The specification for 4G wireless, or long-term-evolution (LTE), is expected to be finished this month, and product rollouts are anticipated for 2010 or 2011. If you are wondering what the status of the chips that will enable LTE is, well, the pipelines seem planned and chip designers have their heads down to deal with the unique challenges of LTE systems.
Despite these challenges, there seems to be a definite creative enthusiasm about the possibilities and new ways of looking at networks, as broadband mobile wireless gets ready to roll. And, in a stroke of compatibility genius that seems rare in our industry, many of the chips will also be compatible with mobile WiMAX, thanks to some similarities in the RF signaling. Regardless of whether or not the two competing standards, LTE and WiMAX converge, we are likely to see chips doing double duty.
So what are the most important issues for LTE that system designers should know about?
"LTE and WiMAX differ in their uplink multiple access approach, with WiMAX using OFDMA for the uplink, while LTE adopts a single-carrier frequency division multiple access (SC-FDMA) approach. The crux of this decision by LTE designers is the technical challenges that broadband wireless presents to the device uplink's RF physical layer," notes Darcy Poulin, principal engineer RF systems & technical marketing, at SiGe Semiconductor.
Cecile Masse, senior RF systems engineer, RF group, analog devices (ADI), elaborates: "It is important to understand the nature of the modulated signal we are dealing with in LTE systems: its bandwidth, statistics, peak-to-average ratio, sensitivity to impairments like phase, amplitude distortion and the implications of using a scalable OFDM signal with sub-carriers modulated with different schemes or with partial usage of the available sub-carriers within a given channel bandwidth."
The deployment environment of LTE is also a concern, Masse noted. "Additionally, LTE is likely to be overlaid with existing services such as WCDMA and GSM. In these cases, system designers must take into consideration the implications of tolerance not only to the various LTE waveforms, but also to other in-band modulation types."
Rupert Baines, vice president of marketing at PicoChip, points out that important considerations for LTE go beyond the chip level. "It will be about small cells, not traditional big units. So small cells, like femtocells, are critical. And, at a genuine system level, driving intelligence towards the edge of the network will be essential. But because of all that, LTE represents an opportunity to sweep away a lot of the 'I wouldn't start from here' problems that have been inherent in the rather slow-moving, conservative world of network infrastructure."
12/01/2008 12:01 AM EST by EETimes.com Janine Love
