METHOD AND APPARATUS TO DERIVE SYSTEM TIMING AT A WIRELESS BASE STATION

Method and Apparatus to Derive System Timing at a Wireless Base transceiver Station (BTS). The present invention relates to wireless communication networks and, more particularly, to timing information in wireless communication networks. A method for providing reference timing to a BTS, the method comprising of the BTS sending a message to a network controller via a station, wherein the message requests for round trip delay time incurred by the message; the BTS estimating a timing offset from a response and determining the correction to be made to the reference timing using the timing offset due to the one way delay from the station transmitting the pilot signal, the actual PN offset at which the station transmits the pilot signal and the actual offset at which the pilot signal is received at the BTS; and the BTS making the correction to the reference timing.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments herein disclose a method and system to provide accurate reference timing to a base transceiver station (BTS). Referring now to the drawings, and more particularly toFIGS. 1 through 3, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.

FIG. 1depicts an integrated base transceiver station within a communication network, according to embodiments as disclosed herein. The figure as depicted comprises of an integrated BTS101, a plurality of base transceiver stations102, a network controller104and a plurality of mobile terminals103. The integrated BTS101may be a macro BTS, a femto base station or any device capable of acting as a base station. The integrated BTS101is connected to the other BTSs in a manner similar to a mobile terminal connecting to a BTS, where the mobile terminal is within the coverage area of the BTS. The integrated BTS101may be visible to a plurality of BTSs102at the same time. The integrated BTS101may also be connected to at least one mobile terminal103. The BTSs102may be connected to a network controller104. The BTSs102may be connected to more than one network controller; i.e., one or more BTSs may be connected to a first network controller104and other BTSs102visible to the integrated BTS101may be connected to a second network controller104. The BTSs102may also be integrated base stations101.

The integrated BTS101may communicate with one of the BTSs102. The integrated BTS101monitors the local wireless channel from that BTS102and may also communicate with the local wireless macro network. The integrated BTS101may request the network controller104using a message to provide round trip delay time of the message that was sent by the integrated BTS101to the network controller104via the BTS102. The BTS102forwards the message along with the round trip delay incurred by the message to the network controller104. The network controller104sends the round trip delay incurred by the message along with the identity of the BTS102(pilot PN offset assigned to BTS102—this is the same pilot PN offset that BTS102applies while transmitting the pilot signal over the air) to the integrated BTS101. The message containing the round trip delay time will be received by the integrated BTS101and the integrated BTS101will use the received round trip delay time to estimate a timing offset to the BTS102, where the timing offset is the offset at which the integrated BTS101should receive the pilot signal from the BTS102, if the integrated BTS101had an aligned clock. The integrated BTS101may monitor the pilot channel of the BTS102to determine the time the pilot signal is received from the BTS102. The integrated BTS101compares the timing offset with the timing offset at which the pilot signal is actually received to determine by how much time the internal clock of the integrated BTS101is adrift. The integrated BTS101may now align its internal clock (reference timing) with the system time. The integrated BTS101may now attempt to keep its internal clock accurate by repeating the procedures thus mentioned, keeping the timing offset of the broadcast pilot signal fixed.

FIG. 2depicts an integrated BTS, according to embodiments as disclosed herein. The integrated BTS101comprises of a BTS module207and a mobile module201. The integrated BTS101may further comprise of an accelerometer208. The mobile module201further comprises of a processor202, a transmitter203, a receiver204, a clock205and a memory206. The mobile module201enables the integrated BTS101to connect to other modules such as BTSs, integrated BTSs, and femto base stations in a manner similar to a mobile terminal connecting to a BTS/base station.

The processor202checks if a communication signal is present. The communication signal may be from a BTS102, a femto base station, an integrated BTS101which has reference timing or another integrated BTS101which has GPS time. If more than one communication signal is present, the processor202selects a communication signal as reference using a suitable means with the help of additional information. In another embodiment herein, the processor202may select more than communication signal as references. The suitable means may also be an appropriate server over the internet. The additional information may comprise of a priority list of carrier number, band class, pilots of candidate references and so on.

Consider that the processor202has selected a BTS102as reference. The processor202sends a signaling message to the network controller104via the BTS102using the transmitter203. The signaling message requests the network controller104to provide a round trip delay with respect to the integrated BTS101.

The processor202receives a response message from the network controller104via the BTS102and the receiver204, which comprises of the round trip delay of the signaling message received from the integrated BTS101. The response message may also comprise of a time reference quality indication which indicates how well the BTS102believes it is keeping time. The response message also comprises of the identity of the BTS102. The processor202computes the expected timing offset of at which the pilot signals from BTS102should be received from the round trip delay as present in the response message and stores the timing offset in the memory206. The processor202may compute the timing offset as the one way delay, which is half of the round trip delay. The processor202further monitors the paging/control channel of the BTS102to determine the time the pilot signal is received from the BTS102. The processor202compares the timing offset with the time the pilot signal is received to determine by how much time the internal clock of the integrated BTS101is offset. Once the processor202has determined the actual pilot offset of the BTS102, the processor202aligns its internal clock with the reference timing as provided by the BTS102, using the estimated timing offset, received pilot timing and the pilot offset. The processor202may store the reference timing in the clock205. In an embodiment herein, the processor202may keep its internal clock slaved to the pilot timing, while keeping the timing offset constant. The processor202may make further determinations of the internal clock, as required, on receiving a request from a mobile terminal103or at periodic intervals of time.

In an embodiment herein, if the accelerometer208detects that the integrated BTS101has moved, the accelerometer informs the movement to the processor202. The processor202may then make a determination of the adjustment that needs to be applied, due to the motion of the BTS101, to the internal clock.

In an embodiment herein, if the accelerometer208detects that the integrated BTS101has moved, the accelerometer informs the movement to the processor202. The processor202may then restart the operations.

In an embodiment herein, the frequency at which the processor202makes ping measurements is a function of the time reference quality provided by the BTS102.

In an embodiment herein, the processor102may send signaling messages to a plurality of references, where the references may be a BTS102, a femto base station which has reference timing, a femto base station which has GPS time, an integrated BTS101which has reference timing or another integrated BTS101which has GPS time. The processor202may then use filtering techniques to estimate timing offset for each reference. Kalman filters may be used for filtering by the processor202.

Embodiments as disclosed herein can be in conjunction with other means like NTP to align the internal clock of the integrated BTS101.

FIG. 3is a flowchart illustrating the process of estimating the system time, according to embodiments as disclosed herein. The integrated BTS101sends (301) a message to the reference BTS102, where the message may be a signaling message. The reference BTS102on receiving the signaling message computes (302) the round trip delay time incurred by the signaling message and sends (303) the signaling message along with the round trip delay to the network controller104. The network controller104then sends (304) the message comprising of the round trip delay time to the integrated BTS101. On receiving the message comprising of the round trip delay time from the network controller104via the BTS102, the integrated BTS101computes (305) the timing offset from the round trip delay as present in the response message and the PN offset. The integrated BTS101may compute the timing offset as the one way delay, which is half of the round trip delay. The integrated BTS101further monitors (306) the pilot channel of the reference BTS102. On the integrated BTS101receiving (307) the pilot signal from the reference BTS102, the integrated BTS101compares (308) the expected timing offset with the offset of the pilot signal received from the reference BTS102to compute (309) the adjustment required to be made to the reference timing by comparing the timing offset with the time the pilot signal is received. Once the integrated BTS102has determined the adjustment, the integrated BTS101applies (310) the correction to the reference timing. The various actions in method300may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed inFIG. 3may be omitted.

The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the network elements. The network elements shown inFIGS. 1 and 2include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.

Embodiments herein disclose a method and system to provide accurate reference timing to mobile terminals connected to a BTS. Therefore, it is understood that the scope of the protection is extended to such a program and in addition to a computer readable means having a message therein, such computer readable storage means contain program code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The method is implemented in a preferred embodiment through or together with a code written in e.g. Very high speed integrated circuit Hardware Description Language (VHDL) or any other coding language, or implemented by one or more VHDL or several software modules being executed on at least one hardware device. The hardware device can be any kind of device which can be programmed including e.g. any kind of computer like a server or a personal computer, or the like, or any combination thereof, e.g. one processor and two FPGAs. The device may also include means which could be e.g. hardware means like e.g. an ASIC, or a combination of hardware and software means, e.g. an ASIC and an FPGA, or at least one microprocessor and at least one memory with software modules located therein. The method embodiments described herein could be implemented in pure hardware or partly in hardware and partly in software. Alternatively, the invention may be implemented on different hardware devices, e.g. using a plurality of CPUs.