Method and system for tracking timing drift in multiple frequency hypothesis testing

#Certain embodiments of the invention relate to communication systems. More specifically, certain embodiments of the invention relate to a method and system for tracking timing drift in multiple frequency hypothesis testing.

#Various communication standards such as Evolved Universal Terrestrial Radio Access (E-UTRA), also called Long Term Evolution (LTE), have been developed to offer comparatively high data rates to support high quality services. LTE is a Third Generation Partnership Project (3GPP) standard that provides for an uplink speed of up to 50 megabits per second (Mbps) and a downlink speed of up to 100 Mbps. The LTE/E-UTRA standard represents a major advance in cellular technology. The LTE/E-UTRA standard is designed to meet current and future carrier needs for high-speed data and media transport as well as high-capacity voice support. The LTE/E-UTRA standard brings many technical benefits to cellular networks, some of which include the benefits provided by Orthogonal Frequency Division Multiplexing (OFDM) and/or Multiple Input Multiple Output (MIMO) data communication. In addition, Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) are used on the downlink (DL) and on the uplink (UL), respectively.

#Mobility management represents an important aspect of the LTE/E-UTRA standard. As a mobile device, also called user equipment (UE) in the LTE/E-UTRA standard, moves within an LTE/E-UTRA coverage area, the use of synchronization signal transmissions and cell search procedures provide a basis for the mobile device or UE to detect and synchronize with individual cells. To communicate with a particular cell, mobile devices in associated LTE/E-UTRA coverage area needs to determine one or more cell specific transmission parameters such as, for example, symbol timing, radio frame timing, and/or a cell ID. In the LTE/E-UTRA standard, the cell-specific information is carried by reference, broadcast, and/or synchronization signals. The latter forms the basis for downlink (DL) synchronization and cell specific information identification at the mobile devices within the associated LTE/E-UTRA coverage area. Two downlink (DL) synchronization signals, namely Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS), are used to allow the mobile devices to synchronize to transmission timing of the particular cell, and thereby obtain cell specific information such as full physical Cell ID, and/or a Cell ID group indicator.

#FIG. 1 is a diagram illustrating an exemplary wireless communication system that is operable to track and compensate timing drift in multiple frequency hypothesis testing (MFHT), in accordance with an embodiment of the invention.

#FIG. 2 is a block diagram of an exemplary downlink synchronization signal structure, which is utilized in accordance with an embodiment of the invention.

#FIG. 3 is a block diagram of an exemplary mobile device that may be operable to track and provide compensation for timing drift in multiple frequency hypothesis testing (MFHT), in accordance with an embodiment of the invention.

#Certain embodiments of the invention may be found in a method and system for tracking timing drift in multiple frequency hypothesis testing. A mobile device is operable to receive a radio frequency (RF) signal from an associated base station. The received signal may comprise a PSS and a SSS, which may be used by the mobile device to acquire cell-specific parameters. In this regard, the mobile device may perform multiple frequency hypothesis testing (MFHT) on a corresponding baseband signal for the received RF signal. The mobile device may start MFHT by applying different initial frequency offsets to corresponding MFH branches. Compensation may be provided for timing drift in MFHT based on the initial frequency offsets that are applied to the corresponding MFH branches. A PSS correlation process on the baseband signal is performed in each MFH branch. Resulting PSS correlation data may be buffered and processed in corresponding PSS timing hypothesis buffers. The timing position of samples in the PSS timing hypothesis buffers may be updated based on initial frequency offsets applied to corresponding MFH branches. The timing positions or sampling positions for samples in the PSS timing hypothesis buffers refer to positions at which magnitudes of the buffered PSS correlation data are accumulated in the corresponding PSS timing hypothesis buffers. A rate at which the timing positions of samples in the PSS timing hypothesis buffers are updated may be determined by the initial frequency offsets that are applied to the corresponding MFH branches. For example, for a MFH branch with an initial frequency offset of 2 ppm, the timing position of samples in corresponding PSS timing hypothesis buffers is updated once every five hundred thousand samples. The timing position of samples in the PSS timing hypothesis buffers may be shifted or updated to advance or retard timing depending on the sign of the initial applied frequency offsets. For example, for positive initial frequency offsets, the timing position of samples in the PSS timing hypothesis buffers may be shifted or updated to retard or delay timing. For negative initial frequency offsets, the timing position of samples in the PSS timing hypothesis buffers may be shifted or updated to advance timing. Energy associated with the PSS transmissions may be accumulated in each MFH branch utilizing corresponding PSS correlation data at updated sampling positions. The received PSS may be detected based on a maximum accumulated energy associated with the PSS transmissions. The mobile device may utilize information that comes from the detected PSS to start camping on a corresponding cell.

#FIG. 1 is a diagram illustrating an exemplary wireless communication system that is operable to track and compensate timing drift in multiple frequency hypothesis testing (MFHT), in accordance with an embodiment of the invention. Referring to FIG. 1, there is shown a wireless communication system 100. The wireless communication system 100 comprises a plurality of cells, of which cells 110-120 are displayed. A coverage area 130 is the overlapped coverage area of the cell 110 and the cell 120. The cell 110 and the cell 120 are geographic areas served by a base station 110a and a base station 120a, respectively. The wireless communication system 100 comprises a plurality of mobile devices, of which mobile devices 110-126 are illustrated. The mobile devices 112-116 are shown located in the cell 110. The mobile devices 122-126 are shown located in the cell 120. The mobile device 118 and the mobile device 119 are shown located in the overlapped coverage area 130.

#A base station such as the base station 110a may comprise suitable logic, circuitry, interfaces and/or code that are operable to manage various aspects of communication, for example, communication connection establishment, connection maintenance and/or connection termination, with associated mobile devices within the cell 110. The base station 110a may be operable to manage associated radio resources such as, for example, radio bearer control, radio admission control, connection mobility control, and/or dynamic allocation of radio resources within the cell 110 in both uplink and downlink communication. The base station 110a may be operable to utilize physical channels and physical signals for communications in both the uplink and the downlink communication. The physical channels may carry information from higher layers to communicate user data as well as user control information. The physical signals such as reference signals and synchronization signals may not carry information from higher layers. Reference signals from the base station 110a may be utilized by mobile devices in the cell 110 to determine channel impulse responses (CIRs). A specified reference signal is assigned to each cell within a network and acts as a cell-specific identifier. Synchronization signals may comprise primary secondary synchronization sequences (PSS) and secondary synchronization sequences (SSS). For example, in E-UTRA/LTE, the base station 110a may be operable to repeatedly transmit the PSS and the SSS in every repetition interval, for example, 5 ms, in the last two OFDM symbols of the first and eleventh slot in each radio frame. The PSS is chosen from a variety of Zadhoff-Chu sequences, carrying the information of the identity of the base station or cell within a cell group. The SSS is a sequence carrying the information about the cell group, encoded with a scrambling sequence, which is unique to an associated mobile device. The scrambling code may be linked or mapped to, for example, the index of the PSS. After successful time and frequency synchronization via the PSS, the frame boundary synchronization and/or the cell identification may be performed via SSS detection. The transmission of the PSS and the SSS may allow timing and frequency offset issues to be resolved before cell-specific information may be determined. This may reduce complexity in initial cell search and/or handover modes for associated mobile devices such as the mobile device 114 and the mobile device 118.