COMMUNICATION SYSTEM

Technical field

[0001 ] The present disclosure relates generally to wireless communication, and more specifically to network nodes and methods for flexible duplex in an OFDM communication system such as a Long Term Evolution (LTE), Wi-Fi

communication system.

Background

[0002] Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. One of the necessary functions in the wireless

communications systems is how to establish two-way communications such as between a user and an access point, in the uplink (UL) and downlink (DL), respectively, or between two users or devices which is known as peer-to- peer/device-to-device, etc.

[0003] The traditional protocols for establishing two-way communications are: Time Division Duplex (TDD), Frequency Division Duplex (FDD), or Full Duplex (FDX). However, any of these traditional protocols is not flexible, which means that once the duplexing protocol is chosen for a system it cannot be changed or the duplexing protocols cannot be switched in between, especially during run-time. Merely the duplexing parameters can change within the method during run-time to allow multiplexing the different users in the system via a central resource allocation, such as for FDMA or TDMA.

[0004] Another disadvantage is different users cannot have different duplexing schemes, which means all users in a system must obey the same fixed duplexing scheme, for example, TDD, FDD, or FDX once decided.

[0005] Further, in order to multiplex the common channel resources among all users in UL and DL, the traditional duplexing protocols TDD and FDD require system-wide coordination because FDMA and TDMA typically require complicated scheduling mechanisms, which fundamentally limits the ability to adapt the available UL/DL communication resources to instant users’ demand.

[0006] Further, the traditional duplexing protocols TDD, FDD and FDX cannot be mixed in a single frequency band.

[0007] Further, it is impossible to adapt UL/DL duplexing independently for each user.

[0008] Lastly, in order to utilize channel reciprocity, TDD is necessary in the traditional duplexing protocols.

Summary

[0009] It is an object of the invention to address at least some of the problems and issues outlined above. It is an object of embodiments of the present invention to improve the flexibility of duplexing schemes and spectrum scheduling. The invention provides higher spectrum efficiency and lower latencies between the uplink and downlink in two ways. It is also possible to utilize channel reciprocity with either FDX, FDD or TDD. By utilizing FDD or FDX, simple low- level mechanisms for controlling the transmission streams in UL and DL is possible.

The invention is also backward compatible with legacy OFDM systems. It is possible to achieve these objects and others by using a node and a method as defined in the attached independent claims.

[00010] According to one aspect, a first communication node is provided, operable for duplex Orthogonal Frequency Division Multiplex (OFDM) based communication with a second communication node in a wireless communication network, wherein the first node is adapted to communicate with the second communication node using the same OFDM numerology and wherein the communication between the first and the second communication node is a synchronized OFDM transmission in time and frequency, the first communication node comprising: a transceiver configured to transmit or receive data; a memory; and at least one processor communicatively coupled to the transceiver and to the memory, wherein the at least one processor is configured to: decide subcarriers to be used for the communication with the second node, assign, for each of the decided subcarriers, a communication direction to be used on the subcarrier, wherein the communication direction for each subcarrier is transmitting, or receiving, or used in both directions simultaneously, or unused, and each of the first and second communication node is adapted to transmit onto the subcarriers a new OFDM-symbol simultaneously.

[00011 ] According to another aspect, a communication method is provided, performed by a first communication node of a wireless communication network for duplex Orthogonal Frequency Division Multiplex (OFDM) based communication with a second communication node in a wireless communication network wherein the first node is adapted to communicate with the second communication node using the same OFDM numerology and wherein the communication between the first and the second communication node is a synchronized OFDM transmission in time and frequency, comprising the steps of deciding subcarriers to be used for the communication with the second node; assigning to each of the decided subcarriers the communication direction, characterized by: the communication direction for each subcarrier is transmitting, or receiving, or used in both directions simultaneously, or unused, and the step of transmitting at each of the first and second communication nodes is further comprised by transmitting a new OFDM- symbol onto the subcarriers simultaneously.

[00012] According to a third aspect, there is provided a computer program product comprising computer-readable instructions which, when executed on a computer, performs a method mentioned above.

[00013] Further possible features and benefits of this solution will become apparent from the detailed description below.

Brief description of drawings

[00014] The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which: [00015] Fig. 1 is an illustration of flexible OFDM-subcarrier allocation with TDD, FDD, and FDX subcarriers.

[00016] Fig 2 is an illustration of cyclic suffix (CS), of duration tcs, in addition to cyclic prefix (CP).

[00017] Fig. 3 is an illustration of extended cyclic prefix (CP ⁺ ), of duration tc _P +, in addition to the cyclic prefix (CP).

[00018] Fig. 4 is an illustration of combination of cyclic prefix (CP), extended cyclic prefix (CP ⁺ ), and cyclic suffix (CS).

[00019] Fig. 5 is a timing diagram for communication between two nodes.

[00020] Fig. 6 is another timing diagram for communication between two nodes.

[00021 ] Fig. 7 is a third timing diagram for communication between two nodes.

[00022] Fig. 8A and 8B are illustrations of near-echo paths between different transmit- and receive antennas.

[00023] Fig. 9 is an illustration of a possible implementation of near echo suppression at a node.

[00024] Figs. 10-11 are block diagrams illustrating a radio access network node in more detail, according to further possible embodiments.

[00025] Fig.12 is a flow chart illustrating a method performed by a radio access network node according to other possible embodiments.

Detailed description

[00026] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[00027] According to an embodiment, the present disclosure provides a design for communication in a flexible duplexing scenario. In a flexible duplexing scenario, a first communication node and a second communication node communicate with each other having synchronized OFDM transmission in time and frequency, both communication nodes use the same OFDM numerology, such as subcarrier spacing, symbol duration and cyclic extensions. Fig. 1 shows an example of flexible OFDM-subcarrier allocation with TDD, FDD and FDX subcarriers. Each subcarrier can be assigned and used in any communication direction, for example, up, down or both up and down simultaneously. Each of the above subcarriers can also be arranged to be unused. The duplexing protocols can therefore be an inband mix of TDD, FDD or FDX. The UL/DL duplexing is separately adapted for each symbol which is transmitted from the two communication nodes. According to Fig. 1 , each link between the first and the second communication nodes can choose and switch OFDM-subcarriers in- band between TDD, FDD, and FDX, independently on each OFDM subcarrier during run-time.

[00028] Several embodiments of OFDM symbols are shown in Fig. 2-4. Fig. 2 shows an OFDM symbol having Cyclic Suffix (CS) of time-duration, tcs , in addition to a cyclic prefix (CP). The CP of an OFDM symbol is obtained by prepending a copy of N _cp samples, which corresponds to a time-duration of t _cp , from the end of the OFDM symbol, excluding the CS part of the original OFDM symbol, to its beginning. This way we obtain a circular signal structure. That is, considering the CP only, the first N _cp and last N _cp samples, are equal in each OFDM symbol. In a similar way, considering the CS only, the CS part of an OFDM symbol is a copy of N _cs samples, corresponding to a time-duration of tcs, from the first part of the original OFDM symbol, excluding the CP part, to the end of the original OFDM symbol. Thus, without considering the CP part, the first N _cs and the last N _cs samples are equal in each OFDM symbol. With both CP and CS, these two concepts are combined. [00029] Fig. 3 shows an OFDM symbol having extended cyclic prefix (CP ⁺ ) of duration t _cp+ , in addition to the cyclic prefix (CP). The CP ⁺ is an inter-symbol interference free portion of the normal cyclic prefix in an OFDM symbol, which means, the CP ⁺ does not receive any inter-symbol interference at the receiving end due to the communication channels’ time dispersion.

[00030] Fig.4 shows an OFDM symbol having a combined duration of the CP+, tc _{P+ ,} and the duration of the CS, tcs, in which, the combined duration is at least as long as the propagation delay, td, between the two communication nodes. The relation of the duration can be expressed as following:

[00031 ] tcs + tcp+ ³ td,

[00032] tcs ³ 0,

[00033] tcp+ ³ 0.

[00034] According to an embodiment, each OFDM symbol uses a Cyclic

Suffix (CS), in addition to the Cyclic Prefix (CP). Timing diagrams for

communication between the two communication nodes are shown in Fig.5.

Transmission of a new OFDM symbol start simultaneously at the two or more nodes communicating over a channel. The communication has a reciprocal propagation delay of max td time units between any transmitter and receiver at opposite channel ends. The duration of the Cyclic Suffix (CS), tcs, is at least as long as the propagation delay between the two communication nodes, i.e. , t _cs ³td. Thus, the interference between the uplink and downlink is isolated and orthogonal for each OFDM symbol and subcarrier, and can be canceled according to equation (1 ) as described bellow.

[00035] Alternatively, each OFDM symbol can use an extended CP (CP ⁺ ) instead of a Cyclic Suffix (CS). The timing diagram for communication between the two communication nodes is shown in Fig.6. The duration of the CP ⁺ , t _cp+ , shall be at least as long as the reciprocal propagation delay of td between the two communication nodes i.e., t _cp+ ³td. Thus, the interference between theuplink and downlink is isolated and orthogonal for each OFDM symbol and subcarrier, and can be canceled according to equation (1 ) as described bellow.

[00036] According to a third embodiment, both a Cyclic Suffix (CS) and an extended CP (CP ⁺ ) are used in combination in each OFDM symbol. The timing diagram for communication between the two communication nodes is shown in Fig.7. The communication has a reciprocal propagation delay of fc/ time units between the transmitter and the receiver at opposite channel ends. The combined duration of the Cyclic Suffix (CS), tcs, and the extended CP (CP ⁺ ) shall be at least as long as the propagation delay between the two nodes, i.e. , tcs + tc _P + ³td. Thus, the interference between the uplink and downlink is isolated and orthogonal for each OFDM symbol and subcarrier, and can be canceled according to equation (1 ) as described below.

[00037] Fig. 8A and 8B describe a generic transceiver node in the frequency domain, which uses an OFDM subcarrier k, and the near-echo paths between the different transmit- and receive antennas. Fig. 8A illustrates near-echoes from the transmit path 1 to the receive paths and Fig. 8B illustrates near echoes from the transmit paths to the receive path 1.

[00038] Fig. 9, with reference to Fig. 8A and 8B, illustrates a possible

implementation of the near echo suppression at a node. The node has two transmit paths with RF outputs, xi(t) and X2(t), and one receive path with RF input yi(t). In this example, one transmit path xi(t) transmits data exclusively and transmit path xå(t) exclusively performs near-echo cancellation, which can also be called near-echo nulling, on the used transmit subcarriers, k G {0, . . . In general, the tasks of data transmission and near-echo cancellation can be performed jointly by all transmit paths combined. The details of near-echo cancellation will be described below.

[00039] At each node, the combined transmit signal from several transmit paths are such that the near echoes from all transmit paths are nulled at each receive path. [00040] Each transmit path can send a RF-signal via an individual transmit antenna or it can be connected directly to a receive antenna via a RF-combiner of any type, or a combination thereof.

[00041 ] Specifically, for an OFDM system node with M transmit paths, m Q {1 , . .

. ,M}, and N receive paths, n Q {1, . . . ,N}, wherein M > N, the jointly transmitted signals over the M transmit paths on subcarrier k ; xV, . . . , x ^M k, will form a null space at the N receive paths.

[00042] Y^near-echo _{= HkXk} = Q (Ί )

[00043] wherein the near-echo channel matrix on subcarrier k between all M transmit paths and N receive paths at the same node is shown as following

and a vector of M transmitted OFDM signals on subcarrier k over the {1 transmit paths is shown as following

Therefore, the partial near-echo at receive path n which originates from the transmitted signal over path m is Which is illustrated in Fig. 8A and 8B.

[00044] The vector Y _/ ^near - ^echo in equation (1 ) represents the near-echoes over the N receive paths on subcarrier k, echo, 1

-.near-echo

'k

near-echo. iV

m

Where

near-echo n

Vk

represents the nulling of the near-echoes at each receive path, n Q {1, . . . ,N}.

[00045] In this way, the near-echo nulling on one subcarrier is independent from the near-echo nulling on the other subcarriers. To achieve independence of the subcarriers in the upstream and downstream synchronization among all transmit- and receive paths at each node, all paths at each node share the same time- and frequency references, which is illustrated in Fig. 9 by the sampling clock reference, Ts, for the analog to digital converters (ADC) and digital to analog converters (DAC), and the carrier frequency reference, f _c , for carrier frequency modulation and demodulation.

[00046] Fig. 10 describes a fist communication node 140 operable in a wireless communication network 100 for duplex Orthogonal Frequency Division Multiplex (OFDM) based communication with a second communication node. The fist communication node 140 comprises a processing circuitry 603 and a memory 604. The memory contains instructions executable by said processing circuitry, whereby the first communication node 140 is adapted to communicate with the second communication node using the same OFDM numerology, such as subcarrier spacing, symbol duration and cyclic extensions, etc., and wherein the communication between the first and the second communication nodes is synchronized OFDM transmission in time and frequency. The first communication node 140 is further adapted to decide subcarriers to be used for the

communication with the second node, to assign, for each of the decided

subcarriers, a communication direction to be used on the subcarrier, and to transmit onto one of the subcarriers a new OFDM symbol, wherein the

communication direction is transmitting, or receiving, or both directions

simultaneously, and each of the first and second communication node is adapted to transmit an OFDM-symbol in a single direction or in both communication directions simultaneously.

[00047] According to an embodiment, each symbol of the first communication node is configured with at least one of a Cyclic Suffix (CS) and an extended Cyclic Prefix (CP+), in addition to a Cyclic Prefix (CP).

[00048] According to another embodiment, the extended Cyclic Prefix (CP+) is an inter-symbol interference free portion of the Cyclic Prefix (CP) in the OFDM symbol.

[00049] According to another embodiment, the combined duration of the

CP+, tc _P+ , and the duration of the CS, tcs, is at least as long as a propagation delay, td, between the first communication node and the second communication node.

[00050] According to another embodiment, the first communication node is configured to choose a portion of a received signal which contains near-echo interference only from a single OFDM symbol and performs near-echo cancellation on each of the subcarriers used for reception separately.

[00051 ] The computer program 605 may be arranged such that when its instructions are run in the processing circuitry, they cause the first communication node 140 to perform the steps described in any of the described embodiments of the first communication node 140 and its method. The computer program 605 may be carried by a computer program product connectable to the processing circuitry 603. The computer program product may be the memory 604, or at least arranged in the memory. The memory 604 may be realized as for example a RAM

(Random-access memory), ROM (Read-Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). Further, the computer program 605 may be carried by a separate computer-readable medium, such as a CD, DVD or flash memory, from which the program could be downloaded into the memory 604. Alternatively, the computer program may be stored on a server or any other entity to which the first communication node 140 has access via the communication unit 602. The computer program 605 may then be downloaded from the server into the memory 604.

[00052] Fig. 11 describes an example of a fist communication node 140 operable in a wireless communication network 100 for duplex Orthogonal Frequency Division Multiplex (OFDM) based communication with a second communication node. The fist communication node 140 comprises a scheduling module 704 for switching in-band between different duplexing schemes during run-time according to an instant bandwidth demand of the fist communication node 140, and a transceiver module 706 for OFDM symbols on decided subcarriers in decided directions. The fist communication node 140 may further comprise a

communication unit 602 similar to the communication unit described in Fig. 10. In an embodiment, the modules of Fig. 11 are implemented as a computer program running on a processing circuitry, such as the processing circuitry 603 shown in Fig. 10.

[00053] Fig. 12 is a flowchart illustrating an example of a method implemented in a communication system, in accordance with one embodiment. The

communication system includes a first communication node and a second communication node which may be those described with reference to Figures 10 and 11. For simplicity of the present disclosure, only drawing references to

Figure 12 will be included in this section. In a first step 302 of the method, the system checks whether the first communication node and the second

communication node have the same OFDM numerology, such as subcarrier spacing, symbol duration and cyclic extensions, etc., if yes, proceed to step 304. If no, the system sets the same OFDM numerology for the first and second communication nodes in step 303, the system in step 304, continues to check whether the communication between the first communication node and the second communication node is synchronized OFDM transmission in time and frequency. If it is synchronized, move to step 306. If no, synchronize the communication in time and frequency in step 305. In steps 306 and 307, the system will decide which subcarriers to be used and assign the communication direction to each decided subcarrier, the communication direction can be transmitting, or receiving, or both transmitting and receiving simultaneously, in some situations, the subcarriers can also be unused. Moving to step 308, now a new OFDM symbol can be

transmitted on the decided and assigned subcarriers. When the bandwidth demand is changed according to user’s instant demand, the system will switch in-band between different duplexing schemes, in which the duplexing schemes can be TDD, FDD and FDX. In this way, the in-band duplexing-mix can be adapted during runtime without causing interference between other users and independent traffic scheduling between the uplink and downlink is possible for each user.

[00054] Reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural and functional equivalents to the elements of the above-described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for an apparatus or method to address each and every problem sought to be solved by the presently described concept, for it to be encompassed hereby. In the exemplary figures, a broken line generally signifies that the feature within the broken line is optional.

[00055] Although the description above contains a plurality of specificities, these should not be construed as limiting the scope of the concept described herein but as merely providing illustrations of some exemplifying embodiments of the described concept. It will be appreciated that the scope of the presently described concept fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the presently described concept is accordingly not to be limited. Accordingly, many modifications, equivalents, and improvements may be included without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.