GSM radio path
GSM is system using time division multiple access (TDMA) frame structure. The TDMA frame has duration of 4.615 ms and consists of 8 timeslots. There is two types of logical channels carried over the timeslots: Common channels and dedicated channels.
Common channels
The common channels are used for signaling and ca be divided into broadcast channels (BCH), continuously sending information from BTS to MS, and common control channels (CCCH).
The Broadcast channels send information on the cell properties such as synchronization, frequency correction, used frequencies and power levels, neighboring cells. There are three different broadcast control channels (BCCH). The common control channels are used when establishing a signaling connection between the MS and BTS. The paging channel (PCH) is used when BTS wants to contact the MS. The MS requests a signaling channel on a random access channel (RACH). The signaling channel is allocated to the MS by using Access grant channel (AGCH)
Dedicated channels
The dedicated channels are divided into dedicated control channels and traffic channels. Call set up signaling and location updating procedures are performed on stand-alone dedicated control channel (SDCCH). In case of a call setup the connection is transferred into a traffic channel (TCH).
Both SDCCH and TCH have a parallel slow associated control channel (SACCH) which is used for transfer of measurement results from MS to BTS and power control commands from BTS to MS. During the short messages are transmitted over SACCH channel, while the fast associated control channel (FACCH) is used to transmit the handover commands to the MS.
Radio path measurements
The radio path measurements are used to keep the connection in good quality and therefore to trigger power changes and handover if needed. Both MS and BTS measure signal level and quality (bit error ratio). In addition to that MS measures the signal levels of all adjacent BCCH frequencies even though it is able to report only six best measurements.
Power control and handover
The BTS sends the raw measurement results received from the MS (downlink) and the results of its own measurements (uplink) to the BSC every SACCH multiframe period. The BSC does not support the measurement preprocessing in the BTS.
The BSC does the preprocessing of the measurement samples namely the book keeping and the averaging. The BSC is able to maintain a table of maximum 32 measurements results for up to 32 adjacent cells per call. After the averaging the BSC makes comparisons with the thresholds related to both power control (PC) and hand over (HO) algorithms.
The BSC determines the RF output power of the MS and the BTS on the basis of the results received from the pc threshold comparison process.
The HO decision is based in signal strength (RXLEV), quality (RXQUAL) and distance measurements. Another possible criterion is the power budget (PBGT) or umbrella condition fulfillment from an adjacent cell. The HO command is given over FACCH, which uses TCH temporally. Handovers can be done to TCH and SDCCH. The intra BTS handover can occur either to a timeslot in a new carrier or to a different timeslot in the same carrier. The intra-BSC handover to performed autonomously by the BSC. If there is an inter-BSC handover to be performed, the BSC sends the list of performed cells to the MSC and MSC performs the handover according to that list.
Handover strategies and parameters
The HO decision process may be triggered in different situations. Similarly to the pc it is controlled by the level (RXLEV) and quality (RXQUAL) in both UL and DL. In addition to these it depends in the distance and some periodic checks (PGBT, UMBRELLA). Only one type of periodic can be used per cell. The main principle when making HO caused by radio criteria is that the new server should be better than the current one.
The parameters, averaging and threshold comparison for level, quality and distance are similar to PC but only one threshold associated. The periodic checks occur every power budget (HO period PGBT) or umbrella (HO period Umbrella) period. In order to be performed the periodic checks require some data for the neighboring cells: the comparison process uses the calculated PGBT (n) or AV_RXLEV_NCELL (n) for neighboring cells instead of fixed thresholds.
Like with PC it is possible by changing the HO related cell parameters to affect the HO algorithm at all stages: preprocessing, threshold comparison, decision making.
BSS Parameters
The following figure showing the example of general parameters on how the structure of the network is defined
GSM is system using time division multiple access (TDMA) frame structure. The TDMA frame has duration of 4.615 ms and consists of 8 timeslots. There is two types of logical channels carried over the timeslots: Common channels and dedicated channels.
Common channels
The common channels are used for signaling and ca be divided into broadcast channels (BCH), continuously sending information from BTS to MS, and common control channels (CCCH).
The Broadcast channels send information on the cell properties such as synchronization, frequency correction, used frequencies and power levels, neighboring cells. There are three different broadcast control channels (BCCH). The common control channels are used when establishing a signaling connection between the MS and BTS. The paging channel (PCH) is used when BTS wants to contact the MS. The MS requests a signaling channel on a random access channel (RACH). The signaling channel is allocated to the MS by using Access grant channel (AGCH)
Dedicated channels
The dedicated channels are divided into dedicated control channels and traffic channels. Call set up signaling and location updating procedures are performed on stand-alone dedicated control channel (SDCCH). In case of a call setup the connection is transferred into a traffic channel (TCH).
Both SDCCH and TCH have a parallel slow associated control channel (SACCH) which is used for transfer of measurement results from MS to BTS and power control commands from BTS to MS. During the short messages are transmitted over SACCH channel, while the fast associated control channel (FACCH) is used to transmit the handover commands to the MS.
Radio path measurements
The radio path measurements are used to keep the connection in good quality and therefore to trigger power changes and handover if needed. Both MS and BTS measure signal level and quality (bit error ratio). In addition to that MS measures the signal levels of all adjacent BCCH frequencies even though it is able to report only six best measurements.
Power control and handover
The BTS sends the raw measurement results received from the MS (downlink) and the results of its own measurements (uplink) to the BSC every SACCH multiframe period. The BSC does not support the measurement preprocessing in the BTS.
The BSC does the preprocessing of the measurement samples namely the book keeping and the averaging. The BSC is able to maintain a table of maximum 32 measurements results for up to 32 adjacent cells per call. After the averaging the BSC makes comparisons with the thresholds related to both power control (PC) and hand over (HO) algorithms.
The BSC determines the RF output power of the MS and the BTS on the basis of the results received from the pc threshold comparison process.
The HO decision is based in signal strength (RXLEV), quality (RXQUAL) and distance measurements. Another possible criterion is the power budget (PBGT) or umbrella condition fulfillment from an adjacent cell. The HO command is given over FACCH, which uses TCH temporally. Handovers can be done to TCH and SDCCH. The intra BTS handover can occur either to a timeslot in a new carrier or to a different timeslot in the same carrier. The intra-BSC handover to performed autonomously by the BSC. If there is an inter-BSC handover to be performed, the BSC sends the list of performed cells to the MSC and MSC performs the handover according to that list.
Handover strategies and parameters
The HO decision process may be triggered in different situations. Similarly to the pc it is controlled by the level (RXLEV) and quality (RXQUAL) in both UL and DL. In addition to these it depends in the distance and some periodic checks (PGBT, UMBRELLA). Only one type of periodic can be used per cell. The main principle when making HO caused by radio criteria is that the new server should be better than the current one.
The parameters, averaging and threshold comparison for level, quality and distance are similar to PC but only one threshold associated. The periodic checks occur every power budget (HO period PGBT) or umbrella (HO period Umbrella) period. In order to be performed the periodic checks require some data for the neighboring cells: the comparison process uses the calculated PGBT (n) or AV_RXLEV_NCELL (n) for neighboring cells instead of fixed thresholds.
Like with PC it is possible by changing the HO related cell parameters to affect the HO algorithm at all stages: preprocessing, threshold comparison, decision making.
BSS Parameters
The following figure showing the example of general parameters on how the structure of the network is defined
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