OQAM/IOTA Downlink Air Interface for 3G/4G

In order to provide higher data rates in the UMTS (3G) downlink, the High Speed Downlink Packet Access (HSDPA), was standardized in UMTS Release 5. However, to support high data rates in the WCDMA system smaller spreading factors are used to handle the shared access. Using higher modulation constellations data rates beyond 10Mbps are then achievable. On the other hand, by decreasing the spreading factor more intersymbol interference caused by the time-dispersive channel is introduced which can only be managed by advanced WCDMA receivers. This increase in complexity has initiated a reinspection of the physical layer. In particular it is known that Orthogonal Frequency Division Multiplexing (OFDM) has the capability to resolve the inherent structure of time-invariant (or slowly fading) channels, i.e. converts the frequency-selective channel into flat fading channels on the corresponding subcarriers. From mathematical point of view the joint transmitter and receiver signaling (that includes a appropriate cyclic prefix) diagonalizes a complete class of linear time-invariant channels on a very low complexity level. Moreover with frequency-selective channel information available at the transmitter it is expected that OFDM with time-frequency scheduling is superior to WCDMA employing time scheduling only. It was already observed that twice the averaged throughput is achievable using multidimensional scheduling. Therefore OFDM was proposed in the 3G Partnership Project (3GPP) as an alternative air interface. The conventional OFDM scheme can be extended in several ways to match the requirements for more mobility and increased bandwidth efficiency. In particular an approach based on Offset QAM in conjunction with Gaussian-like pulse shapes (OQAM/IOTA), also incorporated in the 3GPP OFDM study item, reflects a promising new direction. Due to the enhancement of the physical layer an improvement of the overall system performance is expected while the air interface is still very similar to OFDM. Hence, strategies on adaptive modulation, coding and time-frequency scheduling developed for OFDM can be applied without major modifications. The purpose of this paper is to compare the physical layer capabilities of both system designs in 3GPP propagation scenarios and demonstrate the potentials of OQAM/IOTA.

@unpublished{J04daif,
   author          = "Peter Jung", 
   title           = "{OQAM/IOTA Downlink Air Interface for 3G/4G}", 
   year            = "2004", 
   note            = "Technical Report, Unpublished online:ftp://ftp.hhi.de/jungp/publications/TechReports/iota_techreport04.pdf", 
}