Patent Description:
Cost-effective dense deployment is an important enabler of long-term evolution (LTE) and fifth generation (<NUM>) wireless networks. So-called small cells, access nodes (also referred to as access points or base stations) that each serves a number of proximally located user equipment (UE) terminals with a lower transmit power than conventional base stations, are effective in supporting ultra-dense broadband access. Each small cell is connected to core network via a backhaul connection.

One technique for deploying small cells comprises the placement of radio base stations, oftentimes called evolved node B (eNB) in LTE and next generation node B (gNB) <NUM> terminology, on lampposts distributed along a street. Electrical connections are already available at each lamppost to power lights, and can conveniently be used provide power to the eNBs. Providing wired backhaul access (e.g. using optical fiber) to a large number of lamppost-based base stations may be logistically difficult unless done during the construction of the street on which the nodes are deployed. A simpler solution is to provide backhaul connectivity to couple a first lamppost-based base station in a series to a core network. Each base station in the series can be wirelessly connected to adjacent base stations, creating a multihop connection to the first base station, which has the wired backhaul connection. In some embodiments, the wireless connection between base stations may use unlicensed wireless spectrum.

In such setups, it will be recognized that the lamppost mounted base stations are often in a straight line, resulting in interference between segments. Improvements are needed to mitigate interference over wireless spectrum used for daisy-chained base stations. <CIT> describes a communication method of a first relay node in a network including a first source node, the first relay node, a first destination node, a second source node, a second relay node, and a second destination node, includes receiving, from the first source node, streams X and Y. The communication method further includes receiving, from the second source node, a stream Z. The communication method further includes generating a signal in which the streams Y and Z are aligned in a space. <NPL>, relates to designing a radio interface for mm-wave frequencies.

It is an object of the present technology to ameliorate at least some of the inconveniences present in conventional techniques used to exchange backhaul information among serially connected radio base stations. The present application is defined in the appended independent claims. Further implementations are disclosed in the pending dependent claims. In the following, implementations not falling within the scope of the claims are to be understood as examples useful for understanding the application.

Generally stated, the present technology provides a method that facilitates multi-hop data transmission over a line of sight (LoS) channel and nodes configured for such multi-hop data transmission A node receives a first data stream over two complementary transmissions that are both formed according to an interference alignment precoding matrix. The node transmits a distinct second data stream over two distinct complementary transmissions formed according to a distinct interference alignment precoding matrix. All transmissions are received and sent on the LoS channel. The distinct interference alignment precoding matrices mitigate interference between the first data stream received at the node and the second data stream transmitted by the node.

The present technology also provides a method using a plurality of selectable, linearly aligned antennas and to nodes having such antennas. In a node, a pair of antennas of the plurality of linearly aligned antennas is selected so that a spacing between the selected antennas is a function of a distance between the node and a peer node and of a wavelength of a communication exchanged between the node and the peer node. The selection of the pair of antennas according to their spacing ameliorates a signal to interference and noise ratio of the communication between the node and the peer node.

Either or both above methods may be implemented in a same node. Multi-hop communication between nodes that are aligned on the LoS channel is facilitated when using these methods, alone or in combination. Without limitation, the present technology is suitable for exchange of backhaul information among serially connected radio base stations.

According to a first aspect of the present technology, there is provided a data transmission method according to appended claim <NUM>.

In some implementations of the present technology, the first interference alignment precoding matrix is defined based on a state of the LoS channel between the node and the first peer node, the second interference alignment precoding matrix being defined based on a state of the LoS channel between the first and third node.

In some implementations of the present technology, the method further comprises transmitting, from the node to the first peer node, on the LoS channel, a first channel state information (CSI) reference signal, receiving, at the node from the first peer node, on the LoS channel, a first CSI feedback signal, transmitting, from the node to the second peer node, on the LoS channel, a second CSI reference signal, and receiving, at the node from the second peer node, on the LoS channel, a second CSI feedback signal.

In some implementations of the present technology, the method further comprises decoding, at the node, the first data stream by application of a combining matrix to the first and second transmissions, the combining matrix corresponding to the first interference alignment precoding matrix.

In some implementations of the present technology, at least a portion of the first data stream comprises backhaul information, and at least a portion of the second data stream comprises backhaul information.

According to a second aspect of the present technology, not falling under the scope of the claims, there is provided a data transmission method. The method comprises communicating between a node and a peer node using a pair of antennas of the node. The antennas of the pair are selected among a plurality of linearly aligned antennas so that a spacing between the antennas of the pair is a function of a distance between the node and the peer node and of a wavelength of a communication exchanged between the node and the peer node.

In some implementations of the present technology, communicating between the node and the peer node comprises transmitting a signal from the node to the peer node at a first amplitude and a first phase using a first antenna of the pair and at a second amplitude and a second phase using a second antenna of the pair, the first amplitude being different from the second amplitude and the second phase being different from the second phase.

In some implementations of the present technology, the antennas of the plurality of linearly aligned antennas are beamforming antennas.

In some implementations of the present technology, the method further comprises, for each pair of antennas among the plurality of linearly aligned antennas, transmitting, from the node to the peer node, a channel state information (CSI) reference signal and receiving, at the node from the peer node, a CSI feedback signal, the method also comprising selecting the antennas of the pair according to a most favorable of the received CSI feedback signals.

In some implementations of the present technology, the plurality of linearly aligned antennas comprises at least four antennas, a spacing between any pair of antennas selected among four of the at least four antennas being different from a spacing between any other pair of antennas among the four of the at least four antennas.

According to a third aspect of the present technology, there is provided a node comprising a first receiver and a first transmitter according to appended claim <NUM>.

In some implementations of the present technology, the node further comprises a second receiver adapted to receive, from the second peer node, on the LoS channel, a fifth transmission carrying a third data stream and a sixth transmission carrying the third data stream, the fifth and sixth transmissions being formed according to a third interference alignment precoding matrix and a second transmitter adapted to transmit, to the first peer node, on the LoS channel, a seventh transmission carrying a fourth data stream and an eighth transmission carrying the fourth data stream, the seventh and eighth transmissions being formed according to a fourth interference alignment precoding matrix.

In some implementations of the present technology, the node further comprises a first receive antenna operatively connected to the first receiver, a second receive antenna operatively connected to the second receiver, a first transmit antenna operatively connected to the first transmitter, and a second transmit antenna operatively connected to the second transmitter.

In some implementations of the present technology, the first and second receive antennas and the first and second transmit antennas are beamforming antenna.

In some implementations of the present technology, the node further comprises a processor operatively connected to the first and second transmitters and to the first and second receivers. The processor is adapted to cause the first transmitter to transmit, to the first peer node, on the LoS channel, a first channel state information (CSI) reference signal, and to acquire from the first receiver a first CSI feedback signal received from the first peer node on the LoS channel. The processor is further adapted to cause the second transmitter to transmit, to the second peer node, on the LoS channel, a second CSI reference signal, and to acquire from the second receiver a second CSI feedback signal received from the second peer node on the LoS channel.

In some implementations of the present technology, the processor is further adapted to define the first and fourth interference alignment precoding matrices based on a state of the LoS channel between the node and the first peer node, the state being determined based on the first CSI feedback signal. The processor is also adapted to define the second and third interference alignment precoding matrices based on the state of the LoS channel between the node and the second peer node, the state being determined based on the second CSI feedback signal.

In some implementations of the present technology, the node further comprises a radio base station adapted to receive an uplink data stream from a user terminal on a separate channel, the processor being further adapted to insert the first data stream as a first portion of the second data stream, and to insert the uplink data stream as a second portion of the second data stream.

In some implementations of the present technology, the node further comprises a radio base station adapted to transmit a downlink data stream to a user terminal on a separate channel, the processor being further adapted to extract the downlink data stream from a first portion of the first data stream, and to insert a second portion of the first data stream as the second data stream.

In some implementations of the present technology, the node further comprises a radio base station adapted to communicate with a user terminal, wherein the first data stream comprises backhaul information for the radio base station, and wherein the second data stream comprises further backhaul information for the second peer node.

According to a fourth aspect of the present technology, not falling under the scope of the claims, there is provided a node comprising a radio interface unit, a plurality of linearly aligned antennas and a processor. The radio interface unit is adapted to communicate with a peer node. The antennas of the plurality of linearly aligned antennas are communicatively coupled to the radio interface unit. The processor is operatively connected to the radio interface unit and adapted to select a pair of antennas among the plurality of linearly aligned antennas for the radio interface unit to communicate with the peer node. The processor selects the pair of antennas so that a spacing between the antennas of the pair is a function of a distance between the node and the peer node and of a wavelength of a communication exchanged between the node and the peer node.

In some implementations of the present technology, the processor is further adapted to, for each pair of antennas among the plurality of linearly aligned antennas, cause the radio interface unit to transmit, to the peer node, a channel state information (CSI) reference signal, and acquire, from the radio interface unit, a CSI feedback signal received from the peer node. The processor selects the antennas of the pair according to a most favorable of the received CSI feedback signals.

In some implementations of the present technology, the node further comprises a fiber access point operatively connected to the processor and adapted for communicatively coupling the radio interface unit and a core network.

In some implementations of the present technology, an antenna spacing factor is defined as <MAT>, wherein s is the antenna spacing factor in meters and lambda is the wavelength in meters.

In some implementations of the present technology, the plurality of linearly aligned antennas comprises a first antenna, a second antenna positioned at a spacing s from the first antenna, a third antenna positioned at a spacing <NUM>s from the second antenna and at a spacing <NUM>s from the first antenna, and a fourth antenna positioned at a spacing <NUM>s from the third antenna and at a spacing <NUM>s from the first antenna.

In some implementations of the present technology, the plurality of linearly aligned antennas comprises a first antenna, a second antenna positioned at a spacing <NUM>s from the first antenna, a third antenna positioned at a spacing s from the second antenna and at a spacing <NUM>s from the first antenna, and a fourth antenna positioned at a spacing <NUM>s from the third antenna and at a spacing <NUM>s from the first antenna.

In some implementations of the present technology, the radio interface comprises a transmitter, and the processor is further adapted to cause the transmitter to transmit a signal to the peer node at a first amplitude and a first phase using a first antenna of the pair and at a second amplitude and a second phase using a second antenna of the pair, the first amplitude being different from the second amplitude and the second phase being different from the second phase.

Implementations of the present technology each have at least one of the above-mentioned object and aspects, but do not necessarily have all of them. It should be understood that some aspects of the present technology that have resulted from attempting to attain the above-mentioned object may not satisfy this object. Some embodiments may satisfy other objects not specifically recited herein.

Additional or alternative features, aspects and advantages of implementations of the present technology will become apparent from the following description, the accompanying drawings and the appended claims.

Embodiments of the present disclosure will be described by way of example only with reference to the accompanying drawings, in which:.

Like numerals represent like features on the various drawings.

Various aspects of the present disclosure generally address one or more of the problems related to daisy chaining of nodes such as base stations.

The present disclosure introduces techniques for the transmission of backhaul information between daisy-chained base stations. The base stations may, in a non-limitative example, be installed on a series of communicatively connected lampposts that are substantially linearly aligned along a street. Owing to their placement, the base stations are on a line of sight (LoS) channel covering the entire series of lampposts. This linear arrangement of the base stations could negatively impact the signal to interference and noise (SINR) ratio between on the LoS channel because a signal sent from a first base station to a second base station could project beyond the second base station and interfere with another signal sent from the second base station to a third base station.

In one aspect, interference alignment is used to mitigate this interference and thereby improve the SINR between the various base stations when they are on the LoS channel.

In another aspect, a point-to-point multiple-input-multiple-output (MIMO) technique is used to transmit distinct data streams between two (<NUM>) base stations. Each base station includes a plurality of linearly aligned antennas for communicating with a given peer base station. For transmitting to or receiving from the given peer base station, the base station selects a pair of antennas among the plurality of linearly aligned antennas so that a spacing between the antennas of the pair is tailored to a distance between the base station and the given peer base station and to a wavelength of the communication between the base station and the given peer base station.

In a further aspect, the interference alignment technique and the point-to-point MIMO technique are combined in a same implementation.

The present technology is presented in the particular context of daisy-chained radio base stations mounted on lampposts, data transmission between the base stations containing backhaul information exchanged between the base stations and a core network. However, the present technology is not limited to such application involving radio base stations. Some aspects of the present technology may be used between any peer nodes of any type while some other aspects of the present technology may be used in nodes of any type having at least two peer nodes on a LoS channel.

Referring now to the drawings, <FIG> is a schematic representation of nodes mounted on a series of lampposts, showing backhauling signals exchanged between each node. A network <NUM> including a series of lampposts <NUM>, <NUM>, <NUM> and <NUM> carrying base stations <NUM>, <NUM>, <NUM> and <NUM> communicate on a wireless channel, for example on unlicensed spectrum. The first lamppost <NUM> has a fiber point of access <NUM> for exchanging backhaul information between the first base station <NUM> and a core network (not shown). Backhaul information is further exchanged between the first base station <NUM> and the base stations <NUM>, <NUM> and <NUM> over the wireless channel, using downlink directional antenna beams <NUM> and uplink directional antenna beams <NUM>. The lampposts of the network <NUM> are not placed on a straight line. As a result, no two downlink directional antenna beams <NUM> intersect and there is no intersection between any of the uplink directional antenna beams <NUM>. Because the antenna beams are directional, SINR is well controlled over the entire network <NUM>.

The base stations <NUM>, <NUM>, <NUM> and <NUM> each include one or more transceiver, or alternatively one or more transmitter and one or more receiver connected to antennas for supporting communication, for example LTE or <NUM> communication with proximally located user equipment (UE) terminals (internal components of the base stations are not shown).

In a case where base stations are positioned on lampposts along a street, given typical distances between the lampposts and typical street widths, the widths being significantly less than the distances between the lampposts, the lampposts are substantially aligned on a same line of sight. Furthermore, on many roads, lampposts are positioned only on one side of the road (or in the middle of the road). As a result, the configuration of <FIG> is frequently unavailable.

<FIG> is a schematic representation of nodes mounted on a series of linearly arranged lampposts, showing backhauling signals exchanged between each node, the lampposts being on a line of sight (LoS) channel. A network <NUM> including a series of lampposts <NUM>, <NUM>, <NUM> and <NUM> carrying base stations <NUM>, <NUM>, <NUM> and <NUM> communicate on a wireless channel, for example on unlicensed spectrum. The first lamppost <NUM> has a fiber point of access <NUM> for providing a backhaul connection between the first base station <NUM> and the core network. The wireless connections between the first base station <NUM> and the base stations <NUM>, <NUM> and <NUM> are used to provide a backhaul connection to base stations <NUM>, <NUM> and <NUM>, using downlink directional antenna beams <NUM> and uplink directional antenna beams <NUM>. The lampposts of the network <NUM> are placed on a straight line, which means that all downlink and unlink directional antenna beams are on a LoS channel. This arrangement is detrimental to the SINR over the network <NUM>. For instance, a first downlink directional antenna beam <NUM> emitted from the first base station <NUM> toward at the second base station <NUM> further radiates beyond the second base station <NUM> toward the third base station <NUM>. Each base station may attenuate (i.e. block) a received uplink or downlink antenna beam by, for example, about <NUM> dB; this attenuation does not however suffice to overcome the SINR degradation. In the example of <FIG>, the SINR of the downlink signal received at the second base station <NUM> is of <NUM> dB, the SINR of the downlink signal received at the third base station <NUM> is reduced to <NUM> dB, and the SINR of the downlink signal received at the third base station <NUM> is severely reduced to <NUM> dB.

<FIG> is a schematic representation of nodes mounted on a series of lampposts as in <FIG>, the nodes communicating using MIMO antennas on a LoS channel. A network <NUM> including a series of lampposts <NUM>, <NUM>, <NUM> and <NUM> carrying base stations <NUM>, <NUM>, <NUM> and <NUM> differs from the network <NUM> of <FIG> in that the base stations <NUM>, <NUM>, <NUM> and <NUM> exchange backhaul information using MIMO antenna configurations. The first lamppost <NUM> has a fiber point of access <NUM> for exchanging backhaul information between the first base station <NUM> and the core network. To exchange further backhaul information between the first base station <NUM> and the base stations <NUM>, <NUM> and <NUM> over the wireless channel, each base station splits the backhaul information in two distinct data streams. For instance, the first base station <NUM> splits downlink backhaul information to be sent toward the second base station <NUM> in two streams. The two distinct streams are emitted by MIMO antennas <NUM>, <NUM> of the base station <NUM>, forming two distinct downlink directional beams <NUM>, <NUM>. The two distinct downlink directional beams <NUM>, <NUM> are received at MIMO antennas <NUM>, <NUM> of the second base station <NUM>. In the opposite direction, the second base station <NUM> splits uplink backhaul information to be sent toward the first base station <NUM> in two distinct streams. The two distinct streams are emitted by the MIMO antennas <NUM>, <NUM> of the base station <NUM>, forming two distinct uplink directional beams <NUM>, <NUM>. The two distinct uplink directional beams <NUM>, <NUM> are received at the MIMO antennas <NUM>, <NUM> of first base station <NUM>. Similar arrangements are used to exchange further backhaul information between the base stations <NUM>, <NUM> and <NUM>.

Unfortunately, use of MIMO technology to exchange backhaul information between base stations located on the LoS channel does not ameliorate the SINR of the signals received at each base station.

<FIG> is a block diagram illustrating interference alignment for communication between two nodes. A network <NUM> comprises three (<NUM>) transmitters <NUM>, <NUM> and <NUM> that, in turn, include precoders <NUM>, <NUM> and <NUM>. Each of the three transmitters <NUM>, <NUM> and <NUM> respectively communicate over a channel <NUM> with each of the three (<NUM>) receivers <NUM>, <NUM> and <NUM> that, in turn, include decoders <NUM>, <NUM> and <NUM>. Each transmitter <NUM>, <NUM> and <NUM> has a pair of antennas <NUM> that transmit a signal <NUM> intended for reception at a pair of antennas <NUM> of the corresponding receiver <NUM>, <NUM> and <NUM>. Interfering signals <NUM>, which are unwanted signals, are received at the various antennas <NUM>. For instance, the transmitter <NUM> emits a signal <NUM>, via its antennas <NUM>, the signal <NUM> being intended for reception at the antennas <NUM> of the receiver <NUM>. This signal <NUM> is received as interfering signals <NUM> at the antennas <NUM> of the receivers <NUM> and <NUM>.

The network <NUM> uses interference alignment to mitigate the effect of the various interfering signals <NUM> on the receivers <NUM>, <NUM> and <NUM>. To this end, the precoders <NUM>, <NUM> and <NUM> each apply an interference alignment precoding matrix to data to be sent by the respective transmitters <NUM>, <NUM> and <NUM>. In the receivers <NUM>, <NUM> and <NUM>, the decoders <NUM>, <NUM> and <NUM> each apply a combining matrix corresponding to the interference alignment precoding matrix of the respective precoder <NUM>, <NUM> and <NUM> to decode the intended signal <NUM> while attenuating the interfering signals <NUM>. A complete description of the interference alignment technique used in the network <NUM> <FIG> is found in "<NPL>.

<FIG> is a schematic representation of nodes mounted on a series of lampposts as in <FIG>, the nodes communicating using interference alignment on a LoS channel, according to an embodiment. A network <NUM> including a series of lampposts <NUM>, <NUM>, <NUM> and <NUM> carrying base stations <NUM>, <NUM>, <NUM> and <NUM> differs from the network <NUM> of <FIG> in that the base stations <NUM>, <NUM>, <NUM> and <NUM> do not use MIMO to exchange backhaul information, instead using the interference alignment technique introduced in the foregoing discussion of <FIG>. The first lamppost <NUM> has a fiber point of access <NUM> for exchanging backhaul information between the first base station <NUM> and the core network. The fiber point of access <NUM> could alternatively be connected to any one of the lampposts <NUM>, <NUM> and <NUM>. The placement of the fiber point of access <NUM> within the network <NUM> has no impact on the interference alignment technique. The first base station <NUM> applies an interference alignment precoding matrix to the downlink backhaul information to be sent toward the second base station <NUM>, thereby producing two distinct transmissions <NUM>, <NUM>. The two distinct transmissions <NUM>, <NUM> are emitted by antennas <NUM>, <NUM> of the first base station <NUM>. The two distinct transmissions <NUM>, <NUM> are received at antennas <NUM>, <NUM> of the second base station <NUM>. The second base station <NUM> applies a combining matrix corresponding to the interference alignment precoding matrix applied by the first base station <NUM> to decode the two transmissions <NUM>, <NUM>, thereby acquiring the downlink backhaul information. In turn, the second base station <NUM> extracts, from received downlink backhaul information, further downlink backhaul information to be sent to the third base station <NUM>. To this end, the second base station <NUM> applies another interference alignment precoding matrix to the further downlink backhaul information to be sentto the third base station <NUM>, thereby producing two distinct transmissions <NUM>, <NUM>. The two distinct transmissions <NUM>, <NUM> are emitted by antennas <NUM>, <NUM> of the second base station <NUM>. The two distinct transmissions <NUM>, <NUM> are received at antennas <NUM>, <NUM> of the third base station <NUM>. The third base station <NUM> applies another combining matrix corresponding to the interference alignment precoding matrix applied by the second base station <NUM> to decode the two transmissions <NUM>, <NUM>, thereby acquiring the further downlink backhaul information.

Exchange of uplink backhaul information from the fourth base station <NUM> up to the first base station <NUM> is performed in an equivalent manner. It should be noted, however, that a first interference alignment precoding matrix used, for example, to transmit downlink backhaul information from the first base station <NUM> to the second base station <NUM> may differ from a second interference alignment precoding matrix used to transmit uplink backhaul information from the second base station <NUM> to the first base station <NUM>. These first and second interference alignment precoding matrices are computed independently from each other.

In an embodiment, the base stations <NUM>, <NUM>, <NUM> and <NUM> define interference alignment precoding matrices for transmitting backhaul information to each of their neighboring base stations based on a state of the LoS channel between each base station and each neighboring base station. To this end, for example, the first base station <NUM> sends a channel state information (CSI) reference signal via its antennas <NUM> and <NUM> to the second base station <NUM>. The CSI reference signal is received at the second base station <NUM> via its antennas <NUM> and <NUM>. The second base station <NUM> returns a CSI feedback signal to the first base station <NUM>. The first base station <NUM> uses the CSI feedback signal to define an interference alignment precoding matrix for transmission to the second base station <NUM> while the second base station <NUM> defines a corresponding combining matrix for decoding transmissions received from the first base station <NUM>. The second base station <NUM> also sends a distinct CSI reference signal to the first base station <NUM>, which returns a distinct CSI feedback signal to the second base station <NUM> so that the second base station <NUM> can define an interference alignment precoding matrix for transmission to the first base station <NUM> while the first base station <NUM> defines a corresponding combining matrix. Without limitation, CSI may be obtained using the techniques described in "<NPL>,.

Comparing the techniques illustrated in <FIG> and <FIG>, the interfering signals <NUM> shown on <FIG> intersect the signals <NUM> transmitted from, for example, the transmitter <NUM> and the antennas <NUM> of the receiver <NUM>. Otherwise stated, distinct transmitter and receiver pairs of <FIG> are not in a same line of sight. Summarily stated, transmissions from the transmitters <NUM>, <NUM> and <NUM> interfere with each other. By contrast in <FIG>, transmissions <NUM> and <NUM> from the first base station <NUM> are the only ones that pass beyond the second base station <NUM>, though with some attenuation (typically <NUM> dB blocking), and interfere with the transmissions <NUM> and <NUM>. There is in <FIG> no other transmission arriving, for example at the base station <NUM>, at an angle from the line of sight between the base stations <NUM> and <NUM>. In fact, this (typical) <NUM> dB blocking by the base station <NUM> causes a diffraction phenomenon of the transmissions <NUM> and <NUM> that, in turn, adds phase rotations to the transmissions <NUM> and <NUM> as they pass beyond the base station <NUM>. Attenuation and phase rotation of the transmissions <NUM> and <NUM> beyond the base station <NUM> generally lower the interference levels at the base stations <NUM> and <NUM>. The attenuation and phase rotation are expected to help the interference alignment optimization, in turn reducing the complexity of the interference alignment precoding matrices and of the combining matrices in the base stations <NUM>, <NUM>, <NUM> and <NUM>. It will be understood, however, this effect may vary as it depends on the equipment material at the various base stations <NUM>, <NUM> and <NUM>.

Comparing the network <NUM> of <FIG> with the network <NUM> of <FIG>, the skilled reader will appreciate that, in at least one implementation, the network <NUM> could be adapted to implement the features of the network <NUM> by software modifications its various base stations to replace the splitting of the backhaul information and the MIMO technique of <FIG> with the interference alignment technique of <FIG>. In at least one other implementation, hardware modifications may be made to the base stations, for example to avoid the splitting of the backhaul information of the network <NUM>.

In an implementation, the antennas such as <NUM>, <NUM>, <NUM>, <NUM>, etc. of the base stations <NUM>, <NUM>, <NUM> and <NUM> may be beamforming antennas. Use of conventional (non-beamforming) antennas is also contemplated. In the same or other implementations, the antennas <NUM>, <NUM>, <NUM>, <NUM> may comprise bidirectional antennas. In other implementations the antennas <NUM>, <NUM>, <NUM>, <NUM> may comprise transmit antennas and be associated with further receive antennas (not shown).

<FIG> is a schematic representation of nodes mounted on a series of lampposts as in <FIG>, the nodes communicating using selectable, linearly aligned antennas according to another embodiment. A network <NUM> of lampposts <NUM>, <NUM>, <NUM> and <NUM> carrying base stations <NUM>, <NUM>, <NUM> and <NUM>. The first lamppost <NUM> has a fiber point of access <NUM> for exchanging backhaul information between the first base station <NUM> and the core network. The fiber point of access <NUM> could alternatively be connected to any one of the lampposts <NUM>, <NUM> and <NUM>. Each base station has, for communicating with each peer base station, a plurality of linearly aligned antennas. For example, the first base station <NUM> has antennas <NUM>, <NUM> and <NUM> for communicating with the second base station <NUM> that, in turn, has antennas <NUM>, <NUM> and <NUM> for communicating with the first base station <NUM>. The second base station <NUM> also has antennas <NUM>, <NUM> and <NUM> for communicating with the third base station <NUM>. Likewise, the third base station <NUM> has antennas <NUM>, <NUM> and <NUM> for communicating with the second base station <NUM> and antennas <NUM>, <NUM> and <NUM> for communicating antennas <NUM>, <NUM> and <NUM> of the fourth base station <NUM>.

Communication between the first base station <NUM> and the second base station <NUM> is made using a point-to-point MIMO technique that involves the selection of a pair of antennas at each of these base stations. The selection is made so that a spacing between the selected antennas is a function of a distance between the base stations <NUM> and <NUM> and of a wavelength of a communication exchanged between the node and the peer node.

<FIG> is an illustration of various configurations for pluralities of linearly aligned antennas. These configurations may be implemented in any one of the base stations <NUM>, <NUM>, <NUM> and <NUM> of <FIG>. Without limitation, the configurations of <FIG> each comprise four (<NUM>) antennas. In some implementations, the various antennas shown on <FIG> may be beamforming antennas. Use of conventional (non-beamforming) antennas is also contemplated. In the same or other implementations, the configurations of <FIG> may comprise bidirectional antennas. In other implementations the pluralities of linearly aligned antennas illustrated on <FIG> may comprise transmit antennas and be associated with further pluralities of linearly aligned receive antennas (not shown). The three (<NUM>) configurations of <FIG> provide non-limitative examples of possible configurations that can each be used at any one of the base stations <NUM>, <NUM>, <NUM> and <NUM>.

Configuration A comprises linearly aligned antennas <NUM>, <NUM>, <NUM> and <NUM> that are all connected to a same base station. The second antenna <NUM> is positioned at a spacing s from the first antenna <NUM>, in which s is an antenna spacing factor whose value is determined as expressed hereinbelow. The third antenna <NUM> is positioned at a spacing <NUM>s from the second antenna <NUM> and at a spacing <NUM>s from the first antenna <NUM>. The fourth antenna <NUM> is positioned at a spacing <NUM>s from the third antenna <NUM> and at a spacing <NUM>s from the first antenna <NUM>. When selecting two of the antennas <NUM>, <NUM>, <NUM> and <NUM>, a resulting spacing between the pair of selected antennas will necessary be equal to one of s, <NUM>s, <NUM>s, <NUM>s, <NUM>s or <NUM>s.

Configuration B comprises linearly aligned antennas <NUM>, <NUM>, <NUM> and <NUM> that are all connected to a same base station. The second antenna <NUM> is positioned at a spacing <NUM>s from the first antenna <NUM>. The third antenna <NUM> is positioned at a spacing s from the second antenna <NUM> and at a spacing <NUM>s from the first antenna <NUM>. The fourth antenna <NUM> is positioned at a spacing <NUM>s from the third antenna <NUM> and at a spacing <NUM>s from the first antenna <NUM>. When selecting two of the antennas <NUM>, <NUM>, <NUM> and <NUM>, a resulting spacing between the pair of selected antennas will necessary be equal to one of s, <NUM>s, <NUM>s, <NUM>s, <NUM>s or <NUM>s.

Configuration C comprises linearly aligned antennas <NUM>, <NUM>, <NUM> and <NUM> that are all connected to a same base station. The second antenna <NUM> is positioned at a spacing <NUM>s from the first antenna <NUM>. The third antenna <NUM> is positioned at a spacing s from the second antenna <NUM> and at a spacing <NUM>s from the first antenna <NUM>. The fourth antenna <NUM> is positioned at a spacing <NUM>s from the third antenna <NUM> and at a spacing <NUM> from the first antenna <NUM>. When selecting two of the antennas <NUM>, <NUM>, <NUM> and <NUM>, a resulting spacing between the pair of selected antennas will necessary be equal to one of s, <NUM>s, <NUM>s, <NUM>s, <NUM>s or <NUM>s.

In all configurations A, B and C, a spacing between any pair of antennas selected among the antennas of a given configuration is different from a spacing between at least five other pairs antennas selected among the of that configuration, without redundancy. In any configuration having one less antenna reduces the number of possible antenna spacings without introducing any redundancy. For example, a spacing between any pair of antennas selected among the antennas <NUM>, <NUM> and <NUM> of configuration A is different from a spacing between at least two other pairs antennas selected among the antennas <NUM>, <NUM> and <NUM>, without redundancy. Adding a further antenna in any configuration, for example at an equal spacing s between the antennas <NUM> and <NUM>, may introduce spacing redundancy between the various selectable pairs of antennas.

In an embodiment, the antenna spacing factor is defined according to equation (<NUM>): <MAT>
wherein lambda is the wavelength in meters.

As shown on <FIG>, spacings between any two antenna in configurations A, Band C are all integer multiples of <NUM>s. Other configurations of the plurality of linearly aligned antennas are also contemplated. A configuration may include more or less antennas, the antennas may be positioned at variable spacings that are not necessary integer multiples of <NUM>s, and some redundancy may be found between selectable pairs of antennas.

Returning to <FIG>, point-to-point MIMO causes a data stream to be sent from the first base station <NUM> to the second base station <NUM> with different amplitudes and phases over the two selected antennas. In some embodiments the data can be sent with different amplitudes and different phases. In some such embodiments, different amplitudes can be set for each of the different phases, so that each phase may be paired (uniquely or otherwise) with a particular amplitude.

In an embodiment combining the point-to-point MIMO technique with the interference alignment technique, for a given antenna spacing, a 2x2 channel matrix Hij is defined, in which i is a receiver index and j is a transmitter index. Using interference alignment, we obtain equations (<NUM>) to (<NUM>): <MAT> <MAT> <MAT> <MAT> <MAT> <MAT> <MAT> <MAT> <MAT>
wherein Wi is the ith equalizer vector, and Fj is the jth precoder vector. The actually signal transmitted on each antenna in a form Fj * dj, in which dj is a transmitted data stream from a jth transmitter. Therefore, each transmitter transmits d multiplied by a complex value. Wii and Fj may be solved, for example, using an alternate minimization method proposed in: <NPL>.

For point-to-point MIMO on a LoS channel, given a selected antenna spacing s, the channel matrix is denoted by H. Performing a singular value decomposition to H allows finding the precoding vector F corresponding to the largest singular value. Then the transmitted signals on the transmit antennas look like F * d, where d is the scalar signal and F is the complex valued precoding matrix. Therefore, each transmitter transmits: d multiplied by a complex value.

CSI information may be used for the selection of pairs of antennas between peer base stations. For example, the first base station <NUM> selects a first pair with antennas <NUM> and <NUM> to send a CSI reference signal to the second base station <NUM>. The second base station <NUM> returns a CSI feedback signal to the first base station <NUM>, this CSI feedback signal being received at the antennas <NUM> and <NUM>. This sequence is repeated between the first base station <NUM> and the second base station <NUM> for another pair comprising the antennas <NUM> and <NUM>, and then for a further pair comprising the antennas <NUM> and <NUM>. The base station <NUM> selects the pair of antennas for communicating with the base station <NUM> according to a most favorable of the received CSI feedback signals. This entire process is repeated all links connecting any two neighboring base stations.

The base station <NUM> also selects a pair of antennas for communicating with the base station <NUM>. Each base station independently makes its own selection. Though the selection processes are independent, they are expected to arrive at a same antenna spacing for the transmitting antennas at the base stations <NUM> and for the receiving antennas at the base station <NUM>. However, the base stations <NUM> and <NUM> may not select the same antenna spacing for communicating in the reverse direction because channel conditions in one direction may differ from channel conditions in the other direction. This is especially the case when carrier frequencies used for transmitting from the base station <NUM> to the base station <NUM> and from the base station <NUM> to the base station <NUM> are not the same. When the carrier frequencies are sufficiently close, the base stations <NUM> and <NUM> may select the same antenna spacing in both directions, allowing in turn the use of bidirectional antennas. The present technology does not impose symmetry of the selection of antenna spacings in both directions between a given pair of base stations.

In one embodiment, when deployed for a specific frequency band, the spacings and antenna selections for transmissions within the frequency band may be done using a selected frequency within the band. In one embodiment, a center frequency of the band may be used for the antenna selection for all transmissions within the band. In other embodiments, other representative frequencies may be selected for the band. In one such example of a center frequency use, when a deployment uses a V-band range, it may support frequencies between <NUM> and <NUM>. A center frequency of <NUM> may be used for determination of the antenna spacings.

It may be observed that point-to-point MIMO is applied between a node and a peer node and does not depend on a third node. Point-to-point MIMO can therefore be used between nodes that are not on a same line of sight. For example, the antenna section technique may be used between nodes having a geographical configuration as illustrated in <FIG>.

Optionally, when the base stations of the network <NUM> are on a line of sight, they may at once use point-to-point MIMO along with the interference alignment technique. In fact, these techniques may be used separately or in combination. CSI information obtained by the various base stations may be used at once in the context of the interference alignment technique and in the context of point-to-point MIMO.

<FIG> is a sequence diagram showing operations of a data transmission method using interference alignment on a LoS channel. On <FIG>, a sequence <NUM> comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence <NUM> is best understood when considering at once <FIG> and <FIG>. For illustration purposes and without limiting the present disclosure, the sequence <NUM> is described as implemented in the base station <NUM>. The sequence <NUM> includes operation <NUM>, in which the base station <NUM> receives from a first peer base station, which may be either of the base stations <NUM> or <NUM>, on a line of sight (LoS) channel, a first transmission carrying a first data stream. A second transmission also carrying the first data stream is received at operation <NUM> from the first peer base station. The first and second transmissions are formed according to a first interference alignment precoding matrix. An example of a method for defining interference alignment precoding matrices is described later in the present disclosure. At operation <NUM>, the base station <NUM> transmits, on the LoS channel, a third transmission carrying a second data stream to a second peer base station, which is the other of the base stations <NUM> or <NUM>. A fourth transmission also carrying the second data stream is transmitted to the second peer base station at operation <NUM>. The third and fourth transmissions are formed according to a second interference alignment precoding matrix. The base station <NUM> may also receive on the LoS channel at operation <NUM>, from the second peer base station, a fifth transmission carrying a third data stream. A sixth transmission also carrying the third data stream may be received at operation <NUM>, also from the second peer base station. The fifth and sixth transmissions are formed according to a third interference alignment precoding matrix. The base station <NUM> may transmit on the LoS channel, to the first peer base station, a seventh transmission carrying a fourth data stream at operation <NUM>. An eighth transmission also carrying the fourth data stream may be transmitted at operation <NUM>, also to the first peer base station. The seventh and eighth transmissions are formed according to a fourth interference alignment precoding matrix.

The various transmissions of operations <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> may be received and transmitted in the form of beams exchanged between beamforming antennas at the base stations <NUM>, <NUM> and <NUM>. Use of non-beamforming antennas is also contemplated. Moreover, the various transmissions of operations <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> may optionally be received and transmitted using the above described point-to-point MIMO technique that uses selectable, linearly aligned antennas.

The sequence <NUM> may be generalized to other types of nodes connected in a daisy chain. However, in the specific context here the nodes are base stations such as the base stations <NUM>, <NUM>, <NUM> and <NUM>, at least of part of each one of the first and second data streams comprises backhaul information. If the first peer base station having transmitted the first data stream is the uplink peer base station <NUM>, being located closer to the fiber access point <NUM> that connects that the network <NUM> to the core network, the payload of the first data stream comprises (a) downlink backhaul data for the benefit of the base station <NUM>, for extraction and transmission by the base station <NUM> as downlink data to one or more UEs on a separate channel, for example an LTE channel or a <NUM> channel, and (b) further downlink backhaul data to be transmitted to the second peer base station, which is in this case the base station <NUM>. If, on the other hand, the first peer base station having transmitted the first data stream is the downlink peer base station <NUM>, being located further away from the fiber access point <NUM> that connects that the network <NUM> to the core network, the payload of the first data stream comprises uplink backhaul data from the first peer base station <NUM>. The base station <NUM> receives additional uplink data from one or more UEs, for example on an LTE or a <NUM> channel. The base station <NUM> combines the uplink backhaul data from the first peer base station <NUM> with such uplink data received from one or more UEs and form uplink backhaul data to be inserted as part of the second data stream.

In more details, <FIG> is a sequence diagram showing operations of a method using a combining matrix to extract information from a received data stream. On <FIG>, a sequence <NUM> comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. For illustration purposes and without limiting the present disclosure, the sequence <NUM> may be considered as an optional extension of <FIG> and, for that reason, is also described as implemented in the base station <NUM>. The sequence <NUM> is best understood when considering at once <FIG> and <FIG>. The sequence <NUM> includes operation <NUM> for decoding, at the base station <NUM>, the first data stream received from the first peer base station at operations <NUM> and <NUM> by application of a combining matrix to the first and second transmissions. The combining matrix corresponds to the first interference alignment precoding matrix. Other operations of the sequence <NUM> depend on the direction of information within the network <NUM> of <FIG>.

Operation <NUM> considers the position of the first and second peer base stations in relation to the fiber access point <NUM>. If the first peer base station is the base station <NUM>, being further away from the fiber access point <NUM> than the base station <NUM>, the first data stream received from the base station <NUM> at operations <NUM> and <NUM> comprises uplink backhaul data. The base station <NUM> inserts, at operation <NUM>, the first data stream as a first portion of the second data stream to be sent at operations <NUM> and <NUM> to the base station <NUM> (i.e. the second peer base station). Having received, at operation <NUM>, a third data stream on a separate channel, including for example uplink data received from one or more UEs on an LTE channel or on a <NUM> channel, the base station <NUM> inserts, at operation <NUM>, that third data stream as a second portion of the second data stream to be sent as uplink backhaul data to the base station <NUM> at operations <NUM> and <NUM>.

If, on the other hand, at operation <NUM>, the first peer base station is the base station <NUM>, being closer to the fiber access <NUM> point than the base station <NUM>, the first data stream received from the base station <NUM> at operations <NUM> and <NUM> comprises downlink backhaul data. The base station <NUM> extracts, at operation <NUM>, a first portion of the first data stream and transmits, at operation <NUM>, that first portion on a separate LTE, <NUM> or like channel as downlink data toward one or more UEs. At operation <NUM>, the base station <NUM> inserts a second portion of the first data stream in the second data stream sent as downlink backhaul data to the base station <NUM> (i.e. the second peer base station) at operations <NUM> and <NUM>.

The third data stream received at the base station <NUM> at operations <NUM> and <NUM> is processed in the same or equivalent manner as described in relation to <FIG>.

The first data stream extracted in operation <NUM> may include backhaul information, as expressed hereinabove, and may further include additional information elements, for example at least one of maintenance information and monitoring information for the base station <NUM>. Additionally, the extraction process may be imperfect and errors may be introduced. Forward error correction (FEC) and like techniques may be used to alleviate the possibilities of errors. These issues are independent from the present technology, so the present disclosure does not further address issues related to error correction and detection, and issues related to the inclusion of data, other than backhaul data, in the described data streams. These simplifications are made to simplify the present illustration and are not meant to limit the generality of the present disclosure.

<FIG> is a sequence diagram showing operations of a method of communicating between nodes using selectable, linearly aligned antennas. On <FIG>, a sequence <NUM> comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence <NUM> is best understood when considering at once <FIG>, <FIG> and <FIG>. For illustration purposes and without limiting the present disclosure, the sequence <NUM> is described as implemented in the base station <NUM>. The sequence <NUM> includes operation <NUM> in which a plurality of linearly aligned antennas is provided at the base station <NUM>. In an implementation, the antennas <NUM>, <NUM> and <NUM> are provided at operation <NUM> to allow communication between the base station <NUM> and the base station <NUM>. Another plurality of linearly aligned antennas <NUM>, <NUM> and <NUM> may also be provided at the base station <NUM> for communicating with the base station <NUM>. In other implementations, the plurality of linearly aligned antennas may instead comprise antennas arranged according to one of configurations A, B or C.

In any case, an array comprising the plurality of linearly aligned antennas is positioned at the base station <NUM> for direct communication with the base station <NUM>. A pair of antennas of the base station <NUM> is selected at operation <NUM> among a plurality of linearly aligned antennas of the base station <NUM> so that a spacing between the antennas of the pair is a function of a distance between the base station <NUM> and the base station <NUM> and of a wavelength of a communication exchanged between the base stations <NUM> and <NUM>. An example of a method for selecting the antennas of the pair is described later in the present disclosure.

Operation <NUM> comprises communicating between the base stations <NUM> and <NUM> using the selected pair of antennas of the base station <NUM>. This communication may comprise transmitting, at operation <NUM> a signal from the base station <NUM> to the base station <NUM> or receiving, at operation <NUM> a signal from the base station <NUM> at the base station <NUM>, or both. One or both of the operations <NUM> and <NUM> can be repeated multiple times, as per the need of a particular application.

Channel state information (CSI) may be exchanged between a node and first and second peer nodes, for example between a base station and first and second peer based stations. <FIG> is a sequence diagram showing operations of a method for exchanging channel state (CSI) information. On <FIG>, a sequence <NUM> comprises a plurality of operations that may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. The sequence <NUM> is best understood when considering at once <FIG> and <FIG>. For illustration purposes and without limiting the present disclosure, the sequence <NUM> is described as implemented in a particular embodiment of the base station <NUM> that supports one or both of the interference alignment technique of <FIG> and the point-to-point MIMO technique of <FIG>. The base station <NUM> transmits to a first peer base station <NUM>, on the LoS channel, a first channel state information (CSI) reference signal at operation <NUM>. The base station <NUM> also receives from the first peer base station <NUM>, on the LoS channel, a first CSI feedback signal at operation <NUM>. Operation <NUM> comprises the transmission, from the base station <NUM> to a second peer base station <NUM>, on the LoS channel, of a second CSI reference signal. Operation <NUM> comprises receiving, at the base station <NUM> from the second peer base station <NUM>, on the LoS channel, a second CSI feedback signal.

In an embodiment using the interference alignment technique, the first interference alignment precoding matrix for use for example in operations <NUM> and <NUM> may be defined based on a state of the LoS channel between the base station <NUM> and the first peer base station <NUM> at operation <NUM>. A first combining matrix corresponding to the first interference alignment precoding matrix may also be defined at the same time. The second interference alignment precoding matrix may be defined based on a state of the LoS channel between the base station <NUM> and the second peer base station <NUM> at operation <NUM>, the second interference alignment precoding matrix being used for example in operations <NUM> and <NUM>. A second combining matrix corresponding to the second interference alignment precoding matrix may also be defined at the same time. The third and fourth interference alignment precoding matrices mentioned in the description of operations <NUM>, <NUM>, <NUM> and <NUM> and corresponding third and fourth combining matrices may be defined in similar fashion.

In an embodiment using point-to-point MIMO, the operations <NUM> and <NUM> may be repeated for each selectable pair of antennas of the base station <NUM> that can communicate with the first peer base station <NUM>. Likewise, the operations the operations <NUM> and <NUM> may be repeated for each selectable pair of antennas of the base station <NUM> that can communicate with the second peer base station <NUM>. At operation <NUM>, at the base station <NUM>, the antennas of the pair for communicating with the first peer base station <NUM> are selected according to a most favorable of the CSI feedback signals received at the base station <NUM> from the first peer base station <NUM> at various instances of operation <NUM>. At operation <NUM>, the antennas of the pair of the base station <NUM> for communicating with the second peer base station <NUM> are selected according to a most favorable of the CSI feedback signals received at the base station <NUM> from the second peer base station <NUM> at various instances of operation <NUM>.

Each of the operations of the sequences <NUM>, <NUM>, <NUM> and <NUM> may be configured to be processed by one or more processors, the one or more processors being coupled to a memory. In more details, <FIG> is a block diagram of a node according to a further embodiment. A node may comprise a base station <NUM> that implements the interference alignment technique, or point-to-point MIMO, or both of these techniques. The present description provides a non-limitative example of a base station <NUM> that implements both techniques.

The base station <NUM> comprises a processor <NUM> operatively connected to a memory <NUM>. The processor <NUM> may include a plurality of co-processors. The memory <NUM> may include one or more memory modules. The base station <NUM> also comprises a radio interface unit that includes at least one transceiver <NUM> for communicating with a first peer base station. The radio interface unit may also include another transceiver <NUM> for communicating with a second peer base station. The transceivers <NUM> and <NUM> may each be capable of transmitting and receiving; alternatively, each transceiver <NUM> and <NUM> may be substituted by a distinct transmitter and receiver.

The transceiver <NUM> is operatively coupled to at least one antenna for communicating with the first peer base station. In the example as shown on <FIG>, the transceiver <NUM> is coupled to an array <NUM> of linearly aligned transmit antennas <NUM>, <NUM> and <NUM>. The transceiver <NUM> is also coupled to an array <NUM> of linearly aligned receive antennas <NUM>, <NUM> and <NUM>. The transceiver <NUM> is operatively coupled to at least one antenna for communicating with the second peer base station. In the example as shown on <FIG>, the transceiver <NUM> is coupled to an array <NUM> of linearly aligned transmit antennas <NUM>, <NUM> and <NUM>. The transceiver <NUM> is also coupled to an array <NUM> of linearly aligned receive antennas <NUM>, <NUM> and <NUM>. The arrays <NUM>, <NUM>, <NUM> and <NUM> may be built using, for example, the configurations A, B or C illustrated on <FIG>. In a variant, the transceivers <NUM> and <NUM> may be coupled to arrays of bidirectional antennas. In another variant, the base station <NUM> may not use arrays of linearly aligned antennas, for example when the base station <NUM> implements the interference alignment technique without using point-to-point MIMO. The various antennas shown on <FIG> may optionally be beamforming antennas.

The base station <NUM> may further comprise a fiber access point <NUM>. Referring again to <FIG> and <FIG>, some implementations of the base station <NUM> may include the fiber access point <NUM> while others may not. Although not shown on <FIG> and <FIG>, the fiber access point <NUM> may be located at any base station <NUM> of a daisy chain; the fiber access point <NUM> is not necessarily present in a base station <NUM> located at one end of a daisy chain of base stations <NUM>. Some implementations of the base station <NUM> may include a single transceiver <NUM> or <NUM> and antennas for communicating with one peer base station <NUM>, for example when that base station <NUM> is at one end of a daisy chain of base stations <NUM>.

The processor <NUM> may also be operatively coupled to a radio unit <NUM>. Though not shown, internal components of the radio unit <NUM> may include a processor, a memory, either or both of LTE or <NUM> radio equipment comprising a receive and a transmitter, or a transceiver, and one or more antennas for communicating with UEs.

The processor <NUM> generally controls operations of the base station <NUM>. Without limitation, the processor <NUM> is informed by the transceiver <NUM> of the reception, from the first peer base station, of first and second transmissions carrying a first data stream. The processor <NUM> is configured to apply a combining matrix to decode the first data stream. The processor <NUM> applies an interference alignment precoding matrix to a second data stream to form third and fourth transmissions and causes the transceiver <NUM> to transmit the third and fourth transmissions to the second peer base station.

When the first peer base station is further away from a fiber access point than the base station <NUM>, the processor <NUM> may insert a portion of the first data stream as the second data stream and extract another portion first data stream to form a third data stream. The processor <NUM> then causes the radio unit <NUM> to transmit the third data stream to one or more UEs. When the first peer base station is closer to a fiber access point than the base station <NUM>, the processor <NUM> may insert the first data stream as a first portion of the second data stream. Being informed by the radio unit <NUM> of the reception of a third data stream received from one or more UEs, the processor <NUM> inserts the third data stream as a second portion of the second data stream.

The processor <NUM> may cause the transceivers <NUM> and <NUM> to respectively send CSI reference signals to the first and second peer base stations. Being informed by the transceivers <NUM> and <NUM> of the reception of CSI feedback signals, the processor <NUM> determines the state of channels between the base station <NUM> and the first and second peer base stations. The processor <NUM> defines interference alignment precoding matrices for forming transmissions towards the first and second peer base stations based on the state of the channels. The processor also defines combining matrices for decoding transmissions from the first and second peer base stations, the combining matrices being also defined based on the state of the channels. The processor may also cause the transceivers <NUM> and <NUM> to send the CSI reference signals for each selectable pair of the antennas of the arrays <NUM> and <NUM> and cause the transceivers <NUM> and <NUM> to select pairs of antennas of the arrays <NUM> and <NUM> for receiving the CSI feedback signals (in implementations using bidirectional antennas, the same antennas are used for transmitting the CSI reference signals and for receiving corresponding CSI feedback signals). For corresponding to a given peer base station, the processor <NUM> selects the antennas of the pair according to a most favorable of the received CSI feedback signals.

<FIG> is a graph showing a signal to noise performance of a transmission in view of a distance between nodes when using the interference alignment technique and the point-to-point MIMO technique combined in a same implementation. A graph <NUM> illustrates a variation of achievable SNR, in dB, as a function of a distance, in meters, between two peer nodes, for the three configurations of <FIG>. Results are presented for a <NUM> wavelength (<NUM> carrier frequency), total attenuation and rain fade of <NUM> dB per kilometer, transmit power of <NUM> dBm, transmit and receive antenna gains of <NUM> dB, <NUM> signal bandwidth, noise figure (NF) of <NUM> dB.

Curve <NUM> shows how the SNR decreases as a function of a distance between nodes, in a LoS scenario, assuming a perfect antenna spacing selection. Curve <NUM> represents an achievable performance using Configuration A. Curve <NUM> represents an achievable performance using Configuration B. Curve <NUM> represents an achievable performance using Configuration C. Curves <NUM>, <NUM> and <NUM> are provided for same distances between the nodes. The performance of each configuration varies according to the distance between two peer nodes (between two lampposts on <FIG> and <FIG>). One of the Configurations A, B and C may be selected upon installation of each one the nodes <NUM> in a daisy chain of nodes on a street, based on the present graph <NUM> and based on a known distance between lampposts. The nodes <NUM> will then select the pairs of antennas among the chosen Configuration A, B or C based on the exchanges of CSI information.

Various embodiments of the methods and nodes using at least one of the interference alignment technique and the point-to-point MIMO technique, as disclosed herein, may be envisioned, as expressed in the following paragraphs.

In some implementations of the present interference alignment technique, the first and second transmissions are received in the form of first and second beams, the third and fourth transmissions being transmitted in the form of third and fourth beams.

In some implementations of the present interference alignment technique, the method further comprises receiving at the node from the second peer node, on the LoS channel, a fifth transmission carrying a third data stream and a sixth transmission carrying the third data stream, the fifth and sixth transmissions being formed according to a third interference alignment precoding matrix, the method also comprising transmitting, from the node to the first peer node, on the LoS channel, a seventh transmission carrying a fourth data stream and an eighth transmission carrying the fourth data stream, the seventh and eighth transmissions being formed according to a fourth interference alignment precoding matrix.

In some implementations of the present interference alignment technique, the first data stream includes a payload of the second data stream.

In some implementations of the present interference alignment technique, the second data stream includes a payload of the first data stream.

In some implementations of the present interference alignment technique, the method further comprises receiving, at the node, on a separate channel, a third data stream, inserting, at the node, the first data stream as a first portion of the second data stream, and inserting, at the node, the third data stream as a second portion of the second data stream.

In some implementations of the present interference alignment technique, the method further comprises extracting, at the node, a first portion of the first data stream, transmitting, from the node, on a separate channel, the first portion of the first data stream, and inserting, at the node, a second portion of the first data stream in the second data stream.

In some implementations of the present interference alignment technique, the processor is further adapted to decode the first data stream by application of a combining matrix to the first and second transmissions, the combining matrix corresponding to the first interference alignment precoding matrix.

In some implementations of the present point-to-point MIMO technique, communicating between the node and the peer node comprises receiving a signal from the peer node at the node.

In some implementations of the present point-to-point MIMO technique, the linearly aligned antennas are collectively selected from the group consisting of transmit antennas, receive antennas, and bidirectional antennas.

In some implementations of the present point-to-point MIMO technique, the plurality of linearly aligned antennas comprises transmit antennas, the node having a second plurality of linearly aligned receive antennas.

In some implementations of the present point-to-point MIMO technique, a spacing between any pair of antennas among the plurality of linearly aligned antennas is different from a spacing between at least two other pairs of antennas among the plurality of linearly aligned antennas.

In some implementations of the present point-to-point MIMO technique, a spacing between any pair of antennas among the plurality of linearly aligned antennas is different from a spacing between at least five other pairs of antennas among the plurality of linearly aligned antennas.

In some implementations of the present point-to-point MIMO technique, the radio interface unit is selected from the group consisting of a transmitter, a receiver and a transceiver.

In some implementations of the present point-to-point MIMO technique, the plurality of linearly aligned antennas comprises at least four antennas, a spacing between any pair of antennas selected among four of the at least four antennas being different from a spacing between any other pair of antennas among the four of the at least four antennas.

In an implementation combining the present interference alignment technique with the present point-to-point MIMO technique, there is provided a data transmission method. A first transmission carrying a first data stream and a second transmission carrying the first data stream are received, at a node from a first peer node, on a line of sight (LoS) channel. The first and second transmissions are formed according to a first interference alignment precoding matrix. The first and second transmissions are received at a first pair of antennas of the node, the antennas of the first pair being selected among a first plurality of linearly aligned antennas so that a first spacing between the antennas of the first pair is a function of a first distance between the node and the first peer node and of a wavelength of the LoS channel. A third transmission carrying a second data stream and a fourth transmission carrying the second data stream are transmitted, from the node to a second peer node, on the LoS channel. The third and fourth transmissions are formed according to a second interference alignment precoding matrix. The third and fourth transmissions are transmitted from a second pair of antennas of the node, the antennas of the second pair being selected among a second plurality of linearly aligned antennas so that a second spacing between the antennas of the second pair is a function of a second distance between the node and the second peer node and of the wavelength of the LoS channel.

In some implementations combining the present interference alignment technique with the present point-to-point MIMO technique, the antennas of the first and second pluralities of linearly aligned antennas are beamforming antennas.

In some implementations combining the present interference alignment technique with the present point-to-point MIMO technique, the method further comprises, for each pair of antennas among the first plurality of linearly aligned antennas, transmitting, from the node to the first peer node, on the LoS channel, a channel state information (CSI) reference signal and receiving, at the node from the first peer node, on the LoS channel, a CSI feedback signal, the method also comprising selecting the antennas of the first pair according to a most favorable of the CSI feedback signals received from the first peer node, the method further comprising, for each pair of antennas among the second plurality of linearly aligned antennas, transmitting, from the node to the second peer node, on the LoS channel, a channel state information (CSI) reference signal, and receiving, at the node from the second peer node, on the LoS channel, a CSI feedback signal, the method also comprising selecting the antennas of the second pair according to a most favorable of the CSI feedback signals received from the second peer node, the first interference alignment precoding matrix being defined based on the most favorable of the CSI feedback signals received from the first peer node, the second interference alignment precoding matrix being defined based on the most favorable of the CSI feedback signals received from the second peer node.

In an implementation combining the present interference alignment technique with the present point-to-point MIMO technique, there is provided a node comprising a receiver, a transmitter, first and second pluralities of linearly aligned antennas and a processor. The antennas of the first plurality of linearly aligned antennas are communicatively coupled to the receiver. The receiver is adapted to receive, from a first peer node, on a line of sight (LoS) channel, a first transmission carrying a first data stream and a second transmission carrying the first data stream, the first and second transmissions being formed according to a first interference alignment precoding matrix. The antennas of the second plurality of linearly aligned antennas are communicatively coupled to transmitter. The transmitter is adapted to transmit, to a second peer node, on the LoS channel, a third transmission carrying a second data stream and a fourth transmission carrying the second data stream, the third and fourth transmissions being formed according to a second interference alignment precoding matrix. The processor is operatively connected to the receiver and to the transmitter. The processor is adapted to select a first pair of antennas among the first plurality of linearly aligned antennas for the receiver to receive the first and second transmissions, the first pair of antennas being selected so that a spacing between the antennas of the first pair is a function of a distance between the node and the first peer node and of a wavelength of the first and second transmissions. The processor is further adapted to select a second pair of antennas among the second plurality of linearly aligned antennas for the transmitter to transmit the third and fourth transmissions, the second pair of antennas being selected so that a spacing between the antennas of the second pair is a function of a distance between the node and the second peer node and of a wavelength of the third and fourth transmissions.

Those of ordinary skill in the art will realize that the description of the methods and nodes for multi-hop data transmission between evolved node Bs are illustrative only and are not intended to be in any way limiting. Other embodiments will readily suggest themselves to such persons with ordinary skill in the art having the benefit of the present disclosure. Furthermore, the disclosed methods and nodes may be customized to offer valuable solutions to existing needs and problems related to daisy chaining of evolved node Bs. In the interest of clarity, not all of the routine features of the implementations of the methods and nodes are shown and described. In particular, combinations of features are not limited to those presented in the foregoing description as combinations of elements listed in the appended claims form an integral part of the present disclosure. It will, of course, be appreciated that in the development of any such actual implementation of the methods and nodes, numerous implementation-specific decisions may need to be made in order to achieve the developer's specific goals, such as compliance with application-, system-, and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the field of wireless communications having the benefit of the present disclosure.

In accordance with the present disclosure, at least one of the components, process operations, and data structures described herein may be implemented using various types of operating systems, computing platforms, network devices, computer programs, and general purpose machines. In addition, those of ordinary skill in the art will recognize that devices of a less general purpose nature, such as hardwired devices, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), or the like, may also be used. Where a method comprising a series of operations is implemented by a computer, a processor operatively connected to a memory, or a machine, those operations may be stored as a series of instructions readable by the machine, processor or computer, and may be stored on a non-transitory, tangible medium.

As indicated above, embodiments of the present invention include a data transmission method that comprises communicating between a node and a peer node using a pair of antennas of the node, the antennas of the pair being selected among a plurality of linearly aligned antennas so that a spacing between the antennas of the pair is a function of a distance between the node and the peer node and of a wavelength of a communication exchanged between the node and the peer node.

In one embodiment, this method comprises transmitting a signal from the node to the peer node at a first amplitude and a first phase using a first antenna of the pair and at a second amplitude and a second phase using a second antenna of the pair, the first amplitude being different from the second amplitude and the second phase being different from the second phase. The antennas of the plurality of linearly aligned antennas may be beamforming antennas. This method may further comprise,for each pair of antennas among the plurality of linearly aligned antennas, transmitting, from the node to the peer node, a channel state information (CSI) reference signal, receiving, at the node from the peer node, a CSI feedback signal; and selecting the antennas of the pair according to a most favorable of the received CSI feedback signals. In some embodiment, the plurality of linearly aligned antennas comprises at least four antennas, a spacing between any pair of antennas selected among four of the at least four antennas being different from a spacing between any other pair of antennas among the four of the at least four antennas.

As indicated above, embodiments of the present invention include a node comprising a radio interface unit a plurality of linearly aligned antennas and a processor. The radio interface unit is adapted to communicate with a peer node. The antennas of the plurality of linearly aligned antennas being communicatively coupled to the radio interface unit. The processor is operatively connected to the radio interface unit and adapted to select a pair of antennas among the plurality of linearly aligned antennas for the radio interface unit to communicate with the peer node, the selection being so that a spacing between the antennas of the pair is a function of a distance between the node and the peer node and of a wavelength of a communication exchanged between the node and the peer node.

In one embodiment, the processor is further adapted to cause the radio interface unit to transmit, to the peer node, a channel state information (CSI) reference signal, and acquire, from the radio interface unit, a CSI feedback signal received from the peer node for each pair of antennas among the plurality of linearly aligned antennas, and the processor is also further adapted to select the antennas of the pair according to a most favorable of the received CSI feedback signals. In other embodiments, the node further comprises a fiber access point operatively connected to the processor and adapted for communicatively coupling the radio interface unit and a core network. In another embodiment, an antenna spacing factor is defined as s=<NUM>-Vlamba, where s is the antenna spacing factor in meters; and lambda is the wavelength in meters. In some embodiments, the plurality of linearly aligned antennas comprises a first antenna, a second antenna positioned at a spacing s from the first antenna, a third antenna positioned at a spacing <NUM> from the second antenna and at a spacing <NUM> from the first antenna, and a fourth antenna positioned at a spacing <NUM> from the third antenna and at a spacing <NUM> from the first antenna. In some embodiments, the plurality of linearly aligned antennas comprises a first antenna, a second antenna positioned at a spacing <NUM> from the first antenna, a third antenna positioned at a spacing s from the second antenna and at a spacing <NUM> from the first antenna, and a fourth antenna positioned at a spacing <NUM> from the third antenna and at a spacing <NUM> from the first antenna. In further embodiments the plurality of linearly aligned antennas comprises a first antenna, a second antenna positioned at a spacing <NUM> from the first antenna, a third antenna positioned at a spacing s from the second antenna and at a spacing <NUM> from the first antenna, and a fourth antenna positioned at a spacing <NUM> from the third antenna and at a spacing <NUM> from the first antenna. In other embodiments, the radio interface comprises a transmitter; and the processor is further adapted to cause the transmitter to transmit a signal to the peer node at a first amplitude and a first phase using a first antenna of the pair and at a second amplitude and a second phase using a second antenna of the pair, the first amplitude being different from the second amplitude and the second phase being different from the second phase.

Systems and modules described herein may comprise software, firmware, hardware, or any combination(s) of software, firmware, or hardware suitable for the purposes described herein. Software and other modules may be executed by a processor and reside on a memory of servers, workstations, personal computers, computerized tablets, personal digital assistants (PDA), and other devices suitable for the purposes described herein. Software and other modules may be accessible via local memory, via a network, via a browser or other application or via other means suitable for the purposes described herein. Data structures described herein may comprise computer files, variables, programming arrays, programming structures, or any electronic information storage schemes or methods, or any combinations thereof, suitable for the purposes described herein.

Claim 1:
A data transmission method between a node (<NUM>), a first peer node (<NUM>) and a second peer node (<NUM>) aligned on a line of sight, LoS, channel, comprising:
receiving (<NUM>, <NUM>), at the node (<NUM>) from the first peer node (<NUM>), on the LoS channel, a first transmission carrying a first data stream and a second transmission carrying the first data stream, the first and second transmissions being formed according to a first interference alignment precoding matrix;
transmitting (<NUM>, <NUM>), from the node (<NUM>) to the second peer node (<NUM>), on the LoS channel, a third transmission carrying a second data stream and a fourth transmission carrying the second data stream, the third and fourth transmissions being formed according to a second interference alignment precoding matrix, and wherein the distinct first and second interference alignment precoding matrices mitigate interference between the first data stream received at the node (<NUM>) and the second data stream transmitted by the node (<NUM>) to the second peer node (<NUM>).