From the analogue age, to the digital age — to today’s 3G — mobile base stations have evolved to offer more performance and lower costs. The pace of change in mobile technology is accelerating and, to meet the coming challenges, open standards are heralding a new age of innovation. Dr. Peter Kenington, technical chair of the Open Base Station Architecture Initiative (OBSAI) discusses the evolution of the base station
In 1979, when the world’s first commercial cellular radio network was opened for business in Japan, few could have imagined the mobile phone’s true potential. The first barely portable mobile phones offering the most basic voice calls are very far removed from today’s tiny mobiles with colour screens and myriad functions.
Less visible — and no less dramatic — has been the evolution in the cellular network, particularly the radio access network. Today’s Base Transceiver Stations (BTS) offer several orders of magnitude higher performance than the typical BTS of 25 years ago. What’s really impressive though is the way that the cost of BTSs has dropped. Today, a macro BTS costs about a fifth of what it would have cost in the 80s and offers much higher coverage, capacity and bandwidth.
Through the years the fundamental influence that has driven down the cost of BTSs has been volume. In the analogue cellular age, the mobile industry implemented many different radio interface standards. Base stations were built from scratch by manufacturers who designed and developed all the hardware and software in their products. Manufacturer’s engineering costs were high. Additionally, with the mobile phone not yet a mass market product, base station sales were measured in the hundreds. Consequently, the unit price of each BTS was high.
The rise and rise of GSM
As mobile telephony grew more popular, BTS volumes increased, but it wasn’t until the rise of a worldwide standard, in the form of GSM (Global System for Mobile Communications), that truly high volumes began to be created. The digital age of the cellular base station started in 1991 with the first GSM network in Finland being officially opened.
Since then GSM has grown to dominate the world mobile phone industry. GSM networks exist today in more than 200 countries and are used by more than one in six of the world’s population. Without GSM and its evolution, the mobile industry could not have grown to the massive size it now is.
BTS makers now have a vast market for base stations built around a single worldwide standard. As volumes have gone up from the hundreds to the thousands, price has come down.
The switch from analogue cellular to digital mobiles happened faster than many expected. In the UK it was originally thought that the changeover would take five to ten years. In fact it happened more or less within two years, driven by concerns over the poor security of analogue systems and was further encouraged by operators wanting to re-use the old analogue spectrum.
Outsourcing is a growing trend
Running in parallel with rapid market growth has been a trend for OEMs to outsource more and more base station components to third party specialist manufacturers. There has been a steady trend towards greater integration within base stations. As the cellular market matured, many components could be outsourced to specialist suppliers. This process began with filter components — for example duplex filters and transmit filters — but now includes higher end products, such as power amplifiers and transceiver elements.
This has enabled BTS manufacturers to free up engineering resources to focus on product development while at the same time cutting overheads. Furthermore, the high volumes that filter manufacturers can achieve by selling products to several OEMs are not available to individual BTS manufacturers. Greater integration naturally brings down costs.
The third age of the cellular base station started in 2001 with the launch of the world’s first commercial WCDMA 3G mobile network in Japan. Built around the UMTS (Universal Mobile Telecommunications System) standard invented in the mid 1990s, these networks offer high speed access and are ushering in a new era in mobile phone capability, with data traffic and revenue rising
Performance increase
Base station performance has undoubtedly increased over the years. In saturated markets, mobile operators are striving to avoid churn — subscribers switching from one operator to another. This has led to pressure to improve the Quality of Service (QoS) that the network provides. Base stations now provide much more capacity and coverage than ever before.
This, plus the increasing need to provide indoor 3G coverage, has led to the development of many more types of base station in the form of microcell and picocell base stations. Indoor coverage for 3G services is particularly important with most users expected to be accessing data services from inside buildings.
These small base stations are low cost, easy to site and are a great way to provide indoor coverage for 3G services. In Japan, the installation of picocell base stations or other indoor solutions is running ahead of those in Europe and will probably account for half the country’s BTS population in the near future. Some major European operators and many experts think the same will happen in European countries and elsewhere.
Alongside all these pressures has been vastly increased pressure over the last three years from operators for lower cost base stations as competition has risen and mobile tariffs have been squeezed.
In an attempt to help drive down BTS costs even further, OBSAI has developed a set of open standards governing the mechanical and electrical interfaces between base station modules. Barely two years after its formation, this industry-led group has managed to pull together the widely disparate philosophies of many of the world’s leading BTS makers into a consensus good enough to produce serious specifications. OBSAI has brought the mobile industry a step closer to a new world that promises even more innovative base stations that take less time to develop and incur lower R&D costs.
Compatability
OBSAI-compliant modules provide mechanical, electrical and basic software compatibility. To avoid duplication of effort, OBSAI has made maximum use of existing standards and specifications, sitting alongside the 3GPP and 3GPP2 standards, for example, without duplicating or superseding their content.
If all the different sizes and types of base station were built around these open standards, then even greater volumes could be achieved by module makers, further cutting prices. Furthermore, maintenance and spares stockholding costs would be substantially reduced for operators, who would have a wider choice of module suppliers to choose from.
The actual costs that base station makers can save by adopting OBSAI specifications will vary, but it should be in the tens of percentage points. As well as saving significant R&D costs, a vendor can produce a wider range of products, including more specialised products that would otherwise be uneconomic to produce because of their lower sales volume.
The widespread availability of standard BTS modules will help OEMs to move into new business areas. The OEMs that thrive and survive will become system integrators and software and services providers, moving to offer installation and even operational services for operators.
Looking ahead
With 3G moving into the mainstream and much talk from industry players about so-called 3.5G in the form of higher speed WCDMA enabled by High Speed Packet Access (HSPA) technology (a combined term for both HSDPA and HSUPA) the role of OBSAI looks set to become even more central to the future of BTS makers and their customers. The development of mobile technology is towards IP and an expansion of air interface technologies. Base stations will remain a key component and must evolve to offer even more capabilities built in.
The mobile industry is moving towards widespread IP-based systems. A hot issue in the fixed telecoms world is Voice over IP (VoIP) and it is more than likely that this will migrate to mobile networks in the coming years. The trend is to move away from circuit-switched networks to packet-switched networks and to have a simplified network structure. This will enable advanced IP-based applications that will raise the demand for high speed mobile access, a demand that base stations must meet.
There will be a need for multimode base stations able to cope with different air interface standards and flexibly to adapt to the demands of a specific location.
WiMAX is one high data rate solution on the horizon. The OBSAI standards are evolving to cater for the new technologies and enable standard modules to offer both 3G and WiMAX interfaces.
Another trend in the way in which BTS technology is deployed is remote RF heads. Separating the transceiver from the base station digital interface enables easier siting and lower installation costs. A single basement site could serve several remote base station transceivers mounted at the top of a building or buildings linked by fibre optic cables.
However cellular base station technology evolves in the future, the standards created by OBSAI have opened the door to the fourth age of the cellular base station. It remains to be seen who in the industry will the first to walk through.