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Implementing WiMAX in Legacy Mobile Networks

By Jorg Lippert


As WiFi (News - Alert) hotspots proliferate across the nation and wireless Internet access continues to become a part of everyday life for people on the move, there is a growing need for a universal broadband wireless access network. Because it supports high-throughput broadband connections over long distances and all IP architecture, Worldwide Interoperability for Microwave Access (WiMAX) is emerging as the most likely broadband technology to make that vision a reality. WiMAX can be used for a number of applications, including �last mile� broadband connections, hotspots, backhaul, and high speed enterprise connectivity.

To facilitate rapid deployments of innovative wireless services and technologies, including voice, data, video, and others, the Federal Communications Commission (FCC (News - Alert)) recently announced plans to auction 90 MHz of advanced wireless services spectrum � at 1,710 to 1,755 MHz and at 2,110 to 2,155 MHz. The spectrum auction is scheduled to start on June 29, 2006 according to the FCC. The availability of additional spectrum is expected to give an impetus to the deployment of broadband technologies, like WiMAX.

As more and more WiMAX networks are deployed, they will provide end users with widespread, reliable, cost effective access to basic and advanced IP services. The key benefits WiMAX offers network operators include: high spectral efficiency, higher capacity, and standards-based technology for fixed and mobile wireless access. The technology�s end-to-end IP architecture provides users with optimal connections that enable access to content-rich applications and services, like Voice over IP (VoIP).

While today�s network operators have their hands full growing their existing networks to keep up with demand for voice and simple data services, they do not necessarily need to delay their WiMAX deployments. This is because network operators can choose flexible service delivery platforms that are designed to integrate seamlessly into their legacy networks reducing the cost, complexity and time it takes to deploy WiMAX. Integrated service platforms allow network operators to reuse existing physical plant, operations support systems and back end infrastructure.

Access and Transport

Network operators have a big head start when deploying WiMAX access technology because they can install the new radios at their existing cell sites. In fact, using their existing footprints, most network operators find that they can reach 70-80 percent of their service area. Radios mounted at the tower need to be connected to a central switching station, which can be accomplished using the carrier�s existing Ethernet network or transport network.

Platforms that provide optimum power and system gain enable operators to minimize the number of base stations needed, which translates into reduced capital and operational expenses. Radio spacing also depends on frequency, so WiMAX platforms that flexibly adapt to a range of frequency channels and offer quadrature amplitude modulation help optimize the capacity of the new networks. Some also feature system software that optimizes system parameters for different application traffic demand and user position within a cell and is capable of assigning different priorities to different user groups.

Further integration is available to network operators that choose solutions that use a modular multi-standard base station (MBS) based on GERAN and UTRAN. This is because the MBS allows for the integration of all mobile communication technologies into one system, from GSM and EDGE to 3G/W-CDMA and HSPA, to WiMAX and Flash-OFDM.

Back End Integration

WiMAX is an access technology, but network operators need to do more than install WiMAX radios on their cell towers to provide customers with wireless broadband service. In addition to tying together the physical plant, a good wireless integration platform also ties the WiMAX network to the operator�s back office equipment.

For instance, access and usage policies can be enforced for WiMAX subscribers using existing back office infrastructure. For example, operators who already have Authentication Authorization and Accounting (AAA) servers can reuse them to enforce policy for WiMAX subscribers. For these reasons, it is important for network operators to choose WiMAX platforms and integration solutions that provide them the flexibility to integrate WiMAX as seamlessly and cost effectively as possible into their back office systems. A wireless integration platform that enables flexible authentication methods for casual and trusted users, subscriber management, and back end services is essential for providing a high quality user experience.

The platform works hand in hand with the policy server, which provides necessary portal management. For instance, when a user turns on a laptop that has WiFi, a portal pops up that allows the user or the device to look for available public networks. An existing customer may not see a portal at this juncture because he has already purchased service from the operator and the device has already been authorized and authenticated for the network. However, operators that want to accommodate roamers will need a portal to authenticate and authorize roamers to use their networks.


At the end of the day, WiMAX implies all IP-networking. Therefore, network operators that are finding VoIP to be too challenging to implement on their cellular networks can offer it on their WiMAX networks more easily. Cellular networks are more asymmetrical in terms of available bandwidth, but WiMAX can be implemented symmetrically, which makes it ideal for a full duplex application, such as VoIP.

All-IP also means WiMAX enables seamless interconnectivity with IP multimedia subsystem (IMS) elements, such as content distribution servers. As a result, common content and solutions can be offered for end users, no matter what device or service they use to access their applications. All the network operator needs to have in place are the necessary IMS core elements � CSCF, HSS, Policy Control, Media Gateways � which can be used to enable various multimedia applications over GSM, UMTS, CDMA, and WiMAX networks.

Key Success Factors

In order for WiMAX to succeed in the marketplace, there are key barriers that need to be overcome. First and foremost, the CPEs (customer premises equipment) must be made available in mass quantities at affordable consumer prices. Secondly, harmonizing global spectrum is essential to allow manufacturers to mass produce equipment at low prices and ensure that WiMAX devices work in different geographies. This will provide the technology the economies of scale that are so necessary for its future success. IT

Jorg Lippert is vice president and general manager, Mobile Networks, Siemens (News - Alert). For more information, please visit the company online at

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