10-08-2012, 03:24 PM
Performance evaluation of GSM handover traffic in a GPRS/GSM network
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Abstract
The introduction of GPRS services into GSM networks creates new challenges to network planning engineers. One critical challenge comes from the requirement for providing a certain quality of service for GPRS traffic without significantly degrading the performance of existing GSM services. In a GSM/GPRS integrated network, it becomes necessary to reserve exclusive channels for GPRS in order to provide base-line QoS for GPRS users. On the other hand, the exclusive reservation obviously reduces the capacity of GSM traffic so that has significant impact on the performance of GSM traffic (especially GSM handover traffic). In this paper, we primarily evaluate the performance degradation of GSM handover traffic due to the introduction of GPRS in a GSM/GPRS network when various priority schemes for handover traffic over new call traffic are applied. A simplified case study of a GPRS/GSM network is simulated by using an event-driven simulator. The effect of an increasing GPRS penetration factor on the performance of existing GSM services is also studied. Our key results show that the performance of GSM handover traffic can be significantly degraded by the capacity reduction resulting from the introduction of GPRS but can be amended by using appropriate priority schemes.
Introduction
Many studies have predicted that within next few years there will be an extensive demand for mobile data services, specially wireless Internet [1]. In order to address the inefficiencies of current circuit-switched mobile networks, such as GSM, for carrying bursty data traffic (typical Internet applications show such traffic behavior), packet switching techniques have emerged in mobile networks.
GPRS is a new bearer service that greatly improves and simplifies wireless access to packet data networks, e.g., to the Internet. The basic GPRS concept is to utilize rest traffic channels unused by GSM traffic. In general, GSM traffic has higher priority than GPRS traffic when allocating channels, which means that an ongoing GPRS channel has to be terminated for a pending GSM traffic. On the other hand, in a GSM and GPRS integrated network high GSM traffic load may prevent GPRS traffic from achieving an acceptable quality guarantee if no channel is exclusively dedicated to GPRS. Therefore, given a number of channels for both GSM and GPRS, it is reasonable that a fraction of the channels are exclusively assigned to GPRS and the rest are shared between GSM and GPRS while GSM traffic has higher priority over GPRS traffic. The combination of shared and dedicated traffic channels is so called partial sharing (PS) technique.
Handover handling schemes
When allocating a channel, a simple scheme employed by cellular technologies handles both types of calls (new calls and handovers) without preference. This means that the probabilities of new call blocking and handover failure are the same. This scheme is referred to as the non-prioritized scheme (NPS). However, from the user’s point of view, the forced termination of an ongoing call is considered to be worse than blocking a new call attempt. Therefore, it becomes necessary to introduce methods for decreasing the probability of handover failure as well as new call blocking.
Model description of the studied system
The performance of a cellular network can be investigated by using either simulation or analytical study (or their combination). Simulation models are preferred when studying the behavior of a specific cellular system covering a given area. In this paper we carry out the performance study on the basis of computer simulation. An event-driven simulator has been implemented using a simulation library developed in C++ .
Simulation results
In this section we present simulation results to show the effects of each handover handling schemes on the performance of GSM traffic. All results are presented as curves versus the total GSM offered traffic (i.e., new calls and handovers) in Erlangs.
One of our main objectives is to investigate how the GSM handover traffic is affected by the GPRS PS implementation into the GSM network. We notice that depending on the GPRS penetration factor, Ngprs should change in order to guarantee appropriate QoS for GPRS users. As the number of GPRS subscribers grows, GPRS traffic load is hard to estimate; in lack of realistic traffic distribution profiles for GPRS, the GPRS offered traffic load can be simplified to be proportional to the growth of subscriber numbers. Then, we perform simulations for different values of Ngprs, and the effects of an increasing value of Ngprs on the capacity of existing GSM services are computed. Since the first generation of GPRS mobile phones use multi-slot configurations 1:2 and 1:4 [13], values of Ngprs = 1, 2, 4, 6 and 8 are considered in this paper. Ngprs= 0 means that measured parameters are referred to GSM without GPRS PS implementation.
Conclusions and future work
In this paper a comprehensive performance study of GSM handover traffic in a GPRS/GSM network is performed. A simplified case study of a GPRS/GSM network is simulated under two different scenarios: a basic microcell scenario and an overlaid macrocell/microcell scenario. The performance of GSM services in the target microcell is measured while gradually increasing the GPRS traffic. Different handover priority-based channel allocation schemes are proposed to enhance the handover performance.
[attachment=30984]
Abstract
The introduction of GPRS services into GSM networks creates new challenges to network planning engineers. One critical challenge comes from the requirement for providing a certain quality of service for GPRS traffic without significantly degrading the performance of existing GSM services. In a GSM/GPRS integrated network, it becomes necessary to reserve exclusive channels for GPRS in order to provide base-line QoS for GPRS users. On the other hand, the exclusive reservation obviously reduces the capacity of GSM traffic so that has significant impact on the performance of GSM traffic (especially GSM handover traffic). In this paper, we primarily evaluate the performance degradation of GSM handover traffic due to the introduction of GPRS in a GSM/GPRS network when various priority schemes for handover traffic over new call traffic are applied. A simplified case study of a GPRS/GSM network is simulated by using an event-driven simulator. The effect of an increasing GPRS penetration factor on the performance of existing GSM services is also studied. Our key results show that the performance of GSM handover traffic can be significantly degraded by the capacity reduction resulting from the introduction of GPRS but can be amended by using appropriate priority schemes.
Introduction
Many studies have predicted that within next few years there will be an extensive demand for mobile data services, specially wireless Internet [1]. In order to address the inefficiencies of current circuit-switched mobile networks, such as GSM, for carrying bursty data traffic (typical Internet applications show such traffic behavior), packet switching techniques have emerged in mobile networks.
GPRS is a new bearer service that greatly improves and simplifies wireless access to packet data networks, e.g., to the Internet. The basic GPRS concept is to utilize rest traffic channels unused by GSM traffic. In general, GSM traffic has higher priority than GPRS traffic when allocating channels, which means that an ongoing GPRS channel has to be terminated for a pending GSM traffic. On the other hand, in a GSM and GPRS integrated network high GSM traffic load may prevent GPRS traffic from achieving an acceptable quality guarantee if no channel is exclusively dedicated to GPRS. Therefore, given a number of channels for both GSM and GPRS, it is reasonable that a fraction of the channels are exclusively assigned to GPRS and the rest are shared between GSM and GPRS while GSM traffic has higher priority over GPRS traffic. The combination of shared and dedicated traffic channels is so called partial sharing (PS) technique.
Handover handling schemes
When allocating a channel, a simple scheme employed by cellular technologies handles both types of calls (new calls and handovers) without preference. This means that the probabilities of new call blocking and handover failure are the same. This scheme is referred to as the non-prioritized scheme (NPS). However, from the user’s point of view, the forced termination of an ongoing call is considered to be worse than blocking a new call attempt. Therefore, it becomes necessary to introduce methods for decreasing the probability of handover failure as well as new call blocking.
Model description of the studied system
The performance of a cellular network can be investigated by using either simulation or analytical study (or their combination). Simulation models are preferred when studying the behavior of a specific cellular system covering a given area. In this paper we carry out the performance study on the basis of computer simulation. An event-driven simulator has been implemented using a simulation library developed in C++ .
Simulation results
In this section we present simulation results to show the effects of each handover handling schemes on the performance of GSM traffic. All results are presented as curves versus the total GSM offered traffic (i.e., new calls and handovers) in Erlangs.
One of our main objectives is to investigate how the GSM handover traffic is affected by the GPRS PS implementation into the GSM network. We notice that depending on the GPRS penetration factor, Ngprs should change in order to guarantee appropriate QoS for GPRS users. As the number of GPRS subscribers grows, GPRS traffic load is hard to estimate; in lack of realistic traffic distribution profiles for GPRS, the GPRS offered traffic load can be simplified to be proportional to the growth of subscriber numbers. Then, we perform simulations for different values of Ngprs, and the effects of an increasing value of Ngprs on the capacity of existing GSM services are computed. Since the first generation of GPRS mobile phones use multi-slot configurations 1:2 and 1:4 [13], values of Ngprs = 1, 2, 4, 6 and 8 are considered in this paper. Ngprs= 0 means that measured parameters are referred to GSM without GPRS PS implementation.
Conclusions and future work
In this paper a comprehensive performance study of GSM handover traffic in a GPRS/GSM network is performed. A simplified case study of a GPRS/GSM network is simulated under two different scenarios: a basic microcell scenario and an overlaid macrocell/microcell scenario. The performance of GSM services in the target microcell is measured while gradually increasing the GPRS traffic. Different handover priority-based channel allocation schemes are proposed to enhance the handover performance.