Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2662—Arrangements for Wireless System Synchronisation
  • H04B7/2671—Arrangements for Wireless Time-Division Multiple Access [TDMA] System Synchronisation
  • H04B7/2678—Time synchronisation
  • H04B7/2681—Synchronisation of a mobile station with one base station
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0602—Systems characterised by the synchronising information used
  • H04J3/0605—Special codes used as synchronising signal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W56/00—Synchronisation arrangements
  • H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
  • H04W56/0065—Synchronisation arrangements determining timing error of reception due to propagation delay using measurement of signal travel time
  • H04W56/007—Open loop measurement
  • H04W56/0075—Open loop measurement based on arrival time vs. expected arrival time
  • H04W56/0085—Open loop measurement based on arrival time vs. expected arrival time detecting a given structure in the signal

Definitions

• the invention relates to a method and a radio communication system for the synchronization of subscriber stations, in particular a mobile radio system.
• radio communication systems information (for example voice, picture information or other data) is transmitted with the aid of electromagnetic waves via a radio interface.
• the radio interface relates to a connection between a base station and subscriber stations, it being possible for the subscriber stations to be mobile stations or fixed radio stations.
• the electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system.
• UMTS Universal Mobile Telecommunication System
• 3rd generation systems frequencies in the frequency band of approx. 2000 MHz are provided.
• FIG. 4.1 has a time frame with time slots arranged therein, which can optionally be used for signal transmission in the downward direction or in the upward direction.
• a physical transmission channel in the first time slot for the downward direction is used for the transmission of a general my signaling channel (CCPCH - P ⁇ mary Common Control
• the first time slot for the Aufwarts ichtung is for ei ⁇ nen access signaling channel (PRACH - used physical random access channel).
• PRACH physical random access channel
• a protection time (G2) between the time slots for the downward direction and for the upward direction is specified, which enables the transmission device of a subscriber station that is attempting to set up a connection to be synchronized with the base station.
• This protection time allows a longer maximum distance between the base station and the subscriber stations due to an extended processing time.
• Another guard time (Gl) before the first time slot for the waiting direction is used for a transition between the reception case and the transmission case in the base station.
• This radio communication system is based on a synchronization of the received signals from several subscriber stations m of the base station in order to ensure the orthogonal properties of the spreading codes (CDMA codes) and to reduce any interference that occurs between several neighboring physical transmission channels in the time slots for the uplink direction. Since the capacity of a CDMA radio communication system is mainly limited by the interference between adjacent channels, inter alia, the known CDMA mobile radio system IS-95 uses a fast transmission power control for the uplink direction to limit the interference. Such a rapid transmission power control can be used in the NEN TD-SCDMA system, because of the advantageous Synchronitat be seen from ⁇ without occurs that a degradation of the Systemkapazi- did.
• the invention is based on the object of specifying a method and a radio communication system which, based on a radio communication system with a TDD method, enable the reception of subscriber signals to be synchronized at the location of the base station.
• m is a radio communication system which uses a radio interface organized according to a TDD method with a plurality of time slots, each forming a time frame, the transmission in the downward direction from a base station to subscriber stations and in the upward direction from the subscriber stations to the base station being separated in time an identical frequency band takes place, before or after a last time slot for the downward direction from the base station, at least one first synchronization sequence is sent to the subscriber stations, and the subscriber stations take the first synchronization sequence into account for synchronization.
• the first synchronization sequence may, for m a specifically the time frames m provided first time field from the base station ⁇ sent.
• This arrangement according to the invention for sending a first synchronization sequence in the downward direction in the time frame has the advantage over an exemplary arrangement at the beginning of the time frame that the synchronization sequence has no negative influence on the reception of signals in the subsequent time slots for the downward direction. If, for example, a respective first synchronization sequence is sent from neighboring base stations in parallel, they are received with a different delay depending on the distance from the base stations to the receiving subscriber station, and may overlap with signals sent in the first time slot for the downward direction, what leads to increased interference and reduces the receiving excitement. In order to compensate for this degradation of the receiving quality, the first synchronization sequence had to be taken into account, for example, in a Jomt detection algorithm, which disadvantageously makes the subscriber station more complex.
• a subscriber station performing an attempt to establish a connection uses this first synchronization sequence, which, for example, has a symbol sequence known to the subscriber station and is transmitted with an increased transmission power in order to determine the end of the time slots transmitted in the downward direction or the start of the first time slot in the upward direction. Furthermore, this sequence can be used for the selection of a suitable base station for establishing a connection. Since no further signal transmission takes place in this first time field, this results in rapid synchronization of the subscriber station. At the same time, the subscriber station can make a first estimate regarding the distance to the base station from the relationship between the
• the first synchronization sequence can also be arranged before the last time slot for the downward direction.
• the position of the first time slot for the upward direction within the time frame can advantageously be determined in the same way by the subscriber station.
• This arrangement of the first synchronization sequence in the time frame advantageously enables a subscriber station, which is located, for example, at the radio cell boundary and has been assigned a transmission channel in the first time slot for the uplink direction, to be able to transmit further first synchronization sequences from neighboring ones To receive and evaluate base stations before it starts transmitting in the uplink direction.
• the subscriber station Since the first synchronization sequences of the further base stations may be received by the subscriber station with a greater time delay, but these have to be evaluated in the subscriber station with regard to a possible transfer of the connection, the subscriber station has a larger time field for receiving the first synchronization sequences.
• the described problem can be solved by the subscriber station initiating an intercell handover for the signal transmission in the waiting direction, in which one or more transmission channels m be assigned to another time slot for the upward direction.
• this solution requires a nacnturban size ⁇ ren signaling overhead and unacceptable under certain circumstances delay.
• a first guard time is provided in the first time field.
• This additional signal-free time field ensures that a subscriber station that receives signals in the preceding or following time slot for the downward direction does not have to take the first synchronization sequence into account for the detection or the first synchronization sequence has no negative influence on the receiving act. This case can occur, for example, when processing an exceptionally long channel impulse response in the subscriber station and a possible temporal overlap of several signals.
• a separation time is provided between the time slots for the downward and upward directions.
• This separation time contains no information and is used by the base station for a transition from the send to the receive case.
• the separation time is used by the subscriber station carrying out a connection establishment attempt, since the subscriber station does not yet have precise knowledge of the distance to the base station and the necessary lead time in order to ensure that the transmitted signals arrive synchronously at the location of the base station.
• the separation time enables subscriber stations that are located at a great distance from the base station to send signals in the waiting direction prematurely in comparison to subscriber stations at a shorter distance.
• the length of the separation time corresponds, for example, to twice the maximum signal transit time plus an entire one internal processing time. This length also determines the maximum radius of the radio cell of the base station.
• the separation time is kept constant on the part of the base station, during which the separation time on the part of the subscriber stations is individually shortened by the specific tent for early transmission.
• the subscriber station carrying out the connection establishment attempt signals a connection establishment request in an access signaling channel in a first time slot for the uplink direction to the base station.
• This access signaling channel can be arranged, for example, in a specific, fixedly allocated transmission channel of the first tent slot.
• the subscriber station sends at least one second synchronization sequence before the first time slot for the upward direction.
• a specific second time field can be provided for this, or the second synchronization sequence is sent in the separation time.
• a second guard time is provided after the second synchronization sequence or after the second time field.
• the second synchronization sequence is used in the base station for synchronization with the time structure of the subscriber station.
• the base station for example, despreads the information sent by the subscriber station in the access signaling channel with regard to the connection establishment request, the signals being correlated with the known spreading codes and thereby determining the spreading code used by the subscriber station can be.
• the base station is subsequently able to provide the information to evaluate the subscriber station, it signals the subscriber station in a subsequent time slot for the downward direction, for example information relating to a service channel to be used or a directly assigned transmission channel, an exact adjustment of the synchronization and an adjustment of the transmission power.
• a channel can advantageously be assigned by the base station indicating the time slot relative to the first synchronization sequence.
• a third synchronization sequence is sent in the time slots for the upward direction by the subscriber stations, which is used by the base station, for example, to estimate the required lead time.
• a specific third time field is provided for the time slots, which represents the start of the respective time slot, for example.
• the third synchronization sequence is only sent by one subscriber station to a time slot, so that the base station in each time slot only has to evaluate a third sequence.
• the subscriber stations successively send the third synchronization sequence from time frame to time frame.
• the third time field can be omitted, for example, since this channel is only used for establishing a connection and is not permanently assigned to a connection.
• the second guard time between the transmission of the second synchronization sequence and the beginning of the first time slot for the upward direction with the third time field for the third synchronization chronisationssequenz ensures that no adverse In ⁇ terferenz occurs between the signals of the sequences at the location of the base station.
• This case may th example occurring defects ⁇ , when the subscriber station is less than the real distance to the base station estimates and the second Syncnroni- sationssequenz with an insufficient derivative tent sen ⁇ det, whereby the channel impulse response of the second Synchronisati ⁇ onssequenz m disadvantageous in time to the first time slot protrudes for upward direction.
• the base station transmits at least one general signaling channel in the last time slot for the downward direction.
• This advantageously defines the position of this general signaling channel in relation to the first synchronization sequence, independently of a current number of time slots used for the downward direction, so that the subscriber station can quickly access this general signaling channel.
• the general signaling channel can also contain an indication of the current configuration of the time slots used for the downward and upward directions, so that the subscriber station can determine the start of a time frame.
• the first synchronization sequences of the surrounding base stations can be received by the subscriber station. Relative to this first synchronization sequence, the subscriber station can immediately see the positions of the separation time, the first time slot for the upward direction and determine the general signaling channel since this configuration is identical to the entire network.
• FIG. 1 shows a block diagram of a radio communication system, in particular a mobile radio system
• FIG 3 shows a flowchart of a method according to the invention in connection construction.
• the mobile radio system shown in FIG. 1 as an example of a radio communication system consists of a large number of mobile switching centers MSC which are networked with one another or which provide access to a fixed network PSTN. Furthermore, these mobile switching centers MSC are each connected to at least one device RNC for allocating radio resources. Each of these devices RNC in turn enables a connection to at least one base station BS. Such a base station BS can establish a connection to further radio stations, for example mobile stations MS or other mobile and stationary terminals, via a radio interface. At least one radio cell is formed by each base station BS. The size of the radio cell is generally determined by the range of the general organization channel BCCH, which is transmitted by the base stations BS with a maximum transmission power in each case. In the case of sectorization or hierarchical cell structures, several radio cells are also supplied per base station BS. An operation and maintenance center OMC implements control and maintenance functions for the mobile radio system or for parts of. The functionality of this structure is based on other radio
• the frame structure of the radio transmission in TDD mode can be seen from FIG. 2.
• a TDMA component time division multiple access
• a frequency band B extends over a certain frequency range. Part of the time slots is used in the downward direction DL and part of the time slots in the upward direction UL.
• An asymmetry ratio of 3: 2 in favor of the downward direction DL is shown as an example.
• the frequency band B for the upward direction UL corresponds to the frequency band B for the downward direction DL. The same is repeated for other carrier frequencies.
• the data d are spread individually for each connection with a fine structure, a spreading code c, so that, for example, n connections can be separated at the receiving end by this CDMA component (code division multiple access).
• the spreading of individual symbols of the data d has the effect that within the symbol duration t sym Q
• Chips of the duration t ch ⁇ p are transmitted.
• the Q chips form the connection-specific spreading code c.
• Duration of a time slot 500 ⁇ s
• Modulation type DQPSK or 16QAM bandwidth: 1.4 MHz
• a switchover point SP is provided between the time slots for the downlink DL and for the uplink direction UL, which the subscriber stations MS or the base station BS use for the transition between reception case and transmission case or vice versa.
• the period around the switchover point is shown as an example below the general structure diagram of the radio interface. All configurations according to the invention are specified here. The following information regarding the parameters and the respective number of symbols are examples which can be adapted in terms of the technical implementation or in terms of harmonization with other systems.
• the two time slots ts are only shown as a detail in FIG. 2, the general structure of a time slot zes for the upward direction UL is disclosed in the lower area of FIG.
• a separation time of 12 g symbols Before the separation time g, a first time field zfl with 4 symbols is provided, which the base station BS uses to send a first synchronization sequence syncl.
• the first time field zfl is preceded by a first guard time gpl of 2 symbols.
• a second time field zf2 of 3 symbols is provided, which is used by a subscriber station MS attempting to establish a connection to signal a connection establishment request.
• the second time field zf2 can alternatively also be integrated into the separation time g.
• a second guard time gp2 of 2 symbols can be provided after the second time field zf2.
• a third time field zf3 of 2 symbols is provided in the first time slot ts and in all further time slots ts for the upward direction UL, which is used alternately by the subscriber stations MS for signaling a third synchronization sequence sync.
• the third synchronization sequence sync3 is used by the base station BS to regulate the lead time.
• the first time field zfl is arranged before the last time slot ts for the downward direction DL, which, for example, is provided by a first protection time gpl is framed in order to avoid interference with the surrounding time slots ts.
• the Separati ⁇ onszeit g in this example follows immediately the last time slot ts for the downlink direction DL.
• the structure of a time slot ts for the upward direction UL has, in addition to the described third time field zf3 for the third synchronization sequence sync3, two data blocks with 16 symbols each and a training sequence tseq with a length of 8 m known to the base station BS, which are used for channel estimation .
• the time slot ts is concluded with a third protection time gp3 of 0.5 symbols to compensate for different signal propagation times of the connections in successive time slots ts.
• a time slot ts for the downward direction DL corresponds to this structure except for the third time field zf3, it being possible for the symbols not used due to the absence of the third time field zf3 to be used, for example, additionally for data transmission or for an extension of the training sequence tseq.
• FIG. 3 shows a flow chart of the method according to the invention, in which an attempt to establish a connection is carried out by a subscriber station MS as an example.
• the base station BS periodically sends a general signaling channel BCCH and a first synchronization sequence syncl m downward direction DL in accordance with the structure described in FIG.
• Both the general signaling channel BCCH and the first synchronization sequence syncl are transmitted with an increased transmission power compared to normal traffic connections, in order to also include subscriber station MS at a large distance from the base station BS. for example, at the radio cell edge to ensure adequate reception quality.
• the first synchronization sequence syncl m is determined by the subscriber station MS, which does not yet have a communication link via the base station BS, since the symbol sequence of the subscriber station MS is known per se, and a first synchronization to the time structure by means of the syncl sequence the base station BS performed. Since the subscriber station MS does not know the distance to the base station BS and thus the signal transit time, it continues to carry out a rough estimate of the current distance using, for example, the reception strength of the first synchronization sequence syncl. On the basis of the fixed positions m of FIG. 2 of the separation time g, the general signaling channel BCCH and the access signaling channel R ⁇ CH relative to the first synchronization sequence syncl, the subscriber station MS can, for example, directly determine the position of the general signaling channel BCCH and evaluate its information.
• a statistical calculation model should also compare the reception power and / or reception times of signals from several base stations (if the reception time - time frame start - of signals from two base stations is the same, the subscriber station is probably located at the cell edge), the previously used lead times ( eg with previous connections or previous transmissions within a packet data connection), a trend in the development of the connections to the same base station, the cell size, path damping of the radio interface, the position of the subscriber station within a radio cell and an estimated channel impulse response (signal strength and time) of the transmissions of the base station in the subscriber station.
• a lead time with a low probability of collision should be selected in comparison to repeated transmissions for packet data transmission.
• the collision probability is an image of the probability that other subscriber stations MS will also transmit in the access signaling channel R ⁇ CH and that the transmissions will overlap at the receiving base station BS.
• the collisions can be caused by transmissions in other time slots ts.
• the likelihood of a collision can be reduced by choosing different second synchronization sequences sync2, multiple transmission per time slot and a transmission power that leads to larger reception power differences at the receiving base station BS (capture effect).
• the time of transmission and thus the selected lead time also play a decisive role.
• the subscriber station MS Since the second synchronization sequences sync2 are rather short in comparison to the time slot length, the subscriber station MS sometimes has a large selection of acceptable tent to choose from. A lead time should then be selected that is not likely to be accessible to other subscriber stations. In the case of packet data services with a plurality of sequences separated in time in a time slot, one of the honor tents TA can be assigned by the base station BS. The distance from the subscriber station MS to the base station also plays a role. A subscriber station MS at the radio cell edge has a limited scope, since an excessively long lead time may already result in the subscriber station MS being sent at a time at which subscriber stations MS still want to receive transmissions from the base station BS. In contrast, a subscriber station MS has a number of lead time values to choose from in the middle of the cell.
• Case 1 The subscriber station MS is in the middle of the cell.
• Case 2 The subscriber station MS is at a maximum distance from the base station BS.
• the second synchronization sequence sync2 collides with the transmissions of the first time slot ts for the waiting direction UL.
• the subscriber station MS After a positive decision about the selection of the base station BS - the subscriber station MS generally selects the base station BS whose first synchronization sequence syncl it receives with the greatest reception strength - and the subscriber station MS sends one, knowing the position of the second time field zf2 second synchronization sequence sync2 to the base station BS. It uses the roughly determined distance to the base station BS to set a sufficient lead time (Timmg Advance). It then sends signals in the access signaling channel R ⁇ CH to the base station BS about the connection setup request. Based on the second synchronization sequence sync2, the base station BS recognizes that a subscriber station MS is attempting to establish a connection and uses the sequence sync2 to synchronize with it and then evaluate the RACH.
• the base station BS If the base station BS is able to evaluate the content of the RACH and to assign a transmission channel, it signals this to the subscriber station MS by means of a special confirmation signaling.
• the confirmation signaling can include, for example, information about time slots ts and spreading codes c to be used in each case upward UL and downward direction DL, as well as information regarding a more precise synchronization and transmission power control, or refer to a special service channel on which a further signaling exchange for the establishment of the connection occur can.
• the base station BS can signal an indication of the relative distance to the first synchronization sequence syncl.
• the subscriber station MS After a successful connection establishment, the subscriber station MS periodically sends a third synchronization sequence sync3 to the base station BS, which is used by the base station BS to control the synchronization of the subscriber station MS.
• the periodicity of the transmission of the third synchronization sequence sync3 can be controlled, for example, in such a way that only the subscriber station MS sends the sequence whose spread code number corresponds to a current time frame number.
• the transmission of the sequence sync3 can also be requested, for example, as a function of a respectively determined speed of the subscriber stations MS from the base station BS, a fast-moving subscriber station MS transmitting the sequence sync3 at shorter intervals than a quasi-stationary subscriber station MS due to a rapidly varying signal propagation time .

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• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

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• 1999
  • 1999-04-09 DE DE1999116063 patent/DE19916063C1/de not_active Expired - Lifetime
• 2000
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  • 2000-04-03 CN CN 00806058 patent/CN1185808C/zh not_active Expired - Fee Related
  • 2000-04-03 WO PCT/DE2000/001008 patent/WO2000062445A1/de active Application Filing

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