Microwave Engineering Europe - January/February 2009 - (Page 24)

24 WiFi RAN streamed over Wi-Fi rather than the more expensive and slower outdoor network. However, the iPhone still relies on the GSM or 3G network for all mobile services, speciﬁcally telephony. When a consumer is at home, his iPhone today must use both the Wi-Fi and cellular radios in parallel to maintain mobile service delivery. This is certainly inefﬁcient from a power management perspective. But more importantly, Wi-Fi is not making an impact on mobile services. Rather than using the Wi-Fi signal to improve cellular coverage or the broadband connection to deliver mobile content faster, the phone uses the existing cellular radio and radio access network. It is this functionality that distinguishes Wi-Fi as a feature rather than a RAN technology. If Wi-Fi were used as a RAN, the phone could connect to the mobile network via IP, and telephony services would come to the handset over the broadband link; the cellular radio could effectively be powered down because all GSM/3G services would be delivered to the phone via Wi-Fi and IP. Wi-Fi has a lot of advantages as a RAN technology. Clearly, it is already the dominant radio technology for indoor wireless. Wi-Fi can be used to improve the performance of mobile services in the locations where consumers spend most of their time, at home or in the ofﬁce. Wi-Fi also ofﬂoads the macro radio network. When a handset is connected to Wi-Fi for mobile services, it is not connected to the outdoor network. The effect is to free up more wireless spectrum and capacity for users who need it most: those who are outdoors in a truly mobile environment (car, train, etc.). Because the Wi-Fi connection is attached to the ﬁxed broadband network, operators are also ofﬂoading the mobile backhaul network. Now bandwidth-intensive multi-media services can be routed directly to the internet rather delivered than through the mobile core network. And mobile voice, data and IMS trafﬁc is delivered to the mobile core network over broadband, rather than through the cellular access network. Turn Wi-Fi into a RAN As a RAN technology, Wi-Fi is a perfect complement to today’s outdoor macro network. Wi-Fi augments the capacity and capabilities of the cellular network and does it faster, cheaper and indoors. Today’s 801.11g Wi-Fi technology operates at a theoretical limit of 54 Mbits/s, certainly faster than today’s mobile data rates. In fact, multimegabit data rates far exceed the processing power in the CPUs of currently available mobile devices. There are other beneﬁts as well. Wi-Fi operates in a single, harmonized spectrum band worldwide. Thus, a mobile phone with Wi-Fi can use the radio technology anywhere. As a local radio, Wi-Fi is decoupled from an operator’s RAN evolution (GSM, 3G, LTE and so on). The Wi-Fi in the home or ofﬁce does not become obsolete when a new cellular network comes along. It is important to note that simply adding a Wi-Fi radio to a handset does not turn it into a RAN technology. The early implementations of Wi-Fi focused heavily on data applications and bursts of large data packets. Even today, when Wi-Fi is offered as a feature on a phone (like the iPhone), it is optimized primarily for data services. To employ Wi-Fi as a RAN technology, the radio needs to be optimized for telephony services and for use in a power and space constrained environment. The Wi-Fi Alliance has speciﬁed a series of recommendations for a voice-optimized implementation. The WiFi Multi-Media (WMM) speciﬁcations make speciﬁc references to features needed to leverage Wi-Fi for voice service delivery. There is also an extension to WMM called ‘PowerSave.’ This is a unique power-saving feature that lets the Wi-Fi radio in a device ‘sleep’ between transmit and receive functions. Both the handset and access point save messages, which are exchanged only at pre-determined intervals and thus enable the radio to reduce power draw. Industry experts estimate that this power-save feature can result in a 20 percent reduction in battery drain. There are many other optimizations, which also result in improved performance for voice services over Wi-Fi networks. Commercial off-the-shelf Wi-Fi chipsets can easily obtain performance levels that meet or exceed those of today’s cellular networks. UMA: delivering mobile services over IP In addition to optimizing the Wi-Fi radio for mobile service delivery, a standardized protocol is required to connect the handset over Wi-Fi and IP to the mobile core network. Today, every successful dual-mode service where Wi-Fi is a RAN technology relies on the 3GPP unlicensed mobile access/generic access network (UMA/GAN) standard. UMA/GAN was standardized in 3GPP several years ago and delivers a seamless ● mobile experience, enabling a subscriber to move between cellular and Wi-Fi networks without dropping a call or data session. The essence of UMA/GAN is that it creates a secure tunnel between the handset and the mobile core network so that all existing mobile voice, data and IMS services are delivered to the handset as if it were connected to the macro RAN. This ensures the subscriber receives a consistent user experience (address book, call logs, etc.,) regardless of the network in use. The elements of seamless handover and a consistent mobile experience are critical aspects for mobile operators, who pride themselves on delivering a uniform service on the outdoor macro network. Delivering anything less over Wi-Fi should not be an option. UMA today Today there are more than 10 operators around the world providing UMA/GAN-based services that use Wi-Fi as a RAN technology. Plus, there are nearly 25 dual-mode handsets which support UMA technology. Orange/France Telecom is one of the operators most aggressively leveraging Wi-Fi as a RAN technology. In France, Orange offers a service called Unik that lets subscribers use any of the company’s 4.5 million installed base of Wi-Fi access points to improve coverage and mobile performance. In addition, Orange offers a ‘home zone’ service. For a small fee, consumers can get unlimited calling when they are connected through Wi-Fi. In September 2008, Orange extended Unik to include new 3G/2G/WiFi/UMA handsets. Orange also announced new UMA-enabled 3G handsets from Sony Ericsson and Samsung. T-Mobile in the US is also using Wi-Fi to augment its cellular RAN and deliver home zone services. As the name states, ‘Unlimited HotSpot Calling’ offers consumers unlimited ﬂat-rate calling when they are connected to Wi-Fi for a small fee on top of a monthly service plan. In addition, consumers can attach their phones to Wi-Fi access points anywhere in the world to improve coverage. The connected home By pushing Wi-Fi and UMA/GAN technology into handsets, operators have the ability to deliver an experience commensurate with the macro network but with added beneﬁts. Today’s mobile network does not differentiate between cell locations when Microwave Engineering Europe ● January/February 2009 www.mwee.com 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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