2G BTS draws on 3G technologies

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Two highlights in the rich development of the 3G networks are advanced technologies and high efficiency. However, the GSM network is the most widely applied network in the world. After a decade of development, the GSM network is still favored and constantly evolves due to the maturity of technical applications and business models.

Reviewing the 2G developments from 3G commercial applications, people may ask: Is it possible to apply the high-efficiency and energy-saving technologies of the 3G systems to the 2G systems? Can we smoothly evolve the 2G systems to the 3G systems? Huawei's new-generation EnerG GSM solution will offer you the best answer.

Multi-carrier technology for 2G

I n the traditional GSM base transceiver station (BTS), a radio frequency unit (RFU) can only process one carrier signal, therefore, a 12-TRX macro BTS needs 12 RFUs. Each BTS is cumbersome when equipped with the necessary combiners and duplexers. With technical innovations, each RFU can now process two radio frequency (RF) signals, and a 12-TRX macro BTS needs only 6 dual transceiver units (DTRUs) and less combiners and duplexers. Compared with the BTS with single-TRX's RFU, the new-generation BTS is smaller, leaner, and offers better radio performance.

Currently, Huawei is the only vendor who has developed a QTRU - a type of RFU based on multi-carrier technology. Each QTRU supports the processing of six RF signals. Digital intermediate frequency (IF) combining technology is also used. Six RF signals are combined in the QTRU, and no independent combiner is required. Power of the six RF signals can be shared to improve radio performance. The QTRU based on the multi-carrier technology is the same size as a DTRU, but has three times the capacity of the DTRU.

Multi-carrier technology can bring noteworthy improvements to 2G networks. Take Huawei's indoor macro BTS3012 for example, since the QTRU and DTRU are the same size, the BTS3012 is able to support both the QTRU and DTRU at the same time. The DTRU-based BTS3012 can support up to 12 TRXs and needs combiners. The QTRU-based BTS3012 can support up to 36 TRXs without combiners. To construct a S12/12/12 site, an operator needs three DTRU-based BTS3012s or only one QTRU-based BTS3012 with no combiner.

High efficiency 3G PA technology for 2G

To deploy a wireless network with overall coverage and good performance, thousands of BTSs may be needed. As a result, the costs of BTSs account for the biggest proportion of overall network construction costs. In each BTS that works as a radio transceiver, the RF power amplifier (PA) is the most important component. The linear PA accounts for about 1/3 of the total cost of each BTS, and the RF PA is a main power consumption unit of BTS.

To cut BTS costs, an effective method is to decrease the costs of the RF PA unit for each BTS. This requires the use of a PA that has wide bandwidth, high linear features, and increased efficiency.

The "DPD + Doherty" high-efficiency digital PA technology does quite well. The digital pre-distortion (DPD) technology enables signal pre-distortion. A pre-distorter is cascaded over a PA. Because the non-linear distortions enabled by the pre-distorter are equivalent to those enabled by the PA in quantity but are opposite in function, thus high linear PA output can be achieved.

The Doherty PA technology has two main parts: the carrier (C) amplifier and the peak (P) amplifier. The carrier PA works constantly, while the peak PA works only at the preset peak. The carrier PA works in a nearly saturated state to get higher efficiency, and it amplifies most signals. The peak PA works only at the peak value, and does not consume power most of the time. The linear area with combined output and input features has been greatly expanded from the linear area of a single amplifier, which enables high efficiency when signals are in the linear area.

Huawei's new-generation GSM RF PA improves efficiency up to 50% while saving over 49% in power consumption when compared with a traditional BTS. This is accomplished by coupling power amplification technology with some innovative PA power consumption management technologies like intelligent shut-off of PA power and dynamic adjustment of PA voltage.

If existing sites are replaced by Huawei's new-generation BTSs that adopt the 3G high-efficiency PA and the multi-carrier technology, a medium-sized city with 2,000 sites can save 33.29 million kilowatts (KW) of electricity each year. The environment is spared 22,000 tons of carbon dioxide (CO2) emissions and the operator saves money too.

Distributed architecture for 2G BTS

To reduce 3G network construction costs, Huawei pioneered in launching 3G Node Bs based on the distributed architecture in 2005. In the distributed architecture, the baseband unit (BBU) and the remote radio unit (RRU) are separated and connected through the standard common public radio interface (CPRI).

The distributed architecture divides the traditional Node Bs into two small modules, BBU and RRU. This facilitates site acquisition, simplifies installation, and drastically cuts 3G network construction costs. Based on its mature design and application experience in 3G distributed Node Bs, Huawei launched the DBS3036, a GSM distributed BTS with large capacity, high integrity and high reliability.

By applying advanced 3G RF technologies like multi-carrier technology and the high-efficiency digital PA to the 2G system, Huawei will soon launch the RRU3036 for new-generation 2G distributed BTSs. Each RRU3036 can support up to 6 carriers. For an S6/6/6 site, only three RRU3036 modules are needed. In the future, big, bulky BTSs with high power consumption will be phased out in 2G network construction.

End-to-end IP technology

The GSM and the WCDMA belong to the same standard system and support smooth evolution. The IP radio access network (RAN) technology used in 3G systems has many similarities to the BSS IP technology used in 2G systems. The IP technologies adopted in 3G systems can all be used in 2G systems and guarantee the sustainable development of 2G systems.

In product platform development, the BSC and BTS of the GSM system are both based on an All-IP platform. This dramatically improves the integration of 2G products, decreases power consumption and maintenance costs, and enables smooth evolution to 3G systems. In the past, 5 to10 cabinets were needed for a BSC that supports 2,000 TRXs, including the packet control unit (PCU) and transcoder (TC). Now only one cabinet is required with Huawei's new-generation BSC6000 designed with the IP platform technology. The BSC6000 and the radio network controller (RNC) are both based on the PARC IP platform. The BSC6000 can be upgraded to a RNC by a simple software upgrade and replacement of a few interface boards.

In networking, Huawei's new-generation distributed BTS provides IP interfaces for 2G networks. The Gb interface, Abis interface and A interface are all designed to support IP connection directly. As a result, the structure of the 2G network is simplified, the transmission expenses in 2G networking are curtailed, and increased requirements for digital services can be accommodated. For example, the 3G network of EMOBILE in Japan has saved up to 95% lease expenses on transmission devices each year after adopting Huawei's IP RAN solution.

When 3G IP technologies are used in 2G product development and IP networking, the reliability and efficiency of 2G networks can be greatly improved. Through IP networking, such functions as the BSC pool or the MSC pool can be conveniently enabled. If a BSC or MSC in the network fails in transmission, another BSC or MSC can take up the services and system services will not be interrupted.

Huawei has diversified and upgraded mobile applications by introducing advanced 3G technologies to the 2G system. By adopting the same technologies, 2G and 3G products will naturally evolve from technical convergence to product convergence.

Link: Huawei's next genaration GSM distributed BTS

3G distributed Node Bs are maturing and GSM operators have begun to cooperate with telecom vendors to explore the possibilities of applying distributed BTSs in the GSM field. However, many products are simple imitations of 3G distributed Node Bs in appearance, installation features and transmission media. The fact is that GSM networks are significantly different from universal mobile telecommunications system (UMTS) networks, especially in capacity, evolution and environmental impact.

Not mere imitations

GSM distributed BTSs are not mere imitations of the 3G models, but are definitely inheritance and improvement based on the original. Hardware sharing the same platform represents the idea of modular design and product maturity. As the smallest and lightest BTS in the industry, Huawei's next-generation GSM distributed BTS is based on the latest platform that is applicable to UMTS networks and even long-term evolution (LTE) networks.

The next-generation GSM distributed BTS's baseband unit (BBU) inherits high integrity from the 3G distributed Node Bs. Its common public radio interface (CPRI) and board structure are of mature designs, while the remote radio unit (RRU) has been greatly improved. By adopting the natural heat dissipation mode and compact size, the RRU is of higher stability, larger capacity, and greater output power. The distributed BTS' maturity has been shined based on in-depth commercial test data, and the BTS features optimized radio frequency (RF) components, heat dissipation, and antenna system.

A basic requirement for GSM networks is the assurance of smooth evolution to future networks. Huawei's next-generation GSM distributed BTS enables GSM and UMTS systems to share the same platform, fully supporting coexistence of 2G and 3G networks and smooth evolution to future networks. The product also adopts the IP platform design mode and uses IP technologies from the core to interfaces. Based on extensive experience in the IP field, Huawei has pioneered in using the IP clock server to transfer clocks on IP networks and realized IP mobile networking from network elements to the overall network architecture.

Full display of distributed features

Differing from Node Bs in 3G networks, GSM BTSs require larger capacity. At present, many GSM distributed BTSs in the industry support only two carriers due to technical limitations, which seriously limits coverage scenarios. These BTSs can only be used as components for macro BTSs or for small-capacity indoor coverage. To utilize distributed features, the next-generation GSM distributed BTSs must support large-capacity networking and provide the capabilities of macro BTSs in terms of coverage and expansion.

Huawei's next-generation distributed BTS stands out from all the GSM distributed BTSs that can be installed on towers for its support of S4/4/4 configuration and S12/12/12 after upgrades. The application performance with 30W cabinet-top output power is equivalent to that of a macro BTS.

By using Huawei's next-generation GSM BTS, operators can have up to 36 carriers in baseband processing, and can add two BBUs to expand each single BTS to support 12 cells and 72 carriers. This can greatly enrich the application scenarios of GSM distributed BTSs and handle the requirements of heavy-traffic users and highly-integrated services, whether indoors or outdoors. In each sector, a single RRU of Huawei's next-generation GSM distributed BTS can support 4 carriers, and the capacity can be further expanded through cascading. Since the unit supports transmit diversity and 4-antenna receive diversity, the receive sensitivity can be up to -112.5 dBm at normal temperature. Operators can stop worrying about degraded quality of service (QoS) and won't need to construct more sites or plan more networks, while enjoying the features of distributed BTSs.

With the purposes of reducing energy consumption, noise pollution, electromagnetic radiation and interference, Huawei has transplanted a "green" idea into the design of its next-generation GSM distributed BTS. By adopting digital power amplifier and intelligent power control technologies, Huawei's next-generation GSM distributed BTS achieves a power amplification efficiency of more than 40%. As a result, power consumption is further decreased while the same output power is maintained.

Experience promises a bright future

Engineering experience from 3G networks is greatly helpful in deploying GSM distributed BTSs. With its 3G distributed Node Bs, Huawei helped Vodafone Spain migrate the networks in Madrid and Barcelona. By installing RRUs on towers to improve coverage, Vodafone Spain greatly improved its voice quality and high-speed packet access (HSPA+++++++++++++++++++++++++) data throughput.

In Hong Kong, where features the most complicated wireless environment and great difficulty in site acquisition, Huawei used the ray-tracing model and 3G distributed Node Bs to build a high-quality network, while saving space and rental costs.

In Singapore, Huawei used distributed Node Bs to realize the coverage of two different scenarios in downtown areas and residential areas. By using fiber extensions and reading directly the original network configuration data, Huawei managed to speed up the network optimization with a record-setting delivery of 100 sites per week.

In Japan, Huawei tailored its distributed Node Bs to meet the operator's rigorous requirements for earthquake resistance, moisture resistance, natural heat dissipation, and reliability, and succeeded in constructing the fastest mobile broadband network nationwide with more than 70% coverage.

Although the mature application of 3G distributed Node Bs have significantly influenced the GSM network deployment, operators are still looking forward to a next-generation distributed BTS solution tailored for GSM networks, rather than equipment that enables simple separation in physical architecture. The next-generation GSM distributed BTS can truly help operators build high efficiency, high quality and quickly operable GSM networks that provide competitive services and products.

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