an optimized algorithm to adjust the channel quality in...

© 2013, IJARCSSE All Rights Reserved Page | 184

Volume 3, Issue 2, February 2013 ISSN: 2277 128X

International Journal of Advanced Research in Computer Science and Software Engineering Research Paper Available online at: www.ijarcsse.com

An optimized Algorithm to adjust the Channel Quality in

HSDPA Network Nagendar Yamsani

1, Govindavaram Madhu Sri

2, Sathish Kumar Konga

3 and Sangameswar Kanugula

4

1Assistant Professor, SR Engineering College, Warangal, AP, INDIA

2Assistant Professor, University Post Graduate College, Kakatiya University, Warangal, AP, INDIA

3Dept. of Comp. Science (School of Computing), Debre Birhan University, ETHIOPIA

4SR Engineering College, Warangal, AP, INDIA

Abstract – We investigate single user throughput optimization in High Speed Downlink Packet Access (HSDPA).

Specifically, we propose offline and online optimization algorithms which adjust the Channel Quality Indicator (CQI)

used by the network for scheduling of data transmission. In the offline algorithm, a given target block error rate

(BLER) is achieved by adjusting CQI based on ACK/NAK history. By sweeping through different target BLERs, we

can find the throughput optimal BLER offline. This algorithm could be used not only to optimize throughput but also

to enable fair resource allocation among multiple users in HSDPA. In the online algorithm, the CQI offset is adapted

using an estimated short term throughput gradient without the need for a target BLER. An adaptive step size

mechanism is proposed to track temporal variation of the environment. Convergence behaviour of both algorithms is

analyzed. The part of the analysis that deals with constant step size gradient algorithm may be applied to other

stochastic optimization techniques. The convergence analysis is confirmed by our simulations. Simulation results also

yield valuable insights on the value of optimal BLER target. Both offline and online algorithms are shown to yield up

to 25% of throughput improvement over the conventional approach of targeting 10% BLER.

Keywords – Data transmission, Packet, Optimization, Wireless Network.

I. Introduction

The success of 3rd generation wireless cellular networks is mainly based on efficient provisioning of the expected

wide variety of services requiring different Quality of Service with respect to data rate, delay and error rate. In order to

improve support for high data rate packet switched services, 3GPP has developed an evolution of UMTS based on

WCDMA known as High Speed Downlink Packet Access (HSDPA) which was included in the Release 5 specifications.

HSDPA targets increased capacity, reduced round trip delay, and higher peak downlink (DL) data rates. Evolutions of

HSDPA featuring data rates up to 84 Mbps are under development.

In HSDPA, the user equipment (UE) (also known as mobile station) monitors the quality of the downlink wireless

channel and periodically reports this information to the base station (referred to here as NodeB) on the uplink. This

feedback, called Channel Quality Indicator (CQI), is an indication of the highest data rate that the UE can reliably receive

in the existing conditions on the downlink wireless channel. The frequency of reporting CQI is configured by the

network, and is typically set to once every few milliseconds. Using the channel quality reports, the NodeB accordingly

schedules data on the High Speed Physical Downlink Shared Channel (HS-PDSCH). The NodeB’s selection of the

transport block size (number of information bits per packet), number of channelization codes, modulation and resource

allocation choices such as HS-PDSCH transmit power allocation are guided by the NodeB’s interpretation of the reported

CQI. CQI reports are intended to accurately reflect the HSPDSCH performance that the UE can support in the existing

wireless channel conditions. It is recommended in that, in static channel conditions, the UE report CQI such that it

achieves a block error rate (BLER) close to 10% when scheduled data corresponding to the median reported CQI. In

practice, the accuracy of CQI reports in reflecting HS-PDSCH performance is influenced by the wireless channel

conditions such as the speed of the mobile user and the dispersive nature of the channel. Achieving a certain target BLER

at a given scheduled data rate requires different average HS-DSCH SNR under different channel conditions. Also, the

NodeB often uses different transport block sizes, number of codes and modulation, collectively referred to as the

transport format resource combination (TFRC), to achieve similar data rates. The exact choice of TFRC that the NodeB

uses affects the required HS-PDSCH SNR to achieve a certain target BLER. This variability’s may cause the actual

BLER to deviate from the 10% target. Moreover, the 10% target BLER may not yield maximum throughput under all

conditions of the wireless channel.

The cell throughput optimization in HSDPA can be considered a two part problem: one is code and power allocation

across users and the other is maximizing the link throughput for each user for a given resource allocation. In this paper,

we focus on the link throughput optimization and consider throughput optimization through simple adjustments to the

reported CQI. We propose offline and online algorithms for adjusting the CQI. In the offline algorithm, we first propose

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Nagendar et al., International Journal of Advanced Research in Computer Science and Software Engineering 3(2),

February - 2013, pp. 184-194


an adaptive algorithm to achieve a given target BLER using the stochastic gradient descent method, which adjusts the

CQI offset adaptively based on the short term BLER obtained from the ACK/NACK history. By searching through

different target BLERs, we can find the throughput optimal BLER offline. The proposed algorithm can be implemented

at the UE as well as at the Node B. When applied at the Node B, in addition to achieving the target BLER, it can also

save transmit power. This algorithm could be used not only to refine CQI-BLER alignment but also to enable fair

resource allocation among mobile users in HSDPA. Standard stochastic approximation (SA) algorithms typically require

a decreasing step size. We show the convergence of the offline algorithm with a constant step size.

In the online algorithm, we use a variation of the Kiefer-Wolfowitz algorithm in SA, which does not need to specify a

target BLER. The CQI offset is adapted gradually using an estimated short term throughput gradient. Unlike, the stepsize

in the proposed algorithm does not decrease to zero. In addition, an adaptive step size mechanism is proposed to track

temporal variation of the environment. With a constant step size, we show that the proposed online algorithm converges

to a small neighborhood of the local optimal solution. Our simulation results show that the proposed offline algorithm

can achieve the given target BLER with good accuracy. Both throughput optimization algorithms are shown to improve

the throughput by up to 30% in simulation. The throughput optimal BLER is calculated for popular channel path profiles.

In general, the throughput optimal BLER is not always 10% and depends on the channel path profile. For AWGN

channels, it is about 10%, as is implied in. Considering that the UE implementation in the simulation closely mirrors

commercially shipping devices and already includes several receiver optimizations, the additional gain obtained through

the algorithm is indicative of potential HSDPA throughput enhancement realizable in practice.

II. Related Work

Literature survey is the most important step in software development process. Before developing the tool it is

necessary to determine the time factor, economy n company strength. Once these things are satisfied, then next steps is to

determine which operating system and language can be used for developing the tool. Once the programmers start

building the tool the programmers need lot of external support. This support can be obtained from senior programmers,

from book or from websites. Before building the system the above consideration r taken into account for developing the

proposed system.

We have to analysis the Networking: In the world of computers, networking is the practice of linking two or more

computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and

computer software.

Networks consist of the computers, wiring, and other devices, such as hubs, switches and routers that make up the

network infrastructure. Some devices, such as network interface cards, serve as the computer’s connection to the

network. Devices such as switches and routers provide traffic- control strategies for the network. All sorts of different

technologies can actually be employed to move data from one place to another, including wires, radio waves, and even

microwave technology.

Fig.1 Network architecture

Asynchronous Transfer Mode:

Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous

time-division multiplexing and encodes data into small, fixed-sized cells. This differs from other protocols such as the

Internet Protocol Suite or Ethernet that use variable sized packets or frames. ATM has similarity with both circuit and

packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput

data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which

a virtual circuit must be established between two endpoints before the actual data exchange begins.

Network topology-Common layouts

A network topology is the layout of the interconnections of the nodes of a computer network. Common layouts are:

A bus network: all nodes are connected to a common medium along this medium. This was the layout used in the

original Ethernet, called 10BASE5 and 10BASE2.

A star network: all nodes are connected to a special central node. This is the typical layout found in a Wireless LAN,

where each wireless client connects to the central Wireless access point.

A ring network: each node is connected to its left and right neighbor node, such that all nodes are connected and that

each node can reach each other node by traversing nodes left- or rightwards. The Fiber Distributed Data Interface

(FDDI) made use of such a topology.


February - 2013, pp. 184-194


A mesh network: each node is connected to an arbitrary number of neighbors in such a way that there is at least one

traversal from any node to any other.

A fully connected network: each node is connected to every other node in the network.

Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an

example, with FDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is a

star, because all neighboring connections are routed via a central physical location. Overlay network: An overlay network

is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or

logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. The

topology of the overlay network may (and often does) differ from that of the underlying one.

Fig.2 A sample overlay network: IP over SONET over Optical

For example, many peer-to-peer networks are overlay networks because they are organized as nodes of a virtual

system of links run on top of the Internet. The Internet was initially built as an overlay on the telephone network.

The most striking example of an overlay network, however, is the Internet itself: At the IP layer, each node can reach

any other by a direct connection to the desired IP address, thereby creating a fully connected network; the underlying

network, however, is composed of a mesh-like interconnect of sub-networks of varying topologies (and, in fact,

technologies). Address resolution and routing are the means which allows the mapping of the fully-connected IP overlay

network to the underlying ones. Overlay networks have been around since the invention of networking when computer

systems were connected over telephone lines using modems, before any data network existed.

Another example of an overlay network is a distributed hash table, which maps keys to nodes in the network. In this

case, the underlying network is an IP network, and the overlay network is a table (actually map) indexed by keys.

Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service

guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast

have not seen wide acceptance largely because they require modification of all routers in the network. On the other hand,

an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without

cooperation from Internet service providers. The overlay has no control over how packets are routed in the underlying

network between two overlay nodes, but it can control, for example, the sequence of overlay nodes a message traverses

before reaching its destination. Routers: A router is an internetworking device that forwards packets between networks

by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI

Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding

table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known

as the "black hole" interface because data can go into it, however, no further processing is done for said data).

Network security: In the field of networking, the area of network security consists of the provisions and policies

adopted by the network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of the

computer network and network-accessible resources. Network Security is the authorization of access to data in a

network, which is controlled by the network administrator. Users are assigned an ID and password that allows them

access to information and programs within their authority. Network Security covers a variety of computer networks, both

public and private that are used in everyday jobs conducting transactions and communications among businesses,

government agencies and individuals. Networks can be private, such as within a company, and others which might be

open to public access. Network Security is involved in organization, enterprises, and all other type of institutions. It does

as its titles explains, secures the network. Protects and oversees operations being done.

III. Definition of Loss Characteristics

CQI reports are intended to accurately reflect the HS-PDSCH performance that the UE can support in the existing

wireless channel conditions. It is recommended in that, in static channel conditions, the UE report CQI such that it

achieves a block error rate (BLER) close to 10% when scheduled data corresponding to the median reported CQI. In

practice, the accuracy of CQI reports in reflecting HS-PDSCH performance is influenced by the wireless channel

conditions.

Disadvantages:

1. The code and power allocation across users.

2. To maximizing the link throughput for each user for a given resource allocation.

3. Higher round trip delay.

IV. System Design


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Data Flow Diagram / Use Case Diagram / Flow Diagram

The DFD is also called as bubble chart. It is a simple graphical formalism that can be used to represent a system in

terms of the input data to the system, various processing carried out on these data, and the output data is generated by the

system.

Dataflow Diagram: SERVER CLIENT

IP Address

Browse a

File

Via HiddenLink

yes

Connecting..

no

ROUTER

FIle Transfer

IP Address

Connecting..

Flle Receive

Select Node

yes

no

Connecting..

Detect Hidden Link

Inside a Segment

Via Hidden

Link

Detect Hidden Link

Outside a Segment

Service Time

Browse a

received path

End

File Request

Fig.3 Dataflow Diagram

Activity Diagram:

CLIENT ROUTER

Connecting..

Browse

FILE RECEIVE

IP Address

Via HiddenLink

Browse aFile

NO

Yes

FILE TRANSFER

IP Address

Select a Node

Via HiddenLink

Yes

No

Detect Hidden LinkInside a Segment

Detect Hidden LinkOutside a Segment

SERVICE TIME

Connecting..Connecting..

SERVER

Select aReceiving Path


February - 2013, pp. 184-194


Fig.4 Activity Diagram

Sequence Diagram:

SERVER

CLIENTROUTER

Socket Connection

Socket Connection

Click Transfer

Hidden Link

Set transaction Path

Split to Packet

File Transfer

Acknowledgement

File Received

Fig.5 Sequence Diagram

Use Case Diagram:

SERVERCLIENT

Receiving

Path

socket connectionROUTER

Download Request

IP Address

Path Selection

Browse a File

Receive a File

Packet Spliting

Fig.6 Use-case Diagram

INPUT DESIGN


February - 2013, pp. 184-194


The input design is the link between the information system and the user. It comprises the developing specification

and procedures for data preparation and those steps are necessary to put transaction data in to a usable form for

processing can be achieved by inspecting the computer to read data from a written or printed document or it can occur by

having people keying the data directly into the system. The design of input focuses on controlling the amount of input

required, controlling the errors, avoiding delay, avoiding extra steps and keeping the process simple. The input is

designed in such a way so that it provides security and ease of use with retaining the privacy. Input Design considered the

following things:

What data should be given as input?

How the data should be arranged or coded?

The dialog to guide the operating personnel in providing input.

Methods for preparing input validations and steps to follow when error occur.

OBJECTIVES

1. Input Design is the process of converting a user-oriented description of the input into a computer-based system.

This design is important to avoid errors in the data input process and show the correct direction to the management for

getting correct information from the computerized system.

2. It is achieved by creating user-friendly screens for the data entry to handle large volume of data. The goal of

designing input is to make data entry easier and to be free from errors. The data entry screen is designed in such a way

that all the data manipulates can be performed. It also provides record viewing facilities.

3. When the data is entered it will check for its validity. Data can be entered with the help of screens. Appropriate

messages are provided as when needed so that the user will not be in maize of instant. Thus the objective of input design

is to create an input layout that is easy to follow

OUTPUT DESIGN

A quality output is one, which meets the requirements of the end user and presents the information clearly. In any

system results of processing are communicated to the users and to other system through outputs. In output design it is

determined how the information is to be displaced for immediate need and also the hard copy output. It is the most

important and direct source information to the user. Efficient and intelligent output design improves the system’s

relationship to help user decision-making.

1. Designing computer output should proceed in an organized, well thought out manner; the right output must be

developed while ensuring that each output element is designed so that people will find the system can use easily and

effectively. When analysis design computer output, they should Identify the specific output that is needed to meet the

requirements.

2. Select methods for presenting information.

3. Create document, report, or other formats that contain information produced by the system.

The output form of an information system should accomplish one or more of the following objectives.

Convey information about past activities, current status or projections of the

Future.

Signal important events, opportunities, problems, or warnings.

Trigger an action.

Confirm an action.

V. Implementation

Implementation is the stage of the project when the theoretical design is turned out into a working system. Thus it can

be considered to be the most critical stage in achieving a successful new system and in giving the user, confidence that

the new system will work and be effective.

The implementation stage involves careful planning, investigation of the existing system and it’s constraints on

implementation, designing of methods to achieve changeover and evaluation of change over methods.

MODULES:

1. Server Module.

2. Path Set Module.

3. Packet Transaction Module.

4. Client Module.

Server Module: Server module is used to upload the file to the user and view to the user file request. If the server to

accept the user file request the control is passing to the router otherwise the server to reject the user request,

automatically the request is deleted and user download option is canceled.

Path Set Module: The Path set module is used to set the path to transact the files based on this path selection. The server

to provide the ten possibilities based on the shortest path. Normally, twelve towers are used for this transaction process.

For each transaction, the transaction path takes minimum four towers or five towers.

Packet Transaction Module: A Packet transaction module is used to split the file into eight packets in same size and then

the router send the packets server to client, the client returns the acknowledgement to the server. The server once gets the


February - 2013, pp. 184-194


acknowledgement; send another packet to the client. If tower size is less than the packet size, the server can’t send via the

tower.

Client Module: The Client module can view the server uploaded files and send the download request to the server. For

downloading files the client registers their personal details. After login, the client can change their password and

download the server accepted files.

VI. Test case and Sample Screens

Here are some screens captured from test cases:


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February - 2013, pp. 184-194


VII. Conclusion

We have investigated throughput optimization in HSDPA using two adaptive outer loop algorithms. Both of them

adjust the CQI offset to maximize the throughput. The offline algorithm used an adaptive algorithm to achieve a given

target BLER using the stochastic gradient descent method based on the history of ACK/NACK. By searching through

different target BLERs, the throughput optimal BLER can be found offline. The online algorithm used a variation of the

Kiefer-Wolfowitz algorithm without specifying a target BLER. An adaptive step size mechanism was also proposed to

make the algorithm robust to non-stationary condition. We have shown the convergence of both algorithms with a

constant step size. Simulation results show that the proposed algorithms can achieve up to 30% throughput improvement

over that with 10% target BLER. Interplay between the algorithms proposed here and other system level optimizations.

VIII. References

1. H. J. Kushner and G. G. Yin, Stochastic Approximation and Recursive Algorithms and Applications, 2nd ed. Springer-Verlag,

2003.

2. “3GPP, TR 25.858 version 5.0.0, Physical Layer Aspects of UTRA High Speed Downlink Packet Access” Mar. 29, 2002.

3. J. Derksen, R. Jansen, M. Maijala, and E. Westerberg, “HSDPA performance and evolution” Ericsson Review, vol. 3, pp. 117–

120, 2006.

4. H. J. Kushner and J. Yang, “Analysis of adaptive step size SA algorithms for parameter tracking” IEEE Trans. Automat. Contr.,

vol. 40, no. 8, pp. 1403–1410, Aug. 1995.

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