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The purpose of this project is to model an uplink call admission control based on signal-to-interference ratio (SIR). Through this, the performance of SIR-based call admission control in UMTS systems is investigated and evaluated with various scenarios. With various scenarios, performance of the systems on the Eb/No, calls granted and released are compared. The software used is OPNET Modeler 14.5, that is to design, simulate, configure and analysis the performance of the systems. The modeling is based on the UMTS architecture. UMTS used WCDMA (Wideband Code Division Multiple Access) as its multiple accesses scheme and offers better performance against radio signal interference. The modeling will investigate the various scenarios to find the better performance for an uplink admission control based on SIR.
UMTS is a Third Generation (3G) wireless protocol that is part of the International Telecommunications Union's IMT-2000 and use Wideband Code Division Multiple Access (WCDMA). For modeling, the UMTS scenario will be applied and from this, the performance of the system will be investigated when the numbers of users increase in the urban area; what will affect and effected, how to solve the problems and what will happen when several base stations or Node-Bs are added in the systems . All this have to do with interference or signal-to-interference ratio (SIR). But still, SIR is using the principle of admission control to maintain the quality of performance that is in admitting a new call. This parameter will be studied in this project.
For power control, all UEs transmit on the same frequency band in the concept of equalizing the received power at the base station for all UEs. Because all UEs will produce interference, thus only certain number of UEs can be accepted in order to ensure an acceptable SIR can be maintained.
- Outer Loop Power Control
The outer loop power control is used to adjust the SIR target value within quality of communication. SIR target is decreased when the received quality is better than the quality that has t o be achieved. Besides maintaining the quality of communication, this method also preventing capacity waste and use lower power as possible.
- Inner Loop Power Control
The inner loop power control compares the measured SIR with the . The base station will sends power up command when the is higher than the measured SIR and vice versa. For inner loop power control, the value is provided by outer loop power control algorithm.
CALL ADMISSION CONTROL (CAC)
The purpose of an admission control algorithm is to decide whether a new call should be admitted into the network or not during the time of call arrival. But, it only be admitted if only if it's Quality of Service (QoS) constrain can be satisfied without sacrifice QoS constrain of existing call in the network. The functionality of admission control is located at RNC where here the information from cells can be obtained.
The UMTS (Universal Mobile Telecommunication System) - third generation cellular telephony (3G) - is expected to do more than merely provide better and fast mobile communication. UMTS will also enable combination of voice and data services in a new way, for example facilitating multimedia and end-to-end broadband services.
In UMTS, the terminal is called mobile or user equipment. The fixed network infrastructure that contains the facilities for transmitting over radio is called Radio Access Network (RAN). The components of the RAN are the base stations, which are called Node B in UMTS, and control nodes (Radio Network Controller (RNC)), which connect the RAN to the Core Network (CN). The Core Network (CN) is the long-range network that transports a user's data to its respective destination.
Main objectives of this project are:
- To understand the concept of signal-to-interference ratio (SIR)
- To study the principles of call admission control
- Learn and explore OPNET Modeler 14.5
- To relate between bit error rate and BLER with SIR
First phase: Research and Study
Do some research in journals and books about admission control, signal-to-interference ratio (SIR), UMTS systems and architecture and etc. This is very important because need to know the basic and how it operates for this entire thing.
Second phase: OPNET Learning
Before start modeling, go through exercises and understood how this software works. Besides that, source code for admission control also being studied.
Third phase: Analysis and simulation
Several simulations had been tested with different scenarios and parameters and the result from this were compared and analyzed to achieve the objectives.
Final phase: Report and presentation
Writing report that contains of literature review, methodology and results that been used. All information and results were gathered and compiled in this report. Prepare for the presentation.
ANALYZE THE PERFOMANCE
Comparison between loaded and unloaded users
To enhance knowledge in OPNET and the SIR-based admission control, the thing that has to do is analyze the performance of SIR-based admission control by investigate the value of Eb/No obtained from the simulation. This analysis is done by compared two different scenarios between loaded users in using one Node-B and two Node-Bs. The modeling is based on the UMTS architecture.
From the simulation, the result of Eb/No is taken to compare the value of both scenarios. As we can see in the theories, increasing the value in Eb/No will increase the value of SIR threshold. When the values of SIR threshold increase, the number of call admit will decrease.
ANALYSIS OF RESULT
From the result above, it can be concluded that, for scenario which is using one Node-B with 35 numbers of fixed UEs, the value of is higher than that using two Node-Bs. Because when there is a single Node-B with many users like urban area and the coverage area is also limited, is getting higher and higher thus increasing the interference between users.
When this thing happened, any attempt calls will be blocked, existing calls will hear noise and disturbing users, or existing call will be rejected. Users will have many bad effects and this will give great losses to the provider. From Figure 6.3, the number of request granted or call is admitted is higher for scenario using 2 Node-Bs. This because increasing in will also increase the SIR threshold. So, when the values of SIR threshold increase, the number of call being admitted will decrease.
The number of released call is proportional with the number of request granted, because in this system it applied one user admit, one user will released. That is the reason why the scenario with one Node-B has lower number of released call.
By using fixed nodes user for both cases means the SIR threshold for both cases are not change. From the result above, the interference for 1 node B is higher than the 2 Node B. This will decrease the SIR for the 1 node B and causes the many users cannot reach the SIR threshold. The number of granted request will also decrease. The reason for this case is, with the using single node B; the loaded user shared the same resources channel in a cell will increase the interference between the users and noise in the cell. To overcome this situation and increase the number of request granted, using more than one node B is a better way. As a result, in term of number of request granted, using more than one single node B in loaded cell is a better way to increase the performances, thus will increase the QoS.
For next semester work, the modeling and simulation will be more various in scenarios and several values input will be change in this UMTS system, such as:
- Vary the block error rate (BLER) to see their effects to SIR
- Comparison of bit error rate (BER) with different scenarios; when the number of node-b increase, unloaded cell, and etc.
For advanced, further study and research on SIR-based admission control. Also same goes for OPNET Modeler; further learning and understanding in modeling, analyzing, simulating and source code.
- H. Holma, and A. Toskala, WCDMA for UMTS, 4th Edition, John Wiley & Sons, 2007.
- Jaana Laiho, Ackim Wacker, Tomas Novosad, Radio Network Planning and Optimisation for UMTS, 2nd Edition, John Wiley & Sons, 2006.
- L. Zhao, and Z. E. Magda, SIR-Based Cal Admission Control for DS-CDMA Cellular Systems, IEEE Comunication, Vol. 12, No.4, pp. 638-644, May 1994.
- NetTest, UMTS Technical Note
- W. Bernhard, S. Peter and A. Marc Peter, UMTS: The Fundamentals, John Wiley & Sons, 2003.
- P. Liesberth, S. Abram, S. Bart and P. Eli De, Mobile and Broadband Access Networks Lab Session OPNET: UMTS - Part 1 Background Information.
- S. Abram and S. Bart, Mobile and Broadband Access Networks Lab Session OPNET: UMTS - Part 2 Background Information.