Nokia (News - Alert) Siemens was the first vendor to market a multi-standard base station that is software upgradable from GSM to EDGE, WCDMA to HSPA and HSPA to LTE. It’s also modular, lightweight, and consumes around 70 percent less energy than traditional designs, which eliminates the need for air conditioning. This early lead will only last so long, but over 200 operators have implemented “Flexi” base stations, so the company has staked out a significant position in the market.
OK. So much for the company’s bragging rights. How do these features translate into green benefits?
Operators have thousands of base stations and they are deploying next-generation systems in order to be ready for LTE (News - Alert), which is a high-speed, low-latency technology. The market wants LTE, evidenced by the fact that more than eighteen operators have announced LTE deployment plans, despite the economic climate. And Verizon (News - Alert) has brought its launch forward from 2010 to 2009.
Thousands of base stations would normally consume a lot of energy, but what is more significant is the fact that being energy efficient enabled a lightweight, compact design. Flexi base stations can be carried to rooftops by a service technician: normally heavy-duty cranes or other machinery would be needed. The savings for countrywide rooftop installations are therefore huge. This also means that base stations can be close to the rooftop antennas, which minimizes feeder loss, so less energy is wasted. In addition it allows one radio module to feed all three sectors of a typical antenna site and the fact that the radio module can serve multiple standards (GSM, WCDMA and LTE) means that the 3:1 comparison rises to 6:1 or even 9:1.
Nokia Siemens (News - Alert) is not a recent convert to green technology. The design of the Flexi base station started in 2005 and it revolves around chip set developments: Moore’s on-going law. We can therefore expect further enhancements in future. The use of advanced chips also enables increased spectral efficiency by transmitting more bits in a given time and stopping transmission during pauses. The ability to make remote software upgrades to boost capacity as and when it’s needed and to make air interface upgrades eliminates the need to transport and replace hardware. This feature will make significant medium- and long-term savings: Nokia Siemens says that it will reduce the number of site visits over the life cycle by 15 percent.
Backhauling the traffic
Multi-standard base stations will push up the volume of network traffic and this is particularly true when upgrading to LTE. This air interface has a peak download rate of 172.8 Mbps and a peak upload rate of 86.4 Mbps. Operators need to migrate to LTE because the mobile world is driven by broadband multimedia services and enabled by high-speed access. The industry foresees capacity increases by orders of magnitude and regular backhaul TDM solutions at these levels are impractical for cost reasons. A new architecture is therefore needed to decouple cost from capacity and it is enabled by the adoption of Carrier Ethernet (CE).
CE is a very cost-effective transport mechanism and therefore it has green credentials, particularly when the layer 1 medium is fiber. However, intelligent next-gen base stations in combination with flat architecture of next-gen networks also allows backhaul communications to be optimized and this will enable a significant reduction in the energy requirements of radio access networks (RANs).
Intelligent base stations
Right now the RAN architecture is one-to-many: each base station communicates with a Radio Network Controller (RNC). The exact number of base stations supported by each RNC is a function of the amount of traffic in the network and the performance objectives of the operator, but a typical figure is a few hundred base stations. RNCs perform radio resource management, radio congestion control, and allocation of radio resources for new calls. Additionally, they make all the decisions regarding radio mobility management.
As well as minimizing weight and size, and allowing new air interfaces to be implemented via remote software downloads, the advanced chip sets such as those employed in Flexi base stations also allow most of the functionality of the RNC to be moved to the base station. This allows the base stations to make intelligent handover decisions and thereby communicate with each other directly, i.e. peer-to-peer instead of one-to-many.
The reduced role of the RNC opens up new options for backhaul, such as full meshing of base stations, or at least localized partial meshing of adjacent base stations for the handover. In some next generation network architectures, the RNC may not exist or it is not in the subscriber’s data path. This development reduces the operator’s RAN CapEx and it also simplifies network implementation. When the network becomes capacity constrained there is no longer a need to deploy RNCs for capacity purposes. Additionally, there can be transport savings related to the simplified transport topology of a flat network.
Bob Emmerson (News - Alert) is TMC's European Editor. To stay abreast of the latest news affecting the European market, check out Bob's columnist page.Edited by
Tim Gray
