GB2560898A

GB2560898A - Methods and devices associated with a synchronization process with beamsweeping in a radio access network

Info

Publication number: GB2560898A
Application number: GB1704678.0A
Authority: GB
Inventors: Liu Guang; Vivier Guillaume; Katranaras Efstathios
Original assignee: TCL Communication Ltd
Current assignee: TCL Communication Ltd
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2018-10-03
Also published as: GB201704678D0; WO2018171524A1; CN110679092A

Abstract

A wireless base station 100 configured to operate with beamforming receives a synchronization transmission or segment from a wireless device over a first random access channel. Synchronization may be achieved by the wireless device using a received segment of a first physical random access channel (PRACH) transmission, or by estimating the measured signal strength of the first PRACH transmission. The measured signal strength may be a selected preamble sequence of the first PRACH transmission. A second PRACH transmission may also be scheduled for the wireless device.

Description

(54) Title of the Invention: Methods and devices associated with a synchronization process with beamsweeping in a radio access network

Abstract Title: Synchronization between beamforming basestations and mobile devices using a random access channel.

(57) A wireless base station 100 configured to operate with beamforming receives a synchronization transmission or segment from a wireless device over a first random access channel. Synchronization may be achieved by the wireless device using a received segment of a first physical random access channel (PRACH) transmission, or by estimating the measured signal strength of the first PRACH transmission. The measured signal strength may be a selected preamble sequence of the first PRACH transmission. A second PRACH transmission may also be scheduled for the wireless device.

PRACH Timing PUSCH Timing

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Methods and devices associated with a synchronization process with beamsweeping in a Radio Access Network

Technical Field

Embodiments of the present invention generally relate to wireless communication systems and in particular to devices and methods for enabling a wireless communication device, such as a User Equipment (UE) or mobile device to access a Radio Access Technology (RAT) or Radio Access Network (RAN) using beam sweeping, particularly but nor exclusively in conjunction with a synchronization process in a random access channel (RACH) process. The invention also addresses timing advance (TA) ambiguities in a random access process.

Background

Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3^rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB). More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB.

As with other technologies, the NR access technology deals with issues relating to transmission processes. One such process of interest is the use of RACH in a beam sweeping environment and the manner in which this operates between UEs. In addition, the problems of TA anomalies in this scenario are considered.

In 3GPP there is a continual search for agreements on the implementation of new and relevant features for NR systems. The agreements are relevant to many options. One option of interest (so called option 1) relates to cyclic prefix (CP) which may be inserted at the beginning of each Random Access Channel (RACH) sequences, is omitted and Guard Time (GT) is reserved at the end of the consecutive multiple/repeated RACH sequences. The RACH sequence is first mapped on a number of subcarriers in frequency domain and then transferred to time domain via IFFT (Inverse Fast Fourier Transform) in the form of one OFDM symbol with CPOFDM waveform. Optionally the RACH sequence could be pre-coded by DFT (Discrete Fourier Transform) before mapping to subcarriers with DFT-S-OFDM (DFT spread OFDM) waveform.

NR defines that each UE transmits Physical Random Access Channel (PRACH) according to the configured random access preamble formats. Beam switching time is to be considered in the definition of the appropriate solutions. In general, the region for PRACH transmission should be aligned to the boundary of uplink symbol/slot/subframe.

Referring to figure 1, symbols are shown for option 1 and for two other options referred to as option 2 and option 4. All cases consider the case where a preamble sequence consists of multiple OFDM symbols and the number of OFDM symbols is determined by the PRACH format. In general, more symbols will be required for a larger coverage distance. Option 1 mentioned above, requires that the same OFDM symbol is repeated without CP. This has two key benefits: it enables the receiver to share the same Fast Fourier Transform (FFT) as Physical Uplink Shared Channel (PUSCH) which is assumed to be able to reduce the base station (gNB) receiver complexity; and it allows PRACH latency (due to delayed reception at eNB as a result of eNB-UE distance) to exceed the CP length which can help to improve the coverage distance in a significant way. Both option 2 and option 4 have a CP inserted before each OFDM symbol. Option 2 uses the same RACH sequence in each OFDM symbol while Option 4 could use different RACH sequences.

Referring to Figure 2 an illustration of one FFT receiving PUSCH and PRACH optionl or PRACH option 2/4 is shown. It is assumed that UE1 is transmitting a PUSCH; UE1 is UL synchronized with the gNB; and UE2 is sending the PRACH to the gNB simultaneously. Ideally the gNB hopes to receive both the PUSCH and the PRACH with one FFT, and the FFT window is selected according to the gNB clock.

If option2/4 is used and the latency is bigger than the CP length and within the FFT window two fractional symbols are received. This may damage the orthogonality between subcarriers and may cause significant inter-subcarrier interference to the PUSCH. Also, the PRACH itself cannot be decoded without complete OFDM symbols. If option 1 is used, since all symbols are the same, any symbol acts as the CP for the following symbol so for any latency, a complete OFDM symbol can be received in the FFT window without causing inter-subcarrier interference.

Referring now to Figure 3, the coverage limitation from the CP length is illustrated. Even without PUSCH, the PRACH latency between different UEs should ideally be kept within the CP length otherwise different UEs’ PRACH will cause interference to each other. This is the case with option 2/4. However, as can be seen for option 1, since all symbols are same and continuous in waveform, the latency is not limited by the CP length. In fact, latency for the whole symbol length can be supported.

Different PRACH formats can be used for different sceanrios. Option 1 is used to illustrate the concept but similar design can be done for option 2 or option 4. Each format includes a PRACH burst and a GT. The PRACH burst ensures that the relevant format is robust enough for the gNB to receive it and the GT ensures that the format can tolerate the maximum latency. Figure 4 shown a number of different PRACH formats. For example, Format 0 with a % OFDM symbol GT can support a coverage distance of up to 2.5 Km while Format 5 with a 3 OFDM symbol GT can support a coverage distance of up to 30 Km.

For high frequency operations, to improve the coverage, beamforming and beam sweeping is often used. However, when using beam sweeping techniques a number of problems can arise as a result of opting for option 1 or indeed any other option. For example, in the case of PRACH receiving with beam sweeping, only a number of segments of the whole burst can be received with beam sweeping when the beam duration is less than the PRACH burst length. The gNB should be able to detect the TA value from the received segment(s) however TA anomalies cause further difficulties.

The present invention is seeking to solve at least some of the outstanding problems in this domain.

Summary

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

According to a first aspect of the present invention there is provided a method for enabling a wireless communication device to access services provided by a Radio Access Network, the method comprising: configuring the base station to operate with beamforming in which a transmission from a wireless device is received with a synchronization segment from a first random access channel.

Preferably, a first synchronization is achieved for the wireless device from a received segment of a first PRACH transmission.

Preferably, the first synchronization is derived at least in part by estimating a measured signal strength.

Preferably, the measured signal strength is the measured strength of the first PRACH transmission.

Preferably, the measured signal strength is derived at least in part by a selected preamble sequence of the first PRACH transmission.

Preferably, an UL transmission is scheduled for the wireless device with the first synchronization.

Preferably, the UL transmission including a number of last symbols blanked.

Preferably, a second synchronization is achieved for the wireless device from the UL scheduled transmission.

Preferably, a second PRACH transmission is scheduled for the wireless device which has been synchronised by the first synchronization.

Preferably, a second synchronization is achieved for the wireless device from the said second PRACH transmission.

Preferably, an UL transmission is scheduled for the wireless device with the said second synchronization.

Preferably, the first PRACH transmission uses option 1.

Preferably, the second PRACH transmission uses option 4.

Preferably, the Radio Access Network is a New Radio/5G network.

According to a second aspect of the present invention there is provided a base station arranged to operate with beamforming in which a random access channel segment is received from a first synchronization transmission of a wireless device.

According to a second aspect of the present invention there is provided a nontransitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method of another aspect of the present invention.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 is a simplified diagram showing the symbols in option 1 vs. those for option 2/4, in accordance with the prior art;

Figure 2 is a simplified diagram of an illustration of two UEs using option 1 or option 2/4, in accordance with the prior art;

Figure 3 is a diagram showing the coverage limitation from the CP length, in accordance with the prior art;

Figure 4 is a diagram showing a number of different PRACH formats, in accordance with the prior art;

Figure 5 is a simplified diagram showing PRACH receiving with beam sweeping, according to an embodiment of the present invention;

Figure 6 is sequence diagram showing a TA ambiguity, according to an embodiment of the present invention;

Figure 7 is a simplified diagram showing different coverage zones, according to an embodiment of the present invention;

Figure 8 is a sequence diagram showing overland and/or collision with an incorrect TA value, according to an embodiment of the present invention;

Figure 9 is a sequence diagram showing TA ambiguity with blanked symbols, according to an embodiment of the present invention;

Figure 10 is a block diagram showing a two-step PRACH procedure, according to an embodiment of the present invention; and

Figure 11 is a sequence diagram showing a 2nd PRACH with an option 4 type design, according to an embodiment of the present invention;

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

The present invention generally relates to the support of greater coverage using beam sweeping in a random access channel processing scenario and addressing any TA ambiguity thereby enabling the gNB to adopt fast beam sweeping with improved scheduling flexibility and efficiency. The present invention further augments the approach used by so called option 1 to support coverage distances for which the “round trip” propagation time is greater than one OFDM symbol.

For high frequency operation and to improve the coverage beamforming and beam sweeping may be used, for example, in a RACH related process as is shown with reference to Figure 5. The antenna 100 with multiple elements (beams 1 to 12) can be used to form a narrow beam with very high gain to cover one specific direction. In figure 5, this is shown by the directions in which the different beams are pointing. It will be appreciated that there may be more or less beams and they may point in different directions than those shown. The beams can sweep the whole coverage area of a serving cell (not shown). Previously, one beam could only cover a very narrow area, as a result it was harder for gNB with beam sweeping to support frequency division multiplexed (FDMed) multi-UE multiplexing because the probability of two or more UEs under scheduling being located in the same beam is much smaller than that of a wide beam. Therefore, the use of a single beam limited the possibility to multiplex two users in a frequency of a given beam. As a result, this meant that a single UE would be scheduled in one beam. Also, as high frequency operation has a large bandwidth requirement, the resource block scheduled for such a UE could be massive. To improve the scheduling flexibility, it has been proposed to adopt a very short duration in a time domain to reduce the scheduled resource block size. This very short duration is called “mini-slot” and could be as short as 1 or 2 OFDM symbols long.

As is further illustrated in Figure 5, a number 102 of sequential beams may be used within the duration of the PRACH burst. Beam duration is selected as an integer number of PUSCH symbols which includes CP Different subcarrier spacing (SCS) could be used for PUSCH and PRACH which means the PUSCH symbol with CP and PRACH symbol without CP could be different so it is possible that fractional PRACH symbols can be received within one beam. The beam duration could be a mini-slot 104 if a low SCS is used or several complete slots if a high SCS is used.

As is discussed with reference to Figure 6, it is possible to have fractional symbols and as long as the total segment length of the PRACH is longer than one OFDM symbol 200, this PRACH is decodable. Figure 6 illustrates the TA ambiguity which exists for a latency which is greater than one OFDM symbol. A segment may be referred to as part of a random access channel message or PRACH signal or transmission.

One purpose of PRACH is for the terminal to achieve UL synchronization. When a terminal is switched on, it needs to first synchronize with the DL and then read the system information for UL access (including the relevant PRACH parameters). When the terminal wishes to initiate an UL transmission without a valid TA, it may send a PRACH burst with 0 TA from its DL timing and be sure that this burst will be received by the gNB after a round trip propagation delay. In response to the PRACH, the gNB can indicate to the terminal a TA value so that UL transmission with this indicated TA value can be aligned in time with the gNB clock.

When the latency due to propagation is less than one OFDM symbol, the gNB can detect the difference from phase shift in frequency domain, i.e. ΔΤ. In that case TA = 7

ΔΤ. When the latency is bigger than one OFDM symbol 202 as shown in Figure 6, the gNB can only receive the segment within one beam duration but the gNB cannot know the exact location of this segment in the whole PRACH burst, e.g., how many symbols before or after this segment. Again the gNB can only detect At, i.e., the part less than one OFDM symbol from the segment. In that case however, TA = x OFDM symbol periods + AT. Since gNB does not know the UE position within the cell, it cannot be certain of the TA. This is referred to as TA ambiguity for latency bigger than one OFDM symbol. As previously indicated the present invention is seeking to address this problem associated with TA ambiguity as will be described in greater detail below. As discussed above, at least option 1 has the above mentioned TA ambiguity problem.

Referring to figure 7 a number of symbol zones 300, 302 and 304 are shown in the coverage zone 306 of a gNB 100. The whole coverage zone 306 can be split into a <1 symbol zone 300; a 1-2 symbol zone 302; and a 2-3 symbol zone 304. The TA ambiguity may be estimated with path loss for each of the symbol zones 300, 302 and 304 of the coverage zone 306. There may be more or less symbol zones depending on the system. For example, a default OFDM symbol with 15 KHz SCS lasts about 67ps which represents 10Km maximum coverage distance. So if PRACH format 5 (GT = 3 OFDM symbols) and SCS = 15 KHz combination is configured, the potential coverage distance is 30 Km. The whole cell can be split into 3 zones as shown in Figure 7 or more or less zones as the case may be.

There may be a number of different options for coarse estimation of the TA, these may include a gNB-centric option and a UE-centric option.

In the gNB centric option, a terminal transmits the PRACH with a certain power and the gNB estimates the possible symbol zone based on the received power strength. For the example in Figure 7, three thresholds T1; T2; and T3 can be used for respective symbol zones 300; 302 and 304 and normally T1 > T2 > T3. The required value of T1; T2; or T3 can be selected according the path loss model. Multiple path loss models can be found at (https://en.wikipedia.org/wiki/Radio propagation model) for different scenarios and the gNB can select the model which matches with its installation place. The above thresholds can also be improved gradually with gNB learning.

In the UE-centric option, the basic idea is that the pass loss is estimated by the UE from DL reception. Knowing this coarse estimation, the UE may indicate it implicitly 8 using a different PRACH preamble. For the example in Figure 7, all the PRACH preamble sequences can be split into three groups and each group is connected to a relevant one of the symbol zones 200, 202 or 204. The UE selects a preamble sequence from a group to implicitly indicate its location, in other word the symbol zone which matches the estimated TA.

The UE centric option may include a number of different steps. In a first step the gNB may broadcast guide thresholds for the UE to decide the potential symbol zone. In a second step 2, the terminals carry out a DL measurement and determine the appropriate zone index by comparing the received DL power strength with the signalled thresholds the first step. In a third step, the terminal sends the PRACH with a selected preamble sequence from the group related to the determined zone index. Then in a fourth step the gNB takes the zone information into consideration to indicate the proper TA value to the terminal. A simple comparison of the two abovementioned options is shown in Table 1 below.

	qNB-centric	UE-centric
Advantages	• No broadcasting signalling required and fully eNB internal implementation • More flexible evaluation, e.g., more thresholds, joint decision of power strength and TA value	• More accurate path loss estimation
Disadvantages	• Less accurate when power control is used in UL	• Additional broadcasting signalling • Hard to support many different thresholds • Increased collision probability of PRACH preamble with sequence grouping • Impossible to support joint decision of power strength and TA value

Both options can be used simultaneously and the gNB can make its own decision of TA according to inputs form both gNB itself and UE measurement results.

If the TA is defined as:

TA = a*S + n*S;

Where: S is one OFDM symbol length; 0<a<1; n = 0, 1,2 ... n_max

If it is assumed that so called option 1 is carried out, the gNB can detect any part of a TA which is less than one OFDM, and n can be estimated from the Ambiguity evaluation steps above. a*S, is referred to as fine TA and is represented with TA1 below and n*S is referred to as coarse TA and is represented with TA2 below. So the gNB can indicate to the terminal the estimated TA value as TA = TA1 + TA2. The value of n_max is determined by the GT length of the configured PRACH format.

Solution A is based on path loss estimation with either gNB-centric, UE-centric or a combination of both to solve the TA ambiguity problem. For the ambiguity evaluation, the gNB determines which TA value is more possible, a*S or a*S + n*S (n>0), based on the received PRACH power strength. With respect to TA ambiguity, the gNB does not know the real TA is a*S or a*S and a few symbol, in this case, measured power strength may help to differentiate this. The power strength gap between a*S and a*S + n*S may be relatively large and an absolute measurement value of PRACH power strength may be required for the gNB to decide the correct TA value.

From this point of view, the gNB-centric option is more advantageous than the UEcentric option. For the example in Figure 7, if TA1 is nearly one OFDM symbol long which means the UE may locate close to the border areas of all 3 zones and power measurement results show the UE is in the border area between 1 symbol zone and 1~2 symbol zone. The gNB can then conclude that TA = TA1 and TA2 = 0 with the gNB-centric option. If the UE-centric option is used, there is a risk that the UE indicates to the gNB that it is located in the 1~2 symbol zone and as a result, the gNB concludes that TA = TA1 + TA2 (= 1 symbol). The drawback of Solution A may occur if the estimation of n is wrong, interference will be caused to the slot before or the slot after. This will not be a problem when the estimation of n is made correctly, but the correct estimation probability decreases with the path loss varying in a larger range when LOS (Line of Sight) and NLOS (Non LOS) UEs co-exist as is generally true in the case of high frequency.

Referring now to figure 8 the effect of an incorrect TA value from Solution A is shown and may result in an overlap or collision 400. If the indicated TA is too big the corresponding UE transmission may overlap with another UE’s transmission in the slot 402 before and interference may take place in the region of overlap. The TA may be too big as TA2 has been overestimated due to e.g. a terminal device very close to the gNB or deep in building with a large path loss. If the indicated TA is too small the corresponding UE transmission may fall behind the correct time and may overlap with another UE’s transmission in the slot after 404. The TA may be too big as TA2 has been underestimated due to e.g. a LOS transmission.

It should be further noted that it is likely that NR will put a DeModulation Reference Symbol (DMRS) in the first symbol at the beginning of the slot. As a result, if a collision occurs either with the slot before or the slot after, one DMRS is likely to be corrupted which may cause more problems than collisions on the reception of other symbols.

It is possible that there may be a 2 or 3 OFDM symbol GT for PRACH formats with GT > 1 OFDM symbol. This means n could be at most 1 or 2. For PRACH formats 3 or 4, there may be a 2 OFDM symbol GT so the possible TA cannot exceed 2 OFDM symbol and n = 0 or 1. For PRACH format 5, GT may be a 3 OFDM symbol so n could be 0, 1 or 2.

The above mentioned Solution A may alternatively be supported without ambiguity evaluation. In this case the gNB may only indicate TA1 in the Random Access Response (RAR) 600a as shown in Figure 10 and only the “too late” collision 406 in Figure 8 may occur with all possible values of n. The gNB can thus detect the delay from the DMRS position and indicate the correct TA value in the next scheduling message.

An alternative solution, referred to a Solution B will now be discussed. This can be also based on ambiguity evaluation. In this case the gNB always indicates the terminal TA = TA1, and additionally when the gNB thinks a terminal may have a TA ambiguity issue (TA2 + 0), it will indicate the terminal to blank the last one symbol if PRACH format 3 or 4 is configured for the cell, or the last two symbols if PRACH format 5 is configured for the cell.

Figure 9 shows details of the possible ambiguity with blanked symbols. The example shown relates to the PRACH format 3/4. It should be noted that other PRACH formats may operate in similar ways. If after ambiguity evaluation, a terminal is assumed to have no ambiguity issues, the terminal will be indicated a TA value with a normal UL scheduling message and no symbol will be blanked (shown in figure 9 as DMRS 500). The terminal is assumed to have no ambiguity issues if the gNB is quite confident that this terminal is located within one OFDM symbol for the round trip time in a given area.

If after ambiguity evaluation, a terminal is assumed with an ambiguity risk (TA2 + 0), the gNB will indicate a TA1 value and an UL scheduling with the last symbol blanked. There may be a number of possible cases. A first possible case is that TA2 = 0 (DMRS 502 in figure 9) and in this case the last OFDM symbol will be wasted. In a second case, TA2 = 1 (DMRS 506 in figure 9) and as a result the UL transmission will arrive at the gNB one symbol late and the first OFDM symbol will be wasted. Solution B has no overlap or collision problems when a TA ambiguity is assumed.

The gNB can detect the possible one symbol TA difference from the DMRS of the UL transmission and indicate the correct TA in the next UL scheduling message. A possible drawback of Solution B is that one OFDM symbol resource will be wasted, however the correct TA will be provided from the second UL transmission. The resource waste of one symbol could be minor.

Collisions may still occur even if the gNB thinks a terminal has no TA ambiguity problem. This can come about as a result of the terminal being located outside the one symbol TA zone. It is thus proposed for Solution B to use a conservative threshold in the ambiguity evaluation stage to keep collision probability at a relatively low level with a relative high probability of having one symbol wasted which is considered to be acceptable.

In a further embodiment, Solution B may also be supported without ambiguity evaluation in which case, all UEs blank the last n_max symbol. n_max can be determined from the configured PRACH format included in a System Information Block (SIB) message, so there is no need to indicate the exact number of symbols to be blanked and a single bit indicator can be used to inform if blanking is required or not. This gives the gNB flexibility to blank one or more symbols for some UEs and not for others. This flexibility can be dispensed with and then no indicator is needed but in this case it will be necessary to be specified that all terminals shall blank the last n_max symbols by default for the UL transmission scheduled by the first RAR as shown in Figure 10. The gNB can detect the delay from the DMRS position and indicate the correct TA value from the next scheduling messages with no symbol being blanked.

In a still further embodiment, Solution C is considered. In this case there is a twostep PRACH procedure and the gNB can indicate to the terminal to need to start another PRACH procedure. Optionally the same ambiguity evaluation as described above can be carried out before the gNB sends the indication. If a terminal is 12 assumed to have no ambiguity risk, the gNB can choose to indicate to this terminal to start a normal PUSCH transmission rather than another PRACH procedure with the indicated TA value.

The two-step PRACH synchronization procedure will now be described with reference to figure 10. The gNB receives the 1st PRACH 602 (which has already agreed to use at least option 1) and carries out the ambiguity evaluation. If the evaluation result gives a very low ambiguity probability, the gNB can schedule PUSCH resources 604 in the normal way with TA = TA1. If the evaluation result suggests that there is a significant probability of TA ambiguity, the gNB can indicate to the terminal to carry out a 2nd PRACH 506 and a set of parameters could be included in the first RAR 600a. The set of parameters may include: a dedicated resource block; TA1 from the 1st PRACH; and PRACH parameters such as for example a preamble sequence index.

The gNB then receives the 2nd PRACH 606 and detects TA2 (n*S, n=0, 1,2). In the next RAR 600b, the gNB schedules the PUSCH 604 in the normal way with TA value (= TA1 + TA2). The RAR 600b message may include an UL scheduling message called Msg3 in LTE, and to support a 2nd PRACH scheduling, a new message type may be indicated. Terminals know from the message type indicator if a PRACH or PUSCH/PUCCH is scheduled. Random Access Preamble ID (RAPID) received in the 1st PRACH can be used to address the terminal. The section marked 608 is optional and only required where there is a significant probability of TA ambiguity.

For the 2nd PRACH, a different design from option 1 may be considered. Once TA1 has been obtained and symbol level synchronization is achieved, option 2 or option 4 can also be considered without the risk of inter-subcarrier interference. Best beam information can also be obtained from the 1st PRACH and the gNB can allocate the frequency/time resource according to its beam sweeping pattern so that the 2nd PRACH preamble can fall accurately within the beam duration for this specific terminal. As a result, the 2nd PRACH burst can be shorter than that of the 1st PRACH. Since the 2nd PRACH is under the control and expectation of the gNB, a dedicated PRACH preamble sequence can also be indicated to simplify the gNB receiving and to avoid preamble sequence collision with other UEs.

Option 4 as illustrated in figure 11 may provide a mode of operation for the 2nd PRACH burst. For example, only the last slot of PRACH format 5 (totally 3 slots) is sent for the 2nd PRACH. When carrying out the resource allocation for the 2nd

PRACH, the gNB may need to ensure it has at least one beam that will point in the direction of the specific UE’s within the allocated moment. With TA1 known, the possible latency may only be an integer number of OFDM symbols. From the sequences received, the gNB can detect the TA2 value, for example, TA2 = 0 if sequences 5, 6, 7 are received in order and TA2 = 2 if sequences 3, 4, 5 are received in order.

It should be noted the present invention can support PRACH formats with GT > 3 OFDM symbol. The proposal to use option 4 for the 2nd PRACH, may depend on the beam duration being guaranteed to cover the whole length of the 2nd PRACH. Options 1 and 2 are also possible for this function. Other methods of providing the 2nd PRACH are also possible.

Each of the above explained solutions offer advantages and the solution may be selected depending on a number of different considerations. As previously indicated each solution can be used independently, without the ambiguity evaluation step. However the ambiguity evaluation can mitigate any negative performance aspects, for example, less inter-slot interference for Solution A, less resource waste for Solution B and increased latency for less UEs for Solution C.

The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an 16 embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

1. A method for enabling a wireless communication device to access services provided by a Radio Access Network, the method comprising: configuring the base station to operate with beamforming in which a transmission from a wireless device is received with a synchronization segment from a first random access channel.

2. The method of claim 1, wherein a first synchronization is achieved for the wireless device from a received segment of a first PRACH transmission.

3. The method of claims 2, wherein the first synchronization is derived at least in part by estimating a measured signal strength.

4. The method of claim 3, wherein the measured signal strength is the measured strength of the first PRACH transmission.

5. The method of claim 3 or claim 4, wherein the measured signal strength is derived at least in part by a selected preamble sequence of the first PRACH transmission.

6. The method of any one of the preceding claims, wherein an UL transmission is scheduled for the wireless device with the first synchronization.

7. The method of claim 6, wherein, the UL transmission including a number of last symbols blanked.

8. The method of claim 6 or 7, wherein a second synchronization is achieved for the wireless device from the UL scheduled transmission.

9. The method of any one of claims 2 to 5, wherein a second PRACH transmission is scheduled for the wireless device which has been synchronised by the first synchronization.

10. The method of claim 9, wherein a second synchronization is achieved for the wireless device from the said second PRACH transmission.

11. The method of any one of claims 8 to 10, wherein an UL transmission is scheduled for the wireless device with the said second synchronization.

12. The method any one of claims 1 to 7, wherein the first PRACH transmission uses option 1.

13. The method of any one of claims 8 to 9, wherein the second PRACH transmission uses option 4.

14. The method of any one of the preceding claim wherein the Radio Access Network is a New Radio/5G network.

5

15. A base station arranged to operate with beamforming in which a random access channel segment is received from a first synchronization transmission of a wireless device.

16. A non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method

10 according to any of claims 1-14.

Intellectual

Property

Office

GB 1704678.0

1-16 (partially)