Bookmark & share

By Lv Wu

As construction of 3G networks throughout the world continues to increase every year, first-generation UMTS NodeBs will no longer be able to meet the requirements for network construction and service deployment. Hence, smaller-sized and higher performance NodeBs, which consume less power, are now in great demand. The phased achievements of 3GPP standards and breakthroughs in key technologies have also helped to further facilitate the large-scale commercial application of new-generation NodeBs.


Historical Rules for the Evolution of Base Stations

There has been a rapid development in mobile communications in recent years. We have gone from analog communications to digital communications, from narrowband services to broadband services, with a quick hike of network and subscriber sizes in the process. Base stations, which are an integral part of the mobile communication network, have also undergone a similar evolutionary process.

In 1991, the world's first GSM commercial system was deployed in Europe. At present, GSM networks throughout the world support over 1.68 billion subscribers. GSM base stations (BTSs) have developed from, first-generation BTSs, with basic functions, to second-generation BTSs, featuring higher integrity and output power (more cost-effective and smaller in size), and most recently, to third-generation BTSs, which make provisions for multiple carriers and greater transmit diversity (flexible in deployment). In terms of performance, services, costs, deployment and maintenance, BTSs have been constantly optimized, which has been an essential element in the successful applications of GSM networks.

Since the UMTS commercial network was first deployed in Japan in 2001, by the end of 2005, 94 additional UMTS networks have been deployed worldwide, supporting over 40 million subscribers. First-generation NodeBs were launched from 1999-2002. With the gradual increase of network scale, it has become more difficult to deploy UMTS networks and operators have been placing higher and higher requirements on NodeB performance, cost-effectiveness and flexibility. Under such circumstances, first-generation UMTS NodeBs have been hard-pressed to meet the requirements for network construction and service deployment. The phase achievements of 3GPP standards and breakthroughs in key technologies have helped to boost new-generation NodeBs into large-scale commercial application.


3G Operation Calls for New-Generation NodeB

The two basic characteristics of UMTS network deployment are wide allocation and large quantity of NodeBs. However, first-generation NodeBs, which are now in wide application, have numerous defects:

First of all, NodeB performance is of vital importance for network quality. And a major concern of operators is how best to improve NodeB performance. In deploying high-speed data services, such as HSDPA, traditional NodeBs are restricted by limited base-band processing ability, which greatly affects service throughput.

Second, a major concern in the deployment of UMTS services is how best to control network deployment costs and operation costs. Therefore, NodeBs which account for 80% of total network costs, are crucial for cost reduction.

Third, the resources have almost been totally depleted in NodeBs which are located in urban areas. Therefore, the traditional NodeB construction mode can hardly be applicable for new networks. And finally, 3G standards are developing at a much quicker pace than previous standards, resulting in the painstaking upgrading of NodeBs.

Such disadvantages and inner causes, however, have become the driving force behind the accelerated development of new-generation NodeBs. They will also help to determine the major characteristics of new-generation NodeBs. Furthermore, these NodeBs will adopt the distributed design mode and an open modular structure, where highly efficient power amplification technology and base-band ASIC design will be used to solve problems with the operation and construction of NodeBs. This would also include such problems as, NodeB performance, costs and site selection.


More Advanced Technologies for New-Generation NodeB

New-generation NodeBs are closely tied with the development of 3GPP standards. A few breakthroughs in key NodeB technologies will hasten the evolution of NodeBs that will be smaller in size, with less power consumption, more cost-effectiveness, and have higher reliability.

• About the standards
  
  There are a series of versions of UMTS standards, including R99, R4, R5 and R6. The R99/R4 version standards, which pertain to the wireless part in relation to NodeBs, were frozen in 2000. Additionally, the first-generation NodeBs which were launched from 1999-2002, were all based on these standards.
  
  However, specifications for the HSPDA function that supports high-speed data services, are for the most part, found in the R5 version which was frozen in 2002. Hence, first-generation NodeBs offer very limited support in regards to the HSDPA function. In accordance with the ordinary developmental process, the architecture design and chip design of NodeBs should be started after related standards have been frozen. If one chooses to look at it from the perspective of the progress of 3GPP standards, then it appears that now would be an opportune time for launching new-generation NodeBs.
  
  In terms of the standardization of the NodeB architecture, Huawei, Ericsson, NEC, Siemens and Nortel, got together and initiated a CPRI (Common Public Radio Interface) standardization organization in June of 2003. This organization has been dedicated to the standardization of base-band and RF interfaces, which is helping to lay a solid foundation for the architecture of new-generation NodeBs. 
  
  
• Technical support
  
  Breakthroughs in high-efficiency power amplification, high-integrity multi-carrier RF, and high-integrity base-band ASIC technology have all helped to construct an ideal technical support platform for new-generation NodeBs.
  
  Digital Pre-Distortion (DPD) processing technology has improved NodeB power amplification efficiency, which has jumped from 9% to 19%. Higher efficiency power amplification technology, Doherty, makes use of the carrier amplifier and peak value amplifier in order to amplify the carrier wave and peak value part of broadband signals, which has helped to boost power amplification efficiency to 27.6%. Moreover, the NodeB power amplification linearity is highly improved, which increases power amplification stability, thus allowing broader signal frequency bands to be supported. Meanwhile, when high-integrity RF components are used, the NodeB transceiver multi-carrier technology can be adopted, resulting in a reduction of the size of the NodeB power amplification module.
  
  High-performance base-band ASIC chips have now replaced the previously used "DSP+FPGA" design mode, which has greatly improved NodeB integrity and signal processing performance. Advances in CPRI interface technology have aided in the development of macro RS remote radio heads (RRH) technology and distributed NodeBs, thus, allowing network deployment to become much more flexible.

The Characteristics of New-Generation NodeBs

• Lower power consumption by using an integrated digital power amplifier
  
  Traditional independent analog power amplification technology is already outdated. The new-generation NodeB power amplifier has adopted DPD and Doherty technology, as well as the broadband transceiver structure, to form some important characteristics. Research data recently showed that when a local network, with 5000 NodeBs, decided to adopt new-generation NodeBs, it would save RMB14.70 million Yuan on its power consumption each year (NodeBs are in 3×1 configurations; the electricity power charge is RMB0.7 Yuan per kwh). 
  
  
• Simple upgrading by adopting multi-carrier transceiver
  
  A UMTS network should carry out overall coverage planning during the early phase of construction and its network capacity should be constantly adjusted during operations. New-generation NodeBs now adopt multi-carrier broadband transceiver technology and each TRX supports multiple carriers. This not only helps to reduce equipment costs, but also simplifies network upgrading. 
  
  
• Higher performance, supporting full-performance HSDPA
  
  A typical first-generation NodeB can currently support only HSDPA services with 5 codes of limited performance, and the data throughput per cell is not over 4.8Mbps. Conversely, in a new-generation NodeB, the base-band processing unit adopts the ASIC chip set, which enables it to support full-performance HSDPA services with 15 codes, with the maximum rate reaching 14.4Mbps. This type of function is an important feature of new-generation NodeBs. 
  
  
• Flexible "site-selection" ability by providing open CPRI interface
  
  New-generation NodeBs support CPRI interfaces, through which some macro RS carriers can be pulled away, enabling distributed networking. Some new-generation NodeBs have opted to adopt the distributed design mode, allowing the base-band processing and RF transceiver part to be designed into independent modules. This not only greatly improves flexibility in NodeB deployment, but also helps save CAPEX and OPEX.

Entering the Era of New-Generation NodeBs

The development of GSM and UMTS networks signals that base stations will most likely experience a wave of upgrading in every 4 to 5 years. Based on this rule, since first-generation commercial NodeBs were launched in 2000, the new-generation NodeBs should enter the market sometime in 2005 or 2006.

This rule has in fact already been applied. Since 2005, developments in UMTS networks have entered a brand new phase. Several equipment manufacturers have already launched, or will soon launch, their new-generation NodeBs. Caught up in this wave of new developments, Huawei has decided to focus its attention on customer requirements and made several technical innovations, thus continuing to maintain its position as one of the industry leaders.

Huawei was one of the first manufacturers to adopt DPD and Doherty technology for the RF module of its new-generation NodeB. It also showed the innovation to integrate the broadband transceiver and digital multi-carrier power amplifier into one module, which resulted in greatly improving NodeB efficiency and strengthening network expandability. In an effort to increase the HSDPA transmission rate, Huawei developed its base-band ASIC processing chip, which allows up to 14.4Mbps HSDPA downlink rate per cell. The highly integrated design also helped to curtail NodeB and operation costs. Huawei's new-generation NodeB supports hybrid IP&E1 transmission solution and also enables low-cost transmission for high-speed data services. More importantly, Huawei's new-generation NodeB makes use of standardized, modularized and distributed designed ideas and is in compliance with the future development trend of UMTS networks.

Since being released in February 2005, Huawei's new-generation NodeBs have been put into large-scale application in 22 networks throughout the world. In its joint efforts with operators, Huawei will continue to devote itself to supplying new-generation NodeBs and to creating a brighter future for 3G network development.