CN102595488A - Channel direction information feedback method and equipment thereof - Google Patents

Abstract

Disclosed is a channel direction information feedback method and equipment thereof. According to the method, a base station determines the respective codebook size of each of channel quality based on quality of each channel in a plurality of mobile terminals served by the base station; the base station transmits resources to each of the mobile terminals based on the determined codebook sizes; the base station informs each of the mobile terminals of the codebook sizes and the transmission resources which correspond to the mobile terminals; each of the mobile terminals selects a corresponding sub-codebook in basic codebooks based on the corresponding codebook sizes; each of the mobile terminals uses the corresponding transmission resources to feed back channel direction information based on the determined sub-codebooks; and the basic codebooks are shared by the mobile terminals and the station. According to the technical scheme, the method improves system average throughput under the condition that feedback expense is not increased.

Description

Channel direction information feedback method and equipment thereof

Technical Field

The embodiment of the invention relates to the field of communication, in particular to a channel direction information feedback method and a device thereof.

Background

As is well known, multi-user multiple input multiple output (MU-MIMO) technology has been considered as a key enabling technology to meet the rapidly increasing demand for high data rates in wireless communications, due to advantages in improving average cell throughput. While MU-MIMO offers many advantages over single-user multiple-input multiple-output (SU-MIMO), it also presents more challenges in applications because MU-MIMO is much more sensitive to Channel State Information (CSIT) inaccuracies at the transmitter.

Codebook-based feedback is widely adopted today in Time Division Duplex (TDD) and Frequency Division Duplex (FDD) modes as a means of CSIT acquisition. CSIT errors due to the limited codebook size will significantly degrade the throughput of MU-MIMO. More seriously, with a fixed codebook size, the throughput loss rises with the signal-to-noise ratio (SNR), resulting in a flat throughput versus SNR curve at high SNR for MU-MIMO. When users with different path losses are served simultaneously via MU-MIMO, users with better channel conditions will suffer more throughput loss, which greatly compromises the average throughput of the system, since users with better channel conditions should contribute more to the average throughput.

Therefore, there is a need for a channel direction information feedback method such that an increase in average throughput can be maintained as the received SNR increases.

Disclosure of Invention

The embodiment of the invention provides a channel direction information feedback method and equipment thereof, aiming at solving the problems.

According to an aspect of the present invention, there is provided a base station, comprising: a codebook size determining unit for determining its respective codebook size based on the channel quality of each of the served plurality of mobile terminals; a resource allocation unit for allocating transmission resources to each of the plurality of mobile terminals according to the determined codebook size; and a base transceiver unit for informing each of the plurality of mobile terminals of its corresponding codebook size and transmission resource.

According to another aspect of the present invention, there is provided a mobile terminal including: a terminal sub-codebook determining unit, configured to select a sub-codebook corresponding to a mobile terminal from a basic codebook based on a codebook size determined by a serving base station according to a channel quality of the mobile terminal, where the basic codebook is a codebook shared by a plurality of mobile terminals including the mobile terminal and the serving base station; and a feedback unit, configured to feedback the channel direction information by using the transmission resource allocated by the serving base station according to the determined codebook size according to the determined sub-codebook.

According to another aspect of the present invention, a method for feeding back channel direction information is provided, including: the base station determines its respective codebook size based on the channel quality of each of the served mobile terminals; the base station allocates transmission resources to each of the plurality of mobile terminals according to the determined codebook size; the base station informs each of the plurality of mobile terminals of the size of the codebook and the transmission resource corresponding to the mobile terminal; each of the plurality of mobile terminals selects a corresponding sub-codebook from the basic codebook according to the size of the corresponding codebook; and each of the plurality of mobile terminals feeds back channel direction information by using the corresponding transmission resource according to the determined sub-codebook, wherein the basic codebook is a codebook shared by the plurality of mobile terminals and the base station.

According to yet another aspect of the present invention, a communication system is proposed, comprising the above-mentioned base station and mobile terminal.

The above technical solution makes a good compromise between performance and overhead, so that the average throughput can be improved without increasing the feedback overhead. Since the channel quality varies much slower than the channel direction information, the codebook size for each user can be updated at a much lower rate, and thus the additional signaling overhead is very limited.

Drawings

The invention may be better understood by describing in detail embodiments of the invention with reference to the accompanying drawings, in which:

fig. 1 shows a schematic diagram of a communication system according to an embodiment of the invention;

FIG. 2 shows a schematic block diagram of a base station according to an embodiment of the invention;

FIG. 3 shows a schematic block diagram of a mobile terminal according to an embodiment of the invention;

FIG. 4 shows a flow diagram of a feedback method according to an embodiment of the invention;

fig. 5 shows an effect diagram of a simulation of the method of fig. 4.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

In the following detailed description of the preferred embodiments of the present invention, reference is made to the accompanying drawings, in which details and functions that are not necessary for the invention are omitted so as not to obscure the understanding of the present invention.

An embodiment of the present invention proposes a communication system including a Base Station (BS) and a mobile terminal (MS) described below. Fig. 1 shows a schematic diagram of such a communication system. It should be noted that although only one base station and three mobile terminals (MS1, MS2, and MS3) are shown in fig. 1 for simplicity, more base stations and more mobile terminals may be included in an actual networking. It should also be noted that a base station herein generally refers to any device capable of performing the functions of the base station described below, such as a node b (node b), an enhanced node b (enb), a Base Station (BS), etc., and a mobile terminal herein also generally refers to any device capable of performing the functions of a mobile terminal described below, such as a Mobile Station (MS), a User Equipment (UE), or other portable mobile devices that serve similar functions.

An embodiment of the present invention further provides a base station, as shown in fig. 2, the base station includes a codebook size determining unit 230 configured to determine a corresponding codebook size for each mobile terminal according to a channel quality of the mobile terminal, and a resource allocating unit 240 configured to allocate a corresponding feedback resource to each mobile terminal according to the determined codebook size. In this way, the mobile terminal can determine a sub-codebook using the determined codebook size, and feed back channel direction information using the allocated feedback resource according to the determined sub-codebook, wherein the sub-codebook is a subset of the basic codebook shared by the mobile terminal and the base station.

The base station further comprises a base station sub-codebook determining unit 250 for selecting respective sub-codebooks from the base codebook for respective mobile terminals according to the determined codebook sizes.

The base station further comprises abase transceiver unit 210 for receiving from each mobile terminal an indication of the channel quality of the mobile terminal (e.g. a channel quality indicator) and informing the corresponding mobile terminal of the determined codebook size and the allocated feedback resources. Preferably, the notification is made by means of signalling. Thebase transceiver unit 210 includes various components for Radio Frequency (RF) processing and baseband processing, which are well known to those skilled in the art and will not be described herein for brevity.

The base station further comprises a basestation storing unit 220 for storing indications of the channel quality of the respective mobile terminals received by thebase transceiver unit 210 for use by the codebook size determining unit 230. The basestation storage unit 220 may also be used to store various data and variables required in the processing by the codebook size determining unit 230, the resource allocating unit 240, and the base station sub-codebook determining unit 250. Those skilled in the art will be able to implement the basestation storage unit 220 as various non-volatile memories, buffers, or combinations thereof without departing from the principles and spirit of the invention.

An embodiment of the present invention further provides a mobile terminal, as shown in fig. 3, where the mobile terminal includes a terminal sub-codebook determining unit 320, configured to select a sub-codebook from a basic codebook according to the codebook size determined by the base station in the above-mentioned manner, where the sub-codebook is a subset of the basic codebook shared by the mobile terminal and the base station. A feedback unit 330, configured to feedback the channel direction information according to the sub-codebook by using the feedback resource allocated by the base station according to the determined codebook size.

The mobile terminal further includes aterminal transceiving unit 310 for receiving the codebook size and the allocated feedback resource determined for the mobile terminal from the base station. Theterminal transceiver unit 310 is also arranged to send an indication of the channel quality of the mobile terminal to the base station. Similar to thebase transceiver unit 210, theterminal transceiver unit 310 includes various components for Radio Frequency (RF) processing and baseband processing, which are not described again here.

The mobile terminal also includes a terminal storage unit 340. The terminal storage unit 340 is used for storing various data and variables required in the processing by the terminal sub-codebook determining unit 320 and the feedback unit 330. As such, those skilled in the art will be able to implement the terminal storage unit 340 as various non-volatile memories, buffers, or combinations thereof, without departing from the principles and spirit of the invention.

Although the base station and the mobile terminal of the embodiment of the present invention are described above in the form of separate functional modules, each component shown in fig. 2 and 3 may be implemented by a plurality of devices in practical applications, and the plurality of components shown may be integrated in one chip or one device in practical applications. For example, the codebook size determining unit 230 and the resource allocating unit 240 in the base station may be implemented using a single processor, for example. The base station and the mobile terminal may also comprise any units and means for other purposes.

The base station and the mobile terminal are explained in more detail below with reference to fig. 4.

Fig. 4 is a flow chart of a feedback method according to an embodiment of the present invention. As shown in fig. 4, in step 401, codebook size determining unit 230 in the base station determines its respective codebook size for the channel quality of each MS.

Capacity analysis

Considering a MU-MIMO system in which k users share the same wireless resource via zero-forcing (ZF) multi-user precoding, N is used separately_TAnd N_RTo indicate the number of transmit antennas per BS and the number of receive antennas per MS. It should be noted that in MU-MIMO systemsK may each be equipped with N_RUser of root antenna is regarded as K.N_RA single antenna user. Thus, only N will be considered below_R1, and assume that K is N_T。

Use of h_kTo represent a channel vector between the BS and the kth MS. With ideal CSIT, a precoding vector p for each user (e.g., the k-th user) is selected_kSo as to make a connection toIs provided with

In case of feedback limitation, h is used_kQuantized version of

As CSIT, and selects a precoding vector q for each user (e.g., kth user)_kSo as to make a pair

Is provided with

The difference between the average per MS capacity in the case of ideal CSIT and the average per MS capacity with limited feedback can be calculated for each user (e.g., the kth user) as follows:

<math> <mrow> <msub> <mi>&Delta;C</mi> <mi>k</mi> </msub> <mo>=</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>p</mi> <mi>k</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mrow> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <mi>k</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> </mrow> <mrow> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msub> <mi>&Sigma;</mi> <mrow> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> </msub> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>)</mo> </mrow> </mrow></math>

<math> <mrow> <mo>=</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>p</mi> <mi>k</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <mi>k</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msub> <mi>&Sigma;</mi> <mrow> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> </msub> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>+</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msub> <mi>&Sigma;</mi> <mrow> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> </msub> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> </mrow></math>

<math> <mrow> <mo>&le;</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msub> <mi>&Sigma;</mi> <mrow> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> </msub> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mi>q</mi> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> </mrow></math>

<math> <mrow> <mo>&le;</mo> <mi>E</mi> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>P</mi> <mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <msub> <mi>N</mi> <mi>T</mi> </msub> </mrow> </mfrac> <msub> <mi>&Sigma;</mi> <mrow> <msup> <mi>k</mi> <mo>&prime;</mo> </msup> <mo>&NotEqual;</mo> <mi>k</mi> </mrow> </msub> <mrow> <mo>(</mo> <msup> <mrow> <mo>|</mo> <mo>|</mo> <msub> <mi>h</mi> <mi>k</mi> </msub> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>-</mo> <msup> <mrow> <mo>|</mo> <msubsup> <mi>h</mi> <mi>k</mi> <mi>H</mi> </msubsup> <msub> <mover> <mi>h</mi> <mo>^</mo> </mover> <mi>k</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>)</mo> </mrow> </mrow></math>

<math> <mrow> <mo>&le;</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mrow> <msub> <mi>&alpha;</mi> <mi>k</mi> </msub> <mi>P</mi> </mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> </mfrac> <mrow> <mo>(</mo> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mover> <mi>D</mi> <mo>&OverBar;</mo> </mover> <mi>k</mi> </msub> <mo>)</mo> </mrow> </mrow></math>

$...\left(1\right)$

where, P represents the total transmit power,

is the average interference noise power of the kth user,α_kis the long-term fading coefficient of the k-th user, an

Is D_kIs calculated from the expected value of (c). Equation (2) shows quantizationError of the measurement

The upper limit of (2):

<math> <mrow> <msub> <mover> <mi>D</mi> <mo>&OverBar;</mo> </mover> <mi>k</mi> </msub> <mo>&le;</mo> <msup> <mn>2</mn> <mrow> <mo>-</mo> <mfrac> <msub> <mi>B</mi> <mi>k</mi> </msub> <mrow> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </msup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow></math>

wherein, B_kThe inference process of equation (2) is well known to those skilled in the art and will not be described herein. Bringing (2) into (1) to obtain formula (3)

<math> <mrow> <msub> <mi>&Delta;C</mi> <mi>k</mi> </msub> <msub> <mrow> <mo>&le;</mo> <mi>log</mi> </mrow> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mrow> <msub> <mi>&alpha;</mi> <mi>k</mi> </msub> <mi>P</mi> </mrow> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> </mfrac> <mrow> <mo>(</mo> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <msup> <mn>2</mn> <mrow> <mo>-</mo> <mfrac> <msub> <mi>B</mi> <mi>k</mi> </msub> <mrow> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </msup> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow></math>

Or equivalently

<math> <mrow> <msub> <mi>B</mi> <mi>k</mi> </msub> <mo>&ap;</mo> <mrow> <mo>(</mo> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mrow> <mo>(</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>&alpha;</mi> <mi>k</mi> </msub> <mi>P</mi> <mo>/</mo> <msubsup> <mi>&sigma;</mi> <mi>k</mi> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>N</mi> <mi>T</mi> </msub> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>log</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msup> <mn>2</mn> <msub> <mi>&Delta;C</mi> <mi>k</mi> </msub> </msup> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow></math>

Wherein, B_kIs that user k maintains a constant capacity loss Δ C to the capacity available using ideal CSIT_kNumber of feedback bits required, P transmission power, N_TIs the number of transmit antennas, alpha, at the Base Station (BS)_kIs a long-term fading coefficient for user k, and,

is the average interference noise power of user k.

It can be seen from equation (3) that with a fixed codebook size, users with better channel quality (i.e., with greater effective received SINR (e.g.,

) Users) will suffer more capacity loss, which greatly impairs the average throughput, since these users should contribute more to the average throughput.

In order to maintain a constant capacity loss for each user (so that the total capacity can be kept at a constant interval from the ideal capacity as the SNR increases), the SNR is received efficientlyIncrease of (2), codebook size

Should increase linearly, this means that the BS needs to adjust the codebook size for each user according to its channel quality.

In an embodiment of the present invention, the size of the codebook may be automatically adjusted for each user according to its channel quality.

First, the BS and the MS should share one large codebook, called the basic codebook.

Ideally, the size of the base codebook should be large enough to meet the requirements of the user with the best channel quality. But in some cases this value may be too large to be achieved, so in practice a smaller base codebook size is used to trade off between overhead and performance.

The codebook size determining unit 230 in the BS estimates a codebook size required for each user according to the above formula based on the channel quality of each user.

Assume that the BS and MS share a size of

Is represented as a basic codebookWherein, c_mIs N_TUnit norm vector of x 1. Assume that the minimum codebook size is

This means that for the user with the worst channel conditions (i.e., the user at the cell edge, such as MS1), a size of

And for users with better channel quality (e.g., MS 2), a larger codebook size will be used. An effective received signal-to-interference-and-noise ratio (SINR) (denoted as ρ) for cell edge users is assumed₀) Approximately 0 dB. SINR is p for effective reception_kThe preferred number of feedback bits, which is derived from equation (4), is:

wherein,represents the smallest integer no less than x, the preferred codebook size for this user is

Preferably, the codebook size determining unit 230 of the BS may determine a preferred codebook size for each user (e.g., kth) according to equation (5) based on a Channel Quality Indicator (CQI) reported by each user, where the Channel Quality Indicator (CQI) is ρ_kA quantized version of (a). The CQI may be received by thebase transceiver unit 210 and stored in the basestation storage unit 220.

Instep 420, the resource allocation unit 240 of the BS should adjust the feedback resources allocated for each user accordingly.

Each MS should be allocated feedback resources correspondingly based on the codebook size selected for each MS. Assuming that one feedback channel can accommodate a maximum of N information bits, the BS must allocate the kth user

A strip feedback channel.

Instep 430, each user is notified of the codebook size and the allocated feedback resources via thebase transceiver unit 210.

Once codebook size B has been selected for the kth user_kThe BS needs to inform the kth user of this information. Signaling may be used for this purpose. It should be noted that ρ_kIs long-term channel information and changes much more slowly than short-term channel direction information. Thus, B_kAlso changes slowly and updates at a much slower rate. Therefore, in the technical solution proposed in the embodiment of the present invention, the overhead of the additional signal is relatively low.

Instep 440, the terminal sub-codebook determining unit 320 in the mobile terminal selects an appropriate subset from the basic codebook according to the codebook size allocated thereto received by theterminal transceiver unit 310 in a manner previously determined with the base station.

The size of the base codebook is denoted as M and the codebook size for a particular user is denoted as N. It should be noted that M should always be a multiple of N. The user may select one codeword from every M/N consecutive codewords in the base codebook to form a subset of size N. Preferably, the selection starts with the first codeword.

For example, when the MS is informed by the BS of the preferred codebook size B_kThen, the size is selected from the basic codebook according to a predetermined mode

A subset of (a). For example, as shown below, the MS may be configured per-bit in the base codebookOne codeword is selected from among a number of consecutive codewords, and then the selected codewords are illustratively sequentially arranged to form a codebook for the MS:

<math> <mrow> <msub> <mi>C</mi> <mi>sub</mi> </msub> <mo>=</mo> <mo>{</mo> <msub> <mi>c</mi> <mi>m</mi> </msub> <mo>,</mo> <mi>m</mi> <mo>=</mo> <mi>i</mi> <mo>+</mo> <msup> <mn>2</mn> <mrow> <msub> <mi>B</mi> <mi>max</mi> </msub> <mo>-</mo> <msub> <mi>B</mi> <mi>k</mi> </msub> </mrow> </msup> <mi>j</mi> <mo>|</mo> <mn>1</mn> <mo>&le;</mo> <mi>i</mi> <mo>&le;</mo> <msup> <mn>2</mn> <mrow> <msub> <mi>B</mi> <mi>max</mi> </msub> <mo>-</mo> <msub> <mi>B</mi> <mi>k</mi> </msub> </mrow> </msup> <mo>,</mo> <mi>j</mi> <mo>=</mo> <mn>0</mn> <mo>~</mo> <msup> <mn>2</mn> <msub> <mi>B</mi> <mi>k</mi> </msub> </msup> <mo>-</mo> <mn>1</mn> <mo>}</mo> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow></math>

where i is predetermined and known to the BS and MS and j indicates that this is j codewords in the codebook space (i.e., sub-codebook) used by the MS.

It should be noted that the base station may also select the sub-codebook for each user based on the same manner as the mobile terminal processes instep 440, so as to recover the channel direction information of the user from the information fed back by the user using the sub-codebook. This step may be performed after determining the sub-codebook size for each user instep 410. The sub-codebook determination in the base station may be a separate sub-codebook determination unit (e.g., the base station sub-codebook determination unit 250), or may be the codebook size determination unit 230 or other suitable unit.

Subsequently, instep 450, the feedback unit 330 in the MS feeds back channel direction information using the transmission resources allocated by the base station according to the determined sub-codebook.

In the above-described steps, various data and variables required in the processes of the terminal sub-codebook determining unit 320 and the feedback unit 330 may be stored in the terminal storage unit 340.

Compared to existing solutions (e.g., MU-MIMO with a fixed codebook size), the proposed techniques can achieve higher overall throughput with the same or less total feedback overhead. The advantages of the solution proposed by the embodiments of the present invention will be demonstrated by means of simulations in the following.

Fig. 5 shows a performance diagram of a solution according to an embodiment of the invention. Assume that a MU-MIMO system has 4 transmit antennas and 1 receive antenna (i.e., N)_T＝4，N_R1) and the same asThe number of users served at the same time isk 4. And supposing that the effective receiving SINRs of different users are respectively rho₁＝ρ₂＝10ρ₃＝10ρ₄，B_maxIs sufficiently large. For the prior art (scheme 1) with fixed codebook size, B is chosen₁＝B₂＝B₃＝B₄9 bits. Aiming at the technical scheme (scheme 2) provided by the embodiment of the invention, B is selected₃＝B₄4 bits and selected according to equation (5)A bit. It can be seen that scheme 1 has the same total feedback load asscheme 2. As can be seen from fig. 5, the curve ofscheme 2 is closer to the curve in the ideal CSIT case, and as the reception SNR increases,scheme 2 can obtain a higher capacity than scheme 1, for example, at a reception SNR of 10dB, the capacity ofscheme 2 is higher than scheme 1 by about 0.5bps/Hz, and when the reception SNR increases to 20dB, the capacity ofscheme 2 is higher than scheme 1 by more than 1 bps/Hz.

It can therefore be seen that the solution proposed by the embodiments of the present invention provides a good compromise between performance and overhead, and can improve the average throughput without increasing the feedback overhead, compared to the prior art solutions. Since the channel quality varies much slower than the short-term channel information, the additional signaling overhead is very limited, and therefore the codebook size for each user can be updated at a much lower rate.

Those skilled in the art will readily recognize that the different steps of the above-described method may be implemented by programming a computer. Herein, some embodiments also include a machine-readable or computer-readable program storage device (e.g., a digital data storage medium) and encoding a machine-executable or computer-executable program of instructions, wherein the instructions perform some or all of the steps of the above-described method. For example, the program storage device may be digital memory, magnetic storage media (such as magnetic disks and tapes), hardware, or optically readable digital data storage media. Embodiments also include a programmed computer performing the steps of the above-described method.

The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples mentioned herein are explicitly primarily for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically mentioned examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

The above description is only for implementing the embodiments of the present invention, and those skilled in the art will understand that any modification or partial replacement without departing from the scope of the present invention shall fall within the scope defined by the claims of the present invention, and therefore, the scope of the present invention shall be subject to the protection scope of the claims.

Claims (15)

1. A base station, comprising:

a codebook size determining unit for determining its respective codebook size based on the channel quality of each of the served plurality of mobile terminals;

a resource allocation unit for allocating transmission resources to each of the plurality of mobile terminals according to the determined codebook size; and

and the base transceiver unit is used for informing each of the plurality of mobile terminals of the codebook size and the transmission resource corresponding to the mobile terminal.

2. The base station of claim 1, further comprising:

a base station sub-codebook determining unit, configured to select, based on the determined codebook size, a codebook corresponding to each of the plurality of mobile terminals from a basic codebook, where the basic codebook is a codebook shared by the plurality of mobile terminals and the base station.

3. The base station according to claim 1 or 2, wherein the codebook size determining unit determines the codebook size for each of a plurality of mobile terminals by:

allocating a minimum codebook size to a mobile terminal with the worst channel quality among the plurality of mobile terminals;

using the mobile terminal with the worst channel quality as the reference for comparison, and allocating the feedback bit number for other mobile terminals in the plurality of mobile terminals in linear relation with the logarithm of the channel signal-to-interference-and-noise ratio,

wherein the codebook size and the number of feedback bits have an exponential relationship of 2.

4. The base station according to claim 3, wherein the resource allocation unit allocates transmission resources for each of the plurality of mobile terminals by:

allocating a feedback channel to each of the plurality of mobile terminals so that the feedback bits respectively allocated to each of the plurality of mobile terminals can be all fed back.

5. The base station of claim 4, wherein the base transceiver unit informs each of the plurality of mobile terminals of its corresponding codebook size and transmission resources by:

signaling is used to inform each of the plurality of mobile terminals of its corresponding codebook size and transmission resources.

6. A mobile terminal, comprising:

a terminal sub-codebook determining unit, configured to select a sub-codebook corresponding to a mobile terminal from a basic codebook based on a codebook size determined by a serving base station according to a channel quality of the mobile terminal, where the basic codebook is a codebook shared by a plurality of mobile terminals including the mobile terminal and the serving base station; and

and a feedback unit, configured to feedback the channel direction information by using the transmission resource allocated by the serving base station according to the determined size of the codebook according to the determined sub-codebook.

7. The mobile terminal of claim 6, further comprising:

and the terminal transceiving unit is used for receiving the codebook size and the transmission resource and sending an indication of the channel quality to the service base station.

8. The mobile terminal according to claim 6 or 7, wherein the terminal sub-codebook determining unit selects a sub-codebook in the base codebook by:

dividing the base codebook space into a plurality of subspaces containing consecutive codewords, the number of the plurality of subspaces being equal to the size of the sub-codebook;

selecting a codeword from each of the plurality of subspaces in a predetermined order, sequentially composing the sub-codebook.

9. A channel direction information feedback method comprises the following steps:

the base station determines its respective codebook size based on the channel quality of each of the served mobile terminals;

the base station allocates transmission resources to each of the plurality of mobile terminals according to the determined codebook size;

the base station informs each of the plurality of mobile terminals of the size of the codebook and the transmission resource corresponding to the mobile terminal;

each of the plurality of mobile terminals selects a corresponding sub-codebook from the basic codebook according to the size of the corresponding codebook; and

each of the plurality of mobile terminals feeds back channel direction information using the corresponding transmission resource according to the determined sub-codebook,

wherein the basic codebook is a codebook shared by the plurality of mobile terminals and the base station.

10. The method of claim 9, wherein the determining a respective codebook size based on the channel quality of each of the plurality of mobile terminals comprises:

allocating a minimum codebook size to a mobile terminal with the worst channel quality among the plurality of mobile terminals;

using the mobile terminal with the worst channel quality as the reference for comparison, and allocating the feedback bit number for other mobile terminals in the plurality of mobile terminals in linear relation with the logarithm of the channel signal-to-interference-and-noise ratio,

wherein the codebook size and the number of feedback bits have an exponential relationship of 2.

11. The method of claim 9, the allocating transmission resources for each of the plurality of mobile terminals according to the determined codebook size comprising:

allocating a feedback channel to each of the plurality of mobile terminals so that the feedback bits respectively allocated to each of the plurality of mobile terminals can be all fed back.

12. The method of claim 9, wherein said informing each of the plurality of mobile terminals of its corresponding codebook size and transmission resources comprises:

signaling is used to inform each of the plurality of mobile terminals of its corresponding codebook size and transmission resources.

13. The method of claim 9, wherein the selecting the sub-codebook corresponding to the selected sub-codebook in the basic codebook according to the corresponding codebook size comprises:

dividing the base codebook space into a plurality of subspaces containing consecutive codewords, the number of the plurality of subspaces being equal to the size of the sub-codebook;

selecting a codeword from each of the plurality of subspaces in a predetermined order, sequentially composing the sub-codebook.

14. The method of claim 9, wherein a channel quality indicator is used as the indication of channel quality.

15. A communication system comprising a base station according to any of claims 1 to 5 and a mobile terminal according to any of claims 6 to 8.

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