WO2013046023A1

WO2013046023A1 - Method and apparatus for transmitting demodulation reference signal in communication network

Info

Publication number: WO2013046023A1
Application number: PCT/IB2012/002169
Authority: WO
Inventors: Xiabo Zhang
Original assignee: Alcatel Lucent
Priority date: 2011-09-30
Filing date: 2012-09-21
Publication date: 2013-04-04
Also published as: TW201322709A; CN103037514A; TWI463851B; CN103037514B

Abstract

There is proposed in an embodiment of the invention a method of transmitting a DMRS in a base station. The method comprises the steps of: notifying a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof; mapping the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and transmitting the sub-frame over a downlink channel. The scrambled pseudorandom sequence is generated by multiplying a pseudorandom sequence C by a scrambling sequence V, wherein the scrambling sequence V is a row vector of a matrix II, and the matrix II c *n = 0 satisfies the equations of:, wherein II is a conjugate II * II = α.I transpose of II, I is an identity matrix, and a is a constant. The improved group of DMRS orthogonal sequences according to the invention can be orthogonal to a group of DMRS orthogonal sequences in an existing system and can support a larger number of orthogonal DMRS antenna ports.

Description

Method and Apparatus for Transmitting Demodulation Reference Signal in Communication Network

Field of the invention

The present disclosure relates to the field of wireless communications and particularly to a method and apparatus for transmitting a demodulation reference signal in a communication network.

Background of the invention

The demodulation Reference Signal (DMRS) is included in the LTE frame structure. For the downlink channel, DMRS reflects quality information, about a channel being used, transmitted from a specific base station (eNB) to a User Equipment (UE) served by the eNB. DMRS can be used for the UE to estimate the instant channel to thereby demodulate data in the downlink frame.

For the design of DMRS, a Walsh code, a Golden sequence, a PN code and other traditional sequences are typically used in the prior art, or a variety of sequences designed specifically for mobile communication, e.g., a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence, a Zadoff-Chu sequence, etc., can further be introduced. Generally, the solution adopted in the prior art is to map a specific type of orthogonal sequence onto a location of a specific resource element, in a sub-frame over the downlink channel, used for the antenna to transmit the reference signal.

Summary of the invention

According to some studies, the inventors have recognized that, in the existing LTE frame structure, a fixed length in the time domain at a fixed location of the frame structure is often occupied by DMRSs in the form of a Walsh code, that is, there is a fixed density of DMRSs in the frame structure in the prior art. This results in a significant drawback of the existing DMRS design solution in the LTE/LTE-A, particularly for some application scenarios where a large number of UEs are to be scheduled. The largest number of UEs scheduled by the eNB is also fixed due to the foregoing fixed density/length of downlink DMRSs presented in the downlink frame structure and thus can not be increased adaptively with a varying application scenario.

In view of the drawback of DMRS as identified above, it would be beneficial to the communication scenario under Rl l standard, particularly scenarios of CoMP, MU-MIMO, etc., with a large number of UEs to be scheduled, if such a solution of transmission of the DMRS in a wireless network can be proposed that an eNB can schedule a larger number of UEs over the existing channel resource while transmitting a downlink sub-frame and a DMRS therein to a UE with some compatibility with the DMRS in the prior art.

According to an embodiment of the invention, there is provided a method of transmitting a DMRS in a base station. The method comprises the steps of: notifying a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof; mapping the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and transmitting the sub-frame over a downlink channel.

Optionally the scrambled pseudorandom sequence is generated by the step of: - multiplying a pseudorandom sequence C by a scrambling sequence V to generate the scrambled pseudorandom sequence, wherein the scrambling sequence V is a row vector of a matrix Π , and the matrix Π satisfies the equations of: c*n = 0

Π *Π = Γ

wherein Π is a conjugate transpose of Π , / is an identity matrix, and a is a constant.

Optionally the length of the scrambling sequence V is 2^K with K being an integer and K>0.

According to another embodiment of the invention, there is provided a method of processing a DMRS in a user equipment. The method comprises the steps of: receiving from a base station configuration information of the bases station about a group of DRMS orthogonal sequences and indexes thereof, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and obtaining a configured DMRS in a sub-frame of a downlink channel according to the configuration information; and estimating the downlink channel based on the DMRS.

Optionally the scrambled pseudorandom sequence is generated by the step of: multiplying a pseudorandom sequence C by a scrambling sequence V to generate the scrambled pseudorandom sequence, wherein the scrambling sequence V is a row vector of a matrix Π , and the matrix Π satisfies the equations of:

c*n = 0

n *n = -V

According to still another embodiment of the invention, there is provided an apparatus for transmitting a DMRS in a base station. The apparatus comprises: a notifying unit configured to notify a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof; a mapping unit configured to map the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and a transmitting unit configured to transmit the sub-frame over a downlink channel.

According to a further embodiment of the invention, there is provided an apparatus for processing a DMRS in a user equipment. The apparatus comprises: a receiving unit configured to receive from a base station configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; an obtaining unit configured to obtain a configured DMRS in a sub-frame of a downlink channel according to the configuration information; and an estimating unit configured to estimate the downlink channel based on the DMRS.

The improved group of DMRS orthogonal sequences according to the embodiments of the invention can be orthogonal to a group of DMRS orthogonal sequences in the Release 10 and can support a larger number of orthogonal DMRS antenna ports.

Brief description of drawings

The foregoing and other features of the invention will become more apparent from the foregoing detailed description of embodiments illustrated with reference to the drawings in which identical reference numerals denote identical or like components:

Fig.l illustrates a schematic diagram of configuration of a DMRS in a sub-frame according to an embodiment of the invention;

Fig.2 illustrates a flow chart of a method of transmitting a demodulation reference signal according to an embodiment of the invention;

Fig.3 illustrates a flow chart of a method of processing a demodulation reference signal according to an embodiment of the invention; and Fig.4 illustrates a schematic diagram of configuration of a DMRS in a sub-frame according to another embodiment of the invention.

Detailed description of embodiments

Fig.l illustrates a schematic diagram of configuration of a DMRS in a sub-frame in some embodiments of the invention. The square matrix of 12 rows by 14 columns in the figure represents an elementary transmission element of the downlink channel between a base station and a UE, i.e., a pair of Physical Resouce Blocks (PRBs). Moreover the elementary transmission element is referred to as a sub-frame in this context for the sake of conciseness.

Fig.2 illustrates a flow chart of a method of transmitting a demodulation reference signal according to an embodiment of the invention and will be described below in combination with Fig.l . As illustrated, the method can be applicable to a base station (not illustrated) and includes a configuration information notifying step SI 01 , a group of DMRS orthogonal sequences mapping step SI 02 and a sub-frame transmitting step S I 03.

In the step SI 01 , the base station notifies the user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof, for example, via a specific signaling.

In the step S I 02, the base station maps the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, for example, to an area represented by the shadowed section in Fig.l .

Where the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence. The first group of orthogonal sequences can be a group of Walsh sequences, for example. The pseudorandom sequence can be a Golden sequence, for example.

Specifically a Golden sequence C can be multiplied by a scrambling sequence V to generate the scrambled pseudorandom sequence D.

In an example, it is assumed that there are a Golden sequence C=[cl c2 c3] and a pseudorandom sequence V=[vl v2 v3], then the scrambled pseudorandom sequence D=[cl *vl c2*v2 c3*v3].

The scrambling sequence V can be obtained in the following way:

It is assumed that all of qualified scrambling sequences V constitute a matrix II which shall satisfy the following condition:

Where Π is a conjugate transpose of Π , / is an identity matrix, and a is a constant.

Since the sequence C is a 3x1 vector, two scrambling sequences V will satisfy the foregoing equation. In an example,

Π for example. The first and second

rows in the matrix II can act as two qualified scrambling sequences respectively.

Since the scrambled pseudorandom sequence D=[cl *vl c2*v2 c3*v3] is orthogonal to the Golden sequence C=[cl c2 c3], a group of DMRS orthogonal sequences generated by performing an OCC operation in the time domain with the scrambled pseudorandom sequence D in the embodiment of the invention is orthogonal to a group of DMRS orthogonal sequences generated by performing an OCC operation in the time domain with the pseudorandom sequence C in the prior art. Therefore the improved group of DMRS orthogonal sequences of the invention can be orthogonal to the group of DMRS orthogonal sequences in the Release 10 and can support a large number of orthogonal DMRS radio ports.

Finally the base station transmits the foregoing sub-frame over a downlink channel in the step S 103.

It shall be noted the step S101 and the step S 102 may not necessarily be performed in a required order, that is, the base station can firstly perform S I 02 and then perform SI 02. The invention will not be limited to a specific order in which the steps are performed.

Fig.3 illustrates a flow chart of a method of processing a demodulation reference signal according to an embodiment of the invention. In correspondence to the foregoing transmitting step at the base station side, the method of processing a demodulation reference signal in the user equipment illustrated in Fig.3 includes a configuration information obtaining step S201 , a DMRS obtaining step S202 and a downlink channel estimating step S203.

In the step S201 , the UE receives from the base station configuration information of the bases station about a group of DRMS orthogonal sequences and indexes thereof, for example, via a specific signaling, where the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence. The first group of orthogonal sequences can be a group of Walsh sequences, for example. The pseudorandom sequence can be a Golden sequence, for example.

In the step S202, the UE obtains the configured DMRS in a sub-frame of the downlink channel according to the configuration information.

In the step S203, the UE estimates the downlink channel based on the configured DMRS.

It shall be noted the step S201 and the step S202 may not necessarily be performed in a required order, that is, the UE can firstly perform S202 and then perform S202. The invention will not be limited to a specific order in which the steps are performed.

Since the scrambling sequence V obtained according to the foregoing embodiment of the invention is not composed of binary elements, the generated DMRS can not ensure QPSK modulation. In view of the foregoing concern, a plurality of pairs of Physical Resource Blocks (PRBs) can be bundled together and grouped for scrambling with each group including PRBs, the number of which is an integer times of 2, as illustrated in Fig.4. In Fig.4, for example, the length of the scrambling sequence V is selected as 2, and thus elements in the qualified scrambling sequence V can be ensured to be binary.

Of course, Fig.4 illustrates merely an embodiment, and any number of pairs of physical resource blocks can be bundled together in a practical application as long as the length of the scrambling sequence V satisfies 2^K with K being an integer and K>0.

The technical solution of the invention has been described above from the perspective of the method and will be further described from the perspective of the apparatus.

According to an embodiment of the invention, there is provided an apparatus for transmitting a DMRS in a base station. The apparatus comprises: a notifying unit configured to notify a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof; a mapping unit configured to map the group of DRMS orthogonal sequences to a group of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and a transmitting unit configured to transmit the sub-frame over a downlink channel.

Optionally the mapping unit further comprises: a generating unit configured to multiply a pseudorandom sequence C by a scrambling sequence V to generate the scrambled pseudorandom sequence, wherein the scrambling sequence V is a row vector of a matrix Π , and the matrix Π satisfies the equations of:

c*n = 0

Π *Π = -V

Optionally the first group of orthogonal sequences is a group of Walsh sequences, and the pseudorandom sequence is a Golden sequence.

According to another embodiment of the invention, there is provided an apparatus for processing a DMRS in a user equipment. The apparatus comprises: a receiving unit configured to receive from a base station configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; an obtaining unit configured to obtain a configured DMRS in a sub-frame of a downlink channel according to the configuration information; and an estimating unit configured to estimate the downlink channel based on the DMRS.

Moreover the embodiments of the invention can be embodied in software, hardware or combination of software and hardware. The part of hardware can be embodied in a dedicated logic, and the part of software can be stored in a memory and performed by an appropriate instruction execution system, for example, a microprocessor or specially designed hardware. Those ordinarily skilled in the art can appreciate the foregoing methods and systems can be embodied in computer executable instructions or included in processor control codes, for example, such codes are carried in a carrier medium, e.g., a magnetic disk, a CD or a DVD-ROM, a programmable memory, e.g., a read only memory (firmware), or a data carrier, e.g., an optical or electronic signal carrier. The systems and the components thereof of the embodiments can be embodied in, for example, a very large scale integrated circuit or a gate array, a semiconductor, e.g., a logic chip, a transistor, etc., or a programmable hardware device, e.g., a field programmable gate array, a programmable logic device, etc., in software performed by variety of processor or in combination of the foregoing hardware circuit and software, e.g., in firmware.

Although the invention has been described in connection with the embodiments conceived so far, it shall be appreciated that the invention will not be limited to the disclosed embodiments. On the contrary, the invention is intended to encompass various modifications and equivalent arrangements falling into the sprit and scope of the appended claims. The appended claims shall be accorded the broadcast interpretations so as to encompass all these modifications as well as equivalent structures and functions.

Claims

1. A method of transmitting a DMRS in a base station, the method comprising the steps of:

- notifying a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof;

- mapping the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and

- transmitting the sub-frame over a downlink channel.

2. The method according to claim 1 , wherein the scrambled pseudorandom sequence is generated by the step of:

- multiplying a pseudorandom sequence C by a scrambling sequence V to generate the scrambled pseudorandom sequence,

wherein the scrambling sequence V is a row vector of a matrix Π , and the matrix Π satisfies the equations of:

c*n = 0

n *n = -V

3. The method according to claim 1 , wherein the length of the scrambling sequence V is 2^K with K being an integer and K>0.

4. The method according to claim 1, wherein the first group of orthogonal sequences is a group of Walsh sequences.

5. The method according to claim 1 , wherein the pseudorandom sequence is a Golden sequence.

6. A method of processing a DMRS in a user equipment, the method comprising the steps of:

- receiving from a base station configuration information of the bases station about a group of DRMS orthogonal sequences and indexes thereof, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and

- obtaining a configured DMRS in a sub-frame of a downlink channel according to the configuration information; and

- estimating the downlink channel based on the DMRS.

7. The method according to claim 6, wherein the scrambled pseudorandom sequence is generated by the step of:

c*n = 0

n *n = -V

8. The method according to claim 6, wherein the length of the scrambling sequence V is 2^K with K being an integer and K>0.

9. The method according to claim 6, wherein the first group of orthogonal sequences is a group of Walsh sequences, and the pseudorandom sequence is a Golden sequence.

10. An apparatus for transmitting a DMRS in a base station, the apparatus comprising:

a notifying unit configured to notify a user equipment of configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof;

a mapping unit configured to map the group of DRMS orthogonal sequences to a set of resource elements in a sub-frame, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence; and

a transmitting unit configured to transmit the sub-frame over a downlink channel.

11. The apparatus according to claim 10, wherein the mapping unit further comprises:

a generating unit configured to multiply a pseudorandom sequence C by a scrambling sequence V to generate the scrambled pseudorandom sequence,

c*n = 0

n *n = -V

12. The apparatus according to claim 10, wherein the length of the scrambling sequence V is 2^K with K being an integer and K>0.

13. An apparatus for processing a DMRS in a user equipment, the apparatus comprising:

a receiving unit configured to receive from a base station configuration information of the base station about a group of DRMS orthogonal sequences and indexes thereof, wherein the group of DRMS orthogonal sequences is generated from a first group of orthogonal sequences and a scrambled pseudorandom sequence;

an obtaining unit configured to obtain a configured DMRS in a sub-frame of a downlink channel according to the configuration information; and

an estimating unit configured to estimate the downlink channel based on the DMRS.

14. The apparatus according to claim 13, wherein the scrambled pseudorandom sequence is generated by multiplying a pseudorandom sequence C by a scrambling sequence V,

wherein the scrambling sequence V is a row vector of a matrix Π , and the matrix Π satisfies the equations of: c*n = 0

Π *Π = Γ

15. The apparatus according to claim 13, wherein the length of the scrambling sequence V is 2^K with K being an integer and K>0.