Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-11-09
2004-11-23
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S141000
Reexamination Certificate
active
06822999
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-speed cell searching apparatus and method for a communication system.
2. Background of the Related Art
In a direct sequence code division multiple access (DS/CDMA) communication system, a receiver is first required to synchronize PN sequences prior to detection of data. Mostly, the PN sequence synchronization is performed by two steps of code acquisition and code tracking in sequence.
Here, regarding the code acquisition, many researches have been made for a cell synchronous type system such as the existing IS-95 system whereby the whole cells share timing information using an external reference signal.
The most basic code acquisition-technique proposed up to now is a serial search. This method has an advantage that its implementation is not complex, but has a disadvantage that since the acquisition time is directly in proportion to the period of the PN sequence being used, it takes quite a long acquisition time in case that the period of the PN sequence is long.
Meanwhile, a parallel search has been proposed to acquire the PN sequences having a long period. However, this parallel search has a disadvantage that its implementation becomes complicated in proportion to the reduced acquisition time.
Ultimately, a hybrid method, which properly sacrifices and complements the acquisition speed and the complexity of implementation by adequately combining the serial search and the parallel search for the high-speed acquisition of the PN sequences, has been proposed, and another high-speed acquisition method based on state estimation of a shift register generator (SRG) has been proposed as well.
As the acquisition technique based on the state estimation of the SRG, there is a rapid acquisition by sequential estimation. This technique sequentially performs a hard detection of the received PN sequences a large number of times, carries them as temporary register state values of the receiving part SRG, and then finally decides whether or not it is synchronized through a confirming process. This technique has an advantage that it can greatly reduce the acquisition time without increasing the implementation complexity in comparison to the serial search in theory, but has a disadvantage that its performance abruptly deteriorates in case that it is based on a coherent detection of the PN sequences and has a low signal-to-noise ratio (SNR), and thus it is improper to apply it in a general code division multiple access (CDMA) environment.
Because of this, an acquisition technique based on a new state estimation named a distributed sample acquisition (DSA) technique has been proposed to reduce the acquisition time of the long-period PN sequences in the conventional cell synchronous type system.
According to this DSA technique, the transmitting part generates an igniter sequence having a relatively short period, and transmits the igniter sequence with state samples of the long-period PN sequences being carried thereon. The receiving part first acquires the igniter sequence, demodulates the state samples carried thereon, and corrects the SRG state of the receiver through a comparison-correction circuit at every accurate time point, so that the synchronization of the PN sequences is performed.
Since a pair of SRGs having the same structure and provided in the transmitting/receiving part perform the synchronization by carrying the same state values, i.e., L values stored in the SRG having the length of L, they can transfer the state samples of the transmitting part SRG to the receiving part using the DSA technique. As a result, this technique can acquire the PN sequence much faster than the existing technique that performs the synchronization at the time point where the maximum correlation value for the PN sequences is detected.
The high-speed acquisition using the DSA technique as described above has been limitedly applied to the cell synchronous type DS/CDMA system.
However, in the present environment that the DS/CDMA technique is expected to be applied to a cell asynchronous type system that does not depend on an external reference signal such as an international mobile telecommunication-2000 (IMT-2000), it is required that the DSA technique for more rapidly acquiring the PN sequence is extensively applied to the cell asynchronous type DS/CDMA system which is much more complicated in timing synchronization in comparison to the cell synchronous DS/CDMA system.
Meanwhile, the DS/CDMA cellular system for a mobile radio communication service such as the IMT-2000 to be developed is briefly classified into a cell asynchronous system and a cell synchronous system according as a reference timing between cells is provided or not.
In the cell synchronous system, a respective cell uses a sequence depending on an external reference timing providing resource such as a global positioning system (GSP) and obtained by differently shifting the phase of a single pseudo noise sequence as its scrambling sequence.
On the contrary, the cell asynchronous system uses a sequence differently given to the respective cell irrespective of the external reference timing as its scrambling sequence. For instance, in case of the asynchronous cellular system composed of 512 cells, 512 long-period scrambling sequences are required. For this, the cell asynchronous system such as the next-generation IMT-2000 differently combines the sequences generated using a plurality of (for example, two) fixed shift register generators (SRGs), and produces 512 different scrambling sequences.
The cell asynchronous system wherein the respective cell uses one among the 512 sequences performs a scrambling sequence acquisition for the sequence synchronization. In the scrambling sequence acquisition, a simple search for the frame timing required in the cell synchronous system, and discrimination of the sequence itself used in the present cell is performed as well.
According to the existing cell synchronous system, the serial search, parallel search, and hybrid method, which properly sacrifices and complements the acquisition speed and the complexity of implementation by adequately combining the serial search and the parallel search, have been used for performing the synchronization through the chip correlation of the sequences to acquire the scrambling sequence. Meanwhile, in case of the cell asynchronous system, a three-step cell searching method based on a method of removing a comma-free code and hierarchical uncertainty has been used.
The cell synchronous system using the serial search, parallel search, and hybrid method performs the synchronization by discriminating the timing representing the maximum correlation value obtaining by correlating the received scrambling sequence and the scrambling sequence generated by a mobile station. However, since the cell asynchronous system using the three-step cell searching method identifies both the kind and timing of the scrambling sequence, it should perform an additional synchronizing code transmission and more complicated signal process.
Hereinafter, the cell asynchronous system using the three-step cell searching method will be explained in detail, taking the W-CDMA system of IMT-2000 as an example, with reference to the channel structure and timing as illustrated in FIG.
1
.
Respective 512 cells (i.e., base stations) transmit scrambling sequences of the corresponding cells through primary common pilot channels (P-CPICH), and transmit in parallel a primary synchronization code (PSC) which is commonly used by the 512 cells and secondary synchronization codes (SSC) which are peculiarly used by respective cell (i.e., base station) groups that the cells belong to.
Symbols transmitted through the SCH are transmitted, crossing in time with symbols of a broadcasting channel (BCH) transmitted through the primary common control physical channel (P-CCPCH) of the respective cells, in the transmission ratio of 1:9. Specifically, the primary synchronization code (PSC) and the secondary synchronization code (SSC) are simultan
Kim Byoung Hoon
Lee Byeong Gi
Chin Stephen
Fleshner & Kim LLP
LG Electronics Inc.
Wang Ted
LandOfFree
High-speed cell searching apparatus and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High-speed cell searching apparatus and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-speed cell searching apparatus and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3306088