CN108429611B - Pilot frequency distribution and channel estimation method under macro connection - Google Patents
Pilot frequency distribution and channel estimation method under macro connection Download PDFInfo
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Abstract
The invention provides a pilot frequency distribution and channel estimation method under macro connection, which comprises the following steps: the base station groups users; the base station distributes pilot frequency sequences for different user groups and informs the user of grouping information, pilot frequency sequence patterns and pilot frequency transmitting time slots; the user transmits uplink data and transmits a pilot frequency sequence in a corresponding time slot; and the base station estimates the channel of each user according to the pilot frequency information. The method of the invention uses the space characteristic of the user to group the users, and the users in the same group transmit the pilot frequency sequence in time in an interlaced way, thereby effectively reducing the pilot frequency interference among the users under the macro connection scene, improving the reliability of the channel estimation and further improving the transmission rate of the system. The pilot frequency distribution and channel estimation method provided by the invention is particularly suitable for the Laisi channel with direct path components.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and relates to a pilot frequency allocation and channel estimation method, in particular to a pilot frequency allocation and channel estimation method under macro connection.
Background
In a large-scale mimo wireless communication system, a base station configures a large number of antennas (several hundreds), and a user equipment configures a small number of antennas (several or 1). The massive multiple input multiple output technology is one of the key technologies in future mobile communication. Compared with the traditional multiple-input multiple-output wireless communication, the large-scale multiple-input multiple-output wireless communication system has remarkable advantages: 1. larger channel capacity to support high speed data transmission; 2. the method has narrower beams, and can realize interference-free transmission among multiple users through beam forming; 3. the large-scale antenna can enable the channel to be hardened, thereby reducing the influence caused by fast fading. To achieve the above advantages, a base station in a massive mimo system often needs to know downlink channel state information. In a time division duplex system, a base station performs channel estimation in an uplink transmission process. Based on reciprocity of uplink and downlink channels, the base station performs downlink precoding processing by using the channel obtained by uplink estimation, thereby obtaining the advantages of a large-scale multiple-input multiple-output technology. In a time division duplex system, an uplink channel and a downlink channel have reciprocity only within the same coherent time; coherent implementations are limited by channel variations and are often limited, so the time allocated for uplink pilot transmission is also limited. If each user is assigned a specific, mutually orthogonal pilot, the number of users that can be served by the base station will be limited within a fixed pilot time.
The macro connection is one of typical application scenarios of future mobile communication. In a macro-connection scenario, the base station will serve large-scale users, and it will be difficult to allocate specific, mutually orthogonal pilots to each user within the coherence time. Currently, an effective pilot allocation and channel estimation method for a macro-connection mobile communication scenario is still lacking.
Disclosure of Invention
In order to solve the above problems, the present invention provides an efficient pilot frequency allocation method according to the characteristics of user data services in a macro-connection wireless communication scenario, thereby achieving effective channel estimation and improving the transmission rate of the system.
In order to achieve the purpose, the invention provides the following technical scheme:
a pilot frequency distribution and channel estimation method under macro connection comprises the following steps:
the base station groups users;
according to the preset rule, the base station distributes pilot frequency sequences for different user groups and informs the user of the grouping information, the pilot frequency sequence mode and the time slot of pilot frequency transmission;
the user transmits uplink data and transmits a pilot frequency sequence in a corresponding time slot;
and the base station estimates the channel of each user according to the pilot frequency information.
Further, the step of estimating, by the base station, the channel of each user according to the pilot information specifically includes:
the base station carries out angle estimation; judging a pilot frequency mode and determining active users;
the base station determines the corresponding relation between the estimated arrival angle and the user and determines the direct path component;
the base station detects uplink data transmitted by a user;
and the base station estimates the indirect path component of the user channel and updates the channel estimation result.
Further, the method also comprises the following steps:
the base station detects the uplink data based on the updated channel estimation result;
and the base station performs downlink pre-coding transmission by using the result of the uplink channel estimation.
Further, the grouping modes include the following two modes: grouping according to the arrival angle information of the users, and grouping the users with similar arrival angle information into a group; and grouping according to the physical positions of the users, and grouping the users with similar physical positions into a group.
Further, users of the same group use the same pilot sequence or use different pilot sequences.
Further, users in the group transmit pilots using staggered time slots, thereby reducing interference between pilots. When pilot transmission is performed using staggered slots, the number of users per group is limited by the coherence time.
Further, the user determines whether to transmit data according to the state of the user.
Further, the step of determining the corresponding relationship between the estimated angle of arrival and the user by the base station, and determining the direct path component specifically includes:
the base station estimates the arrival angle of the user and generates a corresponding steering vector according to the estimated arrival angle; projecting the channel estimation in each coherent time slot onto a guide vector, and judging the corresponding relation between the estimated arrival angle and a user according to the projection coefficient and a preset pilot frequency sequence mode; and constructing channel state information according to the corresponding relation between the arrival angle and the user and the corresponding projection coefficient to obtain the estimation of the direct path component of the channel.
Further, the pilot frequency distribution and channel estimation method under the macro connection is suitable for the Rice channel.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the method of the invention uses the space characteristic of the user to group the users, and the users in the same group transmit the pilot frequency sequence in time in an interlaced way, thereby effectively reducing the pilot frequency interference among the users under the macro connection scene, improving the reliability of the channel estimation and further improving the transmission rate of the system. The pilot frequency distribution and channel estimation method provided by the invention is particularly suitable for the Laisi channel with direct path components.
Drawings
FIG. 1 is a schematic diagram of user pilot allocation in the method of the present invention, wherein a base station allocates pilots for different user groups according to a predetermined rule; users in a group use the same pilot sequence but are staggered in time.
Fig. 2 shows a flow chart of a signaling interaction procedure in a wireless communication system according to an embodiment of the present invention.
Detailed Description
The technical solutions provided by the present invention will be described in detail below with reference to specific examples, and it should be understood that the following specific embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention.
The invention provides a pilot frequency allocation and channel estimation method under a macro-connection wireless communication scene. Wherein the base station groups the users according to different characteristics of the users. According to a preset rule, a base station distributes pilot frequency sequences for different user groups; users of the same group may use the same pilot sequence or different pilot sequences. In the uplink transmission process, users send pilot frequency and uplink data, and the base station estimates the channel of each user according to the pilot frequency information.
In an embodiment, we consider a single cell scenario where a base station is configured with M antennas (M is much larger than 1) and serves K single antenna users (K)>M). In wireless communication systems, the coherence time is limited. Therefore, the pilot sequence length for uplink channel estimation is fixed and less than the coherence time. In the embodiment, assuming that the length of the uplink pilot sequence is L, there are L candidate pilot sequences (μ)1,μ1,...,μL) For any two pilot sequences mukAnd muq(where k, q ∈ {1, 2.., L }), which satisfy the following relationship:
in a macro-connected wireless communication scenario, the length L of the pilot sequence is much smaller than the number K of users. Therefore, it is impossible to allocate pilot sequences orthogonal to each other to K users.
In the macro connection wireless communication, a user accesses a base station sporadically instead of always accessing the base station. Therefore, different pilot sequences are allocated to each group of users in different coherence time by adopting a preset random pilot allocation method. As shown in fig. 1, the base station groups users according to their different characteristics. The base station can group the users according to the arrival angle information of the users, and the users with similar arrival angle information are grouped into a group; or grouping according to the physical positions of the users, and grouping the users with similar physical positions into a group. Each group of users uses the same pilot sequence but transmits staggered in time. As depicted in fig. 1, a transmission frame is composed of a plurality of coherent slots, in each of which it is assumed that channel state information remains unchanged. Each coherent time slot is divided into a plurality of sub-slots, the length of which is equal to the length of the pilot sequence.
In particular, assume that each group supports Z users to transmit pilot sequences in a staggered manner, for a total of L groups of users. If ZL is greater than the total number of users, K, then each user may be assigned a particular pilot sequence.
In this embodiment, we consider the rice channel model with generality. The channel from the jth user of the ith group (i.e., user (i, j)) to the base station in the tth coherent time slot may be represented as:
wherein, g(i,j)Representing a large-scale fading coefficient from the jth user of the ith group to the base station;
a representation definition;
is a direct path component;
is the non-direct path component; kappa(i,j)A rice factor representing a channel from a jth user of the ith group to the base station;
relating to the indirect path component, wherein each element of the indirect path component is a complex Gaussian random variable with the mean value of zero and the variance of 1;
related to the direct path component. When the base station is configured with a uniform linear array antenna,
can be expressed as:
where α (.) represents a normalized steering vector, θ(i,j)Is the arrival angle of the direct path of the channel from the jth user in the ith group to the base station, λ is the wavelength of the carrier wave, and d is the distance between adjacent antennas of the base station. The large-scale fading coefficients and the arrival angles corresponding to the direct paths are slowly varying parameters. In a transmission frame time, it is assumed that the large-scale fading coefficient and the arrival angle corresponding to the direct path remain unchanged. Thus g(i,j)And
the parameter t is omitted.
In the jth sub-slot of the tth coherent slot, the user with index j transmits a pilot signal, the users with other indexes transmit data signals, and the signal received by the base station can be represented as:
wherein the content of the first and second substances,
a pilot sequence used for the jth user of the ith group; (.)TRepresenting a transpose;
for the signal vector transmitted by the z-th user in the ith group in the jth sub-slot of the tth coherent slot, assuming
Each element of (a) is a random variable having a mean value of 0 and a variance of 1;
is a noise matrix, and
each column of (a) is a complex Gaussian random variable, the mean is 0, and the covariance matrix is
pu,(i,j)Is the average transmit power of the pilot; p is a radical ofd,(i,z)Is the average transmit power at which the data is transmitted; g is the total number of user groups.
Under rice channel conditions, the channel between each user and the base station has a direct path component. Therefore, the base station can perform angle estimation in one transmission frame time, so that the arrival angle information of all active users can be obtained. Classical angle estimation methods such as multi-signal class estimation and signal parameter rotation invariant estimation methods can be used at this time. Within a frame transmission time, assume that there is K0A user communicates with a base station. Then the base station estimates the resulting K0Each angle of arrival being
The steering vector corresponding to the angle of arrival is represented as
All active users transmit signals within the frame transmission time, so the base station does not know the corresponding relation between the estimated arrival angle and the users. The arrival angle is a slowly varying parameter, and within one frame transmission time, the arrival angle information is assumed to be constant. Therefore, we will determine the correspondence of the estimated angle of arrival to the user according to the pattern of the pilot.
In this embodiment, each user is assigned a pseudo-random pilot transmission pattern and a particular sub-slot transmit pilot. Note that users of the same group are assigned the same pilot sequence pattern, but different subslots. The base station knows in advance the pilot sequence pattern for each user and the sub-slots in which the pilot is transmitted. Thus, the base station can determine the index of the user by detecting the pilot pattern. For the user with index j, the base station performs pilot sequence matching in the jth sub-slot of the coherent time slot. In the jth sub-slot of the tth coherent slot, the matching result of the ith pilot sequence (L ═ 1,2, …, L) is:
wherein, delta ([ i, j)]-l) is a dirac delta function. When the length of the pilot sequence is large (e.g., greater than 50), the influence of the interference term and the noise component may be small. Definition of
Wherein | · | purple2Representing a 2 norm. According to a preset threshold, a base station determines a pilot frequency sequence transmitted by a user in each pilot frequency time slot; then, the base station determines active users according to the judged pilot frequency sequence and a preset pilot frequency mode.
For example, the pilot pattern of the jth user in the first group in a frame is: mu.s1，μ2，…，μ4I.e. inThe pilot sequence transmitted in the jth sub-slot of the first coherent slot is mu1I.e. the pilot sequence transmitted in the jth sub-slot of the second coherent slot is mu2…, i.e. the pilot sequence transmitted in the jth sub-slot of the last coherent slot is μ4(ii) a The pilot pattern of the jth user in the fourth group in one frame is: mu.s3，μ1，…，μ4(ii) a The pilot pattern of the jth user in the eighth group in one frame is: mu.s5，μ2，…，μ1. Thus, the base station is based on
A condition in which the threshold is exceeded may determine an active user.
For users with index j: in the jth sub-slot of the first coherent slot,
and
is greater than a threshold; in the jth sub-slot of the second coherent slot,
and
is greater than a threshold; up to the jth sub-slot of the last coherent slot (the U-th coherent slot, with U coherent slots in one frame time),
and
the threshold is exceeded.
The base station is based on
The case where the threshold is exceeded may be judged to be of the first groupThe jth user, the jth user of the fourth group, and the jth user of the eighth group. The base station determines active users of other index indices on other sub-slots using the same method.
Accordingly, the pilot pattern is, according to the pilot pattern,
containing channel information for the jth user of the first group. Will be provided with
Projected onto a steering vector corresponding to the estimated angle of arrival
(k＝1,…,K0) The corresponding coefficients are obtained as:
definition and
the corresponding average projection coefficients in the U time slots are:
then, the arrival angle corresponding to the jth user direct path component of the first group can be determined according to the following criteria:
The estimate of the corresponding direct path component can be expressed as:
and the base station detects the data by using the estimated direct path component. For example, for a user with index j, data information is transmitted on the j +1 th sub-slot. Let p be assumed during transmissionu,(i,j)＝pd,(i,z)＝pt. The data signal estimated by the base station to be transmitted by the jth user of the first group in the j +1 th sub-slot of the tth coherent slot can be represented as:
when the base station is configured with a large-scale antenna, the interference term will tend to zero. The base station can thus estimate the information data transmitted by the jth user of the first group in each sub-slot, which is expressed as:
and by utilizing the data obtained by estimation, the base station estimates the indirect path component and updates the channel estimation. Defining:
when M tends towards the infinity, the number of M,
becomes accurate, as well as the angle-of-arrival estimation, so the last equation in the above equation holds. Correspondingly, in the t-th coherent time slot, the base station may estimate that the non-direct path component of the jth user in the first group is:
therefore, the updated channel estimation result of the jth user of the first group can be expressed as:
other active users may use the same method for channel estimation.
In order to better understand the above process, the signaling interaction flow between the base station side and the user equipment side will be described below with reference to fig. 2.
Fig. 2 is a flowchart of a signaling interaction procedure in a wireless communication system according to an embodiment of the present invention.
As shown in fig. 2, first, in step S1, the user reports its physical location information to the base station. Then, in step S2, the base station groups the users according to their physical location information. Then, in step S3, the base station informs the user of the grouping information, and the time slot of the pilot sequence pattern, pilot transmission. Next, in step S4, the user determines whether to transmit data according to his or her own status. In step S5, the user transmits uplink data and transmits a pilot sequence in a corresponding time slot. In step S6, the base station performs angle estimation; and judging a pilot frequency mode and determining active users. In step S7, the base station determines the correspondence between the estimated angle of arrival and the user, and determines the direct path component. In step S8, the base station detects uplink data transmitted by the user. In step S9, the base station estimates the non-direct path component of the user channel and updates the channel estimation result. In step S10, the base station detects uplink data based on the updated channel estimation result. In step S11, the base station performs downlink precoding transmission using the result of the uplink channel estimation.
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.
Claims (7)
1. A pilot frequency distribution and channel estimation method under macro connection is characterized by comprising the following steps:
the base station groups users; the base station groups the users according to the arrival angle information of the users, and divides the users with similar arrival angle information into a group; or grouping according to the physical positions of the users, and dividing the users with similar physical positions into a group;
according to the preset rule, the base station distributes pilot frequency sequences for different user groups and informs the user of the grouping information, the pilot frequency sequence mode and the time slot of pilot frequency transmission; the method specifically comprises the following steps:
for the user with the index j, the base station performs pilot frequency sequence matching on the jth sub-time slot of the coherent time slot; in the jth sub-slot of the tth coherent slot, the matching result of the ith pilot sequence is:
where L is 1,2, …, L, δ ([ i, j)]-l) is a Dirac delta function, defined
Wherein | · | purple2The expression is given in the 2-norm,
for the channel from the jth user of the ith group to the base station in the tth coherent time slot,
a pilot sequence used for the jth user of the ith group; (.)TRepresenting a transpose;
as the z-th user of the i-th groupThe signal vector transmitted on the jth sub-slot of the tth coherent slot, assuming
Each element of (a) is a random variable having a mean value of 0 and a variance of 1;
is a noise matrix, and
each row of (a) is a complex gaussian random variable, and the mean value is 0; p is a radical ofu,(i,j)Is the average transmit power of the pilot; p is a radical ofd,(i,z)Is the average transmit power at which the data is transmitted; g is the total number of user groups, and L is the length of the uplink pilot frequency sequence; each group supports Z users to stagger and transmit pilot frequency sequences;
is a signal received by a base station;
the user transmits uplink data and transmits a pilot frequency sequence in a corresponding time slot;
the base station estimates the channel of each user according to the pilot frequency information, and the method comprises the following steps:
the base station carries out angle estimation;
judging a pilot frequency mode and determining active users; the method specifically comprises the following steps:
the base station is based on
Determining a pilot frequency sequence transmitted by a user in each pilot frequency time slot when the threshold is exceeded; then, the base station determines active users according to the judged pilot frequency sequence and a preset pilot frequency mode;
the base station determines the corresponding relation between the estimated arrival angle and the user and determines the direct path component; the method specifically comprises the following steps:
in accordance with the pilot pattern,
channel information of a jth user comprising the first group; will be provided with
Projected onto a steering vector corresponding to the estimated angle of arrival
The corresponding coefficients are obtained as:
definition and
the corresponding average projection coefficients in the U time slots are:
then, the arrival angle corresponding to the jth user direct path component of the first group can be determined according to the following criteria:
The estimate of the corresponding direct path component can be expressed as:
where U is the number of time slots, K is 1, …, K0，K0As to the number of angles of arrival,
for the estimated angle of arrival, phi(1,j)An arrival angle corresponding to a direct path component of a jth user of the first group;
the base station detects uplink data transmitted by a user;
and the base station estimates the indirect path component of the user channel and updates the channel estimation result.
2. The method of claim 1, further comprising the steps of:
the base station detects the uplink data based on the updated channel estimation result;
and the base station performs downlink pre-coding transmission by using the result of the uplink channel estimation.
3. The method of claim 1, wherein the same group of users use the same pilot sequence or different pilot sequences.
4. The method of claim 1 wherein the users in a group transmit pilots using staggered slots, and the number of users in each group is limited by coherence time.
5. The method of claim 1, wherein the user determines whether to transmit data according to his/her own status.
6. The method of claim 1, wherein the step of determining the direct path component comprises:
the base station estimates the arrival angle of the user and generates a corresponding steering vector according to the estimated arrival angle; projecting the channel estimation in each coherent time slot onto a guide vector, and judging the corresponding relation between the estimated arrival angle and a user according to the projection coefficient and a preset pilot frequency sequence mode; and constructing channel state information according to the corresponding relation between the arrival angle and the user and the corresponding projection coefficient to obtain the estimation of the direct path component of the channel.
7. The method of claim 1, wherein the pilot allocation and channel estimation method under macro-connection is applied to a rice channel.
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