Method for transceiving signal through at least two data streams in a wireless communication system

Abstract

A method for transceiving, by a network, a signal through at least two streams in a wireless communication system, includes measuring a channel state for the at least two streams by using a reference signal, determining at least one stream pair including a transmission stream and a reception stream based on the measured channel state, initiating a direction of one or more streams of the at least one stream pair, and transceiving the signal based on the one or more streams of the at least one stream pair.

Claims

1. A method for transceiving, by a network, a signal through at least two streams in a wireless communication system, the method comprising: measuring channel state for the at least two streams by using a reference signal; determining at least one stream pair including a transmission stream and a reception stream based on the measured channel state; initiating a direction of one or more streams of the at least one stream pair; transceiving the signal based on the one or more streams of the at least one stream pair; computing an interference reduction value n of the one or more streams of the at least one stream pair when a decoding for the one or more streams fails; and updating the direction of the one or more streams of the at least one stream pair by comparing the computed interference reduction value n with a predetermined value, wherein the interference reduction value is defined as following equation:
.sub.n=SINR (D.sub.n)SINR(D.sub.n)[equation] where SINR denotes a Signal-to-Interference-plus Noise Ratio, D.sub.n denotes a direction of an n.sup.th stream, where D.sub.n represents a forward direction of the n.sup.th stream when D.sub.n=0 and D.sub.n represents a reverse direction of the n.sup.th stream when D.sub.n=1, and D.sub.n denotes a complementary value of D.sub.n.

2. The method of claim 1, wherein the updating comprises: when the interference reduction value n is greater than or equal to the predetermined value, the direction of the one or more streams is changed to an opposite direction, and when the interference reduction value n is smaller than the predetermined value, the direction of the one or more streams is not changed to the opposite direction.

3. The method of claim 1, wherein the predetermined value is 0.

4. The method of claim 1, further comprising: transmitting a state value of the updated direction of the one or more streams to one or more neighbor mobile stations.

5. The method of claim 1, further comprising: changing the direction of the one or more streams a predetermined number of times; and turning off a stream when a decoding through the one or more streams fails.

6. A network for transceiving a signal through at least two streams in a wireless communication system, the network comprising: a transceiver configured to transmit and receive a radio signal; and a processor, wherein the processor is configured to: measure channel state for the at least two streams by using a reference signal; determine at least one stream pair including a transmission stream and a reception stream based on the measured channel state; initiate a direction of one or more streams of the at least one stream pair; control the transceiver to transceive the signal based on the one or more streams of the at least one stream pair; compute an interference reduction value n of the one or more streams of the at least one stream pair when a decoding for the one or more streams fails; and update the direction of the one or more streams of the at least one stream pair by comparing the computed interference reduction value n with a predetermined value, wherein the interference reduction value is defined as following equation:
.sub.n=SINR (D.sub.n)SINR(D.sub.n)[equation] where SINR denotes a Signal-to-Interference-plus Noise Ratio, D.sub.n denotes a direction of an n.sup.th stream, where D.sub.n represents a forward direction of the n.sup.th stream when D.sub.n=0 and D.sub.n represents a reverse direction of the n.sup.th stream when D.sub.n=1, and D.sub.n, denotes a complementary value of D.sub.n.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings, which are given by illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 illustrates two-user interference two-way communication system model;

(3) FIG. 2 illustrates a block diagram of the interference cancellation;

(4) FIG. 3 illustrates examples of an interference cancellation, where (a) illustrates an interference cancellation when all channel states are good, (b) illustrates an interference cancellation when all channel states are bad, and (c) illustrates an interference cancellation when desired channel state is good and the others is bad;

(5) FIG. 4 illustrates traditional one-way interference channel;

(6) FIG. 5 illustrates examples for choosing forward/reverse transmission, where (a) illustrates an example for choosing forward/reverse transmission when forward throughput=0, and (b) illustrates an example for choosing forward/reverse transmission when reverse throughput=2;

(7) FIG. 6 illustrates examples of all channels having good state, where (a) illustrates all channels have good state when forward throughput=0, and (b) illustrates all channels have good state when reverse throughput=0;

(8) FIG. 7 illustrates an example of opposite transmission with network throughput=2;

(9) FIG. 8 depicts four transmission modes where (a) illustrates a forward transmission type, (b) illustrates a reverse transmission type, (c) illustrates an opposite transmission 1 type, and (d) illustrates an opposite transmission 2 type;

(10) FIG. 9 depicts examples of channel measuring, where (a) illustrates inter-BS and inter-UE channel measuring represented a first step signaling patterns for RSA in a two-user interference channels, (b) illustrates locally channel measuring at BS1 represented a second step signaling patterns for RSA in a two-user interference channels, (c) illustrates locally channel measuring at BS2 represented a third step signaling patterns for RSA in a two-user interference channels, and (d) illustrates exchanging between BS1 and BS2 represented a fourth step signaling patterns for RSA in a two-user interference channels;

(11) FIG. 10, including views (a)-(d), illustrates channel measurement stage in D2D communications;

(12) FIG. 11, including views (a)-(d), illustrates channel information exchange stage in D2D communications;

(13) FIG. 12 illustrates the probability of supporting 2 streams decodable;

(14) FIG. 13 illustrates absolute network throughput gain as a function of probability p;

(15) FIG. 14 illustrates relative throughput gain as a function of probability p; and

(16) FIG. 15 is a block diagram of a wireless communication apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(17) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The detailed description set forth below in connection with the appended drawings is a description of exemplary embodiments and is not intended to represent the only embodiments through which the concepts explained in these embodiments can be practiced. The detailed description includes details for the purpose of providing an understanding of the present invention. However, it will be apparent to those skilled in the art that these teachings may be implemented and practiced without these specific details.

(18) In some instances, known structures and devices are omitted, or are shown in block diagram form focusing on important features of the structures and devices, so as not to obscure the concept of the present invention.

(19) In the embodiments of the present invention, a description is made centering on a data transmission and reception relationship between a BS and a UE. Here, the BS may be a terminal node of a network, which directly communicates with the terminal. In some cases, a specific operation described as performed by the BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with a terminal may be performed by the BS, or network nodes other than the BS. The term BS may be replaced with the term fixed station, Node B, enhanced Node B (eNode B or eNB), access point, Node etc. The term relay may be replaced with the term relay node (RN), relay station (RS), Node etc.

(20) The term terminal may be replaced with the term user equipment (UE), Mobile Station (MS), Mobile Subscriber Station (MSS), subscriber station (SS), Node etc.

(21) Specific terms used for the embodiments of the present invention are provided to aid in understanding of the present invention. These specific terms may be replaced with other terms within the scope and spirit of the present invention.

(22) The embodiments of the present invention can be supported by standard documents disclosed for at least one of wireless access systems, Institute of Electrical and Electronics Engineers (IEEE) 802, 3rd Generation Partnership Project (3GPP), 3GPP Long Term Evolution (3GPP LTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are not described to clarify the technical features of the present invention can be supported by those documents. Further, all terms as set forth herein can be explained by the standard documents.

(23) Techniques described herein can be used in various wireless access systems such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-Frequency Division Multiple Access (SC-FDMA), etc. CDMA may be implemented as a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented as a radio technology such as Global System for Mobile communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a part of Universal Mobile Telecommunication System (UMTS). 3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA for downlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.

(24) We consider a simple network system model 2 pairs of transmitters and receivers in FIG. 1. There are 6 independent links and each fading channel has only two states, good or bad. Hence, binary channel gains are represented as equation 1.
{h.sub.ab,h.sub.cd,h.sub.ad,h.sub.cb,h.sub.ac,h.sub.bd}{g,b},[equation 1]

(25) g: goodchannelstate,

(26) b: badchannelstate.

(27) where h.sub.ij is the fading channel from j transmitter to the i receiver, good or bad channel state can be defined as SNR(Signal-to-noise ratio) is greater or less than a given threshold and the thresholds for good channel and bad channel could be different and configured by network or a UE. Two mixed streams can be decoupled if their powers are quite different by interference cancelation [5].

(28) FIG. 2 illustrates block diagram of a simple interference cancelation. We assume that the fixed coding rate is log.sub.2(1+) and P.sub.j is a transmitted power of j transmitter. n depicts noise variance. detect stream 1 can be successfully detected under the conditions below equation 2 and equation 3,

(29) $\begin{array}{cc}\frac{P_1}{n+P_2},& \left[\mathrm{equation}2\right]\\ \frac{P_2}{n},& \left[\mathrm{equation}3\right]\end{array}$
is condition for detecting for stream 2.

(30) And p is the probability a channel is in the good state as equation 4.
p=Pr(h=g)=1Pr(h=b).[equation 4]

(31) Thus, p=0.5 means highly random channels and a high level of spatial diversity. For ease of analysis, we assume whole transmit power are equal to 1 and g/(n+b),b/n in the remain parts.

(32) There are two detection classes depending on whether they receive the signal through the same channel state or not. Consider the plot in FIG. 3, showing the number of decodable streams in two detection classes. If desired and interference channel states are same, we cannot decode any stream. However, although desired channel state is bad, we can decode the desired signal when interference channel state is good. There is a need a way how to be able to support 2 simultaneous data streams.

(33) 3.1 Traditional One-way Communication

(34) In this chapter, we present the conventional one-way communication scheme. FIG. 4 demonstrates that traditional one-way communication alternates forward and backward directions. They have only a strategy interference cancelation. Unfortunately, if a receiver receives signals from both side through the same channel conditions, there is no way to support 2 streams.

(35) Hence, for the traditional scheme, the probability of supporting 2 streams is equation 5.
Pr(N=2)=4p.sup.2(1P).sup.2,[equation 5]
where N is the number of supporting streams. The network ergodic throughput can be easily understood as equation 6.
C=2Pr(N=2)+Pr(N2)(stream).[equation 6]

(36) 3.2 Proposed Two-Way Communication

(37) In this chapter, we propose two ideas that how to support 2 streams able to be decodable in the two-way communication.

(38) Method 1 (Choose forward/reverse transmission for both Tx-Rx pairs wisely)

(39) We can choose forward or reverse transmission wisely to support 2 streams. For example, if rows of the forward link channel matrix, H.sub.f, have identical entries as equation 7.

(40) $\begin{array}{cc}{H}_f=\left[\begin{array}{cc}g& g\\ b& b\end{array}\right]& \left[\mathrm{equation}7\right]\end{array}$
that link throughput is equal to 0 as shown in FIG. 5-(a). Then, the reverse link channel matrix, H.sub.r=H.sub.f.sup.T, must have different entries which is able to support 2 streams like as FIG. 5-(b). We should select the other direction transmission. In this method, transmits direction for both node pairs is same. To determine transmit direction, both pairs should know the channel state.

(41) Method 2 (Choose forward/reverse transmission wisely with allowing that each Tx-Rx pair have different direction)

(42) However, method 1 cannot provide solution when all channels are same condition. Because rows of the forward link channels and transpose of those also have identical entries. The above situation is described by FIG. 6. To overcome this problem, in this subsection, a new transmission which exploits the interference effect caused by opposite transmission is proposed.

(43) The opposite transmission means that each pair transmits opposite direction simultaneously. In the example as FIG. 7, the pair of A and B selects forward transmission, otherwise, the other pair of C and D transmits reverse direction. The network throughput of opposite transmission is better than reverse/forward selection transmission because there is an additional possibility of channel variation. FIG. 8 depicts four transmission modes considered in the previous sections.

(44) Each mode supports 2 streams if channel matrix has no identical row entries. We can choose any mode for supporting 2 streams. This means that channel diversity can be exploited is larger than traditional one. The probability of supporting 2 streams satisfies equation 8.
1Pr(N=2)=p.sup.2+(1p).sup.4p.sup.212p.sup.2(1p).sup.2+2p(1p)+8p.sup.3(1p).sup.3+(1p).sup.2++p.sup.4(1p).sup.2[equation 8]
where N is the number of the supporting streams with proposed transmissions.

(45) Furthermore, we can easily define the network ergodic throughput is equation 9.
C=2Pr(N=2)+Pr(N2)(stream).[equation 9]

(46) As described earlier, we basically assume that each node is equipped with interference cancellation receiver, but this invention is not limited to the interference cancellation receiver. In other words, this invention is also applied to the case of each node equipped with linear receiver. If all nodes are equipped with a linear receiver, the transmit direction can be determined for sum performance (e.g., Rate or other scheduler metric) maximization for both Tx-Rx pairs.

(47) 4. Details of the Invention: Signaling Pattern

(48) In this section, we consider subsequent signaling patterns for the RSA as discussed in the previous parts. We propose and describe prerequisite conditions based on two different scenarios: 1) in cellular network structures, and 2) in device-to-device communications. Let us assume that channel reciprocity in TDD can be basically utilized and essential patterns are only considered not some efficient schemes to show the main intuition in the sequel. Note that the proposed prerequisite conditions are started from fully-shared CSI among all nodes, and we sequentially suggest the following parts.

(49) 4.1 RSA in Cellular Network Structures

(50) There are three big parts for RSA signaling: 1) locally channel measuring for the requisite global CSI, 2) CSI sharing among all nodes to complete the global CSI, and 3) Tx/Rx role decision stage. Now, we illustrate how these parts can be embraced for the cellular network RSA. Note that there are four nodes {A,B,C,D} which directly matches {BS1,UE1,BS2,UE2}. (Roughly see FIG. 9)

(51) 4.1.1 Locally Channel Measuring Stage

(52) When each BS gathers all channel information to acquire the global CSI to determine transmission direction, let us propose three different procedures to divide responsibilities and avoid inefficiency or role collision of BSs.

(53) For the first part of this stage, we should assemble 1) an inter-BS wireless channel and 2) an inter-UE channel as we illustrate in FIG. 9 Although there is a backhaul between BS1 and BS2, it is definitely compulsory to measure an inter-BS wireless channel due to the global CSI condition. The inter-BS wireless channel can be obtained by the channel estimation using another orthogonal pilot. In contrast to the inter-BS case, it is more delicate to capture the inter-UE channel. In order to open a reliable link between UE1 and UE2, let BS1 control device-to-device (D2D) links in advance. Assuming that these D2D links operate in the same frequency of cellular networks by BS1's command (some resource sharing for BS1 can be needed to synchronize with other-cell UE, i.e., UE2), then UE2 can finally collect the inter-UE CSI.

(54) FIG. 9 depicts channel measuring of BS1 from UE1 and UE2 in order to gather UE1's desired link and UE2's interference link. Note that it is more efficient when BS do channel estimations rather than UE due to the possibility to use a wireless/wired inter-BS backhaul. For example, if there is inter-BS backhaul each UE feeds its channel states from BS1 and BS2 back to only each desired BS and each BS shares the channel states through the inter-BS backhaul. However, if dual connectivity is guaranteed, each UE can report its channel states to BS1 and BS2 directly.

(55) FIG. 9 also describes channel measuring of BS2:UE1's interference link, and UE2's desired link. Note that previously measured inter-UE channel is delivered by UE2 in this step.

(56) 4.1.2 CSI Exchanges Among all Nodes

(57) Sharing all channel information by previously done channel measuring is another important procedure. One great advantage in cellular networks is that the inter-BS CSI sharing can be enough. By the previous stage, BS1 and BS2 obtain {h.sub.ab,h.sub.ad,h.sub.ac} and {h.sub.cb,h.sub.cd,h.sub.db} respectively. Hence, each BS do sharing its own gathered CSI using wireless/wired backhaul. Now, all BSs with the global CSI are ready to execute RSA schemes by the decision process in the subsequent stage.

(58) 4.1.3 Tx/Rx Role Decision Stage

(59) Each BS's roles for RSA are intuitively classified into being a transmitter or Receiver, and UEs should Follow the Policies of Corresponding BSs. By the aforementioned roles, four different modes can be considered as follows: 1) BS1-Rx & BS2-Rx, 2) BS1-Rx & BS2-Tx, 3) BS1-Tx & BS2-Rx, and 4) BS1-Tx & BS2-Tx. Assuming that the criterion for mode-selection is determined by sum-rate maximization, and we need to define the rate R.sub.i corresponding to i-th mode so as to choose the best mode. Now, we verify the details only for the first mode since other modes are similarly considered in substantial.

(60) In the first mode where all BSs take a role as Rx, there are four subcategories depending on the stream conditions:
State.sub.1={h.sub.ab=g,h.sub.ad=b,h.sub.cb=g,h.sub.cd=b},
State.sub.2={h.sub.ab=g,h.sub.ad=b,h.sub.cb=b,h.sub.cd=g},
State.sub.3={h.sub.ab=b,h.sub.ad=g,h.sub.cb=g,h.sub.cd=b},
State.sub.4={h.sub.ab=b,h.sub.ad=g,h.sub.cb=b,h.sub.cd=g}.

(61) Here, we assume all nodes are equipped with interference cancellation receiver. Depending on the channel states, the corresponding sum-rates for mode 1(BS1-Rx & BS2-Rx) are represented as

(62) $R_{11}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_{\mathrm{MS}1}}{h_{\mathrm{ad}}{P}_{\mathrm{MS}2}+n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_{\mathrm{MS}2}}{n}\right),R_{12}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_{\mathrm{MS}1}}{h_{\mathrm{ad}}{P}_{\mathrm{MS}2}+n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_{\mathrm{MS}2}}{h_{\mathrm{cb}}{P}_{\mathrm{MS}1}+n}\right),R_{13}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_{\mathrm{MS}1}}{n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_{\mathrm{MS}2}}{n}\right),R_{14}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_{\mathrm{MS}1}}{n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_{\mathrm{MS}2}}{h_{\mathrm{cb}}{P}_{\mathrm{MS}1}+n}\right).$
In the above, PMS1 and PMS2 denote the transmit power for MS1 and MS2, respectively. If all nodes are equipped with linear receiver, R12 can be only used.

(63) If one BS has interference cancellation receiver, but neighboring BS has not the interference cancellation receiver, R12 and R14 is only used. To calculate sum rate whether each node is capable of interference cancellation or not, we propose that the information of the capability of interference cancellation for BSs and MSs is shared via inter-BS backhaul signaling.

(64) Since each BS has already clues to decide sub-modes based on the global CSI, let R.sub.1=R.sub.1j where j denotes the best sub-mode for RSA.

(65) After deciding R.sub.i,i, the mode-selection problem is ultimately settled as equation 10.

(66) $\begin{array}{cc}\begin{array}{cc}\arg \underset{i}{\max }{R}_1,& \mathrm{for}i=1,2,3,4.\end{array}& \left[\mathrm{equation}10\right]\end{array}$

(67) Even if real-valued channel states can be further considered such as new criterion by the ratio of good/bad channel values, any details are not considered because the above proposed decision process can be essentially applied.

(68) 4.2 RSA in Device-to-device(D2D) Communications

(69) In this section, we consider D2D environment where a wired/wireless backhaul is not available. D2D communication procedures are organized as follows. We first present the channel measurement stage. The second stage is channel information exchange stage, and we finally do decision and transmit stage. Note that the ultimate goal is to want to decide which nodes are the best transmitter and receivers.

(70) 4.2.1 Channel Measurement Stage

(71) One node transmit one pilot at a time where is intended for all nodes. This procedure is needed pilot signaling which have to been recognized by all nodes for measuring channel associated to receiver node. As mentioned above, channel measurement stage is performed by using pilot signal where all nodes already know, as illustrated in FIG. 10, including views (a)-(d). For example, if the node A transmits appointed pilot signal to the others, then the others estimate channel from node A. Node B, node C and node D can estimate their channels, h.sub.ba, h.sub.ca and h.sub.da respectively. And then next node transmit pilot signal, the others also estimate their channels. This process which is one time for all nodes is repeated until all nodes transmit pilot signal to the others.

(72) 4.2.2 Channel Information Exchanges Stage

(73) After channel measurement stage, there are required exchanging their channel information. Similar to channel measurement stage, only one node broadcast to the other nodes at a time as shown FIG. 11, including views (a)-(d). This channel information may be channel quality information/achievable rate of each pair/channel state information, etc. This channel information may also be quantized or not.

(74) 4.2.3 Decision and Transmission Stage

(75) We can assume the four transmit-receiver node pairs denoted [ACBD],[ADBC],[BCAD],[BDAC]. A key design goal of this stage is to enable efficient communication in D2D. The efficient means that is appropriate for their objective utility, such as sum-rate maximization, outage probability minimization, minimizing mean squared error, etc. This decision stage is analogous to Tx/Rx role decision stage of cellular network structures. However, it is different things that there is no centralized controller or helper to determine the transmit-receiver node pair. Each nodes should choose between transmitter and receiver from obtained information for previous stage. For example, consider following assumptions: given as {h.sub.ab=g,h.sub.ac=b,h.sub.ad=g,h.sub.bd=b,h.sub.bd=b,h.sub.cd=g,h.sub.bc=g}, decision for sum-rate maximizing and channel state information exchanged in second stage.

(76) All channels of transmit-receiver node pairs are consist of (or include)

(77) $H_{\left[\mathrm{AC}-\mathrm{BD}\right)}=\left[\begin{array}{cc}g& g\\ g& g\end{array}\right],H_{\left[\mathrm{AD}-\mathrm{BC}\right)}=\left[\begin{array}{cc}g& b\\ b& g\end{array}\right],H_{\left[\mathrm{BC}-\mathrm{AD}\right)}=\left[\begin{array}{cc}g& b\\ b& g\end{array}\right],H_{\left[\mathrm{BD}-\mathrm{AC}\right)}=\left[\begin{array}{cc}g& g\\ g& g\end{array}\right]$
from given channel.

(78) In the first stage, all nodes transmit pilot and channel is measured estimation by the other nodes. In the next stage, channel information is exchanged for all nodes. And then, all nodes recognize the H.sub.[AC-BD] and H.sub.[BD-AC] are not affordable pairs for sum-rate maximization. Therefore, all nodes compare the rates of [ADBC] and [BCAD]. And corresponding sum-rates are

(79) $R_{\left[\mathrm{AD}-\mathrm{BC}\right]}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_1}{h_{\mathrm{bd}}{P}_2+n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_2}{h_{\mathrm{ac}}{P}_1+n}\right),R_{\left[\mathrm{BC}-\mathrm{AD}\right]}={\log }_2\left(1+\frac{h_{\mathrm{ab}}{P}_1}{h_{\mathrm{ac}}{P}_2+n}\right)+{\log }_2\left(1+\frac{h_{\mathrm{cd}}{P}_2}{h_{\mathrm{bd}}{P}_1+n}\right).$

(80) They are able to choose the pair between [ADBC] and [BCAD] to maximize sum-rate, then selected transmit nodes start to send their signals.

(81) Hereinafter, a method for choosing between transmitter and receiver at each node will be described specifically.

(82) In this section, we propose distributed stream-alignment algorithms designed based on the simple principle of distributed stochastic search from the area of multi-agent systems.

(83) To facilitate exposition, some notation is introduced as follows. Let D.sub.n denote the direction of the n-th stream, where 0 and 1 represent the directions forward direction and reverse direction, respectively. Let the complementary value of D.sub.n be represented by D.sub.n. The stream alignment algorithm based on DSS is given below.

(84) Algorithm 1. Stream Alignment Algorithm Based on Distributed Stochastic Search

(85) (1) Randomly initiate stream directions D.sub.n{0,1}.

(86) (2) While (There is Unsuccessfully decoded streams in the network) do.

(87) Each pair of nodes compute the measure of interference reduction defined as equation 11.
.sub.n=SINR(D.sub.n)SINR(D.sub.n)[equation 11]

(88) A pair of nodes, say I, update the state of the stream direction as follow.

(89) Case 1) If the stream is successfully received, namely, SNR(X.sub.n), remains unchanged.

(90) Case 2) If and SNR(X.sub.n)< and .sub.n0, the stream direction is changed by setting D.sub.n=D.sub.n with probability p.

(91) Case 3) If SNR(X.sub.n)< and .sub.n<0, remains unchanged since there is no gain for doing so.

(92) Those nodes updating their stream directions inform their neighbors that are connected by the edges in.

(93) (3) End While.

(94) Two remarks are in order. First, the probability p controls the degree of parallel activities. In other words, the larger the p is, more links update their stream directions and vice versa. p=1 is not the optimal choice as shown by experiments. Second, Algorithm 1 does not converge if it is infeasible to support the successful transmission of all data streams in the network. This problem can be solved by limiting the maximum number of iterations as for the next algorithm.

(95) If a network is over constrained (e.g., having too many strongly coupled links), there may not be a feasible stream-alignment solution for supporting all successfully data streams. In this case, it is desirable to turn off certain links such that the remaining links can have successful communication. This can be realized by Algorithm 2 proposed as follows, which builds on Algorithm 1.

(96) Algorithm 2. Modified Stream Alignment Algorithm Based on Distributed Stochastic Search

(97) (1) Execute Algorithm 1 with K iterations where K is a constant chosen a prior.

(98) (2) While (Network is infeasible) Do Consider an arbitrary transmitting node, say X.sub.n, with an unsuccessful stream. The node checks by binary feedback if the streams of its neighbors are unsuccessful if the n-th link is turned off. The number of positive feedback is denoted as S.sub.n. If S.sub.n>0, then X.sub.n declares the inactive state and the link is removed from the graph (X.sub.n,Y.sub.n). This alleviates a relatively stringent constraint of the network and increase the probability of achieving network feasibility. Execute Algorithm 1 with K iterations given the updated the updated graph.

(99) (3) End Do.

(100) In device-to-device network underlay cellular network, can be configured by BS via physical layer signal or higher layer signal, or predetermined. The probability p can be also configured by BS via physical layer signal or higher layer signal, or predetermined.

(101) 5. Description of the Simulation Results

(102) In this section, we describe simple simulation results for the proposed schemes with different p and make comparisons with the traditional systems.

(103) In FIG. 12, we plot the spatial diversity gains related with the probability p. Intuitively, highly random channel conditions promise good opportunity to achieve high level of spatial diversity. Maximum spatial diversity can be achieved when P is 0.5 in both proposed and traditional communications. The reason why the proposed scheme can provide more spatial diversity is that appropriate channel combinations is on the selectivity on all possible ways.

(104) Not only show FIG. 13 and FIG. 14 us additional opportunities for channel diversity, but also network throughput gains from the proposed schemes. Even if additional bandwidth or antennas need not to be required, proposed two-way channel selection schemes is about 30% greater than the traditional one-way communication.

(105) FIG. 15 is a block diagram of a wireless communication apparatus according to an embodiment of the present invention.

(106) Referring to FIG. 15, a wireless communication system includes a BS 100 and a plurality of MSs 200 belonging to the BS 100. The MSs 200 include both the aforementioned legacy-UE and e-UE.

(107) The BS 100 includes a processor 110, a memory 120, a radio frequency (RF) unit 130. The processor 110 may be configured to implement the functions, procedures and/or methods proposed by the present invention. Layers of a wireless interface protocol may be implemented by the processor 110. The memory 120 is connected to the processor 110 and stores various types of information for operating the processor 110. The RF unit 130 is connected to the processor 110, transmits and/or receives an RF signal.

(108) The MS 200 includes a processor 210, a memory 220, and an RF unit 230. The processor 210 may be configured to implement the functions, procedures and/or methods proposed by the present invention. Layers of a wireless interface protocol may be implemented by the processor 110. The memory 220 is connected to the processor 210 and stores information related to operations of the processor 210. The RF unit 230 is connected to the processor 210, transmits and/or receives an RF signal.

(109) The memories 120 and 220 may be located inside or outside the processors 110 and 210 and may be connected to the processors 110 and 210 through various well-known means. The BS 100 and/or MS 200 may include a single antenna or multiple antennas.

(110) The aforementioned embodiments are achieved by combination of structural elements and features of the present invention in a predetermined manner. Each of the structural elements or features should be considered selectively unless specified separately. Each of the structural elements or features may be carried out without being combined with other structural elements or features. Also, some structural elements and/or features may be combined with one another to constitute the embodiments of the present invention. The order of operations described in the embodiments of the present invention may be changed. Some structural elements or features of one embodiment may be included in another embodiment, or may be replaced with corresponding structural elements or features of another embodiment. Moreover, it will be apparent that some claims referring to specific claims may be combined with another claims referring to the other claims other than the specific claims to constitute the embodiment or add new claims by means of amendment after the application is filed.

(111) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

(112) It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are generally only used to distinguish one element from another.

(113) It will be understood that when an element is referred to as being connected with another element, the element can be connected with the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly connected with another element, there are no intervening elements present.

(114) A singular representation may include a plural representation unless it represents a definitely different meaning from the context. Terms such as include or has are used herein and should be understood that they are intended to indicate an existence of several components, functions or steps, disclosed in the specification, and it is also understood that greater or fewer components, functions, or steps may likewise be utilized.

(115) Mobile terminals presented herein may be implemented using a variety of different types of terminals. Examples of such terminals include cellular phones, smart phones, user equipment, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigators, portable computers (PCs), slate PCs, tablet PCs, ultra books, wearable devices (for example, smart watches, smart glasses, head mounted displays (HMDs)), and the like.

(116) By way of non-limiting example only, further description will be made with reference to particular types of mobile terminals. However, such teachings apply equally to other types of terminals, such as those types noted above. In addition, these teachings may also be applied to stationary terminals such as digital TV, desktop computers, and the like.

(117) Various embodiments may be implemented using a machine-readable medium having instructions stored thereon for execution by a processor to perform various methods presented herein. Examples of possible machine-readable mediums include HDD (Hard Disk Drive), SSD (Solid State Disk), SDD (Silicon Disk Drive), ROM, RAM, CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, the other types of storage mediums presented herein, and combinations thereof. If desired, the machine-readable medium may be realized in the form of a carrier wave (for example, a transmission over the Internet). The processor may include the controller 180 of the mobile terminal.

(118) The foregoing embodiments are merely exemplary and are not to be considered as limiting the present disclosure. The present teachings can be readily applied to other types of methods and apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments.

(119) As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be considered broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the appended claims.