GB2553797A

GB2553797A - Improvements in and relating to random access in a telecommunication network

Info

Publication number: GB2553797A
Application number: GB1615635.8A
Authority: GB
Inventors: Wu Shangbin
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2016-09-14
Filing date: 2016-09-14
Publication date: 2018-03-21
Also published as: GB201615635D0; KR20180030389A; KR102396776B1

Abstract

A user equipment UE transmits a first message comprising a preamble and data, then receives a second message from a base station BS. If the second message is not an acknowledgment indicating successful decoding, it is a plurality of random access response RAR messages, the number corresponding to an estimate of how many UEs are attempting random access. The UE then randomly selects a RAR message, and transmits a third message to the BS. The UE finally receives a fourth message from the BS indicating successful random access or else a failure. The invention is intended to improved performance when multiple UEs need to perform random access requests simultaneously. The UE may transmit a plurality of first messages each comprising a portion of the data. The UE may also be an internet of things IoT device. The estimate of the number of UEs may be based on angle of arrival information.

Description

(54) Title of the Invention: Improvements in and relating to random access in a telecommunication network Abstract Title: Method of random access where a base station sends multiple random access response messages (57) A user equipment UE transmits a first message comprising a preamble and data, then receives a second message from a base station BS. If the second message is not an acknowledgment indicating successful decoding, it is a plurality of random access response RAR messages, the number corresponding to an estimate of how many UEs are attempting random access. The UE then randomly selects a RAR message, and transmits a third message to the BS. The UE finally receives a fourth message from the BS indicating successful random access or else a failure. The invention is intended to improved performance when multiple UEs need to perform random access requests simultaneously. The UE may transmit a plurality of first messages each comprising a portion of the data. The UE may also be an internet of things loT device. The estimate of the number of UEs may be based on angle of arrival information.

UE randomly chooses one of the M RARs

101 loTUE S101

110

BS

Preamble and data

-►

S110

I

MRARs

5111

Msg3 )

Msg4 r~

5112 1

FIG. 4

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

/4

10

11 17

UE BS

FIG. 1

User 1 data

◄- PRACH duration -►

User 2 data

FIG. 2

2/4

101 /

loT UE

110 /

BS

Preamble and data

I S1O1

ACK 4_

BS decodes successfully

S102

FIG. 3

11 17

101 110 /

loTUE S1O1 BS

Preamble and data

S11O

I

MRARs

UE randomly chooses one of the M RARs

5111

Msg3

Msg4 r~

5112 ▼

FIG. 4

3/4

11 17

FIG. 5

4/4

11 17

5300

5301

5302

5303

5304

S305

S306

5307

5308

FIG. 6

Improvements in and relating to Random Access in a telecommunication network

The present invention relates to an improved random access mechanism in a telecommunication network. It relates, particularly, to a fifth generation (5G) network.

In the LTE Advanced Pro and the emerging 5G cellular networks, Machine-to-Machine (M2M) communications and Internet of Things (loT) will play important roles. M2M and loT enable connections between new types of terminals such as body sensors, vehicles, smart meters and the like, alongside the more familiar mobile phones. The upcoming LTE standards and 5G systems commit not only to support a massive number of M2M/loT nodes but also to provide low latency access for M2M/loT. This poses certain problems when it comes to supporting such a large number of new network entities.

It is estimated that by the year 2020, the number of connected loT entities will reach 50 billion, and these devices are expected to experience a low end to end (E2E) latency approximately 10% of that experienced in 4G systems.

Such a large number of nodes introduces pressure on the scarce resource available for random access. When such a massive number of devices try to initiate random accesses to the network, they may collide with each other, resulting in large latencies, which are not generally acceptable.

The massive number of loTs and M2M entities and transactions in a network introduces pressure on the scarce resource for random access. The current LTE standard procedure of random access consists of four steps as shown in Figure 1. In step one S1, a User Equipment (UE) 1 transmits a randomly selected preamble sequence on Physical Random Access Channel (PRACH) to the eNB or BS 10. In step two S2, the eNB 10 transmits a Random Access Response (RAR) on the Physical Downlink Shared Channel (PDSCH) in response to the detected preamble sequence. In step three S3, the UE 1 transmits its identity and other messages (e.g., scheduling request) to the eNB 10 using the Physical Uplink Shared Channel (PUSCH) resources assigned in the RAR in the second step S2. In the last step S4, the eNB 10 echoes the UE 1 identity it received in the third step S3 on PDSCH.

However, when a massive number of nodes try to initiate random accesses, they may collide with each other, resulting in PRACH overload and large - and often unacceptable connection latencies. Currently different strategies have been proposed to deal with massive random accesses in the medium access control (MAC) layer. However, these methods are typically not sufficient to meet the latency requirements as MAC layer signaling is not as responsive as physical layer signaling.

There is therefore a desire to provide an improved random access mechanism which avoids this and other problems experienced in the prior art.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a message exchange according to the prior art;

Figure 2 shows a random access signal structure according to an embodiment of the present invention;

Figure 3 shows a message exchange according to an embodiment of the present invention;

Figure 4 shows a further message exchange according to an embodiment of the present invention;

Figure 5 shows a flowchart demonstrating how a UE performs random access according to an embodiment of the present invention; and

Figure 6 shows a flowchart demonstrating how an eNB reacts toa random access request and performs random access according to an embodiment of the present invention;

Embodiments of the present invention seek to address shortcomings in the prior art, and so allow a substantial increase in random access capacity. This has the effect of reducing latency and so permitting simultaneous access by a plurality of different UEs.

This improvement is permitted, in part, by the use of MIMO-enabled eNB. ΜΙΜΟ refers to multiple-input multiple-output and relates to the provision of a large number of antennas, particularly on an eNB. This has the ability to provide a high degree of spatial resolution.

Furthermore, amendment of the prior art Message 1 (MSG1) enables one-stage transmission to occur. A further improvement lies in the provision of a collision-avoiding algorithm. A still further improvement lies in the ability of an eNB to transmit multiple RARs simultaneously.

In an embodiment of the invention, the structure of the signal transmitted from the UE, seeking access, is altered. The user data is divided into N parts and the signal generated includes the preamble and the user data together. The preamble and user data parts are transmitted in turn on the PRACH. This is illustrated in Figure 2. It should be noted that data signals from different users are assumed independent, which forms the basis for Angle of Arrival (AoA) estimation. If there is no preamble collision, the user data will be transmitted successfully via this signal structure. As a result, latency of UE access is then reduced. On the contrary, if preamble collision occurs, the eNB can estimate how many users are colliding in the spatial domain using the user data.

The preamble referred to is the standard preamble defined in the codebook for the respective communication standard.

Figure 2 shows that the User 1 data comprises several different parts - Data,, - Data_N1- and that these separate parts are transmitted along with the preamble, as shown. A similar arrangement applies to User 2 and other users. This figure shows how collisions are likely, given the potentially large number of transmissions which may be initiated at any given time.

An additional requirement in loT is that the battery life of entities in M2M communication and loTs are expected to be in the region of ten years. This requires highly power efficient transmission schemes. In practice, the user data, shown in Figure 2, can be modulated with constant envelope modulation schemes such as Quadrature Phase Shift Keying (QPSK), which means that power efficient amplifiers can be utilised in the M2M/loT nodes, as the Peak to Average Power Ratio (PAPR) is low.

The general enhanced loT random access procedure according to embodiments of the invention may have two possible outcomes. One is that the UE data sent along with the preamble is successfully decoded by the eNB. This is most likely to happen when preamble collision does not occur. In this case, a one stage transmission process is provided. This is depicted in Figure 3. Firstly, at step S101 the UE 101 transmits the preamble and data, as set out in Figure 2. The BS or eNB 110 decodes the message successfully and transmits, at step S102, an acknowledgement to the UE 101. The benefit of this is that the latency of transmission is largely reduced, since the user data is transmitted along with the preamble.

Alternatively, when/if there are multiple UEs using the same preamble, the one-stage method set out above will automatically fallback to a two stage method, i.e., the UE 101 requests resources in the first stage and transmits data in the second stage as shown in Figure 4. Here, the UE 101 transmits preamble and data is step S101 as set out in Figure 3. In this case, though, perhaps due to collision, the BS 110 fails to decode the UE message successfully. It therefore estimates the number M of users based on AoA information, which may be derived from the ΜΙΜΟ system. The ability to resolve M different users will depend on the number of antennas deployed in the system. As an example, with 16 antennas, it may be possible to resolve 5 to 7 distinct users, based on their AoA information.

Details of how the number M of users may be estimated, follows. It should be noted that this technique is known in the art. Other techniques may be used, as required.

Assume that the concatenated received data symbols at the eNB are x(t) and the steering vectors of the eNB from K (K<Q<N) different AoAs 4¾..¾.... are «(.&.)>

a(S₂)«.), where Q is the maximum number of resolvable UEs. It should be noted that the concatenated received data symbol may contain data symbols from multiple UEs. In addition, data symbols from different UEs are assumed independent. The received signal at the eNB is:

= 75;«(ΐ) 4where ,4 = «<£,.} is the steering matrix at the eNB, s(t) is aggregate data symbols of from UEs, and »&) is the Gaussan noise vector. The eNB will perform the Multiple Signal Classifier (MUSIC) algorithm to obtain the power angular spectrum (PAS) F(£).

Step 1: Compute the N-by-N correlation matrix J? by:

R=E{ }

Step 2: Eigen value decomposition on where u is the N-by-N eigen vector matrix and Σ is the diagonal eigen value matrix.

Step 3: Partition the eigen vector matrix by:

where is the N-by-(N-Q) eigen vector matrix whose columns correspond to the noise subspace.

Step 4: Search through all angles S, the PAS can be obtained by:

Step 5: Find the estimated AoA set s = in the PAS , where £,..., are the roots of:

riUeri ___ji\, — V ce

Step 6: Remove in S = -¾} if is less than a certain threshold ε. Then the estimated number of users = )SL

Once the BS 110 has estimated M, it transmits a total of M RAR messages at step S110. Each UE which receives multiple RAR messages, randomly selects one such RAR message and replies with Msg3 at step S111. The BS acknowledges receipt with Msg4 at step S112.

Msg 3 (S111) and Msg4 (S112) correspond to the messages having the same names in the prior art.

In prior art LTE systems, the eNB will only transmit one RAR back to UEs even if there are multiple UEs using the same preamble. In embodiments of the present invention, the eNB 110 will try to estimate the number M of UEs using the same preamble by distinguishing AoAs from different UEs. Then the eNB will send the corresponding number M of RARs to the UEs.

Consequently, there will be more resources assigned to multiple UEs to avoid RACH overload. Each UE randomly selects one RAR and the remaining steps are the same as current 3GPP. Although there is still a chance that multiple UEs will select the same RAR, the collision probability is further reduced by the extra randomness introduced.

The general UE procedure for enhanced random access according to an embodiment of the present invention is shown in Figure 5. A UE 101 randomly selects a preamble and then forms the random access signal with its data according to Figure 2, and transmits the preamble and data (S200). After transmitting the random access signal, the UE will wait for eNB’s response (S201). If the eNB responds with an acknowledgement (ACK) (S202), it means that the data transmission has been successful (S203).

Otherwise, the UE will receive multiple RARs from the eNB and randomly selects (S204) one among them.

Next, the UE will transmit Msg3 (S205) to the eNB and then receive Msg4 (S206). If Msg4 is ACK (S207) then the connection is established successfully (S208). Otherwise, the UE needs to backoff (S209) before another random access attempt.

Figure 6 shows the procedure from the eNB’s perspective.

Due to the amended access signal structure, the eNB, after receiving the signal from the UE (S300) needs to remove preambles and cyclic prefixes (S301) and then concatenate the user data parts and attempt to decode (S302).

If the data signal is successfully decoded (S303), then the eNB will feedback ACK to the UE (S304). Conversely, if the data signal is not successfully decoded, there are two possible situations. One is that there is only one UE using the preamble, but the channel condition is so bad that the eNB cannot decode the data signal correctly. The other is that there are multiple UEs using the same preamble and the interference among them is too large for the eNB to correctly decode the data signal. Neither situation will impact the user number estimation based on AoA estimation.

Therefore, the eNB will estimate the number of users based on AoA information (S305) and then transmit M RARs (S306) to the UE, where M is the estimated number of users. After receiving Msg3 (S307) from UEs, the eNB will acknowledge the request from the UE if it is successful (S308).

Advantageously, embodiments of the present invention offer improved performance when multiple UEs need to perform random access requests simultaneously. This problem is only expected to worsen with the increased prevalence of M2M and loT nodes.

A further benefit is associated with reduce latency, particularly by the use of a one-stage random access procedure in optimal cases.

If the one-stage process is not viable, then an automatic fall back is provided to prior art techniques.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of random access in a communication network, comprising the steps of:

a User Equipment, UE, transmitting a first message comprising a preamble and data; the User Equipment receiving a second message from a Base Station, BS;

if the second message is not an acknowledgment, the User Equipment randomly selects one of a plurality of Random Access Response, RAR, messages, transmitted from the base station;

the User Equipment randomly selecting one of the plurality of RAR messages and transmitting a third message to the base station;

the User Equipment receiving a fourth message from the base station, wherein the fourth message indicates either a successful random access request or indicates a failure.

2. The method of claim 1 wherein the User Equipment transmits a plurality of first messages, each comprising a portion of the data.

3. A method of random access in a communication network, comprising the steps of:

a Base Station, BS, receiving a first message from a User Equipment, UE, the first message comprising a preamble and data;

the Base Station transmitting a second message to the User Equipment, wherein the second message is either an acknowledgement or one of a number M of Random Access Response, RAR, messages, wherein the Base station estimates a number of possible User Equipments attempting random access and transmits M RAR messages;

the Base Station receiving from the User Equipment a third message;

the Base Station transmitting to the User Equipment a fourth message wherein the fourth message indicates either a successful random access request or indicates a failure.

4. The method of claim 3 wherein the Base Station estimates M by assuming that concatenated received data symbols at the base station are x(£) and steering vectors of the base station from K (K<Q<N) different angles of arrival (AoAs) are «(A.),

«.(Si),.-.where Q is a maximum number of resolvable UEs, and received signal at the base station is:

where .4 = .,, «(%;)] is a steering matrix at the base station, is aggregate data symbols from UEs, and «(0 is the Gaussan noise vector, wherein the base station performs the Multiple Signal Classifier (MUSIC) algorithm to obtain the power angular spectrum (PAS) and performs the following steps:.

Step 1: Compute the N-by-N correlation matrix by:

R=E{ x(fc) }

Step 2: Eigen value decomposition on where u is the N-by-N eigen vector matrix and s is the diagonal eigen value matrix.

Step 3: Partitions the eigen vector matrix by:

U = IL, Os] where is the N-by-(N-Q) eigen vector matrix whose columns correspond to the noise subspace.

Step 4: Searches through all angles g, the PAS can be obtained by:

= ^b;·

Step 5: Finds the estimated AoA set s = (¾.¾..., in the PAS , where 8$ are the roots of:

-—— —

Step 6: Remove in S = ($,,¾.... if is less than a certain threshold ε. Then the estimated number of users As =

5. A user equipment arranged to perform the method of claims 1 or 2.

5

6 A base station arranged to perform the method of claims 3 or 4.

7. A communication system comprising a user equipment of claim 5 and a base station of claim 6.

10

8. A method of random access substantially as herein described and having particular reference to Figures 2 - 6 of the accompanying drawings.

Intellectual

Property

Office

Application No: GB1615635.8 Examiner: Dr Stephen Bevan