WO1995008876A1 - Method and apparatus for controlling signal quality in a cdma cellular telecommunications system - Google Patents
Method and apparatus for controlling signal quality in a cdma cellular telecommunications system Download PDFInfo
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- WO1995008876A1 WO1995008876A1 PCT/FI1993/000386 FI9300386W WO9508876A1 WO 1995008876 A1 WO1995008876 A1 WO 1995008876A1 FI 9300386 W FI9300386 W FI 9300386W WO 9508876 A1 WO9508876 A1 WO 9508876A1
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- msc
- cdma
- mobile switching
- signal quality
- switching center
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/06—TPC algorithms
- H04W52/12—Outer and inner loops
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/06—TPC algorithms
- H04W52/08—Closed loop power control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/38—TPC being performed in particular situations
- H04W52/386—TPC being performed in particular situations centralized, e.g. when the radio network controller or equivalent takes part in the power control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/16—Performing reselection for specific purposes
- H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
Definitions
- the present invention relates to cellular telecom ⁇ munications systems. More specifically, the present inven ⁇ tion relates to a system and a method for controlling the radio signal quality between a plurality of mobile stations (MS) communicating via a plurality of base stations (BS) connected to a mobile switching center (MSC) of a code di ⁇ vision multiple access (CDMA) cellular telecommunications system.
- MS mobile stations
- BS base stations
- MSC mobile switching center
- CDMA code di ⁇ vision multiple access
- CDMA code division multiple access
- the base stations convert these CDMA radio signals originating from, respectively terminating at, the mobile station of the user, into a form appropriate for use in conjunction with terrestrial telecommunications transmission equipment such as the commonly deployed Pulse Code Modulation (PCM) circuit facilities.
- the base stations further relay these user signals in the uplink and downlink direction to the mobile switching center (MSC, also referred to as mobile telephone switching office (MTSO) ) for further processing.
- MSC mobile switching center
- MTSO mobile telephone switching office
- the user communication signals mentioned above comp ⁇ rise digitized voice signals and control information (also referred to as signaling) .
- the MSC performs multiplexing and conversion operations on the mentioned tributaries and relays the voice signal to another user, e.g. within a Pub ⁇ lic Switched Telephone Network (PSTN) .
- PSTN Pub ⁇ lic Switched Telephone Network
- the MSC also inter ⁇ prets, reacts upon and generates signalling information, thus controlling the overall communication link between the users.
- These communications link control functions comprise the management of general call related events such as call setup or tear down as well as CDMA radio link related events such as the deterioration of the CDMA radio link quality and subsequent handoff initiation.
- CDMA Code Division Multiple Access
- the average time delay spread of the multipath radio propagation environment is usually larger than the chip duration of the DS-CDMA signal.
- CDMA Code Division Multiple Access
- FDMA frequency division multiple access method
- TDMA time division multiple access method
- intra-cell interference is avoided by the intrinsic properties of the respective mul ⁇ tiple access method and inter-cell interference is limited by means of pre-planned cellular frequency re-use schemes.
- CDMA unlike FDMA or TDMA operates in a strictly in- terference limited manner.
- mobile assisted soft handoff in con ⁇ junction with signal diversity combining comprises the met ⁇ hod of relaying the user communication signals on the transmission segment between MS and MSC concurrently via a first and a second BS in the uplink and downlink direction and performing signal diversity reception at the MS and MSC in order to enhance the user signal quality.
- This method is invoked by the MSC when a MS communicating initially with only a first BS moves into the overlapping coverage areas of this first BS and a second BS and has reported the avai- lability of a sufficiently strong signal from this second BS to the MSC.
- the MS interrupt its communications with the MSC.
- the closed loop power control method has the objec ⁇ tive to keep the received uplink signal-to-interference plus noise ratio (SINR) of all uplink CDMA signals close to a predetermined threshold value, even against the back ⁇ ground of rapidly changing radio propagation channels un ⁇ dergoing fast and slow fading processes.
- the BS estimates periodically the SINR from each MS CDMA uplink communication and subsequently transmits an appro- priate power control command on the downlink communication channel to the MS which in turn sets the CDMA transmitter power accordingly.
- the CDMA uplink signals from all connected MS stations are received at the BS with the same and in addition to that, minimum SINR necessary in order to maintain the communication link subject to the predetermined signal quality threshold without causing ex ⁇ cessive interference to neighboring base stations.
- SINR is intimately related to the quality of the CDMA communications signal as it is a key parameter in determining the bit error rate (BER) of the digital CDMA demodulation process.
- the BER itself, deter ⁇ mines the frame erasure rate (FER) of the digitally vocoded and framed voice signals and thus the quality of the voice signal as perceived by the user.
- FER frame erasure rate
- the intelligent control of the SINR of the individual CDMA communication links is an important tool for the efficient operation of a CDMA cellular telecom ⁇ munications system. If done properly, it allows high capa- city, in particular soft capacity during periods of system overload or unequal load, and user specific signal quality levels.
- the present invention describes a system and a met ⁇ hod with the objective to optimize the capacity of a CDMA cellular telecommunications system by balancing the re ⁇ ceived SINRs in the system area covered by a particular MSC ,
- the present invention relates to CDMA closed loop power control techniques, as substantially described in "On the System Design Aspects of Code Division Multiple c-cess (CDMA) Applied to Digital Cellular and Personal Communica ⁇ tions Networks", Allen Salmasi and Klein S. GiLhousen, pre- sented at the 41st IEEE Vehicular Technology Conference on May 19-22, 1991 in St. Louis, MO.
- CDMA Code Division Multiple c-cess
- the present invention describes a system and a K :- hod to control the SINR thresholds, also referred to as SINR setpoints, by means of signalling between the base stations and the MSC controlling those base stations. More precisely, th ⁇ a inventive system is characterized by that
- each base station is adapted to periodically re ⁇ port for each active CDMA radio communication to the mobi ' e switching center the corresponding measured signal-to-in- terference plus noise ratio (SINR) ;
- the MSC is adapted to perform an averaging process on * he reported SINR values, in order to calculate a recom ⁇ mended SINR setpoint value;
- the base stations are adapted to receive the re- commended SINR setpoint value for use in an uplink closed loop power control algorithm for the mobile stations (HS) , in order to provide a balanced level control of the SINR values in the whole CDMA cellular telecommunications system area controlled by the mobile switching center.
- the MSC performs firstly a time averaging operation on the reported SINR values in order to eliminate variations due to fast fading on the MS uplink. These time averaged SINR values are then averaged over all active CDMA communica- tions within that particular system area controlled by the MSC in order to obtain an optimal SINR setpoint, reflecting the current system load.
- This SINR setpoint value is then signalled back to the involved base stations which will use it as a target value for the uplink, fast closed loop power control on each of the CDMA communication links.
- the scheme described above provides an outer power control loop between a BS and the control ⁇ ling MSC and provides a control apparatus and method for the SINR setpoints, as used by the fast, closed loop power control scheme between MS and BS. It should be understood that this outer power control loop operates at a much lower frequency (e.g. every 20 ms) than the fast power control loop, typically being invoked every 1.25 ms.
- FIG. 1 is a schematic overview of an exemplary CDMA cellular telecommunications system in accordance with the present invention
- FIG. 2 is a block diagram showing a preferred em ⁇ bodiment of a mobile switching center (MSC) for use within a CDMA cellular telecommunications system
- Figure 3 is a block diagram showing a preferred em ⁇ bodiment of a base station (BS) for use within a CDMA eel- lular telecommunications system.
- MSC mobile switching center
- BS base station
- Figure 1 shows an exemplary embodiment of a CDMA cellular telecommunications system to which the present invention relates.
- Two exemplary independent, active user communications are shown in Figure l.
- User mobile stations MS communicate with base stations BS, of which only two are shown, by means of digital CDMA radio links C,, C 2 .
- the base stations convert these CDMA radio signals originating from the user's MS into a form appropriate for the use in con ⁇ junction with terrestrial telecommunications transmission equipment T 1# T 2 , such as the commonly deployed Pulse Code Modulation (PCM) circuit facilities.
- PCM Pulse Code Modulation
- the base stations further relay these user signals in the uplink direction to the mobile switching center MSC for further processing. Similar processing takes place in the downlink direction from the MSC to BS and further to the MS.
- PCM Pulse Code Modulation
- the user communication signals comprise digitized voi ⁇ ce or data and are multiplexed together with the signalling information related to this connection. They are carried in a digital, framed format suitable for the terrestrial transmission lines T v T 2 between the base stations BS and the MSC. These frames are subsequently referred to as transcoder & combiner frames.
- the MSC performs multiplexing and conversion opera ⁇ tions on the transcoder & combiner frames mentioned above, and relays the transcoded voice signal to another user wit ⁇ hin the public switched telephone network (PSTN) via a trunk facility N.
- PSTN public switched telephone network
- the MSC also interprets, reacts upon and generates signalling information, thus controlling the ove ⁇ rall communication link between the system users.
- These communications link control functions comprise the manage ⁇ ment of general call related events, such as call setup or tear down, as well as CDMA radio link related events, such as the deterioration of the CDMA radio link quality and subsequent handoff initiation.
- the transcoder & combiner frames related to an active communication also contain in the uplink direction information supplied by the BSs which is indicative of the uplink CDMA radio signal quality and is used, e.g. for the signal diversity com ⁇ bining within the MSC during a soft handoff with signal diversity combining.
- the uplink SINR as measured by the BS is used as signal quality estimation.
- MSC uses the reported SINR values to estimate the current load in the system and to calculate a SINR setpoint to be used subse- quently by the base stations as a threshold value for the closed loop power algorithm.
- MSC inserts this calculated SINR setpoint in the downlink stream of the transcoder & combiner frames passing along digital links T.,, T 2 .
- signal quality indicators such as BER (Bit Error Rate) or pseudo BER es ⁇ timates as defined in the frame decoding phase, could also be used as a signal quality measure, without changing the generic principles of the present invention.
- FIG. 2 shows an exemplary embodiment of a MSC used in a CDMA cellular telecommunications system to which the present invention relates.
- Digital links 1,2,3 and 4 connect the MSC with the PSTN, other mobile switching centers and base stations, respectively. These digital links carry the user informati ⁇ on such as voice and, additionally, signalling information.
- the preferred embodiment of the present invention assumes that the signalling information is of packetized type and is multiplexed together with the user information onto one and the same physical transmission facility.
- Tl transmissi ⁇ on facilities together with Signalling System No 7 may ser ⁇ ve as an exemplary embodiment of such a digital link arran- 5 ge ent.
- the user information stream is switched among the mentioned entities by means of a digital switch 5.
- the cor ⁇ responding signalling information is transmitted, received and relayed by a packet switch 6.
- Packet switch 6 is also
- MSC control processor 7 which acts as a sig ⁇ nalling information source and sink, respectively.
- the MSC control processor 7 interprets and reacts upon signalling messages addressed to it and may also solicit signalling messages to other entities whenever appropriate.
- control processor 7 also controls the connection arrange ⁇ ments within the digital switch 5 in accordance with the call status. Moreover, the MSC control processor 7 alloca ⁇ tes and releases transcoder & combiner equipment 8 during call setup and tear down from a corresponding resource pool
- Transcoder & combiner equipment 8 is needed in order to convert between the typically ⁇ -law encoded voice as used in the PSTN and the low rate digital voice coding such as CELP used on the radio links. In addition to the trans ⁇ coding function, transcoder & combiner equipment 8 also
- transcoder & combiner equipment 8 participates in the outer power control loop to which the
- the transcoder & combiner frames arriving and lea- ving on the circuits 9, 10, 11 are buffered in the digital memory 12 for the uplink and downlink direction, respecti ⁇ vely.
- Digital processor 13 reads and writes cyclically the transcoder & combiner frames from and to digital memory 12.
- the SINR used as signal quality indication and attached to the corresponding transcoder & combiner frames arriving from the base stations via cir ⁇ cuits 9, 10 into the memory 12 is inspected and processor 13 performs the diversity selection based on these indica- tions during soft handoff.
- the selected frames are then transcoded and passed on towards the PSTN via circuit 11.
- voice samples arriving from the PSTN via circuit 11 into the memory 12 are transcoded and packed into transcoder & combiner frames by processor 13 and passed on towards the base stations via circuits 9 and/or 10.
- Digital processor 13 also extracts, respectively in ⁇ serts, the reported SINR values, respectively calculated SINR setpoint values from, respectively into, the transco- der & combiner frames. To this end, processor 13 com ⁇ municates via circuit 14 with MSC control processor 7.
- MSC control processor 7 receives the reported SINR values from all active transcoder & combiner units (i.e. from all active communications within the MSCs system area) and can further process them.
- MSC control processor 7 performs firstly a time averaging operation on the reported SINR values in order to eliminate variations due to fast fading on the MS uplink. These time averaged SINR values are then averaged over all active communications in order to obtain an optimal SINR setpoint, reflecting the current system load. This SINR setpoint value is then signalled back to digital processors 13 which, in turn will provide this va ⁇ lue to the BSs via the downlink transcoder & combiner fra- es.
- digital pro ⁇ cessor 13 could perform the SINR time averaging and send the averaged values to MSC control processor 7 for further processing.
- MSC control processor 7 could perform the SINR time averaging and send the averaged values to MSC control processor 7 for further processing.
- the transcoder & combiner equipment 8 by means of the digital processor 13 also extracts, respectively in- serts, the user signalling information from, respectively into, the transcoder & combiner frames and offers, respec ⁇ tively receives, this signalling information to MSC control processor 7 via a circuit 14.
- MSC control processor 7 receives MS signalling information such as pi- lot signal quality measurement reports.
- MSC control processor 7 possesses the necessary informarion to initiate and terminate handoffs.
- MSC control processor 7 can issue the appropriate handoff com ⁇ mands to the MS via circuits 14, 9, 10 and links 3 and 4 as well as via the digital packet switch 6 and link 2 to other mobile switching centers, should this be required.
- Figure 3 shows an exemplary embodiment of a base station used in a CDMA cellular telecommunications system to which the present invention relates.
- Block 15 shows the apparatus required to support a single CDMA communication within a base station, referred to as CDMA channel equip ⁇ ment (only one is shown) .
- the CDMA user communication signals are received from the digital CDMA radio link 16, despread and demodulated by the CDMA demodulator 17, de-in ⁇ terleaved and channel decoded by the de-interleaver & deco ⁇ der 18, converted into transcoder & combiner frames and buffered for the terrestrial transmission within digital memory l c and finally transmitted on the digital link 20 towards ,. ⁇ e MSC.
- the transcoder & combiner frames are received from the MSC via digital link 20, buf ⁇ fered and converted into a presentation appropriate for the base station within digital memory 19, channel encoded and interleaved by encoder & interleaver 21, CDMA modulated and spread by the CDMA modulator 22 and finally transmitted on the digital radio link 16.
- the uplink CDMA closed loop power control algorithm is implemented within the CDMA channel equipment of the BS by means of the SINR estimator & comparator 23, the CDMA modulator 22 and the digital processor 24.
- the SINR estimator & comparator 23 receives the di ⁇ gital CDMA baseband signal from the CDMA demodulator 17 via circuit 25. SINR estimator & comparator 23 estimates the instantaneous SINR of the user signal on a symbol-by-symbol basis and time averages over the duration of a few symbols to obtain a local mean SINR estimate. SINR estimator & com ⁇ parator 23 is provided with a target SINR setpoint from digital processor 24. SINR estimator & comparator 23 compa ⁇ res the local mean SINR value with this target SINR set- point and depending on the comparison result instructs the CDMA modulator 22 via circuit 26 to issue the appropriate power control command towards the MS.
- the CDMA baseband signal is convolu- tionally encoded by the MS on a frame-by-frame basis and that channel decoder unit of deinterleaver & decoder 18 uses a soft decision Viterbi decoding technique to decode the individual frames.
- deinterleaver & decoder 18 may generate on a frame-by-frame basis a signal which is indi- cative of the frame SINR after channel decoding. It should be understood that this frame SINR value may be different from the previously mentioned local mean SINR estimate.
- This frame SINR indicative of the signal quality of an in ⁇ dividual CDMA user information frame, as received by the BS, is multiplexed together with the user information and passed on to digital memory 19.
- Digital processor 24 in conjunction with the buffer memory 19 performs generally the packing and unpacking of the BS internal representation of the CDMA user communica ⁇ tions signal to and from transcoder & combiner frames in the uplink, respectively downlink direction.
- digital processor 24 also multiplexes the previously mentioned frame SINR value together with the user communications signal onto transcoder & combiner fra ⁇ mes in the uplink direction towards the MSC.
- digital processor 24 in conjunction with the buffer memory 19 extracts the SINR setpoint defined by the MSC.
- Digital processor 24 processes this SINR setpoint, computes an appropriate target SINR threshold appropriate to the SINR estimator & comparator 23, and provides this value to the SINR estimator & comparator 23 via circuit 27 for use in the CDMA closed loop power control algorithm.
- signal quality indicators such as BER (Bit Error Rate) or pseudo BER estimates as defined in the frame decoding phase, could also be used as a signal quality measure, without changing the generic principles of the present invention.
- the base station further comprises a control proces ⁇ sor 28.
- the BS control processor 28 receives and transmits signalling information from and to digital link 20 connec- ted to the MSC.
- the base station control processor 28 per ⁇ forms the resource management of the BS, such as the allo ⁇ cation and release of CDMA channel equipment for user con ⁇ nections (calls) .
- the BS control processor 28 thus responds to CDMA channel assignment requests related to a call setup as well as to CDMA channel assignment requests related to soft handover requests from the MSC.
Abstract
Description
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Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/FI1993/000386 WO1995008876A1 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a cdma cellular telecommunications system |
EP93920867A EP0671083B1 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a cdma cellular telecommunications system |
JP52038094A JP3291731B2 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a CDMA cellular communication system |
US08/307,689 US5623484A (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a CDMA cellular telecommunications |
DE69307343T DE69307343T2 (en) | 1993-09-24 | 1993-09-24 | METHOD AND DEVICE FOR CONTROLLING SIGNAL QUALITY IN A CDMA CELLULAR COMMUNICATION SYSTEM |
AU48212/93A AU683422B2 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a CDMA cellular telecommunications system |
FI952518A FI112302B (en) | 1993-09-24 | 1995-05-23 | Signal quality control for CDMA communications |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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PCT/FI1993/000386 WO1995008876A1 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a cdma cellular telecommunications system |
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WO1995008876A1 true WO1995008876A1 (en) | 1995-03-30 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/FI1993/000386 WO1995008876A1 (en) | 1993-09-24 | 1993-09-24 | Method and apparatus for controlling signal quality in a cdma cellular telecommunications system |
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US (1) | US5623484A (en) |
EP (1) | EP0671083B1 (en) |
JP (1) | JP3291731B2 (en) |
AU (1) | AU683422B2 (en) |
DE (1) | DE69307343T2 (en) |
FI (1) | FI112302B (en) |
WO (1) | WO1995008876A1 (en) |
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Also Published As
Publication number | Publication date |
---|---|
DE69307343T2 (en) | 1997-04-24 |
JPH08503829A (en) | 1996-04-23 |
FI112302B (en) | 2003-11-14 |
FI952518A0 (en) | 1995-05-23 |
EP0671083A1 (en) | 1995-09-13 |
US5623484A (en) | 1997-04-22 |
EP0671083B1 (en) | 1997-01-08 |
AU4821293A (en) | 1995-04-10 |
AU683422B2 (en) | 1997-11-13 |
FI952518A (en) | 1995-05-23 |
DE69307343D1 (en) | 1997-02-20 |
JP3291731B2 (en) | 2002-06-10 |
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