Patent Description:
Wireless communication technologies are moving the world toward an increasingly connected and networked society. The rapid growth of wireless communications and advances in technology has led to greater demand for capacity and connectivity. Other aspects, such as energy consumption, device cost, spectral efficiency, and latency are also important to meeting the needs of various communication scenarios. In comparison with the existing wireless networks, next generation systems and wireless communication techniques need to provide support for an increased number of users and devices, as well as support for higher data rates and communications with satellite-based base stations, thereby requiring user equipment to implement preambles that are resilient to long propagation delays. <CIT> discloses a method for transmission of a device-to-device (D2D) signal by a terminal in a wireless communication system, comprising the steps of: a first terminal generating a D2D synchronization signal; and transmitting a subframe comprising the D2D synchronization signal, wherein the D2D synchronization signal comprises a primary D2D synchronization signal and a secondary D2D synchronization signal, and wherein, if at least one of the primary D2D synchronization signal and the secondary D2D synchronization signal in the subframe comprises two or more sequences that are transmitted in the subframe at different times, the two or more sequences are different from one another.

This document relates to methods, systems, and devices for generating sequences for reference signals in mobile communication technology, including 5th Generation (<NUM>) and New Radio (NR) communication systems.

The present invention is defined by independent claims. Preferred embodiments are specified by dependent claims.

There is an increasing demand for fourth generation of mobile communication technology (<NUM>, the 4th Generation mobile communication technology), Long-term evolution (LTE, Long-Term Evolution), Advanced long-term evolution (LTE-Advanced/LTE-A, Long-Term Evolution Advanced) and fifth-generation mobile communication technology (<NUM>, the 5th Generation mobile communication technology). From the current development trend, <NUM> and <NUM> systems are studying the characteristics of supporting enhanced mobile broadband, ultra-high reliability, ultra-low latency transmission, and massive connectivity.

With the development of the NR access technologies (e.g., <NUM>), a broad range of use cases including enhanced mobile broadband, massive machine-type communications (MTC), critical MTC, etc., can be realized. To expand the utilization of NR access technologies, <NUM> connectivity via satellites is being considered as a promising application. In contrast to the terrestrial networks where all communication nodes (e.g., base stations) are located on the earth, a network incorporating satellites and/or airborne vehicles to perform some or all of the functions of terrestrial base stations is referred to as a non-terrestrial network (NTN).

In NTNs, the coverage of a satellite is generally implemented by multiple beams. And the coverage of a beam is generally much larger than that of a terrestrial cell. For example, a satellite beam footprint diameter could be hundreds of kilometers or even larger. Different beams of a satellite have various minimum elevation angles, which means the differential round-trip delay (RTD) of each beam can be very different. A challenging topic brought by various differential RTD is how to effectively support random access from simultaneous UEs.

The present document uses section headings and sub-headings for facilitating easy understanding and not for limiting the scope of the disclosed techniques and embodiments to certain sections. Accordingly, embodiments disclosed in different sections can be used with each other. Furthermore, the present document uses examples from the 3GPP New Radio (NR) network architecture and <NUM> protocol only to facilitate understanding and the disclosed techniques and embodiments may be practiced in other wireless systems that use different communication protocols than the 3GPP protocols.

In the example of the NR system, the following PRACH preamble formats are defined in Tables <NUM> and <NUM>, quoted from NR specification, 3GPP TS38. <NUM> (and which correspond to Tables <NUM>. <NUM>-<NUM> and <NUM>. <NUM>-<NUM>, respectively).

With legacy PRACH preambles, simultaneous UEs are distinguished by their chosen preamble roots and cyclic shifts. In NTN, however, it may not work anymore due to various differential delay experienced by different UEs in the same beam. The large differential delay leads to correlation peak shifting in the whole preamble symbol, which means cyclic shift cannot be used any more.

Due to huge differential RTD in NTN scenario, the cyclic shift of ZC sequence cannot be used to identify different preambles. Therefore, the configuration of cyclic shift is not needed. In current NR specification, cyclic shift configuration Ncs is determined by following IE named zeroCorrelationZoneConfig, as shown in <FIG>.

If the differential RTD in a beam is larger than a single preamble symbol duration Tsymbol, then the IE zeroCorrelationZoneConfig is invalid. Thus, in some embodiments, zeroCorrelationZoneConfig should be designated as an optional parameter, with its presence being dependent on the condition "differential RTD < Tsymbol" being true.

In some embodiments, two new parameters may be introduced. The first is M, referring to the number of roots used in a PRACH preamble. The other is N, referring to the repetition number of preamble symbols generated by a single root. The presence of M and N depends on the condition "differential RTD > Tsymbol" being true. Thus, either "M and N" or zeroCorrelationZoneConfig are needed to define a PRACH preamble format.

Exemplary structures of the PRACH preamble, based on embodiments of the disclosed technology, are shown in <FIG>.

Option <NUM>. A preamble symbol is first generated using Root1. Then it is repeated N times to form a Root1 based preamble, with N ≥ <NUM>. As shown in <FIG>, and without loss of generality, N=<NUM> and the total preamble length is Tpreamble = <NUM>×Tsymbol. In this example, the repeated preamble may be interpreted as a cyclic prefix (CP) enhancement of the current NR PRACH preamble, e.g., <MAT> is extended to the length of a preamble symbol. A larger value of N provides better coverage at the cost of a longer preamble transmission.

Option <NUM>. A preamble symbol is first generated using Root1. Then it is repeated N times to form a Root1 based preamble, with N ≥ <NUM>. This is followed by generated another preamble symbol using Root2, which is also repeated N times. The two parts are concatenated in the time domain to form a preamble. As shown in <FIG>, and without loss of generality, N=<NUM> and the total preamble length is Tpreamble = <NUM>×Tsymbol. In this example, the repeated preamble may be interpreted as a cyclic prefix (CP) enhancement of the current NR PRACH preamble per root, e.g., <MAT> is extended to the length of a preamble symbol. This construction may be extended to use M roots to form the preamble, which is shown in <FIG> with M=<NUM>. In general, the total preamble length is defined as Tpreamble = M×N×Tsymbol.

In some embodiments, the preamble index for the above construction may be defined as the permutation {Root1, Root2,. RootM}, and as compared to the preamble index {Root, CyclicShift} that is used in the current NR specification.

In some embodiments, each of the RootM-based preamble may be repeated two or more times, that may not necessarily be equal. For example, Root1 may be repeated N<NUM> times, Root2 may be repeated N<NUM> times, and so on. In this scenario, the total preamble length is defined as Tpreamble = (N<NUM>+N<NUM>+. +NM)×Tsymbol.

The following cases, in conjunction with <FIG>, show different examples of some embodiments of the presently disclosed technology.

Case <NUM>. Generally a satellite has multiple beams with different elevation angles. As shown in <FIG>, Beam <NUM> has a maximum elevation angle and Beam K has a minimum elevation angle (e.g., <NUM> degree). In each beam, a center point with minimum propagation delay can be determined, which is represented by "propagation_delay_1" in <FIG>. The propagation_delay_1 is broadcast in this beam. All the UEs in this beam use (<NUM>*propagation_delay_1) to pre-compensate its PRACH preamble transmission. From the viewpoint of BS on satellite, the PRACH preambles from this beam have a time uncertainty range of [<NUM>, <NUM>*(propagation_delay_2 - propagation_delay_1)], where propagation_delay_2 is the maximum propagation delay in this beam.

The following assumptions are made in this scenario:.

For these assumptions, the preamble format used is shown in the table below.

In the above table, Nu refers to a single preamble length, and the preamble symbol repetition is defined by the parameter N.

In this scenario, maximum differential delay of Beam K is calculated as <NUM>. 6279e-<NUM> seconds. From the viewpoint of BS on satellite, the PRACH preambles from Beam K will have a time uncertainty range of [<NUM>, <NUM>. 6279e-<NUM>] second, which is [<NUM>, <NUM>] with normalization to symbol length Tsymbol. The total reception window at BS is the summation of time uncertainty range and PRACH preamble length, which is <NUM> (=<NUM>+<NUM>) with normalization to symbol length Tsymbol.

At the BS, and as shown in <FIG>, the following possible PRACH preamble arrivals are possible. In some embodiments, the reception window consists of <NUM> detection windows of length Tsymbol. With repetition N ≥ <NUM>, it is guaranteed that a complete symbol can be captured in a single detection window of length Tsymbol. In some embodiments, N=<NUM> and the receiver uses a sliding correlation window in the time domain to detect the preamble.

In some embodiments, multiple UEs can be distinguished by their randomly chosen ZC roots. In other embodiments, if two UEs chose the same root, but with distinguishable arrival time, they can also be detected.

Case <NUM>. The following assumptions are made in this scenario:.

In some embodiments, multiple UEs can be distinguished by their randomly chosen ZC roots. In this example, <NUM> ( <MAT>) roots are needed per cell to build a preamble pool with <NUM> preamble indexes. In other embodiments, if two UEs chose the same root, but with distinguishable arrival time, they can also be detected.

In this scenario, maximum differential delay of Beam K is calculated as <NUM>. 5324e-<NUM> seconds. From the viewpoint of BS on satellite, the PRACH preambles from Beam K will have a time uncertainty range of [<NUM>, <NUM>. 5324e-<NUM>] second, which is [<NUM>, <NUM>] with normalization to symbol length Tsymbol. The total reception window at BS is the summation of time uncertainty range and PRACH preamble length, which is <NUM> (=<NUM>+<NUM>) with normalization to symbol length Tsymbol.

Embodiments of the disclosed technology provide using a preamble pool that consists of ZC roots only, and wherein different cyclic shifts of ZC sequence are NOT used to identify different preambles. A fixed cyclic shift (e.g., zero) is always used for all ZC sequences in a preamble pool. Furthermore, multiple roots can be used to identify different preambles, where permutation of the multiple roots forms a preamble pool. The PRACH preamble format proposed by embodiments of the disclosed technology is characterized by repetition of preamble symbols with one or more roots.

The embodiments described in this patent document advantageously enable random access in NTN with large differential delay among UEs, and using permutation of multiple roots to build a preamble pool can effectively limit the number of roots used per cell, which is beneficial for short ZC sequence usage, low-complexity receiver design and practical cell deployment.

<FIG> shows an example of a wireless communication method <NUM>. In some embodiments, the method <NUM> may be used for generating preambles in a satellite-based mobile communication technology. The method <NUM> includes, at step <NUM>, transmitting, by a network node, a configuration for random access comprising a value indicative of a number of Zadoff-Chu (ZC) sequence roots (M) and a number of repetitions (N).

The method <NUM> includes, at step <NUM>, receiving, from a wireless device, a random access preamble. The step <NUM> may also be implemented by the network node. In some embodiments, the random access preamble comprises M concatenated ZC sequences with different roots, and each of the M concatenated ZC sequences is repeated based on N.

In some embodiments, the one or more random access preambles is received in a reception window with a size that is based on M and N.

<FIG> shows an example of a wireless communication method <NUM> for generating preambles in a satellite-based mobile communication technology. The method <NUM> may be implemented by a wireless device. The method <NUM> includes, at step <NUM>, receiving, from a network node, a configuration for random access comprising a value indicative of a number of Zadoff-Chu (ZC) sequence roots (M) and a number of repetitions (N).

The method <NUM> includes, at step <NUM>, transmitting, by a wireless device, a random access preamble. In some embodiments, the random access preamble comprises M concatenated ZC sequences with different roots, and each of the M concatenated ZC sequences is repeated based on N.

<FIG> shows an example of a wireless communication method <NUM> for generating preambles in a satellite-based mobile communication technology. The method <NUM> includes, at step <NUM>, transmitting, by a network node, a configuration for random access comprising a value indicative of a number of Zadoff-Chu (ZC) sequence roots (M) and a number of repetitions (N).

The method <NUM> includes, at step <NUM>, receiving, from a plurality of wireless devices, a plurality of random access preambles. In some embodiments, each of the plurality of random access preambles comprises M concatenated ZC sequences with different roots, each of the M concatenated ZC sequences is repeated based on N, and each ZC sequence in the plurality of random access preambles has a fixed common cyclic shift.

In some embodiments, and in the context of methods <NUM>, <NUM> and <NUM>, each ZC sequence has a fixed common cyclic shift. In an example, the fixed common cyclic shift may be zero. In another example, the fixed common cyclic shift may be a non-zero value (in symbols) less than the length of the ZC sequence.

In some embodiments, a difference between a first round-trip delay time between the network node and a first wireless device and a second round-trip delay time between the network node and a second wireless device is greater than a symbol time (Tsymbol) that is a time duration of the ZC sequence. In an example, a length of the random access preamble is M×N×Tsymbol.

In some embodiments, a length of the ZC sequence is <NUM> symbols or <NUM> symbols.

In some embodiments, a satellite comprises the network node.

<FIG> is a block diagram representation of a portion of an apparatus, in accordance with some embodiments of the presently disclosed technology. An apparatus <NUM>, such as a base station or a wireless device (or UE), can include processor electronics <NUM> such as a microprocessor that implements one or more of the techniques presented in this document. The apparatus <NUM> can include transceiver electronics <NUM> to send and/or receive wireless signals over one or more communication interfaces such as antenna(s) <NUM>. The apparatus <NUM> can include other communication interfaces for transmitting and receiving data. Apparatus <NUM> can include one or more memories (not explicitly shown) configured to store information such as data and/or instructions. In some implementations, the processor electronics <NUM> can include at least a portion of the transceiver electronics <NUM>. In some embodiments, at least some of the disclosed techniques, modules or functions are implemented using the apparatus <NUM>. The apparatus <NUM> may be used to implement the various techniques described with respect to a network node (e.g., a base station, an eNodeB or a gNodeB) or a wireless device such as a UE or another mobile-communication capable device.

It will be appreciated that the present document discloses techniques that may be used by various implementations of wireless devices or network-side devices for generating preambles that may be used for random access transmissions. In one advantageous aspect, the random access preambles may exhibit a mathematical property that makes them suitable for long-delay communication such as wireless communication with satellite networks. For example, using distinct ZC roots (instead of distinct ZC cyclic shifts) ensures that concurrent transmissions from multiple UEs can be distinguished by a satellite. If ZC cyclic shifts were to be used, the long propagation delays experienced in satellite communication may result in one or more of the cyclic shifts to overlap, resulting in the satellite not being able to correctly decode the UE signals and leading to degraded performance.

Furthermore, embodiments of the disclosed technology enable the generation of a preamble pool that maintain the aforementioned benefits, but additionally allows the number of ZC roots used to be configured based on system requirements, which enables the use of low-complexity receivers and practically implementable cellular deployments.

It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example and, unless otherwise stated, does not imply an ideal or a preferred embodiment.

Claim 1:
A method for wireless communication, comprising:
transmitting (<NUM>, <NUM>), by a network node, a configuration for random access comprising a value indicative of a number of Zadoff-Chu, ZC, sequence roots, M, and a number of repetitions, N, if a difference between a first round-trip delay time between the network node and a first wireless device and a second round-trip delay time between the network node and a second wireless device is greater than a symbol time, Tsymbol, that is a time duration of each ZC sequence of the M concatenated ZC sequences,
transmitting, by the network node, a cyclic shift configuration, if the difference between the first round-trip delay time and the second round-trip delay time is smaller than the symbol time, Tsymbol; and
receiving (<NUM>, <NUM>), from one or more wireless devices, one or more random access preambles based on the configuration, respectively,
wherein in case the configuration for random access comprises the values M and N the received random access preamble or each of the received random access preambles comprises M concatenated ZC sequences with different roots, and wherein each of the M concatenated ZC sequences is repeated based on N.