CA2060428A1 - Method of accessing a mobile radio land system from one of a number mobile stations - Google Patents
Method of accessing a mobile radio land system from one of a number mobile stationsInfo
- Publication number
- CA2060428A1 CA2060428A1 CA002060428A CA2060428A CA2060428A1 CA 2060428 A1 CA2060428 A1 CA 2060428A1 CA 002060428 A CA002060428 A CA 002060428A CA 2060428 A CA2060428 A CA 2060428A CA 2060428 A1 CA2060428 A1 CA 2060428A1
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- Prior art keywords
- base station
- mobile station
- mobile
- time slot
- reserved
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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- 101100194362 Schizosaccharomyces pombe (strain 972 / ATCC 24843) res1 gene Proteins 0.000 claims description 5
- 238000004891 communication Methods 0.000 abstract description 6
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0866—Non-scheduled access, e.g. ALOHA using a dedicated channel for access
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
ABSTRACT
A method of accessing a base station from a mobile station in a mobile radio system, in which the mobile station communicates with the base station in one or more time slots included in a frame according to the TDMA-principle. In one time slot, there are reserved fields for control information (SACCH, DVCC) which, however, are not used in the uplink and the downlink communi-cation if the time slot represents a digital control channel.
According to the invention, these fields are used by a mobile station (MS1) to transmit control information (R) to the base station (B1) which indicates the time slot order number and how many such time slots which are to be reserved by the base station in order that the mobile station should be able to complete its access message. The method is described both for the full rate mode and for the half rate mode.
A method of accessing a base station from a mobile station in a mobile radio system, in which the mobile station communicates with the base station in one or more time slots included in a frame according to the TDMA-principle. In one time slot, there are reserved fields for control information (SACCH, DVCC) which, however, are not used in the uplink and the downlink communi-cation if the time slot represents a digital control channel.
According to the invention, these fields are used by a mobile station (MS1) to transmit control information (R) to the base station (B1) which indicates the time slot order number and how many such time slots which are to be reserved by the base station in order that the mobile station should be able to complete its access message. The method is described both for the full rate mode and for the half rate mode.
Description
2~428 FIELD OF THE INVl~Nl'ION
The present invention is directed to a mobile cellular radio telephone system having digital voice/traffic capacity wherein digital control channels may occupy the same radio channel time slots as voice/traffic channelsn More specifically, the present invention relates to a method and system for performing the access function on a digital control channel.
~ACKGROUND OF ~E INVEN~ION
The first cellular mobile radio systems in public use were generally analog systems for the transmission o~ speech or other analog information. The systems comprised a plurality of radio channels for transmitting analog information between base and mobile stations by transmitting analog modulated radio signals.
In general, the first cellular mobile radio systems had compa-rably large coverage cells. More recently, digital cellularmobile radio systems for public use have been designed.
Digital cellular mobile radio systems comprise digital channels for transmitting digital or digitzed analog information between base and mobile skations, by transmitting digitally modulated radio signals. Digital cellular mobile radio systems o~er substantial advantages over analog cellular mobile radio systems.
One digital mobile radio system intended to be used as a common system for many huropean countries is the GSM systemO In European countries already having an analog cellular mobila system, the new digital GSM system is intended to be introduced as a new system which is independent of any existing analog system. The GSM system base and mobile stations have not been designed to be compatible with existing systems, however, they are designed to yive optimum performances in various aspects in and of the system itsel~D Accordingly,-there has been a comparatively great freedom of choice in technical matters when designing the GSM system.
Rather than introduce a new independent digital cellular mobile radio system, like the GSM system, in an area with an existing analog cellular system, it has been proposed to introduce a digital cellular mobile radio system which is designed for cooperation with the existing analog cellular ~obile radio system. In order to obtain digital channels within the frequency band allotted to cellular mobile radio systems, there ha~e been proposals to withdraw a number of radio channels allotted to the present analog mobile radio systems and use them in the digital lo cellular mobile radio system. Due to the proposed design of the digital mobile radio system, three or possibly six digital channels may occupy the same frequency band of one previous analog radio channel by using time division multiplexing.
Accordingly, replacing some analog channels by digital channels in time division multiplex may increase the total number of channels.
The intended result is to gradually introduce the digital system and to increase the number of digital traffic channels while decreasing the number of analog traffic channels in the coexis-ting cellular systems. Analog mobile stations already in use willthen be able to continue to use the remaining analog traffic channels. Meanwhile, new digital mobile stations will be able to use the new digital traffic channels. Dual-mode mobile stations will be able to use both the remaining analog and the new digital traffic channels.
With the addition of the new diyital traffic channels, a corre-sponding need ~or new digital control channels arises. The conventional dual-mode systems for the most part utilize existing analog channels, such as dedicated frequencies, as the control channel.
However the new fully digital systems will use digital control channels which occupy TDMA time slots of the same type as used for digital traffic channels.
2 ~ 2 ~
Such digital control channels have earlier been used in the European GSM system. In GSM an access is always performed by a single burst in order to minimize occupancy of the channel dedicated for accesses. Any subse~uent actions like authentica-tion and ciphering is performed on another type of controlchannel assigned after the actual access. This use in GSM of several types of control channels implies considerable complexi-ty. For this reason and for better compatibility with the existing North-American dual mode system it is preferred to use lo only one type of uplink control channel for the fully digital system in the USA. A consequence of this decision is that the control channel used for access in the USA must be able to handle even other functions than access such as authentication or ciphering which require more than one burst in a message. The present invention solves the special problems associated with the use of multi-burst access messages.
BUMMARY OF T~E INYENTION
It is an object of the present invention to provide a procedure usable by a mobile station to access the land system via a digital control channel, taking into consideration that existing EIA/TIA-54 formats for digital traffic channels shall be used with minimum modification for the digital control channel in order to achieve low hardware complexity in the mobile station.
This is accomplished by using the same format ~or both the traffic channels and the control channels except that the CDVCC
and SACCH fields of the traffic channel are used on the control channel to perform the function of structuring the access to the land system from a mobile.
It is a further object of the invention to minimize the pro-bability of collision between access messages by providing a reservation procedure for any bursts following the first burst in an access message. This is accomplished by including in the uplink access bursts an information saying whether another time slot is to be reserved at a predefined time in order to continue 2~6~428 the access message or whether this burst was the last in the message.
It is a further object of the invention to allow multi-burst accesses while rninimizing the access time for one-burst accesses.
5 Thi5 is achieved by having the mobile include in its first access burst whether this is the last burst or whether more bursts are to follow. In the latter case a burst after a predetermined interval is reserved, but several bursts in between are le~t free for any other mobile stations wanting to access the land system.
It is a further object of the invsntion to provide an access procedure which makes it possible to use a full rate or a half rate channel as an access channel for a base station depending on the traffic capacity needed on the control channel. This is accomplished by reserving uplink time slots for multi-burst access messages at intervals greater than one frame. Thereby the capacity (accesses per second) of a full rate access channel is twice the capacity of a half rate channel whereas the time required for an access message does not depend on whether the access channel is full or hal~ rate.
~0 It is a further object of the invention to p~ovid~ an access method with a low probability of causing multiple accesses, i.e.
an access method not making more than one base stakion believe that it has been accessed. This is achieved by using the digital verification color code DVCC when coding/decoding the cyclic redundancy check CRC the same way as for the traffic channels. In other words, this "implicite" DVCC is still used where as the "explicite" DVCC (the CDVCC field in the message) is used for the access procedure.
The two said fields CDVCC and SACCH have 12 bits each, together 24 bits uplink and 24 bits are used on the digital access channel to carry one out o two possible pattern~ uplink and one out of two possible patterns downlink. Thereby two things are accomp-lished: firstly, synchronization is improved uplink (essential for one burst messages) and distinction of a control channel from 2 0 ~ 8 a traf~ic channel i5 fasilitated downlink by usiny in addltlon to the standardized 28-bit sync word also the two possible 24-bit patterns in the CDVCC-SACCH fields as sync words (the other (2**24)-2 patterns are illegal~; secondly, transmitting downlink the messages "fr~e" or "reserved" and uplink the messages "reserve" or "do not reserve" as one out of said two possible 24-hit patterns virtually excludes misinterpretation.
BRIEF DE~;CRIPTION OF THE DRAWING~
Fig.l illustrates a part of a cellular mobile radio system with cells, a mobile switching center, base stations and mobile stations;
Fig.2 illustr2tes a block diagram of a mobile station utilized in accordance with the present invention;
Fig.3 illustrates a block diagram of a base station utilized in accordance with the present invention;
Fig.4A illustrates the frame structure of a radio channel as utilized in accordance with the present lnvention;
Fig.4B illustrates a time slot format for transmissions from a mobile station to a base or land station;
Fig.4C illustrates a time slot format for transmissions from a mobile station to a base or land station with a reservation field according to the present invention;
Fig.4D illustrates a time slot format for transmissions from a base or land station to a mobile station;
Fig.4E illustrates a time slot fo~mat for transmission~ from a base or land station to a mobile station with twa reservation ~`ields according to the presenk invention;
Fig.5 illustrates an example of a radio channel fra~e having six time slots in which control channels and traffic channels are mixed;
Fig.6A is a diagram illustrating the multiburst access method according to the present invention for the full rate mode;
Fig.6B is a similar diagram for the half rate mode;
Fig.7 is a flow chart describing the access method of the present invention.
2~g~
DETAIhE~ DE~CRIPTIOM OF ~ U~TR~T~ EMBODIM~NT~
Fig.1 illustrates ten cells C1 to C10 in a c~llular mobile rad10 system. In actual practice, the method and means according to the present invention are implemented in a cellular mobile radio system comprising many mDre cells than ten. However, for the purpose of explaining the present invention, ten cells is deemed to be sufficient.
For each of the cells Cl through C10 there is a base station B1 through B10, respectively, with the same number as the cell.
lo Fig.l illustrates base stations situated in the vicinity of the center of the cell and having omni-directional antennas. The base stations of adjacent cells may, however, be allocated in the vicinity of cell borders and have directional antennas as is well known to those of ordinary skill in the art.
Fig.l also illustrates ten mobile stations M1 through M10 which are movable within a cell and from one cell to another cell. In actual practice, the method and means according to the present invention are implemented in a cellular mobile radio system comprising many more mobile stations than ten. In particular, thexe are usually many more mobile stations than there are base stations. However, for the purpose of explaining the pre5ent invention, the use of ten mobile stations is deemed to be sufficient. The system of Fig.l also includes a mobile switching center MSC. The mobile switching center is connected to all ten 2s illustrated base stations by cables. The mobile switching center is also connected, by cables, to a fixed public switching telephone network ox similar fixed network with ISDN facilities.
All cabl~s from the mobile switching center to the base stations and cables to the fixed network are not illustrated.
In addition to the mobile switching center illustrated, there may also be another mobile switching center connected by cables to other base stations than those illustrated in Fig.l. Instead of cables, other means may be utilized for base to mobile station switching center communication, e.g. ~ixed radio links.
7 ~ 2 ~
The cellular mobile radio system illustraked in Fig.1 comprises a plurality of radio channels ~or communication. The system is designed both for analog inEormation, e.g. speech, digitized analog information, digitized speech, and pure digital information. According to the system, the term connection is used for a communication channel mobile station in the same system or another system, or a fixed telephsne or terminal in a fixed network connected to the cellular mobile radio system. Thus, a connection may be defined as a call where two persons are able to talX to each other, but also may refer to a data communication channel where computers are exchanging data.
Referring now to Fig.2, an embodiment of a mobile station that can be utilized in a cellular telephone system that operates in accordance with the present invention is illustrated. A speech coder 101 converts the analog signal generated by a microphone into a bit data stream. The bit data stream is then divided into data packages, according to the TDMA principle. A fast associated control channel (FACCH) generator 102 generates control and supervision signalling messages between the system and the mobile station and messages between the mobile station and the system.
The FACCH message replaces a user frame (speech/data) whenever it is to be transmitted. A slow associated control channel (SACCH~
generator 103 provides a continuous channel for the exchange of signalling messages between the base station and the mobile station and vice-versa. A fixed number of bits, e.~. twelvel is allocateA to the SACCH for each time slot of the m~ssage train.
Channelcoders 104 are respectively connected to the speech coder 101, FACCH generator 102, and SACCH generakor 103 for manipula-ting the incoming data in order to carry out error detection and correction. The techniques used by the channel coders 104 are convolutional encoding, which protects important data bits in the speech code, and cyclic redundancy check (CRC), wherein the perceptually significant bits in the speech coder frame, e.g.
twelve bits, are used for computing a seven bit check.
A selector 105 is connected to the channel coders 104 associated with the speech coder 101 and the FACCH generator 102, respec-8 206~8 tively. The selector 105 is controlled by the microprocessor con~roller 130 so that at appropriate times user in~ormation over a particular speech channel is replaced with system supervision messages over FACCH. A two-bursk interleaver 106 is coupled to the output of the selector 105. Data to be transmitted by the mobile station is interleaved over two distinct time slots. The 260 data bits, which constitute one transmitting word, are divided into two equal parts and are allotted two consecutive time slots. The effects of RAYLEIGH fading will be reduced in lo this manner. The output o~ the two-burst interleaver 106 is provided to the input of a modulo-two-adder 107 so that the transmitted data is ciphered bit by bit by logical modulo-two-addition of a pseudo-random bit stream.
The output of the channel code 104 associated with the SACCH
generator 103 is connected to a 22-burst interleaver 108. The 22-burst interleaver 108 interleaves data transmitted over SACCH
over 22 time slots each consisting of 12 bits of information. The 22-burst interleaver 108 utilizes the diagonal principle so that as two SACCH messages are transmitted in parallel, the second message is displaced eleven bursts from the other message.
The mobile station further includes a Sync Word ~ DVCC generator 109 for providing the appropriate synchronization word (Sync Word) and DVCC which are to be associated with a particular connection. The Sync Word is a 28 bit word used for time slot ~5 synchronization and identification. ~he DVCC ~digital verifica-tion color code) i8 an 8-blt code which is sent by the base station to the mobilestation and vice-versa, for assuring that the proper channel is being decoded.
A ~urst generator 110 generates message bursts for transmission by the mobile station. The burst generator llO is connected to the outputs of the modulo-two~adder 107, the 22-burst interleaver 108, the Sync Word/DVCC generator 109, an e~lalizer 114, and a control channel message generator 132 generating channel coded control messages. A message burst comprising data (260 bits)/
SACCH (12 bits), Sync Word (28 bits), coded DVCC (12 bits), and %0~2~
12 delimiter bits, combined for a total of 324 hits are in-tegrated according to the time slot format specified by the standard EIA/TIA IS~54.
Under the control of the microprocessor 130, two different types of message bursts are generated by the bur~t generakor 110:
control channel message bursts from the control channel message generator 132 and voice/traffic message bursts. The control channel message is generated in accordance with commands from the miroprocessor 130 and is sent on a digital control channel ha~ing the same burst formats as kraffic channels but where the SACCH as well as the speech data normally genera~ed in a voice/traffic burst aEe replaced by control information.
The transmitting of a burst, which is equivalent to one time slot, is synchronized with the transmitting of the other two time slots, and is adjusted according to the timing provided by the equalizer 114. Due to time dispersion, an adaptive equalization method is provided in order to improve signal quality. For further information regarding adaptive equalization techniques, reference should be made to U.S.Patent Application Serial No. 315,561, filed February 27, 1989, and assigned to the same assignee. A correlator adjusts to the timing of the received bit stream. The base station is the master and the mobile station is the slave with respect to frame timiny. The e~ualiz~r ll~ detec~s the incoming timing and synchronizes the burst generator 110. The Z5 equalizer 114 is also operable ~or checking the Sync Word and DVCC ~or identi~ication purposes.
A 20ms frame counter 111 is coupled to the burst generator 110 and so is the equalizer 114. The frame counter 111 updates a ciphering code utilized by the mobile station every 20ms, once for every transmitted frame. It will be appreciated that according to this particular example, three time slots make up one frame. A ciphering unit 112 is provided for generating the ciphering code utilized by the mobile station. A pseudo random algorithm is pre~erably utilized. The ciphering unit 112 is controlled by a key 113 which is unique for each subscriber. The 1~ 2 ~ 2 ~
ciphering unit 112 consists of a sequencer which updates the ciphering code.
The burst produced by burst generator 110, which is to be transmitted, is forwarded to an RF modulator 122. The RF
modulator 122 is operable for modulating a carrier frequency according to the ~/4-DQPSK metod (~/4 shifted, Differentially encoded Quadrature Phase Shift Ksying). The use of this technique implies that the information is differentially encoded, i.e.
2 bit symbols are transmitted as four possible changes in phase;
~ ~/4 and ~ 3~/4. The transmitter carrier frequency supplied to the RF modulator 122 is generated by a transmitting fre~uency synthesizer 124 in accordance with the selected transmitting channel. Before the modulated carier i5 transmitted by an antenna, the carrier is amplified by a power amplifier 123. The RF power emission level of the carrier frequency is selected on command by a microprocessor controller 130. The amplified signal is passed-through a time switch 134 before ît reaches the antenna. The timing is synchronized to the transmitting requence by the microprocessor controller 130. The amplified signal i5 passed to a time switch 134 before it reaches the antenna. The time switch is synchronized to the transmitting sequence by the microprocessor controller 130.
A receiver carrier ~requency is generated in accordance with the selected receiving channel by receiving frequency synthesizer 125. Incoming radlo ~requency signal~ are received by receiver 126, the strength of which are measured hy signal level meter 129. The received signal strength value is then sent to the microprocessor controller 130. An RF demodulator 127 which receives the receiver carrier frequ~ncy from the receiving frequency signal from receiver 126, demodulates the radio fr~quency carrier signal, thus generating an intermediate frequency. The intermediate frequency signal is then demodulated by an IF demodulator 128, which restores the original ~/4-DQPSK -modulated digital information.
~1 20~
The restored digital information provided by IF demodulator 128 is supplied to the equalizer 114. A symbol detector 115 converts the received two bit symbo] format of the digital data from the equalizer 114 to a single bit data stre.am. The symbol detector 115 in turn produces three distinct outputs. Control channel messages are sent to a control message detector 133 which supplies channel decoded and detected control channel information to the microprocessor controller 130. Any speech data/FACCH data is supplied to a modulo-two-adder 107 and a two-burst deinter-leaver 116. The speech data/FACCH data is reconstructed by thesecomponents by assembling and rearranging information from two consecutive frames of the received data. The symbol detector 115 supplies 5ACCH data to a 22-burst deinterleaver 117. The 22-burst deinterleaver 117 reassembles and rearranges the SACCH data, which is spread over 22 consecutive frames.
The two-burst deinterleaver 116 provides the speech data/FACCH
data to two channel decoders 118. The convolutionally encoded data is decoded using the reverse of the above-mentioned coding principle. The rec~ived cyclic redundancy check (CRC) bits are checked to determine if any error has occurred. The FACC~I channel coder furthermore detects the distinction between the speech channel and any FACCH information, and directs the decodes accordingly. A speech decoder 119 processes the received speech data from the channel decoder 118 in accordance with a speech decoder algorithm (VSELP), and generates the received speech signal. The analoy siynal is finally enhanced by a filtering techni~ue. Messages on the ~ast associated control channel are detected by FACCH detector 120, and the information is trans-ferred to the microprocessor controller 130.
The output of the 22-burst deinterleaver 117 is provided to a separate channel decoder 118. Message~ on the slow associated control channel are detected by SACCH detector 121, and that information is transferred to the microprocessor controller 1300 The mi~roprocessor controller 130 controls the mobile station activity and the base station communication, and also handles the 12 2060~
terminal keyboard input and display output 131. Decisions by the microprocessor controller 130 are made in accordance with received messages and measurements made. The keyboard and display unit 131 enable an information exchange between the user and ths base station.
Fig.3 illustrates an embodiment of a base station that can be utili~ed in a cellular telephone system that operates in accordance with the present invention. The base station incorporates numerous component parts which are substatially identical in construction and ~unction to component parts of the mobile station illustrated in Fig.2 and described in conjunction therewith. Such identical component parts are designated in Fig.3 with the same reference numerals utilized hereinabove in the description o~ the mobile station, but are differentiated there~rom by means of a prime (') designation.
There are, however, minor distinctions between the mobile and base stations. For instance, the base station has two receiving antennas. Associated with each of these receiving antennas are a receiver 126', an RF dem~dulator 127', and an IF demodulator 128'. Furthermore, the base station does not include a user keyboard and display unit 131 a5 utilized in the mobile station.
Another differance is that a base station handles the commuJl.ica-tion of many mobiles, which can be seen from ths ramification into 3 channel handlers 1, ~, 3, each of which handles one out o~
The present invention is directed to a mobile cellular radio telephone system having digital voice/traffic capacity wherein digital control channels may occupy the same radio channel time slots as voice/traffic channelsn More specifically, the present invention relates to a method and system for performing the access function on a digital control channel.
~ACKGROUND OF ~E INVEN~ION
The first cellular mobile radio systems in public use were generally analog systems for the transmission o~ speech or other analog information. The systems comprised a plurality of radio channels for transmitting analog information between base and mobile stations by transmitting analog modulated radio signals.
In general, the first cellular mobile radio systems had compa-rably large coverage cells. More recently, digital cellularmobile radio systems for public use have been designed.
Digital cellular mobile radio systems comprise digital channels for transmitting digital or digitzed analog information between base and mobile skations, by transmitting digitally modulated radio signals. Digital cellular mobile radio systems o~er substantial advantages over analog cellular mobile radio systems.
One digital mobile radio system intended to be used as a common system for many huropean countries is the GSM systemO In European countries already having an analog cellular mobila system, the new digital GSM system is intended to be introduced as a new system which is independent of any existing analog system. The GSM system base and mobile stations have not been designed to be compatible with existing systems, however, they are designed to yive optimum performances in various aspects in and of the system itsel~D Accordingly,-there has been a comparatively great freedom of choice in technical matters when designing the GSM system.
Rather than introduce a new independent digital cellular mobile radio system, like the GSM system, in an area with an existing analog cellular system, it has been proposed to introduce a digital cellular mobile radio system which is designed for cooperation with the existing analog cellular ~obile radio system. In order to obtain digital channels within the frequency band allotted to cellular mobile radio systems, there ha~e been proposals to withdraw a number of radio channels allotted to the present analog mobile radio systems and use them in the digital lo cellular mobile radio system. Due to the proposed design of the digital mobile radio system, three or possibly six digital channels may occupy the same frequency band of one previous analog radio channel by using time division multiplexing.
Accordingly, replacing some analog channels by digital channels in time division multiplex may increase the total number of channels.
The intended result is to gradually introduce the digital system and to increase the number of digital traffic channels while decreasing the number of analog traffic channels in the coexis-ting cellular systems. Analog mobile stations already in use willthen be able to continue to use the remaining analog traffic channels. Meanwhile, new digital mobile stations will be able to use the new digital traffic channels. Dual-mode mobile stations will be able to use both the remaining analog and the new digital traffic channels.
With the addition of the new diyital traffic channels, a corre-sponding need ~or new digital control channels arises. The conventional dual-mode systems for the most part utilize existing analog channels, such as dedicated frequencies, as the control channel.
However the new fully digital systems will use digital control channels which occupy TDMA time slots of the same type as used for digital traffic channels.
2 ~ 2 ~
Such digital control channels have earlier been used in the European GSM system. In GSM an access is always performed by a single burst in order to minimize occupancy of the channel dedicated for accesses. Any subse~uent actions like authentica-tion and ciphering is performed on another type of controlchannel assigned after the actual access. This use in GSM of several types of control channels implies considerable complexi-ty. For this reason and for better compatibility with the existing North-American dual mode system it is preferred to use lo only one type of uplink control channel for the fully digital system in the USA. A consequence of this decision is that the control channel used for access in the USA must be able to handle even other functions than access such as authentication or ciphering which require more than one burst in a message. The present invention solves the special problems associated with the use of multi-burst access messages.
BUMMARY OF T~E INYENTION
It is an object of the present invention to provide a procedure usable by a mobile station to access the land system via a digital control channel, taking into consideration that existing EIA/TIA-54 formats for digital traffic channels shall be used with minimum modification for the digital control channel in order to achieve low hardware complexity in the mobile station.
This is accomplished by using the same format ~or both the traffic channels and the control channels except that the CDVCC
and SACCH fields of the traffic channel are used on the control channel to perform the function of structuring the access to the land system from a mobile.
It is a further object of the invention to minimize the pro-bability of collision between access messages by providing a reservation procedure for any bursts following the first burst in an access message. This is accomplished by including in the uplink access bursts an information saying whether another time slot is to be reserved at a predefined time in order to continue 2~6~428 the access message or whether this burst was the last in the message.
It is a further object of the invention to allow multi-burst accesses while rninimizing the access time for one-burst accesses.
5 Thi5 is achieved by having the mobile include in its first access burst whether this is the last burst or whether more bursts are to follow. In the latter case a burst after a predetermined interval is reserved, but several bursts in between are le~t free for any other mobile stations wanting to access the land system.
It is a further object of the invsntion to provide an access procedure which makes it possible to use a full rate or a half rate channel as an access channel for a base station depending on the traffic capacity needed on the control channel. This is accomplished by reserving uplink time slots for multi-burst access messages at intervals greater than one frame. Thereby the capacity (accesses per second) of a full rate access channel is twice the capacity of a half rate channel whereas the time required for an access message does not depend on whether the access channel is full or hal~ rate.
~0 It is a further object of the invention to p~ovid~ an access method with a low probability of causing multiple accesses, i.e.
an access method not making more than one base stakion believe that it has been accessed. This is achieved by using the digital verification color code DVCC when coding/decoding the cyclic redundancy check CRC the same way as for the traffic channels. In other words, this "implicite" DVCC is still used where as the "explicite" DVCC (the CDVCC field in the message) is used for the access procedure.
The two said fields CDVCC and SACCH have 12 bits each, together 24 bits uplink and 24 bits are used on the digital access channel to carry one out o two possible pattern~ uplink and one out of two possible patterns downlink. Thereby two things are accomp-lished: firstly, synchronization is improved uplink (essential for one burst messages) and distinction of a control channel from 2 0 ~ 8 a traf~ic channel i5 fasilitated downlink by usiny in addltlon to the standardized 28-bit sync word also the two possible 24-bit patterns in the CDVCC-SACCH fields as sync words (the other (2**24)-2 patterns are illegal~; secondly, transmitting downlink the messages "fr~e" or "reserved" and uplink the messages "reserve" or "do not reserve" as one out of said two possible 24-hit patterns virtually excludes misinterpretation.
BRIEF DE~;CRIPTION OF THE DRAWING~
Fig.l illustrates a part of a cellular mobile radio system with cells, a mobile switching center, base stations and mobile stations;
Fig.2 illustr2tes a block diagram of a mobile station utilized in accordance with the present invention;
Fig.3 illustrates a block diagram of a base station utilized in accordance with the present invention;
Fig.4A illustrates the frame structure of a radio channel as utilized in accordance with the present lnvention;
Fig.4B illustrates a time slot format for transmissions from a mobile station to a base or land station;
Fig.4C illustrates a time slot format for transmissions from a mobile station to a base or land station with a reservation field according to the present invention;
Fig.4D illustrates a time slot format for transmissions from a base or land station to a mobile station;
Fig.4E illustrates a time slot fo~mat for transmission~ from a base or land station to a mobile station with twa reservation ~`ields according to the presenk invention;
Fig.5 illustrates an example of a radio channel fra~e having six time slots in which control channels and traffic channels are mixed;
Fig.6A is a diagram illustrating the multiburst access method according to the present invention for the full rate mode;
Fig.6B is a similar diagram for the half rate mode;
Fig.7 is a flow chart describing the access method of the present invention.
2~g~
DETAIhE~ DE~CRIPTIOM OF ~ U~TR~T~ EMBODIM~NT~
Fig.1 illustrates ten cells C1 to C10 in a c~llular mobile rad10 system. In actual practice, the method and means according to the present invention are implemented in a cellular mobile radio system comprising many mDre cells than ten. However, for the purpose of explaining the present invention, ten cells is deemed to be sufficient.
For each of the cells Cl through C10 there is a base station B1 through B10, respectively, with the same number as the cell.
lo Fig.l illustrates base stations situated in the vicinity of the center of the cell and having omni-directional antennas. The base stations of adjacent cells may, however, be allocated in the vicinity of cell borders and have directional antennas as is well known to those of ordinary skill in the art.
Fig.l also illustrates ten mobile stations M1 through M10 which are movable within a cell and from one cell to another cell. In actual practice, the method and means according to the present invention are implemented in a cellular mobile radio system comprising many more mobile stations than ten. In particular, thexe are usually many more mobile stations than there are base stations. However, for the purpose of explaining the pre5ent invention, the use of ten mobile stations is deemed to be sufficient. The system of Fig.l also includes a mobile switching center MSC. The mobile switching center is connected to all ten 2s illustrated base stations by cables. The mobile switching center is also connected, by cables, to a fixed public switching telephone network ox similar fixed network with ISDN facilities.
All cabl~s from the mobile switching center to the base stations and cables to the fixed network are not illustrated.
In addition to the mobile switching center illustrated, there may also be another mobile switching center connected by cables to other base stations than those illustrated in Fig.l. Instead of cables, other means may be utilized for base to mobile station switching center communication, e.g. ~ixed radio links.
7 ~ 2 ~
The cellular mobile radio system illustraked in Fig.1 comprises a plurality of radio channels ~or communication. The system is designed both for analog inEormation, e.g. speech, digitized analog information, digitized speech, and pure digital information. According to the system, the term connection is used for a communication channel mobile station in the same system or another system, or a fixed telephsne or terminal in a fixed network connected to the cellular mobile radio system. Thus, a connection may be defined as a call where two persons are able to talX to each other, but also may refer to a data communication channel where computers are exchanging data.
Referring now to Fig.2, an embodiment of a mobile station that can be utilized in a cellular telephone system that operates in accordance with the present invention is illustrated. A speech coder 101 converts the analog signal generated by a microphone into a bit data stream. The bit data stream is then divided into data packages, according to the TDMA principle. A fast associated control channel (FACCH) generator 102 generates control and supervision signalling messages between the system and the mobile station and messages between the mobile station and the system.
The FACCH message replaces a user frame (speech/data) whenever it is to be transmitted. A slow associated control channel (SACCH~
generator 103 provides a continuous channel for the exchange of signalling messages between the base station and the mobile station and vice-versa. A fixed number of bits, e.~. twelvel is allocateA to the SACCH for each time slot of the m~ssage train.
Channelcoders 104 are respectively connected to the speech coder 101, FACCH generator 102, and SACCH generakor 103 for manipula-ting the incoming data in order to carry out error detection and correction. The techniques used by the channel coders 104 are convolutional encoding, which protects important data bits in the speech code, and cyclic redundancy check (CRC), wherein the perceptually significant bits in the speech coder frame, e.g.
twelve bits, are used for computing a seven bit check.
A selector 105 is connected to the channel coders 104 associated with the speech coder 101 and the FACCH generator 102, respec-8 206~8 tively. The selector 105 is controlled by the microprocessor con~roller 130 so that at appropriate times user in~ormation over a particular speech channel is replaced with system supervision messages over FACCH. A two-bursk interleaver 106 is coupled to the output of the selector 105. Data to be transmitted by the mobile station is interleaved over two distinct time slots. The 260 data bits, which constitute one transmitting word, are divided into two equal parts and are allotted two consecutive time slots. The effects of RAYLEIGH fading will be reduced in lo this manner. The output o~ the two-burst interleaver 106 is provided to the input of a modulo-two-adder 107 so that the transmitted data is ciphered bit by bit by logical modulo-two-addition of a pseudo-random bit stream.
The output of the channel code 104 associated with the SACCH
generator 103 is connected to a 22-burst interleaver 108. The 22-burst interleaver 108 interleaves data transmitted over SACCH
over 22 time slots each consisting of 12 bits of information. The 22-burst interleaver 108 utilizes the diagonal principle so that as two SACCH messages are transmitted in parallel, the second message is displaced eleven bursts from the other message.
The mobile station further includes a Sync Word ~ DVCC generator 109 for providing the appropriate synchronization word (Sync Word) and DVCC which are to be associated with a particular connection. The Sync Word is a 28 bit word used for time slot ~5 synchronization and identification. ~he DVCC ~digital verifica-tion color code) i8 an 8-blt code which is sent by the base station to the mobilestation and vice-versa, for assuring that the proper channel is being decoded.
A ~urst generator 110 generates message bursts for transmission by the mobile station. The burst generator llO is connected to the outputs of the modulo-two~adder 107, the 22-burst interleaver 108, the Sync Word/DVCC generator 109, an e~lalizer 114, and a control channel message generator 132 generating channel coded control messages. A message burst comprising data (260 bits)/
SACCH (12 bits), Sync Word (28 bits), coded DVCC (12 bits), and %0~2~
12 delimiter bits, combined for a total of 324 hits are in-tegrated according to the time slot format specified by the standard EIA/TIA IS~54.
Under the control of the microprocessor 130, two different types of message bursts are generated by the bur~t generakor 110:
control channel message bursts from the control channel message generator 132 and voice/traffic message bursts. The control channel message is generated in accordance with commands from the miroprocessor 130 and is sent on a digital control channel ha~ing the same burst formats as kraffic channels but where the SACCH as well as the speech data normally genera~ed in a voice/traffic burst aEe replaced by control information.
The transmitting of a burst, which is equivalent to one time slot, is synchronized with the transmitting of the other two time slots, and is adjusted according to the timing provided by the equalizer 114. Due to time dispersion, an adaptive equalization method is provided in order to improve signal quality. For further information regarding adaptive equalization techniques, reference should be made to U.S.Patent Application Serial No. 315,561, filed February 27, 1989, and assigned to the same assignee. A correlator adjusts to the timing of the received bit stream. The base station is the master and the mobile station is the slave with respect to frame timiny. The e~ualiz~r ll~ detec~s the incoming timing and synchronizes the burst generator 110. The Z5 equalizer 114 is also operable ~or checking the Sync Word and DVCC ~or identi~ication purposes.
A 20ms frame counter 111 is coupled to the burst generator 110 and so is the equalizer 114. The frame counter 111 updates a ciphering code utilized by the mobile station every 20ms, once for every transmitted frame. It will be appreciated that according to this particular example, three time slots make up one frame. A ciphering unit 112 is provided for generating the ciphering code utilized by the mobile station. A pseudo random algorithm is pre~erably utilized. The ciphering unit 112 is controlled by a key 113 which is unique for each subscriber. The 1~ 2 ~ 2 ~
ciphering unit 112 consists of a sequencer which updates the ciphering code.
The burst produced by burst generator 110, which is to be transmitted, is forwarded to an RF modulator 122. The RF
modulator 122 is operable for modulating a carrier frequency according to the ~/4-DQPSK metod (~/4 shifted, Differentially encoded Quadrature Phase Shift Ksying). The use of this technique implies that the information is differentially encoded, i.e.
2 bit symbols are transmitted as four possible changes in phase;
~ ~/4 and ~ 3~/4. The transmitter carrier frequency supplied to the RF modulator 122 is generated by a transmitting fre~uency synthesizer 124 in accordance with the selected transmitting channel. Before the modulated carier i5 transmitted by an antenna, the carrier is amplified by a power amplifier 123. The RF power emission level of the carrier frequency is selected on command by a microprocessor controller 130. The amplified signal is passed-through a time switch 134 before ît reaches the antenna. The timing is synchronized to the transmitting requence by the microprocessor controller 130. The amplified signal i5 passed to a time switch 134 before it reaches the antenna. The time switch is synchronized to the transmitting sequence by the microprocessor controller 130.
A receiver carrier ~requency is generated in accordance with the selected receiving channel by receiving frequency synthesizer 125. Incoming radlo ~requency signal~ are received by receiver 126, the strength of which are measured hy signal level meter 129. The received signal strength value is then sent to the microprocessor controller 130. An RF demodulator 127 which receives the receiver carrier frequ~ncy from the receiving frequency signal from receiver 126, demodulates the radio fr~quency carrier signal, thus generating an intermediate frequency. The intermediate frequency signal is then demodulated by an IF demodulator 128, which restores the original ~/4-DQPSK -modulated digital information.
~1 20~
The restored digital information provided by IF demodulator 128 is supplied to the equalizer 114. A symbol detector 115 converts the received two bit symbo] format of the digital data from the equalizer 114 to a single bit data stre.am. The symbol detector 115 in turn produces three distinct outputs. Control channel messages are sent to a control message detector 133 which supplies channel decoded and detected control channel information to the microprocessor controller 130. Any speech data/FACCH data is supplied to a modulo-two-adder 107 and a two-burst deinter-leaver 116. The speech data/FACCH data is reconstructed by thesecomponents by assembling and rearranging information from two consecutive frames of the received data. The symbol detector 115 supplies 5ACCH data to a 22-burst deinterleaver 117. The 22-burst deinterleaver 117 reassembles and rearranges the SACCH data, which is spread over 22 consecutive frames.
The two-burst deinterleaver 116 provides the speech data/FACCH
data to two channel decoders 118. The convolutionally encoded data is decoded using the reverse of the above-mentioned coding principle. The rec~ived cyclic redundancy check (CRC) bits are checked to determine if any error has occurred. The FACC~I channel coder furthermore detects the distinction between the speech channel and any FACCH information, and directs the decodes accordingly. A speech decoder 119 processes the received speech data from the channel decoder 118 in accordance with a speech decoder algorithm (VSELP), and generates the received speech signal. The analoy siynal is finally enhanced by a filtering techni~ue. Messages on the ~ast associated control channel are detected by FACCH detector 120, and the information is trans-ferred to the microprocessor controller 130.
The output of the 22-burst deinterleaver 117 is provided to a separate channel decoder 118. Message~ on the slow associated control channel are detected by SACCH detector 121, and that information is transferred to the microprocessor controller 1300 The mi~roprocessor controller 130 controls the mobile station activity and the base station communication, and also handles the 12 2060~
terminal keyboard input and display output 131. Decisions by the microprocessor controller 130 are made in accordance with received messages and measurements made. The keyboard and display unit 131 enable an information exchange between the user and ths base station.
Fig.3 illustrates an embodiment of a base station that can be utili~ed in a cellular telephone system that operates in accordance with the present invention. The base station incorporates numerous component parts which are substatially identical in construction and ~unction to component parts of the mobile station illustrated in Fig.2 and described in conjunction therewith. Such identical component parts are designated in Fig.3 with the same reference numerals utilized hereinabove in the description o~ the mobile station, but are differentiated there~rom by means of a prime (') designation.
There are, however, minor distinctions between the mobile and base stations. For instance, the base station has two receiving antennas. Associated with each of these receiving antennas are a receiver 126', an RF dem~dulator 127', and an IF demodulator 128'. Furthermore, the base station does not include a user keyboard and display unit 131 a5 utilized in the mobile station.
Another differance is that a base station handles the commuJl.ica-tion of many mobiles, which can be seen from ths ramification into 3 channel handlers 1, ~, 3, each of which handles one out o~
3 time slots o~ one frequency.
When power is applied to the mobile station, the micropxocessor controller 130 executes an initialization procedure. Initially, the serving system parameters are retrieved, meaning that the preferred system, e.g./ wire-line ~B) or non wire-line ~A) is selected. Depending on the choice made, the scanning of the dedicated control channels belonging to the preferred system starts.
The receiving frequency synthesizer 125 is ordered by the microprocessor controller 130 to generate the frequency which 13 ~ 2 ~
corresponds to the first dedicated control channel. When the frequency is stable, the signal level meter 129 measures the signal strength, and thereafter the microprocessor controller 130 stores the signal strength value. The same procedure is performed for the frequencies corresponding to the remaining dedicatsd control channels, and a ranking based on the signal strength of each is made by the microprocessor controller 130. The receiving frequency synthesizer 125 is then ordered to tune to the frequency with the highest siynal strength level so that the mobile station will be able to make attempts to synchronize to that channel.
The radio signal is captured by the receiver 126 and i5 demodu-lated according to the selected carrier ~requency by RF modulator 127, and then demodulated by IF demodulator 128. Synchronization and primary analysis of the digital information in the radio signal is made in the equalizer 114. If the equalizer 114 manayes to detect a Sync Word generator 109, the equalizer 114 will lock to the time slot associated with that Sync Word. The mobile station waits for the system parameter overhead messags decoded by the control channel message detector 133 and transferred to the microprocessor controller 130~ This message contains information about the identification of the system, the protocol capability, the number of available paginy channels ~PC), and their specific frequency allocation.
In the situation where the equalizer 114 is not able to recognize the Sync Word within a specified period of time, the receiving frequency synthesizer 25 is ordered by the microprocessor controller 130 to tune to the channel with the next strongest signal. If the mobile station is unable to synchronize at this second choice, the microprocessor controller 130 orders a change o the preferred systems e.g. from A to B or vice versa.
Therea~ter, the scanning of the dedicated control channels of the new preferred system will begin.
When the mobile station has received the system parameter overhead message, the paging channels are scanned in the same ~ 2~g~42~
manner as the dedlcated control channel~, i.e., by measuriny the signal strength and selectiny the fre~uency with the strongest signal. Synchronization to the paging channels is then performed accordingly.
Upon ~uccessful synchronization on a paging channel, the mobile station will leave the initialization procedure and start an idle mode. The idle mode is characterized by four states, which are controlled by the microprocessor controller 130, and which are sequentially looped through as long as no access to the system is initiated. It should be noted that the scanning of the paging channels is performed whene~er the bit error rate on the current paging channel increases above a certain level in order assure that the mobile station is listening to the paging channel with khe strongest signal strength.
Th~ first state associated with the idle mode is a continuous updating of the mobile station status, e.g. the number of and the location of existing access channels ~AC). This in~ormation is carried to the mobile station in the system parameter overhead message on the paging channel, referred to as a digital forward control channel (DFOCC). This message is decoded in the control channel message detector 133 and sent to the microprocessor controller 130. Certain messages transmitted ~rom the base station in the system parameter overhead me~sage damand respon-ding action~ ~rom the mobile station, e.g. a rescan message will order the microprocessor controller 130 to restart the initialization procedure. As another example, a registration identity messaga ~rom the base station will force the mobile station to make a system access in order to register in accor-dance with the system access mode described hereinbelow.
The second state associated with the idle mode relates to the siutation where the mobile station attempts to match page messages transmitted by the base station. These mobile station control messages, which are sent over the DFOCC, are decoded in the control channel message detector 133 and analyzed by th~
microprocessor controller 130. If the decoded number matches the 1~ 2 ~ 2 8 identification number of the mohile stakion, a connection to th base station will be prepared in the system access mode.
The third state of the idle mode involves listening to orders sent by the base station over the DFOCC. Decoded orders, such as S an abbreviated alert, will be processed by the mobile station accordingly.
The fourth state in the idle mode involves the microprocessor controller 130 supervisin~ the input from keyboard 131 for user activity, e.g. call initiating. A call origination results in the mobile station leaving the idle mode and starting the system access mode.
One of the primary tasks in the system access mode of the mobile station is the mobile station generating an access message. The digital access channels (DAC) available to the mobile, which were updated during the idle mode, are now examined in a manner similar to the measuring of the dedicated control channels as previoiusly described. A ranking of the signal strength of each is made, and the channel associated with the strongest signal is chosen. The transmitting frequency synthesizer 124 and the receiving frequency synthesizer 125 are tuned accordin~ly, and a service request message is sent over the sele~ted channel ln order to inorm the base station about ~he type o~ access e.g.
call origination, page response, registration request or order confirmation. After completion o~ this message, the amplifier 123 oP the mobile station is turned of~ and the mobile stations waits for further control messages on the DFOCC. Depending on the access type, the mobile station will then receive an adequate message from the base station.
If the access type were origination or paging, th~ mobile station is assigment a free traffic channel by the base station, and the mobile station goes over to the traffic channel and leaves the system access mode. The mobile station will then tune the transmitting frequency synthesizer 124 and the receiving frequency synthesizer 125 to the frequencies associated with the 16 2~ 28 chosen traf~ic channel. Thereafter, the equalizer 11~ starts synchronizing. A time alignment procedure i~ controlled by the base station and is based on time delay measurements which are performedat the base station on the received signal. From this moment on, exchanging of messages between the base station and the mobile station are transferred ovPr the fast associated control channel ~FACCH) and the slow associated control (SACCH).
Messages from the microprocessor controller 130 are generated by the FACCH generator 102 or the SACCH generator 103, and data is error protection coded in the channel coder 104. The FACCH data is time multiplexedwith speech data in the multiplexer 105, and interleaved over two bursts by two burst interleaver 106. The data is then encrypted in the modulo-2 adder 107, which is controlled by the cipherin~ algorithm generated by ciphering unit 112. The SACCH data is interleaved over 22 bursts by 22-burst interleaver 108, and is then supplied to the burst generator 110 where the SACCH data is mixed with speech data, FACCH data, the Sync Word, and the DVC from DVCLC generator 109. The RF modulator 122 modulataes the bit pattern according to the ~/4-DQPSK
principle. The power amplifier 123 is activated and the power level is controlled by the microprocessor controllerd 130 during the time of the transmitted slot.
Control messages from the base ætation to the microprocessor controller 130 of the mobile station are also transferred via the 2S FACCH and SACCH. The symbol pattern to a bit data stream which is directed to the speech decoder 119, FACCH detector 12G, or SACCH
detector 121, depending on the type of data used. Speech data and FACCH data are decrypted by the modulo-2 adder 107, and the two burst deinterleaver 116. The channel de~oders 118 detect bit errors and informs the microprocessor controller 130 accordingly.
The SACCH is deinterleaved ov~r 22 bursts by 22-burst deinter-leaver 117 before error detection is caxried out in channel decoder 118.
Messages transmitted from the base station to the mobile station typically include alerting orders, requests to perform channel ~7 2 ~ 2 8 quality measurement~, release call, and hand-of~ ord~rs. Messages transmitted in the opposite direction are those initiated by the mobile station user, e.g. the release order. The last order implies that the user is finished with the call, and the mobile station will leav~ the control of the traffic channel and return to the initialization mode of operation.
Figs. ~A, 4B and 4D illu~trate the structure of the digital channel~ according to the EIA/TIA standard IS-54. Fig.4A depicts the frame structure of a radio channel. According to this example, one radio channel frame consists of typically six time slots which include a total of 1,944 bits or 972 symbols. The frame is 40 ms in length with a data transmission rate of 25 frames per second. Each of the time slots are typically numbered from 1-6, each respectively including Sync Words of 28 bits as defined above.
Figs. 4B and 4D illustrate a time slot format for transmission~
from the mobile station to the land station and from the land station to the mobile station, respectively. The time slot formats commonly include 260 bits reserved for data transmission, 12 bits for a digital verification color code (DVCC), 12 bits for a slow associated control channel ~SACCH), and 28 biks for synchronization and training data (SYNC). The 510t format from the mobile station to the land station includes two 6 bit blocks for guard time (G) and ramp time (R) information~ The slot format from the land station to the mobile station includes a 12 bit block which is reserved for ~uture uses.
In a hal~ rate alternative, each half rate voice/traffic channel utilizes one time slot of each frame. This implies that one frame comprises six half rate traffic channels with the slots being numbered sequentially 1, 2, 3, 4, 5, 5. According to the fullrate alternative, each full rate tra~fic channel utilizes two equally spaced time slots of the frame, e.g., 1 and 4, 2 and 5, or 3 and 6. In this alternative, the time slots are numbered 1, 2, 3, and the configuration of one frame will therefore be 1, 2, 3, 1, 2, 3. It will be appreciated that for purposes of explanation it 18 206~8 will be assumed that the present invention utilizes the ~ull rate alternative for the following examples.
In order to carry out the present method of accessing the land system via the digital control channel the format of the radio s channels according to Figs 4B and 4D is changed as it appears.
from Fig. 4C and Fig. 4E.
Fig 4C shows the slot format o~ the radio channel from a mobile station to a land station when the channel is a digital control channel. In this case there is no need for the slow associated control channel SACCH and the digital verification color code DVCC as it is if the radio channel is a traffic channel. Instead a reservation field RES of 12 + 12 = 24 bits is created for the purpose of transmitting information to the land station as it will be closer described in connection with Figure 6A, 6B.
Figure 4E shows the slot format of the radio channel from a land station to a mobile station when the radio channel is a digital control channel. As described above there is no need for the SACCH and the DVCC. The 12 bit SACCH is now a first 12 bit reservation field RESl and the DVCC is now a second 12 bit reservation field RES2 for the purpose of transmittiny information to the mobile station as it will be closer described in connection with Figures 6A, 6B.
Figure 5 illustrates a standardized frame which comprises both control channels and traffic channels. In this example, time slots 1 and 4 are utilized as control channels and time slots 2, 3, 5 and 6 are utiliæed as traffic channels in the full rate mode o~ the system. In a half rate mode of transmission which will be described in connection with Figure 6B, only time slo-t 1 in each frame is utilized as a control channel, while the slots 2-6 are utilized as traffic channels.
The inventive multi~burst access method will now be closer described in connection with Figure 6A for the full rate mode of the mobile system.
2~04~
The first line a) in Figure 6A shows a number of frames F1, F2,... each including 6 time slots 1-6. Since the transmission in this case is full rate, time slots 1 and 4 in each frame are control channels and can be free for exchanging control in-formation such as access messages, authentication messages and soon. The frame structure in line a) is the frame structure for the digital forward control channel DFOCC and the digital reverse control channel DRECC indicating the time 510ts in a frame for these channels on a particular carrier frequency. Line b) in Figure 6A shows the positions of the time slots for the digital reverse control channel DRECC and line c) indicates the positions of the time slots for the forward control channel DFOCC. The time 510t positions for the DRECC are the reference positions and coincide with the frame structure and time 510ts according to line a). The DRECC time slots are used for transmission uplink ~MS~BS~ and the DFOCC kime slots are used for the downlink transmission (BS~MS). The time slots used for speech transmission are not indicated.
The DFOCC time slots are displaced a certain amount from the DRECC time slots as specified due to signal strength measure-ments, a reversal time from transmit to receive mode and so on.
Initially a mobile station can be in its idle mode look:ing for any control data (info~mation) bursts :in the DFOCC time slots marked by "F" in Figure 6A, line c). However, the present method is not limited to this operation mode but can also be used when the mvbile station performs the tasks in the subsequent access mode as described earlier.
Thus the base station transmits a control message in the DFOCC
time slots "F" and in the RESl and/or RES2 directed to one mobile station or to all mobile stations reading the DFOCC~message on a particular DFOCC frequency channel indicating that time slot #1 on this frequency (or on other frequencies f2, f3,...) is free.
It is assumed that a certain mobile station MSl has got the above message that time slot #l is free (arrow A1). This free time slot 2~6~28 is thus reserved ~or mobile MSl in the DRECC channel i.e when the mobile MSl wants to send to the base station. The reserved time slot is marked by R in frame F~.
When the mobile station MSl sends in this reserved time slot (arrow A2) it also demands that the next time slot #1 should be reserved. The base station only makes a notation that this time slot #1 should be reserved and sends (arrow A3) any control message to the mobile station MSl. Thus time slot R in frame F7 is reserved for the mobile MS1. There is a possibility that another mobile station MS2 has got the free slot message F in frame F2 on the DFOCC but has a weaker signal strength when sending in time slot #1, frame F4 to the base station. The mobile station MSl with the stronger signal will ~Iwin~ and a reservation of the time slot # in frame F7 is made for the mobile MSl.
Thus the base station only makes a reservation of time slot #l in the DRECC for the mobile MSl and the mobile MS1 accepts the reserved time slot. Since in this exemple, the mobile wants to send its control message during 3 time slots it accepts the reserved time slots #l in frames F4, F7. When the mobile station MS1 uses the reserved time slot #1, frame F10 after haviny received a control message ~arrow A5) from the base station, it is using this reserved time slot for the last time, since the mobile MSl has used 3 time slots ~or control messages including the last time slot. Mobile station MS1 therefor responds by sending a message that the used time slot ~1 now is ~ree and sends its last control message in the reservation field RES
(Fig.4C), arrow A6.
Figure ~A also shows the case when another mobile station MS2 has accessed the system via the base station but a little later than did mobile station MSl on the same carrier frequency fl. While time slot #1 was allotted to mobile MSl, time slot #4 in the same frame is allotted to mobile MS2. This mobile station is assumed to make a 2 burst access to the base station. The same procedure as for mobile station MS1 is intiated, arrows B1, B2, but when the base station sends its control message, arrow B3, to mobile 21 2~ 28 station MS2, this will respond that it will not need more kime slots #4 (in addition to its control in~ormation). Mobile station MS2 therefor sends a message, arrow B4, to the base station that this time slot #4 can be free.
As it appears from Figure 6A time slot #l every fourth frame is used by mobile station MSl and time slot #4 is used every fourth frame by mobile station MS2. Thus time slots #1 and #4 in two intermediate frames are empty. These time slots can be accessPd by furthsr additional mobile stations~ It can also be observed that the mobile station its~lf is ordering if it needs more time slots for access or if subsequent time slots can be left free by the base station. This implies that the probability of collision between access messages from mobiles to the base station (i.e. to the system~ is ~inimized.
The access procedure of the prQsent invention can also be used for a half rate channel as an acc~ss channel. Figure 6B shows such a case, where only one time slot in each frame is used for the multiburst accesses.
In Figure 6B, the mobile station MS1 finds a message in the downlink time slot of the second frame and a reservat,ion is made in the base station for mobile station MS1 in this kime slot, arrow Al. The following pro~edure accordiny to arrows A2-A6 is the same as ~or mobile station MSl in the Eull rate mode described in Figure 6A and so it is for the mobile stations MS~, MS3.
Figure 7 is a flow chart describing the various steps taken in the mobile station and in the base station to perform the method according to the present invention.
In block 701, a mobile station of a plurality of mobile stations is in its idle state receiving data messages from the system via a base station on the Digital Forward Control Channel (DFOCC~ in time slots each Wit~l a format as shown in Figure 4E. These messages are directed to individual mobile stations or to all 22 ~60~2~
mobile stations capable of reading this particular DFOCC.
Messages directed to all mobile st~tions, i.e. Broadcast messages contain information about the system and information controlling the actions taken by mobil~ during system access.
In block 702 a need for a system access occure in a mobile station. The reason can be a response to a page or a response to a change in system information like registration control data or the mobile station subscriber wishes to make an origination access.
In block 703 the mobile station initiate its access by reading the reservation field RESl or RES2 in a burst on the DFOCC from the base station (arrow Al in Figure 6A). The value of the field is detected, and is investigated in MS whether this value is indicated as reserved or free by the base station, block 704. If the value of the reservation field RESl, RES2 indicate that the time slot is reserved for another mobile/ the process is transferred to block 705 in the mobile station. If on the other hand the reservation field RES1, RES2 indicate that the time slot is not reserved ("free") the process is transferred to block 706.
In block 705 a reserved time slot is found by the mobile. The number N of this type is maximized (without entering hlock 706~.
If the maximum number N is exceeded ("Yes", block 705) the process i~ aborted and returned to block 701. If Oll the othex hand the maximum number N is not exceeded ("No", block 705), block 703 is reentered after a random delay.
In block 706, the mobile station seizes the time slot indicated as free by the base station by starting the transmitter and sending the first burst in the access message (arrow A2, Figure 6A).
In block 706A it is investigated by the mobile station if the access message contains more bursts to be sent to the base station and the reservation field ~ES in the DRECC is set to reserved and the process is trans-ferred to block 707.
2 ~ 2 ~
If on the other hand this was the last burst in the access message, the sent burst is read by the base station only and the RES is set to free and the process is returned to block 701, while the mobile station waits for the system to respond, bloc~
706B.
.
In block 707 the base station in the system reads the burst transmitted by the mobile station (arrow A2, Figure 6A). The system checks the validity of the data word contain~d in the burst and detects the contents of the received reservation field ~0 RES. If the data word was found valid (checksum OK) and the reservation field indicated rQservation, the system sets the corre~ponding reservation field RESl, RES2 of the DFOCC to "reserved".
In block 708 the mobile station receives (arrow A3) and reads the reservation fields RES1, RES2 set by the system. The received message from the base station is investigated, block 709. If ~he mobile station, in block 709 finds a reservation in the fields RES1, RES2 the mobile station can continue with the access and the process is transferred back to block 706 for transmission of the next burst. If on the other hand a free indication is found, the process is transferred to block 710.
In block 710 a failure is detected. The number o~ o~curancies of this type of ailures is maximized. If the maximum number N is exceeded, the process is aborted and returned to block 701.
2s The blocks 706B and 707 is performed in the base station by the microprocessor 130' which is activated by a signal from the control channel message detector 133' to read the reservation field RES~ Microprocessor 130' thereafter activates the control chann~l message generator 132' to send a control message to the mobile station MS1 in the reserved time slot. Microprocessor 130' also sets time slot #l either to a reserved time slot (block 707) or to a fre~ time slot (block 706B~.
~0~2~
The other ~unction blocks in Fig. 7 are performed in the mobile station MSl by the microprocessor 130 ~Fig.2). Microprocesss:~r 130 is activated by the control channel message del;ector 133 in order to read the control message and the reservation fields R2Sl, RES2 S and in order to activate the control channel message generator 132 to send the control message to the base station.
____ __
When power is applied to the mobile station, the micropxocessor controller 130 executes an initialization procedure. Initially, the serving system parameters are retrieved, meaning that the preferred system, e.g./ wire-line ~B) or non wire-line ~A) is selected. Depending on the choice made, the scanning of the dedicated control channels belonging to the preferred system starts.
The receiving frequency synthesizer 125 is ordered by the microprocessor controller 130 to generate the frequency which 13 ~ 2 ~
corresponds to the first dedicated control channel. When the frequency is stable, the signal level meter 129 measures the signal strength, and thereafter the microprocessor controller 130 stores the signal strength value. The same procedure is performed for the frequencies corresponding to the remaining dedicatsd control channels, and a ranking based on the signal strength of each is made by the microprocessor controller 130. The receiving frequency synthesizer 125 is then ordered to tune to the frequency with the highest siynal strength level so that the mobile station will be able to make attempts to synchronize to that channel.
The radio signal is captured by the receiver 126 and i5 demodu-lated according to the selected carrier ~requency by RF modulator 127, and then demodulated by IF demodulator 128. Synchronization and primary analysis of the digital information in the radio signal is made in the equalizer 114. If the equalizer 114 manayes to detect a Sync Word generator 109, the equalizer 114 will lock to the time slot associated with that Sync Word. The mobile station waits for the system parameter overhead messags decoded by the control channel message detector 133 and transferred to the microprocessor controller 130~ This message contains information about the identification of the system, the protocol capability, the number of available paginy channels ~PC), and their specific frequency allocation.
In the situation where the equalizer 114 is not able to recognize the Sync Word within a specified period of time, the receiving frequency synthesizer 25 is ordered by the microprocessor controller 130 to tune to the channel with the next strongest signal. If the mobile station is unable to synchronize at this second choice, the microprocessor controller 130 orders a change o the preferred systems e.g. from A to B or vice versa.
Therea~ter, the scanning of the dedicated control channels of the new preferred system will begin.
When the mobile station has received the system parameter overhead message, the paging channels are scanned in the same ~ 2~g~42~
manner as the dedlcated control channel~, i.e., by measuriny the signal strength and selectiny the fre~uency with the strongest signal. Synchronization to the paging channels is then performed accordingly.
Upon ~uccessful synchronization on a paging channel, the mobile station will leave the initialization procedure and start an idle mode. The idle mode is characterized by four states, which are controlled by the microprocessor controller 130, and which are sequentially looped through as long as no access to the system is initiated. It should be noted that the scanning of the paging channels is performed whene~er the bit error rate on the current paging channel increases above a certain level in order assure that the mobile station is listening to the paging channel with khe strongest signal strength.
Th~ first state associated with the idle mode is a continuous updating of the mobile station status, e.g. the number of and the location of existing access channels ~AC). This in~ormation is carried to the mobile station in the system parameter overhead message on the paging channel, referred to as a digital forward control channel (DFOCC). This message is decoded in the control channel message detector 133 and sent to the microprocessor controller 130. Certain messages transmitted ~rom the base station in the system parameter overhead me~sage damand respon-ding action~ ~rom the mobile station, e.g. a rescan message will order the microprocessor controller 130 to restart the initialization procedure. As another example, a registration identity messaga ~rom the base station will force the mobile station to make a system access in order to register in accor-dance with the system access mode described hereinbelow.
The second state associated with the idle mode relates to the siutation where the mobile station attempts to match page messages transmitted by the base station. These mobile station control messages, which are sent over the DFOCC, are decoded in the control channel message detector 133 and analyzed by th~
microprocessor controller 130. If the decoded number matches the 1~ 2 ~ 2 8 identification number of the mohile stakion, a connection to th base station will be prepared in the system access mode.
The third state of the idle mode involves listening to orders sent by the base station over the DFOCC. Decoded orders, such as S an abbreviated alert, will be processed by the mobile station accordingly.
The fourth state in the idle mode involves the microprocessor controller 130 supervisin~ the input from keyboard 131 for user activity, e.g. call initiating. A call origination results in the mobile station leaving the idle mode and starting the system access mode.
One of the primary tasks in the system access mode of the mobile station is the mobile station generating an access message. The digital access channels (DAC) available to the mobile, which were updated during the idle mode, are now examined in a manner similar to the measuring of the dedicated control channels as previoiusly described. A ranking of the signal strength of each is made, and the channel associated with the strongest signal is chosen. The transmitting frequency synthesizer 124 and the receiving frequency synthesizer 125 are tuned accordin~ly, and a service request message is sent over the sele~ted channel ln order to inorm the base station about ~he type o~ access e.g.
call origination, page response, registration request or order confirmation. After completion o~ this message, the amplifier 123 oP the mobile station is turned of~ and the mobile stations waits for further control messages on the DFOCC. Depending on the access type, the mobile station will then receive an adequate message from the base station.
If the access type were origination or paging, th~ mobile station is assigment a free traffic channel by the base station, and the mobile station goes over to the traffic channel and leaves the system access mode. The mobile station will then tune the transmitting frequency synthesizer 124 and the receiving frequency synthesizer 125 to the frequencies associated with the 16 2~ 28 chosen traf~ic channel. Thereafter, the equalizer 11~ starts synchronizing. A time alignment procedure i~ controlled by the base station and is based on time delay measurements which are performedat the base station on the received signal. From this moment on, exchanging of messages between the base station and the mobile station are transferred ovPr the fast associated control channel ~FACCH) and the slow associated control (SACCH).
Messages from the microprocessor controller 130 are generated by the FACCH generator 102 or the SACCH generator 103, and data is error protection coded in the channel coder 104. The FACCH data is time multiplexedwith speech data in the multiplexer 105, and interleaved over two bursts by two burst interleaver 106. The data is then encrypted in the modulo-2 adder 107, which is controlled by the cipherin~ algorithm generated by ciphering unit 112. The SACCH data is interleaved over 22 bursts by 22-burst interleaver 108, and is then supplied to the burst generator 110 where the SACCH data is mixed with speech data, FACCH data, the Sync Word, and the DVC from DVCLC generator 109. The RF modulator 122 modulataes the bit pattern according to the ~/4-DQPSK
principle. The power amplifier 123 is activated and the power level is controlled by the microprocessor controllerd 130 during the time of the transmitted slot.
Control messages from the base ætation to the microprocessor controller 130 of the mobile station are also transferred via the 2S FACCH and SACCH. The symbol pattern to a bit data stream which is directed to the speech decoder 119, FACCH detector 12G, or SACCH
detector 121, depending on the type of data used. Speech data and FACCH data are decrypted by the modulo-2 adder 107, and the two burst deinterleaver 116. The channel de~oders 118 detect bit errors and informs the microprocessor controller 130 accordingly.
The SACCH is deinterleaved ov~r 22 bursts by 22-burst deinter-leaver 117 before error detection is caxried out in channel decoder 118.
Messages transmitted from the base station to the mobile station typically include alerting orders, requests to perform channel ~7 2 ~ 2 8 quality measurement~, release call, and hand-of~ ord~rs. Messages transmitted in the opposite direction are those initiated by the mobile station user, e.g. the release order. The last order implies that the user is finished with the call, and the mobile station will leav~ the control of the traffic channel and return to the initialization mode of operation.
Figs. ~A, 4B and 4D illu~trate the structure of the digital channel~ according to the EIA/TIA standard IS-54. Fig.4A depicts the frame structure of a radio channel. According to this example, one radio channel frame consists of typically six time slots which include a total of 1,944 bits or 972 symbols. The frame is 40 ms in length with a data transmission rate of 25 frames per second. Each of the time slots are typically numbered from 1-6, each respectively including Sync Words of 28 bits as defined above.
Figs. 4B and 4D illustrate a time slot format for transmission~
from the mobile station to the land station and from the land station to the mobile station, respectively. The time slot formats commonly include 260 bits reserved for data transmission, 12 bits for a digital verification color code (DVCC), 12 bits for a slow associated control channel ~SACCH), and 28 biks for synchronization and training data (SYNC). The 510t format from the mobile station to the land station includes two 6 bit blocks for guard time (G) and ramp time (R) information~ The slot format from the land station to the mobile station includes a 12 bit block which is reserved for ~uture uses.
In a hal~ rate alternative, each half rate voice/traffic channel utilizes one time slot of each frame. This implies that one frame comprises six half rate traffic channels with the slots being numbered sequentially 1, 2, 3, 4, 5, 5. According to the fullrate alternative, each full rate tra~fic channel utilizes two equally spaced time slots of the frame, e.g., 1 and 4, 2 and 5, or 3 and 6. In this alternative, the time slots are numbered 1, 2, 3, and the configuration of one frame will therefore be 1, 2, 3, 1, 2, 3. It will be appreciated that for purposes of explanation it 18 206~8 will be assumed that the present invention utilizes the ~ull rate alternative for the following examples.
In order to carry out the present method of accessing the land system via the digital control channel the format of the radio s channels according to Figs 4B and 4D is changed as it appears.
from Fig. 4C and Fig. 4E.
Fig 4C shows the slot format o~ the radio channel from a mobile station to a land station when the channel is a digital control channel. In this case there is no need for the slow associated control channel SACCH and the digital verification color code DVCC as it is if the radio channel is a traffic channel. Instead a reservation field RES of 12 + 12 = 24 bits is created for the purpose of transmitting information to the land station as it will be closer described in connection with Figure 6A, 6B.
Figure 4E shows the slot format of the radio channel from a land station to a mobile station when the radio channel is a digital control channel. As described above there is no need for the SACCH and the DVCC. The 12 bit SACCH is now a first 12 bit reservation field RESl and the DVCC is now a second 12 bit reservation field RES2 for the purpose of transmittiny information to the mobile station as it will be closer described in connection with Figures 6A, 6B.
Figure 5 illustrates a standardized frame which comprises both control channels and traffic channels. In this example, time slots 1 and 4 are utilized as control channels and time slots 2, 3, 5 and 6 are utiliæed as traffic channels in the full rate mode o~ the system. In a half rate mode of transmission which will be described in connection with Figure 6B, only time slo-t 1 in each frame is utilized as a control channel, while the slots 2-6 are utilized as traffic channels.
The inventive multi~burst access method will now be closer described in connection with Figure 6A for the full rate mode of the mobile system.
2~04~
The first line a) in Figure 6A shows a number of frames F1, F2,... each including 6 time slots 1-6. Since the transmission in this case is full rate, time slots 1 and 4 in each frame are control channels and can be free for exchanging control in-formation such as access messages, authentication messages and soon. The frame structure in line a) is the frame structure for the digital forward control channel DFOCC and the digital reverse control channel DRECC indicating the time 510ts in a frame for these channels on a particular carrier frequency. Line b) in Figure 6A shows the positions of the time slots for the digital reverse control channel DRECC and line c) indicates the positions of the time slots for the forward control channel DFOCC. The time 510t positions for the DRECC are the reference positions and coincide with the frame structure and time 510ts according to line a). The DRECC time slots are used for transmission uplink ~MS~BS~ and the DFOCC kime slots are used for the downlink transmission (BS~MS). The time slots used for speech transmission are not indicated.
The DFOCC time slots are displaced a certain amount from the DRECC time slots as specified due to signal strength measure-ments, a reversal time from transmit to receive mode and so on.
Initially a mobile station can be in its idle mode look:ing for any control data (info~mation) bursts :in the DFOCC time slots marked by "F" in Figure 6A, line c). However, the present method is not limited to this operation mode but can also be used when the mvbile station performs the tasks in the subsequent access mode as described earlier.
Thus the base station transmits a control message in the DFOCC
time slots "F" and in the RESl and/or RES2 directed to one mobile station or to all mobile stations reading the DFOCC~message on a particular DFOCC frequency channel indicating that time slot #1 on this frequency (or on other frequencies f2, f3,...) is free.
It is assumed that a certain mobile station MSl has got the above message that time slot #l is free (arrow A1). This free time slot 2~6~28 is thus reserved ~or mobile MSl in the DRECC channel i.e when the mobile MSl wants to send to the base station. The reserved time slot is marked by R in frame F~.
When the mobile station MSl sends in this reserved time slot (arrow A2) it also demands that the next time slot #1 should be reserved. The base station only makes a notation that this time slot #1 should be reserved and sends (arrow A3) any control message to the mobile station MSl. Thus time slot R in frame F7 is reserved for the mobile MS1. There is a possibility that another mobile station MS2 has got the free slot message F in frame F2 on the DFOCC but has a weaker signal strength when sending in time slot #1, frame F4 to the base station. The mobile station MSl with the stronger signal will ~Iwin~ and a reservation of the time slot # in frame F7 is made for the mobile MSl.
Thus the base station only makes a reservation of time slot #l in the DRECC for the mobile MSl and the mobile MS1 accepts the reserved time slot. Since in this exemple, the mobile wants to send its control message during 3 time slots it accepts the reserved time slots #l in frames F4, F7. When the mobile station MS1 uses the reserved time slot #1, frame F10 after haviny received a control message ~arrow A5) from the base station, it is using this reserved time slot for the last time, since the mobile MSl has used 3 time slots ~or control messages including the last time slot. Mobile station MS1 therefor responds by sending a message that the used time slot ~1 now is ~ree and sends its last control message in the reservation field RES
(Fig.4C), arrow A6.
Figure ~A also shows the case when another mobile station MS2 has accessed the system via the base station but a little later than did mobile station MSl on the same carrier frequency fl. While time slot #1 was allotted to mobile MSl, time slot #4 in the same frame is allotted to mobile MS2. This mobile station is assumed to make a 2 burst access to the base station. The same procedure as for mobile station MS1 is intiated, arrows B1, B2, but when the base station sends its control message, arrow B3, to mobile 21 2~ 28 station MS2, this will respond that it will not need more kime slots #4 (in addition to its control in~ormation). Mobile station MS2 therefor sends a message, arrow B4, to the base station that this time slot #4 can be free.
As it appears from Figure 6A time slot #l every fourth frame is used by mobile station MSl and time slot #4 is used every fourth frame by mobile station MS2. Thus time slots #1 and #4 in two intermediate frames are empty. These time slots can be accessPd by furthsr additional mobile stations~ It can also be observed that the mobile station its~lf is ordering if it needs more time slots for access or if subsequent time slots can be left free by the base station. This implies that the probability of collision between access messages from mobiles to the base station (i.e. to the system~ is ~inimized.
The access procedure of the prQsent invention can also be used for a half rate channel as an acc~ss channel. Figure 6B shows such a case, where only one time slot in each frame is used for the multiburst accesses.
In Figure 6B, the mobile station MS1 finds a message in the downlink time slot of the second frame and a reservat,ion is made in the base station for mobile station MS1 in this kime slot, arrow Al. The following pro~edure accordiny to arrows A2-A6 is the same as ~or mobile station MSl in the Eull rate mode described in Figure 6A and so it is for the mobile stations MS~, MS3.
Figure 7 is a flow chart describing the various steps taken in the mobile station and in the base station to perform the method according to the present invention.
In block 701, a mobile station of a plurality of mobile stations is in its idle state receiving data messages from the system via a base station on the Digital Forward Control Channel (DFOCC~ in time slots each Wit~l a format as shown in Figure 4E. These messages are directed to individual mobile stations or to all 22 ~60~2~
mobile stations capable of reading this particular DFOCC.
Messages directed to all mobile st~tions, i.e. Broadcast messages contain information about the system and information controlling the actions taken by mobil~ during system access.
In block 702 a need for a system access occure in a mobile station. The reason can be a response to a page or a response to a change in system information like registration control data or the mobile station subscriber wishes to make an origination access.
In block 703 the mobile station initiate its access by reading the reservation field RESl or RES2 in a burst on the DFOCC from the base station (arrow Al in Figure 6A). The value of the field is detected, and is investigated in MS whether this value is indicated as reserved or free by the base station, block 704. If the value of the reservation field RESl, RES2 indicate that the time slot is reserved for another mobile/ the process is transferred to block 705 in the mobile station. If on the other hand the reservation field RES1, RES2 indicate that the time slot is not reserved ("free") the process is transferred to block 706.
In block 705 a reserved time slot is found by the mobile. The number N of this type is maximized (without entering hlock 706~.
If the maximum number N is exceeded ("Yes", block 705) the process i~ aborted and returned to block 701. If Oll the othex hand the maximum number N is not exceeded ("No", block 705), block 703 is reentered after a random delay.
In block 706, the mobile station seizes the time slot indicated as free by the base station by starting the transmitter and sending the first burst in the access message (arrow A2, Figure 6A).
In block 706A it is investigated by the mobile station if the access message contains more bursts to be sent to the base station and the reservation field ~ES in the DRECC is set to reserved and the process is trans-ferred to block 707.
2 ~ 2 ~
If on the other hand this was the last burst in the access message, the sent burst is read by the base station only and the RES is set to free and the process is returned to block 701, while the mobile station waits for the system to respond, bloc~
706B.
.
In block 707 the base station in the system reads the burst transmitted by the mobile station (arrow A2, Figure 6A). The system checks the validity of the data word contain~d in the burst and detects the contents of the received reservation field ~0 RES. If the data word was found valid (checksum OK) and the reservation field indicated rQservation, the system sets the corre~ponding reservation field RESl, RES2 of the DFOCC to "reserved".
In block 708 the mobile station receives (arrow A3) and reads the reservation fields RES1, RES2 set by the system. The received message from the base station is investigated, block 709. If ~he mobile station, in block 709 finds a reservation in the fields RES1, RES2 the mobile station can continue with the access and the process is transferred back to block 706 for transmission of the next burst. If on the other hand a free indication is found, the process is transferred to block 710.
In block 710 a failure is detected. The number o~ o~curancies of this type of ailures is maximized. If the maximum number N is exceeded, the process is aborted and returned to block 701.
2s The blocks 706B and 707 is performed in the base station by the microprocessor 130' which is activated by a signal from the control channel message detector 133' to read the reservation field RES~ Microprocessor 130' thereafter activates the control chann~l message generator 132' to send a control message to the mobile station MS1 in the reserved time slot. Microprocessor 130' also sets time slot #l either to a reserved time slot (block 707) or to a fre~ time slot (block 706B~.
~0~2~
The other ~unction blocks in Fig. 7 are performed in the mobile station MSl by the microprocessor 130 ~Fig.2). Microprocesss:~r 130 is activated by the control channel message del;ector 133 in order to read the control message and the reservation fields R2Sl, RES2 S and in order to activate the control channel message generator 132 to send the control message to the base station.
____ __
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of accessing a mobile radio land system from one of a number of mobile stations communicating with the land system in frames of time slots(TDMA) and capable of accessing a base station in the system by an access message over a digital control channel, c h a r a c t e r i z e d in that a mobile station (MS1) is accessing a base station (BS) in the system by sending to the base station over said control channel (CC) a reservation (RES) for a number of time slots each with a given position (#1) within a frame (F4, F7, F10) which is to be reserved in said base station (BS) for said mobile station (MS1) in order for the mobile station to complete an access message over said digital control channel in the reserved time slots.
2. A method according to claim 1, c h a r a c t e r i z e d in that said base station transmits control data messages in a number of time slots (1,4) in a frame (F1,F2,...) less than the total number of time slots (1-6) in the frame, said control data messages being directed to different mobiles (MS1, MS2,...) in the system, that said mobile (MS1) in an idle state listens for said control data message and makes an attempt to send such a control data message to the base station (BS) together with an indication that the particular time slot (#1) in the frame (F4) on which the control data message from the base station was sent to the mobile station is to be reserved for the next control data message from the mobile to the base station.
3. A method according to claim 2, c h a r a c t e r i z e d in that if said mobile station (MS1) making an attempt to access said base station (BS) has succeeded in said attempt to access said base station, a certain time slot (1, F4) is reserved for this mobile station (MS1), and that the base station sends its control message to said mobile station (MS1) which after having received this control message sends its control message in said reserved time slot (1, F7) to the base station (BS).
4. A method according to claims 2-3, c h a r a c t e r i z e d in that when the mobile station for which said time slot has been reserved is sending a last data control message occupying said reserved time slot (#1), at the same time is sending a message that the reserved time slot (#1) is to be free in the base station (BS).
5. A method according to claim 1, c h a r a c t e r i z e d in that said data control message (D) over said digital control channel (CC) which is sent from said base station (BS) occupies a reservation field (RES1, RES2) which in a certain time slot (#1 or #4) is left free when used as a digital control channel (CC) instead of a traffic channel (TC).
6. A method according to claim 5, c h a r a c t e r i z e d in that said reservation field consists of two field parts (RES1, RES2) in the time slot used as a digital control channel (CC), said field parts corresponding to a slow associated control channel (SACCH) and to a digital verification color code (DVCC) when used as a traffic channel (TC).
7. A method according to claim 1, c h a r a c t e r i z e d in that said data control message (D) over said digital control channel (CC) which is sent from a mobile station (MS1, MS2,...) to a base station (BS) occupies a reservation field (RES) which corresponds to the fields occupied by a slow associated control channel (SACCH) and a digital verification color code (DVCC) in a traffic channel (TC).
8. A method according to claim 1, c h a r a c t e r i z e d in that the particular time slot (#1) in a certain frame (F4) which has been reserved in the base station (BS) for a particular mobile station (MS1) is reserved in the same time slot (#1) and in a frame (F7) a predetermined frame intervals (F5-F6) after the frame (F4) of the first reserved time slot (#1), thereby leaving a number of frames with empty time slots for access from other mobile stations (MS2, MS3).
9. A method according to claims 1-4, c h a r a c t e r i z e d in that two different time slots (#1, #4) in each frame (F1, F2,...) can be accessed and reserved for two different mobile stations (MS1, MS2) when the system operates in full rate mode.
10. A method according to claims 1-4 c h a r a c t e r i z e d in that only one time slot (#1) in each frame (F1, F2,...) can be accessed and reserved for only one mobile station (MS1) when the system operates in a half rate mode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9100579-3 | 1991-02-28 | ||
| SE9100579A SE468031B (en) | 1991-02-28 | 1991-02-28 | PROCEDURES TO RECEIVE FROM A MOBILE STATION TO A RURAL MOBILE RADIO SYSTEM |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2060428A1 true CA2060428A1 (en) | 1992-08-29 |
Family
ID=20382005
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002060428A Abandoned CA2060428A1 (en) | 1991-02-28 | 1992-01-31 | Method of accessing a mobile radio land system from one of a number mobile stations |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH04320120A (en) |
| CA (1) | CA2060428A1 (en) |
| MX (1) | MX9200848A (en) |
| SE (1) | SE468031B (en) |
| TW (1) | TW201374B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0587980A2 (en) * | 1992-09-18 | 1994-03-23 | Roke Manor Research Limited | Improvements in or relating to cellular mobile radio systems |
| US5570467A (en) * | 1993-11-01 | 1996-10-29 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for locating a digital control channel in a radiocommunication system |
| US5610917A (en) * | 1993-04-19 | 1997-03-11 | Ericsson Inc. | Layer 2 protocol for the random access channel and the access response channel |
| US5655215A (en) * | 1993-11-01 | 1997-08-05 | Telefonaktiebolaget Lm Ericsson | Layer 2 protocol in a cellular communication system |
| US5689503A (en) * | 1994-07-15 | 1997-11-18 | Ntt Mobile Communications Network Inc. | Random access system of a mobile communication system |
| US5722078A (en) * | 1993-11-01 | 1998-02-24 | Ericsson Inc. | Method and apparatus for locating a digital control channel in a downbanded cellular radiocommunication system |
| US6175557B1 (en) | 1994-10-31 | 2001-01-16 | Telefonaktiebolaget Lm Ericsson (Publ) | Layer 2 protocol in a cellular communication system |
-
1991
- 1991-02-28 SE SE9100579A patent/SE468031B/en not_active IP Right Cessation
-
1992
- 1992-01-31 CA CA002060428A patent/CA2060428A1/en not_active Abandoned
- 1992-01-31 TW TW81100761A patent/TW201374B/zh active
- 1992-02-27 JP JP4156892A patent/JPH04320120A/en active Pending
- 1992-02-27 MX MX9200848A patent/MX9200848A/en unknown
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0587980A2 (en) * | 1992-09-18 | 1994-03-23 | Roke Manor Research Limited | Improvements in or relating to cellular mobile radio systems |
| EP0587980A3 (en) * | 1992-09-18 | 1995-04-05 | Roke Manor Research | Improvements in or relating to cellular mobile radio systems. |
| US5610917A (en) * | 1993-04-19 | 1997-03-11 | Ericsson Inc. | Layer 2 protocol for the random access channel and the access response channel |
| US5570467A (en) * | 1993-11-01 | 1996-10-29 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for locating a digital control channel in a radiocommunication system |
| US5655215A (en) * | 1993-11-01 | 1997-08-05 | Telefonaktiebolaget Lm Ericsson | Layer 2 protocol in a cellular communication system |
| US5722078A (en) * | 1993-11-01 | 1998-02-24 | Ericsson Inc. | Method and apparatus for locating a digital control channel in a downbanded cellular radiocommunication system |
| US5734645A (en) * | 1993-11-01 | 1998-03-31 | Telefonaktiebolaget Lm Ericsson | Layer 2 protocol in a cellular communication system |
| US5923649A (en) * | 1993-11-01 | 1999-07-13 | Telefonaktiebolaget Lm Ericsson | Layer 2 protocol in a cellular communication system |
| US5970057A (en) * | 1993-11-01 | 1999-10-19 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for distinguishing between a digital control channel and a digital traffic channel in a radiocommunication system |
| US6058108A (en) * | 1993-11-01 | 2000-05-02 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for locating a digital control channel in a radiocommunication system |
| US5689503A (en) * | 1994-07-15 | 1997-11-18 | Ntt Mobile Communications Network Inc. | Random access system of a mobile communication system |
| US6175557B1 (en) | 1994-10-31 | 2001-01-16 | Telefonaktiebolaget Lm Ericsson (Publ) | Layer 2 protocol in a cellular communication system |
Also Published As
| Publication number | Publication date |
|---|---|
| SE9100579D0 (en) | 1991-02-28 |
| SE9100579L (en) | 1992-08-29 |
| SE468031B (en) | 1992-10-19 |
| JPH04320120A (en) | 1992-11-10 |
| MX9200848A (en) | 1992-09-01 |
| TW201374B (en) | 1993-03-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19940731 |