Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims only. It should be further understood that the drawings are merely intended to conceptually illustrate the structures and procedures described herein.
In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope and spirit of the present invention.
The embodiment will now be described in relation to a wireless multi-antenna transmission system, such as, but not limited to, a MIMO system with a general UL feedback scheme for MIMO DL transmission, including different multi-antenna operating modes, e.g., SU-MIMO as well as MU-MIMO, for an exemplary case of two available Tx antennas at a transmitter unit of a base station device, such as a Node B. However, it will be apparent from the following description and is therefore explicitly stressed that these embodiments can be applied to other network architectures with different radio access technologies involving multi-antenna transmitter devices (e.g. base station devices, access points or other access devices) capable of being operated in different operating modes.
In a certain implementation example, an SU-MIMO operation mode with the two Tx antennas 201 and 202 and a multi-codeword transmission mode are considered. Of course, other operation modes may be provided as well. In case that two transmission streams (i.e., spatial multiplexing rate “2”) with independent modulation and coding (multi-codeword MIMO—such as “PARC”) are used, a CQI information might be required for both streams in order to allow link adaptation, whereas in case of a single stream fall-back mode (e.g. single stream beamforming) only a single CQI information for AMC may be needed.
According to certain embodiments, an advanced feedback scheme may be based on a mode indicator for signaling the transmission scheme or method and which may allow transmission of different kinds of CQI and CSI or precoding information in the same signaling setup to the BS 20 in order to facilitate scheduling and link adaptation. Such embodiments may therefore change the interpretation of the feedback information based on the MIMO operation mode, and transmit a mode indicator, which may be needed at the BS 20 in order to correctly interpret the provided feedback information received from the MS 10.
In the present example, the basic MIMO operation mode (e.g., SU-MIMO or MU-MIMO) may be defined semi-statically (e.g., on a longer term scale) by the BS 20, e.g. by using a higher layer signaling. As an alternative or in addition thereto, the basic operation mode may be set by the network operator and/or by the user, or may be derived from any other network signaling. Depending on this basis or initial operation mode, the MS 10 may feed back different kind of MIMO related feedback information (e.g., information related to SU-MIMO or multi-user MIMO).
In the following examples, different possible kinds of feedback information which may be required for different transmission modes are described. In case of SU-MIMO with two transmit antennas, there is the possibility to have single stream transmission as well as two stream transmission. For single stream transmission, the CQI for the stream as well as some precoding and/or beamforming information may be required. If the CQI feedback information requires five bits (same as in SISO), three bits can be provided for precoding information (which allows a precoding codebook of size 23=8). Therefore, in such an example, the feedback information for a user in a channel/system situation that only supports single stream transmission may require a total of eight bits for combined CSI and CQI, wherein three of the eight bits are multi-antenna transmission specific.
In an example using SU-MIMO with two-stream transmission, some CQI information from two/both streams may be required. However, the full CQI information for each stream need not be transmitted. Rather, some relative CQI for the second stream with respect to the first stream may be sufficient. This relative CQI may have a length of three bit. The relative CQI has the effect, that only a certain difference in applicable AMC may be allowed between the streams. For multi-codeword MIMO with two streams and two Tx antennas, the precoding may have only a limited effect on the achievable throughput. Therefore, this feedback information could be left out. Thus, for multi-stream transmission SU-MIMO, the absolute CQI might be needed for the first stream (as in case of SISO) as well as three bits for the relative CQI for the second stream. In this example, the three bits for the relative CQI may be multi-antenna transmission specific.
In order to tell the BS 20 how the spatial feedback information should be interpreted, a mode indicator, which may in the present example consist of a single bit (but is not limited to this single bit), may show if spatial multiplexing or beamforming is signalled. In case of more Tx antennas or more operation modes, a multi-bit mode indicator can be used to differentiate more operating modes.
The transceiver unit 14 may be connected to a signal processing stage 12 which responsible for receiver-related processing, (e.g., demodulating, descrambling, decoding etc.) of received DL data, and for transmitter-related processing, (e.g., modulating, scrambling, coding etc.) of UL data to be transmitted. The signal processing stage 12 may additionally be configured to determine or extract a basic operation mode 68 received for example by a higher-layer signaling from a radio-connected BS, e.g. BS 20 of
In this example, the processing at the receiving end, e.g., at the MS 10, is shown in
In this example, the processing at the transmitting end, e.g., at the BS 10, is shown in
In
The above CQI examples may relate to spatial CQI. In addition thereto, a CQI in the frequency domain can be used, allowing frequency domain packet scheduling. Then, the CQI information in the third portion 74 can be used for the first transmission stream, which may be the same allocation as in case of SISO according to
In an exemplary modification of the embodiment, the feedback information may be divided into two parts. The type of one part of the feedback information might not depend on the transmission mode, whereas the other part of the feedback information may depend on the transmission mode. The part of the feedback information that does not depend on the transmission mode may be a bit field of a fixed length. It may be related for example to the channel quality of one data stream, possibly indicated in the frequency domain.
The part that depends on the transmission mode may be a bit field of fixed length, which may refer to different characteristics of the transmission for different modes. For example, in one mode, the bits in this bit field may refer to spatial preceding information, whereas in another mode, the bits may refer to relative CQI information.
In another exemplary modification of the embodiment, the part of the feedback information that does not depend on the transmission mode may be the only information that a scheduler needs to decide on the scheduling of users. The other bits of the feedback information may be needed to determine the actual transmission mode of the user. For example, the bits that do not depend on the mode may indicate the frequency selective sum CQI for a multi-stream transmission, and the CQI for a single stream for a precoded single-stream transmission. The bits depending on the mode selection may then determine the division of the sum CQI among the streams for a multi-stream transmission, and the precoding for a single-stream transmission.
In the following, an example for the use of the above four bits for multi-user MIMO DL transmission is described. In this example, MU-MIMO as the basic MIMO operation mode may have been signaled via higher layer DL signaling by the NodeB 20 to the MS 10.
For DL MU-MIMO with two Tx antennas, there might only be the possibility to transmit to a single user or two users. The precoding in case of MU-MIMO may use a unitary transmission matrix (e.g., where the transmission vectors for different users are orthogonal). In this example, a user who is in bad channel conditions (and therefore needs the full available Tx power in order to support the minimum modulation and coding scheme), or if the interference produced by MU transmission is so high that the expected throughput would be e.g. less than ½ compared to the case of SU beamforming transmission, the receiver at the MS 10 may choose to set the mode indicator 80 to “0” in order to report for single-stream SU beamforming, so that the calculated and reported CQI in the third part 74 may assume full transmission power as well as no intracell interference due to MU transmission in addition to the precoding vector. The bit allocation of the codeword may then correspond to
Alternatively, in this example, when the MU transmission is reasonable from the user's point of view (i.e., when the minimum modulation and coding scheme can be supported, and interference power results in, for example, more then half of the throughput compared to SU transmission for this user), the receiver at the MS 10 may choose to set the mode indicator 80 to “1” in order to report for MU transmission, so that the reported CQI may assume half the available TX power for its transmission as well as intercell interference from a multi-user transmission with an orthogonal transmission weight in addition to the preferred preceding vector (3 bits). Here, the bit allocation of the codeword may correspond to
The difference between these two reporting modes can be indicated by the 1-bit mode indicator 80 which may indicate if the report is valid for MU transmission or SU transmission.
In this example, the BS 20 may define either SU or MU MIMO operation modes by higher layer signaling. In other examples where this might not be the case (and the MS 10 can define the best operation mode taking its current channel and signal-to-noise ratio (SNR) operation point into account), more feedback information (at least one bit) may be needed.
According to
According to
According to
According to
It should be noted that the above bit allocation and interpretation examples are not limiting and can be extended or amended in various ways. The position, interpretation and bit number of the second and third portions 72, 74 as well as the mode indicator 80 may be changed based on the requirements of other implementations. As an example, in case of four Tx antennas, the interpretation of the feedback information 70 may change depending on the number of transmission streams etc. In an exemplary case of multi-codeword single-user MIMO with up to 4 streams, the strongest stream and also the relative CQI (3 bit) in the negative direction from the strongest stream could be signaled by the feedback information. The following table contains possible information contents of the feedback information 70 and the corresponding total numbers of bits in dependence on the number of transmission streams:
As shown in the above table, in order of stream strength, there may be 24 possibilities for 4 streams (i.e., 4!=4*3*2*1=24), 6 (i.e., 3!) for 3 streams, and 2 for 1 stream. For a single stream no ordering may be needed. Furthermore, the relative CQI may be assumed to have a length of three bits. The relative CQI can be used in a sense that the CQI of the second strongest stream may be approximated as CQI+relative CQI, the one for the third strongest stream CQI+2*relative CQI and so on. In this example, up to nine bits of information may be allocated to the feedback information depending on the number of streams. Other set-ups for four Tx antennas are of course possible as well.
It is further noted that the functionalities of blocks 12 and 16 of
Hence, a flexible and rather straightforward feedback signaling option is described herein, which allows for defining at the receiving end the kind of information should may fed back and in which format, in order to be able to use the same amount of total feedback information independent of the operation mode (e.g., single stream transmission vs. SU-MIMO with two streams vs. multi-user MIMO).
As described above, certain embodiments (e.g., including methods, a system, a transmitter apparatus, a receiver apparatus, and computer program products) may allow for enhanced feedback in a multi-antenna transmission system, wherein an operation mode of a multi-antenna transmission end may be determined at a reception end of a connection, and a feedback information and a mode indicator may be generated based on the determined operation mode and transmitted to the multi-antenna transmission end where the feedback information may be interpreted based on the mode indicator. Thereby, different operation modes can be supported by the same amount of total feedback information and might not require any change in signaling setup.
Conventional methods for compressing frequency domain CQI reporting may be used. For example, the CQI report of a user may be built up based on multiple feedback reports, with the granularity increasing with the number of reports.
It is to be noted that the present invention is not restricted to the embodiments described above, but can be implemented in different network environments involving multi-antenna transmission controlled by feedback signaling. Different signaling format or means may be used for feeding back the mode indicator and the feedback information.
Number | Date | Country | Kind |
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06020735.4 | Oct 2006 | EP | regional |