Pulse or digital communications – Synchronizers – Frequency or phase control using synchronizing signal
Reexamination Certificate
1998-11-20
2003-04-01
Tse, Young T. (Department: 2634)
Pulse or digital communications
Synchronizers
Frequency or phase control using synchronizing signal
C375S368000, C370S510000, C370S513000, C370S514000
Reexamination Certificate
active
06542563
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital radio communication receiver for deciding synchronous words used for decision of received frame synchronization and decision of received frame structure in accordance with correlative thresholds different from each other.
2. Description of the Prior Art
Generally, in the case of digital radio communication, a received bit series is detected by detecting a received signal and received information is correctly extracted by detecting the frame timing in the received bit series. Detection of frame timing and frame synchronization are performed by detecting a bit series having a sharp autocorrelation set to a predetermined position in a frame, that is, by detecting a synchronous word. The synchronous word is also referred to as Sync word or Unique word. Moreover, in figures, a synchronous word is shown as UW that is the abbreviation of Unique word.
A synchronous word is detected by comparing a received bit series with a synchronous word bit series prepared at the reception side. When the number of mismatched bits of the received bit series and the synchronous word bit series is equal to or less than a correlative threshold serving as a predetermined threshold, it is decided that a synchronous word is detected. However, when the number of mismatched bits exceeds the correlative threshold at the timing at which a synchronous word should be originally present, it is decided that synchronous word is false detected.
When frame synchronization is established, it is possible to approximately estimate the position of a synchronous word in a receiver. Therefore, when frame synchronization is established, the false detection probability of synchronous words can be lowered by setting a gate referred to as aperture and detecting an effective synchronous word at the position of the synchronous word or only in a small range around the position.
Frame synchronization is established by detecting synchronous words at a predetermined position continuously by a specified number of frames. This operation is referred to as backward protection and the specified number of frames is referred to as the number of backward protection stages. As the number of stages increases, false frame synchronization does not easily occur and therefore, the reliability of frame synchronization is improved. However, it takes a lot of time until frame synchronization is established. However, when the number of stages decreases, it takes only a short time until frame synchronization is established. However, false frame synchronization easily occurs.
Frame step-out is detected when synchronous words are missed continuously by a specified number of frames at a position at which a synchronous word should be originally present. This operation is referred to as forward protection and the specified number of frames is referred to as the number of forward protection stages. As the number of stages increases, it takes a lot of time to detect frame step-out due to deterioration of circuit quality. Conversely, as the number of stages decreases, it takes only a short time to detect frame step-out. However, the probability of erroneously deciding frame step-out is raised when frame synchronization should be originally held.
Moreover, in the case of a digital radio communication system, frame structures may be changed depending on the communication state. For example, in the case of a system using the voice actuation art, a frame is transmitted only when a voice is significant but no frame is transmitted in principle when no voice is recognized. Even in this case, however, a short burst including a synchronous word is transmitted every certain interval in order to hold frame synchronization. However, the interval is generally different from a frame length.
As described above, when frame structures are changed depending on the communication state, it is necessary that the transmission side communicates the change of frame structures. To communicate the change of frame structures, there is a method of previously setting a bit series for communicating a frame structure in a frame and moreover, there is a method of inserting a bit series for communicating change of frame structures (hereafter referred to as frame structure flag). Moreover, at the reception side, there are a method of detecting a frame structure flag and a method of deciding a frame. structure every synchronous-word detection interval.
FIG. 4
is a block diagram showing the structure of a section for estimating frame synchronization and frame structure of the digital radio communication receiver disclosed in the Japanese Patent Laid-Open publication No. 247114/1997. In
FIG. 4
, reference numeral
1
′ denotes a synchronous word detecting section,
2
denotes an aperture control section,
3
denotes a timing control section,
4
denotes a number-of-frame-synchronization protection stage setting section,
5
denotes a frame synchronization deciding section,
6
denotes an aperture width setting section,
7
′ denotes a correlative threshold setting section,
8
denotes a received signal extracting section,
9
denotes a frame structure deciding section,
100
denotes an antenna,
101
denotes a down converter, and
102
denotes a wave detector.
Then, operations of the conventional example in
FIG. 4
are described below. The down converter
101
converts a carrier wave received from the antenna
100
into an intermediate frequency band and the wave detector
102
demodulates a signal received from the intermediate frequency band to output it as a received bit series. The synchronous word detecting section
1
′ receiving the received bit string takes the correlation between received bit series and synchronous words in accordance with the timing information sent from the aperture control section
2
, performs detection of a synchronous word and decision of a phase in accordance with the number of error bits and the correlative threshold sent from the correlative threshold setting section
7
, and outputs the decision results to the timing control section
3
, frame synchronization deciding section
5
, frame structure deciding section
9
, aperture width setting section
6
, and correlative threshold setting section
7
as synchronous word detecting information. The timing control section
3
outputs the received timing formation used to next perform synchronous word detection to the aperture control section
2
and received signal extracting section
8
in accordance with the synchronous word detecting information. The frame synchronization deciding section
5
decides a frame synchronous state using the number of forward protection stages serving as the continuous detection frequency of the synchronous word detecting information designated by the number of frame-synchronization protection stages
4
and the number of backward protection stages serving as the number of continuous misses, and outputs the decision result to the aperture width setting section
6
and correlative threshold setting section
7
as frame synchronization deciding information. The aperture width setting section
6
sets an aperture width serving as a time width used to next perform synchronous word detection by using the synchronous word detecting information and frame synchronization information and outputs the aperture width to the aperture control section
2
. The correlative threshold setting section
7
sets a correlative threshold serving as a synchronous word detecting condition used to next perform synchronous word detection by using the synchronous word detecting information and frame synchronization information and outputs the correlative threshold to the synchronous word detecting section
1
. The received signal extracting section
8
extracts a received signal from a received bit series in accordance with received timing information. The frame structure deciding section
9
decides a frame structure in accordance with the detection interval of the synchronous word detecting info
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