Due to the similarities between the OFDM/OFDMA modulation schemes found in the WiMAX/802.16 standards and those proposed by the 3GPP standards body for LTE/4G, a great deal of leverage and reuse is possible, said Michael Long, Analog Devices' product line manager for DSP & Systems division. Once the 4G or LTE air interface specifications have been finalized we see a certain move away from all-software, fully flexible baseband modem implementations, noted Long. This shift will, in turn, require further investment from semiconductor manufacturers to deliver cost/power consumption-compatible SoC solutions. However, he added, “In the immediate future (next 24 to 36 months), we foresee all LTE/4G developments continuing to reside on commercial off-the-shelf, board-level solutions such as the one built by BittWare, which use both DSP and FPGA processing elements.”

Consequently, for now, Analog Devices will leverage its 802.16 OFDMA software library, which provides a set of optimized software modules for the implementation of the OFDMA physical layer of an 802.16 base station on TigerSHARC DSP processor. “These code modules, coupled with the TS2012 “6Pac” board from our third-party partner BittWare form the core of our building blocks strategy for supporting the emergingLTE/4G standards,” stated Long.

While Freescale plans to leverage its existing multithread architecture for baseband processing, it will also develop new IPs to streamline its DSP engine, along with data converters, power amplifiers (Pas) and other RF front-end functions. However, to turn this complex strategy into a useful semiconductor solution, it will exploit the attributes of redistributed chip packaging (RCP) as shown in Figure 3.

In fact, packaging will play a crucial role in differentiating an LTE solution from WiMAX design, stated Kaivan Karimi, Freescale's director of global strategy for Networking and Computer Systems Group. While common OFDM base is important, LTE services will demand very small, low-power packaging, he added.

In essence, RCP will enable Freescale to pack three major functions — transceiver, broadband and power amplifier — in a single compact package with significantly lower parasitics. Some key benefits of RCP packaging include 30% size reduction, flexibility, ultralow k compatibility, halogen and lead-free packaging, and elimination of package substrate, wire bonds and flipchip bumps.

With standards rapidly changing and newer specs demanding rigorous computational capability, wireless infrastructure designers are seeking multiprotocol base stations. And hybrid FPGA/DSP-based platforms provide an effective design approach to comply with these ever-changing wireless standards, said Arun Iyengar, Altera's senior director for the communications business unit. Based on system throughput needs, such designs will provide intelligent partitioning between FPGA and DSP, noted Iyengar.

He added, “The partitioning strategy between FPGAs and DSPs depends on processing requirements, system bandwidth as well as system configuration, and the number of transmit and receive antennas. A typical distribution of signal-processing tasks between FPGA and DSP for baseband physical layer (PHY) functions in an OFDMA system, such as LTE, is shown in Figure 4. As shown in the diagram, the baseband PHY processing is partitioned into bit-level and symbol-level processing. For that, Altera is leveraging its high-performance Stratix III FPGA.

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