Microwave Engineering Europe - January/February 2009 - (Page 22)

22 4G TECHNOLOGY FOCUS spectrum but have a dramatic impact on the power consumption of RF transmitters and hence handset battery life. These schemes have the disadvantage of requiring linear power ampliﬁcation, which compromises overall system efﬁciency because RF power ampliﬁers (PAs) are much less efﬁcient when backed off from saturated maximum power. GSM signals operate at constant amplitude, so that the power ampliﬁer can be in saturated mode. Newer UMTS, WiMAX and further evolved standards such as Long Term Evolution (LTE), are based on a variety of different channel coding and modulation techniques (CDMA, OFDM, and so on), with increasing channel bandwidths, and high peak-to-average power ratios (PAPR). Essentially the newer the standard, the higher the data through put, the higher the PAPR and the lower the RF ampliﬁer efﬁciency. The argument for HAT in the handset is about reducing the BOM cost as well as about extending battery life. Replacing the DC-DC converter with a HAT solution can greatly simplify the RF front end of a handset by enabling multi mode, multi band PAs to be used. The HAT based RF front end design in Figure 2 uses just two PAs but covers the same frequency spectrum as the seven PA design shown in Figure 1, matching or exceeding its performance and efﬁciency, and saving an estimated 30 percent the BOM cost of multibanding the RF circuit. Coolteq-l — implementing HAT on the handset Coolteq-l enables the efﬁcient wideband RF front ends that are able to cover three to ﬁve times the bandwidth of a standard design with up to double the efﬁciency. Only two PAs would be needed to design a front end covering all of the operating modes (GSM, EDGE, WCDMA, HSUPA and LTE), compared with seven or more without Coolteq-l. Nujira test results show that a handset PA with its technology is twice as efﬁcient during HSUPA transmissions, and 1.5 times as efﬁcient during W-CDMA transmissions Table 1: Battery capacity and time between charges by technology. compared with the same PA without HAT. For WiMAX, a Coolteq-l based front end can achieve even greater power savings — of up to four times. Modern and emerging standards such as HSUPA and LTE are transmitting ever larger amounts of data and as the user moves away from the basestation, the power transmitted between the handset and the basestation rises to maintain the data rate until a point is reached where the phone hits its power ceiling. The higher the data rate the higher the power, and consequently the quicker we get to a saturation point where the data rate is forced to fall off as we recede from the basestation. A key marketing consideration for handset manufacturers when designing the phone is battery life and this is severly affected by when the user is relatively far away from the basestation. As wireless networks ramp up the data rates, battery life becomes even more critical. Coolteq-l not only simpliﬁes the hand set design by eliminating the need for many PAs, effectively reducing the need to two from seven PAs for a 14-band LTE solution (Figure 1 and 2), but it also enables better battery life. Battery power used is calculated using a statistical distribution of where the handset is relative to the basestation — based on the DG09 industry standard statistical distribution. With such metrics, Coolteq-l can be shown to improve battery life by up to 30 percent when the handset is used as a data terminal The power conundrum According to ABI Research the battery life for WiMAX and other 4G handsets could end up a third of that of 3G (Table 1). The major villain here is the RF power ampliﬁer. Creating an efﬁcient broadband cellular network air interface for LTE is hard, especially if it is to work globally. LTE standards are not only inherently less power efﬁcient from a RF transmission design point of view, but different frequency bands have been licensed LTE around the world, all of which need to be supported if a handset is to achieve global coverage. There is a real risk that the air interface in a 4G handset will turn into a bulky, power hungry monster. The battery life issue is further complicated by the fact that newer services will often be based on faster uplink speeds, and are sometimes ‘always on’. Coolteq-l is a possible solution to this conundrum. Conclusion RF subsystem design for 4G handsets is a challenge because new standards are inherently less efﬁcient and the need to support a very wide range of frequency bands. HAT technology provides a practical, and easy to implement solution to enhance the efﬁciency of the subsystem, more than compensating for the efﬁciency lost through compromises like the use of wide-band PA devices. It is turning out to be one of a key enabling technologies for 4G. Coolteq-l technology is available as IP so that manufacturers can integrate it seamlessly into their handsets. The IP has a small proﬁle and it is suggested that it is used as part of the power management circuitry. Coolteq IP comprises roughly 5 million gates and can be scaled down to 65 nm. The baseband IC will also need to have an interface which is also available as IP and implies a minor modiﬁcation with no redesign implications. Nujira see baseband implementations as not causing any problems. MICROWAVE ENGINEERING EUROPE Free subscription at: www.mwee.com/subscribe Microwave Engineering Europe ● January/February 2009 ● www.mwee.com http://www.mwee.com/subscribe http://www.mwee.com

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Microwave Engineering Europe - January 2009 News Contents Comment Using KPIs to Ensure Quality in a Converging Network Amplifier Error Vector Magnitude Characterisation Using High-Speed Modular PXI Instruments GPS: Making a Play for Femtocells Accelerating Global WiMAX Adoption: The Move to Picocell and Femtocell Base Stations Addressing PA Efficiency for Multi-Mode Wideband Handset Applications Wi-Fi: Mobile Feature or Fundamental RAN? Products Calendar

Microwave Engineering Europe - January/February 2009

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