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RF/Microwave??

3G integration not a linear progression

Posted: 01 Feb 2005 ?? ?Print Version ?Bookmark and Share

Keywords:rf? wireless? bluetooth? uwb? wi-fi?

On the horizon are smart phones and multimedia mobile devices integrated with Bluetooth, Wi-Fi and assisted-gps technology. But beyond the horizon are 3G handsets with an abundance of new connectivity technologies and applications, including FM radio, DTV reception, UWB and others.

If the integration of these new connectivity technologies were analogous to basic mathematics, one might be tempted to think of the integration process as simple addition. Unfortunately, it is not so simple or so serial. It is much closer to calculus and solving simultaneous differential equations. What complicates the issue is the expected usage patterns.

The critical point is that multiple tasks and applications may be operating concurrently. Providing concurrency, which can be defined as the running of multiple technologies or applications at the same time, on a single 3G handset presents several formidable challenges. Moreover, concurrency may raise questions about whether software-defined radios (SDRs) or cognitive radios will, by themselves, be capable of the multifunction DSP and RF processing needed in 3G phones, multimedia handsets and beyond.

Central to attacking the issue of concurrency is the ability to perform simultaneous voice and data communications while also processing other application-intensive tasks.

To enable this, the basic architecture of the platform will differ from that which has dominated 2G and 2.5G handsets. Those architectures have been based on a single- and sometimes dual-processor chipset, usually with limited support for processing-intense applications and multitasking, as well as extremely limited or practically nonexistent support for concurrent processing. With the emergence of 3G phones based on multifunctional architectures with multiple processing elements, usage patterns will shift as consumers come to appreciate the significantly expanded capabilities of their mobile devices. Additional applications will be loaded onto these devices. Consumers will require concurrent processing because they will rather quickly become accustomed to launching multiple applications simultaneously. And they will expect uncompromised ease of use and quality of service.

3G architectures will feature multiple independent processing engines, all of which could be active simultaneously and each engaged to a different level depending on the processing needs of the active applications. In this type of multifunction architecture, one processing element acts as the master processing unit, managing the execution of the multiple concurrent tasks, including simultaneous voice and data processing and such multimedia functions as high-definition graphics, streaming video and stereo audio.

Shifting paradigm?

The usage model five years hence may have multiple applications running concurrently. For example, the applications might be voice (two users talking) with audio (background MP3 or FM) channels over Bluetooth, as well as imaging (retrieval and sending of GPS maps for coordinating on a meeting place) and data (Internet access, list sharing). That requires at least five radiosFM broadcast receiver, Bluetooth/UWB technology, Wi-Fi, 3G cellular and assisted GPSeach with its own air interface and the coordinating central controller to tie it all together.

The presence of multiple radios in a handheld device raises critical RF issues concerning antenna implementations and mutual interference. Other types of systems, such as Wi-Fi access points and laptops, have shown that two antennas can significantly improve RF performance, though at the expense of complexity and cost. Based on the possibility of five or more RF subsystems, 3G phones likely will require more than one antenna and several of the radios will share antennas. This leads to the realization that some sort of "smart-antenna" technology such as single or multiple antenna interference cancellation and multiple-in/multiple-out (MIMO) antenna and DSP technology will probably find their way into 3G handsets.

To date, some success has been achieved with respect to mutual interference by carefully managing RF design and integration practices and by implementing an overriding processing element to coordinate the activities of each RF subsystem. But in 3G phones, multiple radios and antennas add significant complexity that must be addressed. Over time, increasing RF integration at the chip level will push some of these issues to the silicon designer and reduce the challenges for system designers. Since antenna design and RF management are intimately related, future "smart" RF solutions will involve both facets of this issue.

A long-held belief in the wireless industry asserts that the holy grail of wireless technologies is the development of a sophisticated SDR involving some sort of cognitive radio capability. Some believe that SDR will surface during 3G. This paradigm generally holds that a reprogrammable architecture "super-radio" would sense multiple RF air interfaces in the handset's environment and switch to the optimal interface required at a particular instant in timean interface often popularized as the "always best connected" (ABC) interface.

Wireless technologists and system developers continue to pursue the SDR vision because they believe it will simplify architectures and reduce handset costs over an architecture that would support multiple discrete air interfaces. Unfortunately, proponents of SDR struggle with unifying the diverse air interfaces to generate the (single) ABC interface. Now, the wireless industry is experiencing a paradigm shift, whereby 3G handsets will require multiple concurrent radio operation. Consequently, a single ABC air interface is not sufficient. Of course, a modified SDR that does support the multiple concurrent air interfaces can be imagined, but this complicates an already complex investigation.

Along these lines, it could be tempting to extend the logic of SDRs to the entire next-generation 3G handset. That is, the handset's architecture could be reconfigurable to the extent that it would resemble a software-defined handset (SDH). So, as an SDR might support all air interfaces, an SDH would support an SDR as well as all the applications processing elements required to service the anticipated 3G multiradio, multiapplication scenarios. An interesting concept, but it would be subject to the same complexities of concurrency and, as a result, be perhaps even more elusive than SDR.

- Rick Wietfeldt

Chief Technologist, Wireless Terminals Business Unit

Texas Instruments Inc.





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