The application is a divisional application of Chinese patent application No.201080068326.8 (an amplifying and forwarding relay scheme for multi-input multi-output network coding for three-node bidirectional cooperation), which has an application date of 2010, 7 and 29.
Disclosure of Invention
As used herein, a node includes, but is not limited to, a base Station (STA), a mobile device, a mobile terminal, a dual-mode smart phone, a computer, a laptop computer, or any other equivalent device capable of operating under the IEEE 802.11n draft standard.
Consider a multicast (downlink) and multiple access (uplink) channel with one Access Point (AP) and several nodes. In the IEEE 802.11n draft standard, a Reverse Direction (RD) protocol is introduced to quickly schedule bi-directional traffic flows within a transmission opportunity (TXOP). The reverse protocol allows (allows) a node that has obtained a TXOP to grant a reverse transmission to another node while still controlling the TXOP. However, when the channel conditions between two nodes are insufficient to provide fast and reliable transmissions at the two nodes, assistance in transmissions (communications) may be involved through cooperation of a third node, a half-duplex Relay Node (RN). When the transmission between these two nodes involves cooperation by a third node, a half-duplex Relay Node (RN), the situation becomes more complex and wireless network coding can be utilized to further increase system throughput. Each node is both a source node and a destination node.
In the present invention, wireless network coding is introduced into the system and combined with bi-directional cooperation to increase system throughput, as shown in fig. 2 and described more fully below. The present invention describes a Network Coding Amplify and Forward (NCAF) relay scheme in a compromise three-node two-way collaboration scenario.
In the three-node bidirectional cooperation scheme of the present invention, two nodes (nodes)1And node2) Is both a source node and a destination node, and the RN is a relay node, an auxiliary node1And node2In both directions. Relay Node (RN) sequentially slave nodes1And node2Both receive the signal, combine the two signals with precoding matrices for the two signals, and broadcast the mixed signal to two nodes on orthogonal channels. Each node (source and destination) receives a transmission (transmission) of a desired signal from the other nodes and a transmission (transmission) of a mixed signal from the RN. Each node can jointly decode the desired data based on its knowledge of the outgoing (transmission ) signal. This process is illustrated in FIG. 3, described further below. The present invention not only describes the above network coded amplify-and-forward (NCAF) relay scheme, but also solves the design problem of the precoding matrix at the RN for the signals received from the nodes (source and destination) such that the instantaneous capacity of the two-way cooperative system subject to the total power constraint at the RN is maximized, giving Channel State Information (CSI) in both cases.
(1) There is no CSI of the direct link at the RN: only the CSI of the channel from node (source and destination) to RN and the channel from RN to node (source and destination) is known at RN. The CSI of the channel between the two nodes (source and destination) is not known at the RN.
(2) CSI with direct link at RN: only the CSI of the channel from node (source and destination) to RN, the channel from RN to node (source and destination) and the channel between two nodes (source and destination) are known at RN.
In the network coded amplify-and-forward (NCAF) relay scheme of the present invention, the RN no longer forwards the amplified received signal from one node to another as in conventional amplify-and-forward cooperation. Instead, the RN combines two signals received from two nodes by first multiplying the two signals by a precoding matrix. Then, the RN broadcasts (multicasts) a combined signal containing the mixed data of the bidirectional traffic flows. Each end node receives signals from the RN and the nodes then jointly decode their desired signals based on knowledge of their outgoing (transmission ) signals. Diversity still exists in the cooperation.
The NCAF relay scheme of the present invention may prove necessary for future IEEE 802.11n Very High Throughput (VHT) draft standards. The NCAF relay scheme of the present invention has the advantage that only simple processing, i.e. linear precoding, is required at the Relay Node (RN). The NCAF relay scheme is also compatible with legacy cooperation using an amplify-and-forward relay scheme. The NCAF relay scheme of the present invention also solves the problem when the RN cannot decode received data due to insufficient number of antennas equipped at the RN, and is always feasible for any multi-antenna system.
A method and apparatus are described, comprising: receiving a first signal including first data in a first slot of a first channel; receiving a second signal including second data in a second slot of a second channel; determining a first precoding matrix; determining a second precoding matrix, applying the first precoding matrix to the first data to generate precoded first data; applying a second precoding matrix to the second data to produce second precoded data; generating a third signal by combining the precoded first data and the precoded second data; and transmitting the third signal over the first channel and the second channel. Also described are a method and apparatus comprising: transmitting a first signal; receiving a second signal; and jointly decoding a second signal comprising the first training sequence by removing the first training sequence and removing the first signal.
Detailed Description
Fig. 2 illustrates the operation of the amplify-and-forward relay scheme for bi-directional cooperative network coding of the present invention using half-duplex relay nodes. FIG. 2a shows a first communication level, wherein a node1To the node2Transmitting (sending, transmitting) data S with RN1. In the second communication stage, shown in fig. 2b, the node2To the node1Transmitting (sending, transmitting) data S with RN2. In the third communication stage shown in fig. 2c, the RN combines (mixes) the dataTo two nodes1And node2Transmission (transfer). By comparing data S1And data S2Applying precoding matrices to formCombining dataIs f (S)1+S2). The number of stages has been reduced from four stages to three stages. It should be noted that in addition to applying a precoding matrix to the data, a beamforming matrix may also be applied to the data.
First, a system model and some notations are introduced. XiIs a slave nodeiTransmitted signal (i ═ 1, 2, R, and nodeRRepresents RN). QiIs a nodeiAnd Q if beamforming is not usediIs an identity matrix. HijIs a slave nodeDotjTo the nodeiThe channel matrix of (2). Y isijAnd HijIs a slave nodejTo the nodeiAssuming that the elements have variancesIndependent and equally distributed gaussians. WiIs applied to Y at RNRiThe precoding matrix of (2). Total transmission power at nodei(i-1, 2) is PiAnd P at RNR。
RN slave node in first time slot1Receiving YR1=HR1Q1X1+NR1And in the second time slot from the node2Receiving YR2=HR2Q2X2+NR2. The RN then mixes the weighted received signals as its broadcast signal.
XR=W1YR1+W2YR2=W1HR1Q1X1+W2HR2Q2X2+W1NR1+W2NR2
Reception and decoding at one node (source and destination) serves as an example. Demodulation is of course performed at the receiving end. The processing at the other node (source and destination) is similar. Node point1In the second time slot from the node2Receiving Y12=H12Q2X2+N12And receives Y from RN in the third slot1R=H1RXR+N1RI.e. Y1R=H1RW1HR1Q1X1+H1RW2HR2Q2X2+H1RW1NR1+H1RW2NR2+N1R. In the form of a matrix
Similarly, Z2=A2X1+B2N2Wherein Z is2、A2、B2And N2By varying subscripts "1" and "2" and "N" in their respective counterparts1"and" N2"is used herein.
The problem is to determine W1And W2,To minimize the instantaneous capacity of the system subject to transmission power constraints at the RN. W1And W2Is a precoding matrix. Namely, determining W1And W2To maximize
Provided that
Where tr (X) represents the trace of matrix X.
Let QiI 1, 2 is unitary matrix, and the constraint can be simplified to
In the first case, it is assumed that the slave nodeiTo and from the RNjThe CSI of the channel (link) of (a) is available at the RN. Node pointiAnd nodejCSI for links (channels) between (i, j ≠ 1, 2, and i ≠ j) is not available. In this case, it is necessary to maximize the upper limit of f, rather than f itself, due to the lack of information. Namely, determining W1And W2To maximize
(3) Provided that
In the second case, assume that from node i to RN, RN to nodejAnd from node i to nodejCSI for a channel of (i, j ≠ 1, 2, and i ≠ j) is available to the RN. In this case, the design issue is to maximize (1) subject to (3).
Further, the question statement is rewritten in the following form in which symbols are explained after the introduction method.
Determining λ to minimize f2(λ) (4)
Provided that lambda is not less than 0, (5)
Sλ=q (6)
The Lagrangian function is L (lambda, mu) ═ f2(λ)-μT(Sλ-q), (7)
Where μ is the vector containing the lagrange multiplier. Using newton's method, the following iterative method is used for the solution for λ:
step 1: initializing lambda0∈(0,max_λ)。
And 4, step 4: if sum (sign (lambda)k+1))≠length(λk+1) Or sum (max _ λ - λ)k+1))≠length(λk+1) Then, the procedure returns to step 1. Otherwise proceed to step 5.
And 5: if it is notIf < threshold, stop. Otherwise, k is k +1, and proceeds to step 2.
Conditional αiIs defined as when Li≥LRWhen, or when L is satisfied at the same timei<LRAnd Li(Li-1)≥LRTime ", and will condition βiIs defined as "when L is satisfied simultaneouslyi<LRAnd Li(Li-1)≥LRAnd 1 hour. Thus, there are three solution cases:
general case 3 when β is present1And β2When the temperature of the water is higher than the set temperature,λ1,i≥1,i=1,L,LRandλ2,i≥1,i=1,L,LRare all diagonal matrices. The notation in the iterative method is as follows:
wherein,
in a design issue, two nodes (source and destination) issue (transmit, forward) training sequences to the RN so that the RN can estimate the incoming channel. The RN also needs to issue (transmit, forward) a training sequence to the nodes (source and destination) to estimate the channel (link) from the RN to each node, and also to transmit (issue, forward, transmit) information about the precoding matrix used by the RN.
Two basic data frame structures are proposed for use in the present invention.
(1) The RN applies a precoding matrix to the training sequence it receives and forwards, as shown in fig. 4(a) and fig. 5 (a).
(2) The RN estimates an input channel matrix, multiplies the input channel matrix by a precoding matrix, quantizes the generated matrices, and feeds back them. The RN also sends out its own training sequence to the nodes (source and destination) to estimate the channel state (channel condition) from the RN to the nodes, as shown in fig. 4(b) and fig. 5 (b). There is still a need to make other channel estimates, such as CSI of the output channel from the RN to the nodes (source and destination) at the RN, and CSI of the direct link at the RN. These CSIs are performed by other frames (e.g., control frames, etc.).
Referring again to fig. 3a, fig. 3a is a block diagram of the operation of a transmit side exemplary embodiment of the network coded amplify-and-forward relay scheme of the present invention. In the first time slot from the node1Transmitting (transmitting) data S to RN1As signal X1And in the second time slot from the node2Transmitting (transmitting) data S to RN2As signal X2. RN then targets node1And node2Is precoded, mixed (combined), and multicast (broadcast) the precoded mixed data (X)R). The pre-coded mixed (combined) data is modulated without any problem.
Referring again to FIG. 3b, FIG. 3b is a slave node1View of the invention a block diagram of the operation of a receiving side exemplary embodiment of the network coded amplify-and-forward relay scheme of the present invention. Node point1Slave node2Receiving signal Y12And receives a signal Y from RN1RAnd performs joint network and channel decoding. The decoded data is demodulated without any problem.
Referring again to FIG. 3c, FIG. 3c is a slave node2View of the invention a block diagram of the operation of a receiving side exemplary embodiment of the network coded amplify-and-forward relay scheme of the present invention. Node point2Slave node1Receiving signal Y21And receives a signal Y from RN2RAnd performs joint network and channel decoding. The decoded data is demodulated without any problem.
That is, from the point of view (perspective) of a node holding (owning) a transmission opportunity (TXOP), the node comprises means for transmitting (issuing, transmitting) a first signal with data and means for receiving a second signal. The transmission and reception means may be a transceiver or a separate transmitter and a separate receiver or any equivalent means. The node also has means for jointly decoding the second signal by removing (subtracting) the training sequence and the first signal. Optionally, the node further comprises means for decoding the second signal by considering applying the first beamforming matrix to the data of the first signal and applying the second beamforming matrix to the data of the second signal.
From the perspective of a Relay Node (RN), the RN includes: means for receiving a first signal in a first time slot of a first channel; means for receiving a second signal in a second time slot of a second channel; means for determining a first precoding matrix; means for determining a second precoding matrix, wherein the first precoding matrix and the second precoding matrix maximize a joint channel capacity of the first channel and the second channel, respectively; means for applying a first precoding matrix to the first data; means for applying a second precoding matrix to the second data; means for generating a third signal by mixing (combining) the precoded first data and the precoded second data; and means for transmitting the third signal. The transmission and reception means may be a transceiver or a separate transmitter and a separate receiver or any equivalent means. The RN also comprises: means for generating a first estimated channel matrix for a first channel and a second estimated channel matrix for a second channel; means for inserting a first precoding matrix multiplied by the first estimated channel matrix and a second precoding matrix multiplied by the second estimated channel matrix in a training sequence of the third signal; and prior to performing the means for inserting, means for quantizing a first precoding matrix multiplied by the first estimated channel matrix, and means for quantizing a second precoding matrix multiplied by the second estimated channel matrix. Optionally, the RN further includes: means for determining a first beamforming matrix; means for determining a second beamforming matrix; and means for applying a first beamforming matrix to the first data and a beamforming matrix to the second data prior to generating the third signal. Optionally, the RN further includes: means for applying a first beamforming matrix to the first precoding matrix multiplied by the first estimated channel matrix and means for applying a second beamforming matrix to the second precoding matrix multiplied by the second estimated channel matrix before inserting the first precoding matrix multiplied by the first estimated channel matrix and the second precoding matrix multiplied by the second estimated channel matrix between training sequences of the third signal.
Referring again to fig. 4, fig. 4 is a general brief exemplary frame structure for the network coded amplify-and-forward relay scheme of the present invention, but without beamforming at the source node. Fig. 4a shows a case where a training sequence is transmitted from a source node. The RN sends out a training sequence, but the training sequence sent by the RN is effectively a slave node1And node2The training sequence of the received RN is transmitted,and copied and returned to the source node (node)1And node2). In the third level, the RN is towards the nodeiTransmission of two training sequences and mixed data XR. For training sequence and mixed data XRBoth apply precoding matrices. For T1(first training sequence) applying a precoding matrix W1And to T2(second training sequence) applying a precoding matrix W2. Also for mixed signal XRH of (A) to (B)R1X1Applying a precoding matrix W1And to the mixed signal XRH of (A) to (B)R2X2Applying a precoding matrix W2. Note that HR1X1Is a RN slave node1(node)1Sending X1) The received desired signal. Also note HR2X2Is a RN slave node2(node)2Sending X2) The received desired signal. In fig. 4b, each node issues (transmits ) its own training sequence and in addition to issuing (transmitting ) the mixed signal XRIn addition, the RN sends out (transmits ) a precoding matrix W1And W2. Training sequence T not sent out (transmitted ) to RNRA precoding matrix is applied.
Referring again to fig. 5, fig. 5 is a general schematic exemplary frame structure for the network coded amplify-and-forward relay scheme of the present invention, with beamforming at the source node. Fig. 5a shows the case where a training sequence is sent from the source node. The RN sends out a training sequence, but the training sequence sent by the RN is effectively a slave node1And node2Received training sequence of RN, copied and returned to source node (node)1And node2). In the third level, the RN is towards the nodeiTransmission of two training sequences and mixed data XR. For training sequence and mixed data XRBoth apply precoding matrices. For T1(first training sequence) applying a precoding matrix W1And to T2(second training sequence) applying a precoding matrix W2. Also for mixed signal XRH of (A) to (B)R1X1Applying precoding momentsArray W1And to the mixed signal XRH of (A) to (B)R2X2Applying a precoding matrix W2. Note that HR1X1Is a RN slave node1(node)1Sending X1) The received desired signal. Also note HR2X2Is a RN slave node2(node)2Sending X2) The received desired signal. In addition to applying precoding matrices to the training sequence and the mixed signal, the training sequence T is also applied1Using a beam forming matrix Q1And for training sequence T2Using a beam forming matrix Q2. Also for mixed signal XRX of (2)1Using a beam forming matrix Q1And to the mixed signal XRX of (2)2Using a beam forming matrix Q2. In fig. 5b, each node issues (transmits ) its own training sequence and in addition to issuing (transmitting ) the mixed signal XRIn addition, the RN sends out (transmits ) a precoding matrix W1And W2. Training sequence T not sent out (transmitted ) to RNRA precoding matrix is applied. For mixed signal XRA precoding matrix is applied. Also for mixed signal XRH of (A) to (B)R1X1Applying a precoding matrix W1And to the mixed signal XRH of (A) to (B)R2X2Applying a precoding matrix W2. Note that HR1X1Is a RN slave node1(node)1Sending X1) The received desired signal. Also note HR2X2Is a RN slave node2(node)2Sending X2) The received desired signal. In addition to applying a precoding matrix to the mixed signal, the mixed signal X is also appliedRX of (2)1Using a beam forming matrix Q1And to the mixed signal XRX of (2)1Using a beam forming matrix Q2。
Referring to fig. 6, fig. 6 is a flow diagram of an exemplary embodiment of the present invention from the perspective of a node (source and destination), at 605, the node transmits a first signal (message) comprising data. At 610, the node receives a second signal (message) comprising data. At 615, the node jointly decodes a second signal (message) by removing (subtracting) the first data and the training sequence, since the training sequence and the first data and the precoding matrix applied to the first data are known, the second signal being a mixed signal (message) comprising the first data transmitted by the node and third data transmitted by another node (the destination node for the first data and the source node for the third data).
Referring to fig. 7, fig. 7 is a flow diagram of an exemplary embodiment of the present invention from the perspective of a relay node, which receives a first signal (message) in a first time slot of a first channel at 705. The first signal includes first data and a first training sequence. At 710, the relay node receives a second signal (message) in a second time slot of a second channel. The second signal includes second data and a second training sequence. At 715, the relay node determines a first precoding matrix to maximize channel joint capacity. At 720, the relay node determines a second precoding matrix to maximize the joint capacity of the channel. At 725, the relay node applies a first precoding matrix to the second data. At 730, the relay node applies a second precoding matrix to the second data. At 735, the relay node generates a third signal by mixing (combining) the precoded first data and the precoded second data. At 740, the relay node transmits (multicasts, broadcasts, transmits, sends) the third data over (on) both the first and second channels.
It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Further, the software may preferably be implemented as an application program tangibly embodied on a program storage unit. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units ("CPU"), a random access memory ("RAM"), and input/output ("I/O") interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof), which may be executed via the operating system. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit.
It is to be further understood that, because some of the constituent system components and methods depicted in the accompanying figures are preferably implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the present invention is programmed. Given the teachings herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations or configurations of the present invention.