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View Full Version : Handoff in CDMA (Types, Mechanism, and It’s Parameters)



mansoor2
2008-09-26, 10:22 PM
salam.
This is a little post about handoff in CDMA. Maybe you can use this article as reading material in your spare time http://pram.web.id/blog/wp-includes/images/smilies/icon_smile.gif
Handoff : In Cellular Telecommunication, user frequently moves froma certain point to another point in the service area. When it movesfrom a certain cell/sector (A) to another cell/sector (B), it have tobe transfered from A to be B without break the connection (whether itis idle or dedicated state)
So, how many kind of handoff does CDMA have? Below, we are going to discuss it http://pram.web.id/blog/wp-includes/images/smilies/icon_razz.gif
Types of Handoff in CDMA:
Intersector / SofterHandoff. Mobile station communicates with two sectors of the same cell site.It means that user moves from a sector to another sector in the samecell site.http://pram.web.id/blog/wp-content/uploads/2008/05/softer.JPG (http://pram.web.id/blog/wp-content/uploads/2008/05/softer.JPG) 2. Intercell / soft handoff.

Mobile station communicates with two or three sector of differentcell sites. It means that user move from a cell to another cel, and inthe border site it attached to two (two way soft handoff ) or more(three way soft handoff) sectors from different cell sites. Primarycell site can send the forward control message, and other cellremaining are called secondary sites. In case 3 way handoff, it couldbe ended when one of secondary site is dropped by system (become twoway handoff). Soft handoff use more network resources than softerhandoff.http://pram.web.id/blog/wp-content/uploads/2008/05/soft_handoff1.JPG (http://pram.web.id/blog/wp-content/uploads/2008/05/soft_handoff1.JPG)
3. Soft-softer handoff

Mobile station communicates with two sectors of one cell and onesector of another cell. This kind of handoff consume network resourcesequals with the resource for softer handoff and two way handoffaltogether.http://pram.web.id/blog/wp-content/uploads/2008/05/soft_softer.JPG (http://pram.web.id/blog/wp-content/uploads/2008/05/soft_softer.JPG)

4. Inter-frequency / Hard handoff
This handoff usually called brake before make handoff. Becausemobile station terminate it’s old connection and then connect it’s newconnection. Handoff occur when user move from a cell site to anothercell site with different frequency or different MSC.
http://pram.web.id/blog/wp-content/uploads/2008/05/hard-handoff.JPG (http://pram.web.id/blog/wp-content/uploads/2008/05/hard-handoff.JPG)


So… after we have discussed the types of handoff, nowwe’re going to discuss about handoff parameter in CDMA. Maybe thistopic a little bit rough for your spare time http://pram.web.id/blog/wp-includes/images/smilies/icon_razz.gif hehehe…
Pilot Sets
The Pilot Term, means the pilot channel identified bya pilot sequence and a frequency assignment. Pilot is correlated withforward traffic channels CDMA. Each Pilot have a PN code as it’sidentity. There is 64 chips offset between PN’s in the adjacent Pilots.The Pilots identified by the mobile is categorized in to four setscontinuously:


Active set, contains a batch of pilot in active condition, which isassociated with forward traffic channel signed to the mobile. As weknow that CDMA receiver in Mobile Station have 3 Rake Finger, eachfinger can handle 2 Pilot in active set. Candidate set, is a set of pilot which has sufficient signalstrength so the traffic transmitted on it can be demodulated, but notyet in the active set(Max 6 Pilot). Neighbor set, contains neighbor pilots candidate for handoff (Max20 Pilot). Especially for neighbor set, we can configure on the BSSParameter. Remaining set, is a set of possible pilots remaining besides Active, Candidate, and Neighbor set.So.. how it can be classified in to 4 kind of sets? To find the answer… let’s take a look in to picture below,
http://pram.web.id/blog/wp-content/uploads/2008/05/mechanism.JPG (http://pram.web.id/blog/wp-content/uploads/2008/05/mechanism.JPG)Hmm… maybe if I give a little information, it will bemore useful. The picture above explain about handoff thresholdmechanism. As you can see there are areas pointed with number, (1),(2)… Below I’ll try to give some brief explanation: (1). Mobile station measures that Pilot signalstrength is bigger than T_ADD (Pilot Detection Threshold). MS sendsPSMM (Pilot Strength Measurement Message) and then transfer the Pilotto candidate set. (2). HDM (Handoff Direction Message) is sent by BTS to MS using the Pilot to be added to in active set. (3). After MS receive HDM (Handoff Direction Message)and obtain the new traffic channel, now Pilot is in the active set andMS sends HCM (Handoff Completion Message) (4). After Pilot signal strength drops below T_DROP (Pilot Drop Threshold), MS starts the T_TDROP (Drop Timer Threshold) (5). T_TDROP expires, MS send PSMM to BTS.
(6). BTS sends HDM, without related pilot to the mobile.
(7). After MS Receives HDM, Pilot becomes in to neighbor set. MS send HCM to BTS.
(8). NLUM (doesn’t include the Pilot) is received by MS, and Pilot become in to remaining set.
After we have discussed about Pilot Sets, now let’s talk about Search Window and it correlation to Pilot Sets. ^_^
Search Window (SRCH_WIN)
SRCH_WIN_A (active and candidate) search window that MS uses for active and candidate Pilots tracking. should be large enough to catch all usable multipath signalcomponents from BTS, to anticipated the propagation environment. In thesame time, it should be as small as possible to maximize searcherperformance. SRCH_WIN_N (neighbor) search window that MS uses for neighbor set Pilots tracking. larger than SRCH_WIN_A, because beside it has to be large enoughfor it’s own BTS, it is also should be large enough to catch all usablemultipath from neighbor cells. SRCH_WIN_R (remaining) search window that MS uses for remaining set Pilots tracking. at least equals with SRCH_WIN_NWell, there’s a lot more if we want to observe more about handoffand power control in CDMA. Maybe if I have some spare time to write itI’ll post it here. I’m sorry if I filch your spare time :p
Salam…hopefully useful. (adapted from CDMA95.10)

miro
2008-09-27, 02:19 AM
very nice of you

mervinaiene
2008-09-29, 10:47 AM
you are a good source of information. keep it up.

Yachi
2008-10-02, 11:11 PM
ok friend how i can keep it in texte file ,could you share you representation

aasimanwaar
2009-08-10, 03:59 PM
Aoa
nice work as always.. i found many like these posts from u. keep it up.
4m pakistan