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The present work is a discussion on the performance analysis of Modified Cooperative Subchannel Allocation (CSA) Algorithms which is used in Alamouti Decoded and Forward (Alamouti DF) Relaying Protocol for wireless multi-user Orthogonal Frequency Division Multiplexing Access (OFDMA) systems. In addition, the performance of approximate Symbol Error Rate (SER) for the Alamouti DF Relaying Protocol with the Cooperative Maximum Ratio Combining Technique (C-MRC) is analyzed and compared with SER upper bound. The approximate SER is asymptotically tight bound at higher Signal-to-Noise Ratio (SNR). From the asymptotic tight bound approximate SER, Particle Swarm Optimization (PSO) based Power Allocation (PA) is determined for the Alamouti DF Relaying Protocol. The simulation results suggested that the Modified Throughput based Subchannel Allocation Algorithm achieved an improved throughput of 6% to 33% compared to that of existing cooperative diversity protocol. Further, the Modified Fairness based Subchannel Allocation Algorithm rendered fairness of 7.2% to 17% among the multiuser against the existing cooperative diversity protocol.

The random fading nature of the wireless communication channel has attracted many researchers to propose novel techniques to raise the cooperative diversity order [

Previously, it has been reported that the performance analysis of SER upper-bound for Alamouti-coded DF Relaying Protocol used the C-MRC technique along with an optimum PA [

In this paper, the performance of approximate SER for the Alamouti DF Relaying Protocol using C-MRC is analyzed, and compared with SER upper bound. In this, the approximate SER is asymptotically tight bound at higher SNR. From the asymptotic tight bound approximate SER, PSO based PA is determined for the Alamouti DF Relaying Protocol. The link between base station and mobile station contributes diversity order one in the system performance, and also depends on the balance of the two channel links from the base station to the relay station and from the relay station to the mobile station. Therefore, the Alamouti DF Relaying Protocol for wireless systems shows an overall performance of diversity orders two.

To achieve high data rates in mobile communication environment, OFDM is a hopeful method because of its multicarrier modulation technique [

In addition, in this paper the performance analysis of proposed modified CSA Algorithms used in Alamouti DF Relaying Protocol for wireless multi-user OFDMA systems so as to achieve increased throughput than the existing relaying protocols. The modified CSA Algorithms used in Alamouti DF Relaying for PSO based PA gives the enhanced throughput and optimized wireless systems.

The rest of this paper is organized as the following: in Section 2, received signal model is described. Performance analysis of Alamouti DF Relaying Protocol is discussed in Section 3. In Section 4, Modified Cooperative Subchannel Allocation for an Alamouti DF Relaying Protocol is presented. The simulation results are discussed in Section 5 and Section 6 concludes this research work.

In this paper, system model consist of one BS, two RS and one MS for an Alamouti DF Relaying Protocol in wireless multi-user OFDMA systems is shown in

Orthogonal Space Time Block Codes (OSTBC) is using multiple transmit and receive antenna, which gives

full data rate and full diversity gain to the system. Alamouti scheme is used to enhance the quality of the channel in the received signal. The encoder transmit matrix takes two modulated symbol

where

In phase 1, the BS is transmitting information to RS and MS. Let us consider,

In phase 2, the MS receives information from RS and BS is gives as,

Assume, the BS is transmitting a symbol

where

The total SNR at the MS using C-MRC technique as follows:

where

The C-MRC for the received signals at the MS in Equations (2), (4), (5), and (7) are combined and could be expressed as follows:

where

After substitution of Equations (11)-(16) in (9) and (10), the received signal at MS is simplified as,

where

Finally, the total SNR at MS using C-MRC technique as follows:

In this paper, the performance of SER approximation for the Alamouti DF Relaying Protocol with the M-PSK modulation system is analyzed, and compared with SER upper bound. In this, the approximate SER is significantly improves at higher SNR. From the results of asymptotic tight bound approximate SER, PSO based PA is determined for the Alamouti DF Relaying Protocol.

The conditional approximate SER of the system can be follow as,

where

To get the SER of the Alamouti DF Relaying Protocol with M-PSK modulation system can be written as,

where

it is experiential that, substituting

In the sequel, an asymptotically tight SER approximate is provided if all of the channel links

where

Therefore for large value x and y, an asymptotically tight approximations as follows,

In this approximate, the errors become insignificant compared to the orders

Replacing x and y in Equations (38) and (39) with

It is well known that the increasing number of relay in wireless communication system can achieved the diversity gain of the cooperative communication system .the optimum relay selection technique such that the base station can select the optimum cooperative relay depending on the channel quality of each link [

The optimum relay selection for Alamouti DF Relaying Protocol is given by

where

In this paper, the performance of Equal PA (EPA) and PSO based PA for Alamouti DF Relaying Protocol are analyzed and compared. Total transmitted power is

In PSO algorithm, all particles are move towards its optimum value. For each iteration, all the particles in this swarm are updated by its position and velocity for optimization ability. In PSO, each particle maintains its position evaluated fitness and velocity. Where

Problem statement:

The SER of the systems with M-PSK modulation can be tightly approximated as

Here the problem statement is, to minimize the

Such that,

where

For optimum single relay selection case,

Pseudo code for particle swarm optimization

1) Initialize

2) Allocate number of particle

3) Generate random particles

4) Initialize random velocity

5) Evaluate fitness function (SER)

6) If

Yes---update

No---end

7) If

Yes----update

No---update velocity and position of random particle.

Continue until iteration end

From PSO algorithm, evaluate the fitness value from Equation (44) under minimum SER condition is reached. If current fitness value (

In this paper, the performance analysis of a modified CSA Algorithms used in Alamouti DF Relaying Protocol for wireless multi-user OFDMA systems is discussed. The total bandwidth is B and each subchannel or subcarrier is N which has bandwidth of

User Data Rate:

The subchannel allocation matrix

where

To enhance the total throughput of the multi-user OFDMA systems, the Modified Throughput based CSA for an Alamouti DF Relaying Protocol is given by,

Subject to:

value for

Pseudocode For Throughput Cooperative Subchannel Allocation

1) Initialize

2) Assign channel

3) Allocated PSO based power to source and relay as

4) Allocate each subchannel to the user -for j = 1 to J

5) Find i to maximize

6) Allocate subchannel to the user

7) Maximize throughput rate

8) end

9) end

In the first step, the channel value is considered for all the subchannels of the entire user and all the variables are initialized in the Pseudo code. In the next step, user is assigned the highest channel value for that subchannel each. For all the users, a simple two step procedure is continuing until the CSA is reached. In the OFDMA systems, thus throughput Pseudo code does not meet fairness among all users.

To enhance the total throughput with maintaining the fairness in the multi-user OFDMA systems, by using Modified Fairness (Max-Min) based CSA for an Alamouti DF Relaying Protocol is given by:

By modifying the channel values for the Fairness based CSA Pseudo code is as follows:

Pseudo Code For Fairness Cooperative Subchannel Allocation

1) Initialize

2)

3) Assign channel

4) Allocated PSO based power to source and relay as

5) Allocate each subchannel to the user --for i = 1 to I

6) (a) find j satisfying

7) (b) Update

8)

9) end while

10) (a) find i satisfying

11) (b) for the found i find j satisfying

12) (c) update

13) end

14) end

In this paper, the total transmitted power of

In this the number of subchannels allocated to the users is N = 256 and the variance of the noise is

The asymptotic performance of the Alamouti DF Relaying Protocol with 4-PSK modulation system is compared with SER upper bound and the approximation is shown in

From the asymptotically tight bound approximation, the performance of Alamouti DF Relaying Protocol shows the diversity order two.

2 dB and 2.5 dB. In the cooperative wireless communication system, the Alamouti DF Relaying Protocol is achieved improved SNR Compared to Alamouti AF Relaying Protocol, due to a decrease in the effects of additive white noise at the relay station from the decoding method. The Alamouti DF Relaying Protocol can achieve a full diversity gain with the enhanced SNR and reduced approximate SER for the base-to-mobile received signal.

From the asymptotic tight bound approximate SER, PSO power ratios (

Therefore, high power is allocated to the RS in order to maximize the total SNR. In addition for

It is observed that the equal power is allocated to the BS and the RS for

Protocol and DF Relaying Protocol, respectively. The modified cooperative subchannel allocation algorithm used in Alamouti DF Relaying Protocol can achieve a full diversity gain with the enhanced SNR and total throughput for wireless systems.

In this paper, the performance of a Modified CSA Algorithms used in Alamouti DF Relaying Protocol for wireless multi-user OFDMA systems is analyzed. In addition, the SER approximation performance analysis of Alamouti DF Relaying Protocol with PSO based PA is analyzed and compared with SER upper bound. From the simulation results, it is observed that the asymptotically approximate SER significantly improves at higher SNR region and also presents good quality match to the system performance in the reasonable-SNR region; they may not be suitable for low SNR regions.

Due to Alamouti DF Relaying Protocol, it is achieved maximum 33% of throughput for Modified Throughput based Subchannel Allocation Algorithm. In addition, it is achieved maximum 16.6% of fairness among the multiuser for Modified Fairness based Subchannel Allocation Algorithm. Further this research can be extended in the direction of Hybrid DF/AF Relaying Protocol for SNR improvements and throughput of the OFDMA systems.

K. Shoukath Ali,P. Sampath, (2016) Modified Cooperative Subchannel Allocation Algorithms and PSO Based Power Allocation for an Alamouti Decode and Forward Relaying Protocol in Multiuser OFDMA Systems. Circuits and Systems,07,1769-1786. doi: 10.4236/cs.2016.78153