With such higher data rates, 3GPP LTE specifications will require complex signal-processing techniques such as multiple-input, multiple-output (MIMO) along with new radio modulation technologies like orthogonal frequency-division multiple access (OFDMA) and multicarrier code- division multiple access (MC-CDMA). Specifically, as per Texas Instruments' (TI) white paper, the uplink will use OFDMA and the downlink will use single-carrier frequency-division multiple access (SC-FDMA). Both frequency-division techniques employ fast Fourier transforms (FFTs) to segment the allocated bandwidth into smaller units that can be shared amongst the users. According to TI, SC-FDMA is used to reduce power consumption in the handset as the peak to average power ratio of SC-FDMA modulation is lower than that of OFDMA modulation. Also, from a computational standpoint, frequency division techniques scale more easily with bandwidth than code division systems, i.e., higher-bandwidth CDMA systems require much more computational power than OFDMA systems, as indicated in TI's white paper. In addition, the use of different-sized FFTs support implementation across multiple bandwidths allocations including 1.25 MHz, 1.6 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. Plus, the ability to use either paired or unpaired spectrum allocations, has the additional benefit of allowing operators to be much more flexible in the rollout of LTE systems as they can deploy in different-sized bands depending on the available spectrum.

While higher spectral efficiencies can be achieved via MIMO or beamforming, it is also easier to implement MIMO in OFDMA systems than in CDMA systems, where noise is more uniformly spread. When combined with the other physical layer changes there should be a significant increase in the spectral efficiency of the system with the transition from CDMA to OFDMA, said John Smrstik, TI's worldwide marketing manager for communications infrastructure.

As an active participant in the development of LTE standards, Texas Instruments has created a development ecosystem (Figure 2), combining its wireless infrastructure optimized digital signal processors (DSP), software libraries and ATCA/AMC cards from leading systems developers like Mercury Computer Systems (MCS) and Silicon Turnkey Express (STx).

Utilizing the TMS320TCI6482 and the TMS320TCI6487 DSPs, TI has created a series of designs leveraging system-level benchmarks. These benchmarks illustrate various system architectures to support existing 3G standards, WiMAX and LTE. The software library capitalizes on TI's existing WiMAX Wave 2-compliant library, with a host of LTE-specific algorithms. Combined, this hardware/software package provides a starting point for LTE development and enables faster and easier development of prototype systems, noted Smrstik.

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