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RF/Microwave??

Fit handsets with the right mem architecture

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

Keywords:3g? handset? network? umts? bandwidth?

3G is here, and it is one of the most high-profile topics in the mobile and wireless industry. 3G offers potential benefits to users, operators and handset makers, and with each passing day, operational 3G networks are being introduced. By 2007, about 25 percent of all handsets shipped will be 3G-ready.

Providing a bandwidth of 384Kbps in current UMTS networks and over 8Mbps if upgraded to HSPDA (also known as 3.5G, and already defined in the 3G standard), the 3G network is approaching the speed of ADSL connections. This wide bandwidth unplugs a major bottleneck, network inabilities to handle the huge amounts of data required for multimedia content. This bottleneck has, until now, prevented many applications and services from materializing.

Handset makers are also at a crossroads. The camera phone was a catalyst for growth in handset sales in 2004 and 2005so much so that in Japan, camera phone penetration is close to 100 percent. While the global average in 2004 lags far behind with only some 30 percent penetration, analysts are predicting this number to rise to 60 percent by 2007. However, studies show that this year, the growth rate will slow down as a new killer application is being sought to replace cameras in phones as drivers for the handset replacement market.

To overcome this slowdown, handset makers are adding more multimedia capabilities, turning them into portable entertainment stations. In fact, some handsets already offer a full range of multimedia services. They can play MP3s, record video and screen-selected TV programs, run 3D games and take high-resolution still pictures.

With 3G up and running, handset makers are releasing multimedia devices that will beef up replacement sales and simultaneously enable operators to provide band-consuming content to boost operator revenues. A clear indication of this win-win trend can be seen in the formation of alliances between content owners and handset makers and operators. Recent examples include the Motorola-MTV and Motorola-iTunes agreements, as well as the Sony Ericsson-Turner Broadcasting and Samsung-Virgin Records deals.

Driving changes in architecture

To enable this trend, handset architectures are undergoing major redefinition that is only partially noticed by untrained consumer eyes. The latest smart phones, for example, are running at up to 600MHz clock frequencies, comparable to the processing power of laptops some three years ago. Simple camera phones are advancing from low-end 40MHz ARM7 devices to ARM9s running at over 100MHz.

A third alternative uses the ARM7 to manage communications and run the phone OS while implementing a dedicated, powerful multimedia processor to handle the influx of multimedia content. This approach is favored by many handset vendors as a transition measure, enabling them to use the same main processor and thus benefit from reduced costs, shorter development cycles and more efficient inventory management.

More memory

One effect of the multimedia revolution in handsets is on the amount of memory they carry, especially non-volatile memory (nvm) for running and storing code and saving data. Just three years ago, the average handset carried 4MB of storage. Today, capacities are at 64MB and higher. In fact, Samsung's recently-announced SPH-V5400 contains a 1.5GB hard drive.

Higher capacities are only part of the memory-for-multimedia story. Multimedia applications running on small, battery-powered handsets challenge memory performance, power consumption and size. Despite these challenges, memory reliability remains a critical requirement. The same handset that runs multimedia must always be on and/or ready in an emergency to serve as a simple phone or phonebook.

While waiting for 3G to come of age and provide the bandwidth to meet multimedia requirements, memory makers have introduced multiple flash and mechanical hard-drive technologies, marketing them in a wide range of embedded and removable memory products. Handset designers in need of increased NVM and high performance must sort through all these offerings.

More flash choices

NOR and NAND flash memories are vying for market share, each backed by huge companies such as Intel and Samsung. Recently, hard-drive vendors have begun targeting the music handset market in an effort to completely displace flash technology. NOR technology, the older and more entrenched of the two, is better known by most engineers and more reliable than NAND technology. NAND-based memory uses less silicon and is therefore more cost-effective. Note that the first NAND to be implemented in a handset was a NAND-based embedded flash drive (EFD). With a built-in controller that uses a standard NOR interface, the EFD offers XIP boot capabilities so that it can run code and store data, implement error detection and correction (EDC/ECC), and provide protection and security-enabling features for digital rights management.

EFDs were critical to the successful penetration of NAND into the handset market. Today, they coexist with raw NAND die. Together, they are consistently driving NOR into the lower ends of the handset market where less memory is required, while becoming the default memory for multimedia handsets in general and for smart phones in particular.

To better understand where and how NAND, NOR or EFD is used in handsets, it is important to understand the dynamics of the handset segment and its ecosystem and architectures. A number of factors have joined forces to create the right ecosystem in smart phones to support NAND flash and EFDs.

Smart phones target business users in need of devices to increase their out-of-the-office productivity. These devices usually combine a handset and a PDA with a range of additional functionalities. Smart phones feature large screens, a powerful OS, such as Windows Mobile, Symbian, PalmOS or Linux, e-mail applications and Office-like software. Also, smart phones include games, a high-resolution camera (for still images and video) and enough memory to store and play MP3 songs.

Today, a typical smart phone packs anywhere from 32MB to 256MB of embedded memory. In this capacity range, NOR is too costly to compete with NAND. However, the first smart phones that incorporated NAND or EFDs used it as a disk-like solution to supplement rather than replace the embedded NOR flash. This approach was necessary because raw NAND cannot execute-in-place (XIP). Although NAND-based EFDs do offer XIP boot, they require additional SDRAM as the OS is copied to it and runs from it (similar to a PC architecture). This reduces the cost advantage over a NOR-based architecture. To circumvent this need for more SDRAM, applications were stored and executed on the resident NOR flash, and user data was kept on the NAND media.

Smart-phone OS vendors have met this challenge by adding paging capabilities to their operating systems. Thus, instead of shadowing the entire OS image to RAM, only the kernel is copied, while applications are paged in and out of the RAM when needed. This is known as "paging on demand" or "store and download." Paging on demand has reduced the amount of SDRAM needed in NAND-based devices to about half (from 64MB to 32MB) and has maximized its cost benefits. Today, most smart-phone designs implement some kind of NAND technology as an embedded NVM solution, replacing the former NOR-based architecture.

Specialized market

Feature phones constitute the majority of the mobile handset market. They are standard phones enhanced with features to provide entertainment. The killer application of feature phones in 2004 was the camera, which enabled users to not only take pictures and video clips, but also send the images and videos as MMS messages to other users.

To support this enhanced feature set, phones have undergone architectural changes. Today, two architectures dominate this category: enhanced and multimedia-centric. The enhanced legacy architecture offers only a slight improvement over basic voice-centric designs. It introduces additional flash media for storage and strengthens the baseband from an ARM7 to an ARM9. This architecture can support basic camera functions and simple Java games, but not advanced video capabilities and 3D gaming.

A dedicated multimedia co-processor was introduced in the multimedia-centric architecture. The baseband continues to use a relatively weak ARM processor (usually ARM7) and is responsible for all traditional handset functions and the OS execution. The multimedia co-processor, in contrast, is based on an ARM9 and higher, and includes additional multimedia-targeted state machines. This processor handles all multimedia and graphic-intensive applications and is used on demand of the baseband. This architecture typically includes two memory subsystemsone for the baseband to store and execute the OS, communications stack and applications; and another for the multimedia co-processor to store its code and all files managed by the file system (mostly multimedia). Although different, these two architectures both require flash media to store pictures, video clips and games downloaded by the user, but capacity requirements differ, depending on the phone segment.

Low, midrange feature phones

Low- to midrange feature phones provide a basic, low-resolution camera (VGA or lower) and gaming. A low-resolution still picture only occupies 40KB or less, a requirement that NOR can meet. Many feature phones provide 32MB of NOR, the upper limit of NOR as a competitive media, and in many cases, an additional slot for a NAND-based removable card (mostly SD or MMC form factor).

For these devices, NAND media offers a marginal cost improvement, which many vendors do not find compelling enough to warrant a change in architecture. As photo resolutions increase, a growing demand for built-in NAND media is evident. NAND will first serve only as a disk-like solution because paging software is not yet available in RTOSes used in these handsets, resulting in increased pseudo-SRAM size and reducing the NAND/MLC NAND cost advantage. However, to further reduce the bill-of-materials while increasing the storage capacity, memory vendors are joining forces with feature-phone OS vendors to introduce OS paging capabilities. Once ready, these capabilities should accelerate the penetration of bootable NAND into handsets as the only NVM media on board serving as a code and storage media. It is important to remember that most chipsets for feature phones and most operating systems do not support raw NAND, and thus designers turn to EFDs for NAND support.

Mid- to high-end feature phones

At the upper end, feature phones offer a VGA or higher-resolution camera (the mainstream camera for these devices in 2005 is 2Mpixels), and are capable of video recording, some image processing and advanced gaming. These devices are based either on the multimedia co-processor architecture or on a higher-performance baseband processor (ARM11) that is robust enough to manage multimedia. In such handsets, NOR media is not a viable solution, as evidenced by the fact that there's massive penetration of NAND flash technology. The most basic function of NAND in these devices is that of a disk drive, much like the hard drive in a PC. However, many handset vendors are taking advantage of EFDs to eliminate the additional NOR device to store the multimedia processor code.

- Arie Tal

Director of Marketing

Mobile Division

M-Systems





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