When do cell phones go to sleep mode?

[EngIntoHW]

While taking/generating no call, I assume that their transceiver is in sleep mode and wakes up every X seconds to check for incoming calls, right?

What about while having a call? do they stay ON during the whole call?

I googled 'cell phones sleep mode' but didn't find any article that discusses that issue.

You know of any such articles?

Thank you.

 

[Nigel Goodwin]

As fas as I'm aware there is no sleeep mode, what would be the point?.

They are on receive permanently, and periodically transmit to tell the cell towers where they are.

 

[EngIntoHW]

As fas as I'm aware there is no sleeep mode, what would be the point?.

They are on receive permanently, and periodically transmit to tell the cell towers where they are.

I had a short conversation with someone who works in the field and he said that cell phones are usually in sleep mode when not having any call, and they wake up periodically to check for incoming calls (I don't know what's the period).

I just can't find any article discusses that.

 

[cobra1]

i find it highly unlikely that a phone would be in sleep mode and scan for calls periodically. What happens when someone calls you and your phone is asleep, you would have to wait for it to wake and scan for incoming calls then the phone would ring. When i call a mobile it rings near enough instantly 1-2 second delay from dialing to the phone ringing.

Even taking this into account the phone would only be asleep for 1 second then awake again so there would be no point.

 

[EngIntoHW]

Say that it wakes up every 1 sec to check for incoming data (calls, messages, etc).
You know how much power you save that way?

I don't see why a cell phone, being a battery operated device, shouldn't be in sleep mode most of the time.

 

[gabeNC]

I worked for a cell phone company (which would eventually become Verizon) years ago on the CDMA systems and the phones never went to "sleep". The phones were always in communication with the cell towers even if it was just a "beacon" signal. A switch engineer could easily list the cell towers the phone was in communication with, triangulate their position then figure round trip delay to get within 10 meters or so of their exact location. This technique was used frequently to help law enforcement, track current/potential girlfriends and figure out if the boss was in route to the office.

Also part of that communication with the tower involves trying to keep the noise floor at a minimum and when you have many phones transmitting, the tower would tell each phone to amp itself either up or down depending on the proximity of each device.

A common problem would be driving through a city and having the cell site partially "blocked" by a building or a set of trees, the phone would amp itself up very high to maintain a decent signal and then suddenly you round the building and have excellent line of sight. Now this phone is blasting the cell site and causing the noise floor to go up very high. Generally what would happen is that several phones on the peripheral of coverage would drop.

 

[RCinFLA]

If a cell phone did not have sleep mode the standby battery life would be only about 8-15 hours. The receiver draws between 50mA to 100 mA's depending on type of system and particular manufacturer. A very complicated wake up sequence is done to minimize power consumption. Crystal reference oscillator is woke up first as it takes the longest time to stabilize on frequency. The full processor is last thing to come on when receiver frontend is actually delivering data bits to signal processor.

Inactive period current drain is about 100 uA to 200 uA's. A big issue with newest deep sub-micron (<90 nm CMOS process) processors is their leakage current drain when in stop mode.

All this sleep mode activity brings the average current drain over time to about 2 to 4 mA's.

All cellular MA's have sleep modes. It is call discontinuous reception mode. (DRx)

When waiting for a call the network determines the timing between wakeups. It can range from about 0.2 seconds to over 5 seconds but most operators set it to between 0.625 seconds to 1.25 seconds.

The trade off is standby battery life and time to first ring. Setting the DRx longer statistically adds time to the first ring. Most systems create a fake ring back to the caller. For long DRx cycle, the caller may get several fake ring backs before the cell phone rings for the first time. This may result in caller hanging up before the cellphone user answers the call.

All cellphones are randomly assigned to a group paging address. This is the pre-wakeup part of call address. When receiver wakes up it first searches for its paging group address. It is quick and allows the receiver to go back to sleep quickly if not found. If phone detects its paging address group it stays on and does the final search for its unique call address. If does not find its unique address it then goes back to DRx cycling.

GSM phones sleeps much of receiver and transmitter circuitry while in a call during unassigned time slots. CDMA receivers are continuously on during a call. CDMA phone transmitter shuts down Tx RF output and partially sleeps during gaps in voice activity. WCDMA phone transmitter stays up during a call but reduces its power by 5.5 db during voice inactivity gaps to maintain sync pilot transmission. Voice activity power saving is not implemented on all manufacturers phones. Some phones have two microphones, with one facing outward to help differentiate background noise for voice activity function. Similar idea to noise cancelling headset but for microphone pickup.

See attached Word doc.

One other item. A cellphone must also do neighbor cell scanning during standby mode and during a call. It keeps a list of signal quality on alternate cell sites in the area so it is prepared for handover to another cell tower during movement through the system.

GSM operates different in neighbor scans then WCDMA. GSM must examine alternate frequency channels. WCDMA usually stays on same RF channel (but not always) and examines neighbor sync codes to determine virtual digital channel power. Neighbor list is a cell admin broadcast to all phones. UMTS may include both GSM and WCDMA channels in neighbor list as system can handoff between GSM and WCDMA within same network.

Again, this occurs periodically during both standby and in-call modes. During every few sleep cycles in standby mode the receiver stays up a little longer to examine alternate cell site signal quality and update its neighbor list.

 

[ahmed_aref]

nighter the cell tower nor the mobile base station (phone) sleep , the only time for disconnecting the connection between them is that when there is no signal (no coverage area) , any receiving system receive any signal , and never disconnect till you order it , it is the way it is designed for.

Thanks

 

[EngIntoHW]

Thank you very much RCinFLA.

Ahmed, I must say that what RCinFLA said sounds logical.
As he said, a large current is drawn from the battery in RX mode.

 

[Willen]

OK I am asking a simple question:-
Now I am 10 KM far from cell phone tower and my cell phone is receiving far from 10 km and transmitting to 10 km far too. Then, can i say ''My cell phone is transmitting its signal up to 10 km?''

 

[Pommie]

OK I am asking a simple question:-
Now I am 10 KM far from cell phone tower and my cell phone is receiving far from 10 km and transmitting to 10 km far too. Then, can i say ''My cell phone is transmitting its signal up to 10 km?''

I'd go for Yes.

Mike.

 

[RCinFLA]

Comm path has several factor. Height of tower and transmit power. All cellphones adjust their transmit power based on just what is needed by basestation receiver to get a reasonable bit error rate. This is part of the cell site reuse. On GSM, in a urban area, the frequency slot is reuse on basestation four or five cells away. This is how the cell system gets greater call handling capacity. Your phone also reports the basestation signal strength and the basestation will reduce its transmitted power accordingly. Too much transmitted power will just cause interference to other users in farther away cell sites. For CDMA it will degrade other users on same local cell site.

For rural areas where cell site density is lower (farther apart) you have more chance to be farther away from a cell site. This requires your transmit power to be greater which, in turn, consumes more current from battery and reducing you battery life. A GSM phone's transmit power ranges from a few milliwatts to almost 2 watts, with the transmitter final ranging from about 50 mA at low power to about 1800 mA for 2 watts output in 800/900 MHz band. This transmitter current is only for the active transmit slots. CDMA runs up to a watt or about 800 mA for transmitter but it is also on almost continuously during a call.

Cell site density is a factor of economics and statistical call handling capacity needed in a given area. In a dense urban city with a lot of cellphone users there may be a cell site every few blocks. In the country, with low cellphone user density, they may be 10-15 km apart.