Convergence of WLAN and WCDMA

WLAN works in the open frequency band of 2.4 GHz. With the advantages of low cost, flexible networking, supporting high-speed wireless data access, and using open frequency band, WLAN is suitable for applications such as mobile office, mobile business and mobile Internet access. With limited mobility, the WLAN user can roam between access points (AP), and enjoy a relatively high data transmission rate.

1 Complementary Relationship  Between WLAN and WCDMA

The correlation between mobility and bandwidth in the cases of 2G, 2.5G, 3G and WLAN is shown in Figure 1.

WLAN is quite different from 3G in network coverage. With high bandwidth, in densely populated areas, WLAN can partially perform the functions of 3G in the aspect of mobile data transmission. However, due to its relatively low transmission power, the coverage of WLAN is limited. It is estimated by most experts in the industry that even 1 000 WLANs cannot cover a whole city area. Moreover, WLAN doesn’t support high-speed mobility. In contrast, the 3G network supports the trans-WAN mobility.

WLAN and 3G have different service characteristics. Voice communication and data communication are different in many important aspects. For example, voice signal allows bit errors but not time delay, while data signal tolerates time delay but not bit errors. Consequently, a network optimized for data communication is unsuitable for voice communication, and vice versa. WLAN is mainly used to support data transmission. However, the 3G network is designed to support both voice and data transmissions.

Although WLAN is going to integrate some telephony functions, its current network architecture cannot meet the requirements of QoS and scalability as well as of a billing mechanism. Therefore, it cannot support such advanced applications as voice, multimedia and content provision.

In a word, 3G will be the dominant mobile network and cannot be replaced by WLAN, although competition between them in some marginal areas may appear.

2 Benefits to Operators from  Convergence of WCDMA and  WLAN

Once they are fully utilizing the complementary relationship of WCDMA and WLAN, operators will obtain great benefits from the investment and operation of the converged network.

2.1 Enhancing Subscriber Loyalty

The user group of WCDMA, very similar to that of WLAN, comprises high-end commercial subscribers who usually use a lot of mobile data services. It can be estimated, even without correlative data statistics, that most WCDMA subscribers will use services on WLAN. Therefore, if a mobile operator can provide services on both networks simultaneously (with a common billing system), it would undoubtedly enhance the loyalty of its subscribers, which plays a very important role in a telecom operation market emphasizing competition and service quality.

Sonera in Finland and BT Wireless in UK have been providing wireless Internet access services step by step. Using a SIM card for authentication, their subscribers can seamlessly roam between the GPRS network and the WLAN. Also, all the bills of a subscriber has been integrated into his/her telephone bill, which is a  great convenience for subscribers. In China, China Mobile has also begun to provide similar integrated services as Sonera and BT Wireless offer to high-end commercial subscribers. These services will improve user satisfaction.

2.2 Bringing More Room for Flexible Operation

Although mobility management is rather complex in a converged mobile network, it also means a great chance of making profits. In a mobile environment, a phone number belongs to a single person, which enables the delivery of profitable personalized information service in the future. If the convergence of WLAN and 3G at the service and technical levels goes well, it will help operators to better build-up their specific service modes, and make full use of their original billing systems to create more revenues, thus giving  more room for flexible operation. Also, as a user may be served by different networks (3G and WLAN), operators can provide different service packages to users.

2.3 Saving Resources and Costs

Compared with investment in the WCDMA network, low construction cost is the strength of WLAN.  Therefore, mobile operators may provide low mobility terminals with large traffic volume data services through the WLAN at areas such as airports and commercial buildings where mass data services are needed, which may effectively save the 3G network resources for more expensive data services of high mobility, thus creating best profits from network investment and saving costs on 3G network construction.

3 Six Solutions to Convergence of WCDMA and WLAN

The 3rd Generation Partnership Project (3GPP) has actively tracked and studied WLAN technology, and at the stage of protocol version R6, successionally proposed solutions for the integration of 3G and WLAN. After the feasibility study of interconnection between 3G and WLAN, 3GPP suggested six solutions for the interconnection of the two systems, from simple interconnection to totally seamless interconnection, which are outlined as follows:

(1)Common Billing and Customer Relationship Platform

The inter-working between WLAN and WCDMA is based on a single customer relationship. Subscribers receive only a common bill for both network access services, and both networks work independently.

(2) 3G Based Access Control and Billing

The 3G system provides authentication, authorization and accounting (AAA) to ensure the subscriber’s access to both networks with no difference.

(3)Access to 3G-Based Packed Switching (PS) Services

This solution allows access to the 3G-based PS services such as IP multimedia subsystem (IMS), location based services (LBS), real-time messages, multimedia broadcast/multicast service (MBMS) and their package services through the WLAN, without any requirements on the service continuity between WCDMA and WLAN.

(4)Service Continuity

This solution ensures the 3G-based PS services remain available when subscribers are moving across the WLAN and 3GPP systems.  It also keeps the service continuity while handover takes place between the sub-networks of WLAN.

(5)Seamless Services

This solution allows seamless service continuity of the 3G-based PS services across the 3G and WLAN systems; that is to say, data loss and data intermittence are minimized during the handover.

(6)Access to 3G-Based Circuit Switching (CS) Services

This solution allows access to 3G-based CS services through WLAN and provides seamless mobility management for CS services.

Unified authorization and accounting are the first and the most crucial steps to realizing the convergence of WLAN and WCDMA, which is the basis for an operational WLAN, and also the technical guarantee for mobile operators to raise the operation efficiency of WLAN, cut operation cost and unify subscriber management.

4 ZTE´s Solution to Convergence of WCDMA and WLAN

ZTE has provided the OWLAN solution, an overall solution to the convergence of the WCDMA system and WLAN (as shown in Figure 2). ZTE’s solution to the convergence of CDMA2000 1x and WLAN, which is based on the same architecture as OWLAN, was successfully adopted by China Unicom. This has provided valuable experience for other mobile operators.

Providing flexible authentication, the access controller (AC) of ZTE WLAN can be connected directly with the authentication server (AS) of WCDMA or with the RADIUS server through the RADIUS network.

The authentication and billing server of the WAS WLAN is based on the software and hardware platforms of ZTE’s WCDMA system. It performs unified authentication for  WLAN and GPRS/WCDMA networks. The AS can provide a standard billing interface for the access to charging gateways (CG) or directly to the billing center, providing subscribers the “One-Bill Mode” service. ZTE’s WLAN system provides flexible interfaces for network management, and its AS based on the platforms of the WCDMA network can realize unified network management, or the network management based on the Simple Network Management Protocol, which offers mobile operators more options.

5 Conclusion

It can be concluded that the convergence of WCDMA and WLAN gives mobile operators more chances to provide better services for subscribers. ZTE always commits itself to provide mobile operators with solutions that perfectly meet their demands, and help them integrate the WCDMA network and WLAN in the best way to make more profit.