Pulse or digital communications – Spread spectrum
Reexamination Certificate
1999-02-05
2002-08-06
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
C375S145000
Reexamination Certificate
active
06430209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to a spread spectrum communication apparatus including cordless telephones and portable transmitter/receiver, particularly employing the spread spectrum method, in which the receiver starts a communication with a certification process(an ID certifying) after the frame is synchronized. The apparatus have an improved frame re-synchronizing function in its receiver section for acquiring frame synchronization in the case of losing frame sync during a communication.
BACKGROUND OF THE INVENTION
Wireless communication apparatuses with the spread spectrum method have grown in interest in the recent years. Among the spread spectrum communications, a direct sequence method establishes a communication as follows: A transmitter multiplies information signals by a pseudorandom noise sequence(PN sequence), thereby spreading spectrum, then transmits the resultant signals. In a receiver, a PN sequence generator produces the PN sequence same as that of the transmitter, and the received signals are multiplied by the said PN sequence with the same timing as that of the transmitter for despreading spectrum, and thereby the information signals are reproduced. The timing of the produced PN sequence at the receiver should be adjusted to that of the PN sequence sent from the transmitter. This process of adjusting is called a frame-sync-acquisition process.
After this frame-sync-acquisition, an ID certifying process must be done before starting a communication. In the certification process, an ID (identifier) proper to the receiver should be identified with an ID carried by signals being received. When a communication is interrupted by losing synchronization of the generated PN sequence with that from the transmitter caused by any disturbance, the frame-sync-acquisition process must be performed in order to recover synchronization of the PN sequence. In this case, the ID certification is processed after the frame-sync-acquisition. When an ID is not certified, the step of frame-sync-acquisition process is started again, and repeated until ID is certified. After the ID certified, the communication can be resumed. This process from recovering the sync to resuming the communication is called a frame re-sync process.
The frame re-sync process demands a time for certifying an ID in addition to a time for the frame-sync-acquisition. In case that a frame-sync-acquisition method employing a sliding correlator is used, in particular, it takes rather long time to resume the communication if a frame synchronization would be lost due to some disturbance, because the sliding correlator is sliding a delay time of the generated PN sequence slightly step by step in order to search high correlation value made from a sum of products of a number of the PN sequence and a number of received spread signals. When this happens in a telephone apparatus for which a real time action is vital, communication quality is lowered by voice interruptions. The voice interruption time thus need to be reduced for upgrading communications.
SUMMARY OF THE INVENTION
The present invention addresses the problem discussed above and aims to provide a spread spectrum cordless telephone apparatus that can reduce a voice interruption time due to loss of synchronization caused by some disturbance.
In the spread spectrum communication, frame synchronization in a receiver is lost due to interference from the spread spectrum signal in the same frequency band and in the similar PN sequence. In this case, field intensity immediately before loss of synchronization is high. On the other hand, when synchronization is lost due to just noise interference, the field intensity immediately before the loss is low. Therefore, when the field intensity is high immediately before the sync is lost, the apparatus needs the ID certification to avoid receiving other spread spectrum signals from a similar communication system. However, when the field intensity is low immediately before the sync is lost, the apparatus seldom needs the ID certification because the loss has been probably caused by noise interference.
In order to achieve the objective of the present invention, the field intensity immediately before the loss of sync is stored, and when the stored intensity is high, the ID is desirably certified not to receive other spread spectrum signals which have probably interfered with the present communication. When the stored intensity is low, the communication is desirably resumed free from the ID certification in order to shorten a voice interruption time because only noises have probably interfered with the present communication.
The spread spectrum cordless telephone apparatus of the present invention has a structure that allows the apparatus to determine the necessity of the ID certification after frame-sync-acquisition by referring to the field intensity immediately before the sync is lost. The apparatus thus can determine to practice the step of the ID certification only when it is needed, or to skip this step responsive to an outer environment. As a result, this apparatus can reduce the waiting time before the communication is resumed.
REFERENCES:
patent: 5737329 (1998-04-01), Horiguchi
patent: 5978412 (1999-11-01), Takai
patent: 63-250225 (1988-10-01), None
Matsubara Akihiro
Shigyo Masahiro
Matsushita Electric - Industrial Co., Ltd.
Pham Chi
Ratner & Prestia
Tran Khai
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