed, Yahia, Ayah, Amr, Mohamed, Hossam

Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

2 PRESENTATION1.nb

Introduction:

These days the wireless communication has included around two third of world population, which is almost linearly proportional to development both in technical field with expansion in client needs.

As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems

Changing the symbol rate increases the rate at which we can send data, but it also increases the bandwidth required.

In a digital communication system, digital information is processed using modulation and coding before it is transmitted. The choice of modula-tion and coding techniques involves a tradeoff between spectral efficiency and resilience to error.

We propose a multi-user multiple-input multiple output (MIMO) Orthogonal frequency Division multiplexing (OFDM) system with adaptive modulation and coding improve system capacity with maintaining good error performance.

In MIMO OFDM wireless systems Data rates and channel capacity can be improved through the use of Adaptive Modulation and Coding (AMC).

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Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

4 PRESENTATION1.nb

OFDM:

OFDM works up to expectations by means of separating the radio waves into smaller sub signals and afterward transmit at the same time at specific frequen-

cies to the recipient.

OFDM is a broadband multicarrier balance system that offers main achievement and advantages over more established, more customary single-bearer bal-

ance techniques on the grounds that it is a superior fit with today’s high velocity information prerequisites and operation in the UHF and microwave range

The main advantages of OFDM are its multipath delay spread resistance and effective spectral utilization by permitting covering in the frequency domain.

The channel execution may be extremely changing over the subcarriers and changes from symbol to symbol makes efficient use of the spectrum by allowing

overlap compared to conventional multicarrier.

Makes efficient use of the spectrum by allowing overlap compared to conventional multicarrier.

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Adaptive Modulation:

Adaptive modulation scheme is used to evaluate the channel or link performance and power output in the RF link.

By analyzing the channel condition and calculating the parameters like PPSNR, channel bandwidth, modulation, antenna size, link configura-

tion, diversity schemes, transmission power and more it becomes easy to take decision for better communication.

The MIMO OFDM system gives critical space diversity and decrease the multipath fading.

Adaptive modulation technique is generally utilized in link adaption to enhance the performance. With AMC, the modulation and coding

scheme (MCS) is adaptively chosen in view of channel quality indication (CQI).

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Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

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Proposed adaptive OFDM :

In this paper, researcher has proposed an effective MCS selection algorithm for MIMO-OFDM system taking in consideration of effective transmis-sion likelihood, considering into record the HARQ operation.

HARQ is a combination of high-rate forward error-correcting coding and ARQ error-control

Hybrid ARQ (HARQ) enables the implementation of AMC by reducing the number of required MCS levels and the sensitivity to measurement error and traffic fluctuations.

The goal is to amplify the system throughput and keep up the bit error rate (BLER) at an acceptable degree. They estimate the execution of MIMO-OFDM system with improvement of AMC and HARQ.

The new channel adaption algorithm endeavors to amplify throughput and adjustment between different modulation and coding schemes in blend with both space-time block codes (STBC).

SNR is the key factor for spatial multiplexing (SM)and H matrix determinant; the parameters which are found to have the most huge impacts on the system throughput. This paper presents another parameter called instantaneous Bit error rate (I-BER). Based on the value of I-BER, the proposed AMCS scheme picks a suitable modulation, coding, and spatial mode (MCS) to enhance the system performance along with maintaining the quality of service (QOS).

8 PRESENTATION1.nb

Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

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BLOCK DIAGRAM AND DESCRIPTIONWe consider a MIMO OFDM system with 2 transmitter and 2 receiving system sending information over 64 subcarriers. The transmitted OFDM symbol is said

to by x. at receiving end sequence received is given by:

y = ∑q=12 ϵ

2 Ηx + η 3.1.1

Where y is the received symbol sequence at the receiver side, H is the 2X2 channel matrix between the transmitter and the get receiver, and n is the Additive

White Gaussian Noise (AWGN) at the receiver side. Here q is the quantity of transmitter and receiving antenna.

The channel matrix between every transmit/receive pair is thought to be independent and symmetric complex Gaussian random variable with unity variance.

ES is the transmit energy.

The above equation can be written as:

y = ∑q=12 ΗS + η 3.1.2

where

s = ϵ2 x And

s’ = [H]-1y = s + [H]-1y 3.1.3

Where [H]-1 is the pseudo inverse of [H].

Therefore, PPSNR = 1var(s'-s)

3.1.4

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Block Diagram of proposed Model

In Transmitter Section

** the source is a stream of random raw binary data . The encoder keeps M past information bits in memory. Depending on the value of SNR obtained, the code

rate of the Convolutional encoder is set. The rates used are 1/2, 2/3 and 3/4.

** Serial to parallel converters are used to convert serial bit stream to parallel data before interleaving block. Parallel processing is fast and efficient.

** Interleaving is a process of mixing or shuffling the input data bits. We use interleaving to avoid brust errors .

** Binary to Decimal Converter change binary data in decimal numbers depending upon the selected modulation scheme. The regulation plans utilized are

BPSK, 4-QAM, 16-QAM, and 64-QAM.

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Block Diagram of proposed Model

** The modulation scheme is adaptivly selected . IFFT changes frequency signal into time space signal. IFFT of size 64 is utilized. ** Cyclic prefix is the process of shifting first one fourth of data bit sequence at the end of bit sequence. It provides a guard interval to eliminate inter symbol interference from the previous symbols . The channel supposed to be on a multipath fading Rayleigh channel.

In receiver Section

At the receiver just opposite action performed to recover the original signal. Cyclic prefix is evacuated as it is not part of the information or data stream.

** FFT changes the time space signal into frequency domain signal. FFT size utilized is 64.

** Demodulation is just a reverse process of Modulation. Which demodulate with the same modulation type used.

** parallel to Serial converter is just a reverse process of Serial to parallel, which are used to convert serial bit stream to Serial.

** As we have used here Convolutional coding to encode the data therefore to decode the data only Viterbi decoded can be used.

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Flow chart

This Flow shows how the adaptive modulation and coding works

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Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

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What is the meaning of adaptive modulation ?

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Channel State Technique

Adaptive modulation has many techniques and algorithms. Maximum Throughput algorithm was used.

All the adaptive modulation algorithms use thresholds to estimate each modulation type .The main difference between all of these algorithms is how the thresholds are derived.

Channel state technique is represented in the figure below . This technique aims to adapt the modulation and coding scheme after deriving an estimation of the channel behavior.

Two parameters were used to to estimate the thresholds ( Channel attenuation coefficient or PPSNR ).

There are five thresholds represented in the figure, by the letters A,B,C,D and E where A is the lowest threshold value, i.e., A<B<C<D<E

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Channel State Technique

The MT algorithm aims to maximize the overall link throughput by selecting for each SNR value the MCS that allows the maximum throughput.

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Channel State Technique

How were these thresholds derived ?

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Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

20 PRESENTATION1.nb

Results :

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Results :

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Outline:

1- Introduction

2- OFDM

3- Proposed adaptive OFDM

4- Block Diagram of proposed work

5- Channel State Technique

6- Results

7- Conclusion

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Conclusion :

OFDM systems can decrease the multipath fading effect and have effective spectral utilization.

MIMO frameworks help to transmit greater amount of information in a less time duration. This subsequently builds the speed of transmission of information.

The use of adaptive modulation allows a wireless system to choose the highest order modulation depending on the channel conditions. By calculat-ing parameters like PPSNR or Channel attenuation coefficient .

Channel state technique was used which aims to adjust the modulation and coding scheme after deriving an estimation of the channel behavior in terms of attenuation coefficient or PPSNR.

one algorithm named Maximum Throughput is used in channel state technique.

At high ppSNR range, the BER of SAMC is lower than that of and non-adaptive modulation.At low ppSNR ranges (i.e. ppSNR<5), both, SAMC and non-adaptive modulation perform like one another

Here we have focused on the ppSNR calculation and on the basis of ppSNR value we have selected the modulation technique.

The result is shown in graphical representation and the result achieved is satisfactory

The accuracy of transmitting data is quite satisfactory. The BER achieved is drastically reduced.

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Any Questions

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