Picking a Tower Question

CDMA phones will constantly cycle through different PN offsets looking for the best signal . The problem is the phones aren't smart enough to determine which one actually has the best signal unless there's a difference of at least -10 to -15 dbs in strength. Even when there is a so called 'dominant pilot' it might not necessarily be the best one as sometimes phones can be fooled by signal bounce, terrain, and other factors.

 

Dropped calls with full bars is caused by signal pollution, possibly caused by your phone listening/using too many towers or something like that. The network might also not be configured the best way. I've experienced this too in an area where my phone constantly changed active pilots during a call, then, all of a sudden, they start changing more rapidly, the noise level goes up and my call drops.

 

Being right in between two different towers with the phone constantly handing off back and forth can also cause problems. But I've seen this happen many times where it works fine. I think it depends on the how the neighbor list and network is optimized in the area.

 

Yes that is correct but the problem is it's only a temporary thing. The phone can't keep in memory which tower is the strongest.

 

Okay, let's have a little CDMA handoff class.

Soft Handoff in CDMA means that the phone can communicate with up to 3 other sectors at the same time. Meaning, the phone is actually transmitting a signal, and the base stations at 3 different sites are ALL talking to the handset at the same time. It is a little erroneous to say that the phone is switching "back and forth" between towers. (Sorry Larry, not busting you man, just clearing it up a little.)

The situation of having a call drop from full signal down to nothing in conversation, could be several things. It could be that the area he is in is a boundary between two serving switches, or Base Station Controllers. The border sites between the two cannot do a soft handoff, and must do a hard handoff (in this case you are absolutely correct Larry, the phone does have to switch between towers, like throwing a switch). This is very succeptible to failure in CDMA if not set up properly. For example, if the thresholds on the boundary are not set right, then the call could handoff way too soon (hard handoff) to the site on the other side of the boundary, resulting in poor call performance. While these boundaries are supposed to be invisible, if not datafilled right in software, things like this happen.

Just wanted to make sure everyone understands how Soft (between cell sites) Softer (between sectors on the same cell), and Hard (between boundary cells on different BSC's) handoffs work.

As far as scanning PN's, the phone keeps a list of up to 5 PN's (I think) of active candidates for service. These are constantly added and dropped as the signal gets better or worse, and new PN's show up as stronger candidates. Again, if the thresholds are not set properly in between the cells, you can have a whole laundry list of problems.

Edjumucashun is a goowd thang.....

 

Do a search on CDMA and there is some theory stuff on Motorola's website. Also, you only receive a page from one tower, unless they are flood paging you due to no response from the first one. I was a little ambiguous in that soft/softer/hard handoff only happens while you are in a call.

 

Well that's a CDMA thing. The ring actually occurs before your phone rings, often, but not always. While that happens, the network is trying to page/locate your phone which can sometimes take longer.
So, bottom line, GSM networks are much easier to set up, correct? Also, GSM cellsites can be smaller and require less equipment, correct?

 

Neither one is "Easy" to set up, they perform the same functions, just in different ways. The handoffs are a little different between CDMA and GSM, but bottom line, they still accomplish the same goal. I always tell salespeople who gripe about the network, here's a truck, test equipment, and the keys, get after it.......I have yet to have any takers......

Regarding the amount of equipment, both can be deployed from Micro or Pico cells, up to heavy traffic normal cells with multiple carriers. I don't understand what you were trying to ask there.

The ring portion is this: The system pages you on your last known location, if within a specific amount of time there is no response, the system can flood page you within a particular "paging zone", meaning all cell sites in a zone send out a paging message, to see if you respond. This is the paging method of last resort to try and deliver the call, because it uses resources on multiple cell sites. This is done because of what you described, that you may be in between two towers, with a varying signal. This happens in milliseconds, by the way.

As far as taking a little bit to ring, understand, ringing tone, just like dialtone, is a comfort thing to make sure you know it's working. They really don't serve any purpose, except to keep you from hanging up thinking it doesn't work. Call setup times are not always the same, so you're just hearing a ringing noise to let you know "don't hang up", I'm still trying to connect.

K......Next?

 

Thanks for the post! Yes I did know the phones can communicate with up to 3 sectors at the same time. But the problem is those 3 sectors usually have to be in the same neighbor list. When a tower is put up the network engineers decide which PN offsets they want the tower to be able to handoff to and which ones they don't. That list is programmed in to the tower's database. There aren't that many available spaces in the neighbor list so they can become full and when additional towers are added the techs sometimes forget to update the database. Often times the other 3 sectors are useless if your in a bad reception area (ie. the hills) because none of the other sectors in the neighbor list can be communicated with except the originating one. Here in my area, my phone (in standby) constantly bounces around between 4 or 5 different offsets (only two of them are useable). If I originate a call on one of the ones that are unuseable the call will fail because of the neighbor list issue (inability to communicate with other 3 sectors). With my phone set in debug mode I have experimented with this many times. For example, If I originate a call while on offset 183 the call will fail and will have nothing to handoff to because it's too far away. If originate the call on offset 081 the call will work perfectly and even handoff to one of the other sectors (012) on the same tower. It sucks when you have to wait for a certain offset to show up on your screen before you can make a reliable call. Luckily about 80% of the time my phone picks up the right offset. So the point I'm trying to make here is that the quality of your call can often depend on which particular PN offset your call ORIGINATES from because the neighbor list of each PN offset you happen to land on can vary greatly.

 

Yikes, that does suck Larry.

Time for a new carrier!

 

Nope. Most carriers work poorly here and I'm used to it. Up until November Sprint was practically the only carrier that worked at all. But Cingular came in and installed equipment at the same site as Sprint, but mounted theirs about 15-20 feet higher on the Utility tower. So yes they do have better coverage here now but I'm not going to leave Sprint and give up my sweet grandfathered plans ($10 unlimited internet, text msgs, picturemail and videomail all included) just to get slightly better signal here at my house.

 

Wirelessly posted (A phone: BlackBerry7100/4.0.0 Profile/MIDP-2.0 Configuration/CLDC-1.1)

Good point. I wouldn't give all that up either. Especially not to move to evil Cingular.

 

The only real problem area I have to deal with is the downstairs back portion of the house. The front of the house, garage, and upstairs all have reliable service. But when I'm in the kitchen, family room or office room my phone starts to cycle through the PN offsets (which causes problems sometimes). Annoying, but something I can deal with to keep my goodies.

 

As far as the PN's go, there are several things that could be killing you, like T_ADD and T_DROP, where it is not properly dropping PN's out of the list at the proper signal threshold. With 1XRTT, and all of the new parameters, there are so many opportunities for failure it's scary! Maybe if you gripe regularly enough, you can get them to fix that problem. I see a lot of that with guys worried about handoff thresholds, but they don't pay enough attention to dropping or adding PN's at a given threshold. Bad Perfomance Engineers!

Oh yeah, and why don't you see about RF transparent walls? j/k

 

I've complained over and over again. It doesn't do any good. I've even written letters to the RF dept. here in Irvine, CA and still no good.

 

You can actually datafill up to 20 neighbors in CDMA systems. So unless you are in an area with extreme cell density, you should be ok there. There are logs that Engineers can look at that contain pilot signal strength measurement messages or PSMMS. These messages are generated every time a pilots signal strength is measured. This measurement is sent back to the base station controller and logged on their system. These messages can be analyzed over a period of time (I use 2 weeks) and then neighbor lists and neighbor priorities can be determined.

If there is extreme cell density, then the carrier could down-tilt their antennas or utilize lower gain antennas to decrease each sectors foot print, and reduce the soft handoff factor to something more manageable.

Does that make sense?

 

In my lengthy experience with many networks, Sprint PCS has the worst hand off (soft or hard) of any carrier. Thehy also have the worst capacity handling (first in last out on call init should be the norm, but it is FIFO on Sprint so a new call can init...you just get dropped). Don't get me started on their customer service issues. Call Cingular evil, but the networ is better (generally speaking) and the customer service is light years better (especially for business accounts).

If you really want to learn about how the networks operate (I mean REALLY), then sign up for this class:

http://www.lcc.com/WI-LCC/cat_architect.htm