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Figure 7.2. An Illustration of NxDFT-S-OFDM.<br />
With respect to downlink control signaling, per-carrier scheduling grant is used. Additionally, each grant<br />
will also contain a Carrier Indication Field (CIF) that indicates the carrier to which the grant applies to<br />
enable cross-carrier scheduling. The CIF field is added to the existing Rel-8 DCI format. The per-carrier<br />
scheduling has the following advantages: 1) it allows several DCI formats to the same UE in different<br />
component carriers; and 2) it facilitates dynamic grant-based traffic channel load-balancing among the<br />
component carriers on a sub-frame by sub-frame basis.<br />
The PUCCHs corresponding to all <strong>DL</strong> CCs are transmitted on the Primary Component Carrier (PCC).<br />
Multi-bit HARQ feedback signaling format and Channel State Information (CSI) signaling for multiple <strong>DL</strong><br />
CCs are supported in Rel-10. For specific UEs, Uplink Control Information (UCI) can also be transmitted<br />
simultaneously on PUCCH and PUSCH. The power control and UE power headroom reporting are<br />
enhanced to support flexible UE power amplifier implementation for diverse CA scenarios.<br />
An important aspect of the design of Rel-8 LTE is the ability of LTE to use spectrum in a flexible fashion.<br />
This allows, for example, an initial LTE deployment with a small amount of spectrum as well as migration<br />
of GSM/CDMA frequency bands. Then as the usage of LTE grows, the system can efficiently migrate to<br />
increasingly larger bandwidths. To facilitate this spectrum scalability, a number of transmission<br />
bandwidths were defined in Rel-8.<br />
7.1.2 UPLINK TRANSMISSION ENHANCEMENTS<br />
In order to be fully IMT-Advanced compliant for uplink peak spectral efficiency, the LTE uplink must be<br />
extended with the support for uplink MIMO (multi-layer). The extension of the uplink currently under study<br />
in 3GPP can be roughly classified into two categories: 1) techniques relying on channel reciprocity; and 2)<br />
techniques not relying on channel reciprocity. Among the techniques that use channel reciprocity are<br />
Beam Forming (BF), SU-MIMO and MU-MIMO. With these techniques, the enhanced NodeB (eNB)<br />
processes a sounding reference signal from the UE to determine the channel state and assumes that the<br />
channel as seen by the eNB is the same as that seen by the UE (channel reciprocity) and forms<br />
transmission beams accordingly. It is important to note that since the transmitter has information about<br />
the channel, the transmitter may use this information to generate weights for antenna<br />
weighting/precoding. These techniques are especially suited for TDD.<br />
The channel non-reciprocity techniques can be further separated into open-loop MIMO (OL-MIMO),<br />
closed-loop MIMO (CL-MIMO) and MU-MIMO. OL-MIMO is used in the case where the transmitter has no<br />
knowledge of the Channel-State Information (CSI). Since the UE has no knowledge of the CSI from the<br />
eNB, these techniques cannot be optimized for the specific channel condition seen by the eNB receiver<br />
but they are robust to channel variations. Consequently, these techniques are well suited to high-speed<br />
mobile communications. OL-MIMO can be classified into Transmit Diversity (TXD) and Spatial<br />
www.4gamericas.org February 2011 Page 53
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