RU2430470C1 - Method and apparatus for transmitting channel quality information in telecommunication system - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: mobile terminal device (400) is configured to receive a signal (404) from several transmitting antennae, wherein that signal includes several subcarriers (412), and determine channel quality indicator (CQI) messages, the format of transmitting messages for the set of carriers based on the selected configuration of transmitting antennae. The mobile terminal device is also configured to determine several CQI values (409) associated with said subcarriers in accordance with the determined format of transmitting CQI messages, and transmit these CQI values to a base station in a feedback signal (408). The format of transmitting CQI messages is adapted to the selected configuration of transmitting antennae such that the level of detail of transmitting CQI messages depends on the selected configuration of transmitting antennae.

EFFECT: providing methods and devices which support adaptation of the transmission volume channel quality indicator messages using configuration of antennae which include a set of antennae.

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Description

FIELD OF THE INVENTION

The present invention relates to methods and devices for transmitting channel quality indicator (CQI) messages in a wireless telecommunication system, and more particularly, to methods and devices that enable CQI message transmission to be adapted to the antenna configuration in question.

State of the art

In such wireless communication systems that work in accordance with the WCDMA 3GPP standards for high-speed packet data (HSPA) or the 3GPP standards that are currently being developed under the LTE project (long-term development), a base station (also called NodeB or eNodeB) can transmit on a shared channel downlink to several mobile terminals (also called user equipment, UE). One or multiple transmit antennas may be involved in this transmission according to different transmission methods. In order for the base station, for example, to determine the proper data rate, modulation scheme, and transmit power, it must have some measure of how good the channel is currently. Accordingly, the mobile terminal provides a measure of channel quality to the base station by means of Channel Quality Indicator (CQI) values that are continuously returned to the base station on the uplink. The mobile terminal determines CQI values based on measurements taken, for example, from pilot signals transmitted from the base station. Depending on the type of telecommunication system, several possible channel quality levels can be set, each channel quality level corresponding to certain channel quality measurements, and each level can be associated with a corresponding CQI value represented, for example, by a 4-bit word.

CQI messaging enables the base station to adapt its downlink transmission to the changing channel quality. However, the uplink bandwidth is a limited resource. Therefore, there are two competing interests related to CQI messaging. One is to provide as detailed CQI messages as often as possible so that the base station can best adapt its transmissions to the changing channel quality. Another (interest) is to keep the volume of CQI messages low to keep the available uplink bandwidth as small as possible.

Using multi-antenna circuits makes CQI messaging much more complicated than single-antenna circuits. In the multi-antenna concept proposed for the WCDMA high-speed downlink packet data transmission (HSDPA) mode, the selection of the subset of antennas from which the transmission will be carried out is considered to be an extension of the quick adaptation of the communication line. This leads to transmission when the configuration of the antennas, which more closely matches the propagation conditions, compared with schemes with many antennas, in which transmission is always carried out from identical antennas. In HSDPA, Antenna Speed Control (PARC) is one approach for multiple antennas that provides higher downlink data rates. With this approach, separate data rates are provided for data streams mapped to each transmit antenna. When both speeds and a subset of the transmit antennas are selected adaptively, this is denoted as selective PARC (S-PARC). CQI, which is evaluated at the mobile station and transmitted on the uplink to the base station, is part of the process of adapting the communication line and provides the ability to select the antenna and set the effective speed. Since the signals transmitted from different antennas interfere with each other, the estimated CQI varies for each combination of transmitting antennas. With the provision of CQI estimates for each antenna for each combination, an increasing amount of available uplink resource is used, compared to transmission with a single antenna.

The type of receiver used may also increase the number of CQI values that can be returned to the base station. For example, using Serial Noise Reduction (SIC), the receiver places the decoding ordered by transmitting antennas so that there is a separate CQI value for each permutation (and not a combination) of antennas. For HSDPA, a plurality of spreading codes are used either to transmit (at) a higher data rate to an individual user, or to transmit at lower speeds to multiple users simultaneously. To save spreading codes with the previously proposed approach for multiple antennas, spreading codes are reused across all different transmit antennas. In practice, CQI messaging is usually performed under the assumption of some fixed number of spreading codes assigned to the user. To obtain CQI values for different numbers of spreading codes, the CQI values are scaled accordingly. This is possible since all spreading codes are transmitted on the same propagation channel. For OFDM systems, such as LTE and WiMax, the frequency band is subdivided into many separate subcarriers. Depending on the amount of dispersion in the propagation channel, different parts of the frequency band can potentially undergo different fading implementations. In the extreme case, with strong dispersion, each subcarrier may have different fading. The adaptive assignment of different subcarriers to the user (s) introduces additional complexity to the CQI messaging process. For S-PARC, the CQI message transmission volume has already been increased due to the number of different antenna combinations (permutations) to be reported. With the division of the frequency band into subcarriers, the number of CQIs that can be reported increases even more.

As mentioned above, it is required to keep the feedback depth used for transmitting CQI messages low so that the CQI can be transmitted reliably and not consume much of the uplink bandwidth. This becomes especially important when the number of active mobile stations in the system increases.

One approach to reducing the complexity of CQI feedback for S-PARC is described in US Patent Application Publication No. US 2005/0250544 A1 when connected to a SIC receiver. In this approach, the antenna that provides the best speed is first selected and used for transmission with a single antenna. When considering transmission with two antennas, the subset with two antennas is limited and contains the best antenna previously found for transmission with one antenna, and an antenna with the next best speed. This approach is repeated for subsets with three and four antennas and, in general, it is called the “subset property”, which depends on the choice of antenna. Implicitly, the order is set to the antennas so that the first antenna has the highest transmission rate, while the last antenna has the lowest transmission rate. This ordering of antennas from the lowest to the highest speeds is the order in which the SIC receiver processes the received signals. Accordingly, by limiting the order of the antennas and selecting a subset by using this property of the subset, a large number of antenna orderings are avoided.

It is clear that trying to report the order of the antennas for each subcarrier can be expensive for CQI feedback. In addition, this may turn out to be practically impossible, since the transmitted streams can be encoded on different subcarriers, and the SIC receiver uses decoded / re-encoded signals as part of the detection process.

Disclosure of invention

As mentioned above, the number of CQIs that can be reported is increased using antenna configurations including multiple antennas. Therefore, it is an object of the present invention to provide methods and devices that support adaptation of a transmission volume of CQI messages to an antenna configuration of interest.

The above stated objective is achieved by a mobile terminal, a base station and a method according to the claims.

In a first embodiment of the present invention, there is provided a mobile terminal device for use in a wireless communication system. The mobile terminal device comprises a receiver for receiving a signal from M transmit antennas, this signal including several subcarriers. The mobile terminal apparatus also includes a processing module for determining a CQI message transmission format for a plurality of subcarriers based on a configuration of transmitting antennas associated with this plurality of subcarriers, and for determining a number of PC _QI CQI values related to said plurality of subcarriers in accordance with a specific transmission format CQI messages. The processing module is adapted to adapt the CQI message transmission format to the selected transmit antenna configuration so that the granularity of the CQI message transmission depends on the number m of transmit antennas of the selected transmit antenna configuration. The mobile terminal device also includes a transmitter for transmitting P _{CQI CQI} values to the base station in a feedback signal.

In a second embodiment of the present invention, a method is provided in a device of a mobile terminal. This method comprises the step of receiving a signal from M transmit antennas, the signal of which includes several subcarriers. The method also comprises the step of determining a CQI message transmission format for a plurality of subcarriers based on a selected transmit antenna configuration associated with this plurality of subcarriers. The CQI message transmission format is adapted to the selected transmit antenna configuration so that the detail of the CQI message transmission depends on the number m of transmit antennas of the selected transmit antenna configuration. The method also includes the step of determining the number of P _{CQI CQI} values related to the set of subcarriers in accordance with a specific CQI message transmission format, and the step of transmitting P _{CQI CQI} values to the base station in the feedback signal.

In a third embodiment of the present invention, a base station for use in a wireless communication system is provided. The base station comprises a transmitter for transmitting a signal including several subcarriers of M transmit antennas. The base station also includes a receiver for receiving a feedback signal from the mobile terminal device and a processing module for processing the feedback signal for extracting the number P _{CQI of CQI} values related to the plurality of subcarriers and for extracting antenna configuration information defining a selected transmit antenna configuration. The CQI values correspond to the CQI message format, which depends on the selected configuration of the transmitting antennas so that the granularity of the CQI message transmission depends on the number of antennas of the selected transmitting antenna configuration.

Advantages and features of embodiments of the present invention will become apparent upon reading the following detailed description in conjunction with the drawings.

Brief Description of the Drawings

1 is a block diagram illustrating a wireless communication system in which the present invention can be implemented.

2 is a block diagram illustrating a CQI message transmission format for one transmit antenna according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a CQI message transmission format for two transmit antennas according to an alternative embodiment of the present invention.

4 is a block diagram illustrating a CQI message transmission format for four transmit antennas according to another alternative embodiment of the present invention.

5 is a block diagram illustrating an alternative CQI message transmission format for two transmit antennas according to another alternative embodiment of the present invention.

6 is a block diagram illustrating another alternative CQI message transmission format for four transmit antennas according to a further alternative embodiment of the present invention.

7 is a flowchart illustrating a method according to an embodiment of the present invention.

8 is a flowchart illustrating a method for determining CQI values according to an embodiment of the present invention.

The implementation of the invention

Hereinafter, the present invention is described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. However, this invention may be practiced in many different forms, and should not be construed as being limited by the embodiments set forth herein, rather, these embodiments are provided to fully and fully disclose this invention and to fully convey the scope of the invention to those skilled in the art.

In addition, it is recognized that there are various alternatives for reducing the transmission of CQI messages. The invention discloses embodiments for transmitting CQI messages with a degree of detail in time, space, and frequency, which is associated with an adaptive antenna configuration considered for use for transmission from a base station. In addition, signaling schemes for reporting this CQI information from a mobile station to a base station are also disclosed. For OFDM systems, since users are assigned specific time and frequency subcarriers for use, it is necessary to match CQI messages with a similar frequency and time range. Such an analysis takes place, for example, when sub-bands of the entire OFDM signal bandwidth are adaptively planned for users, or when fixed division of the frequency band into subcarriers is used. It is desired to keep the feedback depth used for transmitting CQI messages low so that the CQI can be transmitted reliably and not consume much of the uplink bandwidth. This becomes especially important when the number of active mobile stations in the system increases.

1 is a schematic block diagram of a wireless communication system 420, such as an LTE system, in which OFDM is implemented as a radio access technology in which the present invention can be implemented. System 420 includes a radio base station 400 (also called LTE Advanced NodeB (eNB)) and a mobile terminal device 401, which, for example, may be a mobile phone, laptop, PDA (personal digital assistant), or some other type of user equipment (UE) . It should be understood that certain details and components in the device 401 of the mobile terminal and in the base station 400 are well known to the person skilled in the art. Therefore, for clarity, the description of the mobile terminal device 401 and base station 400 provided below does not include these well-known details and components that are not necessary for understanding the present invention.

As shown in FIG. 1, four transmit antennas 403-1, 403-2, 403-3, and 403-4 exist in the base station 400. However, the present invention can be applied to base stations with any number of antennas. In this application, M will be used to indicate the number of transmit antennas of the base station. Base station 400 also includes a transmitter 410 for transmitting a shared downlink (DL) signal 404, in this example an OFDM signal including several subcarriers 412 for several mobile terminals, for example, for a mobile terminal 401. Different subcarriers 412 can be adaptively distributed to transfer data and / or signaling to different mobile terminals. Figure 1 shows an example time slot diagram of an OFDM signal 404, which in this example is assumed to consist of 600 subcarriers 412 of seven OFDM symbols. Base station 400 also includes a receiver 421 for receiving uplink (UL) signals from mobile terminals, for example, uplink signal 408 from mobile terminal device 401. Feedback information, for example, CQI values 409, may be included in the uplink signal 408. The base station may process the feedback signal 408, for example, extract and interpret CQI values through the processing module 402.

Base station 400 may select data and / or signaling transmission on different subcarriers 412 from all or from a subset of transmitting antennas 403-1, 403-2, 403-3, 403-4 according to different defined antenna configurations. In this application, it is assumed that the base station determines the antenna configuration for a plurality of adjacent subcarriers. Even if the base station selects data transmission from only a subset of the transmitting antennas, this document assumes that the pilot signal is always transmitted from each antenna, for example, for purposes such as measuring channel quality. Therefore, the mobile terminal 401 will always be able to estimate the CQI values for all subcarriers from all transmit antennas.

Mobile terminal device 401 includes a receiver for receiving a downlink signal 404 and a transmitter for transmitting an uplink signal 408. The mobile terminal device is also equipped with a processing module 406, which, for example, can determine the CQI message transmission formats that will be used to transmit the CQI messages, as explained below.

The quality of the downlink channel from the base station 400 to the mobile terminal 401 varies in the frequency band and therefore varies between different subcarriers 412. The channel quality of the subcarrier also depends on which transmit antenna this subcarrier is transmitted from and interference from other transmitters antennas. Therefore, the mobile terminal device should ideally determine one CQI value for each subcarrier for each antenna and for each possible configuration of the transmit antennas. However, since in most cases it may be too costly to transmit CQI values for all possible antenna configurations, the mobile terminal according to embodiments of the present invention selects the antenna configuration for a plurality of subcarriers and estimates CQI values for subcarriers from a plurality of selected antenna configurations . Information specifying the selected antenna configuration, which relates to different sets of subcarriers, is reported to the base station 400 in the uplink signal 408 in the form of antenna configuration information 411, as shown schematically in FIG. 1. After that, the base station can make a transmission decision according to the selected configuration of the transmitting antennas or according to another specific configuration of the antennas that deviates from the selected configuration of the transmitting antennas. In this appendix, the term “selected antenna configuration” is used to mean the antenna configuration that the mobile terminal 401 chooses to consider when evaluating CQI values, while the term “specific antenna configuration” is used to indicate the antenna configuration that the base station 400 decided to use for transmission. In addition, the number of antennas of the selected antenna configuration is denoted by m, with 1 <m <M.

Depending on the type of mobile terminal receiver 405, the calculation of the CQI values may depend not only on the transmit antennas included in the selected antenna configuration, but also on the order in which signals from different antennas are decoded. Therefore, the selected antenna configuration contains the selected antenna order in those cases in which the decoding order affects the estimates of the CQI value. In cases where the decoding order does not matter, the selected antenna configuration defines only the considered subset of transmitting antennas, that is, without ordering. This is described below with reference to several specific examples of embodiments.

According to embodiments of the present invention, the mobile terminal processing module 406 is configured to determine a CQI message transmission format that will be used to transmit CQI messages based on the number m of transmit antennas of the selected transmit antenna configuration. According to embodiments of the present invention, the CQI message transmission format is adapted so that the detail of the CQI message transmission depends on the number m of transmit antennas of the selected transmit antenna configuration. Since the selected transmit antenna configuration may differ between different sets of subcarriers, the CQI message transmission format may also differ between different sets of subcarriers. The following describes in detail several different examples of CQI messaging formats according to various embodiments of the present invention with reference to FIGS. 2 to 6. For simplicity, it is assumed that all of the subcarriers shown in FIGS. 2 to 6 are respectively associated with an identical selected antenna configuration. CQI estimates can theoretically be made for each subcarrier in an OFDM system. But according to embodiments of the invention, the amount of CQI information sent from the mobile terminal 401 to the base station 400 is reduced by performing CQI estimates for groups of subcarriers (in time and / or frequency) instead of performing them for each subcarrier. This is illustrated in FIGS. 2 through 6, which illustrate example system 420. As mentioned above, the OFDM signal consists of 600 subcarriers in system 420.

2 is a schematic representation of a CQI message transmission format for a CQI message for a selected configuration of transmit antennas with a single transmit antenna. To reduce the amount of CQI information, the subcarriers are packed into subcarrier groups of 15 adjacent subcarriers of 7 OFDM symbols, and one CQI value is estimated for each group of subcarriers. In this example, the OFDM signal transmitted over one period of time is divided into 40 tiles. Each tile contains a group of 1 subcarriers of 15 subcarriers of 7 OFDM symbols. If B = 32 bits are allocated for transmitting the CQI message, and each CQI value is represented as 4 bits, then 8 CQI values can be transmitted over each time period, and 5 time periods are required to update the CQI on all subcarriers. 2, it is schematically illustrated that, in each time period, CQI values are reported for 8 groups of subcarriers (indicated as black mosaic elements). In time period 0, CQI values are reported for groups No. 4, 9, 14, 19, 24, 29, 34 and 39 subcarriers, in time period 1, CQI values are reported for groups 2, 7, 12, 17, 22, 27, 32 and 37 subcarriers, etc.

In order to save the number of bits used for transmitting CQI messages when several antennas exist in the selected transmit antenna configuration, the detail of the CQI message transmission format becomes larger, according to embodiments of the present invention, for accommodating CQI information related to the plurality of antennas. The degree of detail can be changed in frequency and / or time. When groups of subcarriers of their adjacent subcarriers become larger, the degree of detail in frequency can be changed. This is shown in FIG. 3 and FIG. 4, which are two other examples of CQI message formats according to embodiments of the invention.

3 is a schematic representation of a CQI message transmission format for reporting CQI values for a selected configuration of transmit antennas with two transmit antennas. In this embodiment, groups of 2 subcarriers from adjacent subcarriers become twice as large compared to the example of the single transmit antenna of FIG. 2. For each group of 2 subcarriers, CQI values are calculated for each of these two transmit antennas. Therefore, CQI estimation is performed in this way to accurately model the interference between the two transmit antennas. According to FIG. 3, it is demonstrated that, in each time period, CQI values are reported for four groups of subcarriers for each of the two transmit antennas (indicated as black mosaic elements). In time period 0, CQI values are reported for groups No. 4, 9, 14 and 19 subcarriers, in time period 1, CQI values are reported for groups No. 2, 7, 12 and 17 subcarriers, etc. Compared to the example in FIG. 2, the degree of detail in frequency is greater since each CQI value in the example of FIG. 3 represents channel quality for a larger group of subcarriers. However, five time periods are still required to transmit the entire CQI message for all subcarriers, and an identical amount of CQI information expressed in bits is reported in each time period.

4 is a schematic representation of a CQI message transmission format for a CQI message for a selected configuration of transmit antennas with four transmit antennas. In this embodiment, groups of 3 subcarriers from adjacent subcarriers become four times larger compared to the example of the single transmit antenna of FIG. 2. For each group of 3 subcarriers, CQI values are estimated for each of these four transmit antennas. Therefore, CQI estimation is performed in this way to accurately simulate mutual interference between the four transmit antennas. According to FIG. 4, it is demonstrated that, in each time period, CQI values are reported for two groups of subcarriers for each of the four transmit antennas (indicated as black mosaic elements). In time period 0, CQI values are reported for groups No. 4 and 9 of subcarriers, in time period 1, CQI values are reported for groups No. 2 and 7 of subcarriers, etc. Compared with the example of FIG. 3, the degree of granularity in frequency of the CQI messaging format becomes even greater in the example of FIG. 4.

As mentioned above, it is also possible to adapt the degree of detail of the CQI message transmission format in time instead of the frequency detail for the case of selected configurations of transmitting antennas with multiple transmitting antennas. This is illustrated in FIGS. 5 and 6, which depict examples of CQI message transmission formats according to embodiments of the present invention for selected transmission antenna configurations with two and four transmission antennas, respectively. In FIG. 5 and FIG. 6, the sizes of the subcarrier groups are identical to those in the example of FIG. 2. However, in the case of two transmit antennas shown in FIG. 5, CQI messages for each group of subcarriers occur in two time slots, with CQI values for one of these two transmit antennas being reported in each of these two time slots. In time period 0, CQI values are reported for groups No. 4, 9, 14, 19, 24, 29, 34 and 39 subcarriers with respect to the first transmitting antenna, in time period 1, CQI values are again reported for groups No. 4, 9, 14, 19 , 24, 29, 34 and 39 subcarriers, but with respect to the second transmitting antenna, during time period 3, CQI values are reported for groups No. 2, 7, 12, 17, 22, 27, 32 and 37 subcarriers with respect to the first transmitting antenna, in time period 4 CQI values are again reported for groups No. 2, 7, 12, 17, 22, 27, 32 and 37 subcarriers, but with respect to the second transmit antenna, etc. 5, ten time periods are required to transmit the entire CQI message for all subcarriers. In the case of the four transmit antennas shown in FIG. 6, similarly twenty periods of time are required to transmit the entire CQI message for all subcarriers. In each time period, CQI values associated with eight different groups of subcarriers are reported for one of the transmit antennas. During the next three time periods, CQI values are reported that relate to the identical eight subcarrier groups, but with respect to the remaining three transmit antennas.

As mentioned above, with reference to the examples shown in FIGS. 2-6, it was assumed that all 600 subcarriers are associated with one selected transmit antenna configuration. However, the present invention is not limited to this case. You can apply different selected transmit antenna configurations for different subcarriers or groups of subcarriers. However, a natural choice is to use an identical selected transmit antenna configuration for multiple groups of adjacent subcarriers, as discussed below. If, for example, it is assumed that the first selected configuration of transmitting antennas with one transmitting antenna is used for the first set of subcarriers containing the first 300 subcarriers of system 420, and the second selected configuration of transmitting antennas with two transmitting antennas is used for the second set of subcarriers containing the remaining 300 subcarriers of system 420, then CQIs may be communicated to the first constellation through the first CQI messaging format, as shown in FIG. 2, and for the second constellation in between the second CQI message transmission format, the scheme of which is presented in Fig.3. According to the resulting combined CQI message format for two sets of subcarriers, eight CQIs can be reported in each time slot, four of them can be assigned to four groups of subcarriers of the first set, and four can refer to two groups of subcarriers of the second set, for each of these two transmitters antennas.

If different selected transmit antenna configurations are used for different sets of OFDM signal subcarriers, but these different selected transmit antenna configurations have the same number m of transmit antennas, then the actual CQI message format of the different sets of subcarriers may be identical. However, the different selected configurations of the transmitting antennas may relate to different orders of antennas or subsets of antennas containing different transmitting antennas, which affects the actual CQI values despite the fact that the CQI message transmission format may be identical.

7 is a flowchart illustrating a method according to an embodiment of the present invention. At step 500, the mobile terminal device receives a signal from several transmit antennas, the signal of which includes several subcarriers. In a next step 501, a CQI message transmission format is determined for a plurality of subcarriers based on a selected transmit antenna configuration associated with this plurality of subcarriers. The CQI message transmission format, as mentioned and explained above, is adapted to the selected transmit antenna configuration so that the detail of the CQI message transmission depends on the number m of transmit antennas of the selected transmit antenna configuration. At step 502, the number P _{CQI of CQI} values related to the plurality of subcarriers is determined in accordance with the determined CQI message format. At 503, certain CQI values are transmitted to the base station in a feedback signal. Steps 502 and 503 may overlap such that some CQI values are determined and transmitted simultaneously, as shown above with respect to FIGS. 2-6. The degree of detail of the CQI message transmission format according to various embodiments of the invention can be adapted both in time and in frequency depending on the number of transmit antennas of the selected transmit antenna configuration.

In one illustrative embodiment of the method of FIG. 7, step 501 includes adapting a frequency granularity of a CQI message format by dividing a plurality of subcarriers by the number Q of non-overlapping subcarrier groups. Thereafter, in step 502, one CQI value is determined for each group of subcarriers for each transmit antenna of the selected transmit antenna configuration.

The number of Q non-overlapping subcarrier groups according to another illustrative embodiment of the present invention depends on the number m of transmit antennas of the selected transmit antenna configuration so that the number P _{CQI of CQI} values determined in step 502 for m transmit antennas of the selected transmit antenna configuration is substantially the same for different selected transmit antenna configurations having a different number of transmit antennas.

In another illustrative embodiment of the method of FIG. 7, a CQI message transmission format is determined such that Q subcarrier groups are divided into T nonoverlapping subsets and so that the number P _{CQI of CQI} values determined in step 502 is transmitted in step 503 for T periods time. This is to ensure that CQI values relating to subcarrier groups of one subset are transmitted at step 503 in each time period. This can be compared with the illustrative embodiments shown in FIGS. 2 to 4, in which, as you can see, the groups of subcarriers are divided into five subsets with CQI values from one subset reported in each time period. The subcarrier groups are preferably divided into subsets such that the number of CQI values transmitted in step 503 in each time period is the same or substantially the same.

According to various illustrative embodiments of the present invention, the selected transmit antenna configuration may specify an antenna decoding order or a subset of antennas, as mentioned above. Information that sets the selected transmitter configuration is preferably transmitted at 503 along with the determined CQI values.

The receiver 405 of FIG. 1 may be of several different types using different methods for receiving and decoding. Base station 400 may also use many different transmission methods. Two different illustrative embodiments of the invention are described below, in which different methods are used for transmission and reception. In a first illustrative embodiment, the receiver 405 is a SIC receiver, and the transmission method used by the base station 400 is an S-PARC. In a second illustrative embodiment, intermittent code modulation in space, time, and frequency is used, and receiver 405 uses MMSE (Minimum Mean-Square Estimation) estimation.

In a first illustrative embodiment, the decoding order in the SIC receiver 405 affects the CQI values 409 obtained during CQI calculation. However, in channel implementations that are frequency selective, the optimal decoding order may vary across subcarrier groups for which CQI values are calculated. A further analysis is that the SIC receiver decodes the signal stream, then re-encodes it to subtract its contribution to the received signal. Accordingly, the antenna decoding the order should correspond to the length of the encoded signal.

In general, base station 400 is required to retain control over user scheduling and assignment of mobile terminal devices 401 to different subcarriers 412 for downlink transmission. In this first illustrative embodiment, a CQI value of 409 is reported for each group of 1, 2, 3 subcarriers on the assumption that the decoding order for the whole set of groups of 1, 2, 3 subcarriers is selected. The decoding order must also be reported back to the base station 400. One approach for decoding the entire set of groups of 1, 2, 3 subcarriers is based on the property of the subset described in US Patent Application 10841911 for SIC reception and described below with reference to the block diagram of the sequence of operations shown in Fig.8.

Step 600: From the aggregate of the plurality of subcarrier groups, calculate the rates for each subcarrier group with the assumption that one transmit antenna is used to transmit across all the subcarrier groups of the population. Perform this for each of the M transmit antennas (in FIG. 1 for antennas 403-1, 403-2, 403-3 and 403-4).

Step 601: For each of the M transmit antennas, summarize the individual speeds for each group of subcarriers in the population to associate the total speed with this antenna.

Step 602: Designate the antenna with the highest speed as the antenna for use with the PARCl circuit. The individual speeds for the selected antenna are used as the 409 CQI values of the subcarrier group for this antenna.

Step 603: Next, create all of the subsets of the two antennas so that each subset of the two antennas contains the antenna selected for transmitting PARCl.

Step 604: For each subset of the two antennas, calculate the individual and total speeds for the second transmit antenna, assuming that the antenna associated with the PARCl signal is also used to transmit PARC2.

Step 605: Select the subset of the two antennas with the highest speed and designate this approach as the PARC2 scheme. The individual speeds for the second antenna are used as the 409 CQI values of the subcarrier group for the second antenna (combined with the previous CQI PARCl values).

Step 606: Repeat steps 603, 604, and 605 for all remaining transmit antennas.

The decoding order for each transmit antenna pattern together with the estimated 409 CQI values of the subcarrier group for different transmit antennas in the circuit is then transmitted back to the base station 400. When transmitting back 409 CQI values for each group of 1, 2, 3 subcarriers, there is a different frequency quantization between setting the CQI values 409 and the antenna order for the SIC receiver 405. This allows the base station 400 to maintain control over the assignment of users and their associated speeds to smaller parts of the frequency band than is specified com SIC-decoding receiver. The specific antenna ordering used above also allows the base station 400 to select the number of transmit antennas used for transmission, and naturally occurs when used in combination with SIC reception.

In a second illustrative embodiment, the receiver 405 is based on a minimum mean square error (MMSE) estimate and does not require transmit antenna ordering for its operation. This receiver 405 detects signals from one transmit antenna, while at the same time suppresses signals from other transmit antennas. This can be used in conjunction with S-PARC transmission or selective bit-interleaved coded modulation in space, time and frequency. Here we consider the latter approach, in which one encoded data stream is transmitted, which is multiplexed by transmitting antennas, as well as in time and frequency. However, it is required to know the subset of antennas expected for transmission, so 409 CQI values can be calculated under identical conditions. Accordingly, in this second illustrative embodiment, instead of calculating the decoding order of the plurality of subcarrier groups and transmitting it back to the base station 400, the selected transmit antenna configuration is determined by determining the subset of antennas from the plurality of subcarrier groups. The subset of antennas and corresponding CQI values 409 are transmitted to the base station 400 in a manner similar to that used in the first illustrative embodiment.

In the aforementioned first and second illustrative embodiments described and in other embodiments, the CQI values 409 and the order of the antennas (or a subset of antennas) should be reliably transmitted from the mobile terminal 401 to the base station 400, which in this document is referred to as transmit antenna configuration information. Typically, this information is encoded to meet certain specific performance criteria.

Consider, for example, the system 420 of FIG. 1 and assume that N is the number of bits in each reported 409 CQI value, L is the number of bits to specify a subset or order of antennas, m is the number of transmit antennas in the selected antenna configuration, and q is the number of groups 1, 2, 3 subcarriers for which 409 CQIs are reported in each time period. Then, the number of bits used to report CQI values in each time period is qmN = 32 bits, with the assumption that N = 4 bits are used to set each 409 CQI of the subcarrier group. Depending on the number of subcarriers that are part of each group of subcarriers, a different number of time periods T is required to transmit the entire CQI message for the entire OFDM signal, which is all subcarriers. If the OFDM signal is divided into adjacent ranges, each containing a plurality of subcarriers, and the order of antennas or a subset of antennas are selected for each constellation (here it is assumed that m is the same for each constellation), then 5qmN + 5L = 180 bits are required to report 409 CQI values and the order of the antennas for the entire OFDM signal bandwidth over five time periods, resulting in 36 bits for each time period for each CQI feedback.

It is attractive that the number of feedback bits can also be reduced without seriously affecting CQI performance. According to one embodiment of the invention, this is achieved by puncturing some bits representing CQI values 409 to reduce the transmission rate of the raw data required in the feedback signal 408. However, if this puncturing is random, then the most significant bits of the bits representing the CQI values of the subcarrier group may be affected, and this may degrade CQI performance. Alternatively, according to a preferred embodiment of the invention, the least significant bits (LSBs) of the bits representing CQI values 409 are replaced with bits representing the order of the antennas (or a subset of antennas). In the above example, the CQI feedback rate of 36 bits in each time period can be reduced to 32 bits. Of course, the degree of detail of the punctured 409 CQI values goes in favor of a reduced speed.

Not in all groups of 1, 2, 3 subcarriers, the least significant bits of their 409 CQI values will be replaced. Accordingly, there must be some mechanism for selecting groups of 1, 2, 3 subcarriers in which these LSBs will be punctured. One option is to select a fixed set of 409 CQI values and puncturing their respective LSBs. However, this can reduce CQI performance unevenly across different groups of 1, 2, 3 subcarriers. Alternatively, groups of 1, 2, 3 subcarriers can be selected according to a (pseudo-) random pattern, and the LSBs of the corresponding 409 CQI values can be punctured so that each group of subcarriers is more uniformly affected.

From the above description, it will be obvious to a person skilled in the art that for the implementation of the present invention some adaptation of the base stations and mobile terminals of the prior art will be required. A natural choice is to implement the present invention by providing the mobile terminal device with new software, although implementations in firmware, hardware, or combinations thereof can also be performed. The processing module 406 in the device of the mobile terminal 401, for example, must be adapted so that it can determine the CQI message transmission format based on the selected transmit antenna configuration and determine the number P _{CQI of CQI} values. This adaptation of the processing module will generally imply new software for the processing module compared to the processing modules of the mobile terminal according to the prior art. In addition to adapting in the mobile terminal device, some adaptation of the processing module 402 in the base station 400 is required. The processing module 402 in the base station 400, for example, must be adapted so that it can correctly interpret the feedback signal 408, that is, correctly extract and interpret the values CQI and transmit antenna configuration information.

An advantage of the embodiments of the present invention is that the bandwidth required for transmitting CQI messages can be balanced for transmission methods including multiple transmit antennas.

Another advantage of the embodiments of the present invention is its applicability to several different types of systems. Such systems include OFDM systems similar to the 4-G, WiMax and LTE systems currently under study.

A further advantage of the preferred embodiments of the present invention is the rather simple implementation and the absence of the need for significant modification of existing mobile terminal devices and base stations.

Another advantage of the preferred embodiments of the present invention is that the CQI message format can be adapted for multiple devices of the mobile terminal, allowing the selection of different antenna configurations for each device of the mobile terminal.

Another advantage of the preferred embodiments of the present invention is that puncturing the low-order bits and replacing them with an antenna configuration or decoding order information reduces the CQI feedback and provides the best coding rate to protect this information during transmission from a mobile terminal device to base station.

The present invention has been described above by describing embodiments of the invention. However, there are many possible modifications, as will be understood by a person skilled in the art.

From the above description, one skilled in the art will understand which modifications of software, firmware, and / or hardware are necessary and / or suitable for implementing the various described embodiments of the present invention.

The drawings and description of the invention disclose typical preferred embodiments of the invention and, although specific terms are used, they are used only in a universal and descriptive sense, and not with the aim of limiting the scope of the invention, which is set forth in the following claims.

Claims (39)

1. The device (401) of a mobile terminal for use in a wireless communication system (420), comprising:
a receiver (405) for receiving a signal (404) from the number M of transmitting antennas (403-1, 403-2, 403-3, 403-4), and this signal includes several subcarriers (412),
a processing module (406) for determining a channel quality indicator, CQI, message transmission format for the population of said subcarriers based on a selected transmit antenna configuration associated with said population of subcarriers, and for determining a number P _{CQI of CQI} values (409) related to said population of subcarriers , in accordance with a specific CQI message transmission format, this processing module being adapted to adapt the CQI message transmission format to the selected configuration of the transmitting antennas so that granularity of CQI transmission messages depends on the number of transmit m antennas transmit antennas selected configuration, and
a transmitter (407) for transmitting said P _{CQI CQI} values to the base station (400) in the feedback signal (408). 2. The mobile terminal device (401) according to claim 1, wherein said set of subcarriers (401) is divided into the number Q of non-overlapping groups (1, 2, 3) of subcarriers according to said CQI message format, and wherein said processing unit is configured to the ability to determine one CQI value (409) for each group of subcarriers for each transmit antenna (403-1, 403-2, 403-3, 403-4) of the selected transmit antenna configuration. 3. The device (401) of the mobile terminal according to claim 1, wherein the processing module (406) is adapted to adapt the degree of detail in the frequency of transmission of CQI messages to the number m of transmitting antennas of the selected transmitting antenna configuration. 4. The mobile terminal device (401) according to claim 2, wherein the number of Q subcarrier groups is based on the number m of transmit antennas of the selected transmit antenna configuration so that the number P _{CQI of CQI} values (409) determined for m transmit antennas of the selected transmit antenna configuration , is essentially the same for different selected transmit antenna configurations having a different number of transmit antennas. 5. The device (401) of the mobile terminal according to claim 2 or 4, in which said Q groups of subcarriers are divided into T non-overlapping subsets according to said CQI message format, and in which the transmitter (407) is configured to transmit said P _CQI values (409 ) CQI over T time periods so that the CQI values related to the subcarrier groups of the same subset are transmitted in each time period. 6. The mobile terminal device (401) according to claim 5, wherein the number of subsets of the T subcarrier groups and the number of Q subcarrier groups are adapted to the number of transmit antennas (403-1, 403-2, 403-3, 403-4) of the selected transmit configuration antennas according to the aforementioned CQI message format so that the number of CQI values (409) transmitted in each time period is substantially the same. 7. The mobile terminal device (401) according to claim 6, in which the number of subsets of the T subcarrier groups and the sizes of the subcarrier groups are further adapted to the number of transmit antennas (403-1, 403-2, 403-3, 403-4) of the selected transmit configuration antennas according to the aforementioned CQI message format so that the number of CQI values (409) transmitted in each time period is substantially the same for different selected antenna configurations containing a different number of transmit antennas. 8. The device (401) of the mobile terminal according to claim 1 or 2, in which the processing module (406) is adapted to adapt the degree of detail in the time of transmission of CQI messages to the number of transmit antennas of the selected transmit antenna configuration. 9. The device (401) of the mobile terminal of claim 8, in which the transmitter (407) is configured to transmit the said number P _{CQI of CQI} values for a number of T time periods, and T depends on the number of transmit antennas of the selected configuration of the transmit antennas. 10. The device (401) of the mobile terminal according to any one of claims 1 to 4, 6, 7, 9, in which said processing module (406) is further configured to select said selected antenna configuration and set up antenna configuration information (411), which is to be transmitted to said base station (400) in said feedback signal (408), this antenna configuration information describing said selected antenna configuration. 11. The mobile terminal apparatus (401) of claim 10, wherein said antenna configuration information (411) defines a subset of transmit antennas associated with each subcarrier (412) of said subcarrier set. 12. The mobile terminal device (401) according to claim 11, wherein said selected configuration of the transmit antennas is a subset of m transmit antennas from said number M of transmit antennas (403-1, 403-2, 403-3, 403-4), wherein m≤M. 13. The mobile terminal apparatus (401) of claim 10, wherein said antenna configuration information (411) defines a decoding order of transmitting antennas associated with each subcarrier (412) of said set of subcarriers. 14. The mobile terminal device (401) according to claim 13, wherein said selected configuration of the transmitting antennas includes all of said number M of transmitting antennas (403-1, 403-2, 403-3, 403-4) so that m = M , and sets the decoding order for said number M of transmit antennas. 15. The mobile terminal device (401) according to any one of claims 11-14, wherein said transmitter (407) is configured to transmit said antenna configuration information (411) in said feedback signal (408) by puncturing the least significant bits of said values (409) CQI by fixed or random pattern. 16. A method in a device (401) of a mobile terminal, comprising:
receiving (500) a signal from the number of M transmit antennas (403-1, 403-2, 403-3, 403-4), and this signal includes several subcarriers (412),
determining (501) a channel quality indicator, CQI, a message transmission format for a plurality of said subcarriers based on a selected transmit antenna configuration associated with said a plurality of subcarriers, said CQI message format being adapted to a selected transmit antenna configuration so that a CQI message granularity depends on the number m of transmitting antennas of the selected transmitting antenna configuration,
determining (502) the number P _{CQI of CQI} values (409) related to said set of subcarriers in accordance with a specific CQI message transmission format, and
transmitting (503) said P _{CQI CQI} values to the base station (400) in the feedback signal (408). 17. The method according to clause 16, in which the said set of subcarriers is divided into the number Q of non-overlapping groups (1, 2, 3) subcarriers according to the aforementioned CQI message format and in which one value (409) CQI is determined for each group of subcarriers for each transmit antennas of the selected transmit antenna configuration. 18. The method according to clause 16, in which the degree of detail in the frequency of transmission of messages CQI adapt to the number m of transmitting antennas of the selected configuration of transmitting antennas. 19. The method of claim 17, wherein the number of Q subcarrier groups is based on the number m of transmit antennas of the selected transmit antenna configuration so that the number P _{CQI of CQI} values (409) determined for m transmit antennas of the selected transmit antenna configuration is substantially the same for different selected transmit antenna configurations having a different number of transmit antennas. 20. The method of claim 17 or 19, wherein said Q subcarrier groups are divided into T nonoverlapping subsets according to said CQI message format, and wherein said P _{CQI CQI} values (409) are transmitted over T time periods such that CQI values belonging to groups of subcarriers of one subset are transmitted in each time period. 21. The method according to claim 20, in which the number of subsets of subcarrier groups T and the number of Q subcarrier groups are adapted to the number of transmit antennas of the selected transmit antenna configuration according to the aforementioned CQI message format so that the number of CQI values transmitted in each time period is essentially the same. 22. The method according to item 21, in which the number of subsets of groups T of subcarriers and the sizes of groups (1, 2, 3) subcarriers are further adapted to the number of transmit antennas of the selected configuration of transmit antennas according to the aforementioned CQI message format so that the number of CQI values transmitted in each time period, is essentially the same for different selected antenna configurations containing a different number of transmitting antennas. 23. The method according to clause 16 or 17, in which the degree of detail in the time of transmission of CQI messages is adapted to the number of transmitting antennas of the selected configuration of transmitting antennas. 24. The method according to item 23, in which the aforementioned number P _{CQI CQI} values are transmitted during the number T of time periods, and T depends on the number of transmitting antennas of the selected configuration of the transmitting antennas. 25. The method according to any one of claims 16-19, 21, 22, 24, further comprising selecting said transmit antenna configuration, setting antenna configuration information (411), said antenna configuration information describing said selected antenna configuration, and transmitting said antenna configuration information to said base station in said feedback signal (408). 26. The method of claim 25, wherein said antenna configuration information defines a subset of the transmit antennas associated with each subcarrier (412) of said set of subcarriers. 27. The method of claim 26, wherein said selected transmit antenna configuration is a subset of m transmit antennas from said number M of transmit antennas (403-1, 403-2, 403-3, 403-4), wherein m М M. 28. The method of claim 25, wherein said antenna configuration information (411) defines a decoding order of transmitting antennas associated with each subcarrier of said set of subcarriers. 29. The method according to p. 28, in which the aforementioned selected configuration of the transmitting antennas includes all of the aforementioned number M of transmitting antennas (403-1, 403-2, 403-3, 403-4) so that m = M, and sets decoding order for said number M of transmit antennas. 30. The method according to any one of claims 26-29, wherein said antenna configuration information is transmitted in said feedback signal (408) by puncturing the least significant bits of said CQI values (409) in a fixed or random manner. 31. A base station (400) for use in a wireless communication system (420), comprising:
a transmitter (410) for transmitting a signal (404) including several subcarriers (412) from the number of M transmit antennas (403-1, 403-2, 403-3, 403-4),
a receiver (421) for receiving a feedback signal (408) from the mobile terminal device (401),
a processing module (402) for processing said feedback signal for extracting a number P _{CQI of CQI} values (409) related to the totality of said subcarriers and extracting antenna configuration information (411) defining a selected transmit antenna configuration whose CQI values correspond to a message transmission format CQI, which depends on the selected configuration of the transmitting antennas so that the granularity of the CQI message transmission depends on the number of antennas of the selected configuration of the transmitting antennas. 32. The base station (400) according to claim 31, wherein said plurality of subcarriers is divided by the number Q of non-overlapping groups (1, 2, 3) of subcarriers according to said CQI message format and in which each of said CQI values (409) is associated with one of the mentioned groups of subcarriers and one of the transmit antennas of the selected configuration of the transmit antennas. 33. The base station (400) according to claim 31, wherein the frequency granularity of said CQI message format is adapted to the number m of transmit antennas of said selected transmit antenna configuration. 34. The base station (400) according to claim 32, wherein said Q subcarrier groups are divided into T non-overlapping subsets according to the aforementioned CQI message format and in which the receiver (421) is configured to receive said P _CQI number (409) CQI in the course of T time periods so that CQI values relating to groups of subcarriers of one subset are received in each time period. 35. The base station (400) according to claim 31 or 32, wherein the time granularity of said CQI message format is adapted to the number of transmit antennas of the selected transmit antenna configuration. 36. The base station (400) according to claim 35, wherein the receiver (421) is configured to receive said number P _{CQI of CQI} values over a number T of time periods, and T depending on the number of transmit antennas of the selected transmit antenna configuration. 37. The base station (400) according to any one of claims 31-34, 36, wherein said antenna configuration information (411) defines a subset of transmit antennas associated with each subcarrier (412) of said set of subcarriers. 38. The base station (400) according to any one of claims 31-34, 36, wherein said antenna configuration information (411) defines a decoding order of transmitting antennas associated with each subcarrier (412) of said number of subcarriers. 39. A base station (400) according to any one of claims 31-34, 36, wherein said processing module (402) is configured to extract said antenna configuration information (411) from the low-order bits of said CQI values (409), which were punctured in a fixed or random pattern to transfer the mentioned antenna configuration information.

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