JPS594252A - System for detecting unique word - Google Patents

Abstract

PURPOSE:To prevent the increase in bit error rate without requiring differential- coding, by using a unique word detector for selecting a correct biphase decoding series. CONSTITUTION:Two decoded signal series comprise a correct series A and its logical NOT series A'. A unique word UW detector of a dual transmission system is installed to both the series for applying the UW detection and a series detecting the correct UW is discriminated as the series A. An input data is converted into parallel data in the detector, the result is compared with u1-un of a UM pattern 22 to be detected as specified, and when the total sum of the number of coincidence of each bit is a prescribed value or over a UW detecting pulse 28 is produced. When the UW detection is executed again after n-bit delay, dual transmission of UW+UW is detected by ANDing the both at an AND circuit 29. In case of the UW+UW', the detecting pulse is obtained by ANDing the UW' detecting pulse from the 2nd output port of a threshold value circuit 24 with the UW detection pulse delayed by n-bit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a unique word detection method for optical burst signals in an optical network constructed of passive optical circuits.

In an all-in-one transmission system in which an optical fiber network is constructed using passive optical circuit elements such as optical star couplers, optical branching and coupling circuits, and optical switches, when one connected transmitter/receiver station sends data, it Since it is entirely proprietary, some kind of multiple access technique is required in order for a large number of connected stations to communicate with each other. Time division multiple accessITimel)ivisionM
The oltiple Access (hereinafter referred to as TI) MA1 method is a method suitable for the above-mentioned transmission path, and takes into consideration the periodic period of time on the transmission path, and divides this period, that is, the TI) MA frame, into each station. It is assigned to Each station transmits its own signals in bursts within its allotted time, and each burst signal is transmitted in a regularly arranged manner on the transmission path. Each station receives these signals and extracts only the signals destined for it.

To arrange burst signals in an orderly manner.

i[1 Always has a unique word TUn at the beginning of each burst.
iqde Word: Synchronization between bursts is established by assigning a specific pid packet, hereinafter referred to as UWI, and detecting this by each station.

Unique word again. It is also used to specify the starting bit of data in each data burst.

The development of the TI)MA method has been focused on practical application in the field of satellite communications, and when applying it to optical communication systems with different modulation and encoding methods, there are challenges that did not exist before. occurs.

The modulation method used in optical communication is to reduce the light intensity to 1” of data.
Since it uses a light intensity modulation method that changes according to the optical power, the series of signals will include a DC component.However, optical receivers that use an AC input method are superior in terms of sensitivity and dynamic range. Therefore, a code without a DC signal component is useful as a transmission line code.One such code is a biphase code.

In biphase codes, phase uncertainty exists during decoding, and differential encoding has conventionally been employed to remove this.

However, with differential encoding, the bit error rate (B13) increases approximately twice, and the cutoff frequency of the optical receiver must be designed sufficiently low in terms of allowable code distortion. .

When performing optical burst transmission, there is a disadvantage that the timing recovery bit added to the beginning of the burst signal becomes long.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and by selecting the correct biphase decoding sequence using a υW groove detector, it is possible to achieve BFiR without the need for differential encoding. The present invention provides a new unique word detection method that can reduce the length of redundant bits added to the beginning of burst signals, while also making it easier to identify different types of bursts using the UW continuous transmission method and reducing the size of the groove detector. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, (1) and (2) are the two biphase decoding sequences (two installed door detectors), and (3) is the above +11. This is a switch for selecting the correct series from the signal series. 14+ and +51 are the UW groove detectors on the side that detected the buy (door detection) (Russ), and this pulse indicates that the series that detected the groove is Since it is unknown which of the two input signals 1f41J receives the correct sequence due to the phase uncertainty of the bi7-factor decoder, the UW groove detector selects the correct sequence. It is to identify.

The configuration of the UW groove detector in 11+ (21) is as follows:
Using the UW transport system shown in the figure is effective in identifying data bursts.

That is, in a TDMA system, there are a reference burst for establishing burst synchronization and a data burst for signal transmission, and a method of continuously transmitting armor can be used to identify these two bursts. for example.

If one bang is UW, and the inverted patter/of that °l″10″ is UW, then the reference burst is Yes+IJW.
It is possible to distinguish between the two by sending UW+UW in a data burst. In Figure 2, C21+ is an n-bit shift register, (2
) is a UW pattern sequence (c) of a fixed foot to the detector power is a summation circuit that calculates the sum of the number of matches of each pit of the fixed button and input button, (241 is a threshold circuit, +251 is a delay circuit of n-b gate, ( 1) is an aperture generation circuit that generates a gate signal every cycle based on the UW detection pulse for burst synchronization, and @ is a control circuit that changes the set value of the threshold value.

The fixed button sequence (2) is used when there is a difference in BBR between the two decoding sequences as will be described later (in the second case, an optimal button different from the conventional button is used).

The two signal sequences decoded by the bi7-engine decoder are the correct sequence (hereinafter referred to as the A sequence) and its logical negation sequence (
UW detectors using the transportation method shown in Figure 2 were installed in both series, and a UW door inspection was performed on each series.The series detected the correct UW. is determined to be the correct series (A series).

In a transport type UW detector, the input serial data is parallelized by a shift register (211) and compared with (UX + U, ...uIll) of the UW button (2) given in advance to the detector power, and each bit is matched. Take the sum of the numbers.

If this value is above a certain value, a UW detection pulse (support) is generated, and when the UW door inspection is performed again after a 1nbtt delay, the AND circuit Detection is performed. In the case of UW+UW, the detection pulse is obtained by ANDing the hour detection pulse from the second output port of the threshold circuit and the n-bit delayed υW detection pulse.

By using this method, it is not necessary to differentiate the pi-phase code, and an increase in pit error rate can be prevented. In addition, the pi-phase code has the characteristic that even if the low cutoff frequency of the optical receiver is set high, the code distortion of the latter half of the bits subjected to 1-bit → 2-pit conversion is extremely small. By targeting information to the latter bits, a receiving system with a high low cutoff frequency can be configured, and accordingly, the length of redundant bits added to the beginning of the optical burst signal for timing recovery can be shortened.

On the other hand, since the UW transport method is used, it is easy to distinguish between reference bursts and data bursts, and
The scale of the UW detector can be made smaller than when sending one IJW pattern.

When designing the unique word ζ tan used in this UW detection method, it is necessary to take into account that the RFRs of the two biphase decoding sequences are different.

In the UW continuous transmission method, a fixed UW button (old, u2゜...
...The UW false detection rate Fs(t) at a point t other than the peak position of the correlation output between unl and the input sequence is.

・・・・・・・・・・・・・・・・・・・・・・・・
It can be approximated by (1). Here, n is the UW pit length, e is the allowable pit error number, and r+ and r2 are the correlation outputs at t and t+n, respectively, when there is no error.

In decoding, - corresponds to the A sequence, 0 corresponds to the X sequence, and Pe takes the pit error rate of each sequence.

It is desirable to set the UW false detection rate for the human series and the X series to be about the same. In equation (1), the influence of differences in coefficients other than the power of the pit error rate is small.

The UW button may be configured to satisfy the following.

The υW non-detection rate Q can be approximated by Q=2'e:11pee+'1, and the larger the value of e, the smaller Q becomes.

For example, in an 8-bit long UW, if the preceding sequence for timing reproduction is a slam of all l (...Ill...Ill), Equation 9 (2) is satisfied and Q is also satisfied.

(Assuming e=1) What is the optimal UW pattern?

11110010° 11110100 Two of these were discovered.

FIG. 3 shows the correlation characteristics of the pattern 11110010. According to this pattern, ps=-10 or less.

Q"10" or less can be achieved.

In addition, in the above actual example, the UW detector is a combination of a summation circuit and a threshold circuit.

As shown in FIG. 4, one chip of read-only memory +) LOMI with a capacity of about 256x2 pits is used.

Bang detection can be performed by directly using the output of the shift register as an address input.

Thereby, the circuit scale of the UW detector can be further reduced.

Also, the combination of [JW jumps] for m-separation of bursts may be in other orders, with different unique words UW, and UW
A combination of the two is also possible.

As described above, according to the present invention, the biphase decoding sequence is selected by the UW detector.

Furthermore, since the system transmits UW continuously, there is no need to differentiate the biphase code, and the redundant bits added to the beginning of the burst signal can be shortened, and different bursts can be easily identified.

This has the effect of reducing the circuit scale of the UW detector.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a biphase decoding sequence selection circuit according to an embodiment of the present invention, FIG. 2 is a block diagram of a unique word detector for a unique word continuous transmission system used in an embodiment of the present invention, and FIG. FIG. 3 is a diagram showing the correlation characteristics of unique word bangs used in one embodiment of the present invention, and FIG. 4 is a block diagram of a unique word bang detection circuit according to another embodiment of the present invention. In the figure, +11. +21 is a unique word detector, (
3) is a sequence selector, (41, +51 are unique word detection pulses, all is a shift register, and C12 is a unique word inversion button detection pulse. The same reference numerals in Figure 1 indicate the same or equivalent parts. Patent application Makoto Ishiita, Director of the Agency of Industrial Science and Technology

Claims (3)

[Claims] (1) Unique word detectors are provided for both the desired decoded sequence decoded from the biphase decoder and having a sufficiently low bit error rate characteristic, and the logical negation sequence that has a slightly worse bit error rate than this desired sequence. A unique word detection method, characterized in that phase uncertainty in decoding a biphase code is removed by selecting a sequence on the side in which a correct unique word has been detected as a desired sequence using a switch. (2) By using the unique word detectors provided in the above two decoding sequence systems to detect unique words only when two types of unique words arrive consecutively, the above two types of unique words can be used to identify different bursts. The method according to claim (1) is characterized in that the circuit scale of the unique word detector can be reduced by using a combination of words and halving the length of one unique word. Unique word detection method. (3) The scope of the present invention is characterized in that, as the above two types of unique words, a specific button optimized according to the difference in bit error rate between the two decoding sequences and its logical negation button are used. Unique word detection method described in (2).