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
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W56/00—Synchronisation arrangements
  • H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
  • H04W56/0045—Synchronisation arrangements compensating for timing error of reception due to propagation delay compensating for timing error by altering transmission time
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0072—Transmission or use of information for re-establishing the radio link of resource information of target access point
• • 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
  • H04W56/009—Closed loop measurements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/08—Reselecting an access point

Definitions

• the present invention relates generally to a method of synchronizing with an uplink channel and a method of determining a propagation delay in a wireless communications system.
• UMTS is a wireless data communication and telephony standard which describes a set of protocol standards.
• UMTS sets forth the protocol standards for the transmission of voice and data between a base station (BS) or Node B and a mobile or user equipment (UE).
• UMTS systems typically include multiple radio network controllers (RNCs).
• the RNC in UMTS networks provides functions equivalent to the base station controller (BSC) functions in GSM/GPRS networks.
• BSC base station controller
• RNCs may have further capabilities including, for example, autonomously managing handovers without involving mobile switching centers (MSCs) and serving general packet radio service (GPRS) support nodes (SGSNs].
• the Node B is responsible for air interface processing and some radio resource management functions.
• Figure 1 illustrates a conventional communication system 100 operating in accordance with UMTS protocols.
• the communication system 100 may include a number of Node Bs such as Node Bs 120, 122 and 124, each serving the communication needs of UEs such as UEs 105 and 110 in their respective coverage area.
• the Node Bs are connected to an RNC such as RNCs 130 and 132, and the RNCs are connected to a MSC/SGSN 140.
• the RNC handles certain call and data handling functions, such as, as discussed above, autonomously managing handovers without involving MSCs and SGSNs.
• BSR base station router
• a BSR collapses, among other functions, the functionality of a RNC and a base station (or Node B) into a single processing entity, thereby reducing latency (e.g., because the Iu interface is eliminated).
• BSRs are, for example, described in U.S. Patent Application No. 11,094,436 and U.S. Patent Application No. 11,094,430, each filed on March 31, 2005. Since latency is greatly reduced with the BSR structure, BSRs often employ hard handoff as opposed to the above described soft handoff approach.
• a hard-handover procedure typically involves sending a layer-3 control message to a UE indicating the channel parameters for the new channel.
• the layer-3 control message may contain one or more of a downlink channelization codes, a downlink scrambling code, an uplink channelization code and an uplink scrambling code.
• the UE e.g., UE 105
• the UE 105 ceases communication on the old channel and begins searching for a new downlink channel associated with the new Node B (e.g., Node B 122).
• the UE 105 transmits to the new Node B 122 in accordance with the channelization parameters indicated by the layer- 3 control message.
• the uplink chip offset is related to the above-described downlink chip offset.
• each radio channel is divided into fixed length time intervals; for example, a Transmission Time Interval (TTI) having 15 slots each with 2560 chips.
• TTI may have a fixed duration (e.g., 10 milliseconds (ms)).
• An uplink channel's TTI starts 1024 chips after reception by the mobile of a downlink channel's TTI. Additionally, the uplink TTI does not begin until the downlink is synchronized by the mobile. Thus, the uplink TTl begins after the downlink is synchronized.
• the chip search ranges can be substantial in UMTS systems, and base stations in UMTS systems typically do not include processors fast enough to perform real-time searching. In other words, larger chip search spaces generate a larger lag, which increases the processing time required for the Node B to synchronize with the uplink TTT, and increases radio outage lengths.
• the mobile is not informed of when the base station is synchronized with the uplink TTI. Rather, the mobile simply begins transmitting data as soon as it is able without taking the base station's synchronization into account.
• data packets transmitted by the mobile may be lost if they arrive at the base station before the base station is synchronized.
• Transmitted data packets which are lost during the above- described search procedure, are then retransmitted at a higher protocol layer. This retransmission of lost data packets may cause latency effects in the uplink (e.g., between 120 to 340 ms).
• Another example embodiment of the present invention is directed to a method of- calculating a propagation delay between a target base station and a mobile station in a wireless communications system, including first receiving a first signal indicating a first measured chip offset between a downlink channel of a serving base station and a pilot signal of the target base station, second receiving a second signal indicating a second measured chip offset between an uplink channel of the mobile station and a pilot signal of the target base station and calculating the propagation delay between the target base station and the mobile station based at least in part on the first and second measured chip offsets.
• Figure 1 illustrates a conventional communication system operating in accordance with UMTS protocols.
• Figure 2 is a flow chart illustrating a process for synchronizing a target
• the RNC 130 After calculating the propagation delay in step S203, the RNC 130 sends the calculated propagation delay to the target Node B 122 in step S205.
• the target Node B 122 uses the received propagation delay to synchronize with the UE 105 in step S207.
• the Node B 122 has no knowledge of the propagation delay between the Node B 122 and the UE 105, and as such, must "search" or analyze a large number of chips for establishing synchronization.
• the Node B 122 is then synchronized with the UE 105 at the start of the new TTl.
• the UE 105 periodically transmits a measurement report to the RNC 130 as part of a layer- 3 control message.
• the layer-3 control message Indicates each pilot signal which the UE 105 is able to decode, a signal strength associated with each of the pilot signals accessible to the UE 105 and a chip offset indicator indicating a chip offset of the UE 105's data downlink with respect to the accessible pilot signals.
• the current serving Node B 120 is able to calculate the propagation delay between the Node B 120 and the UE 105 by measuring when the uplink arrives at the Node B 120 with respect to downlink transmissions sent by the Node B 120 to the UE 105.
• the RNC 130 may then calculate the propagation delay between the target Node B and the UE 105 based on the periodic measurement report sent by the UE 105 and the measured chip difference between the old uplink and the pilot of the target Node B 122 sent by the target Node B 122. To explain these calculations, the variables shown in Table 1 (below) will be used.
• the UE 105 maintains connectivity with the current serving Node B 120 or Bi with respect to P 1 , Di and Ui.
• the propagation delay value rti is calculated by the base-band coder at the current serving Node B 120 or Bi.
• the chip offset Cl for the current serving Node B 120 is expressed as:
• the UE 105 periodically reports the difference in chip offsets between the downlink and the pilot of the target Node B 122, which may be expressed as:
• rake fingers at the target Node B 122 may be spread within a given drift threshold of the expected chip arrival time of the uplink. If the drift exceeds the drift threshold compensated for by the spreading of the rake fingers, the conventional full search process may be employed by the target Node B 122, and any lost packets are retransmitted in a conventional fashion at a higher layer protocol. Thus, drift is one reason why the rake fingers may be spread in proximity to the expected arrival time of the next TTT.

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

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Publications (1)

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Citations (3)

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• 2005
  • 2005-12-28 US US11/318,467 patent/US8089938B2/en not_active Expired - Fee Related
• 2006
  • 2006-12-15 EP EP06845517.9A patent/EP1967033B1/en not_active Not-in-force
  • 2006-12-15 CN CN200680049338.XA patent/CN101347031B/zh not_active Expired - Fee Related
  • 2006-12-15 JP JP2008548577A patent/JP5039711B2/ja not_active Expired - Fee Related
  • 2006-12-15 KR KR1020087014828A patent/KR101407453B1/ko not_active Expired - Fee Related
  • 2006-12-15 WO PCT/US2006/047881 patent/WO2007078872A1/en not_active Ceased

Patent Citations (3)

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