TECHNICAL FIELD

The present invention relates generally to a transmitter, a receiver and methods therein, and in particular to downlink control signaling design for e.g. LTE-Advanced, such as control signaling design for LTE-A downlink transmission mode.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is responsible for the standardization of UMTS (Universal Mobile Telecommunication Service) and LTE (Long Term Evolution). LTE is a technology for realizing high-speed, packet-based communication that can reach high data rates both in the downlink and in the uplink. LTE is considered a next generation mobile communication system relative to UMTS. In order to support high data rates, LTE allows for a system bandwidth of up to 20 MHz. LTE is also able to operate in different frequency bands and can operate in at least FDD (Frequency Division Duplex) and TDD (Time Division Duplex). The modulation technique or the transmission method used in LTE is known as OFDM (Orthogonal Frequency Division Multiplexing).

For the next generation mobile communications system, e.g., IMT-advanced

(International Mobile Telecommunications) and/or LTE-Advanced, which is an evolution of LTE, support for bandwidths of up to 100 MHz is being considered. In both LTE and LTE-Advanced, radio base stations are known as eNBs or eNodeBs, where "e" stands for evolved. Furthermore, multiple antennas with precoding/beamforming technology can be used in order to provide high data rates to user equipments. Thus, LTE and LTE-Advanced are both examples of MIMO (Multiple-Input, Multiple-Output) radio systems. Another example of a MIMO and OFDM based system is WiMAX (Worldwide Interoperability for Microwave Access).

In LTE-Advanced, as specified in 3GPP Release 10 (Rel-10), e.g., Technical

Specification 36.814 V1.5.0 (2009-1 1 ), in order to fulfill LTE-Advanced downlink peak spectral efficiency of 30bps/Hz, up to eight layer transmission will be supported using advanced 8x8 high-order MIMO. It is also agreed in Rel-10 that up to eight UE-specific reference signals (called demodulation RS or DM-RS) should be introduced for the purpose of channel demodulation. So far, DM-RS rank 1 -8 pattern with normal CP (cyclic prefix) has been decided, as shown in Figure 1 .

A total of eight DM-RS ports are defined, multiplexed by CDM+FDM (code and frequency division multiplexing). The DM-RS overhead will be the same, i.e., twelve resource elements (RE) per layer. Up to two CDM groups are supported, FDM. Each CDM group has up to four DM-RS ports. DM-RS port numbering is defined as CDM group 1 : ports 7/8/1 1/13; and CDM group 2: ports 9/10/12/14. Orthogonal cover codes (OCC) are defined across the time domain only. Figure 1 depicts a DM-RS pattern supporting up to rank eight transmission. In the case of Rel-9 dual layer beamforming, i.e., downlink transmission mode eight (TM8), only CDM group 1 (denoted by the numeral "1 ") is used while the REs reserved for CDM group 2 (denoted by the numeral "2") are used for data transmission.

Downlink Control Information (DCI) format 2B has been defined in 3GPP TS 36.212 v9.0.0 (2009-12), the disclosure of which is incorporated herein by reference in its entirety. DCI format 2B enables dynamic rank adaptation between rank-1 and rank-2, as well as transparent configuration of single-user (SU) case and multi-user (MU) case, where DM-RS ports 7/8 with up to two scrambling sequences are dynamically allocated. Figure 2 depicts a table 10 listing different application cases that are implicitly indicated by some information carried in DCI format 2B. The information is encoded by disabled/enabled transport blocks (TB) 12, a 1 -bit new data indicator (NDI) 14, and a 1 -bit scrambling identity (SI) 16. These bits encode the information listed in the "Message" column. SUMMARY

According to one or more embodiments disclosed and claimed herein, minimal extension of DCI format 2B is proposed, to support Rel-10 functionalities, e.g. single cell MIMO, CoMP or possibly relaying/HetNet.

In disclosed embodiments, a new DCI format is proposed in Rel-10 to support Rel-10 MIMO transmission. In some embodiments, only two extra bits are introduced in a DCI format otherwise identical to format 2B, to signal rank up to eight, by reusing the SI bit 16 while at the same time supporting different MU-MIMO dimensioning for the important case of rank-1 and rank-2. This new DCI format can potentially support not only single cell downlink transmission, but also some other Rel-10 functionalities, e.g. CoMP or relaying/HetNet.

One embodiment relates to a method in a transmitter for indicating to a receiver a number of signaling layers used in a downlink transmission from the transmitter by signaling a message in a DCI format. Transmitted in the DCI format are two bits indicating the number of layers used in the downlink transmission.

Another embodiment relates to a method in a receiver for enabling the receiver to determine the number of layers used in downlink transmission. A message is received in a DCI format comprising two bits indicating the number of layers. The receiver is configured to receive data according to the DCI and the number of layers.

Yet another embodiment relates to a transmitter operative to indicate to a receiver a number of signaling layers used in a downlink transmission from the transmitter. The transmitter includes a signaling circuit operative to signal a message in a DCI format comprising two bits indicating a number of layers in the downlink transmission.

Still another embodiment relates to receiver operative to determine a number of layers used in a downlink transmission. The receiver includes a receiving circuit operative to receive a message in a DCI format comprising two bits indicating a number of layers. The receiver further includes a configuring circuit operative to configure the receiver to receive data according to the DCI and number of layers. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a functional block diagram of a prior art DM-RS pattern supporting up to rank eight transmission.

Figure 2 is a table depicting the encoding of DCI bits according to prior art DCI format 2B, and application cases signaled.

Figure 3 is a functional block diagram of a transmitter and receiver in a wireless communication network, with the transmitter transmitting DCI bits according to one embodiment of the present invention.

Figure 4 is a table depicting one encoding of DCI bits, and application cases signaled, according to one embodiment of the present invention.

Figure 5 is a table depicting one encoding of DCI bits, and application cases signaled, according to another embodiment of the present invention.

Figure 6 is a table depicting one encoding of DCI bits, and application cases signaled, according to yet another embodiment of the present invention.

Figure 7 is a table depicting one encoding of DCI bits, and application cases signaled, according to still another embodiment of the present invention.

Figure 8 is a flow diagram of a method by a transmitter of indicating to a receiver a number of signaling layers used in a downlink transmission from the transmitter.

Figure 9 is a flow diagram of a method by a receiver of determining the number of layers used in downlink transmission from a transmitter.

DETAILED DESCRIPTION

As mentioned above, Rel-10 will support up to eight layer transmission. TM8 will remain as specified in Rel-9. DCI format 2B has several deficiencies, and consequently a new DCI format will be required for Rel-10. First, to support up to eight layers transmission, rank will need to be indicated to UE for proper data demodulation. DCI format 2B does not specify this directly, but rather implies rank-1 or rank-2 by whether one TB 12 is disabled or not. Second, according to MU-MIMO dimensioning in Rel-10, rank 1 -2 is applicable to SU/MU, while rank 3-8 is defined for SU only. This differs from Rel-9 TM8, where SU and MU have the same scope of up to two layers transmission. Third, a new DCI format may be used not only used for single cell MIMO, but also for Coordinated Multipoint (CoMP), or possibly relaying/heterogeneous network

(HetNet). A final consideration is that, since Rel-9 TM8 will be a subset of Rel-10 eight layers transmission, DCI format 2B should be re-used as much as possible in the new DCI format. Various embodiments of the present invention are presented herein, as applied to different applications or considerations. Only part of the payload is depicted herein, to describe the proposed DCI format, e.g. 1 -bit NDI 14, 1 -bit SI 16, disabled/enabled TBs 12, and an additional two bits 20, denoted A and B. Additional bit fields for other purposes can of course also be present.

Figure 3 depicts a transmitter 100, such as in a radio base station, with processing circuits 120 operative to determine number of layers to be used in a downlink transmission (based on channel quality or configuration). When the number of layers, i.e. rank value, is determined, the transmitter 100 transmits over a transmitting circuit, Tx, information in a DCI format compatible with 3GPP Rel-10 indicating rank value to a receiver 140, such as in user equipment. In some embodiments, the Rel-10 DCI format is an extension to format 2B, which comprises two bits A, B used to indicate rank value. The receiver 140 receives over a receiving circuit, Rx, the information in the DCI format and from that information, the receiver determines in processing circuits 160 the number of layers used in the transmission.

The transmitter 100 comprises a processing circuit 120 operative to direct a transmitting circuit Tx to transmit a message in a downlink control information (DCI) format, which DCI format comprises two bits (A,B) indicating number of layers, also referred to as transmission rank.

The receiver 140 comprise a receiving circuit Rx configured to receive a message in a DCI format, which format comprises two bits indicating number of layers, and a processing circuit 160 operative to configure the receiver 140 to receive data according to the downlink control information and number of layers.

The mechanisms described herein for enabling signalling between the transmitter 100 and the receiver 140 in the radio communications network may be implemented through one or more processors, such as processing circuits 120 in the transmitter 100 or processing circuits 160 in the receiver 140, together with computer program code for performing the functions of embodiments described herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a machine-readable data carrier carrying computer program code for performing embodiments of the present invention when loaded into processing circuits 120, 160 in the transmitter 100 or receiver 140, respectively. One such machine-readable data carrier may be in the form of a CD-ROM disc. Of course, other suitable data carriers may include non-volatile memory, magnetic disc, and the like. The computer program code may furthermore be provided as pure program code on a server and downloaded to the transmitter 100 or the receiver 140.

SI for Rank Signaling

The table 18 of Figure 4 depicts that, when both transport blocks 12 are enabled, only rank-1 is SU/MU; ranks 3-8 are SU only. In this case, according to one embodiment, signaling overhead is reduced by using the 1 -bit SI 16, along with newly defined bits A,B 20, to implicitly indicate rank values 3-8 to the UE (since 1 -bit SI 16 is not used for SU case). Rank-2 transmission is hybrid SU/MU. In one embodiment, the 1 -bit SI 16 is used to separate co- scheduled UEs. In this embodiment, the new two bits 20 value of (0,0) are used to uniquely indicate to the UE the rank value of 2. Figure 4 depicts one representative encoding of the two bits 20 and the 1 -bit SI 16; other encodings are within the scope of the present invention.

SI for MU-MIMO dimensioning

Further to the embodiment described above, the new bits 20 can also be efficiently used for rank 1 -2 to indicate more complicated SU/MU case for Rel-10 UEs, e.g., indication of DM-RS ports or CDM group. Three SU/MU application cases are considered.

A first case, in which two DM-RS ports are signaled with two scrambling sequences, is depicted in table 22 of Figure 5. Note that the first five rows are the same as DCI format 2B, where 1 -bit SI 16 is used to signal ports 7/8 in CDM-1 . In this case, the two new bits 20 are not used for rank-1 , and are reserved. Figure 5 depicts one representative encoding of the two bits 20 and the 1 -bit SI 16 to signal rank 3-8; other encodings are within the scope of the present invention.

A second case, in which four DM-RS ports in two CDM groups are signaled with one scrambling sequence, is depicted in table 24 of Figure 6. In this case, ports 7/8 in CDM-1 and ports 9/10 in CMD-2 are used, where length-2 OCC will be applied. In one embodiment, rank 1/2 messages in the first ten rows may use the 1 -bit SI 16 for signaling the ports. In another embodiment, the ports are signaled by exploiting the new bits 20. Because co- scheduled UEs are allocated with orthogonal ports, co-scheduling of Rel-9 and Rel-10 UEs can be enabled, even with the same scrambling sequence. Accordingly, the 1 -bit SI 16 is free, and can be used for the signaling of the ports since further separation between co-scheduled UEs is no longer needed. Hence, the use of scrambling sequences is limited. In another embodiment, either the A-bit or B-bit of the new bits 20 can be utilized to do the same thing as the 1 -bit SI 16, to release the limitation of scrambling sequences. Figure 6 depicts one representative encoding of the two bits 20 and the 1 -bit SI 16; other encodings are within the scope of the present invention.

A third case, in which four DM-RS ports in CDM group one is signaled with one scrambling sequence, is depicted in table 26 of Figure 7. In this case, ports 7/8/1 1/13 in CDM-1 are used, where length-4 OCC will be applied. In one embodiment, rank 1/2 messages in the first ten rows may use the 1 -bit SI 16 for signaling the OCC length. Table 26 is the same as table 24 of Figure 6, but with different explanation of re-using the 1 -bit SI 16. In another embodiment, either A-bit or B-bit of the new bits 20 can be utilized to do the same thing as the 1 -bit SI 16, to release the limitation of scrambling sequences. Figure 6 depicts one representative encoding of the two bits 20 and the 1 -bit SI 16; other encodings are within the scope of the present invention. Figure 8 depicts a method 200 of transmitting signaling layer information to a receiver by a transmitter in a wireless communication network, such as an eNB. The transmitter determines a number of signaling layers to be used in a downlink transmission (block 210), and then transmits to a receiver a DCI format including two bits 20 indicating the number of layers used in the downlink transmission (block 220). In various embodiments, as described above, the two bits 20 may be jointly encoded with existing DCI format 2B bits, such as the SI 16, to convey various information in addition to the signaling layer information.

Figure 9 depicts a method 300 of receiving signaling layer information by a receiver in a wireless communication network, such as a UE. The receiver receives a message in a DCI format including two bits 20 indicating the number of signaling layers in a downlink transmission (block 310), and then configures the receiver circuit Rx to receive data according to the DCI and the number of layers (block 320). In various embodiments, as described above, the two bits 20 may be jointly encoded with existing DCI format 2B bits, such as the SI 16, to convey various information in addition to the signaling layer information.

Extension to Signaling Other Scenarios

Note that in the above embodiments, in some cases, e.g., rank-1 , the two new bits 20 are reserved. In one embodiment, in these cases, the two new bits 20 may be utilized to signal other application scenarios, particularly those that primarily target rank-1. Such scenarios include, by way of example and without limitation, single cell MU-MIMO, CoMP, or

relaying/HetNet. The signaling information could communicate to the UE whether the downlink transmission is conducted in one of those scenarios, according to any encodings of the reserved bits, which may be readily devised for particular applications by those of skill in the art, having the benefit of the teachings of the present disclosure.

New DCI formats for Rel-10, based on DCI format 2B and using two new bits 20 to support Rel-10 MIMO transmission, according to embodiments described above, present numerous advantages. First, the rank value of more than two layers - indeed, as many as eight layers - can be implicitly indicated by joint coding using existing 1 -bit SI 16 and introducing only two new bits 20. The standard DCI format 2B can be re-used to the greatest extent possible. Second, for the support of different MU-MIMO dimensioning, 1 -bit SI 16 can be re-used as much as possible to efficiently save control signaling, while still allowing scrambling indication for the important cases of rank-1 and rank-2. Finally, the proposed Rel-10 DCI format can separate SU and MU applications, and may be used for other possible Rel-10 functionalities in the case of rank-1 , e.g. CoMP, relaying, and HetNet.

The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.