Cellular Network Infrastructure » Radio Access Network » OsmoPCU

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h1. GPRS and EDGE bit-rates

This page tries to outline the possible achievable GPRS bit-rates.

There are multiple aspects that relate to the problem

* channel coding, which in turn depends on

** capabilities of the BTS and MS

** performance of the radio channel

* multi-slot operation, which depends on

** capabilities of the BTS and MS

** contention on the radio channel / resource sharing by multiple phones

h2. channel coding

Depending on the characteristics of the radio channel (interference, bit errors, link quality, C/I), the network will

dynamically select the best coding scheme.  The lower numbers (CS-1/MCS-1) have the most error coding and are very

resiliant but have little throughput.  MCS-9 has no error correction coding at all, but t

h3. GPRS channel coding

Each of the 8 GSM time-slots can operate i a number of different coding schemes:

||Coding Scheme||kbit/s||

||CS-1||8.0||

||CS-2||12.0||

||CS-3||14.4||

||CS-4||20.0||

h3. EDGE channel coding

Each of the 8 GSM time-slots can operate i a number of different coding schemes:

||Coding Scheme||kbit/s||

||MCS-1||8.80||

||MCS-2||11.20||

||MCS-3||14.80||

||MCS-4||17.60||

||MCS-5||22.40||

||MCS-6||29.60||

||MCS-7||44.80||

||MCS-8||54.54||

||MCS-9||59.20||

h2. multi-slot capabilities

h3. BTS side

BTS equipment is normally capable to run all timeslots in GPRS mode.  If you're running a single-TRX small BTS, the first timeslot is always allocated for the BCCH/CCCH, leaving 7 time-slots available for voice (TCH) and data (PDTCH).

For example, a total of 7 time-slots in MCS-9 coding scheme would render

 59.20 kbps * 7 = 414.40 kbps

h3. MS side

On the MS (phone) side, things are not that simple.  Normally, phones can not decode all 7/8 time-slots, as they operate in half-duplex mode and need some time for transmit, too.  The capabilities of each phone are specified as so-called _multislot class_

For a table of multislot classes, please see 3GPP TS 45.002, or a summarized version at "wikipedia":https://secure.wikimedia.org/wikipedia/en/wiki/GPRS#Multislot_Class.

h3. multi-slot class 10

For example, a phone with EDGE multislot class 10 permits for a total of 5 active time-slots, which can be either 4+1 (4 downlink, 1 uplink) or (3+2) (3 uplink, 2 downlink).

Under ideal radio conditions (MCS-9), such a phone can thus reach the following two bit-rates:

||Coding Scheme||multislot||downlink||uplink|| 

||MCS-9||4+1||236.80||59.20||

||MCS-9||4+2||177.60||118.40||

h3. multi-slot class 32

||Coding Scheme||multislot||downlink||uplink||