Handover

Introduction

The Handover function implemented in the E6651A operates through MAC messages between the BS and SS. Hence it is accessed via the Protocol FN Test menu in BS Emulator mode. Two E6651A Test Sets are required to perform handover testing of the Subscriber Station.

The Handover menu has 4 lower level sub-menus. Press Mode, BS Emulator, Protocol FN Test for access. Click here to view the Handover menu structure. Each softkey label in the diagram is linked to its description in the Handover Menu Keys table. The Setting Menu is used to configure values for the MOB_NBR-ADV message, MOB_SCN-RSP message, MOB_BSHO-REQ message, and the DCD message.

• Press Mode, BS Emulator, Protocol FN Test, Handover, MOB_NBR-ADV msg. and select [ON] to periodically send the MOB_NBR-ADV message to the SS.

• Press Mode, BS Emulator, Protocol FN Test, Handover, MOB_SCN-RSP msg. to send an unsolicited MOB_SCN-RSP message to the SS.

• Press Mode, BS Emulator, Protocol FN Test, Handover, MOB_BSHO-REQ msg. to initiate a handover from the BS.

• Press Mode, BS Emulator, Protocol FN Test, Handover, DCD msg. and select Apply to set the updated trigger values in the DCD message which is sent to the SS every 4 seconds.

The Handover topic contains the following sections:

• Interconnections

• Setup_the_Serving_BS

• Setup_the_Target_BS

• Typical_BS_Initiated_Handover_Scenario

• Handover_Menu_Keys

Interconnections

Connect the Test Equipment and MS as shown below using a combining device such as an Agilent 11667A Power Splitter. BNC cables are required to connect the Test Sets' 10 MHz References and trigger output/inputs as shown.

Handover Test Setup

Setup the Serving BS

Configure the Serving BS as follows:

1. Indicate to the SS that the BS supports Handover by pressing Mode, BS Emulator, Settings, BSE Setting, More, More, More, More, Mobility Negotiation, and Handover Support to select [ON].

2. Connect to the SS by performing the Network Entry procedure.

3. Press Mode, BS Emulator, Protocol FN Test, Handover, Setting, MOB_NBR-ADV msg, Neighbor #1, Neighbor #2, Neighbor #3 and set a unique BSID, Preamble Index, Frequency and Permutation base for each neighbor enabled. By default, Neighbor #1 is enabled, Neighbor #2 and #3 are disabled.   
   An example of setting up 3 neighbors is provided below:
    

   	Neighbor #1	Neighbor #2	Neighbor #3
   BSID	0x010101	0x010102	0x010103
   Preamble Index	33	66	99
   Frequency	2.501	2.593	2.685
   Permutation Base	3	4	5

4. To advertise the neighbor information to the SS, press Mode, BS Emulator, Protocol FN Test, Handover, and MOB_NBR-ADV msg. to select  [ON].

Setup the Target BS

Configure the Target BS as follows:

1. Press Mode, BS Emulator, Settings, BSE Setting and set the Preamble, UL Permbase and BSID equal to one of the neighbors as defined in the MOB_NBR-ADV message from the Serving BS (refer to step 3 of Setup the Serving BS).  An example is provided below:
    

   Neighbor #1
   Preamble	33
   UL Permbase	3
   BSID	0x010203010101
   Frequency	2.501 (Press Frequency, Center)

2. Press System and select Clock Source [Ext]. Check that the reference indicator on the screen of the E6651A changes to "EXT". If "EXT" is shown in red, the E6651A is not able to lock to the external reference and the interconnect cabling should be checked.

3. Press System, Ext. Trigger and Use Input Trigger to select [ON].

4. Un-pause Target BS.

Typical BS Initiated Handover Scenario

If the example trigger settings have been used, the DUT initiates scanning and sends a MOB_SCN-REQ to the BS.  The DUT completes handover after further message exchanges with the BS.

Using the N6421A Protocol Logging Application, you can observe the following protocol message sequence when logging the Serving BS:

1. SS sends MOB_SCN-REQ message to BS.

2. BS sends MOB_SCN-RSP message to SS.

3. SS sends MOB_SCN-REP message to BS.

4. BS sends MOB_BSHO-REQ message to SS.
   
   If Auto Send [ON] (BS Emulator , Protocol FN Test , Handover , Setting , MOB_BSHO-REQ msg. ,  Auto Send ON/OFF), the BS sends MOB_BSHO-REQ in response to the MOB_SCN-REP from the SS.  If Auto Send [OFF], the SS may send a MOB_MSHO-REQ message to initiate a handover.

5. SS sends MOB_HO-IND message to BS.

An example of the message sequence:

You can observe an Initial Ranging Code of 12 when logging the Target BS:

In the Subscriber Station Information window of the Target BS, you will observe the Connection state and this completes the handover to the Target BS.

Setup Event Trigger Conditions

On the Serving BS, the SS trigger information can be setup in the DCD msg. menu (Mode, BS Emulator, Protocol FN Test, Handover, Setting, DCD msg). It is possible to set up 2 trigger conditions.

An example of setting up an Event Trigger Condition:

1. Select the trigger type using the Trig. Type setting.  The options available are [CINR Metric], [RSSI Metric] and [RTD Metric]. For example, select the [RSSI Metric].

2. Define the trigger condition using the Trig. Function and Trig. Value settings.  For example, set the Trig. Function to [Serving < Value] and the Trig. Value to -60dBm.  When the RSSI of the Serving BS falls below -60dBm, the trigger condition is met.

3. Select the required trigger action using the Trig. Action setting.  This is the action that the SS will perform when the trigger condition is met.  For example, select [Initiate Scanning]
   
   The E6651A supports the following SS trigger actions as defined in the IEEE Std 802.16 Table 358b:

• [Initiate Scanning] - On trigger, MS starts the neighbour BS scanning process by sending MOB_SCN-REQ

• [Perform Scanning] - On trigger, MS should perform scanning

• [Send MOB_SCN-REP] - Respond on trigger with MOB_SCN-REP after the end of each scanning interval

• [Send MOB_MSHO-REQ] - Respond on trigger with MOB_MSHO-REQ

4. Press Apply to set the updated trigger values in the DCD message. This is sent to the SS every 4 seconds.

5. To activate the trigger in the example above, press Amplitude, Source Amplitude and use the knob or down arrow key to decrease the power level value in small increments to below -60dBm

6. Second DCD Trigger can be set to "Off".

Typical MS Initiated Handover Scenario

Handover Menu Keys