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Power matters

3G services require powerful networks to ensure best use of bandwidth and radio resources. Let's look at why power is so important – and how to use it smartly.

May 04, 2005

Third-generation mobile networks based on WCDMA technology are being rolled-out worldwide, opening up for mobile broadband.

 

But powerful services require powerful radio access networks.

Roger Ekstrand, a technical solutions manager at Ericsson, explains: "Ericsson's solutions provide up to 40 percent more output power available for traffic than competing vendors' solutions," Ekstrand says. "Coupled with the high receiver sensitivity of Ericsson's solutions, this means lower capital expenditure for operators, because fewer sites are required for a given coverage and capacity."

 

Customers that have swapped their previous multi-vendor networks in favor of an all-Ericsson system include Austrian operator One. One's technical director Peter Pedersen says: "One is very happy with Ericsson's performance, commitment and dedication to this project. We received a network with good functionality, stability and availability as well as improved coverage and capacity due to Ericsson's high-power base stations." 

In WCDMA capacity and coverage in the downlink are highly interdependent, because multiple users share the same power resource in the downlink. Uplink power limits coverage, while too little downlink power may curb capacity.

 

As a result, the power level required from the RAN varies with the type of services required by the users, the number of simultaneous users, as well as their exact location inside the cells. High-bit-rate services require greater power levels from the radio base station.

 

In WCDMA, the total cell capacity is affected by the decline in signal strength over distance to each user. When there is significant decline, compensation is needed from a comparably larger proportion of the downlink resource. This leaves less of the downlink resource for other users.

 

Moreover, indoor users are, by definition, always close to the cell border, even if a building happens to be close to a base station. A high proportion of the high-bit-rate data users are probably located inside buildings, argues Ekstrand. "In an ideal, theoretical setting, power doesn't matter but in the real world, it does," he says. "In a typical network, between 80 and 100 percent are indoors, at least in cities."

 

With the imminent introduction of the next phase of WCDMA, High Speed Downlink Packet Access (HSDPA), the capacity gains from using high-power base stations will be even more significant to a successful implementation. Ericsson is currently the only vendor offering 30W base stations in addition to the standard option of 20W.

 

Besides higher output power, Ericsson's RAN solutions include unique software features that ensure as many users get access to as much bandwidth as possible at the same time, in order to preclude the proportion of dropped calls or interrupted services. One of these is Channel Rate Switching, a software feature that automatically lets the network continuously increase or decrease the bit rate, depending on radio requirements from the service demanded as well as on the number of simultaneous users.

 

In addition, the trade-off between coverage and capacity in WCDMA systems requires an admission control functionality to avoid system overload and to provide the planned coverage. Ekstrand explains how Ericsson's features help the operator maximize network usage: "When a new subscriber seeks access to the network, admission control estimates the network load and based on the new, expected load, the subscriber is either admitted or blocked out."

 

But as users move from one area to another, admission control must be complemented by congestion control, which may entail a handover rejection if there is insufficient power in the adjacent cell. Channel-rate switching will enable a smoother and more effective handover by adjusting the bit rate to the actual power resources instead of maintaining the same rate, which may lead to an overall lower capacity in the network.

 

Read more here.