Calling All Designers: Time to Get Creative with Cellular Functionality
Cellular handsets play the roles of MP3-player, TV, radio, navigator, camera, web browser, PDA, and, yes, telephone. Feature-creep provides opportunities for the system designer but semiconductor integration takes them away at the same time.
The hottest new feature in handsets is GPS to enable navigation features and location-based services. Implementation options for GPS vary. One option is to add a GPS receiver to an existing design. Receivers such as the uN3010 from Atheros and PMP2525 Hammerhead II from Infineon integrate easily into mobile designs. Coming in BGA or CSP packages and integrating digital and RF functions, the receivers connect to a host processor using a serial port and to an antenna via an external SAW filter.
But the standalone GPS chip is going away, as suppliers of Bluetooth chips integrate the GPS function in their offerings. The NavLink 6.0 from Texas Instruments is one example of a Bluetooth-GPS combination chip, and others will follow. Alternatively, the GPS function can be integrated with the cellular baseband processor. The SH-Mobile G-series of baseband chips for the Japanese market integrate the GPS baseband. Qualcomm has long integrated GPS into its cellular chip set as well, handling the digital functions in the baseband processor and integrating the RF transceiver with the cellular transceiver. System designers should focus on Bluetooth-GPS combination chips for their projects because they are economical and deliver good performance.
FM radio is another function proving popular in certain markets. Oddly, FM receivers are better received where low-cost phones are comparatively popular, while FM transmitters are better received where high-end phones sell comparatively well. FM transmitters enable stored music to be played back from the handset over a nearby radio, such as in a car.
Again, the options are to use a standalone chip, a combo chip, or a baseband processor that integrates the function. None of the latter ship yet, but a few such products will ship in 2009. Infineon has built an FM receiver into its X-Gold 113 and 213 cellular chips, which target low-cost GSM and EDGE handsets. For 3G phones, Broadcom integrates an FM transceiver into its BCM21551 all-in-one cellular chip, and FM is increasingly available in combination with Bluetooth transceivers.
Designers targeting low-cost phones will find Infineon’s baseband processors among the best offerings in the market and their integrated FM a unique differentiator. Designers of feature phones and smartphones will find several options for Bluetooth chips integrating FM from the leading Bluetooth vendors, such as Texas Instruments, Broadcom, and CSR.
Core cellular technology is changing as well. Low-cost GSM and EDGE chip sets now commonly integrate the baseband processor and RF transceiver in a single chip. Some also integrate the power-management unit. The result is that hardware designers have little work to do to complete a handset design. Major additional components required include memories and power amplifiers. Companies with such “single-chip” designs include Broadcom, Infineon, ST (via its acquisition of NXP, which had acquired the design from Silicon Laboratories), and TI. MediaTek, the third-largest supplier of cellular chip sets, is also readying a single-chip design.
Designs of 3G phones are more complex. Figure 1 shows how the block diagram for a 3G smartphone is far more complex than that of a low-cost 2G phone. The latest feature for 3G phones is diversity reception. In what is known as a Type III advanced receiver, two receivers operate simultaneously. The baseband processor performs maximal-ratio combining (MRC) to blend the two signals to create a stronger whole. A key implication of diversity reception is that it requires a second receive chain. Some early designs use a second receiver chip, but transceiver suppliers now offer RF transceivers that integrate the second receive path.
Diversity reception is mostly used to enable 3G downstream rates of 7.2Mbps and faster. It is a key step toward MIMO (multiple-input, multiple-output) receivers. Best known as a key technology in 802.11n wireless LAN, MIMO is also specified in the HSPA+ 3G standard and 4G standards, such as LTE and WiMax. In MIMO, the transmitter simultaneously outputs two or more separate data streams on the same channel, and the receiver pieces them together.
A mobile device is likely to only support MIMO on the receive path, because upstream data rates tend to be lower than downstream rates and to conserve power. From a system-design perspective, little additional hardware is required compared to the diversity receiver because the baseband processor handles the key decoding function. The receive path, however, must be “clean,” minimizing noise and maximizing linearity, for the MIMO signal-processing to work.
The base station, where MIMO transmission is implemented, nearly doubles in complexity, however. Not only must there be more signal processing, but a separate transmission path—including expensive power amplifiers and bulky antennas—is required for each stream. This additional complexity is one inhibitor to the roll out of HSPA+ and 4G technologies.
By offering integrated products, cellular-chip suppliers are absorbing much of what had been in a system designer’s purview. The cellular-chip suppliers, however, have an important disadvantage: time. It may take one or two years for them to complete design of a super chip. Their OEM customer and the cellular operator may take another year or more to qualify the design for mass production.
The opportunity for the system designer is to take a design already in production and enhance it with new functions, exploiting the window of time between when operators and end customers first find value in the function and when the cellular-chip supplier can absorb it into his own design. The window is closing on GPS, but it may soon open on near-field communications (NFC), a type of link that enables electronic-wallet and other functions dependent on proximity for security. Already gaining popularity in Japan, NFC could gain traction worldwide if supported by retailers.
Creative designers, alternatively, can try to turn the tables. Instead of focusing on what functions can be added to the handset, think instead of how cellular connectivity can enhance other systems. One example is remote meter reading, which uses the cellular network to transmit the meters’ output. The Amazon Kindle exemplifies another example: turn around a failed product concept (e.g., an e-book reader) by tying it to wireless technology to enable a new usage model. Chip designers can envisage such applications, but until the market is proven, they cannot afford to develop chips specifically to support the application. System designers, however, have more flexibility, provided they apply their imagination and creativity.
Joseph Byrne is a senior analyst at The Linley Group. With more than 15 years of industry experience, he is one of the industry's leading analysts covering the semiconductor market. He has published numerous reports analyzing various segments of the industry and is the coauthor of A Guide to Wireless Handset Processors and A Guide to High-Speed Embedded Processors. Before joining The Linley Group, Joe served as a principal analyst for semiconductors at Gartner Research and held consulting positions with Gartner, Deloitte Consulting, and smaller firms in the U.S. and Europe. Joe began his career as a microprocessor designer for SMOS Systems, where he honed his technical skills as a principal engineer. He holds a bachelor of science degree in electrical engineering and computer science from Duke University and an MBA from the University of Michigan.
The Linley Group
This article originally appeared in the October/November issue of Portable Design. Reprinted with permission.
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