CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application for International Application No. PCT/SE2018/050089, entitled “WIRELESS NODE FOR RECEIVING A WIRELESS SIGNAL AND METHOD THEREOF”, filed on Feb. 2, 2018, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless node for receiving a wireless signal. Furthermore, the present disclosure also relates to corresponding, methods, computer programs, computer program products and carriers.

BACKGROUND

In wireless communication systems, information is transmitted wirelessly between the different wireless nodes of the system. For example, information may be transmitted downlink (DL), from a wireless node, such as a base station (BS), to another wireless node, such as a user equipment (UE), or, uplink (UL) from the UE to the BS. In the case of Device-to-device (D2D) communication, information may be transmitted from one transmitting node, such as a transmitting TX UE, to one or more receiving wireless nodes, such as a receiving RX UE. D2D communication between devices in the proximity of one another has been proposed to enhance the user data rates, increase the system capacity and reduce latency. For D2D communications various power control algorithms have been discussed, although these are not implemented in practice. Specifically in 3GPP systems, the sidelink (SL) enables D2D communications over resources that may be controlled by the BS. Due to the mobility patterns of D2D scenarios, and the fading channel characteristics between devices, the received power may vary at the Rx UE devices.

Specifically, in 3GPP LTE systems, SL communications are performed on a subframe or slot basis. In the PHY layer, the SL control information is transmitted over the physical sidelink control channel (PSCCH), and the SL data information is carried over the physical sidelink shared channel (PSSCH). The subframe structure for PSCCH and PSSCH is based on the cellular uplink transmission structure, more specifically, the basic structure of physical uplink shared channel (PUSCH). In 3GPP LTE Rel-12 and Rel-13, all SL communications are based on Discrete Fourier Transform Spread (DFTS)-OFDM with subcarrier spacing of 15 kHz and a subframe/slot structure. To cope with high UE mobility (and short channel coherence time) scenarios, in particular in Rel-14 intended for vehicle-to-vehicle (V2V) SL communication, the number of symbols used for the transmission of demodulation reference signals (DMRS) has been increased to four. The subframe/slot structure may comprise of 14 SC-FDMA symbols for PSSCH and PSCCH in LTE V2V sidelink. The last symbol of the subframe is typically not used for transmitting data. Instead, it is used as a guard period (GP), e.g. for switching between SL transmission and reception, as well as between SL transmission/reception and uplink transmission. An important difference from UL transmission, is that there can be multiple receiving, RX UE, wireless nodes involved in the SL communication. Consequently, SL transmissions may not be power controlled to any one RX UE. This can lead to significant received power variation from one time instant to another for a Rx node. Therefore, the first symbol (up to 70 us) of the subframe for SL communication is reserved or dedicated for use as an automatic gain controller (AGC) settling period at the Rx nodes.

In multipath fading channels, the dynamical range of the received power at receiving (Rx) wireless nodes may be large (e.g. >60 dB), which makes variable gain power amplifiers an important part of the Rx wireless node circuitry. A key component of variable gain amplifiers is Automatic Gain Control, AGC, which is designed to exhibit fast initial convergence and adaptive capabilities to maintain an acceptable link quality even in fast fading channels. This is essential for the correct data decoding at RX nodes. The required AGC settling time at an Rx node depends on many factors, e.g., the receiving power range for the data reception, the hardware of the RX node, the AGC implementation type, the convergence rate of the applied AGC algorithm, etc. To ensure sufficient time for AGC convergence, OFDM based systems may use the duration of a dedicated symbol (“AGC symbol”), e.g. in the beginning of a received data frame, slot or packet. Although this dedicated AGC symbol is useful for automatic gain control, it presents an overhead at the communication link that negatively impacts the overall spectral efficiency and user throughput.

The 3GPP New Radio (NR) system is designed to operate on a wide range of frequency channels, propagation conditions, and device capabilities. A key concept is the flexible numerology that allows UEs or wireless nodes to use different subcarrier spacing (SCS), waveform parameterization, cyclic prefix length, slot- and frame structure, depending on the deployment scenario and the carrier frequency. In the example of 3GPP NR, the default transmission unit length consists of 14 OFDM symbols with normal cyclic prefix. A numerology with a larger subcarrier spacing has a shorter transmission duration. Note that the NR frame structure or slot structure also supports the concept of mini-slots/non-slot based transmissions that contain a reduced number of OFDM symbols for a short transmission duration to facilitate ultra-low latency communications. As the transmission duration becomes shorter, 1 symbol duration with a reference numerology of 15 kHz, i.e., around 70 us fixed time duration, reserved for AGC settling can result in a large overhead. This negatively impacts the overall spectral efficiency and user throughput. In an example, a specific numerology (using 15 kHz or 30 kHz) is used for each OFDM symbol within a slot. As can be understood, a higher SCS reduces the OFDM symbol time for each symbol in the slot. The AGC overhead increases as the subcarrier spacing increases or/and the slot lengths decreases.

Normal OFDM/DFTS-OFDM symbols containing data may be transmitted in the first symbol used for AGC settling, and these data can be used for decoding at the RX UEs. However, a problem when doing so is that the data transmitted during the AGC settling period may be distorted, which can affect the overall data decoding performance, depending on a ratio between the AGC settling period to the overall transmission duration of a subframe, slot or mini-slot. For instance, if the data transmitted in the AGC symbol is lost at the RX UE, and the overall transmission duration consists of two symbols, then, it is high likely that the RX UE cannot decode the SL data since 50% of the data is lost due to the AGC impact/overhead. Therefore, the relative overhead of AGC settling duration has an impact on the SL communication performance, and the impact is higher for shorter SL transmission durations. Moreover, to enable early data decoding and low latency, or/and to enable different MIMO technologies used for PSCCH and PSSCH, it is possible that the PSCCH and its associated PSSCH are multiplexed in the same time slot with the same frequency allocation. If some control information is carried in the first AGC symbol, then, the AGC settling period can cause a reliability issue for the control channel, which can also result in a failure for the decoding of PSSCH.

The AGC settling time and the receiver dynamic range depend on a number of factors including the carrier frequency, the bandwidth of the carrier under consideration, the class of UE selected as well as the scenarios and use cases under consideration. Therefore, it is difficult and can be very suboptimal to set a single value of AGC settling time for all SL communication cases.

In one example of a unicast case, there is a single target RX node for the SL transmission and the TX node is typically aware of the capabilities of the RX node.

In a further example of a multicast case, there are multiple target RX nodes for the SL transmission, and each RX node may have different AGC settling capabilities as well as different receiving power ranges. To enable that the SL transmission reaches all RX nodes, the AGC settling duration is limited to the RX node in need of the longest AGC settling period. However, in the multicast case, the TX node is typically unaware of the capabilities of the RX nodes, which makes it even harder or not possible to acquire the AGC settling related information of all RX nodes.

Thus, different solutions need to be considered to mitigate or compensate the AGC settling effects on different SL communication cases.

Thus there is a need to provide a solution which mitigates or solves the described drawbacks and problems, such as to reduce overhead at the communication link that negatively impacts the overall spectral efficiency and user throughput.

SUMMARY

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems described above. The above and further objectives are achieved by the subject matter described herein. Further advantageous embodiments or implementation forms of the invention are also defined herein.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a method for use in a wireless node configured to receive a wireless signal, the method comprising receiving, using a first set of physical resources, a first wireless signal comprising an indicator descriptive of a transmission power used by a second wireless node when transmitting the wireless signal on a second set of physical resources, receiving, using the second set of physical resources, the wireless signal using an Automatic Gain Control, AGC, configuration, wherein the AGC configuration is determined based on the indicator.

At least an advantage of the invention according to the first aspect is to improve overall spectral efficiency and user data throughput by reducing AGC overhead.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a wireless node.

The advantages of the second aspect are the same as for the first aspect.

Further applications and advantages of embodiments of the invention will be apparent from the following detailed description.

