Source: https://patents.google.com/patent/US9628155
Timestamp: 2018-03-23 17:15:56
Document Index: 743760215

Matched Legal Cases: ['§119', 'Application No. 07', 'Application No. 12005822', 'Application No. 12005823', 'Application No. 07', 'Application No. 200810185379']

US9628155B2 - Transmit power allocation for adaptive multi-carrier multiplexing MIMO systems - Google Patents
Transmit power allocation for adaptive multi-carrier multiplexing MIMO systems Download PDF
US9628155B2
US9628155B2 US15170082 US201615170082A US9628155B2 US 9628155 B2 US9628155 B2 US 9628155B2 US 15170082 US15170082 US 15170082 US 201615170082 A US201615170082 A US 201615170082A US 9628155 B2 US9628155 B2 US 9628155B2
US15170082
US20160277076A1 (en )
This application is a continuation of U.S. application Ser. No. 13/601,545, filed Aug. 31, 2012, which is a continuation of U.S. application Ser. No. 12/275,728, filed Nov. 21, 2008, and claims priority under 35 U.S.C. §119 to European Application No. 07 123 861.2, filed Dec. 20, 2007, and the entire contents of each of which is hereby incorporated by reference.
Multiple-input-multiple-output (MIMO) communication systems use a plurality of transmit ports (e.g. transmit antennas) and receive ports (e.g. receive antennas). Multiplexing MIMO systems, which are also known as spatial multiplexing MIMO systems, split an incoming data stream on several transmission channels, resulting in an increased data rate. (Alternatively, a higher robustness may be obtained instead of a higher data rate.) In simple systems, the transmission channels may correspond to the transmit ports, in more complex systems an encoding (precoding) is applied by a multiplexing MIMO precoder in the transmitter which, typically, spreads the transmission channels over the transmission ports. A decoding (detection) corresponding to the encoding is applied by a multiplexing MIMO detector in the receiver in order to recover the transmission channels. An example of such encoding is Eigenbeamforming. Multi-carrier modulation schemes (e.g. OFDM or multi-carrier wavelet modulation) are using a plurality of subcarriers in order to transmit data. In adaptive multi-carrier communication systems the modulation scheme for each subcarrier is chosen based on a signal-to-noise ratio (SNR) of the subcarrier. Waterfilling is a known method for transmit power allocation which optimizes the overall throughput (data rate) while holding the overall transmit power below a maximum value. Waterfilling is efficient for non-adaptive multi-carrier systems (i.e. when all subcarriers are modulated in the same way). For adaptive multi-carrier systems, however, waterfilling shows almost no transmission throughput gain.
The problem to be solved by the present invention is to provide for a MIMO communication device and a method and a computer program product for assigning transmit power allowing for a higher data rate.
Alternatively to comprising a multiplexing MIMO detector, the MIMO communication device advantageously comprises a multiplexing MIMO precoder, whereby said transmission channels correspond to input ports of the multiplexing MIMO precoder.
Advantageously in this case, the MIMO communication device comprises a receiving unit adapted to receive notching information indicating which transmission channels are not used for transmitting information at which subcarriers, whereby the link controller is adapted to determine which transmission channels are not used to transmit information at which subcarriers based on the received notching information.
FIG. 3(a) shows a first example of a SNR increase obtained by the embodiment of the method of assigning transmit power according to the present invention.
FIG. 3(b) shows a second example of a SNR increase obtained by the embodiment of the method of assigning transmit power according to the present invention.
The S/P 10 receives a stream of input data. The input data is given in the form of bits and may comprise user data. The S/P 10 converts (splits) the input data to a number N=>2 of parallel streams, the number N corresponding to the number of transmit paths T1, T2 and to the number of parallel and independent transmission channels (decoupled channels) obtained by means of precoding (e.g. Eigenbeamforming). In FIG. 2, N=2 holds. The splitting ratio depends on the available capacity (data rate) on each transmission channel. The operation of the S/P 10 is controlled by the link controller 4-1, based on the tonemaps described below.
The MIMO precoder 14 precodes the symbol vectors s according to a multiplexing MIMO encoding method. The MIMO precoder 14 has input ports for receiving the symbol vector s and output ports for putting out the precoded vector. The input ports correspond to the transmission channels (e.g. decoupled transmission channels) and the output ports correspond to the transmit ports T1, T2 (i.e. a symbol that is put out from an output port of the MIMO precoder 14 is transmitted—after processing by the corresponding MC modulator 16—on a corresponding one of the transmit paths T1, T2). The MIMO precoder 14, for example an Eigenbeamforming precoder 14, precodes the symbol vector s and puts out a precoded vector of the same size N for each subcarrier. However, generally, precoding may be omitted, in this case the transmission channels correspond to the output ports T1, T2.
In this embodiment it is assumed, that all information that is transmitted from the receiver 1-2 to the transmitter 1-1 is transmitted via the transmitting unit 2-2 and the receiving unit 3-1. The link controller 4-1 determines the transmit power levels based on the notching information as is described below. Alternatively or in addition to receiving notching information, the link controller 4-1 may receive the transmit power levels from the receiver 1-2. In this case, it need not calculate the transmit power levels based on the notching information. The notching information is regular part of the tonemaps, since the symbol mappers 12 must know which subcarrier is notched on which transmission channel.
The link controller 4-2 determines the tonemaps to be used for transmission from the transmitter 1-1 to the receiver 1-2, provides the tonemaps to the symbol demappers 24 and transmits the tonemaps to the transmitter 1-1 via the transmitting unit 2-2. State of the art methods for obtaining the tonemaps may be used. For example, the link controller 4-2 may determine the modulation scheme that is to be used by a given subcarrier on a given transmission channel (e.g. decoupled transmission channel) based on the indicator value of the SNR of the given subcarrier on the given transmission channel. For a high SNR, a high order modulation scheme is chosen and for a low SNR, a low order modulation scheme is chosen. If the indicator value of the SNR is below a threshold value, the given subcarrier on the given transmission channel is not used for transmitting data. The given subcarrier on the given transmission channel is said to be notched. The information about notched subcarriers is part of the tonemaps. The link controller 4-2 may determine a multiplexing MIMO precoding method (e.g. an Eigenbeamforming precoding matrix) and transmit corresponding information (e.g. an index of an entry of a codebook comprising precoding matrices as entries) describing the precoding method to the transmitter 1-1 via the transmitting unit 2-2.
The MIMO detector 22 performs a detection on the received symbol vector y and obtains an estimate ŝ of the symbol vector s for each subcarrier based on the corresponding channel state information and the selected precoding method (e.g. precoding matrix). The MIMO detector 22 has input ports for receiving the received symbol vector y and output ports for putting out the detected estimate ŝ. The input ports correspond to the receive paths R1, R2, R3, R4 (i.e. a symbol that is received on one of the receive paths R1, R2, R3, R4 by the receiver 1-2 is input—after processing by the corresponding MC demodulator 16—to the MIMO detector 22 on a corresponding one of the input ports of the MIMO detector 22) and the output ports correspond to the (decoupled) transmission channels. Detection is also known as decoding, and the MIMO detector 22 may also be called a MIMO decoder 22. When expressed in terms of decoding, the MIMO decoder 22 decodes the received symbol vector y thereby obtaining the estimate ŝ of the symbol vector s which is comprised in the received symbol vector y in encoded form (s is encoded in y). The MIMO detector 22 may, for example, be a Zero Forcing (ZF) detector, a Minimum Mean Square Error (MMSE) detector and a Maximum Likelihood (ML) detector, but other detectors are possible too.
FIGS. 3(a) and 3(b) show examples of the increase of SNR according to the above method. FIG. 3(a) shows the SNR of a first transmission channel obtained by Eigenbeamforming. FIG. 3(b) shows the SNR of second transmission channel obtained by Eigenbeamforming. It is typical that the one transmission channel obtained by Eigenbeamforming is much stronger than the other transmission channels. It can be seen that in regions where the second transmission channel is notched, the SNR of the first transmission channel is increased by 3 dB when compared to classical Eigenbeamforming. A combination of Eigenbeamforming with waterfilling (no SNR curve is shown for this combination) yields approximately the same SNR as pure Eigenbeamforming. Because the SNR is increased, the channel capacity is increased. Therefore, the data rate can be increased. The data rate can be increased, for example, by selecting a modulation scheme of a higher modulation order than would be possible without the increased SNR and/or by selecting an error correction scheme with less encoding overhead (i.e. with a smaller ratio of encoded to unencoded bits).
1. A method of assigning transmit power in a multiple-input-multiple-output (MIMO) two-stream transmission, the method comprising:
receiving a first symbol stream associated with a plurality of subcarriers in accordance with constellation information contained in a first tonemap, the first tonemap including first information indicating subcarriers of the plurality of subcarriers that are not used for transmitting data;
receiving a second symbol stream associated with the plurality of subcarriers in accordance with constellation information in a second tone map, the second tonemap including second information indicating subcarriers of the plurality of subcarriers that are not used for transmitting data;
reallocating, by the circuitry according to the first tonemap when a subcarrier for the first symbol stream is not used for transmitting data and the corresponding subcarrier for the second symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the first symbol stream to the corresponding subcarrier of the second symbol stream; and
reallocating, by the circuitry according to the second tonemap when a corresponding subcarrier for the second symbol stream is not used for transmitting data and the subcarrier for the first symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the second symbol stream to the subcarrier of the first symbol stream.
2. The method according to claim 1, wherein after the reallocating of all of the transmit power to the first symbol stream or the second symbol stream, respectively, the transmit power for the first symbol stream or the second symbol stream is 3 dB more than the transmit power for the corresponding symbol stream.
3. The method according to claim 1, wherein for each of the plurality of subcarriers, when the first and second tonemaps of one of the first and second symbol streams is not used for transmitting information at the subcarrier and the other one of the first and second symbol streams is used for transmitting information at the subcarrier, a preassigned transmit power portion for the one of the first and second symbol streams that is not used for transmitting information at the subcarrier is assigned to the other one of the first and second symbol streams which is used for transmitting information at the subcarrier.
4. The method according to claim 1, wherein the reallocating of the transmit power includes multiplying a symbol of the first or second symbol stream, respectively, with an amplification factor corresponding to the allocated transmit power.
5. The method according to claim 1, wherein the MIMO two-stream transmission is a power-line communication (PLC) MIMO two-stream transmission.
6. The method according to claim 1, wherein the circuitry determines whether the subcarrier of the first symbol stream is used to transmit data according to a signal-to-noise ratio of the subcarrier of the first symbol stream.
7. The method according to claim 1, wherein the circuitry determines whether the subcarrier of the second symbol stream is used to transmit data according to a signal-to-noise ratio of the subcarrier of the second symbol stream.
8. The method according to claim 1, wherein the circuitry determines whether the subcarrier of the first symbol stream is used to transmit data by comparing a signal-to-noise ratio of the subcarrier of the first symbol stream to a predetermined threshold.
receiving each of the first and second tonemaps.
receiving a third symbol stream associated with the plurality of subcarriers in accordance with constellation information contained in a third tonemap, the third tonemap including third information indicating subcarriers of the plurality of subcarriers that are not used for transmitting data;
determining, by the circuitry utilizing the third information, whether a subcarrier of the third symbol stream is used for transmitting data; and
reallocating, by the circuitry according to the third tonemap, when the subcarrier of the third symbol stream is not used for transmitting data, the subcarrier for the first symbol stream is not used for transmitting data and the corresponding subcarrier for the second symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the first symbol stream and all of the transmit power of the subcarrier of the third symbol stream to the corresponding subcarrier of the second symbol stream.
11. A multiple-input-multiple-output (MIMO) communication device, comprising:
a first symbol mapper circuit configured to receive a first data stream, perform a symbol mapping on the first data stream according to a first tone map for a plurality of subcarriers, and output a first symbol stream, the first tonemap including first information indicating subcarriers of the plurality of subcarriers that are not used for transmitting data;
a second symbol mapper circuit configured to receive a second data stream, perform a symbol mapping on the second data stream according to a second tone map for the plurality of subcarriers and output a second symbol stream, the second tonemap including second information indicating subcarriers of the plurality of subcarriers that are not used for transmitting data; and
a power allocation circuit configured to
receive the first and second symbol streams,
reallocate according to the first tonemap, when a subcarrier for the first symbol stream is not used for transmitting data and the corresponding subcarrier for the second symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the first symbol stream to the corresponding subcarrier of the second symbol stream, and
reallocate according to the second tonemap, when a corresponding subcarrier for the second symbol stream is not used for transmitting data and the subcarrier for the first symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the second symbol stream to the subcarrier of the first symbol stream.
12. The MIMO communication device according to claim 11, wherein the reallocation of the transmit power for the symbol stream that is not used for transmitting information at the subcarrier to the one of the first and second symbol streams which is used for transmitting information at the subcarrier increases the transmit power of that symbol stream is by 3 dB.
13. The MIMO communication device according to claim 11, wherein the power allocation circuit is further configured to assign, for each of the plurality of subcarriers when the first and second tonemaps of one of the first and second symbol streams is not used for transmitting information at the subcarrier and the other one of the first and second symbol streams is used for transmitting information at the subcarrier, a preassigned transmit power portion for the one of the first and second symbol streams that is not used for transmitting information at the subcarrier to the other one of the first and second symbol streams which is used for transmitting information at the subcarrier.
14. The MIMO communication device according to claim 11, wherein the power allocation circuit is further configured to multiply a symbol of the first or second symbol stream, respectively, with an amplification factor corresponding to the allocated transmit power.
15. The MIMO communication device according to claim 11, wherein the MIMO communication device is a power-line communication (PLC) MIMO communication device.
16. The MIMO communication device according to claim 11, wherein the power allocation circuit determines whether the subcarrier of the first symbol stream is used to transmit data according to a signal-to-noise ratio of the subcarrier of the first symbol stream.
17. The MIMO communication device according to claim 11, wherein the power allocation circuit determines whether the subcarrier of the second symbol stream is used to transmit data according to a signal-to-noise ratio of the subcarrier of the second symbol stream.
18. The MIMO communication device according to claim 11, wherein the power allocation circuit determines whether the subcarrier of the first symbol stream is used to transmit data by comparing a signal-to-noise ratio of the subcarrier of the first symbol stream to a predetermined threshold.
19. The MIMO communication device according to claim 11, wherein the power allocation circuit determines whether the subcarrier of the second symbol stream is used to transmit data by comparing a signal-to-noise ratio of the subcarrier of the second symbol stream to a predetermined threshold.
20. The MIMO communication device according to claim 11, further comprising:
a third symbol mapper circuit configured to receive a third data stream, perform a symbol mapping on the third data stream according to a third tone map for the plurality of subcarriers and output a third symbol stream, the third tonemap including third indicating subcarriers of the plurality of subcarriers that are not used for transmitting data, wherein
the power allocation circuitry is further configured to
determine, utilizing the third information, whether a subcarrier of the third symbol stream is used for transmitting data; and
reallocate according to the third tonemap, when the subcarrier of the third symbol stream is not used for transmitting data, the subcarrier for the first symbol stream is not used for transmitting data and the corresponding subcarrier for the second symbol stream is used for transmitting data, all of the transmit power of the subcarrier of the first symbol stream and all of the transmit power of the subcarrier of the third symbol stream to the corresponding subcarrier of the second symbol stream.
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