Optimizing the Traffic of Voice Core Domain in UMTS Network through RNC Re-Homing

Introduction

The past few years have seen mobile operators transition to next-generation mobile networks; specifically from third-generation networks (3G) to long term evolution (LTE). Subscriber numbers and network usage are up; and forecasts point to even greater expansion for many years. Mobile operators are challenged to retain existing subscribers, acquire new ones, and manage costs for serving both. With increased traffic, introduction of data, rich multimedia services as well as larger service areas, the mobile operators are facing the issue of radio network congestion and confronting the demands for larger service coverage areas.

Radio access domain is a primary concern of the UMTS deployment strategy, as it is closely coupled with the mobile operators’ most valued asset: spectrum. However, equally important, the core network (CN) is also playing an essential role in enhancing mobility, service control, efficient use of mobile network resources and a seamless evolution from 2G to 3G/4G. Therefore the network evolution calls for a migration to a softswitch core network with a “flat,” all-IP and simplified architecture and open interfaces which interwork with non- 3rd Generation Partnership Project (3GPP) mobile networks.

Mobile operators are looking for a best network structure to maximize quality of service for users and minimize the impact on legacy networks. Therefore a new challenge for the UMTS operators is how to prevent radio network from congestion and meet the demands from the rapid growing network throughput due to the sharply penetrated mobile data services.

Normally the solution is the network expansion, increasing the size and capacity of mobile networks by installing more network infrastructure into the existing networks, which is an expensive and human-resource intensive undertaking. Therefore, from the radio network aspect, the best approach to avoid cell congestion or channel blocking due to the subscriber increase is to enhance the radio coverage and capacity via increasing the radio infrastructure such as base stations (BTS) and Base Station Controllers (BSC) in Global System for Mobile Communications (GSM), radio domain, or Node-B and Radio Network Controller (RNC) in the Universal Mobile Telecommunication System (UMTS) radio domain.

Figure 1 displays the topology of a GSM/UMTS radio domain in which BTS and Node-B are the first reference point for end subscribers to access into the mobile networks. BSC and RNC, standing above cell sites logically, are responsible for the connection, control and management of base stations in the radio domain. In particular, the radio domain in UMTS, according to 3GPP TS 25.401 and 3GPP TS 23.002, is called UMTS Terrestrial Radio Access Network (UTRAN) which includes one or multiple Radio Network Sub-system (RNS). An RNS contains one RNC and one or more Node B. Similarly, the radio domain in GSM is called GSM RAN which includes one or more Base Station Sub-system (BSS). A BSS contains two types of Network Entities: BSC and BTS. BSC plays a similar role as RNC to control and route calls for the base stations. BTS as the cell site in GSM is to access the mobile stations (MS). The re-homing technique towards the radio domain attempts to achieve the optimization of routings, loading and throughput for both 2G and 3G RAN.

Figure 1.

Architecture of the GSM/UMTS network and the impact scope of the cell site re-homing