Patent Publication Number: US-2023139305-A1

Title: Channel Sounding Using Multiple Sounding Configurations

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/215,737 filed 29 Mar. 2021, which is a continuation of U.S. patent application Ser. No. 16/747,881 filed 21 Jan. 2020, now U.S. Pat. No. 11,102,041, which is a continuation of U.S. patent application Ser. No. 16/445,403 filed 19 Jun. 2019, now U.S. Pat. No. 10,581,658, which is a continuation of U.S. patent application Ser. No. 16/354,696 filed 15 Mar. 2019, which is a continuation of U.S. patent application Ser. No. 15/047,190 filed 18 Feb. 2016, now U.S. Pat. No. 10,263,820, which is a continuation of U.S. patent application Ser. No. 12/672,324, filed 5 Feb. 2010, now U.S. Pat. No. 9,300,495, which is the National Stage of International Application No. PCT/EP2008/057559, filed 16 Jun. 2008, which claims the benefit of U.S. Provisional Application 60/954,734, filed 8 Aug. 2007, the disclosure of each of which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to uplink sounding reference signals, and particularly relates to configuring individual mobile terminals with a plurality of uplink sounding reference signal transmission parameters. 
     BACKGROUND 
     Uplink sounding reference signals are known signals transmitted on the uplink direction (i.e., mobile-terminal-to-network). Sounding reference signals can be used by the receiver (i.e., the base station) to estimate uplink channel quality, including the uplink channel quality for different frequency bands. The channel quality estimates can, for example, be used by an uplink scheduler located in the base station to determine a suitable uplink data rate (i.e., uplink rate control) or select a suitable frequency band for the uplink transmission for a given mobile terminal (also known as channel-dependent frequency-domain scheduling). 
     Uplink sounding reference signals can also be used by the receiver to estimate the timing of received signals. Such receive-timing estimates can be subsequently used by the network to adjust the mobile terminal transmit timing in order to time-align the receive timing of the uplink transmissions of different mobile terminals. Other uses of the uplink sounding reference signals are also possible. 
     In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), uplink sounding reference signals can be viewed as OFDM signals (Orthogonal Frequency-Division Multiplexing) in that the signals consist of a number of frequency sub-carriers with suitable modulation applied to each sub-carrier. More specifically, in case of LTE the modulation applied to the subcarriers is based on so called Zadoff-Chu sequences. An uplink sounding reference signal can be characterized in the frequency domain by the index of the first transmitted sub-carrier of the reference signal, the number of transmitted sub-carriers of the reference signal and the spacing between transmitted sub-carriers, also referred to as the repetition factor (RPF) of the reference signal. 
     Uplink sounding reference signals can also be characterized in the time domain. The LTE uplink time-domain structure includes subframes of 1 ms length. Each subframe has two equal-sized slots of 0.5 ms length, each slot including seven symbols. One symbol in each slot is used as a demodulation reference signal that cannot be mixed with sounding reference signals. The demodulation reference signals are used for uplink channel estimation to enable coherent uplink detection. The remaining symbols are typically used for data transmission. Thus, there are two demodulation reference symbols and twelve “data” symbols within each subframe. 
     If sounding reference signals are to be transmitted, a subset of the data symbols, e.g., every Mth data symbol, can be replaced by sounding reference signals. Typically, sounding reference signals are not transmitted in every subframe. Instead, one data symbol in every Nth subframe is replaced by a sounding reference signal, the sounding reference signal including a number of sub-carriers in the frequency domain as described above. The sounding reference signal can be characterized in the time domain by the period (measured in number of subframes) of the sounding reference signal, i.e., how often the reference signal is transmitted. The sounding reference signal can be further characterized in the time domain by the time offset of the sounding reference signal (measured in number of subframes) and the position of the sounding reference signal within the subframe, i.e., which data symbol has been replaced by the reference signal. 
     Different uses of uplink sounding reference signals may require different characteristics for the reference signals. For example, if a sounding reference signal is to be used for channel-quality estimation, a sounding reference signal of relatively narrow bandwidth (i.e., relatively few transmitted sub-carriers) may be sufficient if scheduling is only to be carried out over a limited bandwidth. However, the sounding reference signal is typically transmitted relatively often (i.e., relatively small period) in order to track relatively fast channel variations. On the other hand, for timing-estimation purposes, a relatively wideband reference signal may be needed to yield an accurate timing estimation. At the same time, a relatively long reference-signal period is sufficient for timing-estimation purposes as the propagation delay typically varies relatively slowly. 
     One conventional approach used for both channel-quality estimation and timing estimation purposes involves transmitting a sounding reference signal with wide bandwidth and high rate (i.e., small period). However, this conventional approach uses a relatively large amount of radio resources to transmit the sounding reference signal because of the wide bandwidth and high rate requirements. As such, fewer uplink symbols are available for data transmission. Accordingly, a less radio-resource intensive solution is desired. 
     SUMMARY 
     According to the methods and apparatus disclosed herein, more than one set of sounding signal configuration parameters are determined for the same mobile terminal. The configuration parameters may differ in the frequency-domain and/or the time-domain. The sets of configuration parameter are transmitted to the mobile terminal for use by the terminal in generating different sounding reference signals. Occasionally, more than one sounding reference signal may be transmitted simultaneously when multiple configurations are used. Priorities may be assigned to the different sets of configuration parameters for mitigating signal transmission conflicts. The configuration parameter having the highest priority controls which reference signal is transmitted when a conflict is expected to occur. Sounding reference signals transmitted by the mobile terminal can be used for different purposes such as estimating channel quality and timing. 
     In one embodiment, a method of configuring uplink sounding transmissions by mobile terminals in a wireless communication network is characterized by determining different sets of configuration parameters for sounding signal transmissions for a given mobile terminal. The different sets of configuration parameters are transmitted to the mobile terminal, allowing the mobile terminal to generate different sounding signals for different uses by the wireless communication network. 
     Of course, the present invention is not limited to the above features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an embodiment of a wireless communication network including a base station that provides different sounding signal configurations for a given mobile terminal. 
         FIG.  2    is a flow diagram of an embodiment of program logic for providing different sounding signal configurations for a given mobile terminal. 
         FIG.  3    is a flow diagram of an embodiment of program logic for generating different sounding signals by a given mobile terminal based on different sounding signal configurations. 
         FIG.  4    is a block diagram of an embodiment of different sounding signal configurations for a given mobile terminal. 
         FIG.  5    is a block diagram of another embodiment of different sounding signal configurations for a given mobile terminal. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates an embodiment of a wireless communication network  100  including a base station  110  that services one or more mobile terminals  120 . The base station  110  includes a baseband processor  130 . A parameter generator  140  included in or associated with the baseband processor  130  determines different sets  150  of configuration parameters for sounding signal transmissions for the mobile terminal  120 , e.g., as illustrated by Step  200  of  FIG.  2   . The baseband processor  130  transmits the different sets  150  of configuration parameters to the mobile terminal  120  over a downlink communication channel  152 , e.g., as illustrated by Step  202  of  FIG.  2   . The sets  150  of configuration parameters enable the mobile terminal  120  to generate different sounding signals  160  for different uses by the base station  110  such as channel-quality estimation and timing estimation. 
     The mobile terminal  120  has a baseband processor  170  for receiving the sets  150  of configuration parameters transmitted from the base station  110 , e.g., as illustrated by Step  300  of  FIG.  3   . A sounding signal generator  180  included in or associated with the mobile terminal baseband processor  170  generates different sounding reference signals  160  based on the different sets  150  of configuration parameters, e.g., as illustrated by Step  302  of  FIG.  3   . The mobile terminal  120  transmits the sounding signals  160  to the base station  110  over an uplink communication link  162 . This way, multiple sounding reference signal configurations having different frequency-domain and/or time-domain parameters can be used by the same mobile terminal  120  to generate different sounding reference signals  160 . 
     According to one embodiment, one set  150  of the sounding signal configuration parameters causes the mobile terminal  120  to generate a first one of the sounding reference signals  160  with a relatively narrow bandwidth, but high rate in the time domain. A different set  150  of the sounding signal configuration parameters causes the mobile terminal  120  to generate a second one of the sounding reference signals  160  having a wider bandwidth, but lower time-domain rate. The first sounding signal can be used by the base station  110  for channel-quality estimation while the second sounding signal can be used for timing estimation. 
     Under some conditions, the different sets  150  of configuration parameters may create signal transmission conflicts at the mobile terminal  120  in that different sounding reference signal transmissions may occur within the same subframe or even within the same symbol, e.g., as illustrated in  FIG.  4   . Different priorities can be established or otherwise defined for the sets  150  of configuration parameters. The priorities allow the mobile terminal baseband processor  170  to determine which set  150  of configuration parameters should be used in the event of a sounding signal transmission collision. The configuration having the highest priority controls when more than one sounding reference signal transmission is expected to occur simultaneously, e.g., as illustrated in  FIG.  5    where the second configuration (#2) has the highest priority. The prioritization may be explicit such that each sounding reference signal configuration is explicitly assigned a priority at configuration. Alternatively, the prioritization can be implicit, e.g., depending on the different configuration parameters. According to one embodiment, the configuration having the widest bandwidth (consisting of the largest number of transmitted sub-carriers) is given the highest priority. Other implied priorities may also be implemented by the mobile terminal baseband processor  170 . 
     The embodiments described herein provide for the configuration, use and transmission of multiple sounding reference signal configurations to the same mobile terminal  120 . The configurations may differ in bandwidth and/or the number of transmitted frequency sub-carriers. Additionally, or alternatively, the configurations may differ in the spacing between the transmitted sub-carriers (i.e. in the repetition factor), and/or in signal transmission rate. Additionally, or alternatively, the configurations may have different explicit or implied priorities for avoiding conflicting sounding reference signal transmissions expected to occur simultaneously (or just in the same sub-frame). In one embodiment, the base station  110  explicitly signals the configuration priorities to the mobile terminal  120 . 
     Of course, other variations are contemplated. Thus, the foregoing description and the accompanying drawings represent non-limiting examples of the methods and apparatus taught herein for the transmission of system information. As such, the present invention is not limited by the foregoing description and accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.