Reader Forum: WiMAX-LTE network migration – from myth to reality

Editor’s Note: Welcome to our weekly Reader Forum section. In an attempt to broaden our interaction with our readers we have created this forum for those with something meaningful to say to the wireless industry. We want to keep this as open as possible, but maintain some editorial control so as to keep it free of commercials or attacks. Please send along submissions for this section to our editors at: [email protected] or [email protected].
Generations of wireless technologies address the evolving demand for mobile services. Competing standards within every generation vie for prominence measured in market share. The stakes are high, ranging in the hundreds of billions of dollars. With subscriber services needing to be priced at the order of tens of dollars (or a few dollars in emerging markets), subscriber count is the only remedy to recoup invested capital. This has critical implications for the entire supply chain from silicon and component vendors to equipment vendors and wireless network operators. Betting on a losing technology often leads to extinction, particularly for small companies with limited resources and ability to diversify their investment.
Large infrastructure vendors mitigate the risk associated with commercial success of a wireless standard through an “investment duplication” strategy by developing equipment for multiple standards. However, network operators do not have the luxury of adopting such a strategy, opting instead to hedge their risk through a “migration” strategy from one wireless technology to another. In response, vendors promote their products as “upgradeable” through hardware and/or software/firmware change.
The most recent battle between WiMAX and LTE is reminiscent of older battles such as that between CDMA and GSM in the mid 1990’s and most recently the cannibalization of fixed WiMAX based on IEEE 802.16-2004 in favor of mobile WiMAX based on 802.16e-2005. Today, the battle between WiMAX and LTE in the field of mobile services has largely been settled in favor of LTE, even though LTE is yet to be widely deployed. As part of the 3GPP roadmap adopted by major wireless operators, LTE had a distinct advantage over WiMAX, which was enhanced by where network operators were in the business cycle of their 3G systems investments. Nevertheless, several WiMAX “pockets of resistance” remain: fixed applications in emerging markets; rural markets in developed countries; niche applications in vertical markets such as electric smart grids; and in worldwide geographies in frequency bands above those used currently for mobile systems (e.g. 3.x GHz bands). In these applications, WiMAX has almost universally been used for fixed and portable access (indoor/outdoor modems, USB dongles) rather than mobile access (personal handsets).
This is a critical juncture in time when there is no apparent winner and no sure standard for services other than mobile broadband. With WiMAX in retreat, vendors and operators are ever more involved in spinning and evaluating migration strategies (to TD-LTE in particular). Technology migration becomes a critical part of corporate strategy with great consequences and ramifications. Yet, the decision to migrate and the process of migration are arduous. Making the decision requires a clear articulation of vision and a defined set of objectives to act as an evaluation criteria for the decision which cannot be taken without comprehensive knowledge of the state of ecosystem around each technology. Implementing a migration decision requires management of a complex set of tasks each of which requires diligent preparation.
Both WiMAX and LTE feature similar flat-IP network architecture and both use the same physical layer access technology and multiple antenna system techniques to provide high data rates. The migration from one technology to another requires a comprehensive strategy for each of the elements comprising the network which include:
–Consumer devices: In the absence of dual mode units, subscriber devices need to be replaced.
–Base stations: Migration of the base station between technologies is a possible but intricate proposition that many vendors claim, but few support in totality. Operator due diligence often fails to identify pitfalls in base station migration plans or capture the real cost of migration.
Base station architecture comprises baseband, radio, transport, clock/synchronization and power modules. Since WiMAX and LTE use OFDMA as access technology on the downlink, a radio which constitutes about 40% of the cost of base station should in theory support both technologies. Similarly, equivalent data rates and capacity capabilities of both technologies should in theory allow upgrading a baseband module should that module use programmable devices such as FPGAs, DSPs, and NPUs. However, upgrading the complete base station may fail as WiMAX and LTE have different parameters for clocking and synchronization among other details that sit deep at the heart of every technology. Therefore, the ability to migrate a software-defined base station from WiMAX to LTE is not a certain and straightforward proposition.
–Gateways: The WiMAX ASN gateway and LTE serving and packet data network gateways are major network elements that act as the conduit for any user traffic and control plane signaling between the radio access network and core network. Both technologies have implemented open interfaces to facilitate inter-vendor interoperability. Yet, different vendors support different architectures as, for example, separating the data and control planes on multiple hardware units. Selecting the proper architecture, product and vendor is an important aspect in migrating the gateways from WiMAX to LTE. Fortunately, as the traffic load of WiMAX and LTE base stations is expected to be similar, both technologies would require similar provisioning of resources at the gateway obviating the need for additional equipment.
–Management systems: OSS/BSS systems are a critical part of the network. These systems integrate with other network elements such as the access or packet data network gateways and the AAA/HSS servers. Interoperability testing is required to ensure that the installed systems can support the new network. The strategy for OSS/BSS migration needs to take a holistic account of what options the WiMAX network uses and may require complete overhaul of critical functions. For example, TR069 has been popular for WiMAX device provisioning as it leverages functionality of digital subscriber line networks while mobile device provisioning is typically based on OMA/DM.
Since wireless subscribers expect uninterrupted service, it is not feasible to have a prolonged service interruption during the migration process, greatly increasing the complexity of this process. To mitigate service interruption risks, two networks are operated in parallel until subscribers are moved to the new service. This requires repeating processes already performed for the incumbent network such as RAN planning, design and optimization. To facilitate this process, additional spectrum may be required even though both WiMAX and LTE support efficient frequency reuse techniques such as fractional frequency reuse. Frequency and capacity planning become important processes to manage to ensure that quality of service is maintained during the migration process.
Aside from technical and operational considerations, financial and commercial considerations are key elements to justify the migration decision. Migration needs to be considered in the context of improving competitiveness by providing greater service, better performance and lower cost in addition to long term business vision of the network operator. The scale and ubiquity of technology adoption and its evolutionary roadmap are important factors to this end.
A financial model is an important tool to identify and monetize the different parts of the migration plan. The model would reflect capital acquisitions requirem
ents and operational expense
s such as additional equipment, spectrum, human resources, interoperability testing, equipment/network acceptance testing, planning, design and optimization among other expenses. It also allows the network operator to explore and compare different migration strategies including the timing of investments. A proper understanding of the technology and commercial landscape is essential to build an appropriate model and account for proper inputs.
Planning for migration between wireless technologies is a challenging task. WiMAX and LTE feature similar network architecture and performance which allows one to argue that the cost of migration can be low. Yet, the similarities between the two technologies make the decision to migrate in the first instance a very difficult one to make. Knowledge of the state of ecosystem, the intricacies of wireless equipments and due consideration of financial and business objectives are necessary to take migration from the realm of myth into reality.