USER EQUIPMENT DRIVEN SOUNDING REFERENCE SIGNAL TRANSMISSIONS IN DIFFERENT FREQUENCY LOCATIONS

1. Techniques related to user-device-driven sounding reference signals (SRS) transmission using different zones of operating frequency bands are disclosed. In one example aspect, a method for wireless communication includes receiving, by a wireless device, configuration information for a sounding reference signal from a base station in a first frequency region of an operating frequency band and determining, by the wireless device, one or more configured frequency positions for transmitting the sounding reference signal based on the frequency domain information of a sounding reference signal resource. The method also includes determining, by the wireless device, an additional frequency position within a second frequency region that is different from the first frequency region. The method further includes transmitting, by the wireless device, the sounding reference signal to the base station using the one or more configured frequency positions and the additional frequency position.

BACKGROUND

Sounding Reference Signal (SRS) is a reference signal transmitted by a user equipment (UE) in the uplink direction. The SRS is used by a base station to estimate the quality of an uplink channel for large bandwidths outside the assigned span to a specified UE. The SRS provides information about the combined effect of multipath fading, scattering, Doppler and power loss of transmitted signals.

DETAILED DESCRIPTION

In wireless communications, uplink communication generally refers to transmissions from UE to a base station, and uplink frequency is the frequency used for transmissions from the UE to the base station. Downlink communication generally refers to transmissions from the base station to the UE, and downlink frequency is the frequency used for transmissions from the base station to the UE. The base station can perform uplink channel estimation using reference signals such as the Demodulation Reference Signal (DMRS) on the Physical Uplink Shared Channel (PUSCH). However, channel estimation using the PUSCH DMRS can be limited because the PUSCH DMRS is transmitted only when PUSCH is scheduled. On the other hand, the SRS can be transmitted independently from PUSCH and can provide uplink channel quality estimation independent of PUSCH DMRS. With the advance of the Fifth-Generation (5G)/New Radio (NR) access technology, the SRS plays a more important role because Time Division Duplex (TDD) is the main mode of 5G deployment. In TDD, the base station can utilize the channel estimation results from the SRS not only for uplink (UL) scheduling but also for downlink (DL) scheduling based on channel reciprocity in TDD.

Traditionally, the base station configures SRS parameters and transmits the configuration to the UE. The UE then transmits the SRS using the configuration so that the base station can measure the SRS and determine the channel quality of uplink communication. Because the configuration is done by the base station prior to receiving the SRS from the UE, the base station may not be aware of the deteriorating channel conditions in a timely manner.

The disclosed technologies address these and other problems of conventional systems by allowing the UE to autonomously determine different frequency locations in one or more operating bands to transmit SRS. In 5G/NR communications, an operating band is a frequency band associated with a certain set of radio frequency (RF) requirements. Bandwidths of different operating bands can vary from several MHz to a few GHz (e.g., n41, n78, n261 for TDD; n25, n66 for FDD). The base station informs the UE of the channel bandwidth of a cell within an operating band, as well as the position and width of one or more Bandwidth Parts (BWPs), where a BWP is a set of contiguous resource blocks configured inside a channel bandwidth. The disclosed technologies enable the UE to leverage different zones of operating band(s) in addition to the operating band configured by the base station. The UE can inform the base station of the different zones that it chooses for transmitting the SRS to ensure that the base station can properly detect the SRS. In response to receiving the SRS from different zones of operating band(s), the base station can analyze the channel conditions of the SRS signals (e.g., over a period of time) to determine frequencies with desirable propagation characteristics. In some embodiments, the base station reconfigures the uplink channel(s) using the desired frequency or frequencies to achieve improved propagation characteristics for subsequent uplink communication.

Wireless Communications System

FIG.1is a block diagram that illustrates a wireless telecommunication network100(“network100”) in which aspects of the disclosed technology are incorporated. The network100includes base stations102-1through102-4(also referred to individually as “base station102” or collectively as “base stations102”). A base station is a type of network access node (NAN) that can also be referred to as a cell site, a base transceiver station, or a radio base station. The network100can include any combination of NANs including an access point, radio transceiver, gNodeB (gNB), NodeB, eNodeB (eNB), Home NodeB or Home eNodeB, or the like. In addition to being a wireless wide area network (WWAN) base station, a NAN can be a wireless local area network (WLAN) access point, such as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 access point.

The NANs of a network100formed by the network100also include wireless devices104-1through104-7(referred to individually as “wireless device104” or collectively as “wireless devices104”) and a core network106. The wireless devices104-1through104-7can correspond to or include network100entities capable of communication using various connectivity standards. For example, a 5G communication channel can use millimeter wave (mmW) access frequencies of 28 GHz or more. In some implementations, the wireless device104can operatively couple to a base station102over a long-term evolution/long-term evolution-advanced (LTE/LTE-A) communication channel, which is referred to as a 4G communication channel.

The core network106provides, manages, and controls security services, user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The base stations102interface with the core network106through a first set of backhaul links (e.g., S1 interfaces) and can perform radio configuration and scheduling for communication with the wireless devices104or can operate under the control of a base station controller (not shown). In some examples, the base stations102can communicate with each other, either directly or indirectly (e.g., through the core network106), over a second set of backhaul links110-1through110-3(e.g., X1 interfaces), which can be wired or wireless communication links.

The base stations102can wirelessly communicate with the wireless devices104via one or more base station antennas. The cell sites can provide communication coverage for geographic coverage areas112-1through112-4(also referred to individually as “coverage area112” or collectively as “coverage areas112”). The geographic coverage area112for a base station102can be divided into sectors making up only a portion of the coverage area (not shown). The network100can include base stations of different types (e.g., macro and/or small cell base stations). In some implementations, there can be overlapping geographic coverage areas112for different service environments (e.g., Internet-of-Things (IoT), mobile broadband (MBB), vehicle-to-everything (V2X), machine-to-machine (M2M), machine-to-everything (M2X), ultra-reliable low-latency communication (URLLC), machine-type communication (MTC), etc.).

The network100can include a 5G network100and/or an LTE/LTE-A or other network. In an LTE/LTE-A network, the term eNB is used to describe the base stations102, and in 5G new radio (NR) networks, the term gNBs is used to describe the base stations102that can include mmW communications. The network100can thus form a heterogeneous network100in which different types of base stations provide coverage for various geographic regions. For example, each base station102can provide communication coverage for a macro cell, a small cell, and/or other types of cells. As used herein, the term “cell” can relate to a base station, a carrier or component carrier associated with the base station, or a coverage area (e.g., sector) of a carrier or base station, depending on context.

Wireless devices can be integrated with or embedded in other devices. As illustrated, the wireless devices104are distributed throughout the system100, where each wireless device104can be stationary or mobile. For example, wireless devices can include handheld mobile devices104-1and104-2(e.g., smartphones, portable hotspots, tablets, etc.); laptops104-3; wearables104-4; drones104-5; vehicles with wireless connectivity104-6; head-mounted displays with wireless augmented reality/virtual reality (AR/VR) connectivity104-7; portable gaming consoles; wireless routers, gateways, modems, and other fixed-wireless access devices; wirelessly connected sensors that provides data to a remote server over a network; IoT devices such as wirelessly connected smart home appliances, etc.

A wireless device (e.g., wireless devices104-1,104-2,104-3,104-4,104-5,104-6, and104-7) can be referred to as a user equipment (UE), a customer premise equipment (CPE), a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a handheld mobile device, a remote device, a mobile subscriber station, terminal equipment, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a mobile client, a client, or the like.

A wireless device can communicate with various types of base stations and network100equipment at the edge of a network100including macro eNBs/gNBs, small cell eNBs/gNBs, relay base stations, and the like. A wireless device can also communicate with other wireless devices either within or outside the same coverage area of a base station via device-to-device (D2D) communications.

The communication links114-1through114-9(also referred to individually as “communication link114” or collectively as “communication links114”) shown in network100include uplink (UL) transmissions from a wireless device104to a base station102, and/or downlink (DL) transmissions from a base station102to a wireless device104. The downlink transmissions can also be called forward link transmissions while the uplink transmissions can also be called reverse link transmissions. Each communication link114includes one or more carriers, where each carrier can be a signal composed of multiple sub-carriers (e.g., waveform signals of different frequencies) modulated according to the various radio technologies. Each modulated signal can be sent on a different sub-carrier and carry control information (e.g., reference signals, control channels), overhead information, user data, etc. The communication links114can transmit bidirectional communications using frequency division duplex (FDD) (e.g., using paired spectrum resources) or Time division duplex (TDD) operation (e.g., using unpaired spectrum resources). In some implementations, the communication links114include LTE and/or mmW communication links.

In some implementations of the network100, the base stations102and/or the wireless devices104include multiple antennas for employing antenna diversity schemes to improve communication quality and reliability between base stations102and wireless devices104. Additionally or alternatively, the base stations102and/or the wireless devices104can employ multiple-input, multiple-output (MIMO) techniques that can take advantage of multi-path environments to transmit multiple spatial layers carrying the same or different coded data.

In some examples, the network100implements 6G technologies including increased densification or diversification of network nodes. The network100can enable terrestrial and non-terrestrial transmissions. In this context, a Non-Terrestrial Network (NTN) is enabled by one or more satellites such as satellites116-1and116-2to deliver services anywhere and anytime and provide coverage in areas that are unreachable by any conventional Terrestrial Network (TN). A 6G implementation of the network100can support terahertz (THz) communications. This can support wireless applications that demand ultra-high quality of service requirements and multi-terabits per second data transmission in the 6G and beyond era, such as terabit-per-second backhaul systems, ultrahigh-definition content streaming among mobile devices, AR/VR, and wireless high-bandwidth secure communications. In another example of 6G, the network100can implement a converged Radio Access Network (RAN) and Core architecture to achieve Control and User Plane Separation (CUPS) and achieve extremely low User Plane latency. In yet another example of 6G, the network100can implement a converged Wi-Fi and Core architecture to increase and improve indoor coverage.

The SRS is transmitted from the UE to the base station independently from PUSCH to provide uplink channel quality estimation. The SRS can be transmitted using different modes.FIG.2illustrates example transmission modes for SRS transmissions. In wideband mode, one single transmission of the SRS covers the bandwidth. The channel quality estimate is obtained within a single symbol. However, uplink communication can be impaired if UE remains in a specific operating 5G NR band that has poor channel characteristics (e.g., poor uplink throughput, latency, fading, packet loss, jitter, and signal loss). Correspondingly, using the wideband mode can result in a poor channel estimate with poor channel conditions. To mitigate such problems, the hopping modes (e.g., frequency hopping and/or group hopping) can be used. In the hopping modes, the base station can split the SRS transmission into a series of narrowband transmissions that cover the bandwidth to mitigate the impact of having poor channel conditions. The hopping modes can help address the poor channel estimate issues under deteriorating channel conditions. However, the base station may not be aware of the deteriorating channel conditions in a timely manner. The base-station-driven SRS transmission approach is thus not sufficient to detect real-time or near real-time channel condition deteriorations to provide optimal experiences for applications that require reliability and low latencies.

This patent document discloses techniques that can be implemented in various embodiments to provide a UE-driven SRS transmission approach to enable accurate channel estimations by the base station in a timely manner. The disclosed technologies address the shortcomings of the base-station-driven SRS transmission approach by enabling the UE to autonomously determine different zone of operating band(s) for SRS transmissions. For example, the UE can analyze frequencies that are in proximity to the configured Physical Uplink Control Channel (PUCCH) and/or the Physical Uplink Shared Channel (PUSCH). In addition, the UE can analyze frequencies that are away from the frequencies of the PUCCH/PUSCH channels. Correspondingly, the UE can transmit the SRS signals using different frequency locations that span across different regions of the operating band(s). In response to receiving the SRS signals with varying frequency locations, the base station assesses the received SRS signals to identify the frequencies with desirable propagation characteristics for uplink channel(s). The base station can assess the received SRSs over a period of time and determine that a specific frequency region within a specific operating band provides better propagation characteristics. The base station then re-tunes the uplink frequency for subsequent uplink communication to achieve better transmission performance.

FIG.3is a flowchart representation of an example process/method for wireless communication in accordance with one or more embodiments of the present technology. The process/method300comprises, at Operation302, receiving, by a wireless device from a base station, configuration information for SRS in a first frequency region of an operating frequency band. The first frequency region can be a predetermined or pre-configured region of the operating frequency band. In some embodiments, the base station transmits the SRS configuration information using radio resource control (RRC) messages. Examples of the SRS configuration information in the RRC messages include information about a set of SRS resources for the UE to transmit the SRS, frequency bandwidth allocated for SRS transmission, channel characteristics of the frequency bandwidth, and desired subframes at which the UE is to transmit the SRS. The sounding reference signal can be transmitted in a periodic manner or in an aperiodic manner. In some embodiments, the predetermined frequency region of the operating frequency band is an active bandwidth part (BWP). BWP is a contiguous set of resource blocks within a given frequency bandwidth. The predetermined frequency region can be an active BWP configured by the base station. The predetermined frequency region can also be an initial BWP, a default BWP, or one of the other configured BWPs. In some embodiments, a frequency region comprises one or more subcarriers in the frequency domain.

At Operation304, the wireless device (also referred to as UE) determines one or more configured frequency positions for transmitting the SRS. The one or more configured frequency positions are within the predetermined frequency region of the operating frequency band specified in the configuration information from the base station. In some embodiments, the base station configures the UE to transmit the SRS using a frequency-hopping mode. In the frequency-hopping mode, the SRS transmission is split into a series of narrowband transmissions where each narrowband transmission is associated with one of the one or more configured frequency positions.

At Operation306, the UE determines an additional frequency position within a new frequency region. The new frequency region is different from the predetermined frequency region of the operating frequency band. For example, the UE can be configured with multiple BWPs, with one BWP being the active BWP in the operating frequency band. The UE can autonomously determine additional frequency position(s) in the non-active BWP(s) for SRS transmissions. As another example, the UE can determine that the new frequency region is located in a different operating band and select additional frequency position(s) in the different operating band.

In some embodiments, the UE decides to search for the additional frequency position within the new frequency region in response to the UE detecting that the predetermined frequency region exhibits a channel condition lower than a threshold value. The threshold value is configured by the base station and indicates a minimum channel condition of a frequency region required for SRS transmission. In some embodiments, the UE decides to search for the additional frequency position within the new frequency region regardless of the channel condition of the predetermined frequency region.

In some embodiments, upon determining that a single frequency position exhibits the most desirable channel characteristics for the bandwidth region of interest, the UE configures one additional frequency position for transmitting the SRS. In some embodiments, upon determining that multiple frequency positions exhibit desirable channel characteristics for portions of the region of interest, the UE configures multiple frequency positions for transmitting the SRS in respective portions of the bandwidth region of interest.

For example, a UE can be configured to camp on the n41 operating band (2500 MHz). Once configured, the UE performs transmissions on specific subcarrier(s) or an exact frequency, also known as Absolute Radio Frequency Number (ARFCN) within the n41 operating band. The UE is also capable to monitor and communicate over other subcarrier(s) within the same operating band. The UE can monitor one or more subcarriers that are adjacent to the configured subcarrier(s) and select some of them as the additional frequency position(s).

In some embodiments, when frequency-hopping is configured by the base station, the UE can combine frequency-hopping with the one or more frequency positions in the new frequency region identified by the UE to achieve optimal channel estimation. Alternatively, for the SRS transmission in the additional frequency position(s) identified by itself, the UE can ignore the frequency-hopping configuration from the base station.

At Operation308, the UE transmits the SRS using the one or more configured frequency positions and the additional frequency position(s). In some embodiments, the UE and the base station can agree upon a pre-determined set of candidate frequency positions. The set of candidate frequency positions can also be negotiated and updated based on additional signaling between the base station and the UE. For example, when mobility events occur and the coverage areas of the source and target base stations change, the additional negotiation and updates of the set of candidate frequency positions helps the UE to better tune to the coverage area of the target base station. In some embodiments, the UE can transmit an indication to the base station, e.g., via uplink control information, to indicate the additional frequency positions(s) that it intends to use for SRS transmissions. The indication from the UE can enable the base station to properly detect the SRS transmissions so as to determine the uplink channel conditions.

In some embodiments, after transmitting the SRS to the base station, the wireless device receives reconfiguration information from the base station. The reconfiguration information can include a switch from the predetermined frequency region to the new frequency region. The reconfiguration information can also include channel characteristics information of the predetermined frequency region and/or the new frequency region. For example, the reconfiguration information indicates that for one portion of the region of interest, a configured frequency position within the predetermined frequency region is least likely to experience latency and packet loss and is thus the preferred frequency position. The reconfiguration information also indicates that for another portion of the region of interest, the additional frequency position within the new frequency region is least likely to experience latency, packet loss, and signal loss and is the preferred frequency position. After receiving the reconfiguration information, the UE performs subsequent communication with the base station using the preferred frequency positions as indicated by the reconfiguration information.

FIG.4is a flowchart representation of another process/method for wireless communication in accordance with one or more embodiments of the present technology. The process/method400includes, at Operation402, transmitting, by a base station to a wireless device, configuration information for an SRS in a first frequency region of an operating frequency band. The first frequency region can be a predetermined or pre-configured region of the operating frequency band. As discussed in connection withFIG.3, the configuration information can include information about multiple SRS for the UE to transmit the SRS, frequency bandwidth allocated for SRS transmission, channel characteristics of the frequency bandwidth, and desired subframes at which the UE is to transmit the SRS. The sounding reference signal can be transmitted in a periodic manner or in an aperiodic manner.

At Operation404, the base station receives the SRS from the wireless device using one or more configured frequency positions and at least one additional frequency position. In some embodiments, the one or more configured frequency positions are determined based on the information about the multiple SRS included in the configuration information. The additional frequency position(s) are in a new frequency region of the operating band. The new frequency region is different from the first frequency region of the operating frequency band. For example, the new frequency region can be in the same operating frequency band as the first frequency region, with different locations. The new frequency region can also be in a different operating band.

In some embodiments, the base station receives signals (e.g., via uplink control information UCI) from the UE indicating the additional frequency position(s) within the new frequency region to enable the base station to properly detect the SRS transmissions from the UE. In some embodiments, when frequency-hopping is configured by the base station, the base station receives the SRS using the one or more configured frequency positions and the additional frequency position(s) in combination with the frequency-hopping mechanism. In some embodiments, frequency-hopping is not adopted in the additional frequency position(s) selected by the UE.

The base station determines the channel conditions of the one or more configured frequency positions and the additional frequency positions to determine frequency positions with optimal channel conditions. In some embodiments, the base station transmits reconfiguration information to the UE based on the SRS received from the UE. The reconfiguration information can include a switch from the predetermined frequency region to the new frequency region. The reconfiguration information can also include channel characteristics information of the predetermined frequency region and/or the new frequency region. Upon determining that the predetermined frequency region exhibits unsatisfactory channel conditions (e.g., a measurement result being below a threshold value), the base station transmits reconfiguration information requesting the switch from the predetermined frequency region to the new frequency region. Subsequent SRS transmissions by the UE to the base station are performed using the new frequency region until the base station transmits another reconfiguration information requesting another switch.

In some embodiments, the base station can determine the channel condition(s) based on the SRS transmission from the UE over a period of time. The period of time or the time duration can be predetermined and/or configured by the network operator. For example, the base station can use a timer to control the time duration for tracking SRS transmissions from frequency position(s) in the new frequency region selected by the UE.

Computer System

FIG.5is a block diagram that illustrates an example of a computer system500in which at least some operations described herein can be implemented. As shown, the computer system500can include: one or more processors502, main memory506, non-volatile memory510, a network interface device512, video display device518, an input/output device520, a control device522(e.g., keyboard and pointing device), a drive unit524that includes a storage medium526, and a signal generation device530that are communicatively connected to a bus516. The bus516represents one or more physical buses and/or point-to-point connections that are connected by appropriate bridges, adapters, or controllers. Various common components (e.g., cache memory) are omitted fromFIG.5for brevity. Instead, the computer system500is intended to illustrate a hardware device on which components illustrated or described relative to the examples of the figures and any other components described in this specification can be implemented.

The network interface device512enables the computing system500to mediate data in a network514with an entity that is external to the computing system500through any communication protocol supported by the computing system500and the external entity. Examples of the network interface device512include a network adaptor card, a wireless network interface card, a router, an access point, a wireless router, a switch, a multilayer switch, a protocol converter, a gateway, a bridge, bridge router, a hub, a digital media receiver, and/or a repeater, as well as all wireless elements noted herein.

The memory (e.g., main memory506, non-volatile memory510, machine-readable medium526) can be local, remote, or distributed. Although shown as a single medium, the machine-readable medium526can include multiple media (e.g., a centralized/distributed database and/or associated caches and servers) that store one or more sets of instructions528. The machine-readable (storage) medium526can include any medium that is capable of storing, encoding, or carrying a set of instructions for execution by the computing system500. The machine-readable medium526can be non-transitory or comprise a non-transitory device. In this context, a non-transitory storage medium can include a device that is tangible, meaning that the device has a concrete physical form, although the device can change its physical state. Thus, for example, non-transitory refers to a device remaining tangible despite this change in state.

Remarks