2014 IEEE Students’ Conference on Electrical, Electronics and Computer Science

978-1-4799-2526-1/14/$31.00 ©2014 IEEE

Maximization of throughput with advanced Proportional Fair algorithm for LTE-Advanced

Nilam Dhameliya, Rajni Bhoomarker, Sameena Zafar

Electronics and Communication Department Patel College of Science and Technology

Bhopal, India smily_nilam@yahoo.co.in; jounjarerajni@gmail.com; sameena_zafar82@yahoo.com

Abstract— This Paper represents a novel radio resource allocation algorithm which is advanced form of proportional fair (PFclassical) algorithm. Among all existing Radio resource algorithm proportional fair algorithm gives optimum performance compared to two classical algorithms max-C/I and RR. But advanced PF algorithm gives better performance in terms of providing data rate to low SINR users that mean it provides more data rate to the cell edge users. There is no significant change in user equipment throughput either by increased distance or by increment in number of user’s equipment.

Keywords— Quality of Service (QoS); Packet scheduling; Proportional fair (PF); Radio resource allocation (RRA); Long term evolution-advanced (LTE-A); Throughput.

I. INTRODUCTION Fastest growing of next generation of mobile

communication is awaited to support the outburst of high speed packet application and supposed to provide high data rate (1 Gbps) and thus adopt many aggressive communication scheme. It implies more complicated circuit which require higher energy consumption [1]. The increase in bandwidth might have solved the problem of higher demand of data rate for increasing number of users. While targeting towards 3GPP LTE-A which support of upcoming 100MHz BW system. We are limited by BW availability for wireless cellular communication so for efficient use of available BW, Multiplexing and multiple access techniques like OFDM, OFDMA, SC-OFDM, etc. can be used to provide high data rate to users in poor SINR scenario where we can simply increase the transmission power by use of power adaption techniques. The main problem is the shortage of power moreover keeping in mind the greenhouse effect the power minimization is required. But if transmission power is minimized the problem that arises is, the efficient utilization of transmission power. In short a methodical scheduling algorithm is essential for management of resources in a best efficient manner. Thus with the use of better scheduling algorithm the system throughput can be increased to greater extend.

In a multi user environment at a particular time different users will be experiencing different amount of fading over the whole band, and on a particular band a user experiences fading

in time domain. To overcome this problem, RR, MAX-C/I, PF etc. algorithms are used. [2]

In MAX-C/I algorithm user with higher C/I value will be able to get access to resources most of the time and user with less C/I value will get less access to resources and hence it is not always acceptable from quality of service point of view. In RR algorithm, it allocates resources in a periodic and circular manner without considering the channel condition and hence it will lead to lower overall system performance. In PF algorithm, the overall throughput is high but it provides poor performance for low SINR user. In [3] jitter threshold value has not considered. In [4] maintained QoS in terms of maximum tolerable latency but throughput will effect as the user far away from base station.

In this paper, we proposed such an algorithm which provide better performance for low SINR user and maintain overall throughput and QoS parameters. We also performed analysis on change of delay threshold value in the proposed algorithm. Novel Algorithm has ability to provide guarantee on the data rate required for as many users as possible.

The rest of paper is formed as follows. Section –II represents an idea about packet scheduler, section –III represents simulation algorithm and environment, section –IV represents simulation result and analysis, and section-V represents final conclusion.

II. PACKET SCHEDULER A block diagram of packet scheduler is shown in fig.1 the

scheduler is basically divided into three parts based on functionality [3] [4]. These parts are Schedulability Check, Time Domain Scheduling and Frequency Domain Scheduling.

A. Schedulability Check In the first part of scheduling process, the scheduler selects

those users who are schedulable at that time instance. All other users will be kept idle for the next time instance. Here from the set of total active users, whether a particular user is schedulable or not, is decided by two parameters (Delay and Buffer value).

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Fig. 1. Packet Scheduling Block Diagram.[3]

B. Time Domain Scheduling

The main aim of the time domain scheduler is to provide required quality of service, in terms of time jitter in packet delivery, to the user. It divides the users into two priority groups basing up on the delay they are experiencing. The users, whose time jitter value is below the threshold time, are grouped to in to group-1 and a prioritization is done inside the group basing upon the formula given below.

( )max 1,( )

TBR nLP R n

M⎛ ⎞

= ⎜ ⎟⎝ ⎠

(1)

The users, whose jitter is exceeding the threshold value, are given an absolute priority above the user group-1. The priority among users is also present inside group-2. The prioritization formula for second group is given below.

( ) ( )max max 1,( )

TBR nHP LP R n

M M⎛ ⎞

= + ⎜ ⎟⎝ ⎠

(2)

Where, MHP is the priority metric for higher priority users, i.e. the users of group-2, MLP is the priority metric of lower priority users, i.e. users in group-1. TBR(n) is the target bit rate of user ’n’ and R(n) is the achieved past average throughput over a certain time period. This time domain scheduler increases the time domain allocation share for the users in a regular interval to satisfy the jitter requirement to satisfy the quality of service and also increases the priority of the users who are lagging behind their required data rate. According to priority the top Nmux users, who can be allocated resources at least with the lowest modulation and coding rate, are considered. A modification is done in the time domain scheduler in selection of Nmux number of users for the frequency domain scheduler, because it may happen some of the users among the top Nmux users are in such a condition that no data can be send to that user. In this case we can select (Nmux + 1)th user for scheduling.

C. Frequency domain scheduling

The classical PF frequency domain scheduler selects a PRB and then selects a user, so that the overall throughput can be improved. But, this algorithm selects users according to their priority value and then allocates a resource over which the throughput of that particular user can be maximized. In this way the users having higher value of TBR can be given a chance to access the PRBs to achieve throughput with higher priority, where it can improve its throughput. It will help in minimizing user outage and also will help in maintaining the fairness, in terms of reciprocal of required data-rate, among users. The selection of PRB is done using the formula given below.

arg max iik R= (3)

Where, Ri is the maximum achievable data-rate of a particular user over ith resource block.

III. SIMULATION ALGORITHM AND ENVIORNMENT

The Simulation parameters are set according to the values specified by 3GPP-LTE [8].

TABLE I. SIMULATION PARAMETERS[8]

Parameter Value Carrier Frequency 2GHz Delay Spread 0.001ms LA per frame 1 Sub-frame duration 1ms OFDM symbols per sub-frame 14 BW 5MHz FFT size 512

Advanced Proportional Fair Algorithm

1. Initialize number of user set 2. Choose the users whose scheduling time jitter is

less than delay threshold value and assign priority as per equation (1)

3. Find the maximum priority among the users in group-1

4. Assign priority to the users in group-2 as per equation (2)

5. Sort all the users according to their priority value. 6. According to the decreasing order of priority top

most Nmux users are selected who can be provided some data rate at particular time instance.

7. Choose resource block of Maximum gain for corresponding user thus user throughput can be maximized and set allocation flag of that particular PRB to 1.Repeat for Nmux users.

8. If some resource blocks are not allocated and sorted users do not have good channel condition then consider rest of the users.

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MIMO 1X1 Target FER 0.1 Sub-frame duration 1ms Inter Site Distance 1732mtrs Number of active users 30 Mobility of the users 30kmph Per user file size 2Mb Nmux 10 Delay Threshold 5 & 20ms

IV. SIMULATION RESULTS AND ANALYSIS The performance of the proposed advanced proportional

fair algorithm is compared to classical Proportional Fair algorithm.

For proposed algorithm the value of Nmux is 10. Moreover number of active user is 30 and here output is observed for two different value of Delay threshold. Delay Threshold values are 5ms and 20ms for proposed algorithm. Outputs are compared among classical PF, Advanced PF with Delay Threshold as 5ms and Advanced PF with Delay Threshold as 20ms.

The cumulative distribution of BS instantaneous cell throughput is shown in fig.2. It is clear that with keeping the jitter threshold value less, this algorithm is able to provide better data-rate to the low SINR users. This is because of increase in getting access to the resources. It also can be said that the difference in lowest achievable throughput and highest achievable throughput decreases with decrease in jitter threshold value.

Fig. 2. CDF of Instantaneous Base station Throughput

The cumulative distribution of mobile users’ average throughput is shown in fig.3. With increase in the threshold value the scheduler is trying to achieve high throughput for the low SINR users by increasing the number of allocated resources. With increase in jitter threshold more number of users is capable of achieving throughput almost near to their requirement. Also with increase in jitter threshold value more

number of users is getting successful access to the resources as compared to low jitter threshold value. It can be said that this new algorithm is capable of almost guaranteeing the data rate required, at least to 50 percentile users. Whereas proportional fair algorithm is capable of providing required data rate to only 30 percentile users.

Fig. 3. CDF of Mobile user Throughput

The average throughput of the mobile user equipment vs. distance is shown in fig.4. With increase in jitter threshold value the new algorithm is performing better as compared to low jitter threshold value. With more jitter threshold value the algorithm is trying to bring in data rate fairness among the users nearer to base station as well as far away from the base station. The difference, between the maximum throughput achieved by a user and minimum throughput achieved by a user, is minimum in case of proposed algorithm with a higher jitter threshold value as compared to low jitter threshold valued proposed algorithm and proportional fair algorithm. This increment in jitter threshold value is capable of providing more data rate, as compared to the proportional fair algorithm, to the users far away from the base station.

Fig. 4. UE Throughput Vs. Distance

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The average throughput of the mobile user equipment with respect to SINR is shown in fig.5. With increase in jitter threshold value in case of proposed resource allocation scheme the throughput performance for low SINR users is getting improved. This is because the scheduler is getting an opportunity to allocate more resources to the low SINR users without taking much care of the allocation fairness. For low SINR user proposed algorithm provides better performance compared to Classical PF algorithm which is shown in figure. With change in Delay Threshold value for propose algorithm there is little variation in output.

Fig. 5. UE Throughput Vs. SINR

V. CONCLUSIONS In this paper, we presented advanced proportional fair

algorithm which gives better data rate for low SINR users compared to conventional PF algorithm. In addition it gives improved throughput with increase in delay threshold value

for low SINR users. In other resource allocation algorithm like max-C/I, low SINR users have very less chance to access channel which is covered in proposed algorithm without increasing transmission power. It is clear that proposed advanced resource allocation algorithm is performing better as compared to existing proportional fair algorithm, in user point of view.

REFERENCES

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[5] Troels Emil Kolding, “QoS-Aware Proportional Fair Packet Scheduling with Required Activity Detection,” in IEEE 4th Vehicular Technology Conference, 2006., Sept. 2006, pp. 1–5

[6] Yueming Cai, Jiang Yu, Youyun Xu, Mulin Cai” A Comparision of Packet Scheduling algorithms for OFDMA Systems” in Signal Processing and Communication Systems, 2008. ICSPCS 2008. 2nd International Conference on 15-17 Dec. 2008, pp.1 – 5

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[8] 3GPP-LTE,”LTE physical layer framework for the performance verification” Release 10, no.R1-070674, February 2007.