Random Access for M2M Communications over LTE network

Copyright © 2012, [email protected]

Random Access for M2M Communications over LTE network


Outline

• Problem Statement• Related work• Proposed Design• References


Problem Statement

• To enable full mechanical automation where each smart device can play multiple roles among sensor, decision maker, and action executor, it is essential to construct scrupulous connections among all devices [1]

• In the literature, few realizations of M2M communications have been proposed, such as leveraging Bluetooth (IEEE 802.15.1), Zigbee (IEEE 802.15.4), or WiFi (IEEE 802.11b) technology. However, there is still no consensus on the network architecture of a general scenario for M2M communications [1]


Problem Statement

• It is one of the key issues in the 4-th generation (4G) cellular networks how to efficiently handle the heavy random access (RA) load caused by newly accommodating the huge population of Machine-to-Machine or Machine-Type Communication (M2M or MTC) customers/devices [2]

• Supporting trillions of devices is the critical challenge in machine-to-machine (M2M) communications, which results in severe congestions in random access channels of cellular systems that have been recognized as promising scenarios enabling M2M communications [3]


Related Work

Design focus/improvements UE mixed with MTC

Grouping-based radio resource management

[1]

MTC devices are grouped to guarantee the QoS requirement Yes

ABC [2]Using different combination of

H2H and M2M’s preamble testify the system’s performance

Yes

Cooperative ACB [3] Minimize the maximum number of access among M BSs No

Proposed design

1. Balance the number of access among M BSs

2. MTC will not interfere UE during random access procedure

3. MTC devices are grouped to reduce the random access delay

Yes


Proposed Design

• Problem formulation [3] Consider the random access of M2M communications in

LTE-Advanced with 𝑀 BSs indexed by 𝑚 = 1, . . ., 𝑀and 𝑁 active MTC devices indexed by 𝑛 = 1, . . .,𝑁

Distinct from the ordinary ACB that each MTC device can only access the BS attached by the MTC device, in this letter, we propose that an MTC device is able to access the BS unattached by the MTC device when the MTC device locates within the overlapped coverage area of multiple BSs


Proposed Design

To formulate such a random access problem, we adopt following notations 1) Denote 𝐴𝑚 as the set of MTC devices attaching to

the𝑚th BS and ∥𝐴𝑚∥ as the norm of 𝐴𝑚. When cooperation of BSs are available, 𝐴𝑚 for all m are known by all BSs. Note that NA

M

mm

1


Proposed Design

2) Denote 𝑀𝑛 as the set of BSs that the 𝑛th MTC device can possibly access. The 𝑛th MTC device selects one BS from 𝑀𝑛 to proceed to the random access. In LTE-Advanced, the BS can request the MTC device to perform the exploration of surrounding BSs, and report the exploration result. Thus, 𝑀𝑛 for all 𝑛 are available for all BSs. However, 𝑀𝑛 for 𝑛 = 1, . . .,𝑁, !=𝑛 𝑗 are unknown by the 𝑗th MTC device for 𝑗 = 1, . . .,𝑁.


Proposed Design

3) Denote 𝑁𝑚 as the set of MTC devices that access the th BS. In the ordinary ACB,𝑚 ∥𝑁 for all 𝑚∥ 𝑚are known by each BS. However, if each MTC device can access the BS unattached by the MTC device, ∥𝑁 for all are random variables 𝑚∥ 𝑚unknown by BSs, unless the BS selection strategy of each MTC device is given

4) Denote l , as an indicator function that, for the 𝑛 𝑚 𝑛th MTC device,

)1(,1,0, l n M withinis BS mth the ifotherwise mn


Proposed Design

5) Denote 𝑁′ as the set of MTC devices that can 𝑚only receive the signal from the th BS and these 𝑚MTC devices can only access the th BS. 𝑚 ∥𝑁′ 𝑚∥is the norm of 𝑁′𝑚


Proposed Design


Proposed Design

In the ordinary ACB, although the throughput of each cell can be individually maximized by individually setting p = 1/ (where 𝑚 ∥𝑁𝑚∥ p is the ACB parameter 𝑚of the the th BS) in each BS, the delay experienced by 𝑚an MTC device attached to the th BS may be 𝑚unacceptable when requires to be set to an extremely 𝑝𝑚small value under a large ∥𝑁𝑚∥

our objective is to provide an optimum control of a set of ACB parameters p = [ 1, . . . , ] jointly decided 𝑝 𝑝𝑀by BSs to minimize the largest access delay 𝑀experienced among active MTC devices𝑁


Proposed Design

Through cooperation among BSs to make a joint decision of p = [ 1, . . . , ], the problem can be 𝑝 𝑝𝑀formulated by

MmforpNC2.2

(2) pppCts

NNNbalance

mm

M

MpMp

,...,1,1

1,...,01.1..

),...,,(min

1

21,...,1


Proposed Design

• BS selection strategy for each MTC device BS selection strategy is based on pm, for m=1,…,M (BS

with higher pm has higher probability to be accessed by MTC)

Upon receiving ˜p = { , , . . . , } p, the th 𝑛 𝑝𝑖 𝑝𝑗 𝑝𝑘 ⊆ 𝑛MTC device adopts the strategy

where , is the probability that the th MTC device 𝑄𝑛 𝑥 𝑛 selects the th BS to access𝑥

)3(,0,1

,...,

,...,

,,

niii

k

My y

Mx x

kkn

i

My y

Mx x

iin

kin

MiAAA

A

A

p

pQ

A

A

p

pQ

pp

n

n

n

n


Proposed Design

• Cooperative Access Class Barring Given that the strategy on the selection of the BS in each

MTC device in (3) is known by BSs, ∥ for all 𝑁𝑚∥ 𝑚can be obtained by

The optimal p can be found by algorithm 1 and algorithm 2 proposed by [3]

(4) M1,...,m for QlNM

x Anmnmnm

x

1,,


Proposed Design

Draw a random number-unif(0,1)

Number < ac-Barringfactor

Retry after a certain period

NoYes

System Information (SIB2,P) via broadcast

Draw a random number

q-unif(0,1)

q < pNo

Yes

Random Access Preamble

Random Access Response

Scheduled Transmission

Contention Resolution

MTC eNB

Access B

arring Check

Access C

lass Barring

Random

Access


Proposed Design


Proposed Design

Receiving a service request from MTC device carrying σi

Are there enough PRBs in the AGTI supporting one more MTC

device

The eNB Rejects the MTC request

Is there a cluster with parameter σi

The eNB creates a new cluster for the MTC

The eNB permits the MTC to join a cluster

σi :the random access rate for MTC i

No

Yes

No

Yes


王老師的建議1. 如何更精確反應出每個 BS 下的情況 ? Key paper 所提的 Qn,i 只考量了此 round 期望能 access BS 的 MTC 數，逸懷的方法加入考量每台 BS 實際有 attach上此 BS 的個數，更能反應出目前 BS 實際 loading 情況2. Access Barring Check(ABC) 與 Access Class Barring(ACB) 的差別 ? ABC 與 ACB 都是根據目前 BS 的 loading 來調整其threshold ，所以沒有差別


曾老師的建議1. 可衡量 MTC 與 UE 通過 Random access 的比率2. MTC 與 UE 在 Random access 時，是共享 or 獨有Resource Block(RB)? 目前 3GPP spec 並沒有針對這部分做規範，但根據survey paper ，目前研究都是假設 MTC 與 UE 在 Random access 時是共享 RB

3. UE 及 MTC 發 Random access 的頻率 ? UE 發完 Random access 與 BS 連上後，就不再發Random access MTC 每次的上傳或是下載前，都要先跟 BS 發 Random access


References

[1] Shao-Yu Lien; Kwang-Cheng Chen; Yonghua Lin; , "Toward ubiquitous massive accesses in 3GPP machine-to-machine communications," Communications Magazine, IEEE , vol.49, no.4, pp.66-74, April 2011

[2] Ki-Dong Lee; Sang Kim; Byung Yi; , "Throughput comparison of random access methods for M2M service over LTE networks," GLOBECOM Workshops (GC Wkshps), 2011 IEEE , vol., no., pp.373-377, 5-9 Dec. 2011

[3] Shao-Yu Lien; Tzu-Huan Liau; Ching-Yueh Kao; Kwang-Cheng Chen; , "Cooperative Access Class Barring for Machine-to-Machine Communications," Wireless Communications, IEEE Transactions on , vol.11, no.1, pp.27-32, January 2012

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Random Access for M2M Communications over LTE network