UE TX-RX frequency separation

在36.331的RRC協定中描述了RRC information elements,
其中在SystemInformationBlockType2裡的freqInfo中有三個欄位分別是,
freqInfo{ul-CarrierFreq,ul-Bandwidth,additionalSpectrumEmission},
前兩者屬於optional,為何會是optional呢?
答案寫在36.101這份描述UE radio transmission and reception中的5.7.3
Carrier frequency and EARFCN,按照spec所描述,LTE共有43個band可用
(但實際上並非全部可用,這裡不是重點,日後有機會在補上)
在default的RRC broadcast夾帶的,ul-CarrierFreq是不會出現的!
這意指著UE的downlink與uplink所使用的頻譜位置已被該 X band所鎖定,
(但其實個vendor可以照產品需求,對該UE同時允許多個band),
在此簡單說明EARFCN(E-UTRA Absolute Radio Frequency Channel Number),
這是一個頻段通道的編號,可與頻率對應但有加上偏移植(offset),也有公式可以計算出來,這邊不贅述公式!
但可以知道FDD的EARFCN從0~35999，TDD的EARFCN從36000~65531
(一般業者會將EARFCN設定為中間位置,就是將low與high取中間值)
到這裡是絕大部分各國或各電信業者會按照spec所定義的頻譜規範去使用,
但總是會有例外,假如有一家電信業者,他所能使用的頻譜並不完全match spec中所規範的,那實作上該怎麼??
其實spec早就想到了這個特殊狀況,只需在RRC broadcast夾帶的ul-CarrierFreq設定好ARFCN-ValueEUTRA
(也就是EARFCN的值),這邊一定又會產生一個疑問,那麼downlink又怎麼辦呢?
其實不用擔心,在36.101中的Table 5.7.4-1定義了Default UE TX-RX frequency separation,
這邊定義了uplink的最高頻率點與downlink最低頻率點的間隔,那麼在未改變default的狀況下,
我們變更了ul-CarrierFreq,其實downlink也隨著變動了!
ul-Bandwidth就比較單純點,分別可填ENUMERATED {n6, n15, n25, n50, n75, n100}
這邊的nX則是resource block的數量,可參考36.101的Table 5.6-1: Transmission bandwidth configuration N  in E-UTRA channel bandwidths,
而在RRC把ul-Bandwidth填入後,會造成甚麼樣的改變呢?
簡單說就是,downlink與uplink所使用的RB將不會像default屬於對稱的情況!
所以也跟ul-CarrierFreq相同,downlink與uplink將會是對應著變動的!
PS:這邊還有一點我還找不到在哪邊可以改修default UE TX-RX frequency separation的地方,但spec很明確的說明是可以變動的,
(The use of other TX channel to RX channel carrier centre frequency separation is not precluded and is intended to
form part of a later release.),再找找看吧!

PLMN Priority

PLMN Priority :
⑴RPLMN 曾經註冊過的or上次所使用的
⑵EPLMN  與當前所選擇的PLMN等同地位的
⑶HPLMN  USIM卡上的IMSI中包含的MCC和MNC與HPLMN上的MCC和MNC是一致的，一個UE只有一個HPLMN。
⑷EHPLMN 與當前所選擇的PLMN處於同等地位的HPLMN
⑸UPLMN  存在USIM卡上的一個與PLMN選擇有關的參數，User Controlled PLMN
⑹OPLMN  存在USIM卡上的一個與PLMN選擇有關的參數，Operator Controlled PLMN
⑺其他的PLMN 如:VPLMN,APLMN...

LTE Non Access Stratum (NAS) Overview

1.          Protocols in LTE-NAS

   EPS Mobility Management (EMM)

­ Supports mobility functions in the UE

   EPS Session Management (ESM)

­ Supports establishment and maintenance of IP connectivity between the UE

and the PDN gateway.

2.          Integrity Protection (IP) and Ciphering of NAS signaling messages

3.          Only support PS domain

4.          (used to tunnel CS SMS when combined attached for EPS and non-EPS) or Fallback (CSFB) to other systems (UMTS, GSM or 1X)

5.          Operating modes:

-          PS mode: LTE only

-          CS/PS mode 1: Non-EPS>LTE

-          CS/PS mode 2: LTE>Non-EPS

6.          GUTI(Globally Unique Temporary Identifier)=> <GUMMEI><M-TMSI>

7.          GUMMEI=><MCC><MNC>

8.          <MME Identifier>=> <MME group ID><MME code>

9.          EPS update status:

-          EU1=>”Updated”

-          EU2=>”Not Updated”

-          EU3=>”Roaming Not Allowed”

10.      EPLMN list – EMM, GMM, and MM shall use the same list.

11.      Timer: T34XX are different with UMTS.

12.      EMM procedures:

-          EMM Common procedures: initiated by MME while a NAS signaling connection exists.

-          EMM Specific procedures: attach, detach, Tracing area procedure (only one at time)

-          EMM Connection Management procedures: establish a secure connection with network or request for sending data

13.      EMM Common Procedures:

-          GUTI Reallocation(MME->UE)

-          Authentication(MME->UE)

-          (Security Mode Control)SMC (MME->UE)

-          Identification (MME->UE)

-          EMM Information(MME->UE)

14.      EMM Specific Procedures:

-          Attach (UE->MME) for resisted, T3410

-          Detach(UE<->MME) T3421 (UE side), T3422(MME side)

-          TAU (UE->MME) T3430

15.      Connection Management Procedures:

-          Service Request(UE->MME) T3417, T3417 Extend

-          Paging (MME->UE)

-          Transport of NAS Message (UE<->MME) Carry CS SMS message

16.      EMM-NAS security:

-Integrity Protection (IP)

-Ciphering

17.      NAS Security Parameters: NAS COUNT, NAS Sequence Number (SN), Security Terminology

18.      EPS Session Management(ESM): {Procedure Transaction ID(PTI), EPS Bearer ID, EPS Bearer, Default EPS bearer, ESM and SM coordination}

-          Procedure related to EPS bearer context

n   Default EPS Bearer Context Activation(MME->UE) T3485

n   Dedicated EPS Bearer Context Activation(MME->UE) T3485

n   EPS Bearer Context Modification (MME->UE) T3486

n   EPS Bearer Context Deactivation (MME->UE) T3495

-          Transaction related procedures

n   PDN Connectivity (UE->MME) T3482

n   PDN Disconnect (UE->MME) T3492

n   Bearer Resource Allocation (UE->MME) T3480

n   Bearer Resource Modification (UE->MME) T3481

n   ESM Information Request (Network Initiated in response to PDN Connectivity Request) (MME->UE) T3489

PLMN Selection Process

PLMN selection 為UE保持連線的重要技術之一

2個PLMN是來自不同的operator, 並且在同一個區域內可能會有多個PLMN   

PLMN selection發生的場景可能有下列三種:

1. UE開機或 重回到有PLMN coverage area

2. UE 自行要求 PLMN re-selection

3. UE 在 漫遊其間,週期性的搜尋HPLMN

PLMN selection可分為Auto mode(default )/ manual mode

正常步驟:

 UE開機=>選擇best PLMN=> select cell / registration => EPS process 

當lose cell coverage :

選擇 old PLMN list / select new cell => 假如new cell 不屬於相同的registration area ,則進入TA process

當lose PLMN coverage:

select new PLMN / show all available PLMN on the list

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當UE在idle 時, cell re-selection是為了保證UE可以取得best cell,以便讓UE可以keep service 並 change to the control channel

當UE處於idel :

renew location可以分為兩種(normal location renew & periodic location renew)

目的是讓network can trace UE mobility

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MCC=> Mobile country code (3 bits)

MNC=> Mobile network code (2~3 bits)

組合成每個UE唯一的辨識碼

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 Auto mode下選擇的優先序: 

RPLMN=> HPLMN=> USIM中UE 曾經control 的PLMN=> USIM中operator設定的PLMN=> other PLMNs (根據訊號的強弱選擇)

Manual mode下的優先續:

RPLMN=> selection by UE (所有可用的PLMNs)