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LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks by Najah Abu Ali, Hossam S. Hassanein, Abd-Elhamid M. Taha

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Comparing Spectral Efficiency

A thorough inspection of the spectral efficiencies of the two technologies on the UL and the Dl unveils a close similarity. These efficiencies are summarized in Table 15.1.

In order to achieve these high spectral efficiencies, the two proposals tend to utilize the latest technology advances at the PHY layer. These include multicarrier communication (OFDM, SC-FDMA, and OFDMA), adaptive MIMO with up to four layers, flexible spectrum and fractional frequency reuse, relaying, multi-cell MIMO, etc.

OFDMA Implementation

OFDMA, as a multi access technology, offers a significant improvement in the spectral efficiency for more than one reason. For instance, its inherent multipath interference handling capability facilitates delivering high data rates while experiencing marginal ISI. Also, the possibility of allocating different sizes of bandwidth chunks for users helps providing different data rates and accommodating more users. Moreover, OFDMA integrates smoothly with MIMO technology, which is another rate-boosting technology.

In WiMAX, OFDMA is adopted for the DL as well as the UL. However, LTE resorted to SC-FDMA on the UL to enhance the power efficiency of the MS. This choice, as the 3GPP argues, reduces the PAPR on the UL by 1–2 dB, hence prolonging the lifetime of the battery. In fact, WiMAX adopted an alternative approach to achieve a similar reduction in the PAPR. It depends on designing efficient resource allocation schemes. However, such schemes render ...

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