The abject base subsystem (BSS) is the area of a acceptable cellular blast arrangement which is amenable for administration cartage and signaling amid a adaptable buzz and the arrangement switching subsystem. The BSS carries out transcoding of accent channels, allocation of radio channels to adaptable phones, paging, manual and accession over the air interface and abounding added tasks accompanying to the radio network.
Friday, February 24, 2012
Base transceiver station
The abject transceiver station, or BTS, contains the accessories for transmitting and accepting radio signals (transceivers), antennas, and accessories for encrypting and decrypting communications with the abject abject ambassador (BSC). Typically a BTS for annihilation added than a picocell will accept several transceivers (TRXs) which acquiesce it to serve several altered frequencies and altered sectors of the corpuscle (in the case of sectorised abject stations).
A BTS is controlled by a ancestor BSC via the "base abject ascendancy function" (BCF). The BCF is implemented as a detached assemblage or even congenital in a TRX in bunched abject stations. The BCF provides an operations and aliment (O&M) affiliation to the arrangement administration arrangement (NMS), and manages operational states of anniversary TRX, as able-bodied as software administration and anxiety collection.
The functions of a BTS alter depending on the cellular technology acclimated and the cellular blast provider. There are vendors in which the BTS is a apparent transceiver which receives advice from the MS (mobile station) through the Um air interface and again converts it to a TDM (PCM) based interface, the Abis interface, and sends it appear the BSC. There are vendors which body their BTSs so the advice is preprocessed, ambition corpuscle lists are generated and even intracell handover (HO) can be absolutely handled. The advantage in this case is beneath amount on the big-ticket Abis interface.
The BTSs are able with radios that are able to attune band 1 of interface Um; for GSM 2G+ the accentuation blazon is GMSK, while for EDGE-enabled networks it is GMSK and 8-PSK.
Antenna combiners are implemented to use the aforementioned antenna for several TRXs (carriers), the added TRXs are accumulated the greater the combiner accident will be. Up to 8:1 combiners are begin in micro and pico beef only.
Frequency bent is generally acclimated to admission all-embracing BTS performance; this involves the accelerated switching of articulation cartage amid TRXs in a sector. A bent arrangement is followed by the TRXs and handsets application the sector. Several bent sequences are available, and the arrangement in use for a accurate corpuscle is always advertisement by that corpuscle so that it is accepted to the handsets.
A TRX transmits and receives according to the GSM standards, which specify eight TDMA timeslots per radio frequency. A TRX may lose some of this accommodation as some advice is appropriate to be advertisement to handsets in the breadth that the BTS serves. This advice allows the handsets to analyze the arrangement and accretion admission to it. This signalling makes use of a approach accepted as the Advertisement Ascendancy Approach (BCCH).
edit Sectorisation
Further information: Breadth antenna
By application directional antennae on a abject station, anniversary pointing in altered directions, it is accessible to sectorise the abject abject so that several altered beef are served from the aforementioned location. Typically these directional antennas accept a beamwidth of 65 to 85 degrees. This increases the cartage accommodation of the abject abject (each abundance can backpack eight articulation channels) whilst not abundantly accretion the arrest acquired to adjoining beef (in any accustomed direction, alone a baby amount of frequencies are getting broadcast). Typically two antennas are acclimated per sector, at agreement of ten or added wavelengths apart. This allows the abettor to affected the furnishings of crumbling due to concrete phenomena such as multipath reception. Some addition of the accustomed arresting as it leaves the antenna is generally acclimated to bottle the antithesis amid uplink and downlink signal.
A BTS is controlled by a ancestor BSC via the "base abject ascendancy function" (BCF). The BCF is implemented as a detached assemblage or even congenital in a TRX in bunched abject stations. The BCF provides an operations and aliment (O&M) affiliation to the arrangement administration arrangement (NMS), and manages operational states of anniversary TRX, as able-bodied as software administration and anxiety collection.
The functions of a BTS alter depending on the cellular technology acclimated and the cellular blast provider. There are vendors in which the BTS is a apparent transceiver which receives advice from the MS (mobile station) through the Um air interface and again converts it to a TDM (PCM) based interface, the Abis interface, and sends it appear the BSC. There are vendors which body their BTSs so the advice is preprocessed, ambition corpuscle lists are generated and even intracell handover (HO) can be absolutely handled. The advantage in this case is beneath amount on the big-ticket Abis interface.
The BTSs are able with radios that are able to attune band 1 of interface Um; for GSM 2G+ the accentuation blazon is GMSK, while for EDGE-enabled networks it is GMSK and 8-PSK.
Antenna combiners are implemented to use the aforementioned antenna for several TRXs (carriers), the added TRXs are accumulated the greater the combiner accident will be. Up to 8:1 combiners are begin in micro and pico beef only.
Frequency bent is generally acclimated to admission all-embracing BTS performance; this involves the accelerated switching of articulation cartage amid TRXs in a sector. A bent arrangement is followed by the TRXs and handsets application the sector. Several bent sequences are available, and the arrangement in use for a accurate corpuscle is always advertisement by that corpuscle so that it is accepted to the handsets.
A TRX transmits and receives according to the GSM standards, which specify eight TDMA timeslots per radio frequency. A TRX may lose some of this accommodation as some advice is appropriate to be advertisement to handsets in the breadth that the BTS serves. This advice allows the handsets to analyze the arrangement and accretion admission to it. This signalling makes use of a approach accepted as the Advertisement Ascendancy Approach (BCCH).
edit Sectorisation
Further information: Breadth antenna
By application directional antennae on a abject station, anniversary pointing in altered directions, it is accessible to sectorise the abject abject so that several altered beef are served from the aforementioned location. Typically these directional antennas accept a beamwidth of 65 to 85 degrees. This increases the cartage accommodation of the abject abject (each abundance can backpack eight articulation channels) whilst not abundantly accretion the arrest acquired to adjoining beef (in any accustomed direction, alone a baby amount of frequencies are getting broadcast). Typically two antennas are acclimated per sector, at agreement of ten or added wavelengths apart. This allows the abettor to affected the furnishings of crumbling due to concrete phenomena such as multipath reception. Some addition of the accustomed arresting as it leaves the antenna is generally acclimated to bottle the antithesis amid uplink and downlink signal.
Base station controller
The abject abject ambassador (BSC) provides, classically, the intelligence abaft the BTSs. Typically a BSC has tens or even hundreds of BTSs beneath its control. The BSC handles allocation of radio channels, receives abstracts from the adaptable phones, and controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case ascendancy is in allotment the albatross of the ballast MSC). A key action of the BSC is to act as a concentrator area abounding altered low accommodation access to BTSs (with almost low utilisation) become bargain to a abate amount of access appear the adaptable switching centermost (MSC) (with a top akin of utilisation). Overall, this agency that networks are generally structured to accept abounding BSCs broadcast into regions abreast their BTSs which are again affiliated to ample centralised MSC sites.
The BSC is assuredly the a lot of able-bodied aspect in the BSS as it is not alone a BTS ambassador but, for some vendors, a abounding switching center, as able-bodied as an SS7 bulge with access to the MSC and confined GPRS abutment bulge (SGSN) (when application GPRS). It aswell provides all the appropriate abstracts to the operation abutment subsystem (OSS) as able-bodied as to the achievement barometer centers.
A BSC is generally based on a broadcast accretion architecture, with back-up activated to analytical anatomic units to ensure availability in the accident of accountability conditions. Back-up generally extends above the BSC accessories itself and is frequently acclimated in the ability food and in the manual accessories accouterment the A-ter interface to PCU.
The databases for all the sites, including advice such as carrier frequencies, abundance bent lists, ability abridgement levels, accepting levels for corpuscle bound calculation, are stored in the BSC. This abstracts is acquired anon from radio planning engineering which involves modelling of the arresting advancement as able-bodied as cartage projections.
edit Transcoder
The transcoder is amenable for transcoding the articulation approach coding amid the coding acclimated in the adaptable network, and the coding acclimated by the world's earthbound circuit-switched network, the Public Switched Telephone Network. Specifically, GSM uses a approved beating excited-long appellation anticipation (RPE-LTP) coder for articulation abstracts amid the adaptable accessory and the BSS, but beating cipher accentuation (A-law or μ-law connected in ITU G.711) upstream of the BSS. RPE-LPC coding after-effects in a abstracts amount for articulation of 13 kbit/s area accepted PCM coding after-effects in 64 kbit/s. Because of this change in abstracts amount for the aforementioned articulation call, the transcoder aswell has a buffering action so that PCM 8-bit words can be recoded to assemble GSM 20 ms cartage blocks.
Although transcoding (compressing/decompressing) functionality is authentic as a abject abject action by the accordant standards, there are several vendors which accept implemented the band-aid alfresco of the BSC. Some vendors accept implemented it in a stand-alone arbor application a proprietary interface. In Siemens' and Nokia's architecture, the transcoder is an identifiable abstracted sub-system which will commonly be co-located with the MSC. In some of Ericsson's systems it is chip to the MSC rather than the BSC. The acumen for these designs is that if the compression of articulation channels is done at the website of the MSC, the amount of anchored manual links amid the BSS and MSC can be reduced, abbreviating arrangement basement costs.
This subsystem is aswell referred to as the transcoder and amount adjustment assemblage (TRAU). Some networks use 32 kbit/s ADPCM on the earthbound ancillary of the arrangement instead of 64 kbit/s PCM and the TRAU converts accordingly. If the cartage is not articulation but abstracts such as fax or email, the TRAU enables its amount adjustment assemblage action to accord affinity amid the BSS and MSC abstracts rates.
The BSC is assuredly the a lot of able-bodied aspect in the BSS as it is not alone a BTS ambassador but, for some vendors, a abounding switching center, as able-bodied as an SS7 bulge with access to the MSC and confined GPRS abutment bulge (SGSN) (when application GPRS). It aswell provides all the appropriate abstracts to the operation abutment subsystem (OSS) as able-bodied as to the achievement barometer centers.
A BSC is generally based on a broadcast accretion architecture, with back-up activated to analytical anatomic units to ensure availability in the accident of accountability conditions. Back-up generally extends above the BSC accessories itself and is frequently acclimated in the ability food and in the manual accessories accouterment the A-ter interface to PCU.
The databases for all the sites, including advice such as carrier frequencies, abundance bent lists, ability abridgement levels, accepting levels for corpuscle bound calculation, are stored in the BSC. This abstracts is acquired anon from radio planning engineering which involves modelling of the arresting advancement as able-bodied as cartage projections.
edit Transcoder
The transcoder is amenable for transcoding the articulation approach coding amid the coding acclimated in the adaptable network, and the coding acclimated by the world's earthbound circuit-switched network, the Public Switched Telephone Network. Specifically, GSM uses a approved beating excited-long appellation anticipation (RPE-LTP) coder for articulation abstracts amid the adaptable accessory and the BSS, but beating cipher accentuation (A-law or μ-law connected in ITU G.711) upstream of the BSS. RPE-LPC coding after-effects in a abstracts amount for articulation of 13 kbit/s area accepted PCM coding after-effects in 64 kbit/s. Because of this change in abstracts amount for the aforementioned articulation call, the transcoder aswell has a buffering action so that PCM 8-bit words can be recoded to assemble GSM 20 ms cartage blocks.
Although transcoding (compressing/decompressing) functionality is authentic as a abject abject action by the accordant standards, there are several vendors which accept implemented the band-aid alfresco of the BSC. Some vendors accept implemented it in a stand-alone arbor application a proprietary interface. In Siemens' and Nokia's architecture, the transcoder is an identifiable abstracted sub-system which will commonly be co-located with the MSC. In some of Ericsson's systems it is chip to the MSC rather than the BSC. The acumen for these designs is that if the compression of articulation channels is done at the website of the MSC, the amount of anchored manual links amid the BSS and MSC can be reduced, abbreviating arrangement basement costs.
This subsystem is aswell referred to as the transcoder and amount adjustment assemblage (TRAU). Some networks use 32 kbit/s ADPCM on the earthbound ancillary of the arrangement instead of 64 kbit/s PCM and the TRAU converts accordingly. If the cartage is not articulation but abstracts such as fax or email, the TRAU enables its amount adjustment assemblage action to accord affinity amid the BSS and MSC abstracts rates.
Packet control unit
The packet ascendancy assemblage (PCU) is a backward accession to the GSM standard. It performs some of the processing tasks of the BSC, but for packet data. The allocation of channels amid articulation and abstracts is controlled by the abject station, but already a approach is allocated to the PCU, the PCU takes abounding ascendancy over that channel.
The PCU can be congenital into the abject station, congenital into the BSC or even, in some proposed architectures, it can be at the SGSN site. In a lot of of the cases, the PCU is a abstracted bulge communicating abundantly with the BSC on the radio ancillary and the SGSN on the Gb side.
The PCU can be congenital into the abject station, congenital into the BSC or even, in some proposed architectures, it can be at the SGSN site. In a lot of of the cases, the PCU is a abstracted bulge communicating abundantly with the BSC on the radio ancillary and the SGSN on the Gb side.
BSS interfaces
Um
The air interface amid the adaptable base (MS) and the BTS. This interface uses LAPDm agreement for signaling, to conduct alarm control, altitude reporting, handover, ability control, authentication, authorization, area amend and so on. Cartage and signaling are beatific in bursts of 0.577 ms at intervals of 4.615 ms, to anatomy abstracts blocks anniversary 20 ms.
Abis
The interface amid the BTS and BSC. Generally agitated by a DS-1, ES-1, or E1 TDM circuit. Uses TDM subchannels for cartage (TCH), LAPD agreement for BTS administration and telecom signaling, and carries synchronization from the BSC to the BTS and MS.
A
The interface amid the BSC and MSC. It is acclimated for accustomed cartage channels and the BSSAP user allotment of the SS7 stack. Although there are usually transcoding units amid BSC and MSC, the signaling advice takes abode amid these two catastrophe credibility and the transcoder assemblage doesn't blow the SS7 information, alone the articulation or CS abstracts are transcoded or amount adapted.
Ater
The interface amid the BSC and transcoder. It is a proprietary interface whose name depends on the bell-ringer (for archetype Ater by Nokia), it carries the A interface advice from the BSC abrogation it untouched.
Gb
Connects the BSS to the SGSN in the GPRS amount network.
The air interface amid the adaptable base (MS) and the BTS. This interface uses LAPDm agreement for signaling, to conduct alarm control, altitude reporting, handover, ability control, authentication, authorization, area amend and so on. Cartage and signaling are beatific in bursts of 0.577 ms at intervals of 4.615 ms, to anatomy abstracts blocks anniversary 20 ms.
Abis
The interface amid the BTS and BSC. Generally agitated by a DS-1, ES-1, or E1 TDM circuit. Uses TDM subchannels for cartage (TCH), LAPD agreement for BTS administration and telecom signaling, and carries synchronization from the BSC to the BTS and MS.
A
The interface amid the BSC and MSC. It is acclimated for accustomed cartage channels and the BSSAP user allotment of the SS7 stack. Although there are usually transcoding units amid BSC and MSC, the signaling advice takes abode amid these two catastrophe credibility and the transcoder assemblage doesn't blow the SS7 information, alone the articulation or CS abstracts are transcoded or amount adapted.
Ater
The interface amid the BSC and transcoder. It is a proprietary interface whose name depends on the bell-ringer (for archetype Ater by Nokia), it carries the A interface advice from the BSC abrogation it untouched.
Gb
Connects the BSS to the SGSN in the GPRS amount network.
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